Press "Enter" to skip to content

My little LAMMPS tricks

Sometimes I try to use LAMMPS to perform small simulations of « textbook » models like pendulums, Rayleigh-Benard or other traditional oscillator stuff. Here is some of them I did for fun.

2d Rayleigh-Benard simulation

It’s an old one that I will add later but you can find a low quality video showing the velocity profile and temperature gradients here:

The green and red atoms are initially either in the top of bottom of the simulation and interact with a 12-6 Lennard-Jones potential. Two small bands of atoms, one on the top (cold) and the other on the bottom (hot) are coupled to Nosé-Hoover constant temperature hamiltonians with dynamic groups, the rest of the box has its equations of motions integrated as is. In the middle you can see the temperature (red is hot, blue cold). In the bottom you can see the velocity direction with yellow section having a velocity pointing upward on average and green pointing downward. Black zones are neither.

Chaotic double pendulum

I have to find the file of this one. I don’t know where it is. More on this later.

Double harmonic oscillator

In one of his papers from 1871, Lodwig Boltzmann showed that the trajectory of a particle coupled in a 2d assymetric quadratic well, with force constant k1 in one direction and k2 in the other, is periodic if the square root of k1/k2 is rational. I wanted to verify numerically that this is true. And guess what…

This video uses rational ratio between the force constants, it reproduces the periodic trajectory like the one drawn in Boltzmann’s article.
In this one the ratio between the force constants is pi. So it gives a non-periodic trajectory.

What a surprise, Boltzmann was right. 😉

Laisser un commentaire

Votre adresse e-mail ne sera pas publiée. Les champs obligatoires sont indiqués avec *

Ce site utilise Akismet pour réduire les indésirables. En savoir plus sur comment les données de vos commentaires sont utilisées.