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Total Mass, Physical Mass and Added Mass

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 […]

Air particles and relaxation when using Particle based airbag inflation

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 […]

Visualization of Triaxiality Factor in LS-PrePost

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.

Hybrid LS-DYNA

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 […]

Hybrid LS-DYNA

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 […]

Shell Local Material Axis Definition for Orthotropic Material

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 […]

LS-DYNA and D3VIEW helps BYU Students build PACE F1 Car

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 […]

Visualizing Dynamic Relaxation Convergence

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 […]

Sensor Definitions in LS-DYNA

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

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 […]

LS-DYNA Examples Blog by Student Qui

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 […]

Unloading in MAT_FABRIC (MAT_034)

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 […]

Shell, Solid and Beam Formulations for Explicit and Implicit

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 […]

Modeling rigid bodies

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 […]

Happy New Year !

Wishing everyone a very happy new year.

Significance of IGAP Parameter in *CONTACT in Implicit Analyses

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 […]

Marsha Victory, Thank You For Your Blog Hosting Sponshorship !

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 at lstc dot com. Thanks very much, Marsha, for your support.

Boundary prescribed motion and Contact

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-OPT 4.0 is now released.

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

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 […]

Discrete variables in LS-OPT

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 […]

Fast Debug of LS-OPT driven Optimization Problems

LS-OPT is widely used to optimize designs or parameters using a number of experimentals 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 […]

Free Limited LS-DYNA Version to Assist Displaced Workers

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 at lstc dot com.

Multi Solver Run in LS-OPT

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 […]

Packing LS-DYNA Input Files for Easy Distribution (v1.1a)

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 […]

Damage modeling using GURSON

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

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 […]

Optimizing monotonically increasing load curves

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, […]

Packing LS-DYNA Input Files

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 […]

Termination due to Added Mass

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 […]

971 Release 3.2 is Now Available

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-1Add V option for aopt=3,4– […]

Killing LS-DYNA Jobs

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 expetec 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 […]

10th LS-DYNA Users Conference

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

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 […]

Initially in Contact – TIEBREAK contacts

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 […]

New LS-OPT Support Site

A new LS-OPT support site is established with lots of useful information that covers examples, theory and many download materials.

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. […]

LSDYNA Simulation Notes

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 […]

Quaternions for 3D Graphics

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.

SLURM: A Highly Scalable Resource Manager – Free and OpenSource

Clustered solutions dominate the market today with MPP-LSDYNA being used worldwide when 2 or more processors per job are used. Managing compute nodes manually in a cluster is certainly primitive and hence the need for a good resource manager. SLURM is a open source resource manager with lots of good features and is available from […]

Internal Contact for Solids using *SET_SEGMENT_GENERAL

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 […]

TIEBREAK Example

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 […]

RCB Decomposition and LS-DYNA Built-In Intelligence

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 […]

Interior Contact for Foams, Honeycombs and Rubbers to eliminate Negative Volumes.

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 […]