Is there any way to constraint Simscape solid object custom inertial properties for consistency?

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ENRICO
ENRICO 2024-10-5
评论： ENRICO 2024-10-14
Indeed it appears to be possible to set centre of mass outside convex envelop of solid, as well to assign unconsistent values for inerrtia moments and products. Some contraint I guess shall be imposed?

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Manikanta Aditya
Manikanta Aditya 2024-10-8
编辑：Manikanta Aditya 2024-10-8
Hi Enrico,
Yes, you can impose constraints on custom inertial properties in Simscape to ensure consistency. Some of the points are:
  • Center of Mass: The center of mass (COM) should typically be located within the convex hull of the solid. If the COM is positioned outside this envelope, it can lead to physically incorrect behavior, such as unrealistic movements or rotations.
  • Inertia Matrix: The inertia matrix should be symmetric and positive definite. This means that all the principal moments of inertia (Ixx, Iyy, Izz) should be positive, and the determinant of the inertia matrix should be positive. The inertia tensor should be symmetric. This implies that the products of inertia (Ixy, Ixz, Iyz) should satisfy the symmetry conditions: Ixy = Iyx, Ixz = Izx, and Iyz = Izy.
  • CAD Import: If you are importing the solid from a CAD file, ensure that the inertia properties are correctly defined in the CAD software before importing
Refer to the following documentation to know about specifying custom inertias:
Hope it helps.
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Manikanta Aditya
Manikanta Aditya 2024-10-10
You can use MATLAB functions to determine if a point lies within a given geometry. One useful function is inpolygon, which checks if points are inside a polygon. For 3D geometries, you might need to use more advanced techniques, such as computational geometry methods or specific functions from the MATLAB File Exchange that handle 3D point-in-polyhedron checks.
While Simscape does not directly support defining a density distribution function for custom inertia properties, you can approximate this by dividing your solid into smaller elements, each with its own density and inertia properties. This approach can be complex and may require custom scripting to ensure all elements are consistent with the overall geometry and mass distribution.
ENRICO
ENRICO 2024-10-14
I agree with all you said, but last suggestion how to manage density looks really more complex than the problem in itself in my perspective, since in the end one have just to compute integral average on whole volume to get lumped equivalent sets... Still I think should be managed by the tool more than with a external codiing, for sake of efficiency. In the end is all in one sequence step with inertial parameters calculation.
I'll reflect a while whether do or less something for.
Thanks for now.

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