You can download the LS-DYNA 971 r4 Manual (PDF, 11.5 Mb)
Update The broken link has been fixed
LS-DYNA 971 Release 4 Manual Available for Download
Published by May 13th, 2009 in LS-DYNA Bytes. 3 CommentsThe LS-OPT Version 4.0 beta release is now available at:
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
Published by May 13th, 2009 in LS-DYNA Bytes and LS-DYNA Elements. 0 CommentsDiscrete 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.
Density (RHO) in the material is equal to 1.0
Whne the density in the material card is equal to unity, LS-DYNA uses the VOL parameter in the SECTION_BEAM keyword as the mass value and lumps them to the beam-nodes.
For non-zero and zero-length discrete beams, both methods are valid but methods must yield realistic mass to provide a reasonable timestep.
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.
To enable discrete variables, the user has to mark the variable as ‘Discrete’ and provide a sequence of values separated by either a comma or a space. Discrete sampling of this definition is then performed by LS-OPT in two ways as defined below.
1. Continuous Discrete Sampling.
This sampling approach uses ALL possible values between the lower and the upper bound of the discrete set. For example if the discrete set consists of “2,10,16″, then any value that lies within 2 and 16 is considered as a valid sampling point.
2. Discrete Sampling
In this sampling, LS-OPT will only use values from the set with no interpolation. For the set 2,10,16, only values from the three will be used. Currently, this approach works for D-OPT and SPACE-FILLING sampling schemes only.
Thanks to Dr. Nielen Stander for sharing this information.
Fast Debug of LS-OPT driven Optimization Problems
Published by January 28th, 2009 in LS-DYNA Bytes. 0 CommentsLS-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 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.
LS-OPT uses a paramter named “iteration” in its command file that tells how many optimization iterations must be performed. When this parameter is set to 0 , it runs only ONE run per solver. This is a great way to ensure that all steps excluding the actual solution works as expected.
To validate the LS-DYNA simulation, you can include an additional “dummy” parameter namely “ENDCYC” that sets the number of cycles to solve. If ENDCYC=0, the parameter ENDTIM is used while when ENDCYC>0, the solution is run for ENDCYC cycles. When simulating a “dry” run, you can set this parameter in the LS-OPT command file to a small value such as 10 such that LS-DYNA runs a quick simulation which allows us to verify that it runs and terminates normally and all variable subsitution and result extraction is performed as expected.
Free Limited LS-DYNA Version to Assist Displaced Workers
Published by December 13th, 2008 in LS-DYNA Bytes. ClosedLSTC 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.
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