rickman wrote in :

What? For a wave to have a "bulge" above the top of the tank means
there is a trough well below the top of the tank. The amount of liquid
does not change because you make waves in the tank.


I didn't say it did. Anyway, I've been looking at images on Google,
apparently the single half-wave form is concave in a tank of liquid, not
convex. Maybe that too is possible, I don't know. If it is, then you can add
liquid to what was a brim-fill tank before it overflows once the wave is set
up, which would indicate that a form of storage has been set up.

Look at it another way... Any standing wave shape in a tank will not be flat,
and when the small amount of energy maintaining it is stopped, it will give
back energy until it is flat, so it looks like a way to store energy. A 'tank
ciruit' has to have a way to store energy too.

(As to why I go into these apparently off-topic variations, it's because I
think a person can know something by being very specific, but probably cannot
understand it unless they look at as many other things as possible in which
similar action occurs.)