The bifilar pancake coil at its resonant frequency

[MileHigh]

So, you go back and apply the 500 Hz AC torque signal to the flywheel and observe the flywheel at its self-resonant frequency.  There is no doubt about the resonant rise in the response of the flywheel because you can hear it ringing so loud.

So, is this "resonant rise" something to get excited about?  Is this higher amplitude resonant response from the flywheel a possible key to a mechanical over unity device?

Not really, because after five minutes at resonance the flywheel starts to get really hot.  You quickly realize that all of the shaft power that is going into the flywheel is turning into an incredibly loud ringing sound and the flywheel itself is starting to heat up.  All of the rotational shaft power you are putting into the flywheel is becoming sound and heat.  Or we can call that waste sound and waste heat.

So exciting a flywheel at its self-resonant frequency is essentially exactly the same as exciting a coil at its self-resonant frequency.  In both cases all of the increased supplied power to the resonant system becomes increased waste heat.

If you excite the flywheel at its self-resonant frequency with a high enough peak-to-peak AC torque signal, the flywheel will eventually heat up to the point it starts to get red hot.

Now, don't forget an ideal spring stores energy returns energy, it is not supposed to generate heat.  But the spring inside the flywheel is not ideal, it has hysteresis and any energy that it does not return is converted into heat.  In other words, there is effectively friction inside the resonating flywheel creating heat.

So the energy being burned off in the resonating flywheel due to friction is like the energy being burned off in the resonating coil due to wire resistance.

[Grumage]

Dear MileHigh.

Your original post had me thinking off and on, having had over 40 years experience with the Internal Combustion Engine.

I would never, even with several lifetimes have envisaged a flywheel that oscillated at 500 HZ!

Most practical people recognise that a flywheel stores rotational energy to carry the ICE through its dead cycles. On early electric generation engines the flywheel was made heavier to reduce the flicker of the lights.

Perhaps my post echoes the reason for " no takers " ?

Kind regards, Graham.

[MileHigh]

Graham:

I think that you are missing the point.  For starters the example has no relationship with any flywheel that might be used in an internal combustion engine.  I described a thin disk one meter in diameter.  I described it like this so the thinness and reduced material in the disk would be more amenable to being deformed when torque was applied at the center of the disk.  The deformation is the spring in action.

If the disk is proportioned with a larger width, then the stiffness of the torque spring inside the disk goes way way up and the self-resonant frequency of the flywheel quickly goes up past 20 KHz and becomes inaudible.  Likewise, the amplitude of the  self-resonant oscillations would be so low as to be unobservable with the naked eye.

The whole point of the exercise was to "tune down" the self-resonant frequency to make it audible and observable.  The described dimensions of the hypothetical flywheel and the self-resonant frequency are all arbitrary and for illustrative purposes only.

The point of the exercise is to illustrate how a self-resonating flywheel is a near-perfect analogy for a self-resonating coil.

If you are working in a physics lab as a college freshman you might have a near-frictionless linear air track and you will will do the basic tests with a spring.  The spring they give you to test and measure for the spring constant "k" is like a miniature slinky that is about half a meter long in its relaxed state.  It is a very weak spring and you hang weights on it to measure how far it stretches to determine the spring constant.  The spring that you test serves no useful purpose in the real world that I am aware of, it's only used in physics labs.  However, it still is a spring and when you analyze that very weak spring you end up understanding how springs work in general.  Exactly the same principles are at play with my hypothetical example.

MileHigh

[Zephir]

how a self-resonating flywheel is a near-perfect analogy for a self-resonating coil

Why, what this analogy explains/predict? BTW Does self-resonating flywheel exist?

[Grumage]

Graham:

I think that you are missing the point.

MileHigh

Dear MileHigh.

On the contrary, I don't think there was a point to be missed.

Your flywheel ceased to be a " Flywheel " the moment it stopped rotating. IMO your analogy is more akin to a mechanical oscillator.

From my perspective any flywheel that's rotating at a fixed speed ( doesn't matter what speed ) is resonant. My reasoning ? The flywheel, once up to speed requires far less energy than it took to get there.

Kind regards,  Graham.