We conduct Large Eddy Simulation (LES) studies of turbulent wind over surface waves that propagate in different directions from wind direction. The results are used to better understand how misaligned waves modify the wind turbulence and resulting air-sea momentum flux. Recent observational studies show that the drag coefficient (air-sea momentum flux) is significantly reduced when dominant wind-forced surface waves are misaligned from the local wind. Misaligned waves are particularly common under tropical cyclones and/or in shallow water coastal regions. The results from this study will be used to develop a new parameterization of sea-state dependent drag coefficient (air-sea momentum flux) including the effect of misaligned surface waves. Such a parameterization is needed for various coupled atmospheric, wave, and ocean prediction models. In particular, tropical cyclone prediction models are expected to be significantly improved by including the newly developed parameterization.
The student will obtain extensive experience working on an HPC cluster (command-line Linux, Fortran code compilation, SLURM job scheduler, optimal submission parameters etc.) and will also learn to use available visualization tools. The project will require access to a modest HPC system that provides ~1024 cores (128 cores x 8 nodes, 64 cores x 16 nodes, etc.) and a scratch filesystem.
Milestone Title: Milestone #1 Milestone Description: determine project scope, learn how to work on an HPC cluster, launch presentation Completion Date Goal: 2023-02-14
Milestone Title: Milestone #2 Milestone Description: carry out the initial set of LES runs on the HPC cluster, learn the data analysis and visualization tools. Completion Date Goal: 2023-03-15
Milestone Title: Milestone #3 Milestone Description: analyze the initial sets of LES runs, make a progress report presentation. Completion Date Goal: 2023-04-15
Milestone Title: Milestone #4 Milestone Description: carry out the complete set of LES runs. Completion Date Goal: 2024-05-15
Milestone Title: Milestone #5 Milestone Description: wrap up the data analyses, make the final presentation, write the project report.
Completion Date Goal: 2024-06-15
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Final Report
Better constraining the drag coefficient under shoaling and wind-wave misalignment would be a useful contribution to the physics of air-sea interaction and could potentially improve modeling performance. We'll see how the results shake out!
The results could have engineering impacts; for example, better constraining drag at the wave surface could improve estimates of wind speed at blade level for offshore wind farms.
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In theory better constraining the drag coefficient of shoaling waves could improve things like storm surge model predictions, which of course would have economic and safety implications.
When using HPCs, I always find myself trying to balance willingness to experiment with not wanting to waste energy and computing resources. I think I'm in a much better place with that balance now.
We've tested a number of different permutations of inputs for shoaling and non-shoaling waves which has taught us a lot about how best to sync up our simulations with laboratory observations. So, while there's a lot of work still to do, we've done a lot of the leg work to speed up future simulations while aligning results with observations.