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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