Transformation of Nonlinear Waves in the Presence of Wind, Current, and Vegetation

摘要

Accurate prediction of extreme wave events is crucial for the safe maritime activities and offshore operations. Improved knowledge of wave dissipation mechanisms due to breaking and vegetation leads to accurate wave forecast, protecting life and property along the coast. The scope of the thesis is to examine the wave transformations in the presence of wind, current, and vegetation, using a two-phase flow solver based on the open-source platform OpenFOAM. The Reynolds-Averaged Navier-Stokes (RANS) equations are coupled with a Volume of Fluid (VOF) surface capturing scheme and a turbulence closure model. This RANS-VOF model is adapted to develop a numerical wind-wave-current flume suitable for studying wind-wave, wave-current, and wave-structure interactions. Proper wind/wave/current boundary conditions are devised, two-equation and Shear Stress Transport (SST) turbulence models modified, and new modules capturing fluid-structure interactions are developed.;The wind and current effects on the evolution of a two-dimensional dispersive focusing wave group are examined. The model predictions are validated against experimental measurements with and without following wind. The effects of wind-driven current and opposing wind are investigated based on additional model results. The air flow structure above a plunging breaking wave group is examined. The RANS-VOF model is also applied to investigate the phenomenon of wave breaking and blocking due to strong opposing currents on a flat bottom. The geometric and hydrodynamic characteristics, i.e., the breaking criterion, the wave set-down and set-up, the energy dissipation, and the turbulence and vorticity generated in the wave breaking/blocking process are examined. A new coupled wave-vegetation interaction model is developed by coupling the RANS-VOF wave model with a Finite Element Method (FEM) based structure model using an immersed boundary approach. The wave height decay along and wave kinematics within a vegetation patch are examined.;The study has contributed to understanding of the wind effects on the extreme wave formation and breaking, the characteristics of current-induced wave breaking/blocking, and the vegetation effect on wave transformations. Insights gained from this study shed some light on the formation mechanism for rogue waves, and the breaking- and vegetation-induced dissipation formulations in the present wave prediction and circulation models.