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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