Rotating shaft problem - Please help!
I am given the task of FEA of a rotating shaft. Basically I have a belt driven shaft supported by two bearings on two ends. The structure on which the lower part of the bearing is attached is vibrating (using a rotating eccentric mass whose specs are unknown) and is connected to the ground using a number of strong springs. However, we know the amplitudes in x, y and z directions and frequency of vibration of the structure.
My intention is to find the critical speed of the shaft , and to locate the weak points in the entire assembly.
So far, I tried with a simplified model as attached below:
Following are the inputs I have provided:
- Geometry : stepped shaft, face split at the two ends to provide bearing connection
- Connections :Ground to body bearing at both ends selecting the split faces (purple color in the above image)
- Cylindrical support with all axial, radial and tangential directions fixed.
- Both end faces fixed
- Center of the end faces with remote displacement (this worked with static structural but in model it gave a warning "Participation factors may not be accurate if Remote displacement is applied as constraint using deformable behavior. Please use rigid behavior")Rotational velocity 0.21 rad/s (shaft is supposed to rotate at 2 rpm) [ I read in some previous discussions that rot. vel. in modal affects the resonant frequencies through gyroscopic effects. However I got no change in the frequency values for even a rot. vel. up to 10000 rad/s. Is it because I have not given any damping input, if so where would the input placeholder be?]
- In Analysis settings : Damped - Yes , Coriolis effect - On, Campbell diagram - Off. Is the methodology correct? I am getting frequencies > 1250 Hz
For Static Structural:
- 1 ,2,4,5,6 repeated
- Standard earth gravity for weight effect
- Number of steps = 1 , step end time = 120 sec (because I thought to complete at least one rotation since the speed is 2 rpm)
- Getting very low deformations ( ~ 0.165 micro meter ) and 0,24 MPa max. stress (these seems reasonable considering the material and geometry)
- Am I doing the right steps?
- If not, kindly guide _/\_
- How to simulate the effects of the sinusoidally vibrating base (single speed)? (I checked the harmonic analyses section which left me more confused as it was supposed to give a range of frequencies and a single phase angle - whereas my x , y and z vibrations differed with each other in phase)
- What about the belt drive ? should I add a moment for that condition? Or does the rotational velocity already consider the moment applied?
- I want to estimate the fatigue life of the components/ assembly as well.
- What all information can I extract t be useful for my scenario?