Learning Forum

[Hamid]

 

I am working on the effect of an unbalance mass on a rotating shaft. For which I am performing Modal analysis followed by Harmonic Analysis. I have defined suitable supports as required by my model (cylindrical supports to model bearings). I have two issues linked together basically;

1)      In modal analysis, I have also defined a rotational velocity which is 3000 RPM. The moment I define rotational velocity, it asks me to turn Coriolis Effect ‘ON’. By turning it ‘ON, I have to enable damping in the system otherwise it doesn’t solve (screenshots attached)

 

2)      In Harmonic Analysis, I applied a force to create unbalance (screenshot attached). Rest of the settings are also shown (screenshot #4). When I start run, It gives me an error (MSUP harmonic doesn’t support full damped…….screenshot # 5 attached). I cannot turn off the damping, otherwise modal solution won’t solve.

I am unable to understand where I’m wrong. Any help in this matter will be highly appreciated.

 

Regards.

 

[Aniket]

Ansys employees are not allowed to download files from the forum, kindly post them as inline images.

[April Wang]

Hi Hamid,

 

In WB, rotordynamics cannot be solved by MSUP. 

You can solve the problem by full harmonic analysis. In harmonic analysis, you can directly add rotational force.

 

Hope this answers your question.

 

Regards,

April

[Deepesh]

If I give Rotational velocity in Modal as 10000 RPM, will it be considering it as a centrifugal force? or is there any other way to apply centrifugal force in Modal analysis?

 

Thanks

[Deepesh]

Can anyone help me with this query?

Thanks

[peteroznewman]

A Modal analysis does not allow any force or load of any kind to be used. A Modal analysis computes the natural frequencies and mode shapes of the structure. Only supports and displacements set to 0 are allowed.

[Deepesh]

But inserting rotational velocities, applying various loads (Force, pressure etc.) can be seen available in Modal analysis. Example of applying rotational velocities to a long shaft in Modal. it gives different mode shapes according to the velocity applied, right? isn't this a force?

[peteroznewman]

You are wrong about loads being available in Modal analysis.  Look at the two images below.

When Static Structural is selected, Loads are available to be applied.

When Modal is selected, Loads are grayed out.

Under the Inertial category, Rotational Velocity is the only "load" permitted under Modal for a Rotodynamic Modal analysis. That is because rotational velocity is needed to compute the gyroscopic stiffness that affects the natural frequency.