New question #680409 on Yade:
https://answers.launchpad.net/yade/+question/680409
Hi,
I think I have spotted a mistake in the calculation of the Inertia Tensor for
the "Tetra" shape class (since the day calls for inertia-related amendments :)
). In the Tetra.cpp script, the Inertia Tensor is calculated exactly as in [1].
The thing is, this paper has a typo, and although the non-diagonal inertia
values "a', b', c'" (stated in the source code as: "a__ , b__ , c__") are
calculated correctly, their position in the Inertia tensor seems to be false.
In particular, the terms "-b__" and "-c__" should be in each other's place,
since these terms are defined as:
b' (=b__) term: $$b' = \int_{D} μ*x*z dD $$ : Involving x-z coordinates: should
be present in the (0,2) (2,0) cells of the tensor
c' (=c__) term: $$c' = \int_{D} μ*x*y dD $$ : Involving x-y coordinates:
should be present in the (0,1) (1,0) cells of the tensor
I see this has also been spotted in the Polyhedra_support.cpp script, where the
correct tensor is used:
Matrix3r ret; ret<<
a , -c__, -b__,
-c__, b , -a__,
-b__, -a__, c ;
return ret;
[1] https://thescipub.com/pdf/10.3844/jmssp.2005.8.11
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