prescribed displacement to a node of a rigid body

[ladopico]

Hi,
I want to drive my knee model with a prescribed displacement defined at a node at the top of the femur, which is a rigid body. I get warning messages and the model doesn't run well, could you tell me if it's possible to do it and if I may be doing something wrong by just selecting the node, and apply a prescribed displacement to it?
Cheers,
Carolina.

[maas]

Hi Carolina,

If the node that you are prescribing is part of a rigid body, you should apply a rigid constraint instead of a prescribed displacement. Prescribed displacements can only be applied with deformable geometry, whereas rigid constraints are the way to prescribe rigid bodies. Please give that a try and let me know if that worked.

Cheers,

Steve.

[ladopico]

I understand what you suggest but that will move the whole rigid body and I want to force the displacement in one node and then the rest will move/adjust according to the other constraints. Imagine the knee, with the patella and it's ligaments, and the ligaments and meniscii between tibia and femur, all of these parts interact together, they are connected. I want to force a node at the top of the femur to move 50 mm in the posterior direction, and then the femur as a solid rigid should rotate and maybe traslate in order to fulfil that displacement and the constraints.
I don't know if I explained it well, sorry if it was obvious but just in case.

[maas]

Ah, I see. What you can try to do is set the center of mass of the rigid body at the node you want to prescribe. Since you are not solving a dynamic problem, the location of the center of mass will not affect the result. Then, you can apply the rigid constraint. This should put the node where you need it.

Steve.