This research aims to improve the understanding of breaking wave vortices impinging on the seabed. This has broad impacts on the prediction of a wide range of near-shore processes where wave breaking is fundamental in driving the sediment transport and resulting morphological changes. Detailed laboratory experiments will provide a high quality, comprehensive data set to test and improve a numerical model to better resolve the effects of wave breaking and eddy impingement on the bottom boundary layer structure. In return, the validated model will provide more detailed information to help interpret the measured data as well as a valuable research tool to model prototype wave conditions not reproducible in the laboratory. This research project would benefit society by enabling the development of better engineering tools for coastal zone management and mitigation of coastal hazards. The project will support two PhD students, one at South Dakota State University (SDSU) and another at the University of Delaware (UD), and will provide an opportunity for the new PhD program at SDSU to grow through research collaboration with an established research center. The PhD student from UD will participate in a portion of the experimental program at SDSU and work with the SDSU PhD student on model/data comparison. He/she will also work for a period at the University of Washington (UW) during the development of needed model extensions. To broaden the impacts of the research on STEM education, the lead PI will design a new technical elective on advanced fluid mechanics laboratory, which will be offered to undergraduate seniors and graduate students. The course will include a suite of experiments to give students hands-on experience with measuring bed shear stresses in steady and unsteady flows using different experimental techniques and approaches, emphasizing the importance of careful experimentation and analysis to produce high-quality, reproducible results.

The objective of this research is to understand the structure of the bottom boundary layer and determine the bed shear stresses induced by the impact of breaking-wave-generated vortices on a plane beach. Laboratory experiments will be conducted in a 25 m-long, 0.9 m-wide and 0.75 m-deep tilting flume equipped with a programmable wave generator. The turbulent velocity fields under spilling and plunging waves will be measured in a three-dimensional (3D) flow volume on smooth and rough beds using a volumetric three-component velocimetry (V3V) system. The measured data will be used to study the momentum balance in the near-bed region and to develop more accurate methods for estimating the bed shear stresses in the unsteady, non-equilibrium boundary layer associated with breaking waves. The measured data will also be used to validate a multi-phase (air-water) large eddy simulation (LES) scheme for breaking waves, already shown to accurately describe the processes of wave breaking and eddy formation and evolution, to better resolve eddy impingement on the bottom and resulting modifications to the boundary layer structure.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

National Science Foundation (NSF)
Division of Ocean Sciences (OCE)
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Baris Uz
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University of Washington
United States
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