APDL psd analysis and model frequencies used

  • Last Post 19 December 2018
  • Topic Is Solved
mohamedbenamor posted this 07 December 2018



i was trying to run an APDL PSD analysis but with a material dependent damping which means i defined the damping in the modal analysis using the QR damped method. to consider the material damping on MODOPT the CPXmod must be =yes. in this case the solutions are complex where the real part is the stability of the system and the imaginary part is the natural frequency (figure1). however when running the PSD analysis it always considers the real part of the modal solution which is the stability not the natural frequency which leads to wrong results, to confirm that i desactivated the CPXmod option and compared the two (figure 2&3).

so my question is, is it possible to force the PSD analyses to use the imaginary part of the modal solution ? knowing that i ran the same model under workbench and it runs perfectly.
thank you




Order By: Standard | Newest | Votes
mrife posted this 12 December 2018

Hi Mohamed

Check the Help documentation on the MODOPT command again.  The Cpxmod field needs to be set to 'Off' or 'Real' (without the quotes) if the modal results are to be used in a later mode superposition analysis.

WB Mechanical is a pre and post processor.  It utilizes Mechanical APDL for the solution.  So if you ran the same model in WB Mechanical then right-click the Solution object and select the open folder containing solution files option.  Then open the ds.dat with a text editor and review the solution commands.  Maybe you can take these and implement in your MAPDL model.



  • Liked by
  • SandeepMedikonda
  • mohamedbenamor
mohamedbenamor posted this 19 December 2018

thank you Mike,

i have already tried the CPXmod settings but without any effect but the ds.dat file seems more promissing to solve my problem.