[hw-Multiphysics]

Hi all, I am doing a harmonic response analysis of a rotor that rotates at a certain angular speed, and I currently have two problems now.

1. Why I cannot apply a constant speed in the Harmonic Response? (Like the "rotational velocity" in the static structural analysis)

2. To represent the rotating of my rotor in Harmonic Response, I use a "Rotating Force" with a Synchronous Ratio and an Amplitude. If using this approach, the speed updates at every frequency step. I am not sure whether this is correct.

Many thanks!

[hw-Multiphysics]

Is it because the rotating speed cannot expressed as a sinusoidal load, which violate the definition of harmonic response?

[Martin_Sz]

In harmonic response analysis, applying a constant speed like in static structural analysis isn't possible because harmonic analysis focuses on the response of a system to varying excitation forces over a range of frequencies.
Instead, harmonic response analysis utilizes a rotating force with a synchronous ratio and amplitude to simulate a rotating rotor. The synchronous ratio relates the force frequency to the rotational speed of the rotor. This approach accurately captures the vibratory response of the rotor at different excitation frequencies.
So, using a rotating force with a synchronous ratio and amplitude in harmonic response analysis is the correct way to represent a rotating rotor.

[hw-Multiphysics]

Originally Posted by Martin_Sz

In harmonic response analysis, applying a constant speed like in static structural analysis isn't possible because harmonic analysis focuses on the response of a system to varying excitation forces over a range of frequencies.
Instead, harmonic response analysis utilizes a rotating force with a synchronous ratio and amplitude to simulate a rotating rotor. The synchronous ratio relates the force frequency to the rotational speed of the rotor. This approach accurately captures the vibratory response of the rotor at different excitation frequencies.
So, using a rotating force with a synchronous ratio and amplitude in harmonic response analysis is the correct way to represent a rotating rotor.

Many thanks for your generous help!
My idea is to apply an unbalanced excitation by applying rotating forces with different synchronous ratios which will affect the peak response frequency of the rotor.

I am currently doing harmonic response analysis using a 1D rotor model. If applying the rotating force (ratio = 1, amplitude = 100N), without adding any other loads or boundary conditions, the peak response amplitude happens in 394.5Hz, which is shown in figure 1 below.

However, if I use the same rotating force, only add a Commands(APDL): "Coriolis,on,,,off" ,the peak response amplitude happens in 198Hz, shown in figure 2 below.

From the help document, I learned that the command I mentioned before (Coriolis,on,,,off) means to transfer from the static reference frame to the rotating reference frame. But why the peak response frequency changes only in the rotating reference frame?

Many thanks for you help!
Figure 1
Without Commands(APDL).PNG
Figure 2
With Commands(APDL).PNG