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# Nastran Rotordynamics SOL 108 Damping Problem

Gears Phenom

Hello!

I modell rotordynamics response of shaft due to unbalance excitation, using SOL108. And when I change structural damping coefficient PARAM,G,.04 my results remain the same. I compared results with SOL111 and see that response from direct solver is corespond to zero structural damping.

What is wrong with my model/settings and how can I include structural damping in rotordyn response analysis in SOL108?

2 REPLIES 2

# Re: Nastran Rotordynamics SOL 108 Damping Problem

Siemens Phenom

Did you specify PARAM, W3?

See section 2.1.4 of the Rotor Dynamics User’s Guide

In rotor dynamic analysis the complex stiffness matrix is not used. Thus, for modal solution sequences, the imaginary part of the stiffness matrix must be converted to viscous damping. This conversion is done by dividing by the eigenfrequency.

For direct solution sequences the imaginary part of the stiffness matrix is converted by dividing by:

• Parameter W3 for damping defined by PARAM G specification.
• Parameter W4 for damping defined by GE specification.

# Re: Nastran Rotordynamics SOL 108 Damping Problem

Gears Phenom

With PARAM, W3 all working correct. Thank you!

Also i got another question: when i use freq dependent properties of CBUSH as bearing elements I get fatal message 2170 (PARTN2) add others, when my function is not horizontal i. e. i have function of two points and analysis is crashes when y coordinates of this points are not equal. If i use CBEAR elements - calculation run without problems.