>> I like my point of view very much :-) ... > No luck then. :( it was just explanation why I did the answer. In general I agree with both options, just wanted to "defend" my approach. I also think we come to philosophy area in many places here :-) especially because finally one arrives to the same results and formulas from both sides.
>>> I would suggest that Cundall/Yade DEM makes no assumption of rigidity/overlaps. >> but does not make any assumption on non-rigidity at the same time, right? :-) > It does. Starting from an elastic force-displacement equation in the first place really implies non-rigidity. see my previous (slightly modified): - assuming the particles rigid - computing the force under assumption that in reality there would be no overlap and some deformation. Then the elastic force-displacement equation just computes force assuming some deformation in reality, but the model of particle may remain rigid. >> Relative motion between bodies says nothing about (non)rigidity of the bodies, or? > If you have a sticking (elastic) contact it means two material points from two different objects are co-moving. If at the same time the reference position-orientation of the inertial frames attached to each particle are not undergoing rigid body motion the only solution is that there is an internal deformation somewhere. Relative motion is just relative motion. You can define it both for rigid and deformable particles. In both cases it is just a consequence of the previous paragraph and decision if particles are or are not rigid :-) > But my claim is that there is not one context in which the geometrical overlap would be justified. > Can you evaluate this volume change by the overlaps? NO! Absolutely not. > Overlapped volume is not an approximation of anything. Yes, I agree that from physical point of view, the "purely geometrical" overlaps does not make much sense. In the launchpad question I just described how I would do it, but with no experience in the topic.. But it would be nice to actually compare this geometrical and physical approaches :-) maybe "by chance" the geometrical (non-pysical) overlap justification is not that far from physical evaluation, even for the first sight there is no reason for it (I have a fresh experience with something similar). cheers Jan
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