Galaxy simulation, 500 000 particles

A high resolution galaxy simulation, using 500 000 particles, consisting in 500 mass particles and 499 500 massless particles. Accelerated computation with OpenCL on a GeForce 285 GTX.

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| VIDEO LOG |
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Number of particles : 500000
Massless particle ratio : 0.999

Time step : 0.010
Use GPU : yes
GPU threads : 1024


Use tree optimization : no
Max tree depth : 256
Gravitaty approximation : 0.10

Gravity strength : 0.000100
Gravity smoothing : 0.001000

Particle factor : 10
Brightness : 0
Fog density : 1.0

Lowest acceleration : 0.000000
Highest acceleration : 0.001000

Simulation time : 1h 51m 17s
Simulated time : 5m 0s
Video time : 30s
Playback time scale : 10.00x
Simulation factor : 0.044930
Frame per seconds : 4.5fps

Category:

Science & Technology

Tags:

• science
• cosmological
• astrophysics
• gravitation
• galaxy
• simulation
• particles

[tclyue]

indeed, most of the SPH implementation are based on the "particles" in CUDA SDK. Ideally, it would be great if we can just use tree-code so that both adaptive smoothing length in SPH and the N-body code can be done. hmm..need to get my hands dirty on the GPU^^.

[VelRyphon]

@tclyue That's why I do not code on GPU anymore : even with OpenCL it's still a pain in the *ss...true innovation will come with x86 GPU. You give your portable C++/OpenMP code to GPU-maker compiler, and you're done ! Sweet dynamic allocation handled natively, easy parallelization...I prefer to work on nice code that is readable and portable.

[tclyue]

great, so you've managed to do Barnes-Hut on a GPU. I'm now looking more or less a same problem. Not too familiar with N-body code myself. it would be interesting if I can take a peek at your code?

[VelRyphon]

@tclyue Sorry, I mixed up different simulations. In this simulation, it's done on GPU with direct particle-to-particle interaction, since it's faster than optimized Barnes-Hut on CPU. But as you pointed out, trees are not straight foward to implement on GPUs. I implemented SPH on GPU about 1 or 2 years ago. Difficulty comes from dynamic allocation of arrays, which is not possible on GPU. But with static allocation, you can get what you want.

[tclyue]

What physics is involved in this simulation? N-body(of course) and standard SPH?

[VelRyphon]

@tclyue In order to have real time performance it's only n-body gravition with Barnes-Hut optimization. SPh would lead to much more interesting result : with SPH and more precisely viscosity, no need to impulse particles with orbital velocity, friction would lead to rotation.

[tclyue]

just PMed u

[davespitvalve]

@VelRyphon Ah, I see - so there's not really proper self-gravity or hydrodynamics. I was wondering how you were able to run it so fast!

[VelRyphon]

@davespitvalve This is the trick to simulate arms-like clusters : each particle has an initial velocity which is the perfect circular orbital velocity according to the most massive particles at the center, but the few other massfull particles seeded randomly in the disk perturbate this circular orbit and produces the effect wanted. It is the most simple way to simulate a galaxy without handling collision and density through SPH scheme.

[davespitvalve]

Those rings at the beginning shouldn't be there - your initial conditions aren't quite in equilibrium