{"id":359739,"date":"2024-03-31T17:37:12","date_gmt":"2024-03-31T17:37:12","guid":{"rendered":"\/forum\/forums\/topic\/negative-frequency-during-eigenvalue-analysis\/"},"modified":"2024-04-03T16:22:27","modified_gmt":"2024-04-03T16:22:27","slug":"negative-frequency-during-eigenvalue-analysis","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/negative-frequency-during-eigenvalue-analysis\/","title":{"rendered":"Negative frequencies during eigenvalue analysis"},"content":{"rendered":"

Hello!<\/span><\/p>\n

I generated a model which is a cylinder resting on a foundation, and I extracted the natural frequencies from it to check its accuracy. The cylinder and the foundation pad have the `*CONTACT_AUTOMATIC_SURFACE_TO_SURFACE` defined between them. In the keyword, I just selected the master and slave surfaces and changed the FS and FD parameters.<\/span><\/p>\n

However, after checking the eigout file, I found that the first couple of rigid body modes are showing negative eigenvalues. I checked with different meshing of the foundation pad and the cylinder, and sometimes I can see the negative eigenvalues, and sometimes not.<\/span><\/p>\n

I want to understand why this is happening and if it indicates that I am doing something wrong in my model. Also, apart from doing a convergence study, how to understand if the extracted frequencies are nearly accurate?<\/span><\/p>\n

Thank you in advance for your time and response.<\/span><\/p>\n

Regards,Tonmoy.<\/span><\/p>\n","protected":false},"template":"","class_list":["post-359739","topic","type-topic","status-closed","hentry","topic-tag-contact-behavior-1","topic-tag-eigenfrequency-1","topic-tag-eigenvalue","topic-tag-implicit","topic-tag-ls-dyna"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t