yade-users team mailing list archive

[Vasileios Angelidakis <question680409@xxxxxxxxxxxxxxxxxxxxx>]

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

-- 
You received this question notification because your team yade-users is
an answer contact for Yade.