← Back to team overview

yade-users team mailing list archive

Relative velocity (Shear force)

 

Hi,

one more question about the way in which we compute the relative velocity
between particles. As long as we choose the incremental way to get the total
shearForce, we need the force increment. The force increment is done
according to the relative velocity. Since this must be an increment, I would
expect that the velocities to be accounted for each particle resulted equal
to:

particle 1 ---> deltaV_1 = v_1(t+dt) - v_1(t)
particle 2 ---> deltaV_2 = v_2(t+dt) - v_2(t)

Now I would say that my relative velocity is:

v_rel = deltaV_2 - deltaV_1

And then we get the shear force increment:

deltaFs = v_rel * dt * ks

Question: is that what we do in this line:

Vector3r relativeVelocity = (de2->vel + de2->angVel.Cross(_c2x_)) -
(de1->vel + de1->angVel.Cross(_c1x_));
?

I know what that line means, but it is to say the same thing as I expressed
above?

**************************

One more observation about the relative velocity. I am quite confident to
repeat that we cannot predict the sense of this vector. This is a result of
the motion, and the shear increment that we get can give a positive
contribution or a deduction to the total shear force according to that. Now
(perhaps) it does not make too much different to say

rel_vel = body1_vel - body2_vel
OR
rel_vel = body2_vel - body1_vel

Therefore it should be fine both saying

shearForce -= rel_vel * dt * ks
OR
shearForce += rel_vel * dt * ks

since is the sense of the force increment that at each time step will give
the right contribution. Please, correct me if I am wrong (I have a lot of
doubts on this side).
Thanks, Chiara

Follow ups