Symmetry with RBE3 element

mansin
mansin Altair Community Member
edited October 2020 in Community Q&A

Hi,

I have a problem with planar symmetry on a tube. One end of this tube is full constrained, the distributed force on the other end is applied by the concentrate force (or torque) on dependent node of RBE3 element. To reduce the model, a quarter of this tube is constructed. For the nodes on symmetry plane (X-plane and Y-plane) except the dependent node of RBE3 element, the (156 and 246)DOFs of these nodes are constrained. The model is shown as follow: (Fz=1000, Tz=2000)

 image.png.937e1b55a51655ba6beca8a46d02087f.pngimage.png.a26c308b3f79a1b925972bcefaadb3a7.pngimage.png.33eb4293c52b5cb10303485d739308ae.png

However, the results of the two loads are not reasonable and right.

image.png.2be12d4820ee5d202f5defa919fb69d4.pngimage.png.48fc7ff4c449f17cdcfa7173f7d37437.png

I think the reason is the symmetry constraint of RBE3 element is not setup correctly. How to fix it?

I attach the results of the whole model (Radius=20, length=200, Thickness=2, Fz=4000, Tz=8000):

image.png.d4ad1de09ac229b4e78dd24bb89212e4.pngimage.png.c8b844599d0e47de697cf54a31247a43.png

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Answers

  • Rahul Rajan_21763
    Rahul Rajan_21763 New Altair Community Member
    edited January 2019

    Can you please share the .fem files of symmetry and full part to take a quick look.

  • mansin
    mansin Altair Community Member
    edited January 2019

    Hi, Rahul R

    The two .fem files are uploaded here:

         

    Unable to find an attachment - read this blog

  • tinh
    tinh Altair Community Member
    edited January 2019

    It is a cyclic but not a symetric problem so cannot use symetric constraint.

  • mansin
    mansin Altair Community Member
    edited January 2019

    Hi, tinh

    How to reduce the whole model and setup cyclic constraints on the quarter model?

  • tinh
    tinh Altair Community Member
    edited January 2019

    In force case, rbe3 must have 'calculated' dependent node (not tube center). This is planar symmetry.

     

    In torque case, maybe PERBC will help. This is cyclic symmetry.

  • mansin
    mansin Altair Community Member
    edited January 2019

    In force case, I found that, even though using calculated dependent node with RBE3 element, the concentrated force cannot be distributed equally to all nodes of the truncated model. However, when I use the distributed nodal force directly and planar symmetry constraints, the results are equivalent to those of the whole model.

    In torque case, I tried to use PERBC bulk data to simulate the cyclic symmetry, but I don't get any satisfied results. Doesn't the RBE3 element located in symmetry plane or center suitable for  symmetry constraint s?

    Unable to find an attachment - read this blog

  • tinh
    tinh Altair Community Member
    edited January 2019

     

    I am not sure about PERBC, it's a new feature. Actually I don't trust new features, just look good.

  • tinh
    tinh Altair Community Member
    edited January 2019

    Is this your real problem? Only a torqued tube need FEA and dof reduction?

  • Rahul Rajan_21763
    Rahul Rajan_21763 New Altair Community Member
    edited October 2020
    https://community.altair.com/community?id=community_question&sys_id=bb96847a1b2bd0908017dc61ec4bcb72

    How about trial with MPC?

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