MFluidSolver

IISPH Demo: Vimeo

How Does It Work

This fluid solver uses GLFW, GLM, and GLEW. It reads a JSON configuration file and a JSON scene file, creating a fluid container and a scene container. The fluid generates particles once, then all the particles are subject to fluid forces (currently none). The scene is initially paused. The camera is controlled by a standard arcball interface described below. The solver currently set to display the neighbor particles of the first particle, which can be changed randomly. The solver can also export the backend grid for the fluid particles to the VDB format. The solver runs both SESPH and IISPH.

Dependencies

• Boost (Filesytem, System, Unit Test Framework)
• OpenVDB 2.3.0

Build Instructions (*nix)

By default, the program is set to INFO level logging mode as set in src/MFluidSolverConfig.hpp.in. There are many other options there, including logging settings and defaults, but note that defaults will be overwritten by the configuration file config/config.json.

mkdir build
cd build
cmake ..
make
./MFluidSolver

Unit Test Instructions (*nix)

This will run all tests in the unittest folder. Test results will be printed to stdout, and details are found in build/Testing/Temporary/LastTest.log. This does include a brief performance test on neighbor search.

make test

How To Use

Press P to toggle pausing. Press Press N to randomly pick a particle to show its neighbors. Press E to export a VDB file of the graph to export.vdb (if OpenVDB is enabled in MFluidSolverConfig). Press R to reseed the scene using the fluid source. Press right to step frame by frame (0.001 seconds). Press S to write out a screenshot to screenshot_%05d.tga.

All SPH parameters, as well as several general program parameters, can be found in config/config.json. The scene file, which contains dimensions, particle parameters, camera settings, and particle spawn information, can be edited from scene/scene.json. Parameter names are case sensitive, but options are not. If you change parameters outside of the build folder, you will need to rerun cmake ... You can avoid this issue by editing the files in the build folder. Note the following case-insensitive string options available for several parameters:

neighborSearchType

• naive
• uniform
• indexSortedUniform
• indexSortedUniformInsertionSort
• zIndexSortedUniform
• zIndexSortedUniformInsertionSort

spawnMethod

• jittered
• poissonDisk
• uniform

visualization

• type
  • density (set maxDensityDifference)
  • index
  • neighbors
  • none
  • particle (set particleId)
  • pressure (set maxPressure)
  • velocity (set maxVelocity)
  • velocityDir
• maxDensityDifference
• maxPressure
• maxVelocity
• particleId
• velocityColor (8-bit rgb array)

sph

• maxPressureSolveIterations
• densityTolerance
• calculateMass (boolean, solver calculates based on initial density)
• dInitialDensity (when calculating mass)

The numUpdates parameter can be used to set the number of frames to simulate in order to get accurate and comparable performance ratings.

Arcball

The camera uses the arcball interface and can be controlled with the left and right mouse buttons and the scroll wheel.

The left mouse button is handled by an arcball interface. Clicking and dragging across the center of the GL widget rotates the camera around its focus point in the X and Y directions. Clicking and dragging in a circular motion around the outer edges of the GL widget rotates the camera around its focus point in the Z direction. The movements of the camera should follow the movements of the mouse intuitively.

The scroll wheel zooms the camera. Scrolling up zooms out and scrolling down zooms in.

The right mouse button pans the camera. This changes both the camera's and its focus point's position. Right-click and drag to move the camera in the opposite direction of the mouse. It will look like you're dragging the scene with you.

IISPH Simulation Performance

CPU: Intel i7-4800MQ limited to 2.7GHz
GPU: NVIDIA GeForce GTX 765M
Compiler: GCC 5.3.0
Measured in seconds per frame. Note that this includes time spent updating the viewer and logging input events.

• The performance gain from index sorting is a signficant improvement over a standard uniform grid, especially when insertion sort is not forced.
• The fact that the uniform grid uses the Y axis last (i.e.: change in the Y-coordinate causes the greatest index change) may play a role in making uniform grids comparable to Z-indexed grids, as fluids tend to stay within the XZ-plane. It would be interesting to explore this further.
• Z-indexing may be more beneficial in cases where the XZ-plane is large (i.e.: when there are larger index changes in the uniform grid), as it is in the Cube in Cube scene.
• Index sorted grids sort every frame with std::sort, which is a hybrid of introsort and insertion sort in GCC. This likely explains the deficiencies of using insertion sort only.
• Insertion sort may also be less effective in IISPH where timesteps can be larger than in traditional SESPH, so particles travel much farther and therefore change indices much more frequently.

Missing Required Features

• Partio point export
• OpenVDB level set export
• Optional: Update derivatives
• Optional: Ihmsen boundary conditions
• Optional: Cache neighbor distances
• Optional: Poisson distribution seeding
• Optional: Test bicubic spline kernel
• Optional: Solid body coupling
• Optional: Headless mode

Extra Features

None

Credits

• Original Class Repository from Debanshu and Akshay! Compiled the base Nuparu, CMakeLists.txt, and source structure.
• Nuparu Dependency and Foundation Libraries
• DDS File Loader adapted from opengl-tutorial.org (WTF Public License).