Short and explaination of resonance

How did PetroPower get on my wifes key ring?

Wiki definition

I guess the damping would be the inverse of gain, of the system. So resonance becomes a problem in a mechanical system when the gain is close to one. in a electrical system you are generally trying to attenuate everything except the resonant Hz. Mechanical ssystems avoid resonance [except musical instruments] don't they?

Good point. The Wiki definition links out to 'Galloping Gertie', the (in)famous Tacoma Narrows bridge, which is the subject of a fascinating and well-known piece of film/video/digital recording that illustrates resonance in a readily-absorbed way. The frequency of fluctuations in the air stream as a result of vortices ("swirl") downstream of the bridge coincided with the natural frequency of oscillation of the bridge deck, resulting eventually in the destruction of the bridge.

Er, sorry, beg pardon for this, for damping and gain are not the same thing in control systems terms.

• Gain is the relationship between the magnitude of an action and the magnitude of the input signal. As a simple example, a lever is used to provide a gain in force or a gain in distance, depending on its application. The relative positions of the load, the applied force and the fulcrum determine the gain.
• Damping is what makes oscillatory response die away over time; a simple example is the shock-absorber in a road vehicle, which is there to take the oscillating behaviour out of the springs forming the suspension.

You are right the Tacoma Narrows bridge is spectacular example, but I don't like to use it much as it is a special case.

Tacoma Narrows was an unstable system, and as a result the vibrations built and built until it tore up (same as feed back in an electrical system). Most resonance situations are not unstable, for instance hitting a middle C on a pipe organ does not result in destruction.... at least not usually....

Musical instruments rely on natural frequency and resonance...

In mechanical systems we try to avoid it, but it happens. Starting up a large turbine generator in a power plant the machine may pass through multiple resonance points on the way to full speed.

Try "out of balance tires". I am sure that you, and everyone that he is teaching has had that experience. There are certain speeds (harmonics/resonance) where you will feel the vibration. That will probably "stike a chord" (sorry - couldn't resist), in his audience.

I actually did go there in my explanation... Still not sure if it communicates the idea very well...

With the other (earlier two) short explanations I was completely lost and forgot what I knew before. I guess your explanation restored the faith in short explanation of the terms. Bravo.

Thanks and with regards;

Nadeem

All sounds far too complicated to me!

I'd simply say it's how it naturally wobbles when you hit it!

e.g Put your rule over the edge of the desk and twang it!*

And it depends on the the physical properties and dimensions of what 'it' is...everything from the branch of a tree to a glass of water has a natural frquency at which it will tend to move...hey the galss of water is a good 'un

(*don't spose anyone has a rule these days...probably got boody laser spirit levels and laptops )

Leave it to you Del to develop a practical approach... unfortunatly yours is a great demonstration of natural frequency, not necessarily resonance...

Resonance has to have a sense of a forcing function at the same frequency as the natural frequency, that is why the vibration goes so high. In a free vibration situation "whack it and see how it wobbles" you see the vibration amplitude ring down, in resonance it keeps vibrating...

Yes...a nice but subtle distinction.

Just add the caveat to my explanation....to maintain vibration the forcing function must be in sympathy with this natural frequency...e.g the same or a multiple thereof.

Oh...I try to make it simple and it just gets complicated I'm only a simple cat...

(exit stage left wailing and caterwauling )

Del

I'm right behind you Del....

How about everything has frequency inherent to it at which it will oscillate or vibrate. If some force is placed on it it may start it in to these oscillations. With a pump there are several forces that may cause a part to resonate. One is the 60 Hz frequency of an AC motor. If by chance the resonance frequency of the cage on a ball bearing was 60 Hz or one of its harmonics. This would cause the cage to oscillate. If nothing is done to control the oscillation the cage will self destruct. Shorting the bearing life.

You could try using the crystal glass that explodes when it is in the presence of a high pitch sound.

This is a classic exaple of resonance causing destruction, and is easy to explain because crystal has a frequesncy (Not as abstract a notion to put across as most other materials) as does sound (everybody knows that). This could even be demonstrated with the correct apparatus.

Any thoughts?

Before describing resonance, you'll need to explain what a natural frequency is. In layman's terms, a natural frequency can be thought of as a shape or frequency at which an object or system will respond when some force acts on it. This force usually varies with time. Resonance occurs when the frequency of this force matches the natural frequency of the system.

An example of resonance can be found with the antenna on your car. As you drive, the cylindrical shape sheds vortices at a frequency about equal to f = 0.2*U/D. (U is the speed of the car, and D is the diameter of the antenna.)

Since the antenna is mounted at one end it will want to vibrate at a certain frequency based on the material, the length, and the diameter. When you drive at a speed that induces vortex shedding at a frequency equal to the natural frequency of vibration, you will have resonance and the antenna will vibrate at a maximum amplitude.

You can check this out by watching your antenna as you drive down the road gradually increasing speed. - If your antenna has a spiral wire wrapped around it, this won't work since the spiral wire is there to prevent uniform vortex shedding and hence eliminates the resonance.

Resonance is a vibration that is energized and increases from an outside force. Similar to the antenna vibrating at certain wind speeds, sometimes a road sign (especially on a single post) will oscillate when the right wind velocity and direction will set it in motion. If resonance is unchecked or not damped quickly, the object can vibrate to destruction.

Did you ever try humming with your vaccum cleaner??

It will always be that particular pitch (frequency) at which the cleaner hums that you feel the resonance deep inside your lungs....

I assume you want a really layman explaination.

The resonance will only be felt at that pitch noticably strongly.

It is also a very constuctive thing to do coz u r cleaning AND singing such that no one can hear you.

On a stiff clothesline suspend 7 pendulums - 150, 200, 250, 300, 400, 500 & 600 mm long or 14 with 2 of every length. Swing one pendulum; you can observe resonance in pendulums that are equal in length, a multiple in length or a factor.

Well, a lot of your posts give demonstrations rather than explanations, so perhaps you might be interested in another, rather simple, example. It is popssibe to drive the corresponding string in a piano, near by to another piano, by striking a note on one of the pianos. Only works when the driven piano is stringed of course, so maybe not so easy to find a place to try this out these days.

What about pushing someone on a swing?

Or a disco? (Hee, hee! Had to get that one in somewhere!)

LOL!!

But on a serious note, there was a balcony in a hotel that crashed down several floors because they were having a dance. As the people danced on the balcony the rhythmic motion excited an undamped natural frequency in the balcony causing it to fail. A number of people were killed.

1: systems store, release and internally exchange energy at particular rates.

2: if energy is rhythmically put into a system at the same rate as internal exchange, energy is accumulated in the system.

That is all.

The swing example is the one I like to use, too.

For a definition, how about this one. A situation in which input energy is synchronized to an oscillation.

Steve S:

I agree with Randall ; pushing a swing is a good example. For resonance to occur, you need a "forcing function" (you) to act on a mass-spring -damper system (for example--in this case, the kid on the swing). If you push at the right time, the swing goes higher and higher. That is, the amplitude increases. . If you stop pushing, eventally gravity and friction (both air friction and bearing friction) will slow and stop the swing. So you must time your push to be in sync with the natural frequency of the swing system. This is actually an example of a parametric amplifier. Talk to some of the EE boys if you want to get into Laplace transforms, Bode plots, Nyquist diagrams, etc., if you want to know about that, or if you have insomnia.

Also, I notice you play guitar. So do I. Have you ever used or seen a guitar tuner for an acoustic guitar? It's a little doohickey you clip on the head of the guitar. It has a bunch of reeds which are made to vibrate when you pick a string. The amplitude will be greatest when the string tension is adjusted for the string you are tuning and the tuner will resonate one reed ( highest amplitude), indicating when you are in tune. The forcing function here is when you pluck the string and the mass-spring-damper system is the reed in the tuner. Frictional forces in the reed material and the slight air resistance do the damping.

Maybe you can use one of these as an example. The Tacoma Narrows bridge is an extreme example of resonance..I am fascinated every time I see that on TV. One previous poster described Newton's Pendulum for an example. I have often wondered if it wasn't the air flow past the suspension CABLES that caused the forcing function which brought the bridge down.

Anyway, sorry it's so long. But I've done a lot of acoustic research for the Navy in the past. And just recently, I solved a huge resonance problem in a Combined Cycle Power plant. So this subject is in tune with what I do(sorry).

Hank

I thought the tacoma narrows problem also had to do w/the distance between the towers being such that the span could hit the resonant hz?

just forgot to do that calulation.

had a prof explain it that way in a lecture about radio hz amplifiers, as a cautionary tale about the importance of doing all the calulation, not just the 1's [properties] you intend to utilize.

Hankt

Nice to find someone with similar interests, I suppose we now need to buy a couple beers, find a corner and exchange war stories in loud voices for hours in an obnoxious way that alienates every else at the party.

I work in offshore oil and gas I am currently working a resonance issue regarding a screw compressor installation on a FPSO where the acoustic energy from the compressor is breaking stainless steel pipe with about 1 inch wall thickness, kind of a radical version of Ella Fitzgerald and the wine glass. And so I have been buried in Bode plots, Nyquist diagrams etc...

Oh by the way, I use a variety of electronic guitar tuners, the reed version went out of style long ago (electronic tuners work better on a noisy stage as well). Go to the user group hobbies and join us musicians when you get a moment..

That means I'll share a resonance /cavitation story

I was working for a company making flow control valves [2"-60"]

We had sold a 20" valve to the Tucson water district.

the valves were sleeve valves, where the sleeve had progressively larger holes as the valve.

the valve was housed in a small cinder block building about the size of a single car garage.

as the valve got to about 10% open the pipe would start to shake, by the time it got to 20% the building was shaking as if there was an earthquake.

The repair was to replace the seat, the seat was 0.02 oversized & would allow the oscillations to get to the apparent resonant Hz of the system.

Hi Steve. I thought I'd mention seeing rubber couplers and flow straighteners used to damp destructive frequencies, especially in hypersonic wind tunnels. The scream of Mach seven airflow must be horrendous if not acoustically dampened yet the muffling system can't interfere with the airflow (too much). Perhaps there are some clever solutions to be found in NASA's documentation. Just a thought...

acoustic processing is always a difficult issue in practice

Oh wow! I didn't know my pal Steve S. was taking care of me for my pump and machine train class.

The REAL definition of resonance is when my dear wife comes into my home office on Sunday evening and tells me: "Why do you stay in that office so much . . . . never coming out to spend time with me . . . . always on the computer discussing your machines . . " >>>> and my answer is : "Well, if you were more interesting I'd come out from time to time."

R---E---S---O---N---A---N---C---E

That we have several types of resonance:

Acoustic

mechanical

electrical

hydraulic

& the most dangerous type of resonance of all

personal

It won't cause physical things to break up unless you count your

Entire emotional world

then again maybe there's

Creative resonance

haven't you ever been vibrating w/a new method,process,design or relationship.....

acoustic, hydraulic etc can be incorporate into mechanical vibration.

mechanical wave, electromagnetic wave and emotional wave. hehe.

No matter what type of resonance, it can be described by same frequency occuring in objects. they are coincident frequency.

sometimes this coincident is harm, but ohter things are good.

In electronic equipemnt we use it to sperate similar wave, so that we can selelct what we want to require.

In civil construction. we avoid it to distroy our building and so on.

In emotion world we hope our colleagues has thinking resonance, so that we can do things very well. and work harmonious.

or we would like an enemy. none wish to see it.

or we would like an enemy. none wish to see it

Please explain, that lost something [meaning] in the translation.

No matter what type of resonance, it can be described by same frequency occuring in objects. they are coincident frequency.

and if the coincidental frequency are out of phase, they will cancel each other out.

Haha, very good inquiry.

or we would look like eneny or come to difference. which is the last things we wuld see it.

2]

you are very careful, now change to

same frequency, same phase.

3]

we can use control theroy to compensate these pole points to avoid oscillation.

and get a stable state.

almost of all music instruments are based on resonance principle to enlarge sound output.

but hall will avoid resonance to produce colored tone with lots of absorb material in/on roof wall etc.

As a first step, I usually start with a pendulum demonstration (or something equivalent), and then describe resonance in terms of energy being swapped periodically between different storage mechanisms - first with specific reference to the demonstration, and then more generally. But what do I know...

Fyz