Random response - how to apply a different PSD to each load?

Pioneer
Pioneer

Hi

I'm trying a random response analysis for the first time. (I'm familiar with harmonic response, modal analysis etc)

 

I have some measured acceleration PSD data in x/y/z directions, at one point on my structure so I want to apply a different PSD to each vibration direction and get the response to this combined excitation.

 

Could anyone provide a description the basic principles? Examples only seem to deal wiht the single-PSD case.

The area I am struggling with is the Correlation Table input page in Femap (11.4). The help says:
"you must decide whether you want to correlate the cases. If you don't enter any values for real and imaginary values, the cases will not be correlated. If you do want to correlate the cases, enter the real and imaginary factors and PSD functions"

 

Appreciate any insight you can offer! Whats the significance of correlating the cases?

Regards, Steve

6 REPLIES 6

Re: Random response - how to apply a different PSD to each load?

Solution Partner Valued Contributor Solution Partner Valued Contributor
Solution Partner Valued Contributor
Steve, if you are using FEMAP try this procedure: 1) define a 6..Random Response analysis and accept the default for the wizard forms 2) you should get an Analysis with No Cases Defined 3) Edit the analysis using the MultiSet icon on the right part of the Analysis Set Manager 4) Once you have all the SUBCASEs you want defined come back to the wizard or go directly to edit the Options / PSD Specification You should have the change to define the PSD function for EACH Loads combination (Direct and Cross) Ciao FFF

Re: Random response - how to apply a different PSD to each load?

Pioneer
Pioneer
Thanks for your reply - I'll look into your suggestions and see if I can make it work Smiley Happy

Re: Random response - how to apply a different PSD to each load?

Solution Partner Valued Contributor Solution Partner Valued Contributor
Solution Partner Valued Contributor
Hi SRG, did you manage and solve the PSD issue ?

Re: Random response - how to apply a different PSD to each load?

Siemens Phenom Siemens Phenom
Siemens Phenom

I have attached a pdf that covers the steps to create a multi-input random response in Femap.

 

Regards,

 

Joe

Re: Random response - how to apply a different PSD to each load?

Pioneer
Pioneer

Many thanks for your reply. I haven't tried it yet - I'll let you know when when I have.

Re: Random response - how to apply a different PSD to each load?

Pioneer
Pioneer
Hi, thanks for following up, I never did get to the bottom of it and I've taken another approach. But if I get back to this I'll let you know if I resolved my problems - someone has posted a pdf for me to look at too.