If there are multiple rotors present in the model, or if the rotor is very long, whirl modes can be mixed. In such rotor systems it is difficult to tell if the whirl mode is forward or backward. Therefore, the transformation of the eigenfrequencies from the corotating to the fixed frame as explained above fails. The Campbell diagram may not show a correct result in this case. If you encounter such a case it, is better to plot only <phys>.omega in the Campbell diagram. This variable should be interpreted in the respective frame the interfaces are modeled.