General Mechanical

General Mechanical

Contact issues leading to solver pivot error

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    • ianyylai
      Subscriber

      Hi all, I am running into troubles of contact pairs. The model i am having is as shown below - rectangular parts should be stuck inside tubes when loading applies horizonatlly. However, when simulation is run with the model legs fixed to the ground, solver pivot error occurs - indicating I am having underconstraint model.

      WHen I run with turning on Weak Springs - the following occurs, showing that the vertical tubes failed to block the rectangular parts from moving away. I tried Rough and Frictional, even Frictionless and No Seperation and all of them do the same thing. The only contact that works is Bonded - which I do not want since it gives inaccurate stress results. The surface between those two were slighly apart initially - I learnt that it creates DOF issues from another post. But it is what the model is like so it seems I can't change it without altering the design.

      Does anyone have suggestions on how to make the contacts work without changing the dimensions??

    • Akshay Maniyar
      Ansys Employee

      Hi ianyylai,

      Have you checked the initial contact status for the frictional contact? If it is 'far open' then you can try to increse the pinball radius so that contact is detected and status is changed to 'nearly open' state. Also, can you share some images of contact settings and boundary conditions so that I can have better idea about your model.

      Thanks,

      Akshay Maniyar

       

    • HuiLiu
      Ansys Employee

      1, Is your model well constrained (boundary conditions), ie. no rigid body motion? How do you load your model, by force or displacement? 

      2, Consider "adjust to touch" to ignore the initial gap is that's acceptable.

      3, Also check and see if your substep size is small enough to calculate the correct contact status. 

    • ianyylai
      Subscriber

      Hi, thanks for the reply.

      I believe the model is well constrained, fixed at the bottom and applied a load up there in the middle of the beam. However, I am not sure how to check the initial contact status. HOw do we check it? And how do we "adjust to touch"? The gap between surfaces are just 2mm at most, to facilitate assembly in real life.

      Some of the current faces that are connected are as follow. Hope it helps. I was forced to change the last pic from Frictional to Bonded due to the problem mentioned. That was the main purpose of this post. Thanks a lot for the help!!

       

    • Akshay Maniyar
      Ansys Employee

      Hi ianyylai,

      You can change the interface treatment as 'Adjust to touch' from contact details.

      Also, you can check the initial status of contact by inserting contact tool as shown in image below.

      As Hui mentioned, 'Adjust to touch' will help you to close the contact status and might help in resolving the issue.

      Thanks,

      Akshay Maniyar

    • ianyylai
      Subscriber

      Hi, Akshay. Thanks for the advice. My current initial contact information looks like this - no red and yellow. So, basically I don't want any red, right? Don't want the contacts to be far apart or opened? And then, what "Adjust to touch" does is that it closes the physical gap between surfaces without actually changing the dimensions?

    • ianyylai
      Subscriber

      In addition, I found that when the setting of Frictional is changed to "Adjust to touch" from the default "Add Offset, No Ramping", both the Equivalent Stress and Total Deformation dropped. (Yes I can now run the simulation with frictional somehow, guess its because I strengthened connections in other places. Anyway.)

      Can you tell me under what conditions "Adjust to touch" should be turned on or off? Should it be On when the default "Add Offset, No Ramping" already runs simulations without error?

      Thanks!

    • Akshay Maniyar
      Ansys Employee

      Hi ianyylai,

      It is great that you were able to solve the model. Can you check below Ansys How to video? It explains how you should use initial contact status and then make necessary changes in interference treatment.

      Also, you can check below Ansys help link for more details on interference treatment.

      https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v222/en/wb_sim/ds_geometric_correction.html%23ds_advanced_interface_treatment

      Thank you,

      Akshay Maniyar

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