yade-users team mailing list archive

[Václav Šmilauer <eudoxos@xxxxxxxx>]

> I would not be surprised to find mistakes or inconsistencies here and 
> there as I think Vaclav developped the framework but did not really use 
> it for now.
Right, I never used it.
> If nothing changed since last time we discussed that in Grenoble, you 
> could also find the definition of clumps inertia a bit weird : it is the 
> inertia of a sphere of equivalent mass (I suggested that for 
> quasi-static problems it would be an acceptable approximation, and it 
> was easier to code, so...).
> Consequence of that : clumpRBP->inertia is an isotropic matrix, 
> independant on the coordinate system, and equations above are correct. :)
Clump::updateProperties computes full intertia matrix and changes clump
orientation so that its local axes are principal (eigenvalue problem).
Unless spheres overlap, the inertia matrix should be "exact".
I cannot guarantee that it is correct though. I never verified results
against a by-hand calculation.
> If somebody takes time to compute the correct inertia matrix, then 
> inertia will have to be rotated, I agree.
Don't we have th same problem with regular bodies as well? Inertia
matrix (body-local coords) is used unrotated in NewtonsDampedLaw to
compute angularAcceleration (global coords)? Sega pointed taht out
earlier already IIRC.

v.