Fluid cavity with symmetry plane

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  • jayart
    Junior Member
    • Sep 2019
    • 6

    Fluid cavity with symmetry plane

    Dear all,

    I read in a previous question in the forum that there is a way to constraint a fluid entrapped in a cavity, but is it possible to perform an analysis with this volume constraint to a simplified model (modeled only a quarter of the tissue with symmetry boundary condition)?
    thanks for your help

    Regards,

    Jeremy
  • maas
    Lead Code Developer
    • Nov 2007
    • 3400

    #2
    Hi Jeremy,

    I think that should work as long as the symmetry planes are the coordinate planes that intersect at the origin. I suggest to try it out on a simple model and see if it works. Keep in mind that to get the same results for the quarter model compared to a full model, you will probably have to multiply the penalty by four. Let us know what you find.

    Cheers,

    Steve
    Department of Bioengineering, University of Utah
    Scientific Computing and Imaging institute, University of Utah

    Comment

    • jayart
      Junior Member
      • Sep 2019
      • 6

      #3
      Hi Steve,

      Thanks a lot, this resolved the problem. However, there is a small difference in the displacements of roughly few percent. In my case acceptable.

      cheers,

      Jeremy

      Comment

      • jayart
        Junior Member
        • Sep 2019
        • 6

        #4
        Follow up question

        Hi Steve,

        I wonder how the volume constraint algorithm works in the context of pre-stretching. So I am pre-streching my tissue, basically I pressurize my fluid cavity with a surface_load and thus, the volume of the cavity increases. In the following steps I add the volume constraint to keep the newly obtain cavity volume and add some loads. Now my question is do I have to remove the pressure which I used to pre-stretch my tissue, meaning the volume constraint alone is sufficient to maintain my pre-stretch pressure? Or must/can I keep the pre-stretch pressure after initializing the pre-stretch? If I can keep my prestretch pressure, does it help to converge your algorithm faster? If I recall correctly, you use a augmented Lagrangian iteration, right?

        thanks for your help,

        Jeremy

        Comment

        • maas
          Lead Code Developer
          • Nov 2007
          • 3400

          #5
          Hi Jeremy,

          My suspicion is that when you remove the pressure load when adding the volume constraint, the first time step will have difficulty to converge. In principle, the volume constraint should recover the applied pressure, but since it initially assumes a zero pressure, the cavity is going to collapse, which could lead to convergence trouble or even negative jacobians. I suggest to give it a try and if it doesn't work, I can look into adding an initial pressure or something to counteract this issue. Let me know what you find.

          Cheers,

          Steve
          Department of Bioengineering, University of Utah
          Scientific Computing and Imaging institute, University of Utah

          Comment

          • jayart
            Junior Member
            • Sep 2019
            • 6

            #6
            Hi Steve,

            Yes it has trouble to converge when I remove the prestretch pressure. If I keep the pressure it works well.

            thank you for your help.

            cheers,

            Jeremy

            Comment

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