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C 3D heat diffusion solver. Tests the performance characteristics of several heat diffusion solving algorithms. Simulation is controllable via a browser client with realtime WebSocket visualization.

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3D Heat Diffusion solver

Overview of components

Core solver

Objects can be created with any length and subdivided into discrete partitions. Length (lx,ly,lz) and partitioning (nx,ny,nz) are independent for each dimension. Objects can be initialized using a FLAT or GAUSSIAN method.

Five solvers are (mostly) implimented. Forward-Time Central-Space is implimented for all three dimensions. Crank Nicholson is implimented in 1D and 2D. The matrix and object storage/serialization code was designed before I understood exactly how Crank-Nicholson actually worked. As a result it is heavily optimized for FTCS (dimensionally independent lookups) and embarassingly slow at CN which needs memory contiguous matricies and vectors to really work at all. I have not implimented 3D Crank Nicholson because without rewriting my matrix and object data structures it would be too slow to even test for correctness.

Both FTCS and Crank Nicholson support adding an arbitrary time independent source term and both flat (with the option to specify a non-zero boundary value) and periodic where the boundary conditions wrap around.

Jacobi, Gauss-Seidel, and successive over-relaxation (SOR) solvers for 1D, 2D, and 3D were added at a later point. All three new solvers should work with periodic boundary conditions, non-cubic domains, and the constant source term but those features have not been extensively tested.

heat_test

This is a simple command line utility that bootstraps the solver code and allows running the solver in small input tests. It has no external dependencies beyond the C 11 STL.

heat_server

This is a more complicated simulation server that uses WebSocket to communicate with a command and visualization client running in a browser. The server accepts input in the form of a simple command language that allows specifying the simulation input parameters. Visualization output is performed either as a 2D plot (1D problems only) or as a 2D grayscale image. White represents hot, black cold.

The command language works as follows:

command:arg1=val1;arg2=val2;

trailing punctuation is always retained.

The commands recognized are simulate and cancel. Simulate will start a simulation on one of the processing threads. Cancel will signal the simulation thread to cancel the simulation the next time that processing thread checks in. Processing threads check in to test for canceling and deliver a simulation snapshot timestep at a specifiable interval. Simulator I/O is handled in one thread and there are a configurable number of simulation processing threads. Simulations are assigned to processing threads in FIFO order.

Arguments for the simulate command:

Argument Effect Required? Allowed Values Default
timesteps how many iterations to run. No 1-1000000 10000
dimensions how many dimensions to use for the simulated object. No 1,2,3 1
lx length of x dimension in m Yes 1-1000 1
ly length of y dimension in m 2D and 3D only 1-1000 0
lz length of z dimension in m 3D only 1-1000 0
nx partitions in x dimension in m Yes 1-1000 400
ny partitions in y dimension in m 2D and 3D only 1-1000 0
nz partitions in z dimension in m 3D only 1-1000 0
initial initialization strategy, 0=FLAT,1=GAUSSIAN No 0,1 1
boundary boundary handling strategy, 0=CONSTANT,1=PERIODIC No 0,1 0
method which solver to use, 0=FTCS,1=CRANK_NICHOLSON,2=JACOBI,3=GAUSS-SEIDEL,4=SOR No 0,1,2,3,4 0
zslice which z slice to display in 3D simulations No 0,nz-1 0
callback_interval timestep interval used to check for cancel and return intermediate results. No 1,timesteps 100
smode simulation snapshot format, 0=JSON,1=BINARY, heat_client automatically chooses and sends this value based on browser capabilities No 0,1 0

Usage

Examples

Command Effect
simulate: Run simulation with default parameters
cancel: Cancel the currently running simulation (requires server to be started in one of the multithreaded modes)
simulate:timesteps=100000; Run default simulation but adjust timesteps
simulate:timesteps=1000;dimensions=2;nx=100;ny=100;ly=1.0; Run 2D simulation with default solver and custom problem size
simulate:timesteps=100000;dimensions=2;nx=100; ny=100;ly=1.0;callback_interval=1000; Run a longer simulation and ask for progress update renderings every 1000 timesteps
simulate:timesteps=25;method=4;nx=100;ny=100;nz=100; ly=1;lz=1;dimensions=3;callback_interval=5;zslice=50;dt=1.0; 3D simulation long enough to show a nice average iterations spread
simulate:timesteps=30;method=2;nx=400;ny=400; ly=1;dimensions=2;callback_interval=1;dt=1.0; Nice, big, well performing 2D simulation

Browser Support

The client will operate on any modern browser with WebSocket support. This includes: Safari 5.0.1 iOS 4.2 FireFox 6 Chrome 6 IE10

On browsers with full RFC6455 support it will use binary websocket for drastically improved visualization performance. These browsers are: Chrome 16 FireFox 11

Building the server

Building the server requires Boost and WebSocket (github.com/zaphoyd/websocketpp). If you have trouble building it let me know.

Example make statement:

make CXX=g DEBUG=0 WEBSOCKETPP_PATH=/path/to/websocketpp/headers WEBSOCKETPP=/path/to/websocketpplib.a BOOST_INCLUDE_PATH=/path/to/boost/headers BOOST_LIB_PATH=/path/to/boost/libs

Performance Analysis:

FTCS 3D 1000 time steps

Size Time Volume µs µs/size µs/timestep
10x10x10 cube 00:00:00.143543 1,000 143543 143.543 143.543
20x20x20 cube 00:00:01.131008 8,000 1131008 141.376 1131.008
30x30x30 cube 00:00:03.829194 27,000 3829194 141.822 3829.194
40x40x40 cube 00:00:09.083705 64,000 9083705 141.932 9083.705
50x50x50 cube 00:00:17.804704 125,000 17804704 142.437 17804.704
60x60x60 cube 00:00:30.732263 216,000 30732263 142.278 30732.263
70x70x70 cube 00:00:48.869378 343,000 48869378 142.476 48869.378
80x80x80 cube 00:01:12.005312 512,000 72005312 140.635 72005.312
90x90x90 cube 00:01:44.246772 729,000 104246772 142.999 104246.772
100x100x100 cube 00:02:22.738739 1,000,000 142738739 142.738 142738.739

Performance Analysis of iterative methods

2D

300x300 square simulated for 100 seconds

Method Time dt avg iterations
FTCS 00:00:49.067901 0.001s N/A
JACOBI 00:00:23.413229 1.0s 325
GAUSS-SEIDEL 00:00:20.495972 1.0s 221
SOR 00:00:07.686357 1.0s 75

3D

100x100x100 cube simulated for 10 seconds

Method Time dt avg iterations
FTCS 00:00:10.095005 0.01s N/A
JACOBI 00:00:39.082192 0.1s 28
GAUSS-SEIDEL 00:00:23.739189 0.1s 17
SOR 00:00:10.210998 0.1s 6

100x100x100 cube simulated for 25 seconds

Method Time dt avg iterations
FTCS 00:00:24.048602 0.01s N/A
JACOBI 00:01:16.475670 1.0s 238
GAUSS-SEIDEL 00:00:38.909941 1.0s 131
SOR 00:00:10.885491 1.0s 33

At higher dt FTCS blows up and is wildly inaccurate. At shorter simulation periods, FTCS is competitive. At longer time periods SOR pulls ahead drastically as FTCS is stuck on smaller timesteps.

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C 3D heat diffusion solver. Tests the performance characteristics of several heat diffusion solving algorithms. Simulation is controllable via a browser client with realtime WebSocket visualization.

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