Contact modelling - Stiffness values and points of force application

[Pavlos Silvestros]

Good afternoon everyone,

I have a couple of questions regarding setting up contact models for simulating impacts.

1) Could I confirm that the dimensions of the stiffness and dissipation contact_parameters entered into the HuntCrossleyForce model in OpenSim (3.3) are Pascal (Pa) and non-dimesional (coefficient) respectively? These are estimated through the Sherman et al 2011 paper.

2) Is it possible to extract and visualise the point of application of the applied force between the contact surfaces during an impact (such as attached picture)? I haven't found this information in the outputs from ForceReporter but I assume this could be done through the API?

Thank you in advance!

Best regards,
Pavlos

[Carmichael Ong]

1) I've tried to step through the documentation from Simbody in the past (https://github.com/simbody/simbody/blob ... leyForce.h). These are the conclusions I drew:
- stiffness is actually plane strain modulus, and has units of (N/m^2)
- dissipation coefficient units are (seconds / m)

2) The numbers from getRecordValues() should be the force and moment, and from those values I think you should be able to use a shift theorem step to calculate where the center of pressure for the whole contact sphere is. I'm not sure of a direct way to get the point.

[Pavlos Silvestros]

Hi Carmichael,

Thanks for the response!

1) Thanks for confirming, I have also had a look at these now.

2) That's a good idea, but unless geometric constraints exist for the point of force application then many solutions exist for an equivalent force system. I will try and have a look deeper into the HuntCrossleyModel API to see if I can extract the point of interest between the two contacting surfaces.

Cheers!

Pavlos

[Tao Liu]

Hello Pavlos,

I was wondering if you were able to extract the point loads in the contact instead of the resultant contact forces (using getRecordValues)?

Thanks,
Tao