# COSTANT ANGULAR VELOCITY IN HARMONIC ANALYSIS

Hi everyone!

I would like to perform a harmonic analysis on a MEMS gyroscope structure to obtain the frequency response function. In brief, the structure is excited in the x-direction by a harmonic force and when there is an angular rate around the z-direction, the structure starts to move along the y-direction. I attach an image of my very simple structure.

I have performed an initial harmonic analysis with no angular velocity and I had no problem. My results match very well the analytical ones.

The problem starts when I try to apply a constant angular velocity on the structure and perform the harmonic analysis. I summarize the steps which I followed (I am using APDL at the moment but I can use also Workbench):

1) I built the model (the central rectangular plate is meshed with shell181 elements, while the beams suspension system is meshed with beam188 elements);

2) I activate the Coriolis effect using a stationary reference frame;

3) I apply on the central plate the constant angular velocity around the z-axis, using the CMOMEGA command (CMOMEGA, NAME-OF-THE-CENTRAL-PLATE-SELECTION,,,VALUE-OF-VELOCITY);

4) I perform a full harmonic analysis, applying the harmonic force along the x-direction.

My results are completely wrong and they are the same as the case of no velocity applied. I doubt this is related to having applied a constant angular rate.

Any advice?

Thanks for your time.

Best regards,

Francesca

## Answers

Hi @Francesca_Pistorio ,

Please refer to the following post-

Regards,

Ashish Khemka

Hi Francesca,

Can you please comment why this did not help?

Regards,

Ashish Khemka

Dear,

@Ashish Khemka, thank you for your answer. The problem is that the angular velocity is applied around the z-axis. The ENTIRE structure should rotate around the z-axis. Beam elements are instead in-plane elements and their axes are around x or y. I don't know if it could be the reason of my error. The other doubt is this: can I apply a costant angular velocity in a harmonic analysis?

Thank you for the help.

Best regards,

Francesca Pistorio