Surface Contact Problems

Main Forum
1

Hi,

I have a model with two separate knee implant pieces, and am running some anterior drawer tests on the model. The results I am getting are much too small, and I was wondering if there was an issue with the contact force I placed between the pieces. Is there friction in the model? If there is, is there a way to reduce it?

This is my contact force code:

//Contact Force to keep implants from going through each other
AnyForceSurfaceContact FSurf = {
AnySurface &sMaster = Main.HumanModel.BodyModel.Left.Leg.Seg.Thigh.STLpoint.Femur;
AnySurface &sSlave = Main.HumanModel.BodyModel.Left.Leg.Seg.Shank.STLpoint.Tibial;
PressureModule = 9.3e9*2;
ForceViewOnOff = On;
MeshRefinementMaster = 0;
MeshRefinementSlave = 0;
SingleSidedOnOff= On;
};// end of surface contact

Thanks,
Caroline

2

Dear Caroline,

  1. AnyForceSurfaceContact does not contain its frictional force. The direction of the force depends on the interection volume of two STL files.

  2. It seems that you try to do some laxity analysis using FDK based on ligaments and contacts.
    If the distance based on FDK analysis is too small, there may be two several things which you can try to change.

  • The initial relative location between two STL files may matter
  • Ligament stiffness properties may matter
  • Wrapping surfaces for ligaments can change your results

I hope this may be helpful to you.

Best regards,
Moonki

3

Moonki,

Thank you for your help. Could you explain how to wrap surfaces for the ligaments? I am not sure how to add code to do that.

Thanks,
Caroline

4

Dear Caroline,

I’m not sure how you could implement your ligaments, but there is a class called ‘AnyKinSPLine’ which can accept some wrapping surfaces inside, such as ellipsoid, sphere and cylinder.

Of course, you should define your own wrapping surfaces using some classes such as AnySurfCylinder, AnySurfEllipsoid and AnySurfSphere in order to reflect the surface of your implants and bones.

I hope this may be helpful to you.

Best regards,
Moonki

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