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07-14-2015
03:42 PM

07-14-2015
03:42 PM

Negative Moments of Inertia

I am struggling to understand why my assembly is displaying negative values of IXY and IXZ my IXX is correct with a positive value. The negative IXY and IXY seem to be correct but negative which is impossible?

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07-15-2015
09:32 AM

07-15-2015
09:32 AM

Re: Negative Moments of Inertia

Do you have assigned (as apposed to calculated) mass values? This can create negative numbers.

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07-15-2015
12:56 PM

07-15-2015
12:56 PM

Re: Negative Moments of Inertia

Yes, Unfortunately I have shrinkwrap models where I don't have the originals and I have to assign the mass and moments of inertia.

Other than getting real models do you have any suggestions on how to get this to represent correctly.

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07-15-2015
01:07 PM

07-15-2015
01:07 PM

Re: Negative Moments of Inertia

The only way I know if is to get the correct information and type it in. You don't necessarily need the original models, you just need the info. For instance if your shrinkwrap represents outside vendor or customer geometry maybe you could get it from them. Short of that I don't have any additional suggestions.

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07-15-2015
05:09 PM

07-15-2015
05:09 PM

Re: Negative Moments of Inertia

I appreciate the response. I have been grappling with this for some time. If I discover anything I will share. I can only guess my coordinate systems somewhere is rolled in the wrong direction. But I haven't figured out which one

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07-17-2015
05:47 AM

07-17-2015
05:47 AM

Re: Negative Moments of Inertia

Why do You think negative value for Ixy Ixz.. are impossible? It depends on orientation of coordinate system.

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01-15-2020
10:14 PM

01-15-2020
10:14 PM

Re: Negative Moments of Inertia

I agree with MichalLukac, only the moments of inertia, Ixx Iyy and Izz, must be positive.

Ixy, Ixz, and Iyz are called the products of inertia and they can be negative. Search up definition of "inertia tensor".