Rigid Body mass matrix

[sushi75]

Hi everyone!

I just have a quick question regarding the weight point generator. Looking at the Nastran output file, we have a 6*6 rigid body mass matrix. I'm not sure I fully understand the physical meaning of it!

Can someone bring me some guidance on it? I try to find in the Nastran doc how each term is calculated, but didn't find anything.
I guess the diagonal terms of the first block is the mass, but the remaining terms of the diagonal and other terms confuse me a bit!

Thanks a lot for your help!

T

 

[jbrackin]

Look in the NXN Basic Dynamics User's Guide, there is a section on GPWG with examples and discussion.

From Femap: Help/NX Nastran then open Basic Dynamics User's Guide and see Appendix J

 

[rb1957]

"rigid body" usually refers to the 6 degrees of freedom that need to be restrained in order that your model doesn't fly off into outer space.

in one case you can apply balanced loads and reactions to a model but you still need to restrain 6 dof to keep the math happy. you can restrain 1 node that has all dof active (like a beam/plate element) or 6 single dof 3/2/1 (if you know what I mean ... 3 (x,y,z) at one node, x,y at a 2nd, z at a 3rd).

any help ?

another day in paradise, or is paradise one day closer ?

 

[sushi75]

This Basic Dynamics User s guide is a gold mine!

cheers

T