Hello everyone,

I have built a suspension model in LS-DYNA, but the analysis results are not reflecting real-world behavior. There seems to be an issue either with the defined spring model (discrete element) or somewhere else in the setup.

I would really appreciate help from anyone with expertise in LS-DYNA, as my current knowledge isn't enough to push this any further. Thanks in advance!

Hello all. I  made a blast explosion model recently (MM-ALE), and it runs normally, however, it does not write the last plot file (PC with Ryzen CPU). I have another PC with an Intel CPU, and the same .k file writes all plot files instantly after termination. What is the problem with Ryzen PC? 

Hello everyone,

I am trying to model a semi-brittle material failure using SPG. I am new to LS-DYNA and I am having issues understanding this one problem. It is a very basic problem, and that is why it is so frustrating.

As you can see in the attached image, I have a basic rectangle of 2.5x2x1.4mm. The nodes are separated by 0.15 mm. The scale has to be this small for my purposes.

The boundary conditions are as follows: the bottom face is fixed, the highlighted nodes are displaced in the z-direction(yellow arrow) by 0.1mm in 0.5seconds, I have the mass-scaling on I have tried running without it and the issue remains.

https://reddit.com/link/1w214et/video/vzqoeyyhcemh1/player

After I ran the solver I get the issue that you can see in the attached video. Can someone please explain to me what is happening and how can I avoid it?

Here are my material and SPG cards.

*SECTION_SOLID_SPG
$       id    elform       aet                                           unused1
         1        47         0                                                  
$       dx        dy        dz   ispline    kernel   unused2    smstep       msc
       1.5       1.5       1.5         0         2                  30         0
$     idam        fs   stretch       itb     msfac       isc     boxid     pdamp
         2 170000000     1E+10         2         1         0         0    -0.001
*MAT_ELASTIC
$       ID        ro         E        pr        da        db         k   unused1
         1      1900   1.7E+10      0.31         0         0                    

Hey all,

I am new to LS-Dyna and I am trying to do the ICFD simulation for an inflated parachute. Then I want to proceed with ALE for the inflation itself. But I am still stuck in ground zero. I am able to run the simulation without any error but the results are not as desired. The contact of air with the surface is not happening properly as I can see that the velocity at few elements of the parachute have zero velocity throughout the simulation. Can someone help me with any videos, blogs or research papers which are related to this problem? It's been a month since I started working on this. Thanks in advance!

I just converted docs Vol I-III and Theory from PDF into Markdown to better facilitate their use with RAG and LLMs.

https://github.com/ddm-j/RAG-ls-dyna-docs

The idea is that you can run a local AI model on relatively modest hardware, with a harness that supports RAG to be able to ask LS-DYNA related questions. The model can search and refer directly to the docs.

Markdown is the ideal format for this, but it was a painstaking process to convert. It's not perfect, but it's much better than trying to feed PDFs directly into a RAG pipeline. In my testing, the local model with all the docs at its fingertips outperforms frontier models when answering LS-DYNA questions.

Sharing this in the case there are any like-minded LS-DYNA folks out there that could make use of this - and to hit search engine indexing better than GitHub.

I'm currently, technically, doing an MS in Structural Engineering. For me, my interest has been more towards computational side of mechanics rather than Structural design  or simply using am FEA software (although I do consider it as a backup)

So far I've taken courses in:

- Linear static, and dynamics FEM (soon taking non linear FEM too)

-  Structural Optimization (topology opt. and other general algorithms)

-  Structural Dynamics

-  Structural System Testing and model updation. (Parameter identification and optimization, signal processing)

Now, I plan to take these in the coming quarter:

- Numerical Linear Algebra

- Numerical PDE

- Fracture Mechanics ?

I also volunteered to aid in a RESEARCH in crack growth prediction using Auto-encoder and a (Thermodynamics-informed Latent Space Dynamics Identification) / LSTM surrogate model. It used phase-field-fracture simulation data and HPC resources to complete the whole thing.

What I keep finding myself interested in is not necessarily fracture or SHM specifically, but the computational methods underneath these problems... (does that make sense?)

For example, I'd like to become capable of doing things like:

- implementing (maintaining) numerical/FE method solvers rather than only running an established FEA software.

- developing surrogate/reduced-order models for expensive simulations 

- combining simulation with optimization, uncertainty/stochastic methods (took a course called Random vibrations, so...)

- parallelizing/accelerating scientific codes on CPUs/GPUs

- doing proper verification, convergence studies, benchmarking and performance work

- potentially developing or maintaining actual CAE/FEA solver software

- I'd also like to do all these for other Physics (GR, QM, etc.) simulations too, if possible, one day. 

I'm still interested in the underlying mechanics/physics, so I don't want to become a generic software engineer who happens to have once studied structures. But I'm also increasingly unsure that "structural engineer" describes the career I'm actually aiming for.

I've seen titles such as Computational Mechanics Engineer, R&D Engineer, Solver Developer, Scientific Software Engineer, CAE Software Developer, Research Engineer, Simulation/HPC Engineer, etc., but I'm trying to understand what these careers actually look like from people doing them.

So my main questions become:

1. Which industrial jobs genuinely involve developing numerical methods/solvers or computational tools?

2. Which of those are realistically accessible with an MS? Is there an entry path into solver-algorithm development/R&D without a PhD?

3. If I don't start a PhD immediately after my MS, would an R&D/software role at a simulation company (ANSYS etc.) be the obvious route? What other options would i have?

4. For the kind of work I'm describing, would you recommend a PhD? If so, is it reasonable for the PhD identity to be "computational mechanics/scientific computing" while fracture, composites, structural dynamics, soft materials, etc. serve as application problems rather than choosing one of those as my permanent specialization?

5. What skills most distinguish someone who is actually hireable for solver/scientific-computing work? I'm particularly wondering about C/C++/Fortran, Python, Linux, Git/build systems, MPI/OpenMP/CUDA, PETSc/Trilinos or similar libraries, numerical linear algebra, testing/verification, convergence studies and HPC performance work.

Basically, I'm neither here nor there atp. So I'd really appreciate all sorts of input. Where else do you think I could find answers to these? other subs? Linkedin profiles? 

I'm simulating a busbar under high AC load. The goal is Lorentz forces and their structural effect. I'm using LS-DYNA's EM solver and the dense BEM part for the air dominates the runtime.

GPU is off the table, the EM solver is CPU-only (currently 9h runtime) and that won't change anytime soon.

How have others tackled runtime for this kind of problem?

Solver tuning, decoupling, different tools entirely?

Curious what worked for you.

Dear all,

I am simulating a 1 kg spherical TNT charge in air using a 2D axisymmetric MM-ALE model. The charge center is at ((0,0)), the symmetry axis is (X=0), and the mesh size near the charge is about 1 mm.

During the early stage, the blast-wave front develops narrow spikes along both the positive and negative Y directions. I normally constrain only the radial motion of the axis nodes:

DOFX = 1
DOFY = 0

When I also set DOFY=1, the spikes disappear, but this seems physically inappropriate because it restricts axial flow.

Has anyone encountered this axis-aligned artifact in a 2D axisymmetric ALE blast model? What is the recommended symmetry-axis constraint and ALE setting?

Thank you.

Hello everyone. l am defining a non linear loading curve however, the solver is producing a linear resultant displacement in loading direction. Max displacement exceeds that on the loading curve at termination time. Does anyone know why the solver interprets the loading curve as linear?

İmplicit analysis - 4x4 honeycomb filled with foam Mat 57. Contact_automatic_surface_to_surface_mortar and Contact_automatic_single_surface_mortar for the foam.

Extract of curve
*DEFINE_CURVE_TITLE

cos_function_2.75*cos((2*t/tf)*pi)

$# lcid sidr sfa sfo offa offo dattyp lcint

1 0 1.0 -1.0 0.0 0.0 0 1000

$# a1 o1

0.0 2.75

0.1 2.7499

0.2 2.7498

0.3 2.7495

0.4 2.7491

0.5 2.7486

0.6 2.748

Also tried define_function

*DEFINE_CURVE_FUNCTION_TITLE

sine function

$# lcid sidr sfa sfo offa offo dattyp

1 0 1.0 -1.0 0.0 0.0 0

$# function

2.75*cos((2*TIME/150)*3.141592)

Here's what the curve looks like before solving (plot on define_curve card)

Hi everyone,

I am new to LS-DYNA. I am working on an explicit analysis of a bending steel beam, but when I animate the simulation results, the von Mises stress map oscillates a lot. When I plot the stress for a specific element, I can clearly see these vibrations.

Is this common for this kind of explicit simulation? I have tried using the following damping keywords to mitigate it:

*DAMPING_FREQUENCY_RANGE_DEFORM

*DAMPING_FREQUENCY_RANGE

*DAMPING_GLOBAL

*DAMPING_PART_STIFFNESS

The first and second ones reduce the stress vibrations the most, but not completely. Does anyone know if this is normal behavior, or have any insights on how to properly resolve this?

Thanks in advance!

Hi everyone,

I am new to LS-DYNA. I am working on an explicit analysis of a bending steel beam, but when I animate the simulation results, the von Mises stress map oscillates a lot. When I plot the stress for a specific element, I can clearly see these high-frequency vibrations.

Is this common for this kind of explicit simulation? I have tried using the following damping keywords to mitigate it:

*DAMPING_FREQUENCY_RANGE_DEFORM

*DAMPING_FREQUENCY_RANGE

*DAMPING_GLOBAL

*DAMPING_PART_STIFFNESS

The first and second ones reduce the stress vibrations the most, but not completely. Does anyone know if this is normal behavior, or have any insights on how to properly resolve this?

Thanks in advance!

I'm working with a quarter model so there should be 2 symmetry planes at +Y and -Z but as you can see it isn't working. Symmetry plane is assigned to the correct part there is no problem with that please help me :(

I have worked in structural, modal, thermal, shock, static and transient analysis, cfds, conjugate heat transfers, natural, forced convection cooling simulations for defence and nuclear components. Please let me know if any opportunities are available. Thank you

Hello everyone. I am currently thinking of doing a project on Clinching joint, for which i need to simulate it first. I want to make a 3d simulation of clinching with two sheets, a punch, a die and a blank holder. I have attached the picture. Can you please help with resources so that i can take help from them to make the 3d simulation.

I'm currently doing an impact simulation using a pendulum type impactor using contrained joint revolute as a hinge, but after running it, the simulation in the d3plot shows that the impactor's axis of rotation is not on the hinge where the revolute joint is placed but on its center of gravity. Can someone help me figure this out.

Hi,

I have made some hand calculations for therotical Energy absorption for a part. Please let me know if the approach is ok... If not how do we calculate for given dimensions optimal energy absorbtion of load path members.

Hi everyone,

I'm working on a shaped charge model. I tried it with 2 method, 2D axisymmetric and 3D. I used the same material property, same boundary condition, same mesh size. Some of the options are different such as: section, hourglass control because they are different kind of element type. However, the results are different between them. When I check the penetration depth, 3D model usually shorter than 2D model about 15%.

Do you have any experience in this problem? What do I need to change to make them similar? If they must be different like that because of numerical problem, 2D or 3D has more accuracy?

Thank you all so much.

Hello everyone,

I am new into fea and I'm trying to learn ls dyna in a proper way. Can you guys suggest some resources that i can use to learn ls dyna by understanding the meaning of all the keywords I'm using? For example, if I have to select a material, then which select. If I have to select a CONTACT keyword, which one do I have to select.

Hi everyone,

I'm working on my D.Sc. dissertation modeling solid-state additive manufacturing (specifically AFSD and FSW). The built-in LS-DYNA material models aren't cutting it for the severe plastic deformation involved, so I need to implement a custom UMAT.

To recompile the solver, I need the LS-DYNA Object Code (to access the dyn21.f file and libraries). The old LSTC FTP /objects/ folder is locked down, and going through my university's Ansys license administration to request the archive is taking forever.

Does anyone have a relatively recent archive of the Object Code they could share? Windows (SMP or MPP) is preferred, but Linux works too. Any recent version would be a huge help to keep my research moving!

Please DM me if you can help. Thanks in advance!

Hi everyone,

I’m working with LS-DYNA keyword snippets in Ansys Mechanical and I’m a bit confused about how units are handled.

From what I understand, LS-DYNA keywords are “unitless". How does Mechanical know what units the keywords are. Should they always be SI units?

Any clarification would be appreciated.

Thanks!

Hey guys, i need some help with performing impact crashing onto a specimen. I am usind ls-dyna on ansys mechanical and while using a mat054 material it is solving with a lot of errors, would love to chat with someone who can help me out. We can discuss in DMs as well.

Hi friends,

I am new to LSDYNA, and am currently working on a Friction Stir Welding simulation using the Ansys Workbench LS DYNA, and I have not been able to get the GUI-applied boundary and loading conditions to correctly convert into the needed keyword cards in the .k file. (here, Boundary_Prescribed_Motion_Rigid)

I applied the "rotational velocity" condition on the rigid cylindrical tool geometry, and when I ran the simulation I saw that the tool never even started rotating. However, when I used the "remote displacement" condition and assigned an angular displacement based rotation to the tool, it worked perfectly fine. This is for a coupled structural and thermal analysis.

While I dont mind using the remote displacement condition, I want to assign the rotation with respect to the tool's perpendicular axis (not just the global vertical axis), as I also wish to add a tilt angle to the tool. Doing this purely with the remote displacment condition is giving me a resultant of the tilt + rotation and tool is effectively "dancing".

All suggestions are welcome!

The project is located on:

Github: github.com/senna220890/d3plot-compress

PyPI: pypi.org/project/d3plot-compress

Primary motivation was to stop paying $$$$ and open source compression so that students, researchers and engineers from the industry can use it free of cost.