Layman's explanation of random-on-random vibration 1

[Tunalover]

Anyone out there have a writeup that explains random-on-random vibration in terms a non-vibration-expert can understand?

Tunalover

 

[ivymike]

I used the STFI method to arrive at the following:

Sine on Random Vibration
Sine-on-random tests combine multiple sinusoids with broadband random noise. The sine tones may be stationary or sweeping, harmonically or non-harmonically related, and have varying levels across a frequency band. Sine-on-random is an excellent tool for simulating a moving vehicle subjected to random vibration due to road variations while the engine speed is increasing or decreasing.

Random on Random Vibration
Random on random testing involves creating fixed or sweeping narrow bands of random vibration superimposed over a broadband random vibration base. Random on random vibration profiles most typically apply to testing components and systems of tracked vehicles, where the narrowband random vibration simulates track laying components and the broadband random base the rest of the vehicle.

 

[MiketheEngineer]

That helps -- Uhhhhhh

 

[Tunalover]

ivymike-
What does SFTI stand for?


Tunalover

 

[SomptingGuy]

Is that supposed to be funny? I thought it was. A recursive joke if ever there was one. Was the reordering intentional or just a typo?

- Steve

 

[Tunalover]

Make that STFI. I mistyped the acronym.


Tunalover

 

[GregLocock]

Tunalover - STFI=google

I'm really really dubious about the truth of " the narrowband random vibration simulates track laying components", but don't have any evidence. The reason I say that is that a periodic impact has a spectral structure that has sharp spikes at the fundamental, and then 3rd 5th and so on harmonics. However, I can't readily find a vibration spectrum from a tracked vehicle.








Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[floattuber]

Per the title of this thread, that definition doesn't seem like a very layman's way of explaining things.

 

[GregLocock]

OH, fair enough

Imagine a pair of white noise sources.

filter one via a bandpass filter, that sweeps through the frequency range. Amplify it a bit. Add the output of that to the other source's unfiltered output.

So the spectrum would look like

    xx
 xxx  xxxxxxxxx
0--------------

and then a bit later

      xx
 xxxxx  xxxxxxx
0--------------

in reality of course the broadband signal will have an upper frequency limit.

Incidentally if you are programming this yourself do NOT use a string of random numbers to generate the random noise. You will destroy your driver system.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Tunalover]

Still looking for a layman's description. Of course in many complex subjects I realize it's hard to come up with one.

Tunalover

 

[kchan711]

Here's my shot at layman's terms:

Random Vibration: Earthquake

Random-on-Random Vibration: Car suspension (or some other indirectly connected chassis) on top of shaking ground while driving on a dirt road.

The Earthquake is completely random, while the car suspension has a defined range of motion; however, it vibration (oscillation up and down) is random due to its interaction with the uneven road and its interaction with the unpredictable earthquake.

Random-on-Random...

Kyle Chandler

http://www.chiefengineering.net

 

[floattuber]

Tunalover, when you say layman, are you talking about an average joe off the street or an engineer who has no experience with vibration?

 

[Tunalover]

I suppose an engineer who has little experience with vibration.

kchan711 seems to have a pretty good description.



Tunalover

 

[Tunalover]

ivymike-
What is the STFI method? Speak plain man!

Tunalover

 

[ivymike]

search the friendly internet.