Optionally natural frequencies and harmonic response can be calculated using the software. The setting Calculate natural frequencies has to be activated for this.
First the nonlinear static equilibrium is calculated. Then the natural frequencies and the harmonic response are calculated using the linear equations of motion with the tangent stiffness matrices from the static equilibrium. Therefore the results are only valid for small amplitudes around the static solution.
The natural frequencies are calculated using the given rotation speed. The critical frequencies are the intersections between shaft speed and natural frequency at this shaft speed. The critical frequencies are shown in a special report or they can be found in the Campbell diagram.