Campbell Diagram
For eigenfrequency analyses, Campbell diagrams are very useful for determining potential critical speeds. Therefore, a Campbell Diagram is generated as a result template for each of the rotor interfaces, namely, the Solid Rotor; the Solid Rotor, Fixed Frame; and Beam Rotor interfaces. This can be added from the Add Result Template window.
The default Campbell Diagram uses a Color Expression node to indicate the directivity of the modes. A purple, green or red color will indicate if the corresponding mode is a backward, straight-line, or forward mode respectively.
Since the equations in the Beam Rotor and Solid Rotor, Fixed Frame interfaces are formulated in a fixed reference frame, the Campbell Diagram shows the eigenfrequencies in the fixed reference frame.
The equations in the Solid Rotor interface are, however, formulated in a corotating reference frame. Therefore, the eigenfrequencies computed by this interface can be considered as frequencies of the vibration observed from the corotating frame. The frequencies in the fixed frame and the corotating frame are related to each other by a very simple relation. For a forward whirl mode, an eigenfrequency in the corotating frame can be converted to an eigenfrequency in the fixed frame by adding the angular speed of the rotor. Similarly, an eigenfrequency in a backward whirl mode can be converted to fixed frame by subtracting the angular speed of the rotor.
For details about the identification of the whirl modes, see Identification of Whirl in the theory section.
Refer to the Forward and Backward Whirl section for the different variables provided in the interface to identify the whirl.
When you have solved for the eigenfrequencies, you can also evaluate forward and backward natural frequency variables, named <phys>.omegaf and <phys>.omegab (for example, rotbm.omegaf), respectively, in the fixed frame.