Nils Berglund | Winnowing 2: Separating triangles by size using wind @NilsBerglund | Uploaded October 2024 | Updated October 2024, 5 minutes ago.
This is a variant of the video youtu.be/jd5dmbsgqic , illustrating the process of winnowing, but with triangular instead of circular particles.
Using wind to separate particles according to their size is an old method, going back to winnowing, or separating grain from chaff by throwing it into the air after it has been threshed. In this simulation, the particles have different sizes, but the same mass. They are subjected to gravity, and to a horizontal force proportional to their radius, modeling the effect of wind. The wind stops a short distance above the bins at the bottom, to avoid that the particles bounce on the bins' walls.
The video has two parts, showing the same simulation with two different color gradients.
Particle size: 0:00
Kinetic energy: 2:36
In part 1, the particles' color depends on their size. In part 2, in depends on the direction of their velocity.
To save on computation time, particles are placed into a "hash grid", each cell of which contains between 3 and 10 particles. Then only the influence of other particles in the same or neighboring cells is taken into account for each particle.

Render time: 4 minutes 12 seconds
Compression: crf 23
Color scheme: Turbo, by Anton Mikhailov
gist.github.com/mikhailov-work/6a308c20e494d9e0ccc29036b28faa7a

Music: "Sunshine on Sand" by the Unicorn Heads@UnicornHeads

Current version of the C code used to make these animations:
github.com/nilsberglund-orleans/YouTube-simulations
https://www.idpoisson.fr/berglund/software.html
Some outreach articles on mathematics:
https://images.math.cnrs.fr/auteurs/nils-berglund/
(in French, some with a Spanish translation)

#molecular_dynamics #winnowing