Waves hitting a randomized square grid of hexagons
Channel: Nils Berglund
Date: 2021-11-21

This simulation shows a planar wave hitting an random arrangement of reflecting hexagonal obstacles. The obstacles are arranged on a randomized square grid, have a random radius and are turned by a random angle. The result is probably not very different from similar simulations we have seen with circular obstacles. The important fact is that the random arrangement leaves only a few open channels that are larger than the wavelength, and is therefore quite effective at reflecting or trapping the energy of the wave.   
This simulation has two parts: 
Wave height: 0:00
Wave energy: 1:29
The color scale is indicated by the bar on the right.
There are periodic boundary conditions between the top and bottom boundary, and imperfect absorbing boundary conditions on the sides. 

Render time: 21 minutes
Color scheme: Plasma by Nathaniel J. Smith and Stefan van der Walt
https://github.com/BIDS/colormap
https://github.com/yuki-koyama/tinycolormap

Music: "Establishment 85" by Noir et Blanc Vie@NoirEtBlancVie

See also https://images.math.cnrs.fr/Des-ondes-dans-mon-billard-partie-I.html for more explanations (in French) on  a few previous simulations of wave equations. 

The simulation solves the wave equation by discretization. The algorithm is adapted from the paper https://hplgit.github.io/fdm-book/doc/pub/wave/pdf/wave-4print.pdf 
C code: https://github.com/nilsberglund-orleans/YouTube-simulations
https://www.idpoisson.fr/berglund/software.html 
Many thanks to my colleague Marco Mancini for helping me to accelerate my code!