Mechanical APDL Structural Analysis Guide

CORIOLIS -- Used for including Coriolis effects in the modal analysis when the base analysis is

static.

9.5. Considerations for Rotating Structures

When modeling rotating machinery, there are special considerations for performing a linear perturbation
modal analysis that includes Coriolis effects.

If the base analysis is a full transient analysis, it is recommended that you include Coriolis effects
(CORIOLIS command) in the full transient analysis to achieve an accurat e linear perturbation analysis.
These Coriolis effects are automatically carried over to the linear perturbation analysis.

If the base analysis is a static analysis, then the linear perturbation procedure depends on whether the
Coriolis effects are based on a rotating reference frame or a stationary reference frame formulation. The
difference comes from the fact that in a rotating reference frame, the stiffness matrix is modified by
the spin-softening effect.

Stationary Reference Frame

1. Static solve: Issue the OMEGA/CMOMEGA commands only if the centrifugal force is needed in the
   prestress solution.


2. First linear perturbation solve: Issue the CORIOLIS command. Use LoadControl = INERKEEP on the
   PERTURB command to retain OMEGA/CMOMEGA loads if they were defined in the base analysis.


3. Second linear perturbation solve: Issue OMEGA/CMOMEGA commands to specify the rotational velocity
   if not done in the base analysis.

Example input to perform perturbed modal solve in a stationary reference frame:

/solution

antype, static! Static analysis

nlgeom, on! Non-linear analysis

rescontrol, define, all, 1! Define restart files

f,...! Define loads (for example nodal force)

solve

finish

/solution

antype, static, restart, last, last, perturb! Do a linear perturbation analysis

perturb, modal,,, nokeep! Perturbation modal

coriolis, on,,, on! Coriolis in a stationary reference frame

solve, elform! First Perturbation solve (form the stiffness matrix)

modopt, qrdamp,...! Choose the eigensolver (for example QRDAMP)

mxpand, ...! Expand the solutions

omega,...! Define the rotational velocity

solve! Second Perturbation solve (solve the eigenproblem)

finish

Rotating Reference Frame

1. Static solve: Issue the OMEGA/CMOMEGA commands.


2. First linear perturbation solve: Issue the CORIOLIS command to include the Coriolis effect, and use
   LoadControl = INERKEEP on the PERTURB command to retain OMEGA/CMOMEGA loads.


3. Second linear perturbation solve: No specific commands are needed.

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Considerations for Rotating Structures