d3VIEW - AI Powered Data-to-Decision Platform

Generic DOE Data Analyzer Workflow now available in d3VIEW

Wed, 22 May 2024 00:00:00 +0000

When we have a dataset on hand, it is often of our interest to run a quick analysis and get some insights. The analysis usually includes making predictions of a new dataset, grouping records, identifying important features, and optimization. We can achieve these goals by building a machine learning model and use the trained model to make predictions, cluster analysis, feature important analysis, and optimization. All of these can be easily done with the 012_DOE_DataAnalyzer workflow available for all users. There are four components of this workflow.

Study of Machine Learning Parameters for Robustness

Mon, 29 Apr 2024 00:00:00 +0000

NOTE: Robustness reported in this article is being revised with corrections in derivative calculations. Updated results will be published shortly from these corrections.

Introduction

A natural approach of understanding an unknown model is to get some sample points from the model and use these points to build a response surface model (RSM) to represent the true model.

In this process, two factors play a vital role in RSM accuracy. One is the sampling points to use for building the model and the other is the selection and training of the model. Given so many choices of sampling methods and learning models, an inevitable question we are all asking is, which sampling type and learning model we should use. In this article, we will explore how different combinations of sampling methods and learning models affects the accuracy of the RSM model.

Apply Simulated Annealing on a curve to find the optimum

Wed, 26 Apr 2023 00:00:00 +0000

Similar to the dataset_simulated_annealing_optimizer worker, which takes a dataset as input, we can consider the curve_simulated_annealing_optimizer worker. It takes a curve as input and returns the optimal y value of the curve as output.

Inputs and output of the curve_simulated_annealing_optimizer worker

A curve can be considered as a dataset with two columns with each representing one coordinate of the points on a curve. The difference between the curve worker and the dataset worker is the way the model is built. With a curve input, curve interpolation techniques are used to find the values on a new location of the curve.

Simulated Annealing with Polynomial Regression

Fri, 21 Apr 2023 00:00:00 +0000

Simulated annealing

Simulated annealing is an optimization method to find the global optimum of the objective function. It is inspired by the process of metal annealing which heats the metal to a very high level and cools down in a controlled manner. In the SA algorithm, a random point is selected to start with. A new point is proposed at each iteration by making small changes to the current point. The point is then evaluated by the objective function to get a score (energy, cost) so that it can be compared to the previous point. If the new point has a better score, it will be accepted; Otherwise, it is accepted with a certain probability determined by the probability distribution. This probability distribution is determined by a parameter called the “temperature”. It decreases gradually at each iteration.

Compare curves with Dynamic Time Warping

Mon, 27 Feb 2023 00:00:00 +0000

Given two curves, a baseline and a candidate curve, how do we know how similar they are to each other? In machine learning, it is common to compare the predicted values (candidate curve) of a testing set to the true values (baseline curve) by RMSE (Root Mean Square Error). By comparing RMSE values of different candidate curves, we can learn which one is more similar to the baseline curve and thus identify the machine learning model that performs the best.

Choose Machine Learning Models With Cross Validation

Mon, 20 Feb 2023 00:00:00 +0000

Machine learning techniques (https://www.d3view.com/introduction-and-application-of-d3view-ml/) are becoming unprecedentedly popular. And it plays an important role in data analysis. It is critical to find the model that demonstrates the best performance. Intuitively, we can build a few different models with the data given and see which model gives the best score, either it being RMSE (root mean squared error), R squared for regression models or accuracy, precision for classification models.

Overfitting

You may have already sensed the problem with this approach. A more complicated model is always going to perform better. An extreme example is we can just connect all data points with lines or equivalently assign y values to each x values as they are in the given data. The error will be zero. However, when this complex model is applied to some new data, it will produce more errors. This is called overfitting. It happens because data contain noises or random errors. For example, when we are measuring a person’s height multiple times, we may have different readings each time due to factors such as the angle of our eyes to the reading, or the light in the environment or simply we want to quickly finish the work and move forward. Though the person’s height remains unchanged, the readings we have are different. These noises generate uncertainty in the target y values. Therefore, a good model should keep this uncertainty to its consideration.

Introducing Calendar View for Simulations and Physical Tests

Thu, 12 Jan 2023 00:00:00 +0000

Many of us would agree that calendars play an important role in our day-to-day life aiding in tracking events, staying on top of task completion, etc. Calendar in d3VIEW helps keep track of Simulations and Physical tests records created by users in an organized manner.

How to access Calendar:

All the simulation and physical test records can be viewed in the calendar with just a click from the default table view.

Text Parameterize GUI: A Workflow Tool to Parameterize Input Files

Thu, 13 Oct 2022 00:00:00 +0000

The new ‘Text Parameterize GUI’ worker helps to create machine generated designs by providing a simple to use interface to parameterize any part of a text file. Examples of such applications include single stage Design of Experiments, Sensitivity Analyses, Multi-stage Optimization and for generic machine learning problems.

Text Parameterize GUI icon

Locate the ‘Text Parameterize GUI’ worker under the Shapes menu which contains the most commonly used workers, for easy access. Generally, we’ll use this worker at the beginning of a workflow to set-up our text input file.

Workflow Provider: Execute Workflows within a Workflow

Thu, 13 Oct 2022 00:00:00 +0000

d3VIEW has a new worker called ‘Workflow Provider’ which allows us to execute other workflows we may have saved on the platform within the current one we are building and executing. This saves us time from rebuilding parts of a workflow that can be taken from an already built one.

Workflow Provider Worker Icon

Find the ‘Workflow Provider’ worker under the shapes menu, which houses the generic and most used workers for a workflow.

Multi-objective optimization with Pareto front

Fri, 23 Sep 2022 00:00:00 +0000

Optimization

Decisions are made based on preferences. Either it is to minimize the monthly expense for a person living with a tight budget or to maximize the revenue of a restaurant for a business owner, we need to consider our preference or criteria (minimize or maximize) to form a solution. This process is called optimization and optimizing based on a preference is an objective. When we only focus on single objectives, we can easily sort out the best solution. However, in reality, we frequently need to take multiple objectives into consideration. And more than often, the objectives we want to optimize are conflicting each other. For example, when a car has the most comfortability and the best performance, we know it is going to cost a fortune on the fuel. In order to solve these multi-objectives optimization problems, we can consider the Pareto front.

Kriging interpolation

Tue, 20 Sep 2022 00:00:00 +0000

In the previous post, we have discussed about how interpolation works in general and reviewed a few commonly used interpolation methods. All these methods only consider the adjacent a few points. This works fine most of the time. However, in reality, data points further away from the interpolation point may also have some impact on its value. The scale of the impact though depends on the distance to the interpolation point. Usually, points further away contribute less than those close-by points.

Using d3VIEW-Workflows to Build and Launch DOE Simulations

Thu, 15 Sep 2022 00:00:00 +0000

Workflows is d3VIEW’s application for streamlining complex business processes. With its capabilities, we can create and employ automated DOE studies for quicker analysis. Using the application’s new shape worker, *TEXT_PARAMETERIZE_GUI, we can set-up custom parameters for our text-based files, generate sampling points from these parameters, create simulations from the text, launch the DOE studies from the simulation, apply templates and create a report through a smooth and simple execution of workers.

Simlytiks Dashboards

Wed, 14 Sep 2022 00:00:00 +0000

d3VIEW’s visualization application Simlytiks® now has a new page layout called Dashboard that allows users to set-up a free-form presentation-styled page using dedicated widgets. Add custom text, images, data filters and aggregators, and Simlytiks charts as well.

Iris Class Dashboard

To better illustrate Simlytiks Dashboard capabilities, we’ll be looking at the Iris Class dataset which looks at how sepal and petal dimensions of an Iris flower indicates the Iris class: Setosa, Versicolor and Virginica.

New Envelope Feature to Aid Material Selection in d3VIEW

Wed, 07 Sep 2022 00:00:00 +0000

d3VIEW supports material calibration and storage of calibrated materials in a scientific database native to d3VIEW. Once materials are stored in the database, d3VIEW supports filters to search and retrieve the materials of choice.

Recently, we have been working on supporting visual selection through “Brushing” – a term often used to describe the ability to drag-and-select interested data points directly in a visualizer. Examples of such brushing include dragging-and-selecting curves when viewing ‘Engineering Stress vs Strain’ or dragging along a dimension in a ‘Parallel Chart’ as shown in the images below.

Curve reconstruction procedure for use in Machine Learning

Wed, 10 Aug 2022 00:00:00 +0000

Introduction

Given a set of points, we want to construct a curve that shares some specific patterns described by a group of curves.

From the description of the problem, there are two pieces of information available to us. First, the points available (Prediction Points) are part of an unknown curve we want to reconstruct. Second, this unknown curve (Prediction Curve) shares the same characteristic patterns defined by a group of known curves (Input curves). The information determines that a simple interpolation will not fulfill the goal of integrating the characteristic patterns to the reconstructed curve.

Introduction and Application of d3VIEW-ML

Thu, 21 Jul 2022 00:00:00 +0000

Machine learning is a data analysis technique that builds a model with the data and uses the model to predict. It learns from the data, identifies patterns and produces reliable predictions that help with decision making. As modern computational techniques advance, machine learning becomes more and more popular. There are two major groups of learning algorithms, supervised and unsupervised learning. Many regression and classification models we know of are supervised learning, such as linear regression, lasso regression, support vector machine, decision tree classification, random forest classification. They are supervised in the sense that the data we use to train the model have a “correct” label. And using this information, we can evaluate the performance of the learned models. On the other hand, when the data we used for training don’t have any label information, it is unsupervised. For example, clustering algorithms such as k-means assign data into groups. In this process, it doesn’t require the training data to have the correct labels as references.

Interpolation methods for time series data

Fri, 29 Apr 2022 00:00:00 +0000

It is not unusual that due to various limitations, researchers can only collect limited number of samples. Meanwhile, for many analyses, we desire a higher resolution. In two-dimension case, we have X and Y coordinates of our points. We are interested in what happens in between any of the two points.

We can draw a curve passing through these points to describe the relationship between X and Y values. With such a curve at hand, we can estimate the unobserved values in between any observed points. From this perspective, we consider interpolation as a procedure of looking for a function to describe the relationship between X and Y and using this function to estimate the values at any location.

Protected: Material Calibration Using d3VIEW Workflows

Fri, 18 Mar 2022 00:00:00 +0000

Battery Cycle Detection using ‘Current’ Time-series Data

Mon, 10 Jan 2022 00:00:00 +0000

Battery data have many interesting properties. One of them is cycles. When we consider the whole range of the data, there are a few of the metrics we are interested in. For example, test net capacity and energy, test cumulative capacity and energy, etc. From these transformed curves, we can obtain some metrics that help us to evaluate the performance of the batteries. More than often, we are interested in cycle based metrics such as cycle charge/discharge capacity/energy, cycle net capacity and energy and so on. This requires us to be able to effectively identify each cycle start time. One way to obtain this information is by analyzing the current data.

Test vs CAE in d3VIEW

Fri, 03 Dec 2021 00:00:00 +0000

As simulations drive a large portion of product development, reliance on test-data at critical development stages is invaluable to further our understanding of reality and assess our simulations. Among a wide variety of tests conducted today, the test-data can be broadly grouped into coupon-based (for material calibration), component based (for sub-system validation) and full-system tests. The costs associated with these tests vary.

The challenge for any simulation engineer lies in their ability to 1) access the test data in its raw or sanitized form, and 2) have the ability to overlay against their simulations as quickly as possible. Today, in most companies, the test-data and the simulation-data are housed separately which decreases the visibility of the test-data significantly. In addition several challenges still exist in processing the raw-test-data and making it available in a form that can be utilized easily by the simulation engineers.

d3VIEW’s New Multi-User, Loadcase and Region Simulation Tracker with Built-in Analytics

Fri, 15 Oct 2021 00:00:00 +0000

In virtual product development, a single pane of glass view to track evolutionary changes across all domains in both input (variables) and its corresponding output (results) is critical for decision-making. There are two broad categories of designs that are frequently evaluated – A) Machine Generated Designs (MGD) and B) Human Generated Designs ( HGD). MGD data visualization involves the viewing of a group of data such as sequential domain-reduction and is usually viewed using traditional methods such as Table View, Parallel Chart, etc to study the influence of the (inputs) variables on the outputs (results). Simlytiks, a data-visualization application in d3VIEW, has been facilitating the visualization of DOE and sequential DOE for a number of years and is well-accepted in the industry for large amounts of data (see example). However, visualization of HGD is non-trivial since the inputs are dynamic and are often associated with a dynamic timeline and outputs. In all or most companies, the tracker information is maintained by engineers using a NAS-available Excel file using traditional methods of entry and limited visualizations.

Data Drilling in Simlytiks

Thu, 07 Oct 2021 00:00:00 +0000

d3VIEW’s Data Visualization Application, Simlytiks, offers a wide-variety of charts with different options for an enhanced data-mining experience. One of these chart features includes data drilling which involves navigating through multiple dimensions of data. A chart with data-drilling capabilities presents data columns in hierarchical layers allowing us to explore different levels within the same container.

Figure 1: Top layers contain information about lower layers. We drill down from top layers to view lower layers and drill back up to review top layers again.

Initial layers show a more broad summary, generally getting more detailed and specific as we navigate down the levels. Though, the layers don’t necessary have to connect in hierarchical format. These charts can showcase columns of data in any order with their drilling capacity as a way to view the correlation between columns or important aspects collectively. And, drill-down paths aren’t necessarily linear as certain paths may connect back to others because of shared data records.

Curve Digitization in d3VIEW

Mon, 27 Sep 2021 00:00:00 +0000

In several instances, time-history curves may need to be imported from either an Image (PNG/JPEG,.) or PDF files for use in comparison with simulations or for material calibration. d3VIEW Workflows now has the ability to digitize these images into a usable data curve.

This post reviews the 5-step process in digitizing the image from a given image as shown below:

Image Annotations

Fri, 17 Sep 2021 00:00:00 +0000

Simlytiks application in d3VIEW converts raw data into descriptive analytics using a variety of visualizers to facilitate a quick understanding of the data and to aid in decision making. Among the library of visualizers, one that belongs to the category of InfoGraphics is the newest addition called Image Annotator. It is one of the powerful visualizations in Simlytiks that helps associate data with meaningful images. Infographics has been seen as early as 25,000 years ago in the Serra Da Capivara caves of Brazil and it not new for humans to use data associated with Images to describe information. In this post, we walk you through the aspects of creating a visualization using ImageAnnotator using realistic simulation and non-simulation data to demonstrate its flexibility to work with a variety of data formats and types.

Storing and Viewing Scientific Data in d3VIEW

Tue, 14 Sep 2021 00:00:00 +0000

d3VIEW being a data-to-decision platform, houses many applications. Database is one among them where we can organize large amounts of data including scientific data such as curves/images/movies/etc.

Main features of the Database application include

Creating a database & organizing large volume of imported data
Visualizing data
Exporting data

1. Create Databases With and Without Importing Data

Databases can be created in 4 different ways.

Database with manually added fields
Database with fields imported by uploading a file
Database with fields imported from sample datasets
Database creation using Workflows

Let’s look at the different ways:

Explore Non-Scientific Data in Simlytiks®

Wed, 18 Aug 2021 00:00:00 +0000

As a data-to-decision platform, d3VIEW supports a wide-variety of data. Let us see how Simlytiks, d3VIEW’s data visualization application, helps in visualizing non-scientific data.

Data types supported in d3VIEW

Current visualizers in Simlytiks^® with bubble chart highlighted.

Leading the way in this enhancement is Simlytiks’ Bubble Chart visualization, which effortlessly harmonizes with simple data, as well as scientific data, to create smooth comprehension. Bubble Chart supports more than just data in the x and y, with options like color-coding nodes or varying opacity based on particular column data.

Generate Part Contours with New d3VIEW Workers

Fri, 13 Aug 2021 00:00:00 +0000

Measuring the behavior of materials via specific procedures such as tension or shear tests aids in designing sound and safe products. d3VIEW supports this process by offering tools such as Material Calibration workers in our Workflows application. Recently, two new workers have been created for this, Key Value Generate Part Contours and Curves Generate Part Contours Animation, which help visualize forces and energies from testing by mapping them as colored contours on a material specimen.

Pedestrian Protection Data Visualization and Analytics in d3VIEW

Fri, 06 Aug 2021 00:00:00 +0000

Last week’s blog explained how d3VIEW supports crash safety through customized aPLI (Advanced Pedestrian Legform Impactor) templates. This week, we’ll look into how d3VIEW’s templates help with Pedestrian Head Protection.

Pedestrian protection criteria specify that pedestrians should not suffer head injury during impact of 160+ points on a vehicle hood. Regulations state that impact should not exceed a HIC value of 600 for each point. To deduce the HIC, or head injury criteria, we take the value between states T1 and T2 during impact. Each HIC value will then aid in determining a vehicle’s predicted score.

Using aPLI Templates for Crash Safety in d3VIEW

Wed, 28 Jul 2021 00:00:00 +0000

Data-processing in d3VIEW is made simpler and easier with its ‘Templates’ application. Templates help standardize and organize data imported from a wide range and variety of simulations and test data-sources. We tailor these templates to suit the business needs of users from different science areas.

One of the templates generated in d3VIEW for crash safety is the aPLI (Advanced Pedestrian Legform Impactor) template, which tests the impact of automobiles on pedestrian lower extremities. The templates aim to extract and provide insights into aPLI performance along with capabilities to verify the predictions with any available tests.

Identify Application Pages with Highlighted Headers

Fri, 23 Jul 2021 00:00:00 +0000

With over 12 applications on the d3VIEW platform, differentiating them could get a bit challenging when you are in the thick of things. That’s why each application has a unique icon and color to distinguish one from the others. And now, these individualized icons and colors are present on their respective application page header.

Some important application pages with their app icon and app color highlighting the bottom of the page header.

As shown in the above image, the application pages now present their icons on their page headers next to their names. The headers are also highlighted at the bottom in their unique app colors. This shows users what application page they have landed on.

Progressive Data Visualization in Simlytiks Using Placeholders

Fri, 16 Jul 2021 00:00:00 +0000

As d3VIEW is focusing on taking its users’ experience to the next level, Simlytiks, which is our visualization application has been spruced up. We have been working on extending functionality to improve usability and understanding of Simlytiks. One important improvement in the works pertains to the visualization placeholders – what the user sees before picking specifications for a chart, graph, etc. The updated placeholder images show detailed illustrations of each option available for each visualization. The key intention involves adding more clarity, so users feel empowered to create effective visualizations without any hesitation. Let’s go over some examples of how these extensive illustrations aid in setting up remarkable visualizations quickly.

d3VIEW Intern Spotlight: Meet Our Summer Interns

Fri, 09 Jul 2021 00:00:00 +0000

At d3VIEW, we aim to promote growth not just for the platform but for our employees. Even more, we are always open to allowing college students a chance to expand beyond their classroom. Currently, we have three interns, working towards undergraduate degrees, integrating their school learnings with d3VIEW in-practice work. Read on to learn about their experience working with the platform and the company.

Amy Tang

School: University of Michigan, College of Engineering
Area of Study: Computer Science

New and Refined Workflows User Interface (and a sneak peak into Workflows)

Thu, 01 Jul 2021 00:00:00 +0000

d3VIEW’s Workflows application has gotten a make-over. The new user-interface is more lucid and quite easier to navigate. Menus have been structured to keep options contained and grouped to make the Workflow application even more user-friendly. Read on to learn more.

Edit Mode Refinements

The new edit-mode menus are located at the top left. Click the corner menus icon to open the side panel menu to see more options.

Crashworthiness Tools in d3VIEW

Thu, 17 Jun 2021 00:00:00 +0000

d3VIEW isn’t just a general data mining and visualization platform. It caters to specific industries and concentrations, enhancing and accelerating product design. Crashworthiness, the pinnacle of vehicle safety and an important element in vehicle design, is no stranger to the platform. Featured below are some tools d3VIEW has specifically designed for crashworthiness.

Crash Workers

The Workflows application uses a plethora of workers to employ for complicated business tasks (over 900 if we’re counting). Some are precisely coded for crash simulations with the most prominent as follows.

New Workflow Features

Thu, 10 Jun 2021 00:00:00 +0000

d3VIEW platform is continually enhanced for improved efficiency, better usability and more intelligent processes. The Workflows application has recently been updated with a lot of these enhancements. In addition to the abundance of amazing features that exist already, the app now has some remarkable improvements to add to the mix. Highlighted below are a few important additions.

Assign Worker Outputs to Worker Inputs

Choose to assign executed worker outputs to other worker inputs on the canvas via the output worker. This compliments assigning via the input worker and will override any previously assigned inputs.

Application Features: Scientific Databases

Thu, 03 Jun 2021 00:00:00 +0000

d3VIEW’s application for scientific databases boasts intelligent features that make managing and organizing data painless. Not only does the app organize data into an advanced table, but it’s filters, viewing and visualization capabilities enhance the experience of data governance. Let’s review these amazing features.

Scientific Data Support

Databases support an array of data types that include scientific data such as curves, movies and images.

Advanced Data Tables

Database records are set up in a highly customizable data table. Choose from an array of visualization types, change the visibility of columns, edit text display and even visualized data columns.

d3VIEW’s Powerful Data Extractions

Thu, 27 May 2021 00:00:00 +0000

Data extraction is a powerful process for transforming data for data mining. In simplest terms, extracting data means structuring it, and we need structured data to support faster decision-making.

Yet, data extraction can go deeper than this, as it can further transform already structured data to reveal even more insights. When we start transforming on this level, the game changes. Complex transformations can be built upon one another to unveil profound value in our data we may have never discovered otherwise.

Highlighting Our Favorite Curve Transformations

Thu, 20 May 2021 00:00:00 +0000

Did you know d3VIEW has over 900 workers for employing data extractions and scientific processes? Many of these workers also correspond to transformations that can be applied individually to data responses, particularly curve responses. Curves may very well be the most used way to visualize scientific data which is why curve transformations can be so powerful. Let’s take a sneak peak at our favorite ones on the platform.

Curve Scale

View Post

User Roles in d3VIEW

Thu, 13 May 2021 00:00:00 +0000

A multitude of ways to explore and interpret data promises numerous roles that do the exploring and interpreting. Just about every field and discipline uses data to supplement, advance or clarify decisions. At d3VIEW, we have room for them all with specialization for engineers and scientists. Here, we’ve put together a list of our main roles with some basic descriptions of what they can do on the platform.

Test Engineer

Test engineers create and perform real-world examinations of products and prototypes. Once they acquire data from their experiments, they can upload it onto the platform for analysis.

Test Engineer Process: How d3VIEW Aids in Virtual Product Development

Thu, 06 May 2021 00:00:00 +0000

d3VIEW offers solutions for a variety of sciences and disciplines. Test Engineers are not excluded from this as the platform has a dedicated application for physical tests that works in tandem with other features and applications to enhance product development.

1. Prototype and Testing

The first step of the process involves the physical testing phase. The engineer executes experiments and evaluates the prototype in real-world situations.

Highlighting Our Favorite Visualizers in Simlytiks

Thu, 22 Apr 2021 00:00:00 +0000

d3VIEW’s Simlytiks application offers over 40 different possibilities for exploring your data through our rich visualizer library. Simlytiks visualizers are exactly what they sound like: data presented into visual displays such as graphs, charts and even animations. Here, we’ll go over some of our favorites and show a sneak peak at what they can do.

Bar Chart

Who doesn’t like the simplicity of a colored bar chart? Stack multiple values for each bar which are colored coded and show the respected values. There is also a horizontal version of this visualizer if you prefer to view your data from left to right.

d3VIEW Applications: A Cheat Sheet on How They All Connect

Thu, 15 Apr 2021 00:00:00 +0000

The d3VIEW Applications collaborate together to make your data-to-decision^TMexperience seamless. Each application has a specific role, from data management in Databases to data exploration in Simlytiks, as part of the whole. Structure your data-to-decision^TM making based on how they connect to get the most out of your experience on the platform. The following graphics showcase some connective maps on how the integrated applications can be utilized.

Simulation Engineer Map

Physical Test Engineer Map

Data Scientist Map

Advanced Simulation Engineer Map

Project Manager Map

To learn more about some of d3VIEW’s applications, please visit the platform page here.

Layout Editor for Templates

Fri, 09 Apr 2021 00:00:00 +0000

Simlytiks Layouts can now be edited directly under a template. In the Templates application, open a template to edit it. Tab over to the Layout Section and use the list of responses to create pages populated with visualizations. The editor is set up just like Simlytiks and uses basic placeholders, so you can get an idea of how the exploration will look when the template is applied.

About Templates

Templates, or data extractions, provide ways to dig deep into your data. They include no-code or low-code options for finding important insights, such as generating a 3D view of a driver-impact analysis. To learn more about Data Extractions, please visit this page.

New Ranking Table Visualizer for Simlytiks®

Fri, 26 Mar 2021 00:00:00 +0000

In addition to the 40+ visualizers, Simlytiks^® now has yet another new way to visualize your data. The new Ranking Table visualizer presents your data in table format with sized and colored bars for quick and easy comparisons between tests, models, occurrences, specimens, data samples, etc.

New Simlytiks Layouts: Save Your Visualization Format

Thu, 11 Mar 2021 00:00:00 +0000

You can now save and implement your method of exploring for Simlytiks datasets. Layouts allow you to integrate a particular visualization set-up for your data. Save multiple layouts to switch between different explorations easily, or create a main layout to apply a standard to similar datasets.

Saving a layout preserves pages, visualizations, including their customizations, and even filters. A particular layout will be available for a dataset as long as it meets the layout requirements, i.e. similar responses and data type.

Machine Learning in d3VIEW

Fri, 26 Feb 2021 00:00:00 +0000

d3VIEW provides advanced capabilities that can accelerate your data analysis and exploration. One of these features includes machine learning, the ability to train AI to predict outcomes.

Machine Learning helps complicated business processes that can be hard to define without demonstrating its concepts. ML can also aid in data mining, finding relationships in data more efficiently.

The process involves showing examples of the operation to be learned. For example, as illustrated below, the machine is presented with concrete, correlating data about an SUV, motorcycle and car. After it processes this, the machine can then decipher the correct counterpart when given the image of a motorcycle.

Advanced Data Tables: View and Manage Metadata

Fri, 05 Feb 2021 00:00:00 +0000

d3VIEW makes it easy to access and review your metadata on the platform with advanced data tables. Keep assets such as your simulations or physical tests organized for simple tracking.

The clean and simple interface helps visualize tabular data effectively.

Selecting and grouping metadata is a breeze. Color code metadata groups and compare them on Simlytiks with just a couple clicks!

Navigate the d3VIEW Platform with New Simulated Tours

Fri, 22 Jan 2021 00:00:00 +0000

d3VIEW has just upgraded their platform tours, simulating basic processes so new and current users can learn how to navigate the platform better. Tours have been created for the d3VIEW basics and the most important applications.

Current applications with guided tours.

Explore User Friendly Navigation with Dashboard Pages and Filters

Thu, 14 Jan 2021 00:00:00 +0000

d3VIEW makes navigation more efficient with advanced filtering for Dashboard pages. Populate your dashboard with important application pages that you can sift through and access quickly on the same page. Each page presents your application metadata in an advanced data table.

UPDATE: Add page and Dashboard pages panel is now located at the top of the page instead of the left side bar.

Updated Dashboard’s pages panel.
Each tab is a different application page.

Old Dashboard’s pages panel.

Then, customize your filters to only show the most relevant information. Filters stay present even after closing out of the platform. The attraction of this lies in the capability to make endless amount of application pages with customized or more specific filters.

Enhanced PowerPoint Reporting with Slide Layout Customization

Thu, 07 Jan 2021 00:00:00 +0000

Reporting data in d3VIEW just got easier with the ability to change, modify and add layouts while saving PowerPoints in Simlytiks. While using the PowerPoint builder, save the current slide layout, export it to upload later or load one from a JSON file. When exporting the data set to a PPT, upload a previously exported layout or choose between already saved or master layouts.

Snap shots of the prompts for saving, exporting and uploading slide layouts.

d3VIEW’s PowerPoint Builder works with the Simlytiks application to make reporting quicker. It takes away the extra steps of downloading data or visualizations and adding them to a separate PPT. The builder contains the important elements of PowerPoint with the ability to edit Simlytiks charts creating an integrated experience.

3 Ways to Report Data Exploration in Simlytiks

Mon, 12 Oct 2020 00:00:00 +0000

The endless amount of data exploration on Simlytiks makes the ability to effortlessly share our findings for reporting crucial. Reporting an exploration can be implemented via exporting or sharing single visualizers, pages or data sets. We’ll go over the most effective ways of exporting or sharing with the intention of efficiently reporting your findings.

For reporting data exploration specifically, certain features over others help organize or share visualized data more productively. These include:

d3VIEW Launches New Website Debuting Platform Depictions

Mon, 12 Oct 2020 00:00:00 +0000

With Enhancing Illustrations,
New FAQs and Application Pages

We just launched our new website that summarizes the data-to-decision platform through depictions of our most important applications. Explore the enticing and catchy illustrations on the landing page to learn more about what makes up d3VIEW.

Click on any of the top six icons to view an explanation of how that application enhances the platform and helps engineers and scientists analyze, organize and explore their data more efficiently and effectively. Each preview on the home page has a separate application page for a more extensive dive into its most valuable aspects. The Simlytiks Application preview for example presents an informative and captivating illustration about how the app processes your data and turns them into rich, explorative visualizations. Click the Learn More button to view more information in Simlytiks separate application page.

Dr. John Hallquist Video on LS-DYNA

Tue, 21 May 2019 00:00:00 +0000

Visualizing LS-OPT®Sampling points in d3VIEW

Tue, 06 Nov 2018 00:00:00 +0000

LS-OPT offers several sampling schemes among which D-OPT, Space filling and Latin Hypercube are among the popular schemes. Using d3VIEW’s LS-OPT output parser, the three schemes were used to generate experiments for variables that ranged from a mininum of 0.0 and a maximum of 1.0. Following images compare the distribution of the samples for all three samples, samples from D-OPT, samples from LatinHyperCube and Space-Filling. As you see, if one is interested in a strong sensitivity analysis, D-OPT or Space filling may provide them as the samples are concentrated towards the lower and upper limits. If one is interested in samples that spread across the limits, Latin Hypercube might be a good choice.

Crashing A 1998 Toyota Into A 2015 Toyota Shows – How Far Car Safety Has Advanced

Tue, 16 May 2017 00:00:00 +0000

Rare video of Dr. John Hallquist on how DYNA3D (now LS-DYNA) started in LLNL

Tue, 16 May 2017 00:00:00 +0000

A very rare and treasurable video of Dr. John Hallquist discussing about the problem that resulted in today’s LS-DYNA commercial software.
You can read the full article here Computer History Museum

Free SSH and SFTP Tool for Windows

Sun, 21 Jun 2015 00:00:00 +0000

Windows users usually have a need to connect to Linux based systems and rely on Putty or commercially available tools. One software that system administrators use and recommend is MobaExtern – that is free and extremely powerful. If you are on a Windows platform this tool may greatly help connecting to other machines seamlessly.

You can visit http://mobaxterm.mobatek.net/

2015 LS-DYNA European Conference

Sat, 13 Jun 2015 00:00:00 +0000

2015 LS-DYNA European conference will be held in Wurzburg, Germany. You can get more information from here .

LS-DYNA Conference 2014

Fri, 13 Jun 2014 00:00:00 +0000

The 13th LS-DYNA conference was the largest conference which was attended by over 650 attendees from around the world.

You can find the papers from the conference here

Following are some pictures from the hugely successful LS-DYNA conference recently held in Dearborn, Detroit.

1. Dr. John Hallquist, President and CEO of LSTC, presenting the latest developments in LS-DYNA.

Commenting LS-DYNA Keyword Blocks

Thu, 24 Apr 2014 00:00:00 +0000

A clever way to comment out blocks of keyword can be easily achieved using the *COMMENT keyword.

Example: In the following example, the keyword *MAT_ELASTIC and all cards until the next keyword is commented out by simply adding a *COMMENT in front of it.

*MAT_ELASTIC 1, 1.0e-9, 210.00, 0.3 *SOME_OTHER_KEYWORD .... ....

*COMMENT*MAT_ELASTIC 1, 10e-9, 210.00, 0.3 *SOME_OTHER_KEYWORD .... ....



Frequency Domain and Fatigue Analysis in LS-DYNA
Wed, 23 Apr 2014 00:00:00 +0000
Dr. Yun Huang and prepared an excellent package to get started in Frequency Domain and Fatigue Analysis in LS-DYNA.
You can download the package by copying and pasting this link into a new browser window: http://ftp.lstc.com/anonymous/outgoing/huang/package/LS-DYNA_freq_domain_2014.01.16.zip  
(From FTP.LSTC.COM)





Parameter NLOC in *SECTION_SHELL
Wed, 23 Apr 2014 00:00:00 +0000
NLOC value (default = 0 ) allows you to specify an offset of the reference surface from the nodal surface. Image below illustrates the significance of this value.



Cohesive Element Timestep
Tue, 11 Mar 2014 00:00:00 +0000
Cohesive material models are well suited for representing the behavior of structural and non-structural adhesives that is now increasingly used. To accommodate extreme dimensions of the element such as zero volume or near-zero volume, the timestep of the Cohesive element is based on the characteristic stiffness and mass of the element instead of the characteristic length.
Thanks to Thomas Borrvall for sharing valuable information on this.


Parameter DIR in DEFINE_COORDINATE_SYSTEM
Mon, 09 Dec 2013 00:00:00 +0000
In earlier versions of LS-DYNA, the axis N1-N2 was always set as the local-x but in new versions (since LS-DYNA v971), the N1-N2 vector can be configured to be either X,Y,or Z. Image below shows the influence of DIR in the local system set up.



Recommended settings for Spotwelds
Fri, 25 Oct 2013 00:00:00 +0000
When using spotwelds, there are several non-default parameters that are recommended to improve the spotweld behavior and model robustness. Following are some of the important parameters:
1. CONTACT_CONTACT/OUTSEG

This parameter helps to get a list of all spotweld nodes and the parent segment information. This is helpful in earlier designs to ensure the spotweld node is tied to the desired parent element.
2. CONTROL_CONTACT/SPOTSTP

When a spotweld node is untied, LS-DYNA silently deletes the element and continues the calculations. It is recommended to set this parameter to 2 so LS-DYNA can delete the weld, print the node of the sptoweld and continue. This helps to tract the untied nodes and the deleted welds. 


Total Mass, Physical Mass and Added Mass
Thu, 02 May 2013 00:00:00 +0000
LS-DYNA reports three types of mass information for the model. The total mass and the physical mass is the same which is the mass of the model before any added mass is calculated. Added mass is the mass required to add to the nodes for all elements whose timestep is below abs(DT2MS). 
The effective mass is the "total mass or physical mass + added mass".


Air particles and relaxation when using Particle based airbag inflation
Mon, 29 Apr 2013 00:00:00 +0000
When using particle based airbag inflation method using *AIRBAG_PARTICLE, the initial air in the airbag can be modeled using control-volume approach or as particles. This is governed by the parameter IAIR. When IAIR=1, a uniform-pressure model is used to specify the initial atmospheric temperature inside the bag. When IAIR=2, one can specify the number of air particles specified using the NP_AIR parameter. The number of gas particles and the air particles must be specified such that the molar mass per particle should roughly be equal for both air and gas during collision.


MPP LS-DYNA Intermittent Profiling Information
Wed, 26 Sep 2012 00:00:00 +0000
During MPP LS-DYNA execution, often there is a need to know how each of the “threads” are doing in terms of overal CPU utilization. Until now, one has to wait till the job is fully finished so we can review the load-balance information from the main D3HSP file. 
From LS-DYNA 971 r7 onwards, there is now a new “sense-switch” control named “prof” that can be now used to output CPU utilization while the job is running. This is a great feature to probe long-running jobs and to ensure that the run is performing well.


TSRFAC – Gradual introduction of strains in Airbags with Reference Geometry
Tue, 19 Jun 2012 00:00:00 +0000
In Airbags with reference geometry (*AIRBAG_REFERENCE_GEOMETRY), when the airbag bag element in folded state is smaller or larger than the reference state, stress needs to develop. LS-DYNA suppresses these initial strains so no stresses develop to avoid bag distortion and to improve stability. This may cause the bag to deploy but its final shape may not be accurate when compared with the intended bag shape.
If you induce the strains quickly, then the bag geometry is altered during the early simulation cycles. To avoid this, it is necessary to induce the strains gradually ie over a certain period of time. That is where the TSRFAC with a load-curve comes into play. You simply define a curve whose x-axis is time and y-axis is a scale factor for the strain.

The choice of time is user-dependent but if you can induce the strains before the bag attains fully deployed state,

the bag can potentially deploy whose final shape may be much closer to the desired shape.


Hugely Successful LS-DYNA Conference 2012
Sat, 09 Jun 2012 00:00:00 +0000
Recently held 12th LS-DYNA Conference, June 4-5 2012, was a huge success with over 680 attendees from over 21 different countries. It was great to see users from all over the world attend and present some fascinating work in LS-DYNA. The concluding talk on LS-DYNA developments and roadmap from Dr. John Hallquist and the development speakers showcased some powerful features in the upcoming versions of LS-DYNA.
Below are some personal pictures taken at the conference. You can view more pictures from  2012 LSTC Conference Pictures 


Past, Present and Future of Writing
Fri, 08 Jun 2012 00:00:00 +0000
My son’s, who is in 3rd grade, rendition of how we may be writing in the future …..




Visualization of Triaxiality Factor in LS-PrePost
Fri, 02 Mar 2012 00:00:00 +0000
Stress Triaxiality is the ratio of Hydrostatic stress and the von-Mises stress and is known to have a great influence on the plastic deformation.

You can view this factor in LS-PrePost now as shown below.




LS-DYNA Advanced Class in Detroit
Fri, 24 Feb 2012 00:00:00 +0000
Its been a while since my last post. I wanted to take the time to share that I will be teaching an LS-DYNA Class in Detroit, Michigan. You can visit  Registration  for more information. FEA Information will be including more information on this in its next publication.



LS-Prepost on Mac !
Fri, 27 May 2011 00:00:00 +0000
LS-PrePost development version 3.2 is now released for Macs. Below is a screenshot of LS-PrePost running on a MacBook Pro.

You can download it  Here 
Click to Enlarge:





Oasys 4th LS-DYNA Update Meeting in Pune and Bangalore
Sat, 16 Apr 2011 00:00:00 +0000
I will be attending the upcoming LS-DYNA Update meeting in Pune (May 3, 2011) and Bangalore (May 5, 2011). You can find more information at  LS-DYNA Update meeting . If you are in Pune or Bangalore, it will be great to see you there.


Tensile failure in Low Density Foams
Tue, 14 Dec 2010 00:00:00 +0000
When modeling low-density foams, it is important to consider potential failure under tensile loading. In LS-DYNA, the most popular constitutive material model is MAT_LOW_DENSITY_FOAM (MAT_057), in which the default treatment of foams under tensile loading is linear with no failure. The Elastic Modulus (Emax)  in tension is computed to be the max( max(slope of the stress-strain curve in compression), E). With this treatment, the element does not fail and its stiffness in tension is based on Emax.


Viewing Contact Frictional Energy
Tue, 14 Dec 2010 00:00:00 +0000
When friction is enabled in contact treatment using static or dynamic fricition coefficients (FS, FD in *CONTACT), the energy dissipated due to friction can be recorded and visualized. The parameter that tells LS-DYNA to ouput the frictional energy is  FRCENG  in *CONTROL_CONTACT.  FRCENG  by default is set to 0 to ignore the recording and output of the frictional energy. When  FRCENG  is set to 1, LS-DYNA outputs the frictional energy as “Surface Energy Density” into a binary database name “INTerface FORce” (INTFOR) file. The INTFOR file is not output by default and hence to request the output, you must use the keyword *DATABASE_BINARY_INTFOR with a frequency of output time (DT) AND provide a command line argument “s=Intforc_file_name”. Upon completion of the simulation, you can read the INTFOR file using LS-PrePost using File/Open/Interface Force File option and use FCOMP button to fringe the frictionaly energy.


Hybrid LS-DYNA
Thu, 21 Oct 2010 00:00:00 +0000
With the recent growth of multi-core chips, scalibility of pure MPP LS-DYNA beyond 128 cores has shown degration due to several factors including latency and network communications. LSTC has recently developed a new code named “Hybrid LS-DYNA” that provides sustained scalibility for large number of cores and also yields digit-2-digit repeatibility when changing the number of cores per job. Both these offer tremendous advantages as we move forward to take advantage of multi-core chips. A surpise advantage that we recently saw is the ability to run IMPLICIT jobs in Hybrid LS-DYNA on comptuers with substantially less memory.


Mat224 Keyword Manual Pages
Wed, 20 Oct 2010 00:00:00 +0000
Several of you requested the manual pages for the newly developed tabulated Johnson-Cook constitutive law now labeled as MAT_224.

Here are the three pages of the keyword manual.
 MAT224 All Pages  [ Click the image to enlarge]


 MAT224 Page 1  [ Click the image to enlarge]



 MAT224 Page 2  [ Click the image to enlarge]





LS-DYNA Material Selector
Tue, 05 Oct 2010 00:00:00 +0000
Finding a good material law can sometimes be a daunting task even for experienced users. To facilitate a quick review of possible material laws for a given material criteria, a  LS-DYNA Material Law Browser  was created for personal use and I hope its useful for others.
Please send any feedback you may have at info@d3view.com


Shell Local Material Axis Definition for Orthotropic Material
Tue, 05 Oct 2010 00:00:00 +0000
Most orthotropic material rely on the parameter AOPT to define the change/update the default material axes defined by LS-DYNA. The default axis for every shell element is based on the order of the node numbers if INN=0 which is then based on N1-N2 and the cross-product of N1-N2 and N1-N4. The default material axes may not necessarily coincide with the direction of the intended axes for a given material. To help reorient the default material axes, LS-DYNA provides the parameter AOPT to reorient and further rotate the reoriented axes by using the BETA parameter in *SECTION_SHELL and/or *ELEMENT_SHELL_BETA. The following table attempts to illustrate this. I have ignored AOPT = 3, as I am yet to find a better way to illustrate it in an easier way, but I will update it when its done.


LS-DYNA and D3VIEW helps BYU Students build PACE F1 Car
Sat, 28 Aug 2010 00:00:00 +0000



Over six months ago, two students, Rob Moncur, pursuing his MS, and Satyan Chandra, pursuing his UnderGraduate Studies, in  Brigham Young University (BYU)  set out on a path to build a  LS-DYNA  crash-analysis model of the PACE F1 car in under 8 weeks. Under the guidance of their professor, Dr. Greg Jensen, and with minimum support from myself, Rob and Satyan achieved, what seemed initially a very challenging task, to build a working crash-analysis model of the PACE F1 car as part of their course work. You can find their final report PACE_LSDYNA_FINALREPORT_Aug28.


Experimental Data Management inside d3VIEW
Thu, 19 Aug 2010 00:00:00 +0000
As a simulation engineer, we always like quick access to experimental data. Over the years, with a powerful framework that was developed within d3VIEW, this is now possible to import and visualize experimental data. With a few configurations, you can further tie this with simulation data for easy overlay and comparison. This following video shows how it can be done.

Experimental data management in d3VIEW from d3view on Vimeo.


Thick shells in contact
Fri, 13 Aug 2010 00:00:00 +0000
During one of my recent trips, a question was raised about how LS-DYNA treats thick shells in contact in particular if the contact would detect the surface sides. This simulation  Thickshells in contact  shows that LS-DYNA treats the thickshells as solids in which all external (free) surfaces are included in the contact. ERODING contact would also regenerate the free surfaces upon element deletion.



Visualizing Dynamic Relaxation Convergence
Thu, 29 Jul 2010 00:00:00 +0000
Understanding the rate of convergence when employing Explicit Dynamic Relaxation can be very useful to track model sensitivity and to solve convergence problems. d3VIEW now has support to auto-extract the convergence information after a simulation is completed. It also processes DR graphics data to identify points of divergence.
Attached is a snapshot from a recent simulation that was used to study the number of cycles used to check for convergence in the event of a gravity initialization of a rigid sphere on a foam block. This study showed that if we have a higher number of cycles to check for convergence, then it is possible that we completely miss the convergence point and the problem could continue to oscillate about a median point. In a test problem of  Gravity Initialization  using Explicit DR, depending on using 100 or 1000 cycles between convergence checking, the sphere in the case of 1000 cycles actually converged on its rebound of the surface of the foam.


SPC Constraints in Dynamic Relaxation to Improve Convergence
Tue, 27 Jul 2010 00:00:00 +0000
Dynamic Relaxation (DR) is a simple but effective technique to initialize structures to pre-loads prior to any primary load application. LS-DYNA has supported DR for several decades and is used by several users. Recently, in an attempt to improve convergence (Explicit DR or Implicit DR), there was a need to  HOLD  certain portion of a structure to reduce undesired movement. The problem with enforcing such constraints using BOUNDARY_SPC was they continue to be present in TRANSIENT phase as well which may not be desired.


Visualizing User Generated Results into LS-OPT
Thu, 10 Jun 2010 00:00:00 +0000
To view results from manual what-if studies, LS-OPT provides a great way to import these results so we can take advantage of its data visualization package. The attached image, an excerpt from the LS-OPT Manual, shows how we can do this.



Sensor Definitions in LS-DYNA
Tue, 18 May 2010 00:00:00 +0000
Sensors can be used to trigger entities based on certain criteria. The following image is a high-level steps involved to take advantage of sensors in LS-DYNA.



*RIGIDWALL_{DISPLAY} option
Mon, 03 May 2010 00:00:00 +0000
Rigidwalls are analytical representations of surfaces or volumes that are frequently used to represent stiff structures that are either stationary or in motion. Viewing of such analytical definitions in D3PLOTs were not possible for most rigidwalls. A new option in LS-DYNA named DISPLAY that can now be used to any *RIGIDWALL definitions which causes LS-DYNA to create an element that matches the dimensions of the rigidwall which can then be viewed alongside other elements. Optionally, a PID with material properties can be associated.


New Coordinate based Joint Definition – *CONSTRAINED_JOINT_COOR_{JOINT_TYPE}
Mon, 03 May 2010 00:00:00 +0000
Several joints are available in LS-DYNA that can be defined between two rigid bodies or nodal rigid bodies. The difficult part of the joint definition from the pre-processing point of view is the creating of nodes that defines the joint axes and subsequent merging of them to the respective rigid bodies. To simplify this problem, LS-DYNA R5 59341 and later versions has a new keyword named  *CONSTRAINED_JOINT_COOR_{JOINT_TYPE}  that only requires the two rigid body IDs (or nodal rigid body ID) between which the joint is the modeled and the actual coordinates of the joint axis or points. Using this information, LS-DYNA will internally create all necessary nodes and assign them to the respective rigid bodies (or nodal rigid bodies).


Dr. Benson’s notes on Hydrocodes.
Fri, 30 Apr 2010 00:00:00 +0000
A nice  publication  on hydrocodes by  Dr. Benson .


LS-DYNA Examples Blog by Student Qui
Fri, 30 Apr 2010 00:00:00 +0000
 Update  The blog no longer seems to exist.
I recently came across a nice blog written by QUI. It is remarkable that he is willing to share examples and his experiences in LS-DYNA. The broad spectrum of LS-DYNA applications can never be fully covered by a single blog or a small set of publications. It is great to see such new sites emerging and I hope more users come forward to share their experiences.


Unloading in MAT_FABRIC (MAT_034)
Thu, 15 Apr 2010 00:00:00 +0000
 This is a post by Guest Author Satish Pathy who works full time for LSTC 
In *MAT_FABRIC, element formulation 4 & 14 will allow you to input unloading curve for the material. Recently in a model it was noticed, that when a large compressive stress develops in the fibers, lsdyna would release some of these stresses by inverting the elements and thus leading to numerical instability. This could be avoided by activating compressive stress elimination, CSE=1. However, it still does not improve the fabric behavior with the current unloading method.


Mass scaling for MAT_SPOTWELD elements
Mon, 05 Apr 2010 00:00:00 +0000
Deformable spotwelds modeled using beams or solids elements can invariably limit the global timestep due to its small dimensions. LS-DYNA provides two methods to scale the spotweld timestep. The first method is the well-known global mass-scaling using DT2MS in CONTROL_TIMSESTEP. When DT2MS is non-zero (usually a negative number), the  density of the spotwelds are modified such that each spotweld element’s timestep is equal to abs(DT2MS). The second method involves the use of DT in MAT_SPOTWELD which when non-zero, LS-DYNA modifies the densith of ONLY the spotweld elements such that the spotweld timestep has a minimum timestep of DT. When both DT2MS and DT are non-zero, LS-DYNA first processes the spotweld elements such that the spotweld timestep is DT and then re-processes the elements such that the spotweld element’s timestep is greater than abs(DT2MS).


Nature by Numbers
Fri, 19 Mar 2010 00:00:00 +0000



Shell, Solid and Beam Formulations for Explicit and Implicit
Mon, 22 Feb 2010 00:00:00 +0000
Control cards are often handy to overwrite local values. A good example would be if we need all parts to use a certain element formulation THEORY which is specified in *CONTROL_SHELL. As with any global control cards that manipulate local values, the global values specified in *CONTROL keywords are used ONLY if the local values are either zero or blank. If any of the parts that uses a SECTION_SHELL keyword whose ELFORM parameter is non-zero, then THEORY is ignored and the value from ELFORM will be used.


Modeling rigid bodies
Wed, 13 Jan 2010 00:00:00 +0000
LS-DYNA allows the modeling of rigid-bodies by assigning any part with the MAT_RIGID material law (MAT_020). This is by far the most easiest method available when compared with all finite element codes. When using MAT_RIGID, there are three distinct ways to model a rigid part and they are briefly explaine below.
 1. Finite Element based rigid bodies 
In this method, we first discretize the geometry using nodes and elements and use this information in LS-DYNA. The mass, inertia tensor and the center-of-gravity is then computed based on the density in MAT_RIGID keyword and the finite elements description.


Happy New Year !
Fri, 01 Jan 2010 00:00:00 +0000
Wishing everyone a very happy new year.


Significance of IGAP Parameter in *CONTACT in Implicit Analyses
Tue, 01 Sep 2009 00:00:00 +0000
In traditional explicit analysis, there is no convergence criteria that is checked for each time step. However, in Implicit calculations, incremental displacements are evaluated such that a displacement norm and the energy norm are within a pre-defined tolerance before convergence is assumed to be obtained. This is the so-called iterative scheme in Implicit Non-Linear Analyses (Static and Dynamic).

Any non-linear problem will eventually involve contact between surfaces for large deformation problems. LS-DYNA handles these contact much the same as in Explicit analysis where a penalty-force is imposed if a node is found to be inside a volume of another part. In the case of the Implicit a penalty is imposed by adding a stiffness matrix when the contact is detected and the penalty force is added to the right hand side.

In certain cases, the sudden detection of contact penetration and subsequent addition of the stiffness causes some difficulty in convergence for Implicit analyses. To overcome this, LS-DYNA introduced a parameter called IGAP where the stiffness is not added instantaneously but rather ramped up to 100% over a certain number of iterations. Also, no force vector is added to the right hand side. This has a tendency to cause a ‘sticky’ condition which seems to help overcome convergence issues.  IGAP is now set to ON by default. Care must be taken to ensure no excessive penetration is present in the model even with IGNORE=1.


Marsha Victory, Thank You For Your Blog Hosting Sponshorship !
Sun, 16 Aug 2009 00:00:00 +0000
I am pleased to inform that Marsha Victory has continued the sponsorship of D3VIEW blog hosting. If this blog has been of help to you, please take a moment to thank Marsha. She can be contacted at marsha@lstc.com.
Thanks very much, Marsha, for your support.


Boundary prescribed motion and Contact
Sun, 09 Aug 2009 00:00:00 +0000
When nodes are involved in both contact (penalty) and prescribed motion, contact failure is expected to occur. This is because the boundary conditions are always processed after all the contacts are handled that results  in nodal accelerations being updated to enforce the boundary conditions. I will soon publish some examples to illustrate this phenomenon.


LS-DYNA 971 Release 4 Manual Available for Download
Wed, 13 May 2009 00:00:00 +0000
You can download the  LS-DYNA 971 r4 Manual  (PDF, 11.5 Mb)
 Update  The broken link has been fixed


LS-OPT 4.0 is now released.
Wed, 13 May 2009 00:00:00 +0000
The LS-OPT Version 4.0 beta release is now available at:
 LS-OPT 4.0 
The Presentations folder has an overview and outlook

of LS-OPT. The main feature is the next generation

post-processor (Viewer).
Note that LS-OPT/Topology will be available

later in 2009 as a separate module.


Mass calculations for Discrete Beams
Wed, 13 May 2009 00:00:00 +0000
Discrete beams, like discrete springs, require valid mass at the nodes to compute the timestep. Unlike continuum based elements, the length of the discrete beams, are not used in the timestep calculations. Hence realistic density in the discrete beam material model must be used. There are two methods this can be achived.
Density (RHO) in the material card is not equal 1.0 

When the density in the material  is anything but unity, it is required to set appropriate value for the parameter “VOL” in the SECTION_BEAM keyword. When VOL is non-zero and RHO in the material card is not unity, LS-DYNA computes the mass by simply multiplying these two parameters and lumps it equally to the two nodes that make up the discrete beam.


Discrete variables in LS-OPT
Mon, 09 Feb 2009 00:00:00 +0000
Starting version 3.0, LS-OPT supports the definition of discrete variables. Discrete type of design parameters are helpful when there is a need to find the optimum values from a “set” of values. A good example would be the choice of element formulation. The possible values for LS-DYNA for a quad can only be a subset of formulations listed under ELFORM in SECTION_SHELL. Any value chosen by LS-OPT that does not uniquely match the subset will result in non-physical or error terminations by the solver such as LS-DYNA.


Fast Debug of LS-OPT driven Optimization Problems
Wed, 28 Jan 2009 00:00:00 +0000
LS-OPT is widely used to optimize designs or parameters using a number of experiments obtained by running LS-DYNA simulations. The number of experiments (simulations) per iteration is dependent on the number of variables defined in LS-OPT in addition to the type of point-selection (DOPT, LatinHyperCube, etc). When a large number of simulations are involved, it is important to validate the the sequential following steps.
(Click to Enlarge)

Each of the above steps must work well for LS-OPT to consider the experiment as a valid simulation.

To ensure the steps work well, we can set two parameters that will cause LS-DYNA and LS-OPT to work together in running a “dry” run.


Free Limited LS-DYNA Version to Assist Displaced Workers
Sat, 13 Dec 2008 00:00:00 +0000
LSTC has introduced a free limited LS-DYNA version for U.S. unemployed LS-DYNA users as a result of the current poor economic conditions. A free LS-DYNA course may also be introduced in the coming months. Please contact Marsha Victory at 925 449 2500 or send her an email at marsha@lstc.com.


Multi Solver Run in LS-OPT
Tue, 11 Nov 2008 00:00:00 +0000
In LS-OPT, one can run a multi-disciplinary optimiztion or a multi-solver type optimization problem, where the variables can be shared among the different solvers. In performing DOE or any optimization using LS-OPT, it is important that consistent experimental points are used in the evaluations. To ensure this, one can use  solver experiment duplicate solver_1  command or using the LSOPTUI, select the SAMPLING/Duplicate options.


Packing LS-DYNA Input Files for Easy Distribution (v1.1a)
Wed, 15 Oct 2008 00:00:00 +0000
In a  previous  post  about a simple Python script that scans a LS-DYNA input file to package all INCLUDED files recursively so the entire model can be compressed and sent to the recipient.
Based on some new suggestions, largely by Brian Wainscott, I have attached a revised script that handles the included files a little more nicely. It works by scanning the main input file and copies all INCLUDED files to a more generic directory (INCLUDES) and also updates the path in the main file.


Tolerance used for Tying Slave Nodes in TIED contacts
Wed, 15 Oct 2008 00:00:00 +0000
TIED contacts help “bond” two surfaces of different mesh densities. When using the default constraint method, the projection distance of the slave node onto to the closest master segment must be zero and this is achieved by LS-DYNA by updating the slave node coordinates such that it lies on the master surface. This coordinate update is done during initialization and does alter the geometry. To avoid significant element distortion, LS-DYNA uses a built-in tolerance to discard slave nodes that are “too-far” from the master surface. In some cases, the internal tolerance could lead to slave nodes being discarded by LS-DYNA which may otherwise be required to be tied. To enable this, LS-DYNA allows a user-defined tolerance using SST as shown below.


Damage modeling using GURSON
Mon, 13 Oct 2008 00:00:00 +0000
Material parameter identification of GURSON material requires a process of fitting using an optimization package such as LS-OPT to match against a measured response such as a test. Following is a stress-strain curve that is achieved as a process of parameter identification using LS-OPT and LS-DYNA.



Characterizing plasticity material models using data from test
Thu, 09 Oct 2008 00:00:00 +0000
It is common to perform a uni-axial tensile test on a material sample to generate stress-strain curve for use in numerical models in LS-DYNA. The problem frequently encountered by analysts is the cleaning of the test data that is usually noisy. I recently wrote a small Python utility that takes any test generated force-deflection curve that does auto cleaning and generate an effective stress vs effective plastic strain curve for use in any plasticity models directly in LS-DYNA.


Optimizing monotonically increasing load curves
Thu, 09 Oct 2008 00:00:00 +0000
In cases where a monotonically increasing curve such as pressure_vs_leakage in *AIRBAG or effective_stress_vs_effective_strain in plasticity models in *MAT are to be parametrically identified by an optimization software such as LS-OPT to match against a physical test, it is important to ensure that the points identified by LS-OPT satisfy the non-negative slope. To satisfy this, it is common to place constraints on the points such that the f(Xi+1) is greater than or equal to the f(Xi). This method is less desired as LS-OPT has inherent difficulties in removing points that do not satisfy the constraint.


Packing LS-DYNA Input Files
Thu, 04 Sep 2008 00:00:00 +0000
In these days, a finite element model consists of several INCLUDE files either relative or absolute. When collaborating with other people, it is very difficult to remember sending the included files and also if we do remember, it is cumbersome if not difficult to find them and zip them as one file. I recently encountered this problem and wrote a simple utility in PYTHON to make this a little easier. Once you download this file, you simply invoke this using “pack_dyna main_input_file.k” and it handles all the rest of packing to give you one BZIP2 file to send to your contacts. In some cases, you may want to ignore absolutely references files (/some/path/to/a/include/file.k). To enable this, you can set the variable RELATIVE_FILES_ONLY to 1 which will cause the program to include only relatively included files (path/to/a/relative/file.k).


Termination due to Added Mass
Thu, 04 Sep 2008 00:00:00 +0000
In older versions of LS-DYNA (950 and lower) , when mass-scaling was active and over the course of the simulation when the percentage of added mass was greater than ENDMASS in *CONTROL_TERMINATION , LS-DYNA would terminate that job with no additional message. However, recent versions of LS-DYNA terminate the job AND provide a list of 20 nodes into D3HSP file which are sorted by the magnitude of their nodal mass (LS-DYNA uses a lumped mass approach). This usually helps since we can now review these 20 nodes to identify local instability especially in a large model.


971 Release 3.2 is Now Available
Fri, 15 Aug 2008 00:00:00 +0000
Here are the release notes.
 
Features and enhancements included in 971 R3.2 that were not available 
in 971 R3.1 include the following:

New Material Models:
*MAT_255 ()

Enhanced Material Models:
support of user defined failure for:
– *MAT_123 (VP=1)
– *MAT_103
– *MAT_024 (VP=1)
*MAT_191 now supports end release for beams
*MAT_187 updates
*MAT_126 add corotational local coord. system for formulation-1
Add V option for aopt=3,4
– *MAT_026
– *MAT_126
*MAT_036 added a cap to out-of-plane shear stress, when M is integer
*MAT_172 added hourglass properties for shells
*MAT_236 addes interior strain point calculation
*MAT_ADD_THERMAL_EXPANSION now supports *LOAD_THERMAL_VARIABLE_SHELL
*MAT_SEATBELT added error termination if the maximum slope in the
loading curve exceeds that of the unloading curve.
Added warning if modulus in a load curve table exceeds Young’s
modulus for several material models.
Print Warning if prca and prcb are blank in
– *MAT_002
– *MAT_022
– *MAT_054
– *MAT_055 
Added warning message or error termination if
user inputs improper stress-strain curve for fitting for:
– *MAT_027
– *MAT_077
– *MAT_177
– *MAT_178
Added the negative NUMINT option to material 123
Added viscoplastic strain rate to:
– *MAT_024 (VP=1)
– *MAT_123 (VP=1)
– *MAT_224 (VP=1)

Implicit:
Added synchronization of implicit time step after an adaptive
remeshing.
Added arclength method node control in MPP

Boundary Conditions:
Added implicit treatment of boundary prescribed orientation.

Airbag:
*AIRBAG_PARTICLE
added flag on AIRBAG_HYBRID_CHEMKIN to turn on/off digitized load
curves

Output:
messag: 
– Add list of untied nodes to MESSAG file for automatic tiebreak 
contact option
d3plot
– enable particle database in d3plot
intforc
– add MPP support for recent IOOPT option for intfor file.
– Added IOOPT=3 for *DATABASE_BINARY_INTFOR

Contact:
Update for new weld option (Honda)
Add a new feature to *TERMINATION_CONTACT allow the job to terminate when
the maximum contact force is reached.
Add guided cable contact to MPP
Add flag to turn on shell element offsets in contact.

General:
Added optional thickness scaling for *INCLUDE_STAMPED_PART
Added damage type DG_TYP=4 to DEFINE_CONNECTION_PROPERTIES
Added MPP support for IFLAG=1 in CONSTRAINED_EXTRA_NODES
Added new keyword *COMMENT
Added “date” option for *VENDOR keyword added to R3
Added a new command line option: ncheck=n
where n is the of number of times to check the existence of input file.
Support for constrained_extra_nodes option in selective mass scaling scheme
Add warning about not supporting prescribed motion during modal
superposition.
Added user-specified spin speed for PRESCRIBED_ORIENTATION_VECTOR
_____________________________________________________________________________
The remainder of this file describes (sometimes quite cryptically) many other
enhancements, additions, and bug fixes made since the release of
LS-DYNA version 971 R3.1. These items are listed chronologically
with the most recent items listed first.
_____________________________________________________________________________

improvements to global search for 2d_thermal contact

several minor bug fixes in sensors

Fix for *CONTACT_AUTOMATIC_…_TIEBREAK with OPTION=3 fixed in SMP – MPP was ok

Fix restart bug related to SPH and full deck restart.

Fix for rigid to deformable switching involving solid type 4
tetrahedron.

Fixed again two surface force transducers when used with segment based contact.

Fix for MPP handling of tied thickness when specified on the contact card.

Fix for MPP “groupable” override flag in pfile, for tied interfaces

Correct Implicit handling of tied nodes with failure constraints.

Fix for MPP output of peak pressures in intfor file: last state had 
all 0 for these.

enabling r-adaptive load_thermal by initizlizing temperature after rezoning

Fixed MPP brick weld initialization so that it will not hang.

Fixed bug in ansys outout.

Fixed bug for *AIRBAG_WANG_NEFSKE/HYBRID: Negative parameter A23
with Part-ID > 9999999 was not working in single precision.

Fix. Parameters from ELEMENT_BEAM_SECTION were not
transformed and stored correctly. Manual has to be updated, too.

Fixed possible division by zero in material 120.

A bug fix in springback compensations

Fix vc problem in automatic contact.

fix for rigid body coordinates for implicit to explicit switch

Fix: update orientation option for SMOOTH forming
contact (MPP only)

Fix for *DEFINE_CURVE_FUNCTION option RCF (now RCFORC)

Fix for interior contact option 2

Fix for *PARAMETER. Allowed a -minus sign before any parameter definition.
For example, -&VAR1.

Fix *sensor_define_node when n2>0

Fix for frictional energy calculation for auto tiebreak
contact

Fix 2 minor include transform bugs

Fix for case including both shell and 3D EFG.

Fix for coordinate ID’s related to orthotropic materials to transformm
to internal IDs in the keyword reader. This fix is to ensure that the
dyna.str file works as intended.

Fixes related to triangular shell element coordinate system to account
for invariant numbering.

Fix for material 57 to correct the calculation of internal energy
density which was inaccurate for the large time step sizes of the
implicit solver.

Fix for INCLUDE_TRANSFORM related to material 181.

Fixed potential 2 surface force transducer memory errors when used with
segment based contact.

Fix for rotations in MPP output of drdisp.sif file

Fix format to tell users to check D3HSP for printed curve IDs. The


curves may be internally generated in the keyword reader.

Fix for MPP rb compression in d3plot when used with pre-decomposition

Fixed MAT_236 for shells

bug fix calculating enclsosure radiation view factors for
axisymtric geometries.

Fix for *MAT_ADD_THERMAL and solid element constitutive models, e.g.,
type 3

Minor fix for MAT_073 reading.

Fixes for thermal option related to *LOAD_THERMAL_ELEMENT_…

Fixes for laminated shell theory (materials 22, 54, 55, 76, 114)
All Materials used 2x the correct weight on the on the top and bottom 
integration points for Labotto quadrature. For materials 76 and 114 with
user defined integration, the unsorted material properties were used for 
calculating shear strain terms, fxi,fyi and zi1. Since the sort routine
orders them top to bottom, this likely caused all the material properties 
to be flipped if the user input the points in the order from bottom to top.
This would cause incorrect results if diffrerent properties were used in 
each layer unless Labotto quadrature was used.
For materials 22 and 54, and 55, the unsorted material angles were used 
for calculating the shear strain terms, hi1, and hi2. For orthotopic 
material properties, the calculated hi1 and hi2 terms were therefore 
incorrect unless Labotto quadrature was used.

Fix for load_thermal_element option for erroneous error check leading to
termination.

Fix for fitting of Ogden foam model due to out-of-range numbers

Fix related to METALF when NDOF=3.

Fix related to type 4 triangular shell and buckling.

Fix for GCEOUT file

bug fix for M136

bug fix for AIRBAG_SHELL_REFERENCE_GEOMETRY

Fix memory clobber for implicit solid spotwelds

Fix for spotweld option to convert subset of beam elements.

Bug fix for *control_forming_template

Several MPP rigid-rigid contact:
friction handling, force summation, and surface reorientation.

Fix for load curve reading problem related to seatbelt shell elements.

MPP modifications to bucketsort for AUTO_TIEBREAK contacts, to better
handle very thick materials

Fix for material type 61 which goes unstable for tet types 10 and 13.

Update for handling 1000000 load curves efficiently.

Fix for *CONSTRAINED_JOINT_TRANSLATIONAL_MOTOR not working correctly in MPP

Fixed a bug in *LOAD_DENSITY_DEPTH if number of parts if more than 8

Fix for surface force transducers for segment based contact. This memory bug
could have happended when not all processors have 2 surface force transducers.

Fix for material 36 with hardening rule 7 (3 load curves).

Fix use of wrong variable in MPP d3part initialization.

Fix truncation error for *MAT_123

Fixed a segment based contact bug that caused the optional thickness on
*PART_CONTACT to be ignored if shell thickness updates were active and no parts
used the thickness scale factor on *PART_CONTACT.

Fix problem in automatic tiebreak options 8/10/11 where the mass of the
slave node was being used, but was not being passed, resulting in NANs.

Fixed a bug in MAT_SPOTWELD_DAIMLERCHRYSLER when used with damage types 1 
and 2. The density of the material changed to a wrong value after damage 
initialization.

Fix for joints in the presence of implicit-explicit switching.

Fix for *MAT_MUSCLE related to small stepsize

Fix for *DAMPING_PART_MASS related to velocity boundary conditions being
affected by damping applied to deformable nodes with prescribed motion.

Fix for *DAMPING_GLOBAL related to nodal points that have prescribed motion.
This damping changes the applied displacements from the specified
values. This fix corrects this problem for the nodes of deformable
bodies.

Use local rigid body accelerations for airbag pop option. Previously
the global accelerations were used which is in conflict with the
users manual’s instructions.

Bug fix for selective mass scaling in conjunction with 10-noded tets

Add MPP support for recent IOOPT option for intfor file.

Fix problem of MPP reopening intfor file during adaptive problems.

MPP fix for reorientation of surfaces with inconsistent normals

Fix storage allocation for constrained_linear with 2000+ nodes.

Fix for smooth contact problem related to undefined node set.

Bug fixed for 2D axisymmetric EFG in centering the stress point.

MPP fixes to output of d3part database

Fix possible bug in mat 173 principal stress direction calculation

Add option for alternative version of Mat 85 (does not affect existing models)

Fix for adaptive remeshing for ESORT=2

Fix MPP tied contact for implicit-explicit switching

Fix uninitialized variable in MPP rigid-rigid contact

Fix for thick shell type 26 to properly handle offset from midsurface.
Warping stiffness must be active.

Fix for thickness offset related to type 16 shell and warpage active.


Fix for PRESCRIBED_ORIENTATION

Fix flexible rigid body for initialization, rigid and flexible switching.

Fix for eigenvalue problems with only solid elements and no rigid bodies.

Fix for MAT_ARUP_ADHESIVE in *INCLUDE_TRANSFORM

Fix for *ELEMENT_MASS_NODE_SET

Fix for mat type 172 with shell type 16

Fixed for *AIRBAG_HYBRID_CHEMKIN

Fix: Internal energy is now computed for shell type 18.

Fix bug at corners when multiple boundary conditions are used 
with SPH elements

Fix for file SSSTAT in restart. Also we sperated the output interval
of *DATABASE_SSSTAT_MASS_PROPERTIES and *DATABASE_GLSTAT

Bug fix for ale interface force binary plot fsifor.


Minor fix for MAT_100_DA with DG_TYP=3: Default for GFAD now 1.e-15
(was 0.0 before, leading to no failure at all).

A bug fix for mapping with symmtric condition


Fix for Boundary Prescribed Orientation for Implicit.

Fix for energy calculation in material model 12

2.

Fix for *DEFINE_CURVE_FUNCTION: did not work for
translational and rotational motors.

Fix to damping when IGNORE is set to 1

Fix for Brode loading and shell sets is now fixed.

Bug fix for tiebreak contact option 11 with VDC damping and negative 
ncpu 

Added penalty formulation for treating contact between rigid bodies and
the rigid road surface.

Fix for format problem in DYNA.INC file related to *LOAD_PRESSURE_SHELL.

Fixed type 9 beam spot weld failure. The moment term in the failure
calculation may have used the wrong beam length since the wrong beam
element ID was used. The 3-sheet calculation was OK. Therefore for
models using 3-sheet welds, the bug may have not caused much trouble
since the 3-sheet calc is used for an entire block of beam elements if
any one of the beam participates in a 3-sheet weld.

Bug fix for tiebreak contact options 10/11 with viscous damping VDC.

Fix related to deformable to rigid switching, when the
Inertial properties are specified for the merged body.

MPP fix for rigid to rigid contact.

Fixed related to table lookups in CONSTRAINED_
JOINT_GENERALIZED_STIFFNESS.

Fix related to inconsistencies between Madymo an ls-dyna force
calculations for rigid to rigid contact using a force deflection curve.
Energy is now conserved.

Fix MPP explicit initialization for implicit joints 

Fix for possible memory clobbering when *RIGIDWALL_PLANAR and 
*PART_COMPOSITE are used together

Fixed a problem with solid welds. Weld failure types 7 and 8
use tied contact info to identify properties of the shells to which the
welds are tied. It is possible for the tied contact to be on a different
proceessor than the weld in which case the info cannot be found, so
message passing was added to weld initialization.

Fix for *INITIAL_AXIAL_FORCE_BEAM: resultant force was too high.

Fixed output of two-pass adaptivity

Fix related to implicit nonconvergence of materials 77, 177, and 178.

Fix related to implicit consistency flag (ncpu<0)

Fix for *ELEMENT_MASS_PART and shells: corrected mass calculation

Fox for RBE3 with DOF’s release. Problem occurred when consistency
option is active.

MPP fix/change for better handling of adaptive constraints if they occur
at decomposition boundaries AND they are involved in a tied interface.

Fix handling of sense switches (sw1,sw2,…) for implicit.

Fixed contact for Genoa material.

Fix for jumps in sliding interface energy when adaptive steps occured.

Bug fix for material 187.

Fix for non working thinning for thick shell elements and material types 2, 22, 55, and 58.

Fix for *SET_BEAM_GENERAL with the ALL option to exclude phony beams for
springs and dampers if BEAM is set to unity on the DATABASE _BINARY_
D3PLOT database.

Fix for RBE3 constraints for MPP Explicit.

Fix l2a problem related to output of optional joint energies

Fixed problem with INCLUDE_TRANSFORM for material model 176.

Fix for bug related to nonphysical stresses that develop soon after
the calculation begins. Keyword CONSTRAINED_SHELL_TO_SOLID.

Fix related to material type 120 related to FPE on selected platforms.



Killing LS-DYNA Jobs
Mon, 11 Aug 2008 00:00:00 +0000
Running LS-DYNA jobs (either interactively or as a batch job) can be interrupted with sense-switch controls by creating files “d3kil”, “D3KIL” and “switch” in the running directory. This works as expected without the use of any “jobid” definition. However, when using a jobid parameter either using *KEYWORD_ID or in the command line (jobid=jobname), LS-DYNA expects this jobid string to appear in the fiels such as “jobid.d3kil” or “jobid.D3KIL” or “jobid.switch” files in the running directory of the master node.


Effects of Initial Penetrations
Sun, 10 Aug 2008 00:00:00 +0000
It is well known that the presence of initial penetrations can spoil the accuracy of the analysis. A few days ago, while working on ODB barrier, some strange spikes in energies was suspicious even with IGNORE turned on. To understand this, I simply did a simple  shakedown  and generated some 100 d3plots to capture the effects. After analyzing the results, the strange effects were attributed to the presence of initial penetrations. What is interesting is these small penetrations can introduce contact stresses in the structures and can propagate through them. Attached is a clip generated from the barrier study where the simulation was run with no external loads, body forces, and boundary conditions. You can see the source of initial penetrations and how they travel at the top of the barrier (cladding sheet).


Nice article on Inertia Tensors
Thu, 07 Aug 2008 00:00:00 +0000
Came across this  nice article (PDF, 101kb)  about inertia tensors.


10th LS-DYNA Users Conference
Mon, 02 Jun 2008 00:00:00 +0000
The 10th bi-annual LS-DYNA Users Conference is less than a week away. You can visit the  conference home page  for more details.
While you are there, look for information on d3VIEW in booth 101 hosted by FEA Information, Marsha Victory.


Curve Offset in LS-DYNA
Sun, 06 Apr 2008 00:00:00 +0000
LS-DYNA offers ability to offset a defined curve. This helps us to for example to define an arbitrary fire time for airbags by simply changing the offset value rather than to change the entire curve. Depending on the type of curve, LS-DYNA adds two points at the beginning of the curve for positive offsets and NONE for a negative offset value when the offsets are applied to the Abscissa. If the curve represents a time history curve (default) and the offset is greater than zero, then LS-DYNA add two points: one at ZERO and the other at 0.999*OFFSET_VALUE to ensure that the ordinate (function) is zero until a x-value of 0.999*OFFSET_VALUE. The following is depicted below.


Initially in Contact – TIEBREAK contacts
Wed, 02 Apr 2008 00:00:00 +0000
When using TIEBREAK contacts, options other than 1, ties nodes ONLY if the nodes are initially in contact. Nodes not initially in contact will not be tied but can interact with master segments like the traditioanal compression-only contacts. To enforce the “initially” in contact condition, the  [initial_separation-(slave_thickness+master_thickness)*0..5] < 0 which causes the  initial penetration or initially in contact condition. If this value is greater than zero, you can use SST or MST values to enforce the condition.

The only method to verify if the intended nodes are actually tied is a quick normal mode analysis.



New LS-OPT Support Site
Mon, 31 Mar 2008 00:00:00 +0000
A new  LS-OPT support site is established with lots of useful information that covers examples, theory and many download materials.


Ten Recommendations to Improve Contact Stability for Explicit and Implicit Simulations
Fri, 28 Mar 2008 00:00:00 +0000
Here are 10 things (based on experience) that one can use to improve contact stability in any LS-DYNA simulations. They are not in any particular order.
1. Avoid duplicate contact definitions.

The general thumbrule is no pair of node/segment or segment/segment (in soft=2) should be treated for penetration by more than one contact defintion
2. It is extremely important that the interacting segments are similar is size and stiffness.

Rigid segments , in particular, interacting with deformable segments always use penalty (soft=0) treatment.



3. Always use a thickness offset (SLDTHK) and reasonable stiffness (SLDSTF) for segments that belong to solid elements.

This is important when using non-structural materials such as foams, rubbers, honeycomb, etc.


LSDYNA Simulation Notes
Thu, 27 Mar 2008 00:00:00 +0000
While working on a simulation model, it is often very convenient for oneself or to others to make necessary notes that documents the changes in the input file. While each person’s method of documenting changes in short sentences could vary, a formal pattern of documentation could help unify the documentation so anyone can easily follow the evolution of the input files.
Here is a generic pattern that could be followed subject to changes


Quaternions for 3D Graphics
Thu, 27 Mar 2008 00:00:00 +0000
A recent investigation to determine the best viewing configuration for any arbitrary model required me to understand the ‘QUAT’ that appears in LS-PREPOST every time you rotate a model or change its view. If you are interested to understand this, you can view this  Powerpoint  document for more information.


Internal Contact for Solids using *SET_SEGMENT_GENERAL
Thu, 20 Mar 2008 00:00:00 +0000
In an earlier post on  CONTACT INTERIOR , we saw how adding interior contact can help prevent negative volumes. An additional method that is available in LS-DYNA is the use of SET_SEGMENT_GENERAL to generate the interior segments of solids. When a list of parts are defined using PART_SLDIO in the SET_SEGMENT_GENERAL, LS-DYNA generates both external and internal segments of the parts for inclusion in contact treatment. This allows a very fast method (and reversible) way of including interior segemnts so the solid elements can be prevented from inversion.

It must be noted that the default thickness for these internally generated segments is zero which may still result in nodal release due. To prevent this a non-zero value of SLDTHK and an appropriate stiffness value using SLDSTF must be defined to create a stable contact. When a nonzero value of SLDTHK is specified, solid segments will use a contact thickness that is equal to SLDTHK.


TIEBREAK Example
Mon, 10 Mar 2008 00:00:00 +0000
Here is a TAR file that consists of a simple setup to demonstrate TIEBREAK interface contact in LS-DYNA. The example can be used under TENSION, COMPRESSION, TORSION and PEELING type of load.
acumulatori camere

constructii interioare

avion romania spania

cablu electric

camera digitala canon

componente motor

sofer curier

plante de decor

excursii roma

montaj faianta

admitere farmacie bucuresti

garduri vile

ghid constructii

hoteluri grecia

hotel mamaia

ghid de interviu

laptopuri toshiba

aprtamente litoral

pensiuni munte

articole fotbal

biciclete second hand

oferte sejur spania

sonerii telefoane

calculatoare ieftine
Tiebreak Example


RCB Decomposition and LS-DYNA Built-In Intelligence
Wed, 13 Feb 2008 00:00:00 +0000
Domain decomposition is central to MPP-LSDYNA as it determines the final load balance on each of the compute nodes. The default (and most widely used)  decomposition method is the   Recursive Coordinate Bisection (RCB)  which recursively halves the model using the longest dimension of the input model.

army assessment risk

dodge car

accessory pipe water

ochelari de soare

reteta slabire

medicamente

aer conditionat

avocat timisoara

program tv

online dating service

asbestos trust

Halving the model along the longest computed length of the  model may seem like a good choice but will eventually result in unequal portions of the models for a model with varying element count and element formulations. This leads into the question about how MPP-LSDYNA handles the weighting of the element count and the formulation. To demonstrate this, consider a simple plate which has a fine and a coarse mesh as shown below, run using 2-CPUs. In the first 2 cases, the element formulation chosen for both parts is the default “type 2” formulation and both parts use “ELASTIC” material law.


Interior Contact for Foams, Honeycombs and Rubbers to eliminate Negative Volumes.
Thu, 24 Jan 2008 00:00:00 +0000
Under large compressive forces, elements belonging to either Foams, Honeycombs and Rubbers tend to invert causing numerical instabilities. To avoid such difficulties, which is one of the primary causes of simulation waste (unusable simulation results), a good set of modeling practices are first necessary as outlined in an  earlier post .
As an added protected against “Negative Volume” issues, LS-DYNA allows the definition of internal contact treatment using *CONTACT_INTERIOR specifically designed for soft materials. The only argument necessary to define the keyword is a part set consisting of soft materials that require interior contact treatment. Once the part set is determined, LS-DYNA monitors the smallest thickness dimension of each solid element in the part set checks if its value is less than Fa*Initial_Smallest_Thickness_Dimension. If the current smallest thickness dimension falls below the value, LS-DYNA applies contact forces to separate them much like in classical contact definitions. This additional force help to keep the opposing surfaces of the element away from each other to avoid element inversion problem. A graphical representation of the problem is shown below.


Reduce D3PLOT File Size for RigidBodies
Tue, 22 Jan 2008 00:00:00 +0000
A simple variable ‘DCOMP’ can be used in *DATABASE_EXTENT_BINARY keyword to suppress unwanted information about rigidbodies to help reduce the size of D3PLOT files. Please note that this feature has no effect if your model has only deformable elements.


Improving Load Balance in MPP-LSDYNA for ALE and SPH
Thu, 17 Jan 2008 00:00:00 +0000
In an earlier post on  decomposition and  region domains  we saw how customized PFILE can be used to improve load balancing. Two new commands “aledist” and “sphdist” can now be included in “PFILE” that allows LS-DYNA to distribute the ALE and SPH information across all processors. This will greatly improve the load balancing when using increased number of processors. The default and modified decomposition is shown below.



Modified Crushable Foam
Thu, 17 Jan 2008 00:00:00 +0000
LS-DYNA now offers a modified version of  *MAT_CRUSHABLE_FOAM  in the form of  *MAT_MODIFIED_CRUSHABLE_FOAM . In the new material model, the strain rate effects can be included in the foam a *DEFINE_TABLE . To reduce or eliminate the noise in the evaulation of the new yield stress as a function of strain and strain-rate, LS-DYNA offers a modified strain-rate calculation and also a max variation of strain at every cyle. This is depicted in the following image.


D3VIEW 2.0 Beta Released
Sat, 12 Jan 2008 00:00:00 +0000
As of today,  D3VIEW 2.0beta  has been officially released in a closed environment.
 Update  Due to heavy traffic, the site is currently down. Should be up shortly.


CONTACT_AUTO_MOVE to eliminate initial contact clearances
Thu, 10 Jan 2008 00:00:00 +0000
In many situations, initial clearances between two contact surfaces can cause convergence issues in IMPLICIT analyses while wasting simulation time in EXPLICIT analyses. To remove the initial contact clearance, LS-DYNA offers a capability using *CONTACT_AUTO_MOVE that helps to improve convergence in IMPLICIT analyses since contact is detected immediately.
Contact AUTO_MOVE associates itself with another contact (two-way and one-way ONLY) and

attempts to move the MASTER nodes during the initialization(cycle 0) such that the minimum

clearance is 0.5*0.5*(slave_thickness+master_thickness). This causes LS-DYNA to see an

initial penetration of 0.5*(slave_thickness+master_thickness) at cycle 1 causing both slave

and master segments to receive forces from the contact algorithm.


Timestep Calculation
Thu, 10 Jan 2008 00:00:00 +0000
Attached is a simple Excel sheet that can be used to quickly evaluate the timestep calculated by LS-DYNA for solids, beams and shells.

It must be noted that for solid elements, Q is based on the C1 (default = 0.06) only.
timestep.xls
 Update 

For solid elements using MAT_SPOTWELD, LS-DYNA uses a slightly different method of computing the characteristic length. Rather than using the traditional method (ElementVolume/LargestSurfaceArea), MAT_SPOTWELD based solid elements use LargestArea/DiagonalLength. This is done to overcome a small timestep due to bad spotweld geometry.


Non-Structural-Mass (NSM) Lumping in LS-DYNA
Wed, 09 Jan 2008 00:00:00 +0000
LS-DYNA provides three ways to account for the non-structural-mass lumping on structures.
 1. Traditional Node Based Mass Lumping using ELEMENT_MASS_{OPTION}  

This method relies on the preprocessors to compute the node-based additional mass that is to be lumped based on the total non-structural-mass that is to be included. The input (into a preprocessor) would simply be the desired additional NSM that is to be lumped on a set of nodes or elements.

Optionally, users can include an optional PID which would then allow users to track the lumped mass by PID. Option allows for a single node (default) or a set of nodes to which the mass is to be lumped. When the OPTION is set to SET, then equal amounts of mass is lumped to all nodes that belong to the SET.


Yield Stress, Strain-rate Dependency in MAT_024 and the significance of SIGY
Thu, 20 Dec 2007 00:00:00 +0000
*MAT_PIECEWISE_LINEAR_PLASTICITY (*MAT_024) is widely used material model for metals and in some cases plastics. Its popularity is widespread since it  offers several plasticity models and can also be strain-rate dependent. One particle parameter, the Yield Stress, in the material card can appear in more than one place and can be sometimes confusing to know which value is used by LS-DYNA. Here is the hieararchy of the final value of the Yield Stress used in LS-DYNA.


d3View v2.0beta – LS-DYNA Simulation Data Manager – Releasing Shortly
Mon, 17 Dec 2007 00:00:00 +0000
Since the first release of d3View, there have been many incremental but bold steps that were taken to tackle the problem of simulation data management especially related to LS-DYNA. I am proud to announce the next generation of simulation data manager that will be available shortly to worldwide users in the form of d3View v2.0 beta. It is a result of over 5 years of part time development with a simple goal of using web 2.0 technologies to help LS-DYNA users manage, mine, compare, and collaborate their simulations.


Force Deflection to Effective Stress vs Effective Strain
Thu, 13 Dec 2007 00:00:00 +0000
Attached is a simple code that I wrote a while back to convert a force-deflection/engineering-stress_strain/true_stress_strain curve to effective stress vs effective strain curve. The input is a simple LS-DYNA valid keyword file with *define_curve keyword. Its not an elegant code but works in most cases. A sample curve is also included.
I am working on extending this to cover all materials with a HTML front-end. You should see this in the next release of d3View.


Initializing Velocity
Thu, 13 Dec 2007 00:00:00 +0000
Initial velocity is always specified to a single node and can carry only one value. Multiple initial velocity definitions for the same node will always use the last encountered value. To illustrate this, if we have nodes N1,N2 and N3 and we define a initial velocity for all nodes to be ‘V1’ followed by N2 to have a velocity of 0 followed by N3 to have a value of ‘V3’, the final velocities for the nodes will be N1->V1, N2->0, N3->v3.


Simulation “Pack” to Perform Design or Numerical Variable Studies
Mon, 10 Dec 2007 00:00:00 +0000
In an iterative simulation process, the main problem or difficulty is to use the existing results to understand its dependency on certain variables (design or just numerical). This difficulty, often causes us to rerun the simulations in a more controlled environment. Let me illustrate this with a simple problem in which we have some v1-v10 variables that we are changing to improve r1-r10 responses in some fashion.  Unfortunately, the v1-v10 variable magnitudes are very hazy at the beginning in many cases so we incrementally change them over a certain span of time. At the end of this period, if we were to answer the question of ‘what is the effect of v1 against r1’, we naturally are not comfortable to do this unless the entire simulations were done by an optimization tool.


Tiebreak Example # 1
Tue, 20 Nov 2007 00:00:00 +0000
Here is one of the simplest set up of a tiebreak test problem that was developed earlier. You can test the tiebreak under any load case by simply including the appropriate included file.

The main file is named “main.k”.
tiebreak_example.tar
Thanks to Brian Wainscott, LSTC, who was instrumental in helping to understand some important aspects of this problem.


*DEFINE_CONTACT_VOLUME for *SET_{OPTION}_GENERAL
Mon, 19 Nov 2007 00:00:00 +0000
I am glad to announce that the latest version of LS-DYNA will support the use of *DEFINE_CONTACT_VOLUME in any *SET_{OPTION}_GENERAL keyword. As most of you know, *DEFINE_CONTACT_VOLUME offers many advantages over *DEFINE_BOX such as definition in a local system and multiple shapes such as sphere, ellipse, box, and cylinder.
With this support, my earlier post on subsystem swapping will be much easier.
The various options are as shown below:
Defining *set using *define_contact_volume

• Users now can use contact_volume to define *set_node, *set_segment or

*set_any_element.

• Angle definitions in *define_contact_volume, D_ANGC and D_ANGS, is ignored

when that contact_volume is used to define *set

Input example description:

*SET_NODE_GENERAL

Card2 OPTION A1 A2 A3 A4 A5 A6 A7

Type A F F F F F F F

OPTION can now be:

VOL: all nodes inside the specified contact_volume will be included in this nodal

set

DVOL: all nodes inside the specified contact_volume will be excluded from this

nodal set

*SET_SEGMENT_GENERAL

Card2 OPTION A1 A2 A3 A4 A5 A6 A7

Type A F F F F F F F

OPTION can now be:

VOL: generates segments inside contact volumes

DVOL: all nodes inside the specified contact_volume will be excluded from this

segment set

VOL_SHELL: please refer to BOX_SHELL in the table on page 27.18 of users

manual

VOL_SLDIO,....

VOL_SOLID.....

DVOL_SHELL

DVOL_SOLID

*SET_SHELL_GENERAL, *SET_SOLID_GENERAL,......

Card2 OPTION A1 A2 A3 A4 A5 A6 A7

Type A F F F F F F F

OPTION can now be:

VOL: elements inside contact volumes

DVOL: all elements inside the specified contact_volume will be excluded from

this element set


MIT Open Course Ware
Mon, 19 Nov 2007 00:00:00 +0000
Recently, I came across this MIT Open Course Ware and thought it might be useful for others as well. MIT has made more than 1800 courses available at no cost.


Class Notes
Wed, 14 Nov 2007 00:00:00 +0000
Recently, I was teaching a class for Black & Decker, and one of the students, Kevin, was taking notes that I thought captured my lecture quite well.
I asked him to provide a scanned copy which is included here for others who may find it helpful.

notes.ppt


2007 Japan LS-DYNA Conference Summary By Sven Holcombe
Fri, 09 Nov 2007 00:00:00 +0000
Sven Holcombe of JARI sent us this  great presentation summary  that covers some of the paper presentation at the 2007 Japan LS-DYNA Conference. Its has been a lot of work for Sven I am sure and its greatly appreciated for his effort.
Thanks a lot, Sven.
(I removed the preview since the loading time of the entire site was slow with it).


Membrane Thinning in Shell Elements
Sun, 04 Nov 2007 00:00:00 +0000
In 2D shell elements, the stress in the normal (fiber) direction is iteratively reduced to zero to meet the plane-stress condition. The strains are however nonzero in the fiber direction and will be linear though the thickness. Under membrane straining, LS-DYNA allows an option to account for the reduction in the shell thickness in the fiber direction. This option can be turned on using the ISTUPD (Integration Shell Thickness UPDate) which simply scales the thickness of the shell using the strain computed along the thickness direction (epsilon 33).


Eliminating Contact Force Interference in Spotweld Forces Using SPOTTHIN in *CONTROL_CONTACT
Fri, 02 Nov 2007 00:00:00 +0000
In mesh independent deformable spotwelds (see  here ), the actual spotwelds are represented using either beams or solids (single or cluster). The nodes of the beam or solid element representing the spotweld are then tied to the sheet metal using a tied interface (TIED_SHELL_EDGE_TO_SURFACE or TIED_NODES_TO_SURFACE). The forces experienced by the beam are the result of this tied interface and then the stiffness of the beam element. A simple spotweld modeling using beam element is shown below.


Contact and Global Timestep
Thu, 01 Nov 2007 00:00:00 +0000
You may have seen this popular message that is printed out by LS-DYNA for every simulation.
  The LS-DYNA time step size should not exceed     0.456E-06

to avoid contact instabilities.  If the step size is

bigger then scale the penalty of the offending surface


Lets review this to understand a little more. As we know, Explicit time integration scheme is conditionally stable and the global computing timestep must be less than (LS-DYNA uses a 10% reduction factor) models highest natural frequency. It is difficult to compute the highest natural frequency and so it is approximated using the well known ratio of characteristic length and the sound speed. Contacts in LS-DYNA are treated using the penalty stiffness method (default contact-impact treatment) which uses invisible linear springs between the slave node (or segment for pinball) and the master segment. The stiffness and the mass of the contact springs are computed based on the parent element and its material properties. The computed contact spring stiffness and the mass as used to compute a “contact timestep” much like we do for the traditional spring elements


Shell Element Stress and Strain Output to D3PLOT – A Brief Overview
Thu, 01 Nov 2007 00:00:00 +0000
A few questions recently from some users while teaching a class prompted me to write this overview regarding the data output, particularly for shell elements, into D3PLOT and how the post-processors plot them. The brief overview is listed in the form of list items for a quick read.
1. Element output are always element centered and is in global system unless specified using CMPFLG in *DATABASE_EXTENT_BINARY. Element centered data such as strain and stress tensor are output for each element’s integration point both in-plane and out-of-plane. Strains are not included by default and must be turned on using STRFLG in *DATABASE_EXTENT_BINARY. Additionally, only 3 layers are written by default in the fiber or normal direction and can be user-defined using the value MAXINT parameter in *DATABASE_EXTENT_BINARY keyword. For more information you can see the other post  here.


Blog Statistics – Thank You!
Wed, 31 Oct 2007 00:00:00 +0000
Just wanted to post some stats (courtesy http://www.statcounter.com) we gathered for the blog. It has been extremely gratifying that readers come back to look for information. We want to thank all our readers, and we hope to continue providing useful posts that help LS-DYNA users worldwide.
(Click image to enlarge)







Coverage of Japan LS-DYNA Conference – Courtesy Sven Holcombe
Mon, 29 Oct 2007 00:00:00 +0000
I am glad to write that Sven Holcombe from Japan will be providing us a brief first-hand coverage of the Japan LS-DYNA Conference that is going to happen on Oct 30 & Oct 31! Please thank Sven when you get a chance.
Details of the conference can be found here  2007 Japan LS-DYNA Conference 
Thanks a lot, Sven. Hope you have a great time at the conference and we look forward for your coverage details soon. I am certain it will be helpful for all those who are not able to attend.


Makefile – Is This Just for Programmers?
Mon, 29 Oct 2007 00:00:00 +0000
Recently, I have been assembling models outside of any pre-processors and found that the use of Makefile can often be very helpful in putting together models on the fly provided you have a good process of storing the models in subsystems. A simple example is show below.
# Comment starts with a pound sign
# Content of Make File
# some global variables
LS_DYNA=/path/to/lsdyna/
LS_PREPOST=/path/to/prepost

# targets
side_impact_model:
      @ cat barrier.i vehicle.i > side_impact_model.k
      @ ${LS_DYNA} i=side_impact_model.k
      @ ${LS_PREPOST} c=sideimpact.lspcom
front_impact_model:
      @ cat wall.i vehicle.i > front_impact_model.k
      @ ${LS_DYNA} i=front_impact_model.k
      @ ${LS_PREPOST} c=frontimpact.lspcom
pack:
      @ tar -cvf files.tar *.i
      @ gzip files.tar
Here’s how to use it.


Subsystem Swapping Made Easy with *SET_NODE_GENERAL, *SET_SEGMENT_GENERAL, and *INCLUDE_TRANSFORM
Mon, 22 Oct 2007 00:00:00 +0000
In web technology, it is a common practice to build applications that “share nothing”. For example, if a web application is running on a web server, and you need move the application to another machine, it is extremely simple to do this if the app does not use data on the machine its running on. “Share nothing” principle promotes easy porting without the headache of migration its dependencies. Implementing such “share nothing” apps requires proper design and involves a good process developement.


iPhone Support
Sat, 20 Oct 2007 00:00:00 +0000
This blog is now optimized for viewing on iPhones.



Automatic Tiebreak – Some Quick Notes
Fri, 19 Oct 2007 00:00:00 +0000
I posted a detailed document on the TIEBREAK contacts. Here are a few things that I noticed after the I wrote the article.
1. Scale down the penalty stiffness down to 0.1 if you see instability.

2. It is important to have the two surface to be “just in contact” and not “too far” or “penetrating”.

3. Do not have the parts in TIEBREAK in any other contact if possible to avoid duplicate contact treatment.

4. If you still see instability, remove the TIEBREAK and see if the regular a3 contact works.

5. Also, just for verification, a quick Eigenvalue extraction will ensure the right nodes are tied to right master segments.


Strains and Stress in NonLinear Finite Element Method
Fri, 19 Oct 2007 00:00:00 +0000
Came across this nice document that talks about the strains and stress computations used in many nonlinear finite element codes. If you know the author of ths material, please do let me know.
You can also find the entire set of materials  here 


More on LSCASEDRIVER
Tue, 16 Oct 2007 00:00:00 +0000
In an earlier post, we saw how *CASE keywords can help us perform sequential and sequential+dependent simulations. But here I want to talk a little more about the LSCASEDRIVER program itself. LSCASEDRIVER is a simple yet powerful utility that is sometimes built into the LS-DYNA executable, but it can also be used in a standalone mode. Its main job is to read the input supplied to it and look for *CASE keywords and write multiple input files based on the the content in each CASE block. As you know, CASE blocks can be input to form a binary tree and this nested information is parsed and output into individual input files by the LSCASEDRIVER program. The argument to run LSCASEDRIVER is as simple as:


Encryption Comes to LS-DYNA v971 !
Mon, 08 Oct 2007 00:00:00 +0000
Encryption has been around for several years but it finally comes to LS-DYNA in the form of GPG encryption which can be used at no additional cost to encrypt LS-DYNA input files to protect important proprietary data such as material definitions. Any portion of the input file can also be encrypted in multilple blocks of information except the *KEYWORD and the *INCLUDE keywords. Information related to the encrypted data will not be output to D3HSP file. The following images show the process of encryption.


Sense-Switch Controls for Interacting with Running LS-DYNA Jobs
Mon, 08 Oct 2007 00:00:00 +0000
There are several sense switch controls that are available to interactively request LS-DYNA respond to certain pre-defined calls. The well documented sense-switch controls for Explicit calculations are listed below.
 General Sense-Switches 
Type       Response
----       ------------------------------------------------------------
sw1        a restart file is written and ls-dyna terminates
sw2        LS-DYNA responds with time and cycle numbers
sw3        a restart file is written and ls-dyna continues calculations
sw4        a plot state is written and ls-dyna continues calculations
sw5        LS-DYNA enters interactive graphics phase
swa        LS-DYNA flushes all output i/o buffers
stop/quit  halt execution

However, for Implicit LS-DYNA jobs, the following sense-switch controls can be used which are not yet documented and will be included in the list of options in the future versions of LS-DYNA.


Interactively Terminating LS-DYNA Jobs
Fri, 05 Oct 2007 00:00:00 +0000
There are several methods available to interactively termination an running LS-DYNA job. They are briefly discussed here.
 1. Sense Switch ‘SW1’ 

This command is typed by first typing ‘Control-C’ followed by ‘SW1’. This causes LS-DYNA to terminate gracefully by writing all the information from memory to the file system.
 2. Creating a file ‘D3KIL’ in the working directory 

By simply ‘touching’ (ex. touch file_name in a unix environment) a file named ‘D3KIL’ in the running directory, LS-DYNA will behave as in step 1 above. In addition, any of the sense-switch controls can be included in the first line as shown below.



sw4




Features Every LS-DYNA Simulation Must Have
Thu, 04 Oct 2007 00:00:00 +0000
LS-DYNA is a general-purpose simulation software. This is a good thing for analysts since it provides tremendous flexibility in simulating a wide range of events. The downside to this is the fact that every simulation requires ‘best practices’ to ensure it meets the quality and accuracy requirements of th event that is being simulated. Additionally, LS-DYNA is super backward-compatible. You can run legacy models that could be a couple of decades old using the latest release with no change to the input file. Backward compatibility however requires that default values that was found to work in the past may no longer be applicable today as better alternatives may be available. This post highlights some important non-default settings that must be present in all simulations.


Determining Prony Series Constants for Modeling Creep and Relaxation
Wed, 03 Oct 2007 00:00:00 +0000
Came across this excellent tutorial that talks in detail the steps involved in determining the Prony series constants.
Determining a Prony Series for a Viscoelastic Material From Time Varying
Strain Data





Energy Output to D3PLOT Files
Wed, 03 Oct 2007 00:00:00 +0000
Several options exist in LS-DYNA to output the energies, stress and strain information for shells, solids and beams depending on the choice of parameters in *DATABASE_EXTENT_BINARY keyword. These are important to understand and enable proper postprocessing of the results when using any post-processors to read in D3PLOT. It must also be noted that increased output is extremely beneficial during early design studies but may result in poor performance and the use of excessive storage if continued for the entire design cycle.


Accelerometer Mass
Tue, 02 Oct 2007 00:00:00 +0000
Starting 971, LS-DYNA allows the direct input of the physical accelerometer mass in the *ELEMENT_SEATBELT_ACCELEROMETER keyword which is lumped equally to the three nodes that is used in defining the accelerometer. This eliminates the need to create additional *ELEMENT_MASS keywords to account for the physical accelerometer mass.


Nodal Time History in Local Coordinate System
Tue, 02 Oct 2007 00:00:00 +0000
In several simulations, the response of a nodal point (displacement, velocity, and acceleration) is helpful to be output in a user-defined local coordinate sytem. LS-DYNA offers several options to enable the local system output of nodal time history data and here are some examples of it. All nodal time history data is output to either NODOUT or NODOUTTF (971 and beyond) only.
1. ELEMENT_SEATBELT_ACCELEROMETER

This is one of the most commonly used feature where a nodal rigid body is first defined use three nodes such that N1 and N2 form the local X-Axis and N3 lies in the XY plane. With this information, LS-DYNA first computes the cross product of N1N2 and N1N3 to determine the local Z and this step is followed by a cross-product of local ‘X’ and local ‘Z’ to determine the local ‘Y’. The node N1 is then referenced in *DATABASE_HISTORY_NODE whose output is then output in a local coordinate sytem.


A Simple ALE Sloshing Example
Tue, 18 Sep 2007 00:00:00 +0000
Sloshing problems can be simulated using several techniques in LS-DYNA that range from using a simple MAT_ELASTIC_FLUID modeling to a complex ALE or SPH modeling. In this post, a simple problem is set up to demonstrate the fluid representation using ALE element formulation 11 that uses a null material and an EOS (Gruenesium). The sample problem is available for download.
LS-DYNA ALE Sloshing Example – Keyword File


Tiebreak Contact in LS-DYNA
Tue, 04 Sep 2007 00:00:00 +0000
Tiebreak contacts in LS-DYNA have undergone significant enhancements in recent versions. A brief overview is provided in the PDF document below. Special thanks to Jim Kennedy for requesting this and also to Dr. Brian Wainscott, LSTC, for sharing some intricate details about TIEBREAK contacts.
Download TieBreak Contacts (PDF) 





Mesh Refinement Studies Involving Shell Elements
Tue, 28 Aug 2007 00:00:00 +0000
In many situations, we tend to change the mesh density to study its effect on simulation responses. Two issues things that are seldom addressed are the contact thickness and the mass-scaling which blend in with the true effects of the mesh refinement. As stated in some of the earlier posts, LS-DYNA computes the contact thickness that is some fraction of the element edge length if SSTHK=0. For any mesh studies involving shells, one must always use SSTHK=1 such that the contact thickness is independent of the element dimensions. The second issue is the use of mass-scaling which can be minimized by choosing a DT that results in identical mass-scaling in all the comparitive runs. This can cause additional difficulties when several parameters such as contact stiffness  in SOFT=1,2 are based on global DT which if changed will change stiffness. To avoid this, it is recommended to choose the minimum DT of all mesh variations as global DT for all simulations involving mesh refinements.


DKT Triangular Shell for Crash
Mon, 27 Aug 2007 00:00:00 +0000
Default element sorting for 3-noded shell elements uses the collapsed BT formulation which is not recommended but is maintained for backward compatibility. The first option that LS-DYNA offers is to sort these elements to use a C0 triangular shell formulation which may provide better answers than the default formulation. LS-DYNA 971 (R3 and later) now offers the sorting to use a DKT formulation that shows encouraging results for crash analysis. You can read the  original paper (PDF)  for more information. You can invoke the DKT sorting by setting the ESORT=2 in *CONTROL_SHELL keyword.


Consolidating Multiple Contact Definitions to a Single Contact
Thu, 23 Aug 2007 00:00:00 +0000
Over the last few years, the simplicity of defining a global AUTOMATIC_SINGLE_SURFACE contact to treat the interactions between multiple parts of varying stiffnesses and element types has changed the way we model contact interfaces. They are not only simple to define but also promote better modeling since they hugely eliminate the need to manually identify contact surfaces which may be prone to errors. Legacy models which could have several hundred contact definitions (one-way and two-way types) can be extremely difficult to convert to a single contact definition since it requires a thorough review of manually defined segments. Here are some approaches that could be followed to migrate the legacy models to use a single consolidated contacts.


Contact Surface Generation for Solid Elements
Thu, 23 Aug 2007 00:00:00 +0000
By default, when a solid part ID is included in a contact slave or master part set, LS-DYNA generates a segment list for only the outer skin of the solid element volume. This is truly only if the slave or master set type is a segment list since for a node slave or master list, all nodes of the solid part ID will be included.

In certain situations, such as in foams or rubbers or honeycombs, it may be necessary to include the segment list of the interior elements of the solid PART ID. In such cases, the use of *SET_SEGMENT_GENERAL can be used along with PART_IO which causes LS-DYNA to not only generate the list of segments for the outer skin but it also generates the segments for ALL interior elements as well. This allows the automatic inclusion of interior segments in contact even for non-EROSION type contacts when the outer solids erode.


Principal Stress Calculator for Shell Elements in DYNAIN File
Wed, 01 Aug 2007 00:00:00 +0000
Recently, there was a request to ouput the principal stresses for each element at lower and upper surfaces of each shell element in DYNAIN file to use in some failure theories. I beleive this feature is a routine output in PamStamp simulations. To enable this, the attached ‘C’ code can be used that reads in a DYNAIN file (valid output from LS-DYNA) to use the stress-tensor and output the principal stresses for each element at lower and upper surfaces.


LSTC’s New and Improved Rigid Hybrid III 50th Percentile Dummy for LS-DYNA Simulations
Fri, 08 Jun 2007 00:00:00 +0000
A new and improved rigid hybrid III dummy is available in beta version. If you are interested in beta testing of this dummy, please contact  Sarba (sarba@lstc.com)  for more information. The dummy is provided at no charge if you already have an existing license of LS-DYNA.


History of LS-DYNA – By Dr. David Benson
Tue, 05 Jun 2007 00:00:00 +0000
Came across this nice presentation  by Dr. David Benson.





Smoothing Length in SPH
Thu, 31 May 2007 00:00:00 +0000
 Update  James Kennedy reported a minor print error with regards to default smoothing length calculation. This has been corrected. Thanks James.
In Smoothed Particle Hydrodynamics (SPH), the particles not only pocess time-history variables such as density, displacement, velocity, acceleration, strrain-rate, stress-rate, etc but they also act as interpolation points. The space and time dependent variable called smoothing length is used to determine the region of influence of the neibhoring particles.


Viscous Damping Coefficient (VDC) in SPH Contact
Wed, 30 May 2007 00:00:00 +0000
Viscous Daming Coefficient (VDC) is freqeuntly used in contact interface definitions (*CONTACT) to damp out oscillations normal to the contact segment. It is specified in percentage of the critical damping where a value of 90 is 90% of critical damping. In one recent applications using SPH for gravity initialization of a filled fluid container, using a critical damping coefficient of 90 (%) significantly reduced the noise in the particle contact interaction with the lagrange elements. The attached image shows the force time history with and without VDC.


Interface Binary Output for Single Surface Contact
Tue, 29 May 2007 00:00:00 +0000
When requesting interface binary file, which consists of a number of useful data such as pressure/friction_energy, etc that can be contour plotted, LS-DYNA by default outputs these variables for ALL segments included in the SINGLE SURFACE contact. Visualizing the output can be tedious since it involves recursive blanking to expose the inner regions of interest in the case of a large model. The recommended approach in such cases is the use of multiple FORCE_TRANSDUCER (with SPR=1) with selected regions of interest defined using either SET_PART_LIST or SET_SEGMENT entities that allows easy viewing of interior regions.


True Total Strain to Effective Plastic Strain
Tue, 29 May 2007 00:00:00 +0000
While converting true-stress vs true-strain curve into effective stress vs effective plastic strain, the removal of elastic strains can be based on a constant or varying strain value. For relatively small hardening, both methods should yield identical plastic strains but significant hardening, using an instantaneous elastic strain as opposed to a constant elastic strain is highly recommended. The following figures demonstrates both approaches.
1. True Stress Strain Curve (Click image to enlarge)




Speeding up numerical studies using Discrete Optimization in LS-OPT
Mon, 30 Apr 2007 00:00:00 +0000
In an earlier post on  simulation based product design  we saw that in many cases a large portion of effort early on in the design cycle is usually spent on determining the best practices to simulate a physical event. We can speed up such simulations by the discrete variable support in LS-OPT version 3.1. An example of the LSOPT command file in which two parameters in LS-DYNA, SOFT and SSTHK, are defined as discrete variables, is included here. The command file can be viewed using LSOPTUI – a graphical user interface for LSOPT.


Sinusoidal Motion using *DEFINE_CURVE_FUNCTION
Wed, 25 Apr 2007 00:00:00 +0000
Here is a simple way to prescribe sinusoidal motion using *DEFINE_CURVE_FUNCTION.
*PARAMETER

ramp, 10.0

rfreq, 600

rshift, 0.0

*DEFINE_CURVE_FUNCTION

curve_id

&*sin(&freq*TIME+&shift)
The parameter “amp” is the amplitude, “freq” is the frequency of the oscillation (2PI/T, T is the time period), and “shift” is the phase shift. TIME is the simulation time that will be replaced with the current simulation time by LS-DYNA. The curve id can be referenced by any of *LOAD or *BOUNDARY_PRESCRIBED keywords.


Unloading Behavior in MAT_083
Mon, 23 Apr 2007 00:00:00 +0000
There are three different ways to model unloading behavior when using material model MAT_083. They are graphically depicted below (these figures may appear in the next release of the LS-DYNA keyword and theory manual).
Option 1 – Default (Click image to enlarge)

In the default option (1), HU=0, and the table is positive which then refers to a series of loading curves. Unloading in this case is then to the loading curve that corresponds to the lowest strain-rate. There is also no rate-dependency so unloading will always occur along the curve that corresponds to the lowest strain-rate (quasi-static or nearly zero).




Time Integration, Characteristic Length, and Mass Scaling
Tue, 17 Apr 2007 00:00:00 +0000
A short presentation on the Explicit and Implicit time integration schemes which I use in my advanced LS-DYNA class is included here. Its a evolving document but the latest version is available for download.

Time Integration (PDF, 346 Kb)
Note: Fixed the corrupted PDF file. Sorry for the inconvenience.


Free LSTC USSID
Mon, 16 Apr 2007 00:00:00 +0000
A modified version of the NHTSA finite element model of the USSID is now available at no charge.  LSTC USSID version 1.0 (LSTC FTP site) 
LSTC USSID





Stress Relaxation in Viscoelastic Material Models
Mon, 16 Apr 2007 00:00:00 +0000
LS-DYNA allows several ways to model of stress relaxation often seen in viscoelastic materials when subjected to a sudden constant strain. The methods to model the stress relaxation is briefly discussed here.
1. Curve Input

When using MAT_GENERAL_VISCOELASTIC material model, one can directly input the time log dependence of the relaxation modulus using LCID parameter. The stress relaxation curve can be either from a shear test or a tensile test in which the stress is divided by the initially applied strain. LS-DYNA then internally perfoms a least square fit to determine the prony series coefficients upto N terms. When using the load curve, users can optionally input the initial BETA value (1/time unit) as the BSTART but is not mandatory.


SPH Contact Definitions
Sat, 14 Apr 2007 00:00:00 +0000
SPH is now widely used in several high strain-rate and large-deformation problems which may otherwise be difficult to simulate when using traditional mesh based approaches. LS-DYNA allows mesh-based and mesh-free techniques such as SPH to exist and interact in one simulation allowing users to take advantage of both procedures. The interaction or coupling between the SPH and other elements can be defined using traditional tied or penalty based contact definitions. Since there is no mesh connectivity for the SPH particles, it is imperative that only one-way type of contact defintions are applicable in which the SPH is always defined to be the slave and the elements are defined to be master. LS-DYNA has several types of one-way based contact definitions which are identified by the presence of the string  NODES_TO_SURFACE or ONE_WAY  in any of the contact keyword.


Interface Component Analysis
Thu, 15 Mar 2007 00:00:00 +0000
Interface component analysis is a unique feature that helps to speed design variation studies for non-structural components using a model fragment of the full system model. It works by first storing the displacement time history of user-defined nodes to a disk on a file system. The stored file is a binary file and its name must be specified using the  z  option on the command line execution. Once the file is stored, users can use it in their subsystem models to study design variations by reading the stored time-history data and linking this to the list of user-defined nodes in the subsystem that are within the neighborhood of the original nodal coordinates.


MultiStage Dependent or Independent Simulations using *CASE
Mon, 12 Mar 2007 00:00:00 +0000
A powerful feature of LS-DYNA v970 and beyond that has yet to gain widespread popularity is the *CASE keyword. Here are two examples to highlight the use of *CASE.



 Sequential and Independent Simulations 

Ex: Head Impact (FMVSS 201)



*keyword

$

$ Impact 1

$

*case_begin_1

*title

position 1 impact

*include

vehicle_model.i

*include

head_position_1.i

*case_end_1

$

$  Impact 2

$

*case_begin_2

*title

position 2 impact

*include

vehicle_model.i

*include

head_position_2.i

*case_end_2

$

$ ....

*end




 Sequential and Dependent Simulations 

Ex: Cumulative Bumper Damage



*keyword

$

$ Impact 1

$

*case_begin_1

*title

position 1 impact

*include

vehicle_model.i

*include

impactor_position.i

*case_end_1

$

$  Impact 2

$

*case_begin_2

r=1.d3dump01

*title

position 2 impact

*include

vehicle_model.i

*include

impactor_position_2.i

*case_end_2

$

$ ....

*end







Modeling Off-Axis Dependent Yield Stress for Honeycombs using MAT_126
Thu, 08 Mar 2007 00:00:00 +0000
Honeycomb cell structures are popular among weight conscious designers due to their high strength to weight ratio. In the automotive space, aluminum based honeycomb structures are widely used to represent barriers to simulate a controlled energy absorption. Honeycomb structures are highly anisotropic and requires adequate testing to characterize them. This post focusses on the characterization of the off-axis angle dependency of the yield stress. It is well known that honeycomb structures are stronger along the direction of the cell axis and is considerably weaker in the other two orthogonal directions. The transition of the strength from the strong axis to the weak axis is known to be non-linear and can be captured by using  LCA  in material model  MAT_126 . A typical curve describing the average yield stress as a function of the off-axis angle is shown below.


Choice of Rigidwall Treatment
Tue, 27 Feb 2007 00:00:00 +0000
There are two different methods that are available in LS-DYNA to treat nodes impacting a rigidwall (also referred as stonewall). The first method, which is the default method, is the constraint type that is used for all deformable nodes impacting a rigidwall. The second optional method is the penalty approach that is used for ALL rigid nodes or optional deformable nodes impacting the rigidwall. The primary difference between the two methods is in the conservation of energy and momentum.


Best Practices for Building Flexible Models with Reduced File Sizes
Mon, 26 Feb 2007 00:00:00 +0000
As LS-DYNA model sizes continue to grow, there is a greater need to reduce the file sizes or rather the model footprint. If good modeling practices are maintained, there can be tremendous file size reductions even for large models and this post will review some of the best practices aimed to reduce the model input/output sizes.
1. Set Definitions

Several options exists in LS-DYNA to create sets of nodes, elements, etc that are referenced by other entities. It is always a good practice to refrain from defining keywords that refer entities at node or element level. Avoiding the direct reference to nodes and elements not only helps to reduce the file size but they also help us to in making modeleling changes. Consider a case of a rigidwall definition which requires a node set to be associated as slave nodes. By picking individual nodes in the model , unless they are sequentially numbered, the resulting SET_NODE_LIST will consist of a large number of input lines. Any future updates to the model, will rely heavily on the pre-processing software to auto update the updated node from the sets. An alternative and concise solution to address both the process and the size would be to define a SET_GENERAL or a just a simple 3-dimensional box using DEFINE_BOX that the rigidwall can refer to determine the slave nodes at runtime during the initialization process. The same guideline can be used to define node or element entities that are referenced by keywords such as *CONTACT, *AIRBAG, *INTIAL , etc. to help achieve a more elegant definition of entities.


Transient Removal of Initial Penetrations Using DPRFAC Parameter for SOFT=2 Contacts
Fri, 23 Feb 2007 00:00:00 +0000
Beginning LS-DYNA versions 971, a new option for SOFT=2 contact called DPRFAC in Optional Card ‘C’ in *CONTACT keyword allows transient removal of any initial penetrations. This option is useful to quickly zero out any initial penetrations rather than just to remember them. The following figure shows how the effective penetration that is used to compute the contact forces is gradually increasing and a subsequent drop in the  initial penetration  recorded during initialization.


Load Balance Checker for MPP LS-DYNA
Wed, 21 Feb 2007 00:00:00 +0000
A simple ‘C’ program is included to extract the processor based timing information from D3HSP file and output load balance summary. Future versions of MPP-LS-DYNA may include more information such as the summary shown below.
Usage: load_balance_checker d3hsp_file_name {threshold_factor}
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/*
 Load Balance Diagnosis for MPP LS-DYNA
 Author: Suri Bala, Livermore Software
 Copyright: Livermore Software
 Credits: Brian Wainscott, Jason Wang
 Contact: suri@lstc.com
 Usage: exe_name d3hsp_file_name {threshold_factor}
 Description: Performs a load balance check for all processors
 Compilation: cc source_file_name.c -o exe_file_name
*/
#include
#include
#include

#define LINE_WIDTH 128

int main(int argc, char *argv[]) {

 FILE *d3hsp = NULL;
 char buffer[LINE_WIDTH];
 int i, num_threads=0, host_count=0;
 float *hosts, ratio, sum =0, average_timing=1, min_timing=1e20, max_timing=-1e20;;
 float threshold_factor = 0.2, max_threshold=0, min_threshold=0;


 // if no d3hsp file is specified, exit out
 if( argc == 1 ) {
    printf("Usage: %s d3hsp_file n", argv[0]);
    exit(-1);
 }

 // open the d3hsp file
 d3hsp = fopen(argv[1], "r");
 if( !d3hsp ) {
   printf("Could not open file %sn", argv[1]);
   exit(-2);
 }

 //if threshold is specified accept it
 if( argc==3) {
   sprintf(argv[2], "%10.4f", threshold_factor);
 }

 // start reading the lines from d3hsp file
 while( !feof(d3hsp) ) {
     fgets(buffer, LINE_WIDTH, d3hsp);
     // get the num of threads
     if( strncmp(buffer+1,"Parallel", 8) == 0 )  {
         sscanf(buffer+25,"%d", &num_threads);
         hosts = (float *) malloc(num_threads*sizeof(float));
     }
     // store the host based timing
     if( buffer[25] == '#' ) {
         sscanf(buffer+65," %e ", &hosts[host_count]);
         if( hosts[host_count] > max_timing) max_timing = hosts[host_count];
         if( hosts[host_count] < min_timing) min_timing = hosts[host_count];
         sum += hosts[host_count];
         ++host_count;
     }
 }

 average_timing = sum/num_threads;
 max_threshold = (float)1.0+threshold_factor;
 min_threshold = (float)1.0-threshold_factor;

 fprintf(stdout, "n  Load Balance Summary nn");
 fprintf(stdout, "     Processor Number            Ratio           Status            Remarksn");
 fprintf(stdout, " --------------------------------------------------------------------------------------------n");
 for(i=0; i<host_count; i++)="" {="" ratio="hosts[i]/average_timing;" fprintf(stdout,="" "="" %10d="" %2.2f",="" i,="" ratio);="" if(=""> max_threshold) fprintf(stdout,"%20s%10s%20s","Overloaded"," "," Better decomposition is needed");
     if( ratio < min_threshold ) fprintf(stdout,"%20s%10s%20s","Underloaded"," "," Better decomposition is needed");
     fprintf(stdout,"n");
 }
 fprintf(stdout, " --------------------------------------------------------------------------------------------n");
 fprintf(stdout, "     Total number of threads: %10dn", num_threads);
 fprintf(stdout, "     Timing n");
 fprintf(stdout, "     Average CPU (seconds)  : %10.4fn", average_timing);
 fprintf(stdout, "     Maximum CPU (seconds)  : %10.4fn", max_timing);
 fprintf(stdout, "     Minimum CPU (seconds)  : %10.4fn", min_timing);
 fprintf(stdout, "     Thresholds n");
 fprintf(stdout, "     Maximum threshold used : %10.4fn", max_threshold);
 fprintf(stdout, "     Minimum threshold used : %10.4fn", min_threshold);
 fprintf(stdout, "nn");

 fclose(d3hsp);
 exit(0);

}


</host_count;>
 Sample Output 


MPP and Deformable to Rigid Switching
Mon, 19 Feb 2007 00:00:00 +0000
You may have read the previous post on deformable to rigid switching which works by turning a predefined set of deformable components into a rigidbody at a user-defined time to save on element processing costs. This may not necessarily be true when running using any of the MPP-LSDYNA executables since the domain decomposition routines do not account for the additional rigid bodies that get created due to switch definitions. As a result of this, there is an increased possibility of the computationally expensive deformable components being lumped on just a few processors while the remaining processors handle the computationally inexpensive rigid bodies. This creates a poor load balance situation and may result in insignificant improvement in job turnaround time.


Load Balance in FMVSS 207/210 Simulations for MPP
Fri, 16 Feb 2007 00:00:00 +0000
Analyses involving automotive seat designs for loadcases such as FMVSS 207/210 has shown some poor load balance on compute nodes when using the default decomposition in MPP LS-DYNA. In FMVSS 207/210 type simulations, the computationally expensive portion of the model lies at the seat and its immediate viscinity while the rest of the model involves relatively less computations as they are not in contact or remains elastic saving contact and plasticity treatments. In such cases, the region based domain decomposition, available from LS-DYNA 971 onwards, seems very promising to help achieve improved load balance which significantly improves job turnaround time. A sample region based domain decomposition is shown below where the seat and its immediate environment is defined as a region using a box definition and is first distributed equally to all processors. Subsequent regions are defined at the front and rear portions of the seat to again distribute them equally to all processors.


Initial Velocity in Local Coordinate System
Tue, 13 Feb 2007 00:00:00 +0000
In several loading situations, initial velocities are often defined along directions that do not coincide with the global coordinate system. In such cases it is very cumbersome to determine the directional components along global axes when the vector direction does not coincide the global system. In such instances, the easiest modeling approach would be to define the velocities along any global direction and then use INCLUDE_TRANSFORM to rotate the coordiate axes. A simple example is shown below where the intent is to define an initial velocity along a vector which is at an angle of 45 degrees to the global-x axis. To accomplish this, the velocity is first defined along the global ‘x’ direction in the included file which is then included in the main input file using the INCLUDE_TRANSFORM that used DEFINE_TRANSFORMATION keyword to perform rotation about the origin at an angle of 45 about the global ‘y’ axis (0, 1, 0).


Curve Extrapolation
Mon, 12 Feb 2007 00:00:00 +0000
Curves are used widely to define a XY data that are used by several entities in LS-DYNA. They help us to define either a time-dependent function, used in loads and boundary conditions, and/or a strain/strain-rate dependent function used frequently in constitutive models. Three most salient features of curve representation, that occur internally in LS-DYNA and which is not quite obvious to the user, is the process of ‘digitization’, ‘extrapolation’ and ‘interpolation’. In this post, the internal extrapolation is addressed.


Bulk Viscosity for Shells and Solids in LS-DYNA
Fri, 26 Jan 2007 00:00:00 +0000
In any wave propagation code, such as LS-DYNA, which belongs to a family of ‘Hydro’ codes, bulk viscosity is essential to treat shocks. Smooth initial data can lead into shock discontinuities and if left untreated can result in severe instabilities. LS-DYNA has the capability (performed by default) to automatically detect the shocks and treat them by adding a pressure term that is based on the element dimension, density, strain-rate and some user-defined coefficients (Q1 and Q2). The addition of the pressure term guarantees unperturbed solution away from the shock and satisfies Hugoniot jump conditions that requires the conservation of mass, momentum and energy across the shock front. The automatic detection of the shock was originally performed by looking at the divergence of the velocity field which is now replaced with the trace of the strain-rate tensor in multidimensional problems. The divergence of a vector field such as a velocity shows us the amount of flux or density that is flowing in (sink or compression or convergence) or out of (source or expansion or divergence) of a certain area. The divergence of a vector field provides us with a scalar function whose values are positive for out-flow (source, expansion,divergence) and negative (sink, compression, convergence). Fortunately, in multi-dimensions, the trace of a strain-rate tensor provides us this information very easily which is computed every cycle by LS-DYNA. If the trace of the strain-rate tensor is negative (compression, convergence, sink), then LS-DYNA automatically adds a pressure them that is based on the element dimension (square-root of Area for 2D and cube-root of Volume for 3D) while a positive trace is ignored.


Limitations of Using LCSR for Strain-Rate Inclusion in MAT_024
Fri, 26 Jan 2007 00:00:00 +0000
The widely popular material model *MAT_PIECEWISE_LINEAR_PLASTICITY (MAT_024) supports various methods to include the strain-rate effects. One of the methods is the scaling of the quasi-static stress-strain curves using a load-curve, LCSR, that defines a scale-factor as a function of strain-rate. This method works by first finding the yield-stress, SIG_QUASI_STATIC, as a function of the effective plastic strain, that may be defined using a load curve LCSS or using discrete points using ES-EPS, and then multiplies this value by the scale-factor by looking up the curve LSCR to give a ‘scaled’ yield stress, SIG_SCALED. Plasticity of the material is then determined by comparing the trial stresses with the scaled stress, SIG_SCALED. If the trial stress is greater than SIG_SCALED, then the plastic strain increment is computed and the trial stress is scaled back to the yield surface using the radial-return algorithm. The primary limitation of this method is in its assumption that the stress-strain curves at higher strain-rates is a simply y-scaling of the quasi-static curves which is not the case in many materials. It is well known that at higher strain-rates, the materials not only show an increase in the yield strength but they also exhibit brittleness that is not captured by the LCSR method. This is graphically demonstrated in the figure below. The black curve is the quasi-static curve that can be input using either EPS-EPSS or LCSS parameters. The dark colored curves, red and blue, show the scaled curves as a function of strain-rates using the LCSR parameters. The lighter counterparts of red and blue curves show the actual behavior that is often seen in the physical tests where some amount of brittleness is observed.


Modeling Loading and Unloading Behavior in Seatbelt Materials
Wed, 24 Jan 2007 00:00:00 +0000
Seatbelt constitutive model, invoked by using *MAT_SEATBELT, in LS-DYNA provides features to model the loading and unloading characteristics from a uni-axial test. Parameter LLCID provides ability to model the loading curve which allows the definition of force as a function of engineering strain. Parameter ULCID, provides ability to model the unloading curve again allowing the definition of force as a function engineering strain. Inherently, LS-DYNA models the seatbelt as an elastic-plastic where the first non-zero point on the loading curve, LLCID, is taken as the yield force/stress. Unloading always following the loading curve when the force level is below the first non-zero value. Unloading int the post-yield region is done by first shifting the unloading curve, ULCID, along the x-axis (striain) until it intersects the current yield point on the loading curve before unloading along the unloading curve. This is shown in the following figure.


Identifying Necking in Metals and Plastics
Tue, 16 Jan 2007 00:00:00 +0000
When characterizing materials such as Metals and Plastics in LS-DYNA, most constitutive models provide a yield criteria that accounts for a 3D state of stress which reduces to a uniaxial yield stress in 1D. This allows us to directly input the true stress-strain curve from a one-dimensional state of stress testing such as in uniaxial testing which then can be used for any 3D problems. One important consideration in the usage of such one-dimensional testing data is the phenomenon called necking which occurs in both Metals and Plastics. It is well known that post-necking stress state is no longer uni-axial but is a 3D state of stress. This limits us to use uniaxial information only upto necking and use some sort of iterative process to characterize the post-necking behavior. The first task therefore is to identify the necking point on a uni-axial true stress-strain curve. This is done by plotting the true stress-strain curve against its derivative. The intersection point of these curves is the necking point. When this curve overlay is done using the raw test data, which is sampled at a high frequency, the derivative may be extremely noisy and this may provide multiple intersection points. A sample of such noisy overlay is shown here:


Speeding up Simulations for Focused Studies
Fri, 22 Dec 2006 00:00:00 +0000
In several situations, simulation models (new or inherited), are quite often burderend with several expensive features that may have negligible effect on the response that is purely used for comparative numerical studies. When a large portion of any simulation model turnaround time consists of features that are irrelavant to the focued study, it is imperative that such features must be turned off to improve the overall turnaround time. Alternative methods could include the usage of a faster and increased number of processors which involves additional cost and availibility. However, a more effective solution would to simply review the model and look for expensive features that has little no bearing on the objective of the study and suppress them. A list of features that was encountered recently while studing the effects of the parameter DPRFAC, the results of which will be published soon, was the following:


Initial Penetrations in Contact Interfaces
Wed, 20 Dec 2006 00:00:00 +0000
1. Introduction

Contact definitions allow the modeling of interaction between one or more parts in a simulation model and have become a necessity in any small or large deformation problem. The main objective of the contact interfaces is to eliminate any â€œoverlapâ€? or â€œpenetrationâ€? between the interacting surfaces and they accomplish this by first detecting the amount of penetration and then applying a force to remove them. Depending on the type of algorithm used to remove the penetration, both energy and momentum is conserved. This article discusses the presence of penetration in non-tied penalty-based contact interfaces during the initialization of the problem, usually termed as â€œinitial penetrationâ€?, its effects on the accuracy, robustness of the model and how LS-DYNA has features that can minimize its adverse effects.


Prescribing Motion to a Rigidbody with Respect to a Local System
Tue, 19 Dec 2006 00:00:00 +0000
LS-DYNA offers several ways to prescribe a motion to a rigidbody using *BOUNDARY_PRESCRIBED_MOTION keyword. To prescribe a motion to a rigidbody along a local coordinate system, LS-DYNA offers two method to accomplish this. To demonstrate the differences in these two methods, we will consider a rigidbody that has initial rotational velocity and a prescribed displacement. The initial rotational velocity is NOT a prescribed motion so is defined using *INITIAL_VELOCITY keyword while the displacement is a prescribed motion using the *BOUNDARY_PRESCRIBED_MOTION keyword. Our objective is to prescribed the displacement in a local coordinate system that is embedded to a the rigidbody.


Deformable Spotwelds in LS-DYNA
Sat, 16 Dec 2006 00:00:00 +0000
Over the years, spotweld representation for crash and NVH applications have evolved from a crude to a detailed modeling resulting in reduced pre-processing effort while greatly enhancing the accuracy of numerical models. Here is link that gives a brief overview of spotwelding process in LS-DYNA. Please note that the document is over 2 years old and has not been updated since. Please refer to the latest LS-DYNA keyword and theory manual for more information.


Modeling Press-Fit Conditions to Include Initial Stresses
Wed, 06 Dec 2006 00:00:00 +0000
In many designs, parts are often press-fitted as part of an assembly which causes an initial stress condition that is important to consider in simulations. To induce initial stresses that occur in such press-fit conditions, one can either linearly/non-linearly scale the overlap (penetration) or the contact stiffness over a certain interval depending on the following choice of analysis techniques available in LS-DYNA.
Scaling of Overlap (Penetration)
Linear/Nonlinear scaling of overlap is usually applied in transient simulations by constraining one part and moving the second part from an initial position that has 0% overlap to a final position that induces 100% overlap.This is shown in the following figure. In this method, the contact stiffness remains constant but the overlap can be thought of as being scaled over a certain interval.


Full-Newton and Quasi-Newton Iterative Schemes
Tue, 05 Dec 2006 00:00:00 +0000
When running problems using Implicit solution sheme in LS-DYNA, the default iterative non-linear solver used is the BFGS method that employs a ‘Quasi-Newton’ method in which the global stiffness matrix is reformed only every ILIMIT steps and in between these a relatively inexpensive update to the stiffness matrix is performed. This default stiffness matrix update scheme works very well and relative fast when there is no significant contact is involved and the non-linearily of the problem is moderate. The default method often fails to converge when the non-linearity of the problem grows or when significant amount of contact is involved. For such problems, a more expensive Full-Newton method is recommended by setting ILIMIT=1 which forces LS-DYNA to reform the stiffness matrix at every iterative step to yield a more accurate stiffness estimation. When full-newton method is employed, it is often necessary to set a large maximum allowable reformations using the MAXREF parameter to allow sufficient number of stiffness reformations before terminating or reduction of the solution timestep (when AUTO timestep control is activated). Recommended value of MAXREF depends on the problem but typical values could be around 200 which should be sufficient for any large non-linear problem to converge on a solution.


Monitoring Incremental Elapsed Time as a Function of Simulation Time
Tue, 05 Dec 2006 00:00:00 +0000
When running explicit simulations in LS-DYNA, it is very important to understand the total CPU clock and the total Elapsed time used by the solver. This information is available at the bottom of every D3HSP file written by LS-DYNA as shown below. The total elapsed time reported in the file is the difference between the times of termination and execution. This report of Elapsed time is a static number and gives a good overview of the turnaround time for the simulation. It however, lacks the ability to provide insight at incremental intervals that is sometimes very useful to verify that it did not spend too much time during the solution. There are two ways to view incremental elapsed time and they are briefly discussed below.


Damping for Airbags
Wed, 22 Nov 2006 00:00:00 +0000
When simulating airbag deployment, using the classical uniform-pressure (CONTROL VOLUME) or non-uniform-pressure (ALE, Particle), users frequently encounter oscillations. These oscillations are generally categorized as local and global. To reduce both forms of oscillations, LS-DYNA provides two types of damping that are briefly discussed here.
1. Mass-Weighted-Damping

The parameter MWD in *AIRBAG_{OPTION} keyword provides a means to introduce Mass-Weighted-Damping that is applied to the airbag nodes that make up the airbag. By default, no damping is associated with the airbag nodes. When MWD is nonzero, LS-DYNA determines a nodal damping force that is based on the relative bag velocity, mass, and the MWD parameter. This damping force is computed every cycle and is applied to each node that belongs to the airbag. The bag velocity is defined as the mass-weighted average velocity (see figure below) and the MWD parameter is based on Alembert’s principle. As it can be seen in the figure, MWD can be thought of as being equivalent to a some fraction of the inverse of the global simulation timestep and its value is usually based on the amount of oscillations observed in the model. The best value of MWD is one that critically damps the oscillations and can be computed based on the lowest natural frequency (2*Lowest_Frequency). Since the oscillations are observed usually in the fully-deployed state, estimating its lowest natural frequency requires an intermittent eigenvalue extraction. Intermittent eigenvalues can be extracted by first deploying the airbag using traditional Explicit solution and then switching “intermittently” to Implicit solution method to extract the necessary eigenvalues/eigenvectors at any user-defined time which in this case could correspond to the fully deployed state. Intermittent eigenvalues can be invoked using IMGLAG parameter in *CONTROL_IMPLICIT_GENERAL (see the post Intermittent Eigenvalue Extration). If intermittent eigenvalue extraction is not possible, then a good number is roughly 0.01-0.1% of the inverse of the global timestep. Mass based damping affects rigid body motion and is effective for low frequency noise. It must be noted that MWD is unit dependent (1/Time_Unit).


General Guidelines for Crash Analysis in LS-DYNA
Wed, 01 Nov 2006 00:00:00 +0000
LS-DYNA is a general purpose finite element software and is designed for use in various applications. Based on the use of the software for a specific application, LS-DYNA offers several parameters that can be changed from their default values to improve the accuracy, robustness, and stability of the simulation. For performing crash analysis using LS-DYNA, the attached document provides a list of best practices that can be used to improve simulations. Please note that the recommendations in the document are based on experience and apply to the software version that existed at its original publication date. It must be noted that the guidelines, if implemented in simulation models, do not always guarantee stability, accuracy, and robustness as they depend on a number other factors as well.


A Few “Words” on Memory Settings in LS-DYNA
Fri, 27 Oct 2006 00:00:00 +0000
Memory in LS-DYNA is specified in “words” at the execution time. The term “word” refers to the amount of data that can be written to or read from a memory in one operation. The following figure will aid in the relationships of bits, the most basic data type, to words on various computers. One bit is a basic unit of data which can be transmitted and can be either 0 or 1. A sequence of 4 bits is called as a Nibble and a sequence of 8 bits is called as one ‘Byte’. 16-bits or 2 bytes is equal to one word on a 16-bit computer. 32-bit or 4 bytes is equal to one word on a 32-bit computer. 64-bit or 8 bytes is equal to one word.


Modeling Symmetric/Unsymmetric NonLinear Discrete Springs
Fri, 20 Oct 2006 00:00:00 +0000
Discrete springs provide a easy way to model complicated systems by using their responses in the material definitions. This post brings attention to the way LS-DYNA handles the default behavior in tension or compress when the material input does not pass through the origin (0,0) but simply begins from origin. When only one of either compression or tension data is provided, LS-DYNA extrapolates the slope, obtained from the first two pair of points from the defined region, and uses it to compute the force for any deformation in the undefined region. The default cross-region extrapolation may be inaccurate when the behavior of the discrete spring in the undefined region is supposed to represent either a symmetric or unsymmetric non-linear behavior. For representing both types of data, symmetric or unsymmetric , in tensile and compressive regions, the user must always provide a force-displacement or rotation/moment curve that passes through the origin. Figure below shows this default treatment and also highlights the input that must be provided to model the sysmmetric, or unsymmetric data when the non-linear data only in compression is provided for a discrete spring using a material model such as *MAT_SPRING_NONLINEAR_ELASTIC.


Limitations of Penalty Joint Treatment in LS-DYNA
Thu, 19 Oct 2006 00:00:00 +0000
LS-DYNA supports various joint definition types such as spherical, cylindrical, etc (please refer to the LS-DYNA User’s manual for a complete list). Irrespective of the joint definition type and the elements associated, translational constraints are applied to the joint nodes to model appropriate behavior. The constraints are applied using the default penalty formulation whose stiffness depends on the maximum frequency of all joints in the model, timestep and the timestep-scale-factor (TSSFAC). The default penalty formulation computes the necessary forces in an attempt to model the joint behavior based on the joint type but in some instances the forces generated by the penalty treatment may be insufficient to maintain the constraint. As a good practice, it is always recommended to monitor the relative displacements between the joint nodes to see if there is any separation which would indicate a insufficient forces being generated by the penalty treatment. There are two ways to fix if there is some relative displacement between the nodes. The first approach would be to increase the penalty scalefactor RPS in *CONTRAINED_JOINT keyword whose value is based on trial-and-error appraoch. The second approach is to switch the penalty formulation to an implicit Lagrange-Multiplier formulation which computes the exact force to enforce the joint constraint. Beginning 971 and onwards, this option is now available for both SMP and MPP versions of LS-DYNA and can be invoked using the *CONTROL_RIGID keyword using the parameter LMF.


Best Practices for Modeling Recoverable Low Density Foams – By Example
Thu, 12 Oct 2006 00:00:00 +0000
Attachments:
mat57_default.k
Modeling recoverable foams poses several challenges in crash worthiness as well as in low-to-medium impact velocity conditions. This is due to its relatively low stiffness when compared with structural materials which has an indirect effect on its contact-impact interactions with other materials. To review the best practices when modeling such components, we can consider a simple example of a rigid steel ball (solid elements) impacting a block of foam (solid elements). To model the interaction between the rigid block and the foam, a two-way contact such as *AUTOMATIC_SURFACE_TO_SURFACE is included. The foam is constrained using SPC definitions on the bottom face. The complete model set up is as shown in Figure 1. The recoverable low density foam is modeled using *MAT_LOW_DENSITY material model whose inputs include density, elastic-modulus, and a load curve to define its engineering stress-strain behavior for compression. The tensile behavior for this model is elastic (uses the compression Young’s modulus, E) and optionally has a cut-off stress value after which the stress remains constant in tension. Unloading behavior by default is along the loading curve but optionally we can provide some energy dissipation parameters HC and SHAPE which control both the amount of energy dissipation and the shape of the unloading curve. For simplicity, we will first ignore any hysteresis and assume that the unloading curve follows the loading curve. As mentioned before, we are going to simulation the impact using all default parameters and then we incrementally update the modeling parameters by monitoring the simulations results.


Storing Re-Usable Models in a Central Location with *INCLUDE_PATH
Thu, 12 Oct 2006 00:00:00 +0000
Beginning version 971 and later, LS-DYNA allows easy way to store models in a central location for use at run time. This feature can be turned on using *INCLUDE_PATH which takes unlimited number of absolute directory names. When INCLUDE_PATH is used, LS-DYNA first checks the file, specified using *INCLUDE keyword, in the local directory and if its not available, it will scan all the directories listed using INCLUDE_PATH in the order of definition. This feature eliminates the need to specify absolute file names. A sample use of this feature is shown below.


Simulation Based Product Design Using LS-DYNA – Single Code & Single Model Benefits
Fri, 06 Oct 2006 00:00:00 +0000
Over the past decade, the ability of simulations driving the design has grown rapidly and today’s confidence in simulations results is a good testament to it. Two significant areas that have contributed to this is the “Numerical Modeling Awareness” and “Design Domain Knowledge” gained over the years by design and analysis community. Numerical modeling awareness is an expertise that is developed over time and goes beyond the ability to learning specific software. It is an awareness in which an analyst, and in essence the corporation, gains expertise in a single or multiple numerical tool set which is used and calibrated against established prototype results to gain more confidence in the modeling procedures and the numerical intricacies involved in a complex software such as LS-DYNA. Design domain knowledge is again an expertise which is gained by a deep understanding of the product and its performance. It’s a knowledge that is more than just knowing how to surface but rather the ability to design a part for a specific criterion in an aggressive timeline yet meeting all the design requirements. In today’s environment, the iterative process quickly fails and mandates a well established standard operating procedure to achieve design requirements. The two areas in a classical LS-DYNA simulation environment that can be grouped together into “Horizontal Changes” (Design Evolution) and “Vertical Changes” (Numerical Changes) are shown below.


Implicit Dynamics – Now with Birth, Death, and Burial Properties
Tue, 03 Oct 2006 00:00:00 +0000
When solving static or quasi-static type problems, the default Implicit Static solver (IMAS=0 in CONTROL_IMPLICIT_DYNAMICS) requires a well-conditioned model, with no rigidbody modes, to get good convergence behavior. It is often difficult to prevent rigidbody modes especially when its dependent on contact-impact conditions. In such cases, use of Implicit Dynamics solver (IMAS=1) can help us to achieve better convergence since rigidbody modes has negligible effect on the convergence. In versions prior to 971 (revision 3), when IMAS=1, LS-DYNA included dynamic terms for the entire duration of the problem. Consequently, when using the implicit dynamics solver for solving static or quasi-static problems, the loading rate would have be reduced substantially to reduce the dynamic effects. Starting from 971 (revision 3), LS-DYNA now allows birth, death and burial times for the implicit solver which can be used to control the presence of the dynamic terms without altering the loading rate. TDYBIR (default =0) can be used to activate the dynamic affects. TDYDTH (default = 1e28) allows to specify a death time when the dynamic terms must be ignored. The parameter TDYBUR (default = 1e28) allows to specify a burial time (must be greater or equal to the death time) which if greater than the death time, the dynamic effects are linearly reduced to zero from death to burial time. Graphically, it can be represented as shown below (The following image has now been included in the latest LS-DYNA User’s Manual).


Overview of Mass-Scaling in LS-DYNA
Mon, 02 Oct 2006 00:00:00 +0000
Mass-scaling is a term that is used for the process of scaling the element’s mass in explicit simulations to adjust its timestep. The primary motivation is to change (usually increase) the global compute timestep which is limited by the Courant’s stability criteria. LS-DYNA allows two different types of mass-scaling using the DT2MS parameter from *CONTROL_TIMESTEP with the default set to no mass-scaling. When DT2MS is less than zero, LS-DYNA adds mass of each element whose timestep is below abs(DT2MS) such that the element’s updated DT is equal to abs(DT2MS). When DT2MS is greater than zero, LS-DYNA adds mass to elements whose DT is below abs(DT2MS) and “removes” mass from elements whose DT is greater than zero. DT2MS>0 is seldom used while DTM2<0 is frequently used for overcoming the smallest computed timestep. Care must be taken when using DT2MS<0 to ensure that the added mass does not have an adverse effect on the simulation accuracy. It is common practice to limit the percentage of added mass to less than 5% (at part level) in dynamic simulations. Optionally, users can set ENDMASS in *CONTROL_TERMINATION to terminate a simulation based on percentage of added mass based on the total mass of the model. When ENDMAS is greater than zero, LS-DYNA terminates when the percentage of added-mass reaches ENDMAS and a report of up to 20 nodes (sorted in the descending order of its added mass due to mass-scaling) is written to both standard output and D3HSP file. It must be noted that the percentage of added-mass is based on total mass of the model which included rigid body, rigid walls, etc… and could be misleading if looked at the global level. LS-DYNA outputs the percentage of added mass at component level which is a better indicator of amount of added mass due to mass-scaling. The concept of mass-scaling for both options of DT2MS is graphically illustrated below.


Example of *DEFINE_CURVE_FUNCTION
Thu, 28 Sep 2006 00:00:00 +0000
Starting in LS-DYNA version 970 and later, we can now use expressions instead of digitized values to define an XY curve.  Optionally, the expressions can refer to other curves which could be defined using either digitized points or using expressions themselves. Here is an example of its usage:
Polynomial Expressions

You can define a generic polynomial of any order upto a maximum of 30 using the general expression label “POLY” (Please note that the current ls-dyna manual shows this as POLYL which is incorrect) and its argument list is given by:


Modeling Friction in Contact
Thu, 28 Sep 2006 00:00:00 +0000
In contact-impact interactions, friction plays an important role in accurately capturing the sliding behavior. In LS-DYNA, the coulomb treatment of friction is used where a static and a dynamic friction can be defined which are used to determine the shear force while resisting penetration. By default, all contact definitions model a friction-less sliding which is a good start for initial models. The first step in activating friction in contacts is to use a non-zero static friction parameter, FS, in the *CONTACT_{OPTION} keyword. Optionally, one can define a dynamic friction, FD, which will only be used for a non-zero decay coefficient, DC. It is common to see a positive sliding energy when using non-zero friction parameters. It must be noted that non-zero friction parameters do not apply for FORCE_TRANSDUCER and TIED contacts which remain tied for the duration of the simulation. When TIED contacts are defined with failure parameters and are defined to be converted into penalty-type contacts after failure, then the non-zero friction parameters will be used to determine the shear contact forces. Figure 1 illustrates the nature of the penetration removal process when a node is detected as penetrating the closest master segment. When a penetrating node is first detected, by checking the sign of the projected normal distance to the closest master segment, a penalty force is first calculated based on the stiffness and the absolute penetration value. This force is then resolved in a local coordinate system embedded at the master element (contact point) to determine the normal and shear components. The sliding resistance is then computed using the friction parameters of the master segment and the normal force component as shown.


Contact Thickness in Single Surface Contact
Mon, 25 Sep 2006 00:00:00 +0000
Single surface contacts have dramatically eased the way we currently model the contact-impact treatment for complicated simulation models in LS-DYNA. One of the important considerations is the final thickness used by contact algorithms especially for shell elements. By default, LS-DYNA considers the minimum of thickness specified in the *SECTION_SHELL or from *ELEMENT_SHELL_THICKNESS and the 40% of the smallest shell element edge length. The default logic is based on historical reasons where large penalty contact forces where applied for non-physical shell element thickness specified in SECTION_SHELL keyword to account for mass/stiffness of the component. The default logic greatly helps in overcoming instability related to improper shell thickness definitions. However, the dependence on mesh edge length could lead to different shell contact thicknesses for a part with varying mesh densities as shown in figure below. The minimum of both thicknesses (SECTION_SHELL, 0.4*shell_edge_length) could lead to a smaller thickness that could allow increased clerances. For a part with mesh densities, it is possible to have a varying contact thickness across part surface which could lead to oscillatory contact response especially for sliding dominated contact interaction.


Identifying Problem Areas for Poorly Converging Implicit Solutions
Thu, 21 Sep 2006 00:00:00 +0000
For non or poorly converging implicit solutions, the parameter D3ITCTL parameter in *CONTROL_IMPLICIT_SOLUTION may come handy to isolate regions of interest. When D3ITCTL is non-zero, LS-DYNA outputs the model information at each Iterative step into a binary file named D3ITER which is in the same format as D3PLOT. The number of steps for which the iterative plots are to be stored is limited by the value of D3ITCTL. To save disk space, it is recommended to set D3ITCTL = 1, which indicates LS-DYNA to dump the iterative plots for every step with a maximum number of just 1 step stored into the database. With this definition, if LS-DYNA terminates abruptly without finding a converged solution, we can view the D3ITER files in LS-PREPOST to identify the problem areas. It may be necessary to scale the nodal displacements in order to visualize the movements of the nodes.


Mapping of Deformed Nodal Coordinates for SubSystem/Component Analysis
Thu, 21 Sep 2006 00:00:00 +0000
Several analyses sometimes requires the mapping of nodal positions (coordinates) from a previous run for use in current run.  For single component this is a rather easy task since it just involves writing a DYNAIN file for part(s) of interest using *INTEFACE_SPRINGBACK_LSDYNA keyword which would consist of final deformed nodal coordinates and element history variables. One major drawback with DYNAIN file is its inability to write information about nodes not used by the part referred in PSID. This causes issues for nodes used in other definitions such as *CONTRAINED_EXTRA_{OPTION} , beam third node, joint nodes, etc. Consequently, storing the deformed nodal coordinates using this approach or by any other external pre-processors soon becomes an issue. There are two options to map nodal coordinates. The first one is the ability to use the full-restart capability in LS-DYNA. This approach allows the mapping not just the nodal coordinates but also all other history variables. If the interest is only on the nodal coordinates, then the keyword *INTERFACE_COMPONENT_NODE is a more elegant approach that allows to define a set of nodes (any list of nodes) and using the “z=filename” at the command line argument during the first run to store the nodal information into a interface file whose default name is “isf1”. The file “isf1” is a binary file and consists of nodal coordinates of the node set at every output state which is specified using OPIFS in *CONTROL_OUTPUT. We won’t be using the ISF1 file directly but will only extract the nodal-coordinates for a particular state of interest (usually the last state). If only the final nodal coordinates are of interest, then using OPIFS can be set to ENDTIM. The binary interface file can then be used to extract the final nodal coordinates which can then be embedded into the second run. Using the interface force file approach, the element history variables can also be mapped using the “dynain” file (output using *INTERFACE_SPRINGBACK keyword) but without the nodal coordinates that is included in the “dynain” file.


Number of Shell History Variables in *INTERFACE_SPRINGBACK
Tue, 19 Sep 2006 00:00:00 +0000
*INTERFACE_SPRINGBACK provides an easy way to store a part’s state at the end of a simulation for later use. The part’s state consists of element history variables such as stress and strain tensor (in the form of *INITIAL_STRESS/*INITIAL_STRAIN) and also nodal values such as its final coordinates (*NODE). Optionally, when using the THICKNESS option, it allows to output the nodal thickness (in the form of *ELEMENT_SHELL_THICKNESS). One additional parameter that determines the number of shell history variables to be output is the NSHV. When NSHV=0, LS-DYNA outputs the stress tensor, strain tensor and effective plastic-strain at each integration point. This may be sufficient for most reuse but in some instances, such as mapping accumulated plastic strain, the default value of NSHV may be insufficient. In such cases, it is always recommended to set NSHV to a very large number to let LS-DYNA output ALL associated shell history variables depending on the constitutive model used by the shell.


Built-In Filtered Nodal Acceleration Output Using IACCOP in *CONTROL_OUTPUT
Mon, 18 Sep 2006 00:00:00 +0000
Starting in LS-DYNA v971, nodal accelerations can be filtered before being output to the ASCII file “NODOUT”. The type of filter can either be a built-in filter based on low-pass Butterworth frequency filter or can be user-defined. The filtering process is turned on by setting the IACCOP=2 in *CONTROL_OUTPUT keyword. The filtering process works by storing the nodal instantaneous accelerations at every compute cycle until a output state is reached. When the output state is reached, then the previously stored acceleration profile starting from the previous output state (or from time zero if the current output state is the first) is filtered and the last ordinate value of the filtered data is written to the NODOUT ascii file. To allocate sufficient memory for the storage, DT2MS parameter in *CONTROL_TIMESTEP must be defined so LS-DYNA can estimate the amount of required storage. For more information, please see *CONTROL_OUTPUT keyword in the LS-DYNA Keyword Users Manual.


Contact Force Output to RCFORC
Mon, 18 Sep 2006 00:00:00 +0000
The ASCII file “RCFORC” contains the incremental forces contributed by contact algorithms. Due to the nature of the contact-impact interactions, the raw output tends to be very noisy and is of little value. To eliminate the inherent noise in the contact force output, LS-DYNA averages the force magnitude over the preceing output interval which results in a smoother and useful time history of the contact forces. The averaging is performed for all values between two output states as shown in the following figure. For more information, please read Remark #5 under the *DATABASE keyword in the LS-DYNA Keyword User’s Manual.


Simulation Model Decomposition Using Recursive Coordinate Bisection  (RCB) Method
Mon, 18 Sep 2006 00:00:00 +0000
In the area of distributed computing using Massively Parrallel Processing (MPP) LS-DYNA, finite element model decomposition is performed after initial processing of the input deck to “distribute” the model content to compute nodes. There are two primary goals for model decomposition. First goal is of of course to “break-down” the given problem into smaller pieces based on the number of processors assigned. LS-DYNA writes the broken down pieces of the model in the form of a structured input file (scrXXXX) that will be reinitialized by respective compute nodes. This is shown in the following figure:


Contact Modeling in LS-DYNA
Fri, 15 Sep 2006 00:00:00 +0000
This 4 part article, orignally published in the FEAINFORMATION newsletter between August and December 2001, can be downloaded here: Contact Modeling.pdf





Airbag Leakage Modeling in LS-DYNA
Thu, 14 Sep 2006 00:00:00 +0000
In the area of numerical simulations involving the use of airbags to absorb impact energy, passively or actively, accurate definitions of airbag leakage parameters play a crucial role in predicting the response of impacting objects (ex. occupants). LSDYNA provides various options for airbag leakage modeling that may appear overwhelming at first but are actually quite simple to use. This article discusses these various methods and options that are applicable to leakage modeling in airbags for control-volume and ALE inflation schemes.


Deformability Switching in LS-DYNA
Thu, 14 Sep 2006 00:00:00 +0000
Among several simple yet powerful techniques available in LS-DYNA, switching of bodies that affects their deformability (at run time) is certainly one of them. Switching of bodies with negligible internal strains to a rigidbody at userâ€s specification can be useful to eliminate the calculation of element-centered variables such as stresses, which in many applications could dominate the total computation time. Additional benefits of using this feature could include the reduction of new model development time where regions of non-importance can be treated as a rigidbody for faster turnaround time. This paper presents an overview of how the switching works in theory and how they can be invoked in LS-DYNA which is supported both in SMP and MPP versions for both implicit and explicit solvers.


Seamless Mesh Coarsening for Shell Elements in LS-DYNA
Tue, 12 Sep 2006 00:00:00 +0000
Element count in finite element simulations are increasing faster than the â€œMoores law” used in chips. There are several reasons for this increase among which the single-model-multi-loadcase philosophy is certainly one of them. Earlier approach of building load-case-dependent models were both cumbersome, data duplication and big challenges for design change integrations. In todayâ€s simulations, one-model is tied or integrated closely to a design data. Load-case-dependent simulations then inherit the primary or â€œmasterâ€? model and study its response under specific load conditions. One major drawback, besides its obvious advantages, is the model content overhead. A very good example is the load-case involving focused studies that is limited to a small region of the model such as head-impact analysis or pedestrian-impact analysis. Inheriting the master model for such load cases brings a huge overhead of model content whose details may have limited influence on the response. Updating the model to reduce or eliminate the undesired model contact would certainly be not recommended as this results in a deviation from the one-model philosophy. Consequently, the feature of seamless mesh coarsening in LS-DYNA for crash or NVH models is promising as it provides a very convenient way of reducing model content and the process is completely reversible by adding/removing just a few keywords.


Automatic Timestep Control for Implicit Simulations
Mon, 11 Sep 2006 00:00:00 +0000
The known advantage with implicit simulations is that the solution is unconditionally stable allowing larger values of timestep. In implicit static simulations (IMASS=0 in *CONTROL_IMPLICIT_DYNAMICS), the simulation time has no real significance but is rather an indication of the applied load magnitude. For example if we have a simulation where a load is applied linearly such that it reaches 100% of its magnitude at the termination time of 100seconds and the current simulation time is 20seconds using an arbitrary timestep of 1second, then we can interpret that our load (assuming linear scale) is 20% of its maximum load. In the case of implicit dynamic simulations (IMASS=1) time takes real meaning and unlike explicit solution, the timestep is unconditionally stable and thus allows us to choose a large timestep.


One-Way and Two-Way Contact Definitions
Mon, 11 Sep 2006 00:00:00 +0000
This post will give you a brief summary of one-way and two-way contact definitions. The one-way/two-way refers to the treatment of slave nodes impacting the master segments.
One-Way Contacts

One-way was one of the first implementations in contact treatment and was done so such that it is computationally efficient. In the one-way contact treatment, the slave nodes are represented by discrete points with no physical connectivity between the nodes. The master is however defined is represented by segments (either 3 or 4-noded). In one-way, only the slave side is checked for penetration against the master segments. Since the master nodes do not undergo any checking, it may be possible that it could penetrate the segments or elements on the slave with no application of contact forces to prevent the penetration. Consequently, users are encouraged to define the â€œfinerâ€? mesh as the slave side and the coarser mesh as the master side to reduce the possibility of master node penetrating the slave side. Following figure shows the condition of contact involving a coarse-slave against a finer-master and a fine-slave against a coarse-master to illustrate the need for the slave side to be finer for better contact penetration detection in one-way contacts. Due to the nature of the one-way treatment, the resulting contact-impact is dependent on slave/master definition. Switching slave and the master sets, could result in different behavior depending on the geometry and the mesh sizes. Examples of one-way type contact definitions are all contacts with either NODES or ONE_WAY string present in the contact keyword. A complete list of one-way contacts are listed here.


Use of *SENSOR in LS-DYNA 971
Sun, 10 Sep 2006 00:00:00 +0000
A powerful new feature available in LS-DYNA version 971 is the *SENSOR keyword. To briefly summarize the Keyword Manual description, *SENSOR allows boundary conditions and various model entities to be activated/deactivated based on element, force, and/or node based criteria.
Options are available for modeling very elaborate systems, but we will focus on a very simple example which can be downloaded here: sensor.k.  The cards of primary interest are as follows:
*SENSOR_DEFINE_NODE

1,5,29,Z,,COORD

*SENSOR_SWITCH

1,Sensor,1,LT,16

*SENSOR_CONTROL

1,DISC-ELE,1




Element Formulation Switch for Implicit
Fri, 08 Sep 2006 00:00:00 +0000
Under-integrated elements are widely popular in the explicit field for their robustness and computational efficiency.  However, their use in Implicit without appropriate stabilization methods can cause singularities and may result in poor convergence behavior.  LS-DYNA offers parameters such as ISHELL, ISOLID, and IBEAM in the keyword *CONTROL_IMLPICIT_EIGENVALUE which can be used to switch to an alternate element formulation during an Implicit solution.  All necessary mapping of element history variables is automatically treated before and after the switch.  The switching of element formulation, when defined, is applied for all implicit solutions types such as eigenvalue extraction, implicit static linear, implicit static non-linear, and implicit dynamic.


LS-DYNA Simulation Template
Fri, 08 Sep 2006 00:00:00 +0000
Using the newly implemented feature of embedding FORTRAN type expressions in LS-DYNA using the *PARAMETER_EXPRESSION keyword, it is becoming easier to develop analysis templates that can provide flexible ways of changing analysis settings.  A partial input file highlighting the possibilities is shown below, and the full file is available here: main.k.  Using this as a template, one can import any model (prior to defining *CONTROL and *DATABASE keywords) and run the desired analysis.  Parameter names used in the *PARAMETER_EXPRESSION card can be carefully chosen to reflect the names of the keywords in which they are used.  LS-DYNA outputs the computed parameter values into the D3HSP file so they can be extracted and directly embedded for future runs if desired.


Strain-rate Effects in Implicit
Fri, 08 Sep 2006 00:00:00 +0000
When migrating input files or using internal switching from Explicit to Implicit solution type, the influence of strain-rate effects, if defined for the materials used, should always be considered.  If the problem is intended to be static or quasi-static during the implicit solution, it is recommended that strain-rate effects be ignored.  LS-DYNA now offers a convenient way to achieve this by setting the parameter IRATE=1 in *CONTROL_IMPLICIT_DYNAMICS which works for all implicit solution types.


Dynamic Solution Type using IMFLAG in *CONTROL_IMPLICIT_GENERAL
Thu, 07 Sep 2006 00:00:00 +0000
There are two classical solution methods available in LS-DYNA to solve a given problem.  The widely popular â€œExplicitâ€? solution scheme, using the central-difference method, is applied to short-duration transient dynamic problems while the â€œImplicitâ€? solution scheme is used for static problems.  Both of these methods have their advantages and disadvantages which depend entirely on the problem at hand.  The Explicit approach of using small timesteps to â€œmarch forwardâ€? is ideal for solving short-duration transient dynamic problems and requires a relatively small amount of memory to solve even very large problems.  The Implicit method is ideal for solving static or low-strain rate problems but has large memory requirements that increase exponentially with problem size.  Improvements in LS-DYNA allow seamless switching between the two solution schemes allowing the user to choose the best method for a given problem.


Ensuring Stable, Robust, and Accurate LS-DYNA Models
Thu, 31 Aug 2006 00:00:00 +0000
LS-DYNA simulation models, both large and small, frequently suffer from undetected modeling errors that can cause runs to die prematurely. Sometimes even minor model changes can introduce stability issues indicating a lack of robustness. Runs that die prematurely squander significant resources, something which I generally refer to as â€œsimulation wasteâ€?.
A recently developed procedure that has proven successful in boosting stability and robustness in most cases is known as â€œmodel shakedownâ€?. During the pre-processing stage, a â€œshakedownâ€? can be done early in the development process to detect and remove any modeling/software issues that are likely to cause numerical instabilities. Repeating this process frequently during the product lifecycle helps ensure clean and robust models and minimizes simulation waste.


Include File Listing
Mon, 31 Jul 2006 00:00:00 +0000
Added support to view the name and type of included files defined in the main input file. Here is a snapshot:



Title Customization
Fri, 28 Jul 2006 00:00:00 +0000
Job Titles can now be easily customized as demonstrated below.



Summary View Customization
Wed, 26 Jul 2006 00:00:00 +0000
Implemented draggable module windows so users can customize their summary view. This feature is demonstrated in the image below.



Model Notes Module
Tue, 25 Jul 2006 00:00:00 +0000
When a model is post-processed, its often very difficult to repeat it when viewed again at a later time since we may have moved on to a different model and would have lost track of the model history. To document a model as soon as we review its results, a “Web Observer” is now made available which allows the user to document the observations as you see it. Eventually, the information will be hooked up to a database so when its viewed again, all the recorded model observations are available so the user does not have to “reobserve” the results. A short demo of how the notes feature is used is shown below.


Web Browser to Paper
Mon, 17 Jul 2006 00:00:00 +0000
Implemented feature to print using any standard web browser. Just use the browser’s print option to print any page of the d3hsp tabs. The web view and the print view should be nearly identical. There will be continuing improvements to make the print view consistent with the web view. If you find any major differences, we would be very happy to hear from you.


Problem with IE has been fixed
Tue, 11 Jul 2006 00:00:00 +0000
Just wanted to update that the navigational problem when using Internet Explorer has been fixed. 


Added Number of Entities in Main Tabs
Mon, 10 Jul 2006 00:00:00 +0000



LS-DYNA Warning Messages
Mon, 10 Jul 2006 00:00:00 +0000
Started implementing an interface to view warning messages reported by LS-DYNA. Future upgrades will include more association between warnings and their related entities.


Airbag Definitions
Sun, 09 Jul 2006 00:00:00 +0000
Airbag or Control Volume definitions are now displayed as shown below. Currently, only the general parameters are shown but eventually, all the parameters based on the inflation models will be rendered along with appropriate curve defintions such as mass-flow, temperature, etc…



Export Bill of Materials
Sat, 08 Jul 2006 00:00:00 +0000
Added new feature to support the export of bill of materials (BOM). The current order of the columns are fixed but will later be allowed to be customized. BOM can be exported in either CommaSeperatedValues(CSV)/Excel or a well-formed XML file.



Application Maintainence
Thu, 06 Jul 2006 00:00:00 +0000
During the software development cyclce, numerous sample D3HSP files are used for testing purposes. As and when we get new bugs reported using our feedback form, they are fixed in a “live” mode. Fixing bugs this way for a production code during the early software deployment helps to address users issues quickly. During these live software upgrades, done almost daily,  you may experience some difficulties but the service should be up quickly.


Bill of Materials and more!
Sun, 14 May 2006 00:00:00 +0000
Completed the implementation of the viewing the bill of materials of the finite element model with full listing of element type, mass, material family, etc… Additionally, when each part row is clicked, it opens a new layer showing the detailed material information and any related curve display. Our idea was to have one place to view a complete part information. Here’s a snap shot!
Update
A few of you reported that the part listing is a little slow. Thanks for letting us know. The current part list display is a brute force method and will be optimized soon.


Database Cross-Section
Wed, 03 May 2006 00:00:00 +0000
Implemented viewing of cross-section information. LS-DYNA^Â® outputs nodes/elements for automatic cross-section definition (via *SET_PART) and this information is captured in the D3HSP file as shown below.



Simulation Timing Information
Sat, 22 Apr 2006 00:00:00 +0000
Implemented feature to view timing information. Three types of data can be viewed.
1. Timing distribution based on some major routines in LS-DYNA such as contact, element, etc. AND individual contact based.
2. When running in distributed environment, you can view the host/processor based timing distribution.
3. Using data available in 2, you can view the deviation of each processor from the average (optimum) timing information. Percentage deviation of each processor from the optimum (average) timing is plotted against each processor/host. The deviation chart is broken down further to faster processors, whose individual timing is lower than the average, and slower processors, whose timing is higher than the average. In the example below, you can see that processor number 7 is performing at optimum level while processor number 9 is the slowest. You can diagnose the problem further by outputting the decomposed model for each processor to look at its contents for performing tuning.


New Server!
Thu, 20 Apr 2006 00:00:00 +0000
Upgraded the server. Should expect a 3x speed up. Also enabled cache to render static pages.


Contact Definitions
Wed, 19 Apr 2006 00:00:00 +0000
Added extraction and viewing of contact interface definitions. The view part is currently hooked up as an initial interface but will be redesigned as we hook up other options. Any suggestions on the display are welcome.



Multiple Curve Plotting
Sat, 15 Apr 2006 00:00:00 +0000
Implemented multi-curve plotting support for both IE and Firefox. Here is the snapshot:



Job File Name and Title
Thu, 13 Apr 2006 00:00:00 +0000
Implemented feature to view the job name and the job title at the top of the page. This is helpful to associate the contents quickly to the job name/title irrespective of the page location.



Scalable Vector Graphics
Thu, 13 Apr 2006 00:00:00 +0000
Fixed a major bug affecting SVG rendering in Mozilla Firefox. Now plotting of any SVG is rendered properly in both Internet Explorer and Firefox. Firefox rendering seems a little slow though. Example of svg usage is a simple pie-chart showing mass-distribution.



HyperElastic Fit
Tue, 11 Apr 2006 00:00:00 +0000
Added support to view hyperelastic fit information.


Implicit Solution History
Tue, 11 Apr 2006 00:00:00 +0000
For every implicit converged step, LS-DYNA reports the number of iterations it took to converge and the number of stiffness reformations it had to make. To view this, d3View added a support to view the stiffness reformations, number of iterations, energy, and displacement norm time-history.







About d3VIEW
Mon, 01 Jan 0001 00:00:00 +0000



End User License & Services Agreement (EULSA)
Mon, 01 Jan 0001 00:00:00 +0000

END-USER LICENSE AND SERVICES AGREEMENT
PLEASE READ THIS END-USER LICENSE AND SERVICES AGREEMENT (“AGREEMENT”) CAREFULLY. BY INSTALLING OR USING THE SOFTWARE THAT ACCOMPANIES THIS AGREEMENT, ANY COMPONENTS OF THE SOFTWARE, OR ANY UI OR BACKEND SERVER THE d3VIEW APPLICATION CONNECTS WITH (ALL COLLECTIVELY AND EACH INDIVIDUALLY REFERRED AS THE “SOFTWARE”), OR BY USING THE d3VIEW SERVICES THAT ACCOMPANY THIS AGREEMENT, OR ANY d3VIEW WEBSITE or UI THROUGH WHICH THE SERVICES ARE PROVIDED (ALL COLLECTIVELY AND EACH INDIVIDUALLY REFERRED AS THE “SERVICES”), YOU AGREE TO BE BOUND BY THE TERMS OF THIS AGREEMENT. IF YOU DO NOT AGREE TO ALL THE TERMS, DO NOT USE, ACCESS, OR USE THE SOFTWARE OR SERVICES.


Master Services Agreement (MSA)
Mon, 01 Jan 0001 00:00:00 +0000

Effective Date. This Master Services Agreement (“Agreement”) is effective as of the date (i) you (“Customer”), or (ii) any third party acting on Customer’s behalf, including without limitation a procurement agent, purchasing entity, or affiliate (“Customer’s Buyer), accepts a quote, issues a purchase order (“PO”), or otherwise engages d3VIEW Inc. (“Provider,” “we,” “us,” or “our”) to perform services.
Customer acknowledges and agrees that any Customer’s Buyer acts as Customer’s authorized agent for purposes of procuring the services, and that Customer shall be fully bound by, and responsible for, all obligations under this Agreement, regardless of whether such services are ordered or accepted directly by Customer or through a Customer’s Buyer.

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d3VIEW Intern Spotlight: Meet Our Summer Interns

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