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[adn74]

Hello everyone, 

I use the student version of ansys and I have a problem with the modal analysis from the workbench. I made 2 models of the same structure. the first one by using APDL and the second one with spaceclaim (workbench). When I compare the frequencies, I don't find the same values. However I did a static analysis and I find the same displacements. The structure is composed of walls, columns and beams. On the modal analysis in apdl, the different frequencies make the whole structure move while on the worbench only the columns move for all modes (really surprising). The rest of the structure is fixed while I only put a boundary condition at the slab. It is as if the structure is very very stiff and only the columns are flexible but it's not. So i need help. you will see the difference between the two models apdl/worckbench on the pdf file. I added loads by using density for the modal analysis because you can't add a pressure in modal analysis.

apdl_worckbench_results.pdf

[Saumadeep]

Unfortunately, Ansys employees are not allowed to download the attached files. So, can you please share screenshots of the Analysis setup in APDL as well as Mechanical?
Also, in meantime you can look through this free course on How to perform Modal Analysis in Ansys Mechanical (Topics in Modal Analysis - ANSYS Innovation Courses), to make sure that the Modal analysis was setup properly.
Also, refer to this Ansys Help link to understand how to setup Modal analysis in APDL - Chapter 3: Modal Analysis (ansys.com)

Regards, Saumadeep
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[bhagwantP]

Hello adn74, I suspect whether boundary conditions have been defined properly or not in APDL. As per your comment in one case (APDL) whole structure is moving while for other only columns. Wil you please verify that? Thanks