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A
atibbitts1-Visitor
1-Visitor
July 14, 2015
Question

Negative Moments of Inertia

  • July 14, 2015
  • 4 replies
  • 8751 views

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?

4 replies

C
Chris321-Topaz I
21-Topaz I
July 15, 2015

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

A
atibbitts1-VisitorAuthor
1-Visitor
July 15, 2015

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.

C
Chris321-Topaz I
21-Topaz I
July 15, 2015

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.

A
atibbitts1-VisitorAuthor
1-Visitor
July 15, 2015

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

M
MichalLukac8-Gravel
8-Gravel
July 17, 2015

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

    J
    jbush11-Garnet
    11-Garnet
    January 16, 2020

    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".

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