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CMS analysis in ANSYS Workbench 14.0

  1. Jun 18, 2012 #1
    Hi,

    I have a question regarding CMS analysis in ANSYS Workbench 14.0. I really hope that one of you experts out there can/is willing to help me.

    I've tried normal substructuring (Guyan) and obtained the expected results in a modal analysis. Now, since the Guyan reduction yields significant deviations for most eigenmodes, I would like to try CMS. I've chosen a simple system, namely a 3-element cantilever beam:

    |------o------o------o

    I want to find the eigenmodes for this full model system by condensating the midmost element to a superelement, i.e. obtaining:

    |------o SE o------o

    The two midnodes are defined as remote points.
    I have done the procedure in analogy to the Guyan reduction, i.e. first I have generated the superelement. This is done in a separate analysis on the basis of only the midmost element (the one transformed to superelement):

    o------o

    The two nodes are defined as remote points in the model. The generation command is (partially copied from a tutorial):

    /FILNAME, BEAM2
    /SOLU
    /COM
    NSEL, S, NODE, 1001 , N1
    NSEL, A, NODE, 1002 , N2
    M, ALL, ALL
    ALLSEL, ALL
    CMSEL, ALL
    NUM_MODES = 100
    /SOLU
    ANTYPE, SUBSTR
    SEOPT, BEAM2, 2
    CMSOPT, FIX, NUM_MODES, 0, 100000
    ESLN, S
    SOLVE
    FINISH
    SAVE

    Strangely, this doesn't result in an error as it did when using Guyan reduction (another command of course). But it generates a .sub file I've tried to use in an analysis of the reduced model (the one with the superelement in the middle). The usage command is:

    /PREP7
    ET,500,MATRIX50
    TYPE,500
    MAT,1
    SE,BEAM2
    FINISH
    /SOLU

    This command is taken from my Guyan reduction procedure. The analysis goes through, but I obtain completely wrong eigenfrequencies.
    Can anyone tell me where my error(s) is/are? It would be highly appreciated.

    Kind regards,
    Martin Ulriksen
    Student in structural engineering, Aalborg University, Esbjerg, Denmark.
     
  2. jcsd
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