General Mechanical

General Mechanical

Topics relate to Mechanical Enterprise, Motion, Additive Print and more

Pre-stress modal analysis cannot handle 1mm thickness with 2000Pa pressure

    • Weihan Lin

      Hi all,

      I've been trying to use pre-stressed modal analysis to do simulation on my 2-meter-long rubber boat. The simulation works under 200Pa pressure, 0.05m mesh and 1.6mm thickness.

      However, when I increase the pressure to 2000Pa, the errors always say "element has excessive distortion or thickness" or "solution not converged" (2nd one most cases). I tried different end time from 10 sec to 1000 sec, and I tried different subset of 100 to 100000, and none of them work.

      I tried different mesh size, and it works. With a 0.1m mesh, it can solve the problem. However, 0.1m mesh is way too large and I do want to use a finer mesh to get a more accurate result.

      Does anyone know why this is happening and how can I use a finer mesh?

    • Sahil Sura
      Ansys Employee


      Hello Weihan Lin,
      For this case, you are not getting the results for the linked modal analysis as the structural analysis hasn’t converged. The following can be some of the suggestions that might help you address this situation.


      • If the obtained maximum stress at the last converged step is greater than the yield stress of the material, the model is getting much more deformed than it is expected. This can be rechecked by defining proper boundary conditions.
      • Verify the contacts and the model behavior is set according to the physical behavior, unnatural rigidity or constraints cause elements to deform much more than expected.
      • Verify the geometric nonlinearities are included in the model by turning On the Large Deflection option.
      • Update the mesh and ensure considerable elements across the thickness considering this exact scenario.
      • Ramp up the load with proper increments. Considering the auto time-stepping option and defining timesteps or substeps accordingly to slowly ramp up the load will help the solution to converge.
      • Go for a linear material behavior for a particular loading portion

      Please check if the following post serves helpful - Element has excessive distortion. ( 

      Hope this helps!



      For more exciting courses and certifications, hit this link: Ansys Innovation Courses | Ansys Innovation Space

      If you are not able to open the links, refer to this forum discussion: How to access the ANSYS Online Help

      Guidelines for Posting on Ansys Learning Forum


Viewing 1 reply thread
  • You must be logged in to reply to this topic.