A Study of Two-Dimensional Unsteady Breaking Waves in Finite-Depth Water.

Wave Breaking;Energy Dissipation;Eddy Viscosity Model;Wave Spectra;Naval Architecture and Marine Engineering;Engineering;Naval Architecture & Marine Engineering

Tian, ZhigangSchultz, William W. ;

University of Michigan

关键词: Wave Breaking;    Energy Dissipation;    Eddy Viscosity Model;    Wave Spectra;    Naval Architecture and Marine Engineering;    Engineering;    Naval Architecture & Marine Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/75959/tzglife_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Laboratory experiments are conducted to study two-dimensional unsteady breaking waves in finite-depth water. An eddy viscosity model to simulate energy dissipation in breaking waves is proposed. Numerical simulations are performed to compare to the experimental results and good agreement is found. An energy-convergence rate based wave breaking criterion is evaluated. Our study revealed that the criterion is sensitive to the choice of local wavenumber, but a particular wavenumber based on local wave geometry distinguishes breaking waves groups from non-breaking ones. This study is published in Physics of Fluids (Tian Z., Perlin, M. & Choi, W. 2008, 20, 066604).Kinematics and dynamics of breaking waves are studied. Characteristic time and length scales associated with the wave groups and the breaking waves are defined. Correlations among the scales are demonstrated. Energy dissipation in breaking waves is quantified and is shown to scale accurately with the scales. Characteristic scales of the breaking crests are used to determine and parameterize the energy dissipation rate. The resulting normalized dissipation rate is on the order of 10-3. This study has been accepted to the Journal of Fluid Mechanics for publication.In experimental studies, spatial evolution of wave frequency spectra is observed, as is temporal evolution of wavenumber spectra. For non-breaking wave groups, energy loss near the spectral peak appears to depend on frequency spectral bandwidth. In breaking wave groups, higher frequency components lose energy while lower frequency ones gain to 50% of the energy loss in the higher frequency band.An eddy viscosity model is proposed to simulate energy dissipation in breaking waves. Numerical simulations with the model are performed to compare to the experimental measurements. Both the magnitude and the trend of the total energy measured in the experiments are approximated well. Good agreement as regards energy dissipation due to wave breaking and surface profiles after breaking is achieved. This work is part of the study mentioned above that has been accepted to the Journal of Fluid Mechanics.In the appendices, wave breaking onset prediction using the global wave steepness is revisited. Additionally, air flow separation over non-breaking waves is observed.