Neural SPH: Improved Neural Modeling of Lagrangian Fluid Dynamics

Much of this code is an adapted version of the LagrangeBench code available at https://github.com/tumaer/lagrangebench. Our core functions are the following two:

• relax_wrapper in neural_sph/rollout.py - core relaxation algorithm
• case_setup_redist in neural_sph/utils.py - setup needed by the relaxation routine including neighbor list preallocation, box size for periodic boundary conditions, etc.

Install

# set up environment and install dependencies
python3.10 -m venv venv
source venv/bin/activate
pip install -r requirements.txt  # install dependencies
pip install -e .  # install neuralsph as a package

# on a cuda12 machine run this line in addition:
# pip install --upgrade jax[cuda12_pip]==0.4.20 -f https://storage.googleapis.com/jax-releases/jax_cuda_releases.html

Usage

Pre-trained models

Run python download_checkpoints.py to download all pre-trained model weights from LagrangeBench.

Datasets

Run bash download_data.sh all datasets/ to download all datasets from LagrangeBench.

Run the code

We show how to obtain the numbers we get on a rollout with our SPH relaxation on the example of a 2D LDC checkpoint stored in CKP_DIR=ckp/pretrained/gns_ldc2d/best:

# baseline without relaxation
python main.py eval.test=True load_ckp=$CKP_DIR eval.infer.n_trajs=-1 \
    eval.infer.metrics_stride=10 eval.n_rollout_steps=400 \
    r.variant_p=None

# rollout including 5-step relaxation with $\alpha=0.03$
python main.py eval.test=True load_ckp=$CKP_DIR eval.infer.n_trajs=-1 \
    eval.infer.metrics_stride=10 eval.n_rollout_steps=400 \
    r.loops=5 r.acc=0.03

RPF Force Smoothing

To implement the external force smoothing on the reverse Poiseuille datasets, we replaced the force function in the force.py file contained within the LagrangeBench datasets by the following two functions.

2D:

def force_fn(r):
    """Smoothed version of the 2D RPF force function using the error function"""
    sigma = 0.025 
    erf_mitte = lax.erf((r[1] - 1) / (jnp.sqrt(2) * sigma))
    erf_left = lax.erf(r[1] / (jnp.sqrt(2) *sigma)) 
    erf_right = lax.erf((r[1] - 2) / (jnp.sqrt(2) * sigma)) 
    res = erf_left + erf_right - erf_mitte
    return jnp.array([res, 0.0])

3D:

def force_fn(r):
    """Smoothed version of the 3D RPF force function using the error function"""
    sigma = 0.05
    erf_mitte = lax.erf((r[1] - 1) / (jnp.sqrt(2) * sigma))
    erf_left = lax.erf(r[1] / (jnp.sqrt(2) *sigma)) 
    erf_right = lax.erf((r[1] - 2) / (jnp.sqrt(2) * sigma)) 
    res = erf_left + erf_right - erf_mitte
    return jnp.array([res, 0.0, 0.0])   

For simplicity, we added the external force functions for RPF and dam break directly to the case.py > case_builder and one can configure them with the CLI arguments r.is_subtract_ext_force and r.is_smooth_force, see defaults.py for more details.

Citation

Cite the ICML 2024 paper as

@article{toshev2024neural,
  title={Neural SPH: Improved Neural Modeling of Lagrangian Fluid Dynamics},
  author={Toshev, Artur P and Erbesdobler, Jonas A and Adams, Nikolaus A and Brandstetter, Johannes},
  journal={arXiv preprint arXiv:2402.06275},
  year={2024}
}