General Mechanical

General Mechanical

Only partial match between MSUP and FUll Harmonic analysis

    • julius.langenhorst
      Subscriber

      Hello,

      I'm trying to find the frequency response of a structure that is subjected to accelerations in x-, y-, and z-direction, respectively. Using Full Harmonic gives satisfying results but computational times are too long which is why I want to switch to MSUP. I know from solution #855002 on the Customer Portal that the required required must extend past the range of interest. I'm interested in the first 6 modes and work with the first 200 modes. The only matching result from MSUP is in z-direction. The first image below is from the Full Harmonic and the second from the MSUP analysis, both show displacements.

      Below are parts of the APDL code I'm using:

      antype,MODAL
      modopt,LANB,200,0,0,,OFF
      mxpand,200,,,YES,,YES
      outres,ERASE
      outres,ALL,ALL
      outpr,ERASE
      outpr,ALL,NONE
      resvec,ON
      allsel
      modcont,ON
      thexpand,OFF
      acel,89,0,0
      allsel
      save
      solve
      lsclear,INER
      acel,0,89,0
      allsel
      save
      solve
      lsclear,INER
      acel,0,0,89
      allsel
      save
      solve
      lsclear,INER
      finish

      The part below is repeated in the same way for the other two directions.

      antype,HARMIC
      hropt,MSUP,,,YES
      hrout,OFF,OFF,ON
      harfrq,NINT(first eigenfrequency),NINT(sixth eigenfrequency),,,%freq_array%
      nsubst,5000
      dmprat,0.0001
      kbc,1
      resvec,ON
      lvscale,1,1
      lvscale,0,2
      lvscale,0,3
      outres,ERASE
      outres,ALL,ALL
      outpr,ERASE
      outpr,ALL,NONE
      solve
      save
      finish
      /SOLU
      allsel
      expass,ON
      numexp,ALL
      solve
      finish

      Post-processing is done in /post26. I'm getting the displacement using the NSOL command.

      I would like to know why there's no response in x- and y- direction when using MSUP. How must the code be changed to solve this problem?

      Thank you in advance!

    • Chandra Sekaran
      Ansys Employee

      In the modal analysis you create 3 load vectors. But looks like you have only one load vector created in the Z direction. Can you rerun the modesup harmonic with lvscale applied to only load vector 3. I wonder if load vector 3 even exists. 

    • julius.langenhorst
      Subscriber

      Thank you for your answer!

      The picture in my original post should be the result of load vector 3. The way I structured my analysis is as follows (I probably didn't made that clear enough before):

      • Modal analysis and creation of three laod vectors
      • First MSUP analysis with subsequent post-processing using first load vector:
      lvscale,1,1
      lvscale,0,2
      lvscale,0,3
      • Second MSUP analysis with subsequent post-processing using second load vector:
      lvscale,0,1
      lvscale,1,2
      lvscale,0,3
      • Third MSUP analysis with subsequent post-processing using third load vector:
      lvscale,0,1
      lvscale,0,2
      lvscale,1,3

      Each MSUP analysis is started by issuing a new /solu command and closed with finish. This way all three load vectors should be used except, of course, they weren't created in the first place. But I used this evaluation scheme on other models and there was a response in x- and y-direction (both for MSUP and Full Harmonic).

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