# SingleSidedOnOff

Could u tell me when should i turn on the SingleSide calculation? In your examles, in THA turn on the Single Side calculation, but with the Single Side off in the TKA example.
What’s more, the AnyScript Reference Manual showed that if there is a depth function, the Fv=Avf(dv)nv. But the equation seems to be wrong with out Pressure Modular. Could explain how to use the depth function?
Anyway, thank u very much!

Hello,

the option for single sided calculation is an option that can be used to speed up the contact force calculation. If this option is switched off, the calculation of the contact force is performed from both sides (an approximation of the penetration volume is calculated from surface 1 to surface 2 and from surface 2 to surface 1) and the results are averaged. This gives a better approximation in case that the meshes are different. In some cases when there are smooth surfaces available (e.g. in the THA model where two spheres are in contact), the approximation for the calculation from one side is good enough and to increase the speed of the simulation, the single sided calculation can be switched on.

To your second question: If a depth function is specified, it takes the role of the PressureModule. In this sense you can think of the PressureModule as the coefficient of a linear function.

I hope my explanations helped to solve your problem.

Best regards
Daniel

Thanks! But there is a big difference between SingleSidedOn and SingleSidedOff in the results of maximum penetration and contact area in THA. The penetration will increase with the decline of contact area when the SingleSideOff. Could u explain this for me?

And there is another question. U said we could regard the pressure module as the liner function of depth. But the value of the pressure module of PE is around 1e11 N/m3. But i tried the interpolation fuction of depth from FE results (e.g. 0.0001m, 0.00015m), the results of hip force showed totally wrong value. So i tried to multiply the value with 1e5. But it didn’t work, showed the value was beyond the range.

Hi,

did you check the results in the model view to make sure that the implants are not penetrating through the objects (so that the right surfaces are in contact)?
What kind of FE results did you compare too? Could you try to explain a bit more detailed what you did?

Best regards
Daniel

I have attached the results in attach files. And i am sure that the right surfaces are in contact. There was a large difference between Single Side On and Single Side Off. So could u tell me the detail of contact mechanism of FDK? Such as the formulation of Pressure Module.

I used the gait data from Bergmann (data base of Hip 98) to calculated the hip force, contact area and maximum penetration. And i applied the results of hip force to a same size FE model which output the contact area and maximum penetration to compare with anybody for the validation.

But i found it was difficult to match the results of contact area and penetration simultaneously. I know FDK contact is just a simple model. But I don’t think the results of FDK is twice different from FE.

Thanks a lot.

What’s more, the hip force of SingleSidedOn and SingleSidedOff were same. So i was confused which one should i adopt on my calculation. Or could u tell me which one is right?

Hi,

for my impression the differences in the penetration depth is rather small. But it is obvious that even a small difference in the penetration could cause a larger difference in the contact area, which doesn’t really matter if the forces are similar. As you already figured out, that this is a rather simple model and does not replace an FE model if you are interested in contact areas which might change due to deformation.

Best regards
Daniel