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Old Apr 5th 2019, 09:05 AM   #1
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Inertial "moment" of a solid given an inertia tensor

Hi all,

I am programming some software computing inertial forces of some moving structure.

So far, the structure have been represented as a cloud of mass points. For each mass point, inertial forces are computed using some formulas like in this article: https://fr.wikipedia.org/wiki/Force_...#Formalisation

That is: some "Euler force" and centrifugal force are computed (Coriolis forces are neglected).

The program works well and was validated.

Now, there is some need to give to structure sub-elements not only a mass, but also an inertia tensor :

____| Ixx Ixy Ixz |
I = | Iyx Iyy Iyz |
____| Izx Izy Izz |

Intuitively, I would say adding some inertia matrix to the element will lead to some "inertial" (fictitious) torque on it, as well as there are "inertial" forces exerted on mass points.

Does anyone have an idea how to model these "fictitous moments" (provided they exist) ?
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Old Apr 5th 2019, 11:57 AM   #2
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The elements in the interia tensor are not true moments, they are moments of inertia.

The leading diagonal entries (with repeated suffixes) give the overall moI.

The off diagonal entries (with cross suffixes) give the spatial distribution of these inertias.
that is in terms of rotational inertias the spatial distribution of the masses.
These entries are called products of inertia.
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Last edited by studiot; Apr 5th 2019 at 12:15 PM.
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Old Apr 5th 2019, 05:16 PM   #3
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Nice to see the presentation of that navy again...Chen's first language is not English...haha...
Hi, taalf, it seems to be differrent methods of calculation about rigid body issues, no additional force. (or say torque)

Last edited by neila9876; Apr 5th 2019 at 05:18 PM. Reason: corerct word
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  Physics Help Forum > High School and Pre-University Physics Help > Kinematics and Dynamics

fictitious, inertia, inertial, moment, solid, tensor

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