🎉Community Raffle - Win $25

An exclusive raffle opportunity for active members like you! Complete your profile, answer questions and get your first accepted badge to enter the raffle.

Join and Win

Effective Adjustment of CBUSH Stiffness

Altair Forum User

I am trying to squeeze a femur model with two sets of stiff springs top and bottom, and allow it to rotate with the other (spring BCs come from a research paper). Instead, the model bends where the mesh meets the springs that should remain mostly straight.

However, I have tried adjusting all DOF stiffnesses in the PBUSH card without luck.

All springs have been assigned to the local coordinate system (shown in right on photos) using CBUSH card. It seems to me I need to stiffen K2 or K6 (y-tension, z-moment), but neither of these solves the issue.

Attached graphs show 'TY' stresses.

<?xml version="1.0" encoding="UTF-8"?>

Unable to find an attachment - read this blog

Find more posts tagged with

English

HyperMesh

Accepted answers

All comments

tinh

I forget saying 3d elems don't have dofs 456, too.

So cbushs bind to femur like hinges regardless their Ks

Altair Forum User

If 4, 5, 6 don't matter, how come changing stiffness of K6 made a big difference?

I changed K6 to Rigid and the model went flying in a wrong direction. However making K6 0 actually made the model a lot better. This doesn't really make sense to be, since I thought that making the stiffness higher would constrain the motion more.

Addl Edit: My main issue is that I am having trouble visualizing the degrees of freedom for the springs and how the stiffness will change their motion. Changing stiffnesses according to the CID that I've assigned to them is not making them change movement in a predictable way...

tinh

Because dofs 456 have affection at the constrained node

If you make Ks too different I think it will move much by smaller.

Try making them equally.

I think spring Ks must come from your research, too.