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Why is the definition of TSTEP necessary for Nonlinear Direct Transient Analysis?

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Dear Support-Team,

I am currently working on a Nonlinear Direct Transient Analysis to be solved with OptiStruct. I have read in a variety of sources that for this kind of problem  NLPARM and TSTEP load collectors must be defined. I have also read that some entries made in NLPARM will override entries written into TSTEP. If this is so, why do I have to define a TSTEP load collector in the first place? Further, is my assumption correct that NINC-, DT-settings in NLPARM (also in NLADAPT and NLOUT) refer to time incrementation when performing a Nonliniear Direct Transient Analysis??

 

I'd be very grateful for your Help!

 

Cheers!

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First of all, thanks for your reply tinh!

 

I understand what you are getting at. Still, I'm not quite clear about one thing. In TSTEP I am defining " time step parameters for control and intervals at which a solution will be generated and output in transient analysis" (quote from OptiStruct Help-webpage on Bulk Data Entry TSTEP). I understand what the different parameters are meant to do (N, DT, NO and so forth). But when I define them and leave similar parameters in NLPARM blank intentionally to avoid overriding the solver won't stick to the defined parameters. For example, when I define N=1000 and DT=0.001 in TSTEP I would expect to have 1000 increments solved by OptiStruct. The Out-file shows, that a lot less increments are actually solved. Even when I put DIRECT=yes in NLADAPT to specify fixed increments.

 

Thinking about it, I still have a lot of stuff I am not sure about regarding HyperMesh/OptiStruct.

 

Maybe somebody can clear things up for me? :)

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