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SOL103 - Removing rigid body modes in a Craig Bampton reduction

Siemens Experimenter Siemens Experimenter
Siemens Experimenter

Hello,

 

When doing a Craig Bampton reduction of a free body (ie no restraint is applied to the body), I would like to generate the K and M matrices of the reduced system but without the rigid body modes.

For example, if the modes of my models are 0 Hz, 15 Hz, 45Hz, 55Hz, I would like my reduced model to contain only the 15 and 45 Hz.

For experimentation purpose, I'm working on a very simple mass spring 1D model. I tried to set a minimal frequency value in the EIGRL command but I always end up with a 0 Hz in my reduced model. Is there a way to tell Nastran not to take into account the rigid body mode when reducing my model?

 

Thanks,

Damien

 

PS: I've joined my input data 

2 REPLIES

Re: SOL103 - Removing rigid body modes in a Craig Bampton reduction

Siemens Creator Siemens Creator
Siemens Creator

Before the run the SOL103 Real Eigenvalue solution, change the lowest frequency to 0.1 Hertz. That will eliminate the "zero Hertz" or free-body modes.

Re: SOL103 - Removing rigid body modes in a Craig Bampton reduction

Siemens Experimenter Siemens Experimenter
Siemens Experimenter

That's what (I thought) I did by specifying a minimal frequency of 0.5 Hz in my input file (line 28). However, if the rigid body mode is not present in my f06 file anymore, it is still here when I compute the eigen values given by the K and M matrices of my super element in the punch file. And I'd would like to have a super element without rigid body mode. Is this possible?

 

Thanks,

Damien