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  1. OMG Issue

CAD — Several properties in the CadBrep::PropertyStruct need clarification.

  • Key: CAD-42
  • Legacy Issue Number: 4653
  • Status: closed  
  • Source: NASA ( Russ Claus)
  • Summary:

    double inertial_moment_spherical;
    double gyration_radius_spherical;
    CadUtility::VectorStruct first_moments_centroidal;
    CadUtility::VectorStruct inertial_moments_centroidal;
    CadUtility::VectorStruct inertial_products_centroidal;
    CadUtility::VectorStruct principle_moments_centroidal;
    CadUtility::VectorStruct gyration_radii_centroidal;

    are unclear.

    Jim Stevens identified the following:

    The "centroidal" moments are the various mass properties with respect to the center of mass for the body. This is the more "typical" case for mass properties. They correspond to similar mass property calculations in the structure that are with respect to a specific coordinate system.
    Principle moments are moments inertia along the principle axes through the center of gravity of an object.
    When defining a moment of inertia around an arbitrary axis thru the center of mass you end up with product terms. There is
    one axis definition for which the product terms are zero, which is called the principle axis and the moments of inertia when
    using that axis definition are the principle moments.
    Radius of gyration is related to the moments of inertia and the mass along each axis.
    I am not sure about the meaning of first moments. I am pretty sure that inertial_moment_spherical and
    gyration_radius_spherical have to do with representing the model with a single sphere that would have
    the same overall inertial characteristics as the analyzed body.
    Jim Stephens

    Based on Jim's comments I am not certain that we need the first moments or the spherical inertial moment and gyration radius.

  • Reported: CAD 1.0b1 — Wed, 31 Oct 2001 05:00 GMT
  • Disposition: Resolved — CAD 1.0
  • Disposition Summary:

    see above

  • Updated: Fri, 6 Mar 2015 20:58 GMT