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An in-house numerical model developed at McMaster University was used in this research to investigate the effect of the wave breaking on the performance of Tuned Liquid Damper (TLD). In this model, the Volume Of Fluid VOF method was used to construct the free surface and the surface tension was taken into consideration to evaluate the wave breaking. The model was implemented on incompressible, 2D flow water within the TLD that was harmonically excited. . The ability of the TLD to cancel out the external excitation was examined via damping effectiveness of the TLD. The damping effectiveness is calculated as the ratio of the net energy experienced by the TLD to the input excitation energy; both energies were calculated as the area under the force-displacement curve. The investigation of the effect of the wave breaking was done through changing the fluid height ratios, amplitude and frequency ratios. The fluid height ratio was changed as h/L= 0.5, 0.35, 0.125 which is above and at and below the critical fluid level for wave breaking occurrence respectively. The critical height is defined as the height at which the waves start to break. It was found that at high fluid ratios wave breaking did not occur, in contrary, at critical level wave breaking did occur and even more breaking waves recorded to have taken place at much lesser levels. The effect of the fluid height ratio on the damping effectiveness of the TLD was investigated, it was seen that the damping effectiveness of the TLD improves as water level becomes shallower. The amplitude ratio was also examined; the behavior of the TLD in general did not change i.e. increasing the amplitude enhances the damping of the TLD. The frequency ratio range was selected to cover the near-resonance region. It was found that the TLD damps most excitation close to the resonance. The wave breaking occurrence was assured via the free surface visualization for several cases and found in agreement with different wave breaking shapes reported experimentally. / Thesis / Master of Applied Science (MASc)

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Modeling of wave energy transformation and breaking on fringing reefs is inherently difficult due to the unique topography of reefs. Prior methods of determining dissipation are based on empirical data from gently sloping beaches and offer only bulk energy dissipation estimates over the entire spectrum. Methods for deducing a frequency-dependent dissipation have been limited to hypothesized linkages between dissipation and wave shape in the surf zone, and have used bulk dissipation models as a constraint on the overall dissipation for mild sloping beaches. However, there is no clear indication that the constraint on the overall level of dissipation is suitable for the entire reef structure. Using these constraints the frequency-dependent dissipation rate can be deduced from laboratory data of wave transformation over reefs, taken at the Coastal and Hydraulics Laboratory. The frequency-dependent dissipation rate can then be integrated over the spectrum to derive an empirically-based counterpart to energy flux dissipation. Comparing the bulk energy dissipation estimates for the reef system to the frequency based method allows for the modification of wave breaking parameters in the frequency based estimation. Since this method is based on the Fourier transform of the time series data, it allows the dissipation to be found as a function of the frequency. This analysis shows that there is a correlation between the amount of energy in the low frequencies of the wave spectrum and certain characteristics of the frequency-dependent dissipation coefficient.

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Two different air-water interfacial flows are studied including plunging wave breaking and flow past a vertical surface-piercing circular cylinder using complementary CFDShip-Iowa version 6 including Cartesian grid solver and orthogonal curvilinear grid solver. The plunging wave-breaking process for impulsive flow over a bump in a shallow water flume has been simulated using the exact experimental initial and boundary conditions. The overall plunging wave breaking process is described with major wave breaking events identified: jet plunge, oblique splash and vertical jet. These major events repeat up to four times before entering the chaotic breaking. The simulations show a similar time line as the experiments consisting of startup, steep wave formation, plunging wave, and chaotic wave breaking swept downstream time phases. Detailed wave breaking processes, including wave profile at maximum height, first plunge, entrapped air bubble trajectories and diameters, kinetic, potential, and total energy, and bottom pressures are discussed along with the experimental results. The simulations show differences and similarities with other experimental and computational studies for wave breaking in deep water and sloping beaches. The geometry and conditions in the present study are relevant to ship hydrodynamics since it includes effects of wave-body interactions and wave breaking direction is opposite to the mean flow. Large-eddy simulation with the Lagrangian dynamic subgrid-scale model has been performed to study the flow past a surface-piercing circular cylinder for Re and Fr effect. The flow features near the air-water interface show significant changes with different Reynolds numbers from sub-critical to critical regime. It is shown that the interface makes the separation point more delayed for all regime of Re. Remarkably reduced separated region below the interface is observed for critical Re regime and it is responsible for much reduced wake and recirculation region behind the cylinder and it recovers in the deep flow. At different Fr, significant changes are shown on the air-water interface structures. At lower Fr, relatively smaller bow waves are observed in front of the cylinder with Kelvin waves behind the cylinder and small amount of free-surface roughness and turbulence are also seen in the wake region. For higher Fr, the bow wave increases remarkably with the larger wake region and deeper depression and it breaks with similar features of plunging breakers. Much more small air-water interface structures including splashes and bubbles are observed behind the cylinder. It is hard to distinguish the Kelvin waves behind the cylinder due to much larger free-surface oscillations and turbulence. As Fr increases, the Kelvin wave angle decreases and deeper and narrower depression region behind the cylinder are observed. The flow features around the cylinder are significantly changed due to this cavity region behind the cylinder.

The research presented in this dissertation focuses on understanding the dynamics of waves and currents in the presence of wave breaking. The simplest approach, direct numerical simulation of the ocean dynamics, is computationally prohibitive--waves typically have periods of tens of seconds, while currents vary on times from hours to days. This work uses a multi-scale asymptotic theory for the waves and currents (Craik and Leibovich, 1976; McWilliams et al., 2004}, similar to Reynolds-averaged Navier-Stokes, in order to avoid resolving the wave field. The theory decomposes the total flow into the mean flow (current) and fluctuations (waves), then takes a moving time average of the total flow equations to determine the wave forcing on the current. The main challenge is extending this theory to include a physical model for dissipative wave effects, notably breaking, in terms of the wave age, wind speed, and bottom topography. Wave breaking is difficult to observe, model, and predict, because it is an unsteady, non-linear process that takes place over disparate scales in both space and time. In the open ocean, white-capping often covers less than 2% of the surface, yet still plays an important role in the flux of mass, momentum, heat, and chemicals between the atmosphere and ocean. The first part of this dissertation proposes a stochastic model for white-capping events, and examines the stability of the ensemble average of these events. Near the shore, the decreasing ocean depth causes waves to overturn and break. Over time, this drives currents that erode sediment from beaches and deposit it around coastal structures. These currents are often so strong that their effect on the wave field, and thus their own forcing, is significant. A detailed analysis of this phenomena makes up the second part of this dissertation.

Determining the largest breaking wave height which can occur in water of finite depth is a fundamental reference quantity for the design of coastal structures. Current design guidelines are based on investigations which predominantly used monochromatic waves, thereby neglecting group effects which are inherent to the free propagation of waves in deep water. The Coastal Engineering Manual (CEM) states that wave grouping and its consequences is of significant concern, with breakwater armour damage being generally attributed to higher waves associated with wave groups. However, the CEM also acknowledges that there is little guidance and few formulae for use in practical engineering. This thesis describes a laboratory-based investigation into the effect of wave groupiness on wave shoaling, breaking and surf zone processes. New optical-based techniques for data abstraction, developed within this study, have allowed examination of the interaction between deep water intra-wave group processes and shallow water shoaling processes. The applicability of existing methods for predicting breaking wave height and position is evaluated, along with the implications of groupiness on engineering design in the nearshore. The effect of wave groupiness on overtopping and hazard on emerged rock platforms is similarly assessed. Wave group testing has revealed that the spatial phasing of intra-group processes during shoaling can result in considerably different shoaling and breaking regimes. Under certain regimes, wave breaking occurred further shoreward and in a more plunging manner than under other regimes. Within the mid to inner surf zone, waves were also observed to propagate into shallower water before breaking than is predicted by existing design guidelines. This could result in under-prediction of wave height by up to 100%. Expressions are developed for the prediction of maximum wave heights and surface elevation on plane slopes. These expressions implicitly include non-linear group effects and group-induced water-level variations within the surf zone, and are found to provide conservative upper envelopes for the range of data observed within the current testing regimes. Predictive schemes are similarly developed for overtopping hazard on emerged rock platforms based on critical wave and water-level conditions. Variations in maximum overtopping flow values due to intra-wave group processes of up to +/-35% were found. These group effects were found to reduce by up to 30% the threshold wave conditions before the initiation of hazard.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第14147号 / 工博第2981号 / 新制||工||1442(附属図書館) / 26453 / UT51-2008-N464 / 京都大学大学院工学研究科都市環境工学専攻 / (主査)教授 後藤 仁志, 教授 細田 尚, 准教授 牛島 省 / 学位規則第4条第1項該当