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Topics related to LS-DYNA, Autodyn, Explicit STR and more.

full restart a fsi analysis

    • Ezreal Zed
      Subscriber

      How to resolve error message:" Request 0 threads but only 1 threads were actually created." ? this error happen in full restart a fsi analysis.

    • Ian Do
      Ansys Employee

      Hello Ezreal,

      If you model FSI (fluid structure interaction), restart will not work. We cannot carry the FSI load history from run1 to run2.

      Restart in general is a complex procedure that is not guaranteed to work 100% of the time for LAG modeling. If you have multi-physics model, that is even worse. It is to be used only in rare cases. 

      Please describe the physics you want to model and maybe I can suggest an approach.

      This error seems to be on the machine level (decomposition?) - not solver level.

      Regards,

      Ian Do 

       

      • Ezreal Zed
        Subscriber

        Hello Lan

        Thanks for your reply! Please forgive me for not seeing your message until now, I want to use a metal ball penetrating into ground, and then put some explosive into the hole and detonate, so I think full restart can do this. I use two versions DYNA solver, one's error is "nagative volume in solid element", it looks like some elements of ground have sharp angles, they can continue in run1, but can not restart in run2, the other one's error is in the photo above. In my restart analysis, I only use stress_initialization to initialize the ground part, delete other parts and then add explosive and air part to make it become a FSI analysis, I can not understand that why the ground part elements are OK in run1, but negative volume or the above error in run2.

        Thanks again and best regards,

        Ezreal Zed

    • Ian Do
      Ansys Employee

      Hello Ezreal,

      For detonation related info, I am not sure I can discuss it here. Let me check on our restrictions.

      [Q1] ” one’s error is “negative volume in solid element”, it looks like some elements of ground have sharp angles”

      [A1] This already meant that you have inverted some solid LAG elms. The solution is wrong already. No sense to carry on. When mat fails, failed LAG elms get removed. You need to get proper mat failure data. 

      [Q2] error in above pic

      [A2] I do not know this error – machine or platform related maybe(?) – you can check with your computer admin people(?).

      [Q3]  In my restart analysis, I only use stress_initialization to initialize the ground part, delete other parts and then add explosive and air part to make it become a FSI analysis,

      [A3] With LS-DYNA restart is never guaranteed even for a simple LAG model! For the ALE model with FSI it is not suggested. This requires a lot of time for debugging typically because the result mapping is never straightforward. This may be something requiring a support ticket. Not something that can be diagnosed on this platform.

      Regards,

      Ian

       

      • Ezreal Zed
        Subscriber

        Hello lan

        Thank you very much for your answer! I will check my analysis.

        Regards,

        Ezreal

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