yade-users team mailing list archive

[Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>]

> Q2. Please help me understand why the angle is multiplied by 0.5 in 
> the equation to calculate the rotation of shear displacement  in 
> SCG/CohesiveFrictional Law:
> angle = dt*0.5*currentContactGeometry->normal 
> <http://beta.arcig.cz/%7Eeudoxos/yade/doxygen/d1/d50/classSpheresContactGeometry.html#51c56fa736132889c4afa86047c92ae5>.Dot(Body::byId 
> <http://beta.arcig.cz/%7Eeudoxos/yade/doxygen/d7/d80/classBody.html#091394366c2647e1fabe183e01708f67>(id1)->state->angVel+Body::byId 
> <http://beta.arcig.cz/%7Eeudoxos/yade/doxygen/d7/d80/classBody.html#091394366c2647e1fabe183e01708f67>(id2)->state->angVel);
> axis = angle*currentContactGeometry->normal 
> <http://beta.arcig.cz/%7Eeudoxos/yade/doxygen/d1/d50/classSpheresContactGeometry.html#51c56fa736132889c4afa86047c92ae5>;
angle = normal*mean_angVel*dt

> Q3. The position/velocity integration  follows the 2nd order explicit 
> method, as was upgraded by Bruno :). The velocity and angular velocity 
> are in the (t+dt/2) timestep, while the position & acceleration (also 
> rotation) are in the (t) time step.   But it is not adjusted back to 
> the current time step:  v(t) = v(t-dt/2) + v(t+dt/2).   Ommitting this 
> will make the velocities in the simulation ahead of time by dt/2?  Is 
> this alright? Why?
1) At iteration "N", v(N)=v( (N-1/2).dt ) , not N+1/2 as you suggest. 
Consequently v(t) = v(t-dt/2) + v(t+dt/2) cannot be computed : v(t+dt/2) 
is unknown.

2) Yes, v(t) is not defined, but we don't need that (except for some 
viscous laws, as explained by Vincent).
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Chareyre Bruno
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