You can observe inertia effects, applied via the CORIOLIS command, in either a stationary reference frame or a rotating reference frame. In both cases, you specify angular velocity by issuing an OMEGA or CMOMEGA command.

The dynamic equation incorporating the effect of rotation is given by

where [M], [C] and [K] are the structural mass, damping, and stiffness matrices, respectively.

[K_SP] is the spin softening matrix due to the rotation of the structure. It changes the apparent stiffness of the structure in a rotating reference frame.

[B] is the rotating damping matrix. It changes the apparent stiffness of the structure in both a stationary and a rotating reference frame. Note that it is not activated by default, but by using the RotDamp flag on the CORIOLIS command. In a stationary reference frame, this effect is produced when damping is present in a rotating part (see Adding Damping in the Rotordynamic Analysis Guide). In a rotating reference frame, this effect only comes from stationary bearings (COMBI214).

[G] is a "damping" matrix contribution due to the rotation of the structure. It is usually called Coriolis matrix in a rotating reference frame, and gyroscopic matrix in a stationary reference frame.

[K_SP], [B], and [G] are rotational-velocity-dependent matrices.

{F} is the external force vector in the stationary reference frame. In a rotating reference frame, it is the sum of the external force and the effect of the centrifugal force.

Without the inertia effect applied via the CORIOLIS command, the program does not generate the [G] and [B] matrices, and the usual effect of the angular rotation velocity specified by the OMEGA or CMOMEGA command applies. An exception exists, however, involving a nonlinear transient analysis using element MASS21; in this case, the inertia effect due to rotation applied via an IC command (or a D command over an incremental time) is included without having to issue the CORIOLIS and OMEGA or CMOMEGA commands.

For additional information, see Acceleration Effect and Rotating Structures in the Mechanical APDL Theory Reference.