Issue 4653: Several properties in the CadBrep::PropertyStruct need clarification. (cad-ftf) Source: NASA (Mr. Russell W. Claus, claus@grc.nasa.gov Russell.W.Claus@nasa.gov russell.w.claus@nasa.gov) Nature: Uncategorized Issue Severity: 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. Resolution: see above Revised Text: The PropertyStruct is modified (in section 2.5.14) to: struct PropertyStruct { double surface_area; double volume; double mass; double solid_density; // Solid density is provide as a reference value CadUtility::VectorStruct centroid; CadUtility::VectorStruct inertial_moments; CadUtility::VectorStruct inertial_products; CadUtility::VectorStruct principle_x_axis; CadUtility::VectorStruct principle_y_axis; CadUtility::VectorStruct principle_z_axis; CadUtility::VectorStruct gyration_radii; // Items relative to the frame CadUtility::VectorStruct inertial_moments_centroidal; CadUtility::VectorStruct inertial_products_centroidal; CadUtility::VectorStruct principle_moments_centroidal; CadUtility::VectorStruct gyration_radii_centroidal; // Items relative to the centroid double surface_area_error; double volume_error; double mass_error; // Error Values }; With supporting documentation as: surface_area Value indicates surface area of geometric body. volume Volume of geometric body. mass Mass of geometric body. solid_density Solid density of body which is provided for reference. centroid Centroid or center-of-mass for geometric body. inertial_moments Moments of inertia relative to the frame. inertial_products Inertial products relative to the frame. principle_x_axis Principal x axis relative to the frame. principle_y_axis Principal y axis relative to the frame. principle_z_axis Principal z axis relative to the frame. gyration_radii Radius of gyration along each axis. inertial_moments_centroidal Moments of inertia relative to the centroid. inertial_products_centroidal Inertial products relative to the centroid. principle_moments_centroidal Moments of inertia along the principle axes through the center of gravity of a geometric body. gyration_radii_centroidal Radius of gyration through the centroid. surface_area_error Error associated with surface area calculation. volume_error Error associated with volume calculation. mass_error Error associated with mass calculation. Actions taken: October 31, 2001: received issue July 5, 2002: closed issue Discussion: The identified data members need additional documentation and some rarely-used items were removed End of Annotations:===== X-Sender: claus@popserve.grc.nasa.gov X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Wed, 31 Oct 2001 14:43:21 -0500 To: cad-ftf@omg.org From: "Russell W. Claus" Subject: PropertyStruct issue for CAD Services V 1.0 Cc: jcad_services@yahoogroups.com Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; format=flowed X-UIDL: M2ad9dKad9Gml!!gN/e9 Issue: Several properties in the CadBrep::PropertyStruct need clarification. Discussion: 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. ------------- Russ Claus NASA Glenn (216) 433-5869 / fax (216) 433-5802