Скачать или смотреть Granular material simulation (DEM) C++/SFML

Yo,

Had a pretty bad injury at work recently so I've had time to work on something i've wanted to do for a very long time : discrete element modeling.

I've started with an event driven model (ED or hard sphere model) where every collision's time of impact (toi) is predicted before it happens. Impacts are then ordered and solved in subframes according to their time of impact. There is no penetration and particle collisions are solved with instantaneous velocity change. This method is good for few particles that collide not frequently. When the mean time between collision decreases, the number of collision solves goes up exponentially (a solve may trigger 2 or 3 new collisions due to the new positions and velocities of the particles). For 100 particles, I already had to solve 500 collisions, which is not a viable option for simulating close packed material.

I then switched to a "molecular dynamics" model (MD or soft sphere). The particles are considered as deformable bodies. They are allowed to cross each other a little. A spring-damper force proportional to this penetration is then used to separate crossing particles. The contact has to last several frames for this simulation to be stable so the timestep has to be very small. I've used a spatial hashing grid to reduce the number of collision pairs to solve.

I've still room for optimization but i'm very happy with the results so far. I'll do some pneumatic transport simulation with this program in the future.