Jump to content
Sign in to follow this  
sbasude

Effective Adjustment of CBUSH Stiffness

Recommended Posts

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.

1.PNG

2.PNG

Femur_Model_6_26.fem

Share this post


Link to post
Share on other sites

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...

Share this post


Link to post
Share on other sites

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.

sbasude likes this

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
You are posting as a guest. If you have an account, please sign in.
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...