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CompositeInertia
2D/3D

CompositeInertia[{centroid1, mass1, inertia1}, ... , {centroidn, massn, inertian}] returns the list {centroid, mass, inertia} of the inertia properties of a composite body B made up of the n specified subcomponents.
• In Modeler3D, arguments to CompositeInertia can have the form {centroidn, massn, inertian, rotationn} to specify subcomponents that are rotated relative to the composite body B.

• Given a local reference frame XYZ_B affixed to the composite body B, each argument to CompositeInertia specifies the inertia properties of a subcomponent of B, in the XYZ_B reference frame.
• Each centroidi is specified by {x, y} or {x, y, z} and each massi by a scalar.
• In Modeler2D each inertiai is specified by a scalar, while in Modeler3D each inertiai is given as a list of the elements of the inertia matrix, {Ixx, Iyy, Izz, Ixy, Iyz, Izx} or a full inertia matrix.
• All given inertia properties are assumed to be centroidal.
• If the inertia properties of a 3D subcomponent are known in a non-XYZ_B reference frame xyz_B, the rotationi argument is used to specify the rotation of the xyz_B reference frame, relative to XYZ_B. The rotationi are specified by {angle, axis}, a virtual rotation vector, or a set of Euler parameters.
• If any of the subcomponents are voids, their mass and inertia properties must be negated so that the inertia of the subcomponent is subtracted from the composite body.
• See also:
ParallelAxis, PrincipalAxes.

Further Examples

Load the Modeler3D package.

Here are inertia properties transformed from a noncentroidal to centroidal reference frame.

Here are the principal axes of the resulting inertia properties.

This rotates the original inertia matrix into the principal frame.

Here is the result of combining two sets of inertia properties.


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