STRUCTURAL DAMPING VS MODAL DAMPING

Nancy Jewel Mcdonie

Hello all experts, 

I want to know what is the difference between structural damping (direct transient frequency response) and modal damping (modal transient frequency response); why in direct transient frequency response we need to convert structural damping to equivalent viscous damping? 

loistf

I can tell about the modal vs structural. When you are in direct transient , the damping matrix can be non-diagonal, anything you want. However, in modal analysis you need to stick to a diagonal matrix, otherwise you would lose the efficiency of the method.

Rajashri_Saha

Hi Nancy,

Transient Analysis does not allow the use of complex co-efficient. That is the reason structural damping is included by adding equivalent viscous damping.

In Optistruct this can be done by adding the cards PARAM,W3 and PARAM,W4.

Thanks

Rajashri