Disk
Disk features represent different types of mounting on the main rotor and are mainly used to provide inertial information of these mountings. These features will affect the dynamics of the rotor. Typical examples of mountings include flywheels, pulleys, gears, impellers, and rotor-blade assemblies. Mounting offset is also accounted for in modeling the inertial effects. Therefore, mass, moment of inertia, and offset are the inputs for this feature. If the moment of inertia is specified about the center of mass of the mounting, which has an offset from the mounting point, then the moment of inertia tensor about the mounting point is given by
where roff is the vector from the centroid of the mounting to the mounting point on the rotor, and I is the identity tensor. The center of mass of the mounting can be specified using two methods: relative to the mounting point or by absolute position.
The offset of the mounting point from the center of mass is
,
for relative position or
for absolute position.
The contribution to the virtual work, including the frame acceleration and offset effect, is
where Is is the moment of inertia about the mounting point in the spatial frame and is given by