Surface contact

Main Forum
1

Dear AnyBody Team!

Currently, I am faced with the following problem:

I would like to use fdk with the appropriate surface contact model in example of total knee arthroplasty. However, using “AnyDrawForceSurface” the reaction elements of the tibiofemoral joint look very strange (attachments). I am confused whether this is a modelling, model or visualisation issue?

In comparison, the patellofemoral joint looks quite plausible. IMO the surfaces were adequately prepared, considering your contact model appendix, etc.

Thanks!

Best regards,
Malte

2

Hi Malte,

Here are some possible reasons for this behaviour.

[ul]
[li]Please ensure to use the latest version of AnyBody i seem to recall there has been made an improvement to the surface contact that could relate to what you see, which AMS version are you using.
[/li]
[li]Please ensure that the surfaces you are displaying are actually the ones being used for the contact… this could also explain this
[/li]
[li]wrongly applied scaling could also cause issues, if by mistake the surfaces for contact are being scaled i think it could cause issues.
[/li][/ul]

Best regards
Søren

3

Hi Søren,

thanks for your response! Actually, the issue occurred using AnyBody 6.1.1. I double/triple/… checked your second point, but everything seems reasonable. Regarding the scaling, the implant components are scaled down according to:

AnyFunTransform3DLin ScaleFun = {
AnyVec3 ScaleXYZ = .GlobalConv * {1, 1, 1};
ScaleMat = {{ScaleXYZ[0],0,0},{0,ScaleXYZ[1],0},{0,0,ScaleXYZ[2]}};
Offset = {0,0,0};
};

However, there are more complex transformations involved regarding the implant positioning in the segment. Do you think there might be the problem?

Thanks and best regards!
Malte

4

Hi Malte,

Please try to make a simple model having one surface fixed and the other one moving on a prismatic joint, then slowly drive the two surfaces together and inspect the outcome.

Try initially to simply insert the raw surfaces using no scaling, then add scaling.

If you still have issues, we would very much like to see the model, if you do not wish to share it on the forum? we can find another way to share it.

Best regards
Søren