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[hwmachine]

[hwmachine]

Hi everyone.
I am doing harmonic response analysis by ANSYS APDL to evaluate the variation of the natural frequency of the rotating structure causing by the unbalanced excitation. 

First I build a simple equal-radius cylindrical shaft using BEAM188. Second I give it a constant force on one end side. Then, I make it rotate in the axial direction with using CMOMEGA, also the Coriolis effect is activated. Finally, the SYNCRO is set up as the unbalanced excitation. The screenshots are shown below.




However, during the postprocssing, I found the peak value variation of amplitude-frequency response curve is not what I supposed, for example, when the ratio in SYNCRO is 3, then the frequency of the peak value should be twice of the frequency when I change the ratio in SYNCRO to 2, which can be considered as the resonance of the rotating structure is advanced because of the ratio of unbalaced excitation is increased: 3-1=2*(2-1). The screeenshot below shows how the frequency changed when the ratio = 2, 3, 4. X-axis is the frequency in HARFRQ (0-10000Hz), y-axis is the displacement amplitude.

Can someone please tell me if I made some mistakes in doing unbalance harmonic response analysis, or maybe what I supposed is wrong: the variation of natural frequency is not proportional to the ratio in SYNCRO?
Many thanks!!!

[Ashish Khemka]

Hi,

Please see if the following link helps you:

Chapter 7: Rotordynamic Analysis Examples (ansys.com)

How to access the ANSYS Online Help

Regards,

Ashish Khemka