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No output from MomentOfInertia[ ]?

Posted 3 years ago

Hello, I am trying to calculate the moment of inertia of a hyperboloid body, but wolfram always gives me the same input as output ! This is my input:

MomentOfInertia[
  ImplicitRegion[
    x^2/A^2 + y^2/A^2 - z^2/C^2 <= 1, {x, y, z}] /. {A -> 2, 
    C -> 6}] // MatrixForm

I want it as a symbolic calculation if it is posible. And can anybody explaines to me how can i apply the following moments formula on the hyperboloid body:

Underscript[\[Integral], {x,y,z}\[Element]reg](y^2+z^2  -x y -x z
-y x    x^2+z^2    -y z
-z x    -z y   x^2+y^2
)

moments formula

Any help, please, it's very important to me.

POSTED BY: Ibrahim Bakry
2 Replies

Your hyperboloid is unbounded:

RegionMeasure[
 ImplicitRegion[(x^2/A^2 + y^2/A^2 - z^2/C^2 <= 1) /. {A -> 2, 
    C -> 6}, {x, y, z}]]

As for the integral, I would rather avoid the underscript and other 2D notations:

Integrate[{{y^2 + z^2, -x y, -x z},
   {-y x, x^2 + z^2, -y z},
   {-z x, -z y, x^2 + y^2}},
  Element[{x, y, z}, Cuboid[]]] // MatrixForm
POSTED BY: Gianluca Gorni
Posted 3 years ago

Thank you, after bounding the hyperboloid I got some results, but it takes a long time!

POSTED BY: Ibrahim Bakry
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