Shock response analysis

[Michael87]

Hello forum members

I have to do a shock analysis on a body housing, because the housing will be tested on a shaker.
This is the first time i have to do this.

So i have a body and i inserted a half sine acceleration on the mounting holes of this body to simulate the shaker test.

Now i have several questions:

Which Nastran solver i have to take? Is it the sol 111 or 103 repsonse simulation?
How can i enable the damping? The displacements are really high when i simulate the eigenvalues of the body.
Do i have to put a constraint on the body to fix it on the floor?

Thank you very much

PS: Please excuse my bad english

 

[BlasMolero]

Dear Michael,
Welcome to dynamic response, I sugget to contact with your FEMAP & NX NASTRAN local vendor and ask them for help (dynamic training is what you need), if you don't have previous experience in Dynamic analysis then this forum is not magic, dynamic analysis is complex, and should be performed only for experienced FEA users.

Said that, the type of dynamic response you will need to run is fully dependent of the type of excitation you have:

1.- if you receive a response spectrum curve of acceleration vs. freq. (typical from seismic asnalysis) then you need to perform a Response Spectrum Application analysis, here you are a tutorial step-by-step:

http://www.iberisa.com/soporte/femap/dinamico/response_spectrum_4story.htm

2.- If you have a harmonic dynamic excitation then a Time History Analysis, ie, a Modal Transient Dynamic Response Analysis (SOL112) is the required analysis to perform, see here a step-by-step tutorial of harmonic pressure vs. time:

http://www.iberisa.com/soporte/femap/dinamico/tuberia.htm

3.- To simulate a shake test this is a base mnotion analysis where an enforced motion of acceleration vs. freq is prescribed to the base of the structure. This is a frequency sweep, and the required type of analysis is named as modal dynamic frequency response (SOL111).

To learn how to perform a frequency sweep go to FEMAP > HELP > EXAMPLES > EXAMPLE 17: Frequency Response of Tower with Seismic Excitation and choose the DIRECT METHOD, not the LARGE MASS Method. As a result you will get the dynamic response of the structure in the form of X-Y plots of response vs. frequency and also dynamic stress.

Regarding DAMPING, this is one of the most complex thing in dynamic analysis. Well, the contractor will tell you the value that allow you to use, if not given this value then use a 2% of modal critical damping. In FEMAP select the function type “7..Critical Damping vs. Freq”

Best regards,
Blas.

PD
In eigenvalue analysis (SOL103) displacement results are meaningless, these are normalized values that only serve to see the deformed shape of each mode, this is a typical error I see many times in the market ...



~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[Michael87]

Dear BlasMolero,

Thank you so much for your help!
I've been searching for a long time for this kind of information you answered me.
I understand much better now the complexity of this simulation.
I'm going to contact the local vendor for a course in this.

Again thank you and have a nice day