General Mechanical

General Mechanical

Modal analysis – Fluid structure interaction – Skipping frequencies – ANSYS APDL

    • pierluigi.olmati

      Hi All,

      I d like asking suggestion about the following matter. I am performing a unsymmetric modal analysis of a tank filled with fluid. Modal shapes of the fluid are convective (e.g. 0.1Hz~1Hz) and impulsive (e.g. 2Hz~20Hz). The problem is that the convective modes are a lot (1000 modes?) therefore I cannot calculate convective and impulsive modal shapes of the fluid (and structure) in one simulation because I would end up having thousands of modal shapes.

      --> There is any way to skip and/or select a range of frequencies in the unsymmetric modal analysis?
      Currently I am using the following commands:

      MODOPT, UNSYM, 20, 0.01, 1,,, BOTH (for the convective modal shapes)
      MODOPT, UNSYM, 200, 2, 20,,, BOTH (for the impulsive modal shapes)

      --> There is a way to calculates modal shapes in two frequencies range in the same simulations? (e.g. 0.1Hz~1Hz and e.g. 2Hz~20Hz)

      Thank you!

    • Ashish Khemka
      Ansys Employee



      You can select one frequency range in one analysis.



      Ashish Khemka

    • pierluigi.olmati



      Hi Dr. Khemka,

      Thank you really much for your answer. Maybe you are able to help me with this related topic as well.

      I use *[GET, EF_X, MODE, counter, EFFM, , DIREC, X] to get EFFM for each modal shape. However, some of them give me EFFM=0. Is it normal for an [MODOPT, UNSYM, 20, 0.01, 1,,, BOTH] analysis? Never happen to me for any traditional (symmetric) modal analysis. Also, if I do not use [BOTH] I get a sum of EFFM that is much larger than the total mass of the model.

      Thank you, Pierluigi




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