Node has no stiffness. Stiffness matrix is singular

Aaron McCrary
Aaron McCrary Altair Community Member
edited November 2020 in Community Q&A

I created a simple component mode synthesis model with a CBN method, but the stiffness matrix that I exported in a *.pch file has a determinant of zero. This is causing my model to be ill-conditioned.

I tried finding where the cause of this problem was, and I came across these warnings. I'm note sure what they mean, but they led me to set AUTOSPC to No.

image

When I did this however, I ran into similar problems where I got this message that the boundary nodes have no stiffness.

image

How can I resolve this problem, so the rotational degrees of freedom have a nonzero stiffness, so these messages go away, or what other ways are there to fix my stiffness matrix, so it is not singular? The element property type I am using is PSOLID.

Thank you

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Answers

  • tinh
    tinh Altair Community Member
    edited November 2020
    Hi Please keep AUTOSPC as YES But remove SPCD dofs 4, 5, 6 (nodes of psolid have no these dofs)
  • Aaron McCrary
    Aaron McCrary Altair Community Member
    edited November 2020
    tinh said:

    Hi Please keep AUTOSPC as YES But remove SPCD dofs 4, 5, 6 (nodes of psolid have no these dofs)

    Keeping AUTOSPC as YES did not fix my problem of having a stiffness matrix with a determinant of zero. The load types I have are ASET, and I need dofs 4, 5, 6 active in my model for post processing. Is there a different card image I can use instead of PSOLID that will enable these dofs?

    This is an image of the model I have created.

    image

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