Plotting the Frequency Response function in abaqus

[spk86]

Hello everyone,
I'm a new guy to this forum.
I'm really not sure if my particular problem has been discussed earlier in any of the threads but as I seriously didn't get any idea from threads I searched I'm just posting my problem in here...kindly help me if someone knows how to do it

Problem -
I have to do the simulation of a "stator of a permanent magnet synchronous machine" in Abaqus.
We have the experimental data with the modes and corresponding natural frequencies.
While doing the simulation, considering the stator as a homogenous isotropic material-steel, I'm getting results which do correlate to that of the experiments (for mode shapes and freq with an acceptable +/- error) but I'm getting additional mode shapes. I did some research on the net as to why I'm getting these "additional" eigenmodes and freq and I found that we have to treat the stator as a "transversely isotropic material" due to its peculiar method of construction.

Due to this peculiar construction (which actually is to reduce the Eddy current losses) the real stator (in experiment) exhibits only pure radial modes (all other modes such as radial shear, extensional, circumferential modes blah blah all dissapear)
The stator frame is made up of sheets of electric steel and bonded together using resin due to which we have to consider isotropic behavior in the X-Y plane (in-plane of laminates) and anisotropy in the Z direction (here Z is the axial direction- perpendicular to the plates). The material was defined under elastic->orthotropic->fill out the matrix D1111 to D2323. so far so good
The values used to fill out the matrix was calculated from values of Ep, Ez, vp and vz (Youngs modulus and poisson's ratio for x-y plane and z-dir)
I did the eigen freq calc once again and found that I'm still getting additional mode shapes and freq (however, much closer to the experimental data).

Thanks for listening to my "big problem description" and now coming to the help I'm seeking in this forum

1 - is my approach of defining the material using this transversely orthotropic material matrix in the right direction or should I do treat this "stator material" in a different way.?? Has anyone anytime done such a FE simulation of stators.??

2- There could be a possibility that even though I get those "additional mode shapes" the amplitude response of those mode shapes, as compared to the experimental mode shapes of the stator, could be significantly less and thereby neglected. For this comparison I need the freq response of the stator...am I right.?? (or can it be done in a different way.??)

3- I tried to find out the FRF using the function "Steady State Modal Analysis" with a "hammer input" at a node and finding out the output response @ another node (similar to what has been done in the experiment). I can get the curves "Accn/Disp/Vel vs Freq) which I guess doesn't help me much as those are absolute values. Is there a way to plot FRF directly or indirectly in Abaqus.?? I'm sort of new to this whole modal analysis and abaqus software

Thanks for reading my prob patiently..I just wanted to be as descriptive as possible.

Please do help me if anyone knows the solution or can point out some directions...i'm totally exhausted with my resources

Regards,
Paul

 

[GregLocock]

1 - I don't know
2- yes
3- that analysis is far more informative than looking at pretty mode shapes. To get the equivalent in abaqus you'll have to add damping to your model.

You'll probably have mor eluck on the abaqus forum.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[spk86]

Hey Greg,
I was looking forward for an answer from you..you are the guy who normally responds in here from what I could see..
Thanks for the answers
I did give damping for my model (individual modal damping). The problem is that the curve I get from the Accn vs Freq doesn't come even near to the experimental results.
The stator is the part of an alternator of an electric car. We are trying to build up a flexible drive train model, in Simpack, after validation using Abaqus (and later exporting it to Simpack). So I posted it in automotive section as normally the electrical guys are interested in the magnetic flux distribution and stuff and not the structural analysis...

Anyways, will try my luck in Abaqus forum.

Thanks once again.

Paul

 

[jeyaselvan]

"I did give damping for my model (individual modal damping). The problem is that the curve I get from the Accn vs Freq doesn't come even near to the experimental results".
Your statement assumed that the experimental damping from modal analysis is correct. The measurement of damping is experiments do have huge amounts of error, particularly for lightly damped systems. The resolution of the FRF and the dynamic range of the DAQ system. FRF estimators could all matter. May be if your predicted shape is as close to measured, you have every reason to be happy.

Jeyaselvan