Torsional Analysis of Motor shaft

An output depends on the input and the way it was processed. Since you do not give any indication about the way you came to the result it is quite difficult to give an explanation about the critical frequency you obtained.

Are the coupling torque values and the stresses (where are they located?) you mention computed or measured? What type of motor? of coupling (stiffness linear or not?internal damping?)? of inertial load? What generates the harmonics?

The motor is squireel cage type and torsional analysis is carried out for reciprocating gas compressor. Motor rpm is 596. Vibratory stress values are below 3000 PSI of all the elements. Flywheel selected is found ok.

Yeah you are true that output depends upon input....i am performing this torsional analysis on one of the analytical software. The values and other charts are computed and measured with this software.

"The values and other charts are computed and measured with this software."

You should NOT use the term "measured" since the values are computed and "displayed" by SAME soft. "Measure" means use of a device to quantify a signal from a sensor. It is not your case.

I sincerely doubt your results are correct, not only because of what you gave but also because of the soft which can have an error. It is not the 1st time it could happen.

Bring more details as number of cylinders for the compressor, and other aspects of the system you analyse. The best is to make a sketch with inertia and compliances (give values) indicating where the perturbing torque is introduced, its value versus time, aso.

Any way for such machines the trend is to have a stiff shaft and work in sub-critical domain. In rotary machines there applications where the working rpm is in the overcritical domain but it implies a very fast crossing of the critical range which is not possible with a piston compressor coupled with a AC motor.

This "Torsional Analysis" you are doing... are you doing it in your spare time on your kitchen table while your mammy cooks supper or are you doing it in a university laboratory under supervision and guidance??

Please inform.

i am not doing torsional analysis in my spare time. This is my Final Year project. can you really help me in solving this torsional problem???????????

Every mechanical system has natural resonance frequencies, which are determined by its Mass, Stiffness, and Damping. I would expect a motor shaft to be very stiff, which would make the torsional frequency relatively high.

this problem is solved. Torsional natural frequency was coming below first harmonics because i used very soft coupling but when i tried rigid coupling in place of soft coupling it worked and torsional natural frequency avoided resonance.

thanks to all of you!!!!!!!!!!!