General Mechanical

General Mechanical

LS DYNA SIMPLE SIMULATION doesnt run

    • kaitova
      Subscriber

      Hi,


      sounds like showing off, i am trying to run simple simulation based on this tutorial. 


      I have several errors, one is working directory, another one with solverand a few more.


      Could you please help to solve this model, it should not be difficult I think I just miss something.


      Thank you


      Link for description of the task


      file:///C:/Users/kaitova/OneDrive%20-%20TECHNIPFMC/Desktop/Getting%20Started%20—%20Welcome%20to%20the%20LS-DYNA%20support%20site.html


      version ansys R19.2


       

    • peteroznewman
      Subscriber

      That is not how you create links.  Here is a link to the LS-DYNA Tutorial page and the full URL is shown below.


      https://www.dynasupport.com/tutorial/getting-started-with-ls-dyna/getting-started


      I can't open your archive because of an error:


    • kaitova
      Subscriber

      Hi Peter,


      Thank you for advises. Here is a link to the tutorial, I have tried to modify the model, now it is running, I am not quite sure that I should check the deformation to compare it with displacement in the tutorial. The mesh is very coarse. My idea was to check if I can make any LS dyna model, but maybe it is not a proper tutorial to do that because it includes coding. Please, see the model attached anyway .


      Thank you for help.


       

    • kaitova
      Subscriber

      Hi Peter, I must apologize, the model is attached in the first post in this thread. I can not modify my reply because it is under moderation.


      Thank you

    • peteroznewman
      Subscriber

      LS-DYNA is not included in the Student license and I don't have access to it anywhere else, so I can't help you.


      What is included in the Student license is Explicit Dynamics.

    • Wenlong
      Ansys Employee

      Hi Kaitova,


      Ansys employees cannot download attachments from the student community, so can you insert as images the error messages (maybe along with several screenshots of the model setup)?


      Regards,


      Wenlong


       

    • kaitova
      Subscriber

      Hi Wenlong, thanks


      I have managed to run the model, for me it is now important to identify results (which output should I request from ansys) and compare it with the tutorial. So far. I could not see that results are the same. Here are some print screens for the probe of node 7, they are not equal  to the tutorial. The analysis set up pictures are attached as well. Is displacement equal to deformation - I am trying to understand if it is.


       





      Thank you


       

    • Wenlong
      Ansys Employee

      Hi,


      Thanks for the detailed explanation. I would suggest two things:


      1. Change the boundary condition. Instead of using a fixed boundary condition at the bottom, apply a boundary condition like this:



      Only in this way can you achieve a shear stress free deformation, and be able to test the Poisson's effect. The training material website in LS-DYNA does not say what boundary condition it uses, but I believe that's the one they use to get the exact 3e-5m lateral displacement. Here is what I got using these BCs.




      2. Double-check your units. The input.k file (the keyword file) is the final input that is sent to the solver. So it is a good idea to check there whether your units are consistent. You can find the consistent unit system in here: https://www.dynasupport.com/howtos/general/consistent-units


      The input file can be found by right click on your "Solution (D6)" --> "Open Solver Files Directory" ---> Open "input.k".


      Alternatively, you can find it in the "LSDNYA Pre" tab --> "Write Solver file". In the keyword file, you can check what exact value you will input to LS-DYNA solver. 


      For example, in my input, I am using ton, mm, MPa, ms,





       


      Regards,


      Wenlong


       



      Useful Links



       

    • kaitova
      Subscriber

      Thank you Wenlong, 


      i finally had time to make it.


      all your advises were useful.


      I have 2 questions:


      1. in the input file there is a "define curve" several times, and only the last one shows the 7 MPa value, I was going to ask why it is several times but now I understand that it must be a curve for the pressure defined as a load and it is several times because it is shown step wise.


      2. another question was about final result value,lower than it should be, but after double checking the units, i can see that that was a reason.


      I actually have a question, what is control termination? and why value there is in ms?


      Thank you for help.

    • Wenlong
      Ansys Employee

      Hi,


      *Control_termination defines how long the simulation runs, and since the unit system I use is mm, g, N, MPa, so the corresponding time unit is ms. Please refer to the consistent unit system website I sent in the previous post. 


      If you want to learn more about Ansys LS-DYNA keywords cards, you can search LS-DYNA keyword manual, where volume 1 is about setting up the model, and volume 2 is about material modeling. 


      Regards,


      Wenlong


       

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