Thanks for the example! Now I see that why is right that the shear force change sign. It's global but its application is related to the ids of the bodies. cheers, chia
2010/3/31 Václav Šmilauer <[email protected]> > > > Hi V., if I correctly understood, the shear force (the incremental > > one) behaves as you describe, but the TOTAL shear force (the one that > > we store in the simulation) is really expressed in the global system > > (right?). > > (let's suppose that https://bugs.launchpad.net/yade/+bug/493102 is > solved for the rest of this discussion) > > shearForce (the total, current one) is defined for interaction (not for > particle), in global coordinates. Now, let's say shearForce is > (-1,-1,-1), and that we have 2 bodies, A and B, which are assigned to > id1 and id2. It means that you apply (-1,-1,-1) to A (id1) and > -(-1,-1,-1)=(1,1,1) to B (id2). > > If you swap the particles (A=id2, B=id1), then shearForce will be > computed in the inverse sense: > > See e.g. ScGeom::updateShear (or updateShearForce), where it is clear: > normal is already inverse (always from id1 to id2), then everything is > symmetric for id1 and id2 (therefore the same if you swap id1/id2); > relativeVelocity will be inverted, so will be shearVelocity, > shearDisplacement and shearIncrement / shearForce increment. > > (This will happen similarly in Dem3DofGeom, but it is less obvious to > follow in the code) > > With swapped particled (A=id2, B=id1), therefore, shearForce will be > (1,1,1). But we apply now (1,1,1) to B (which is now id1) and (-1,-1,-1) > to A (which is now id2). > > So you see real forces on bodies are the same. > > > Moreover if my external force on the particle is in one direction, I > > would always expect an opposite sign for the total shear force (we > > oscillates around the same value but the sign should always be > > opposite to it). > Sorry, I am not clear as to what you mean here. > > HTH, Vaclav > > > > _______________________________________________ > Mailing list: > https://launchpad.net/~yade-dev<https://launchpad.net/%7Eyade-dev> > Post to : [email protected] > Unsubscribe : > https://launchpad.net/~yade-dev<https://launchpad.net/%7Eyade-dev> > More help : https://help.launchpad.net/ListHelp >
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