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Shell Element Stress and Strain Output to D3PLOT – A Brief Overview

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 […]

Blog Statistics – Thank You!

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

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 […]

Makefile – Is This Just for Programmers?

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 # […]

iPhone Support

This blog is now optimized for viewing on iPhones.

Automatic Tiebreak – Some Quick Notes

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 […]

Strains and Stress in NonLinear Finite Element Method

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

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 […]

Encryption Comes to LS-DYNA v971 !

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 […]

Sense-Switch Controls for Interacting with Running LS-DYNA Jobs

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 […]

Interactively Terminating LS-DYNA Jobs

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 […]

Features Every LS-DYNA Simulation Must Have

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, […]

Energy Output to D3PLOT Files

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 […]

Accelerometer Mass

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

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 […]

A Simple ALE Sloshing Example

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 […]

Tiebreak Contact in LS-DYNA

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

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 […]

DKT Triangular Shell for Crash

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 […]

Contact Surface Generation for Solid Elements

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, […]

Consolidating Multiple Contact Definitions to a Single Contact

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 […]

Principal Stress Calculator for Shell Elements in DYNAIN File

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 […]

Smoothing Length in SPH

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 […]

Viscous Damping Coefficient (VDC) in SPH Contact

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 […]

Interface Binary Output for Single Surface Contact

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 […]

True Total Strain to Effective Plastic Strain

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 […]

Speeding up numerical studies using Discrete Optimization in LS-OPT

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 […]

Sinusoidal Motion using *DEFINE_CURVE_FUNCTION

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 &amp*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 […]

Unloading Behavior in MAT_083

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 […]

Time Integration, Characteristic Length, and Mass Scaling

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.

Stress Relaxation in Viscoelastic Material Models

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. […]

Free LSTC USSID

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

SPH Contact Definitions

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 […]

Interface Component Analysis

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 […]

MultiStage Dependent or Independent Simulations using *CASE

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 $ […]

Modeling Off-Axis Dependent Yield Stress for Honeycombs using MAT_126

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 […]

Choice of Rigidwall Treatment

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 […]

Best Practices for Building Flexible Models with Reduced File Sizes

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 […]

Transient Removal of Initial Penetrations Using DPRFAC Parameter for SOFT=2 Contacts

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 […]

Load Balance Checker for MPP LS-DYNA

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} Download Source Preview /* Load Balance Diagnosis for MPP LS-DYNA Author: Suri Bala, Livermore Software Copyright: […]

MPP and Deformable to Rigid Switching

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 […]

Load Balance in FMVSS 207/210 Simulations for MPP

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 […]

Initial Velocity in Local Coordinate System

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 […]

Curve Extrapolation

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 […]

Bulk Viscosity for Shells and Solids in LS-DYNA

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 […]

Limitations of Using LCSR for Strain-Rate Inclusion in MAT_024

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 […]