Response Spectrum Analysis Contact Results

[Transient1]

Hi,

I've performed a response spectrum analysis and I want to make sure that the right procedure in post processing contact results is something like:

summtype,comp
/INP,,mcom
ESEL,S,REAL,# !Select Contact Target
FSUM,,CONT !Get reaction forces

I'm a little confused about when I would want to use COMP or PRIN on the sumtype command. This procedure doesn't give the results I would expect (effectively zero). I'm reviewing the model now and any insight into post processing the results would be helpful.

 

[TERIO]

One thought on your problem:

Response spectrum analysis is linear while contact is nonlinear. In this case ANSYS treats contact elements as linear in their initial state (e.g., open or closed). This could be causing you some trouble.

 

[Transient1]

Terio,

That was the problem exactly. Even with a linear contact element (bonded) ANSYS fixes the nodes. I haven't exactly worked out the procedure, but it is better to join fastened parts with individual beam elements and get the reaction forces from the beam elements. However, apparently the sign gets lost for each modal combination so without accounting for that the reaction loads would be very very conservative.

 

[TERIO]

Transient1,

Yes, you lose signs in the modal combination. The eigenvalue/vector part of the analysis only tells you mode shape and peak values for that mode. It does not tell which direction and when that peak value occurs for each mode. The various combination methods have varying degrees of conservatism from SRSS (each mode peaks randomly in time) to Absolute Sum (assume each mode peaks simultaneously). Other methods are based off SRSS with some adjustment for closely spaced modes that will likely peak near the same time.

NUREG/CR-6645 analyzes a piping system and compares different modal combination methods with time history analysis which could give some idea of the conservatism in the different methods (search for NUREG/CR-6645 at NRC Adams

http://adamswebsearch.nrc.gov/scripts/securelogin.pl

).