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[Question #698173]: The incremental contact shearforce is "-" in HertzMindlin and "+" in Viscoelastic models, which is opposite with each other.
New question #698173 on Yade:
I am thinking of using HertzMindlin or Viscoelastic model for numerical simulation, and I read the source code of both models in advance. And I found that the tangential contact force in both source code is calculated in an incremental way , but the sign of the increments is opposite in these two files. In HertzMinlin course code, the sign of difference is "-", while in the Viscoelastic source code, the sign of difference is "+". I am not very familiar with C++ and I tried my best to understand the meaning behind these two equations, but I am still confused. I wonder if someone who is familiar with these two models can tell me why they are the opposite? Thank you!
In the HertzMindlin source code, the shear force (without the viscous term) is calculated as:
shearElastic = shearElastic - phys->ks * (incidentVs * dt);
which can be found in line 382 of https://gitlab.com/yade-dev/trunk/-/blob/master/pkg/dem/HertzMindlin.cpp
In the Viscoelastic source code, the shear force (without the viscous term) is calculated as:
shearForce += phys.ks * dt * shearVelocity;
which can be found in line 125 of https://gitlab.com/yade-dev/trunk/-/blob/master/pkg/dem/ViscoelasticPM.cpp
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