/CFD

Primary LanguageC++

CFD Upsampler

The goal of our tool is to upsample CFD simulations from a small grid to a larger grid in the hope of saving on computation time. My model is based on the SRCNN architecture. You can find the paper here : https://arxiv.org/pdf/1501.00092.pdf The results are not very impressive yet. It's not clear that the original idea was viable. However it might be the case that I have a problem somewhere in my process that I have not been able to spot.

Requirements

You need the following packages :

  • tensorflow (make sure to also have tensorflow-gpu otherwise it will only use the cpu)
  • keras (normally it should already be in the tensorflow packages but I had issues so better make sure it's there)
  • Pillow (it's a library to manipulate images)
  • Numpy (should be already installed in most environments)
  • Sklearn (should be already installed in most environments)

Training the network

  • For some reason, transferring files to google cloud from my local computer is extremely slow. Therefore, I'm using github as an intermediary. However, there is a limit on the number of files you can upload, therefore I compressed my data folder into a data.zip file that you need to unzip.

  • In order to train the network you then run upsample.py. If the training is really slow, your gpu is not being used. Make sure that tensorflow-gpu is installed and that all required packages and drivers are up to date. Setting up an environment from scratch is pretty hard, so I strongly suggest using prebuilt images from your favorite cloud provider. I personally use the official tensorflow image from google cloud : https://cloud.google.com/deep-learning-vm/. The parameters are the following :

    • Epochs : The script expects an integer. One Epoch is when an ENTIRE dataset is passed forward and backward through the neural network only ONCE.
    • Batch size : The script expects an inteher. The batch size is the total number of training examples present in a single batch.

  • In order to generate custom data, you need to run generate_data.py which is located in /CFD/palabos-v2.0r0/examples/showCases/cylinder2d. The parameters are the following :

    • Number of batches (there will be an equal number of small batches and big batches. Each batch corresponds to a 2 seconds simulation with a given Reynolds number, one with a small grid size, the other with a bigger grid size so we get parallel data)
    • Upsampling rate (an integer to decide how large the big grid is going to be relative to the small grid. The trained model use was trained with a value of 2)
    • Mean Reynolds number. In order to generate the data, we will sample our Reynolds numbers with the provided mean and the provided variance (see below).
    • Variance : as explained above
    • N : an integer used to build the grid.
    • lx : N*lx corresponds to the dimensionality of the x-axis.
    • ly: N*ly corresponds to the dimensioanlity of the y-axis.

An already trained network is already provided (upsample.h5).

Running a simulation

In order to run a simulation you need to use the file run.py in /CFD/palabos-v2.0r0/examples/showCases/cylinder2d. The parameters are the following :

  • N : like above
  • Re : like above
  • lx : like above
  • ly : like above

Upsampling a simulation

In order to upsample a simulation, you need to use the file predict.py in CFD/ The parameters are :

  • pathSmall = path of small grid images (the already trained network was trained for small images with size 100x100)
  • pathBig = path to save upsampled images