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Element mass properties - Product of Inertia sign convention

Element mass properties - Product of Inertia sign convention

Element mass properties - Product of Inertia sign convention

(OP)
Hi everybody,

I am glad to be part of eng-tips forum community - definitely one of the most helpful of the web - and I am very thankful to be able to write my very first post about Femap w NX Nastran.

I am an MSc student in mechanical engineering and I am working on my final thesis, dealing with modeling and simulation of ICE sub-assemblies dynamics by means of a lumped parameters approach.
I have the FE model of the components to be represented as rigid bodies, described by their mass and inertia properties.

Here comes my question: when asking Femap to calculate mesh mass properties, what is the sign convention adopted for products of inertia Ixy, Iyz, Izx?

As far as I am concerned, the following definition stands for inertia matrix:


The former can be represented as

if we assume




But sometimes, some authors use the following:




In Femap "mass properties tool" output, what is the sign convention adopted?
Moreover, aa I right assuming the same definition holds for both mass properties output and mass element definition?

I haven't been able to find any hint either in Femap and NX Nastran help.

Thank you for your kind attention.

Ciao,
Edo

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