Ligament passing through the wrapping surface

[Xijin Hua]

Dear OpenSim experts:

I am now using an OpenSim model to simulate a novel 3D printed device. I developed the representation of 3D printed device as four ligament elements in the model, and also developed a cylinder wrapping surface on which the four ligaments will wrap during a drop landing simulation. However, I am now having a problem that the ligament will penetrate into the wrapping surface during simulation, as shown in the attached figures. At the beginning of the simulation, the ligament wraps on the cylinder surface very well (figure 1), but during the drop landing, one of the ligament penetrates into the wrapping surface (figure2 and 3, in figure3, you can see the ligament become a straight line passing through the wrapping surface rather than wrapping on it). Is there anyone could you please tell me why this happened and how to solve this problem? Thanks in advance.

The wrapping set for the ligament were defined as following:

<PathWrapSet>
<objects>
<PathWrap name="pathwrap">
<!--A WrapObject that this PathWrap interacts with.-->
<wrap_object>foot_r_tibia</wrap_object>
<!--The wrapping method used to solve the path around the wrap object.-->
<method>hybrid</method>
<!--The range of indices to use to compute the path over the wrap object.-->
<range>-1 -1</range>
</PathWrap>
</objects>
<groups />
</PathWrapSet>

[Ayman Habib]

Hello,

Depending on how the pathpoints that define the ligament are defined, if a path point ends up inside the wrap-object then wrapping is not applied. You should keep that in mind when defining which body/frame the wrap object is attached to.

Hope this helps,
-Ayman

[Xijin Hua]

Dear Ayman

Thank you very much for your reply. It is helpful and very much appreciated.

Best regards

Xijin

[Xijin Hua]

Dear Ayman

Thanks for your quickly reply. One more question: what will happen if this case occurs? does that mean the length of the ligament and the force generated by the ligament will decrease significantly at the moment when the ligament transfer from wrapping the surface to passing through the surface? Thanks in advance.

Best regards

Xijin