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Moment of Inertia, what is the reference system

Hello,

I am specifying the moment of inertia for the two wheeler vehicle model. I wanted to know if the moment of inertia in motion view is set according to the global coordinate or the center of gravity of the body. Then I'll be extracting those values only from the CAD file. One more thing, the values of Ixy, Ixz, and Iyz are mostly set to 0 for all the components by default in motion view, is this because the scooter model is assumed to be symmetrical about y axis ? or can we specify these values as well?

Regards

Draucis

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MotionView/MotionSolve

Accepted answers

Praful

Hello Draucis

Inertias can be specified in any coordinate system. By default, inertias are specified in the CM coordinate system (which is at the CG)

The inertia coordinate system can be changed from CM to any other by turning on the Use inertia coordinate system.

If you are providing the inertias from CAD or any other tool with respect to the CG, make sure the 2 coordinate system orientations (CAD as well as MV) match.

As far as the products of inertia (Ixy, Iyz & Izx), they are default 0, indicateing they are considered symmetrical about each of the axes. You can change them as you wish for your model. Make sure that they are represented correctly. Pay attention to any inertia specific warnings from the solver.

Regards

Praful

All comments

Praful

Hello Draucis

Inertias can be specified in any coordinate system. By default, inertias are specified in the CM coordinate system (which is at the CG)

The inertia coordinate system can be changed from CM to any other by turning on the Use inertia coordinate system.

If you are providing the inertias from CAD or any other tool with respect to the CG, make sure the 2 coordinate system orientations (CAD as well as MV) match.

Regards

Praful

draucis

Hello Draucis

Inertias can be specified in any coordinate system. By default, inertias are specified in the CM coordinate system (which is at the CG)

The inertia coordinate system can be changed from CM to any other by turning on the Use inertia coordinate system.

If you are providing the inertias from CAD or any other tool with respect to the CG, make sure the 2 coordinate system orientations (CAD as well as MV) match.

As far as the products of inertia (Ixy, Iyz & Izx), they are default 0, indicateing they are considered symmetrical about each of the axes. You can change them as you wish for your model. Make sure that they are represented correctly. Pay attention to any inertia specific warnings from the solver.

Regards

Praful

Thank you so much, Praful, your constant support is appreciated. And yes the coordinate systems of the two software are already aligned, I'll look for the warnings from the solvers if any.

Thanks again

Draucis

Praful

Thank you so much, Praful, your constant support is appreciated. And yes the coordinate systems of the two software are already aligned, I'll look for the warnings from the solvers if any.

Thanks again

Draucis

You are always welcome Draucis.

There are 2 ways that the CAD/CAE tools report or use products of inertia. If you look at the inertia matrix in a dynamic equation the product of inertia are negated. Based on this, some tools report with the negative sign while others report without that negative sign.

MV uses without the negative sign and the solver applies the negation. In my experience, most CAD softwares and MV match,, while FE softwares are likely to report with the negative sign.

Regards

Praful

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