How to simulate a vibration beam test?

[helicalsweep]

Hello everybody,

I performed a experimental modal analysis und a vibration test of a cantilever beam and meassured the eigenfrequencies.
Then I excited the cantilever beam with the resonance frequency of the first mode via a electro magnet and performed a decay test. The wave form of the excitation was a sinus.
The data of motion was recored by a accelerometer.

Now I wanted to reproduce this experiment in NX Nastran 7.5 with a SEMODES 103 Response Simulation.

If I perfomed a semodes 103 simulation the values of simulation are similar to the experiment.
But if I tryed to performe a response simulation with a enforced motion location for my recorded acceleration as excitation, i lost the first eigenfrequency and also some other frequencies do not have the same value as i know from testing an simulation with semodes 103.

I tried to excite my sytem with a nodal force location and everything was fine.

So do have someone an suggestion to solve my problem?
This would be very helpfully.

Best regards,
Martin

 

[ZeroExperience]

You can try using a different another FEA code to compare your results.

If you are a student, you can download a free Student Edition of MSC Nastran, one of the best solvers for linear dynamic analysis.

You can refer to the following information regarding the Free Student Edition of PAtran and MSC Nastran.

http://www.mscsoftware.com/contents/Academia/Student-Center/Default.aspx

If you manage to get the student edition of Patran and MSC Nastran, you can use the following videos for dynamic analysis.

Normal Modes:

http://youtu.be/RdSEeXgmfD8

Response Analysis:

http://youtu.be/gqAxO7slGlU

http://youtu.be/uRTU7NgJNLI

http://youtu.be/7QXpSXaQuPI

http://youtu.be/QvzdmnS-uAY