Hi Dario,

The modulus in the .osim file is actually modulus divided by thickness. I think a refined contact model is in the works but not sure if/when it will be implemented.

Thanks,

Anne

Hello, I am trying to perform a muscle-actuated forward dynamic simulation of running, like Hamner's work. Using gait2392.osim, I have been able to scale, perform inverse kinematics, and RRA of running at 3.3 m/s (note this model does not have arms). Now I am trying to run CMC but am having problems...

When I run Forward Dynamics on a model that has contact, I get forces and torques for the contact elements from the ForceReporter. Are these forces applied to a body's origin? i.e. this is not the force applied to the body at the center of pressure right? since at COP would mean torques are 0.

What units does the XML Ligaments section use for the force-length curve? Is it x = length in mm and y = force in N? with slack length defined in m?

For anyone who runs into this problem, I found a solution. I increased the stiffness and now the parts bounce with much less penetration. Although, the stiffness seems unrealistically high, which suggests other parameters may need adjustment.

James, thanks for all your help.

I dropped each part separately onto an infinite plane to test out the mesh. I found that the femur penetrates the plane a LOT before it bounces. I also dropped a sphere onto an ellipsoid and found the same thing, a lot of penetration. The amount of penetration seems unreasonably large so I suspect a...

Hi James, Thanks for the reply. However, the tibiofemoral kinematics are set to <prescribed>false<prescribed> in the model so I don't think that is the case. The tibia drops under gravity (+y) and should bounce off of the femur, which it doesn't. I'm using a mesh so later I can substitute in a more ...

I would like to run a forward dynamics simulation of 2 bones bouncing to check I have contact implemented correctly. I have checked and double checked my geometry and syntax but contact does not occur. Any reason why? What I am I missing?

Thanks,

Anne

Does OpenSim still require contact geometry meshes to be watertight?

Hi Ryan, Thanks for the suggestions. I re-looked at my GRFs and the shape of the waveform didn't look right. Good lesson learned: If Visual3D has parts where inverse kinematics are NaN, it will linearly interpolate the GRF even though the force plate data isn't NaN. I ended up with a 'large' portion...