On 7 May 2010 16:40, Bruno Chareyre <[email protected]> wrote:
> > >> I tried the sample example with the two balls and the time step estimated >> by PWave. I attach the figure. >> > Mmmm... It is not "that" better. I expected better matching with corrected > kinetic (as in the simple mass-spring test). > > > Now I suppose that if the kinetic energy is computed correctly (is it?) >> the problem relies on the elastic energy. You said yourself that the total >> energy is "approximately" constant. >> > > ret+=.5*(b->state->mass*(b->state->vel+b->state->accel*dt/2).SquaredLength()+(b->state->angVel+b->state->angAccel*dt/2).Dot(diagMult(b->state->inertia,(b->state->angVel+b->state->angAccel*dt/2)))); > > Ah! I see. At time "t" we have contact forces F(t-dt) and velocities > V(t-dt/2). > Now I see as well. Thanks! So, you need in fact to __substract__ accel*dt/2, and you will get at time > "t" the energy of time "t-dt". Sorry if I wrote something different in > previous mails. > It explains why it match better with non-shifted curves, you shifted the > wrong way. ;) > > Now replying to another question : > > > plasticDissipation += > (shearDisp+(1/currentContactPhysics->ks)*(shearForce-prevForce)).dot(shearForce) > > Is shearDisp the total shear displacement, right? I would compute the > dissipation incrementally, something like > > plasticDissipation += [delta_us + (Fs_max_current - Fs_max_prev)/ks] * > Fs_max_current > > The equations are almost the same. shearDisp is the increment. > The problem in your equation is it doesn't handle the transition > plastic->elastic or elastic->plastic (when the increment of displacement is > partly elastic and partly plastic), it is the reason to use > shearForce/prevForce instead of max_current/max_previous. If the increment > is fully plastic, it makes no difference : in such case > shearForce=max_current and prevForce=max_previous. Perfect! Thanks for explain me ;) Chiara > > > Bruno > > _______________________________________________ > Mailing list: > https://launchpad.net/~yade-users<https://launchpad.net/%7Eyade-users> > Post to : [email protected] > Unsubscribe : > https://launchpad.net/~yade-users<https://launchpad.net/%7Eyade-users> > More help : https://help.launchpad.net/ListHelp >
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