simtk.org

Hello,

I try to compute contact knee forces and compare them to in vivo forces for many gaits. As I try to get a more subject-specific model in order to make better predictions, I use the more complex model created in this paper http://www.sciencedirect.com/science/ar ... 9014007179. This one takes into account the fact that the patient has a varum-valgus knee and provide two contact points (medial and lateral) at the knee.

I tried to do some computation with the datas given in this following link https://simtk.org/projects/kneeloads.

I was doing a IK and ID analysis in a static gait, the results were quite good. I tried to go further and do a static optimization. After specifying the Ground reaction forces and the kinematics from the IK, I hit the button run and the interface start to freeze and nothing is computed.

Is it because of the constraints condition of the model (weld constraint of the medial condyle in the tibia plate) and i have to specify something else in the SO ?

An other question, the SO solver need both the kinematics and the GRF to compute muscle forces, this means the SO solver is doing a ID analysis before computing muscle forces ? Thus why not directly put ID results as an input ?

Thanks

I was doing a IK and ID analysis in a static gait, the results were quite good. I tried to go further and do a static optimization. After specifying the Ground reaction forces and the kinematics from the IK, I hit the button run and the interface start to freeze and nothing is computed.

What is said in the Messages window? Most likely, the optimizer is looking for a solution and cannot find one. You can change the integrator settings in the Static Optimization Setup File. Maximum number of integrator steps, integrator tep size, error tolerance, can all be changed and may help.

An other question, the SO solver need both the kinematics and the GRF to compute muscle forces, this means the SO solver is doing a ID analysis before computing muscle forces ? Thus why not directly put ID results as an input ?

Because many people have no interest in doing ID analysis.

jimmy wrote:

What is said in the Messages window? Most likely, the optimizer is looking for a solution and cannot find one. You can change the integrator settings in the Static Optimization Setup File. Maximum number of integrator steps, integrator tep size, error tolerance, can all be changed and may help.

Absolutely nothing, and this is especially what I found very strange. Because I've already had optimizations issues with previous models but the console was telling me what was going on. Here just after I hit the run button, the opensim interface start to freeze, and it is impossible to cancel the SO.

Thanks for your help James.

Sorry for the new post, but if you want more information, this is what I see on the screen when the simulation is "running" :

Also my IK datas and grf datas seems to be ok so I really struggle to understand why the interface is freezing. Is it because of a not powerful enough computer ? Mine is pretty old.

Thanks

Does a red circle appear in the bottom-right corner of the GUI? If so, you can click on it for more details.

Thanks for your reply,

I don't know why, but after waiting for 10/15 minutes, the static optimization began to run normally, I guess that's because of the low performance of my computer and the high number of frame it had to analyze.

Sorry for this.