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Problem with mass matrix – APDL

- November 27, 2023 at 5:07 pm
  
  Diona Çejku
  Subscriber
  
  Hello everyone,
  I've been working on extracting mass matrices from Ansys APDL using the following code for analysis:
  ANTYPE,MODAL
  MODOP,LANB,10
  /STATUS,SOLU
  /SOLU
  OUTPR,BASIC,1
  /OUT,SCRATCH
  SOLVE
  
  /POST1
  SET,FIRST
  
  *dmat, m0, D, import, full, file.full, mass
  *print, m0, matm.txt ! Exports Mass to Text File
  *export, m0, mmf, matmMMF.txt ! Exports Mass as MMF
  
  /OUT
  FINISH
  
  However, I've encountered an issue where the extracted matrix is not diagonal. I've double-checked my code and inputs, but I'm still unable to identify the source of the problem. I would highly appreciate if anyone could help to resolve this issue.
  
  Thanks :)
- November 28, 2023 at 3:13 pm
  
  mrife
  Ansys Employee
  
  Hi Diona
  Why would the mass matrix be diagonal? My guess is that you are assuming a lumped mass formulation...if so please see the help on the Mechanical APDL command LUMPM. You may also want to read the MAPDL Theory Guide, chapter 12.5 (Element Reference -> Lumped Matrices) as there are some caveats to using this.
  Mike

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