A rotordynamic analysis involves most of the general steps found in any Mechanical APDL analysis, as follows:
| Step | Action | Comments |
|---|---|---|
| 1. | Build the model |
A rotating structure generally consists of rotating parts, stationary parts, and bearings linking the rotating parts to the stationary parts and/or the ground. Understanding the relationships between these parts is often easier when the model is constructed to separate and define them. For more information about how to build the different parts, see Selecting and Components in the Basic Analysis Guide |
| 2. | Define element types |
The elements that you select for the rotating parts of your model must support gyroscopic effects. The CORIOLIS command documentation lists the elements for which the gyroscopic matrix is available. All rotating parts must be axisymmetric. Model the stationary parts with any of the 3D solid, shell, or beam elements available in the MAPDL element library. You can also add a stationary part as a substructure. For more information about how to generate and use a superelement, see Benefits of Substructuring in the Substructuring Analysis Guide. Model the bearings using either a spring/damper element COMBIN14, a general stiffness/damping matrix MATRIX27, a bearing element COMBI214, or a multipoint constraint element MPC184. |
| 3. | Define materials | Defining the material properties for a rotordynamic analysis is no different than defining them in any other analysis. Use the MP or TB commands to define your linear and nonlinear material properties. See Defining Material Properties in the Basic Analysis Guide. |
| 4. | Define the rotational velocity. | Define the rotational velocity using either the OMEGA or CMOMEGA command. Use OMEGA if the whole model is rotating. Use CMOMEGA if there is a stationary parts and/or several rotating parts having different rotational velocities. CMOMEGA is based on the use of components, see Selecting and Components in the Basic Analysis Guide |
| 5. | Account for gyroscopic effect | Use the CORIOLIS command with
RefFrame = YES to take into account
the gyroscopic effect in all rotating parts, as well as the rotating
damping effect (RotDamp = YES). |
| 6. | Mesh the model | Use the APDL meshing commands to mesh the parts. Certain areas may require more detailed meshing and/or specialized considerations. For more information, see the Modeling and Meshing Guide. |
| 7. | Solve the model |
The solution phase of a rotordynamic analysis adheres to standard MAPDL conventions, keeping in mind that the gyroscopic matrices (as well as possibly the bearing matrices) may not be symmetric. Modal, harmonic and transient analyses can be performed. Performing several modal analyses allows you to review the stability and obtain critical speeds from the Campbell diagrams. A harmonic analysis allows you to calculate the response to synchronous (for example, unbalance) or asynchronous excitations. A transient analysis allows you to study the response of the structure under transient loads (for example, a 1G shock) or analyze the startup or stop effects on a rotating spool and the related components. Prestress can be an important factor in a typical rotordynamic analysis. You can include prestress in the modal, transient, or harmonic analysis, as described in the Structural Analysis Guide for each analysis type. |
| 8. | Review the results | Use POST1 (the general postprocessor) and POST26 (the time-history postprocessor) to review results. Specific commands are available in POST1 for Campbell diagram analysis (PLCAMP, PRCAMP), animation of the response (ANHARM) and orbits visualization and printout (PLORB, PRORB). |