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Rotation machinary NVH signature

Creator
Creator

Any one has seen vibration/noise with even strongth for almost every order?

 

Untitled.jpg

 

 

3 REPLIES

Re: Rotation machinary NVH signature

Siemens Phenom Siemens Phenom
Siemens Phenom
Hello,

We've seen problems with tach signals that cause every harmonic to be represented. Does the rpm time curve have harmonics or is it noisy? That may not be the case here though. It looks like you may have several resonant bands that are exciting the orders as you pass through them. For example, it looks like you have resonances ~400-500 Hz, 600-750 Hz, 750-850 and 1000-1100 Hz and as you pass through these frequencies the orders are getting excited. Have you tried an Operating deflection shape or Modal Analysis at these frequencies to see what is moving?

Re: Rotation machinary NVH signature

Creator
Creator

Thanks Kevin!

I was trying to identify the cause of a bad alternator from order tracking.  Since the unbalancing (1st order) was not very strong, I had a hardtime finguer out what those higher order means.

A good alternator on the same machine (with all the resonents except those from the alternator itself) would be much different as shown below.

Untitled.jpg

Re: Rotation machinary NVH signature

Creator
Creator

I have also compared measured vibration waterfalls of another "bad" alternaor with that measured by adding more unbalance to the flywheel.  The results had a much stronger 1st order, while all the higher orders kept at the same levels.

The original data:

Untitled2.jpg

Data with added unbalancing:

Untitled1.jpg