Smoke Simulation

Assignment 2: Smoke Simulation!

Due: March 5th, 2010

Starter code: For MSVC 2005, For MSVC 2008

Overview

The purpose of this assignment is to experiment with incompressible fluid simulation implemented with a Semi-Lagrangian approach. You will implement a 3D Smoke simulator using the techniques described in the following resources:

Class slides
Fluid Simulation: SIGGRAPH 2007 Course Notes (Chpts 1-5) by Bridson, Fedkiw, and Muller-Fischer

The startup code includes an incomplete fluid animation system. Although rendering and most of the necessary data structures have been written, this will be a challenging assignment. You will need to implement the following:

(60 points) Air, smoke density and temperature simulation (MACGrid.h)

(25 points) Implement a Semi-Lagrangian approach to solve the advection step for air velocity, smoke desnity, and temperature

Implement MACGrid::advectVelocity(): GriddedData for U,V,W components of the velocity have already been setup for you See member variables MACGrid::mU, MACGrid::mV, and MACGrid::mW.
Implement MACGrid::advectTemperature(): GriddedData for temperature has been setup for you. See member variable MACGrid::mT.
Implement MACGrid::advectDensity(): GriddedData for density has been setup for you. See member variable MACGrid::mD. Additionally, values in mD will automatically be rendered for you.
Implement MACGrid::updateSources(): Initilialize a smoke source, for example, have smoke come up from the bottom of the container
Implement buoyancy forces

Look at MACGrid::addExternalForces()
Implement MacGrid::computeBouyancy()

(25 points) Solve the poisson equation for pressure

Implement MACGridd::project(). Use the function cg_solve() to solve a system of linear equations using the conjugate gradient method described in class.

(10 points) Add vorticity confinement forces

ImplementMACGrid::computeVorticityConfinement()

(30 points) Boundary conditions and solid objects

Smoke should be contained within a closed box (e.g. boundary conditions with the sides of the grid should be correct -- see the Bridson notes for details)
Implement a solid object within the grid (any shape).

(Extra Credit - Up to 20 points)

Implement a preconditioner for the conjugate gradient step. Document which preconditioner you used, plus the speedup you got
Add dynamic objects, for example, an object that the user can move with the mouse
Add mouse interaction forces
Implement a better numerical scheme to avoid numerical dissapation, for example, cubic interpolation such as the one described in "Visual Simulation of Smoke" by Fedkiw, Stam, and Wann Jensen.
Implement fluid viscosity. Compare and show the results with and without viscosity.

Submission

ZIP your .cpp, .mel, .h, .vcproj, and .sln files and submit to Blackboard. For full credit, your application must build without modifications for either msvc 2005 or 2008. Only complete submissions will be graded.
Briefly write-up which questions you completed in a file called README.txt.
If you used any additional sources, you must include them in your writeup
Include movies showing off your work

IMPORTANT!

If you used — or looked at — any source code you found somewhere else or which someone else wrote, even a single line, you SHOULD describe that in the writeup. You are not allowed to use any fluid simulation code available on the web! Please talk to us before using any existing code for this assignment except for the code provided by us.

Questions for you to answer (10 points)

Theoretical Questions

Notes

Dependencies

This project was built and tested with GLUT, Boost 1.37 and Boost 1.42, and Devil 1.6.7 on MSVC 2005. GLUT and DevIL are included these with the source, but you will need to download Boost. We use Boost's UBLAS library for its very effecient matrix data structures and operations (especially for sparse matrices). DevIL is an image library used to implement screen capture.

Built in features

Simulation controls

Play: Press '>' or right click to start the simulation
Pause: Press '=' or right click to pause the simulation
Reset: Press '<' or right click to reset the simulation

Camera controls

Rotate: Left click, drag to rotate.
Zoom: Middle click, drag to zoom.

Rendering options

Velocity display: Press 'v' or right click to toggle the drawing of velocity vectors.
Render density as transparent, white cubes
Render density as sheets with interpolation between cells (looks smoother)

Recording mode

Press 'r' or right click to toggle screen capture. Every frame will be saved to the /output directory which you can assemble into a movie file with tools such as Adobe AfterEffects or VirtualDub. Alternatively, you can use FRAPS to create

Configurable grid size

Edit the global dimensions 'theDim' defined in GriddedData.cpp

Important data structures

Gridded data: Gridded data is a low level data structure for implementing any data stored in a grid. See GridData.h for details.
MAC Grid: MAC Grid implements a staggered grid described in the Bridson fluid notes. X,Y,Z components of the velocity are stored at each face. Other quanitites such as density and temperature are stored in the cell centers.

Hints

Start small! Carefully check your calculations with a tiny grid, say 2x2x1, in debug mode. Then test in release mode with a larger grid.
Release mode is much faster than debug mode
Test your smoke with a 2D Grid, for example, set the grid dimensions to 10x10x1
Don't forget you can visualize your velocities!
If you find cg_solve does not converge, it's likely that your system of equations are not setup correctly.

Make sure your A matrix is positive semi definite. You can check in matlab or write a function to test

Checking your projection step: remember that the projection step ensures that the resulting fluid is non-divergent. Therefore, after calling project, computing the velocity divergenceof each cell should be zero. If this is not the case, there's a problem.