How can I define CONM2 elements (Hypermesh) in order to obtain a more realistic vehicle frame behavior ?

Altair Forum User

Hi. I'm working on a vehicle frame. I supposed mechanical connections (between the tubes) as rigid elements (rbe2). But I wanted to take into account the mass of these connections. Rigid elements don't have any mass so I created concentrated mass on the independent nodes. In that way, I thought CONM2 elements were connected to the structure. But, I didn't notice any change on frame behavior (stress and displacement). 

I tried to add inertia properties (Card Edit>>elements>>Edit>>CONT), but it failed. 

 

I'd like to add masses that are taken into account in the post processing results... 

 

Thank you in advance

tinh

Please show us results of the two cases: with and without conm2 and tell us how you conclude it has no change.

Altair Forum User

Of course. This is a part of my structure.

 

For instance, I put in the center of the rigid element (surrounded in red) a cencentrated mass of 1 tonne. The center of gravity (Post>>Summary) changed (the added mass is taken into account by the software). The frame is symmetric and I added a mass only on a side (right side is heavier than left side), so theoretically the displacement and stress field shoud be assymmetrical (analysis was done with one load oriented along z). However it's not the case. It seems that the software took into account the mass to calculate total mass or center of gravity. But, it didn't make a link with gravity/weight. 

 

Displacement

Stress

 

 

 

Q.Nguyen-Dai

When you define 'mass', to get the gravity effect, do you define also gravity acceleration? Something g=9.81m/s^2 ?

Altair Forum User

Lucie

 

Can you share the model file?

 

Thank you

Altair Forum User

I forgot to add a GRAV card (Thanks @Q.Nguyen-Dai) and to create combined load (load + gravity). It works now. Weight is taken into account. 

 

Thank you guys for your help !