Campbell Diagram 1

[danielho]

I would like to ask, for a Campbell Diagram, are the natural frequencies plotted in the diagram corresponds to a bearing of constant stiffness and damping properties?

Also, is there anyone who is familiar to the SAMCEF software for the ROTOR module? Can this software be used to plot the critical speed map because as far as I have tried, I can't seem to model the speed dependent stiffness and damping properties of a fluid film bearing using this software.

 

[MikeyP]

No, when operating at high speed, hydrodynamic bearings have stiffness and damping properties that vary with speed and hence the natural frequency varies with speed.

M

--
Dr Michael F Platten

 

[danielho]

thanks for your reply.
If that's the case, then what is the difference between a campbell diagram and the critical speed map?

 

[MikeyP]

It depends on your definition of those things! There is no standard definition. In rotordynamics terms, a Campbell diagram plots natural frequency vs RPM with the shaft orders plotted on top, You can then see the danger areas where natural frequency coincides with rotation order (critical frequencies).

One example of what I would call a critical speed map just shows the variation in natural frequency with bearing stiffness and does not relate bearing stiffness to a particular speed.

... But that is just the definition as per the software that I use.

M

--
Dr Michael F Platten

 

[danielho]

I see...it is one of the requirement of my final year project, that i plot a critical speed map of the centrifugal compressor, however, the FEM software i am using doesn't seem to be able to do just that!

From the papers I read, I understand that the undamped critical speeds may be obtained by superimposing the speed dependent direct stiffness curves on the critical speed map.

I guess I was just confused by the critical speeds obtained in a Campbell Diagram and that from a Critical Speed Map, as I was trying to find the connection between them.

 

[MikeyP]

FYI the rules of this website state that students are not allowed to post questions.

M

--
Dr Michael F Platten