Can Hunter-Crossley force in OpenSim handle ellipsoid geometry?

[Xiao Hu]

In the literature and this forum, I have seen that the Hunter-Crossley Force has been applied to model the contacts on plane and sphere geometries. The paper "Seth A, Sherman M, Reinbolt JA, Delp SL. OpenSim: a musculoskeletal modeling and simulation framework for in silico investigations and exchange. Procedia IUTAM. 2011;2:212-32. Epub 2011/01/01. doi: 10.1016/j.piutam.2011.04.021. PubMed PMID: 25893160; PMCID: PMC4397580." suggests that OpenSim can also apply the Hunter-Crossley Force to ellisoid geometry. But, I have not seen any discussion about it on the forum, and have not found any way to do it, neither.

So, can the Hunter-Crossley Force be applied to ellipsoid geometry in OpenSim?

[Carmichael Ong]

Not sure if there were any issues with implementation or if it just didn't come up as a need in the past, but it doesn't look like ellipsoid contact geometry was added to OpenSim. It might be possible to write similar code to the current contact geometry (e.g., sphere) to wrap the SimTK ellipsoid class in OpenSim.

Many models that users have created will use multiple spheres instead to create a larger contact surface.

[Thomas Uchida]

The contact model makes several assumptions (see the Simbody Theory Manual, Section 11.2.2, https://github.com/simbody/simbody/blob ... Manual.pdf) and has parameters that likely known only approximately. Given these sources of uncertainty, the precise shape of the contact geometry may not make too much difference in terms of accuracy.