What about your boundary conditions for the structure? Have they been adequately represented? As Greg suggested, did you have a look at the mode shapes? possibly lots of local modes, which may not be of concern !
Gear driven machines & those machines with VFDs are more vulnerable. If you are concerned about the influence of dynamic torques in the drive train, then torsional analysis helps.
As per ISO 2151, it could either refer sound pressure or sound power. You have to get it clarified. If it is catalogue sepcification,it is often the sound pressure level. The manufacturers do not intend to publish higher numbers (sound power) in the catalogue.
"I did give damping for my model (individual modal damping). The problem is that the curve I get from the Accn vs Freq doesn't come even near to the experimental results".
Your statement assumed that the experimental damping from modal analysis is correct. The measurement of damping is...
Hi Jimmy,
That attachment was of a beating. The beating was between 90Hz (torsional excitation frequency) and 97Hz(torsional natural frequency).
(the data attached is more illustrative)
The beating pattern could be due to the existence of a) two closer torsional excitation frequencies or...
Hi Jimmy..
Yeap.. that was almost close to 10yrs back..it was on a test rig with motor(thru VFD) & compressor through a disc pack bibbys coupling on either sides of the torque transducer, wherein we had that isssue. I managed to pull back a snap shot of the measured data..the units are as...
Hi Jimmy,
3. Since this is a 6 cyliner engine, the thrid torsional order and its harmonics are expected to be dominant apart from the torsional excitations from the airend, which are at the lobe meshing order and its harmonics. The lower half orders and first order excitation comes from the...
Hi Jimmy,
1 & 2. Yeap. You can easily tune away the coupling torsional mode by changng the stiffness of the coupling. Usually you get the dynamic torsional stiffness from your coupling manufacturer. If it is not available, you may estimate this by back calculation from your measured torisonal...
Hi Jimmy,
Is it possible you can do a runup and establish your torsional resonance (possibly a speed fluc meas on flywheel ring gear)? It looks that the torsional resonance appears to be your first resonance, being lowest,and often seen in these applications. Do you have a resilent coupling in...
Hi Jimmy,
Sorry for commenting a little late on the thread.
I have earlier worked quite a lot on a beating noise problem with a screw compressor, for which you can see more information on thread384-276533 Beating / modulating noise and vibration.
My question here is " Are you concerned about...
TTFN: Yes, the shaker (LDS) has a standard slip table. But what I have shown is the excitation in the vertical direction, where the armature is comnected to an expander and then the test fixture and UUT.The lab has informed the nat freq of expander with armature to be at 1800Hz.
BrianE22: Yes...
Thanks for your kind replies.
Tobalcane : In fact, in the initial trial, we had some slipping between the bolt and chasis. This was then torqued and was ensured through wrench for later tests.
TTFN : The frequencies ar 18.9Hz and 59Hz. The first freuency is very lighly damped and hence I can...
We were trying to do a vibration test of compressor assembly in a electrodynamic shaker at an external lab. Initially, the test lab personnel did a sine sweep from 5 to 1000Hz at an input acceleration of 1g and a sweep rate of 1 oct/min. Thereafter we need to do a resonance dwelling at the...
The requirement of FE / non FE based software should be decided by your range of interest of waves. If you are interested only in plane waves, then non FE based (typically transfer matrix based)software will serve the purpose. On the the other hand if you interested in higher order propagation...
Thanks to all for the responses.
Tmoose : The vibration was measured in the axial direction (helical gears)in the gear housing.
Johnny : The problem is with a drive train resonance as discussed below and hence any changes in coupling could not make significant changes in shifting the same...
Thanks Stteva & Tmoose for the observations. Thanks Johnny for a deeper insight.
The gear is of single helical type. The problem is observed in majority of the production lot and not to specific machine and hence I am approaching more from a design view point. The torsional pulsation in the...
I am referred to a gear (helical) rattle under both unloaded and loaded (?) condition. The gear box is that of a screw compressor (positive displacement). I can understand rattle under unloaded condition, due to a probable higher dynamic torque, which would aid in the separation of the gear...
Thanks for all of your replies.
Walt : I was trying to simulate the operational load as static, since the bearing stiffness is influenced by the load. In fact I am trying to create a scenario of bearing stiffness at operating stiffness by applying an equivalent static load. Hence apart from the...
I was trying to measure the axial natural frequency of a male rotor on its bearing(antifriction) in rest ( load equiavlent to its normal operating condition). I have prediction value (just the first mode, which is very similar to SDOF system) based on bearing stiffness and this is 386Hz. The...
This looks perfect for a sinusoidal vibration... usually since the vibration shaker cannot handle all ranges of disp, vel, & acccln, the specs looks quite normal. May be you should consult a vibration test lab with the specs and they might help u
