close
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 […]

Tolerance used for Tying Slave Nodes in TIED contacts

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 […]

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 […]

D3VIEW Update : LS-DYNA Examples Project Now Available for Public

The LS-DYNA Examples Project , managed using D3VIEW, is now available for public usage. If you want to become part of the team to contribute to the examples set, you can send me an email at INFO at D3VIEW dot COM.

Effects of Initial Penetrations

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 […]

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 […]

Reduce D3PLOT File Size for RigidBodies

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

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 […]

Modified Crushable Foam

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 […]

D3VIEW 2.0 Beta Released

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.

Timestep Calculation

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 […]

CONTACT_AUTO_MOVE to eliminate initial contact clearances

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 […]

Non-Structural-Mass (NSM) Lumping in LS-DYNA

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 […]

Yield Stress, Strain-rate Dependency in MAT_024 and the significance of SIGY

*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 […]

d3View v2.0beta – LS-DYNA Simulation Data Manager – Releasing Shortly

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 […]

Force Deflection to Effective Stress vs Effective Strain

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 […]

Initializing Velocity

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 […]

Simulation "Pack" to Perform Design or Numerical Variable Studies

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 […]

Tiebreak Example # 1

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 […]

*DEFINE_CONTACT_VOLUME for *SET_{OPTION}_GENERAL

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 […]

MIT Open Course Ware

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

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

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 […]

Membrane Thinning in Shell Elements

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 […]

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 […]

Contact and Global Timestep

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 […]