distribution forces with mpc

[tillo]

Hi.
if I impose a force in a point to distribute to other knots with an mpc how it is redistributed?
based on the number of links,the distance?

 

[frias]

depends on whether you use a rbe3 or rbe2

 

[tillo]

I wanted to use a rbe2

 

[Onda]

dear tillo,
from your previous post, to which I answered you have not yet submitted!
Also it would be nice that when you answer a post, then you reply saying whether the answer was helpful or not and why.
in any case, a rbe2 is a rigid connection between the nodes, so all knots connected with this type of mpc move like the master node.
It follows that by applying a force to the master node, this is distributed to all dependent nodes in order to satisfy the balance of the rbe2 element.
of course the forces are divided according to the rigidity of the elements to which the knots are connected. If for example some nodes of the rbe2 are connected only to this and no other element, these nodes are given no load.
a rbe2 is in general a link that heavily modifies the state of the elements to which it is connected and must be used very carefully.
If for example connect the four knots of a shell with a rbe2 the shell will not see any shift to the knots and its stress will be null. the contour shells instead see one side to deformation nothing and one side with normal deformation and therefore they will have a peak of abnormal stress.
to pass a load you use a rbe2 only if you want to simulate a very rigid fitting that is not modeled to the analysis, otherwise to distribute the load between multiple knots you use a rbe3 that has the advantage of not adding non-existent rigidities to the model.
However everything is extensively treated in the basic guide of nastran the linear static user guide, which I recommend reading why it explains the concepts much better than I can do it.
wave