Menu

Discussion Forum

New Discussion
Filter

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

Complex number of eigenvalue frequency?

Posted May 6, 2021, 10:29 p.m. EDT Structural Mechanics Version 5.6 1 Reply

Dengfei Yang
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

I have a question about eigenvalue frequency:

My material has no damping properties ，Why do my eigenvalue frequency calculations result in complex numbers. （The complex number represents the existence of damping）

1 Reply Last Post May 7, 2021, 12:45 p.m. EDT
Dave Greve Certified Consultant
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 3 years ago May 7, 2021, 12:45 p.m. EDT
Updated: 3 years ago May 7, 2021, 12:45 p.m. EDT

There are two ways to get complex eigenvalues with no explicit energy loss:

  1. Rigid body motion. These are the lowest eigenvalues. The physical picture is that it costs energy to put a body in motion. These can be removed by using a Rigid Motion Suppression node.
  2. Small imaginary part (compared to a much larger real part). I attribute these to numerical artifacts.
There are two ways to get complex eigenvalues with no explicit energy loss: 1. Rigid body motion. These are the lowest eigenvalues. The physical picture is that it costs energy to put a body in motion. These can be removed by using a Rigid Motion Suppression node. 2. Small imaginary part (compared to a much larger real part). I attribute these to numerical artifacts.

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content