Animate Sand as a Fluid

Course project for Physically-Based Simulation in Computer Graphics HS21, ETH Zurich

Group 19: Yifan Yu, Bo Li, Yitian Ma

Usage

To setup the environment, use

pip install -r requirements.txt

You can change the simulation settings in src/simulator.py

global_params = {
    'mode' : 'apic',                            # pic, apic, flip
    'flip_weight' : 0.99,                       # FLIP * flip_weight + PIC * (1 - flip_weight)
    'dt' : 0.01,                                # Time step
    'g' : (0.0, 0.0, -9.8),                     # Body force
    'rho': 1000.0,                              # Density of the fluid
    'grid_size' : (64, 64, 64),                 # Grid size (integer)
    'cell_extent': 0.1,                         # Extent of a single cell. grid_extent equals to the product of grid_size and cell_extent

    'reconstruct_resolution': (100, 100, 100),  # Mesh surface reconstruction grid resolution
    'reconstruct_threshold' : 0.75,             # Threshold of the metaball scalar fields
    'reconstruct_radius' : 0.1,                 # Radius of the metaball

    'num_jacobi_iter' : 100,                    # Number of iterations for pressure solving using jacobi solver
    'damped_jacobi_weight' : 1.0,               # Damping weighte in damped jacobi

    'simulate_sand': False,                     # Simulate sand or water
    'sand_dt': 0.001,                           # Time step for simulating sand

    'scene_init': 0,                            # Choose from 0, 1, 2 to init the particle positions differently
}

The scene_init parameter corresponds to: 0 - Centered dam break, 1 - Fall from sky, 2 - Cornered dam break.

Run with GGUI:

python main.py

During running with GUI, you can press Space to reconstruct the mesh of current frame and export that into a obj model file. The output will reside in ../results.

You can also run without GUI and reconstruct each frame:

python main.py 300

where the simulation contains 300 frames.

If the simulation dt is too small, add a second cmdline argument to reconstruct surface every few number of simulation steps:

python main.py 300 10

You can also export frames as PNGs to output/{method}_{scene_init}/ by changing OUTPUT in src/main.py to True, the default frame number is 300. By default, each frame is acquired per 3 steps of fluid simulation, and 30 steps of sand simulation. The included GIFs in output-fluid and output-sand is generated by the output PNGs using FFMPEG.

Dependencies

• taichi==0.9.0
• numpy
• scipy
• PyMCubes
• connected-components-3d

Presentation & Demo

Presentation Slides

Presentation Video

Gallery

Water

PIC:

FLIP:

APIC:

Rendered:

water_low.mp4

Sand

PIC:

FLIP:

APIC:

Rendered:

sand_low.mp4