confusion about 'RadiusMeasure' and 'strength' using in contact elements


#1

Hi, when using contact elements between an exoskeleton strap and the human, I have two confusion things. I would be very appreciated if someone can give me some ideas about this.

1.After adding contact elements between straps and human body, how to analyse it?
It seems pressure of the normal force or friction force is one of the ways to analyse it.
To calculate the pressure, P=F/A.

To calculate the contact area, does it use the parameter that set at ‘UserDefinedRadiusLimit’?
But it seems it related to the value ‘RadiusMeasure’. The normal force keeps unchangeable when the value of ‘UserDefinedRadiusLimit’ is bigger than ‘RadiusMeasure’; otherwise, it becomes zero.
If it is the contact area radius, it doesnot make sense, when the radius is small, it should still have some force. I cannot figure it out…

2.And also about the strength setting, how much you should set. If you set bigger, you will get larger normal or friction force. That’s confusion to say how much contact force is on this node or that node since you can adjust the strength bigger or smaller.


#2

Hi Longbin,

It is good question and you are not the first to ask about this topic.

The Radius settings are related to if there can be contact or not it do not relate to e.g. a strap size

Please see this explanation on the contact elements.

https://github.com/AnyBody/support/wiki/All-about-FrictionContactMuscles

These contact elements are essentially artificial muscles. They are recruited as any other muscles, in most cases you will want these muscles to be strong, so that the recruitment will utilize them to unload the real muscles. If you make them too weak the model will feel “pain” and look for ways to shift the load away from this point.

Hope it made it clearer

Best regards
Søren