SmartFlow

A Deep Learning solver for the Shallow Water Equations

SmartFlow is an extension of MattFlow, which is a 2-stage Runge-Kutta numerical solver for the Shallow Water Equations (SWE)*. The project comprises the implementation of Deep Learning architectures out of the corresponding papers. The models are trained on data produced by MattFlow, aiming to predict the successive states of the fluid.

*SWE is a Computational Fluid Dynamics (CFD) problem, which models the surface of the water via a coupled system of three hyperbolic Partial Differential Equations (PDEs).

Requirements
python3
tensorflow >= 2.2.0
numpy >= 1.19.2
matplotlib >= 3.3.2
mattflow >= 1.3.4
pandas >= 1.1.3
scikit-learn >= 0.24.2
scipy >= 1.5.3

Contents

• Install
• Input - Prediction - Ground Truth
• Dataset format
• Dataset types
• Preprocessing
• Model
• Architectures
• Reference papers
• License

Install

pip install smartflow

git clone https://github.com/ThanasisMattas/smartflow.git

Input - Prediction - Ground Truth example

Dataset format

Each data example is the state of the fluid at some time-step and the corresponding label is the state at the next time-step. A state comprises a 3D matrix, U, where the channel axis consists of the 3 state variables of the SWE, surface height, flux-x and flux-y, populating the discretized 2D domain. The main idea is that the state matrix can be regarded as a 3-channel image, where each pixel corresponds to a cell of the mesh and each channel to a state variable.

Input data scenarios

• A single frame (one time-step)
• 2 frames (in order to give the model the opportunity to learn gradients)
• Only the surface height channel
• All 3 channels
• With/without updating boundary conditions
• Different sizes and frequency of water drops.

The best performance occurred with 2 frames, all 3 channels, updating BC and using the highest grid resolution, meaning that there is no redundant information at this point.

Dataset Preview

30 frames every 1000 frames

Dataset types

SmartFlowDS

Base class for SmartFlow datasets

• Both NCHW and NHWC formats are supported
• Input frames have updated ghost cells, but labels don't (those cells will not be predicted). Therefore, after inference the prediction will be padded with ghost cells, before it is fed back to the model for the next prediction. Boundary conditions are required by the numerical scheme and can be easily evaluated upon inference, hopefully providing some valuable information to the model.
• Time-steps at which a drop falls cannot be used as labels, because there is no way to infer when and where a new drop will fall, using information from the previous state of the fluid. However, those frames can perfectly be used as input.
• Data augmentation: Random flip, rotate and shuffle of the train batch.

DSequence

• Used when training on GPU or when the dataset does not fit into the memory.
• Derived from SmartFlowDS and keras.utils.Sequence, in order to load one batch at a time from a numpy memmap.

DSet

• This subclass is preferred when the dataset does fit into the memory or TPUs will be deployed on the google colab cloud.
• Derived from SmartFlowDs and tf.data.Dataset.

Preprocessing

Normalization (mean - std)

• On-devise, using the normalization_layer().
• On dataset creation, using the Normalizer class, ​sacrificing portability in order to relieve the GPU while training.

Stats type

• Per frame or batch
• Channelwise or using the whole volume

Visualization

Checking that:

• Flip and rotation orientation of input and ground truth are coherent.
• Input dataset is shuffled.
• Examples with new-drop-frames as labels are removed, because it is not possible to infer where and when a new drop will fall.
• Input is normalized.

Model

Setup

loss MeanSquaredError
metrics MeanAbsoluteError
optimizer Adam with learning rate scheduler
monitors val_loss
loss_weights [0.2, 0.8] (When multiple heads i.e. Inception_v3)

Callbacks

• checkpoint
• earlystopping
• tensorboard
• learning rate schedule
• garbage collector

Architectures

• Inception-v3
• Inception-ResNet-v2
• Inception-ResNet-like
• ResNet
• Simple CNN
• Fully-Connected NN

Reference papers

• He, K., Zhang, X., Ren, S., Sun, J. Deep Residual Learning for Image Recognition. 2015. arXiv: 1512.03385.
• Szegedy, S., Vanhoucke, V., Ioffe, S., Shlens, J., Wojna, Z. Rethinking the Inception Architecture for Computer Vision. 2015. arXiv:1512.00567.
• Szegedy, C., Ioffe, S., Vanhoucke, V., Alemi, A. Inception-v4, Inception-ResNet and the Impact of Residual Connections on Learning. 2016. arXiv: 1512.00567.
• Ioffe, S., Szegedy, C. Batch Normalization: Accelerating Deep Network Training by Reducing Internal Covariate Shift. 2015. arXiv: 1502.03167.

License

GNU General Public License v3.0

(C) 2021, Athanasios Mattas
[email protected]