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Complex number of eigenvalue frequency?

Posted 7 mag 2021, 04:29 CEST Structural Mechanics Version 5.6 1 Reply

Dengfei Yang
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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 7 mag 2021, 18:45 CEST
Dave Greve
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Posted: 4 years ago 7 mag 2021, 18:45 CEST
Updated: 4 years ago 7 mag 2021, 18:45 CEST

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.

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