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## Autodesk Robot Structural Analysis

Valued Mentor
Posts: 323
Registered: ‎11-01-2011

# Time History Analysis for a rotating motor

966 Views, 3 Replies
11-23-2011 11:40 PM

I have a motor attached to a steel grating sitting on steel columns and beams. As the motor rotates it causes the entire system to vibrate. I am trying to model the centrifugal force using a time history analysis. But the problem is that the settings only alow for one direction. Is there a way to create several time history functions in different directions, or maybe just simply to create 4 functions (+ve x, -ve x, +ve y, -ve y) and then combine them together. I would really appreciate the assistance.

Ali Al-Hammoud
Structural Design Engineer
MZ & Partners Engineering Consultancy
Product Support
Posts: 343
Registered: ‎06-23-2008

# Re: Time History Analysis for a rotating motor

11-24-2011 01:44 AM in reply to: AJA14

Hi,

yes, it is possible to combine several time functions related with loads in different directions.

Rotating load resulting from centrifugal forces about for instance X axis can be obtained combining Y force changing according to sine function and Z force changing according to cosine. Of course both trigonometric functions should use the same frequency.

Attached the compressed file containg a simple example and its description in text file.

Such approach corresponds to steady-state conditions.

In case of analysing starting the motor or braking it (transient conditions) the forcing functions would be more sophisticated but it can be done too.

Best regards,

Pawel Pulak
Support Specialist
Product Support
Autodesk, Inc.

Contributor
Posts: 22
Registered: ‎05-19-2011

# Re: Time History Analysis for a rotating motor

10-04-2012 12:09 AM in reply to: pp2008

Hi Pawel,...

.....I'm working lately on a rotor engine's foundation and found your sample file very useful. As the compressed file size of my model exceeds the 1.5 MB I cannot upload it but I'll try to explain my "problem" on the sample you posted some time ago!

When looking at your "engine" I can see two time history functions defining its motion and related to its own static load (force Y and force Z)!

What I want to know is how to find maximum displacement for node 17 (DL1 + time history)? I know that I can make a static load of  the time history case in whatever time step I want and than summon it with DL1 case,....but is there some other way for doing this?

Regards!

Valued Mentor
Posts: 475
Registered: ‎09-07-2011

# Re: Time History Analysis for a rotating motor

10-04-2012 12:15 AM in reply to: mark.martin.se

Check on the box to include results for starting case in TA definition

Results

Go to displacements table, filter for node 17.  The change tab to "global extreme".

It will give you maximum deflection and the associated time step.