Multi-Body Load in Nastran

[dbat]

Is there a method to apply different body loads to different areas of an FE model for a linear static run using NEi or MSC NASTRAN?

So far, I've used a brute force method by scaling the density values of the mat cards based on the higher proposed body load, and perform the analysis run using the lower body load in the GRAV card. This method works okay for a simple model, but I would prefer not to modify the density values especially when working with a very complex FEM with various mat cards.

Any thoughts would be appreciated . . .

 

[gio1]

As far as I now body loads in MSC Nastran are defined through global accelerations, which apply to the whole model. Applying different densities to each body would then be the only way of infering different loads.

Cheers

Gio1

 

[rb1957]

could you make your model out of two super-elements ?

then either apply different body forces to each super-element or post-process one (scaling the body force results by the factor needed).

 

[dbat]

rb1957,

Sorry - I'm not all to familar with super elements . . . Therefore, I can't say ya or na if I can utilize this element type for my model, but thanks for the suggestion.

I'll take your idea into consideration, doing some reading up on super elements, and determine if this element type would be applicable from me to use.

 

[NoranTech]

In NEi nastran you may want to look at the continuation for the GRAV entry. It allows for 3 tables which define how the GRAV load can vary with position. Just let us know if you need more help.

TID1, TID2, TID: TABLEDi set identification numbers that define position dependent scale factors in the x, y, and z directions of the basic coordinate system.

Noran Tech

 

[GregLocock]

Can you explain what real situation you are trying to represent?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[dbat]

Hi GregLocock,

Well, I can't really go into details of this model . . . Anyway, I'm trying to find a more reasonable method to apply different G-loads to different parts of a structure, which I've been told that can be accomplished with other codes, such as Abaqus and LS DYNA.

I've assumed that if this can be done with other codes then there's got to be a way to accomplish this with NASTRAN.

Anyway . . . thanks to all for your inputs and quick responses. I hope to use this forum more in the future.

 

[GregLocock]

Well, if it is dynamic then changing the density will screw up your responses.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.