General Mechanical

General Mechanical

APDL: How to get access to nodal acceleration in mode-superposition transient analysis?

    • Clemens_C
      Subscriber

      I did a mode-superposition transient analysis with a cantilever. In /post26 I can get the displacement of nodes (with NSOL,,,U, Y), which is nice.

      But I also need the nodal acceleration. Unfortunately I don't have access to that data. I don't understand why, because I set (VAout=YES) in TRNOPT. I tried a few options with the OUTRES command:

      OUTRES,ALL,ALL or OUTRES,NSOL,ALL or OUTRES,A,ALL

      But nothing works when I try the command NSOL,,,ACC,Y. :(

    • Erik Kostson
      Ansys Employee
      Hi
      So this should work.

      Try to add this after you are done with /prep7
      ! *** SOLUTION CONTROLS FOR MODAL ANALYSIS ***
      ! --------------------------------------------
      /SOLUTION
      ANTYPE,MODAL
      MODOPT,,5,,,, MXPAND,ALL
      SOLVE
      FINISH
      ! *** SOLUTION CONTROLS FOR MSUP TRANSIENT ANALYSIS ***
      ! ----------------------------------------------------
      /SOLUTION
      ANTYPE,TRANS
      TROPT,MSUP
      TIME,1 ! change the end time as needed
      NSUB,200 ! change this as needed
      DMPSTR,0.01
      OUTRES,ERASE
      OUTRES,ALL,ALL
      OUTRES,NSOL,ALL
      SOLVE
      ! *** TIME HISTORY POST PROCESSOR ***
      ! -----------------------------------
      /POST26
      NSOL,3,3,ACC,Y,AY_2,
      XVAR,1
      PLVAR,3
      This works on my end.

      All the best

      Erik
    • Clemens_C
      Subscriber
      Hi Erik thank you for your fast response!
      I'm sorry but that didn't solve my problem. :((
      When I try your code, it says "The label ACC cannot be used, as the data is not available.Pleasecheck the OUTRES command.The NSOL command is ignored."

      Why do I get that message? I used
      "OUTRES,ERASE
      OUTRES,ALL,ALL
      OUTRES,NSOL,ALL"
      right before solving the loadsteps.

      For the Modal Analysis I used:
      "/SOLU
      ANTYPE,MODALMODOPT,LANB,number_modes,,,,off
      MXPAND,number_modes,,,YES,,YES" -> is that ok?

      I have 2 loadsteps and solve them with LSSOLVE -> It worked perfectly in the Full Transient Analysis...
      I would be so grateful if you could help me again!
    • Erik Kostson
      Ansys Employee
      Hi

      Can you try without lssolve so use only one step and just use the code above with solve only.

      thank you

      Erik
    • Clemens_C
      Subscriber
      Hi sorry, it didn't work with only 1 loadstep as well.
      No I have 1 more problem: the time variable is equal to the computed frequencies from the modal analysis. -> only 10 values for 10 frequencies. :(
    • Erik Kostson
      Ansys Employee
      Not sure what is happening here . I would try to do a simple example of msup on beam and try it on something simple and add the first commands in my post because that worked fine.
      Also read through the apdl manual:
      5.4.4. Expand the Mode-Superposition Solution

      See if that helps
      -
      all the best

      Erik
    • Clemens_C
      Subscriber
      Thank you for your help but it still doesn't work. I won't do MSUP again.
    • Erik Kostson
      Ansys Employee
      Hi

      I would look on the help manual
      5.4 Mode-Superposition Solution
      See if there are any points there.

      I normally do this (MSUP) in Workbench where post26 is not used.
      and it works fine.

      Sometimes it can be tricky to get these results it seems in APDL.

      All the best

      Erik

    • maimang
      Subscriber
      By default in a mode-superposition transient analysis, reaction force and other force output contains only static contributions. If you want to postprocess the velocities, accelerations, and derived results (Lab = TOTAL, DAMP, or INERT on the FORCE command), set VAout = YES to activate velocity and acceleration output.
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