Opening a release valve in a dam

In this somewhat less dramatic variant of videos such as    • Simulating a dam break with Lennard-J...   , the dam does not break, but a release valve is opened near its base, allowing the water to flood the other side of the dam. The thing I found noteworthy is the vertical motion of particles near the dam: notice how blue and green particles from the top rush down when the valve opens. I don't know if this is a documented phenomenon (if any engineer knowledgeable in dam building reads this, let us know), or if it is rather due to the red particles being "frozen" to the ground by the high pressure.
This simulation involves 6521 particles, subjected to constant gravity, a viscous friction, harmonic repulsive forces from the boundaries and wall, and Lennard-Jones interaction. Initially, all particles are at the left of the wall. They don't start quite at equilibrium, which is why some splashing is observed. At a given time, a small part of the dam is removed, allowing particles to enter the region on its right. At the beginning of the simulation, each particle is given a color that depends on its y-coordinate: particles near the top are blue, while those near the bottom are red. They keep their color throughout the simulation, making the motion of each particle easier to see. In a sense, this is a Lagrangian, rather than Eulerian picture of the flow.
There is no thermostat in this system, the only source of change of total energy is the viscous friction. The temperature shown at the top left shows the mean kinetic energy per particle. To make the visual impression of a wave clearer, triangular regions between neighboring particles have been colored like one of the three particles chosen at random.
The simulation has two parts, showing the same evolution at two different speeds:
Time lapse: 0:00
Slow motion: 0:54
In the first part, time has been accelerated by a factor 3.
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.
The Lennard-Jones potential is strongly repulsive at short distance, and mildly attracting at long distance. It is widely used as a simple yet realistic model for the motion of electrically neutral molecules. The force results from the repulsion between electrons due to Pauli's exclusion principle, while the attractive part is a more subtle effect appearing in a multipole expansion. For more details, see https://en.wikipedia.org/wiki/Lennard...

Render time: 1 hour 4 minutes 18 seconds
Color scheme: Turbo, by Anton Mikhailov
https://gist.github.com/mikhailov-wor...

Music: "Lay It Down" by Silent Partner

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