Integrator Error in Scone

[Saadia Talay]

Hi! I am getting this error in SCONE when I try to load the London Lumbar Spine Model (https://simtk.org/projects/llsm/). Can you please help me with it?

[Thomas Geijtenbeek]

This is an error from OpenSim / SimTk. It appears that the model you are using is not suitable for forward dynamics simulation. Does the model simulate well in OpenSim, i.e. can you simulate it for a number of seconds within a reasonable time frame?

[Saadia Talay]

The model doesn't come with sample kinematic files so I haven't tried. Is there any way to overcome this error?


Also, when I try to load another model, the full-body lumbar spine (https://simtk.org/projects/fullbodylumbar), SCONE is unable to read some of the vtp files. I have simulated this model and it runs fine on OpenSim.



When I try to convert it to an hyfydy model, I get the following error:

[Thomas Geijtenbeek]

There is a difference between inverse simulation, in which you estimate muscle force from motion, and forward simulation or predictive simulation, in which you generate motion from muscle force. I suspect you have only tried the former. Models used in predictive simulations have different additional requirements that those used in inverse simulations. SCONE is designed for predictive simulations only.

In order to perform a forward simulation in OpenSim, you need to press the "Simulate" button. You'll find that the model won't simulate properly.

During conversion, it detects there are various bodies with extremely low mass. This causes the model to not work well in a forward simulation. Please look at the SCONE tutorials and examples for models that are suitable for forward simulation.

The .vtp files that are missing need to be copied to the SCONE geometry folder, or in a "geometry" subfolder where the model is located.

[Saadia Talay]

Thank you. Is there a source I can refer to get more information about the additional requirements needed for a predictive model? The LLSM is made for predictive FEM modelling so I am hoping I can make it work in SCONE.

Also, when I try to load the LLSM model, it clamps all muscle fibers to 0.

I get the following messages:

Capture1.JPG (48.3 KiB) Viewed 540 times

The .osim file does state fiber lengths for all these muscles and they are comparable to the fiber lengths stated in the example files. What could be the reason for this error?

I copied the .vtp files to a geometry model and was able to successfully load the model. However, the software is unable to detect the legs of the model. I get a leg count of 0. Is there a way to overcome this?

[Thomas Geijtenbeek]

Please check the recently updated guideline on model requirements. To test performance of an OpenSim model, it is advised to first hit the "Simulate" button in OpenSim.