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E-mail from Frank:
Martijn and I have been looking at the rigid body rotations in MercuryDPM and especially the difference between how it is done for multispheres and other objects (including superquadratics).
This is my current understanding: inertia_ is the initial moment of inertia matrix, rotation of a particle are encoded using a quaternion. For multispheres there is a master-slave relation between particles. The center-of-mass motion and rotation of a multisphere are stored at the master particle.
For multispheres the angularAccelerateMaster method is used, while for other particles angularAccelerate is used. Both function should do the same, but for different types of particles.
angularAccelerateMaster seems fine to me (in principle), while angularAccelerate solves
Here I have used the subscript ‘lab’ to denote the laboratory frame of reference. It is related to the quantities in the frame of the ‘principal axis’ by a rotation, e.g. , where is the moment of inertial matrix actually used in the code.
I think here a term is missing in the update performed by angularAccelerate! The (correct) equation of motion is
This is actually done in angularAccelerateMaster, but in the frame of the ‘principal axes’
I have a few remarks:
Here is in the principal axes frame of reference. For the quaternion we have, applying the quaternion algebra, and where vectors are treated as quaternions with zero scalar part. Note that the angular velocity in the principal axes frame of reference was used. Therefore the multiplication with the angular momentum vector is on the right ().
With kind regards,
Update: still to do
We need an implementation of TriangleWalls that allows only one contact per wall group
HC: Convex works, concave not
JA: Uses TriangleWalls for Sydney code, but could do without
TP: Needs it for the screw conveyor, Luca advises against it.
Update: Hong on holiday
Three build systems. How to merge together.
Oomphlib coupling wroks again; using an external oomphlib directory and the vendor branch.
|Migration to git|
We will move from svn to git, using gitlab.utwente.nl
For everyone who is new to git or wants to know more about it: Git Course