Wave interference and harmonic oscillation

[einstein1921]

1. when wave is destructive interference ,where is the energy? for example, two plane wave have opposite phase ,they will destructive interference completely,but where is the energy? in antireflection film, the reflection wave is disappear!why? where is the energy? where is the wave?
2.in what situation ,a simple harmonic oscillation can move non harmonic, and why?
anything would be highly appreciated!

 

[elemis]

To answer your second question, a simple harmonic oscillator can undergo 'damped' in the presence of frictional forces like drag.

There are varying degrees of damping including lightly, critically and heavily damped systems.

 

[sophiecentaur]

1. when wave is destructive interference ,where is the energy? for example, two plane wave have opposite phase ,they will destructive interference completely,but where is the energy? in antireflection film, the reflection wave is disappear!why? where is the energy? where is the wave?
2.in what situation ,a simple harmonic oscillation can move non harmonic, and why?
anything would be highly appreciated!

A very reasonable question. The energy is just 'somewhere else'. The total amount of energy / power will be the same but it has just been redistributed from the nulls / nodes to the peaks / anti-nodes.

This is a self contradiction if you don't qualify it a bit. A simple harmonic wave can propagate over a boundary into a medium that is not linear or can encounter a non linear element in a circuit and then it can become distorted. When a guitar string which is (mostly) oscillating at its fundamental is brought next to a fret, by lowering the bridge, then the restoring force is no longer proportional to the displacement (linear) and the energy in the standing wave will be redistributed into other modes - the string will buzz and the motion is no longer simple harmonic.
A diode placed across an LC resonator will change the simple sinusoid into a half sin wave, which will rapidly decay because the energy becomes dissipated. There are so many examples of this sort of effect.