Predictive capability of computational fluid dynamics simulations for the prediction of plunging breaking wave is assessed. Laminar flow simulations are performed for dam break, solitary wave run up on a slope and flow over a submerged bump using OpenFOAM, a finite volume solver with volume-ofluid (VoF) interface capturing method, and Proteus, a finite element solver with coupled level-set/ volume-ofluid (CLSVoF) methods. CLSVoF predicts wave elevation before the plunge, and primary and secondary plunger shapes better than VoF in all the cases. The primary limitation in the simulation is the airflow, which results in diffused plunger tips in VoF simulations, and results in surface peel-off in CLSVoF simulations. Future work should include 3D turbulent flow simulations.

This investigates the velocity fields of a plunging breaking wave impinging on a structure through measurements in a two-dimensional wave tank. As the wave breaks and overtops the structure, so-called green water is generated. The flow becomes multi-phased and chaotic as a highly aerated region is formed in the flow in the vicinity of the structure while water runs up onto the structure. In this study, particle image velocimetry (PIV) was employed to measure the velocity field of the water dominant region. For measurements of an aerated region that cannot be measured by PIV, a new measurement method called bubble image velocimetry (BIV) was developed. The principle and setup of the BIV method were introduced and validated. Mean and turbulence properties were obtained through ensemble averaging repeated tests measured by both methods. The dominant and maximum velocity of the breaking wave and associated green water are discussed for the three distinct phases of the impingement-runup-overtopping sequence. The distribution of the green water velocity along the top of the structure has a nonlinear profile and the maximum velocity occurs near the front of the fast moving water. Using the measured data and applying dimensional analysis, a similarity profile for the green water flow on top of the structure was obtained, and a prediction equation was formulated. The dam breaking solution used for the green water prediction was examined with determining initial water depth based on the experiment conditions. Comparison between measurements, the prediction equation, and the dam breaking flow was made. The prediction equation and the dam break flow with appropriate initial water depth may be used to predict the green water velocity caused by extreme waves in a hurricane. To demonstrate the aeration of the breaking wave and overtopping water, void fraction was also investigated. There is strong aeration in the region of overtopping water front generated by a plunging breaker. Void fraction of overtopping water was measured using a fiber optic reflectometer (FOR). The measured velocity and void fraction were also used to estimate flow rate and water volume of overtopping water.

¡@The ocean ambient noise of coast is mainly influenced by sea waves, boats or ships, or human¡¦s coast activities. Among them, most of the ambient noise is from the breaking wave noise caused by wind, and its frequency range is quite wide (0.5~50 kHz). The breaking wave noise mechanism of surf zone is very complex, and has a variety of signal features. In this research, the location is at the Sizih Bay near Kaohsiung Harbor. Hydrophone was used to collect the noise and the wave motion process of surf zone was recorded simultaneously with a digital video camera. It was shown from the experiment results, as the wave evolved in the surf zone, it would eventually become unstable and collapsed, so a large amount of air would be trapped in water and forming bubble clouds. The oscillating bubble cloud from breaking wave would generate high frequency sound. The results also indicated that when breaking wave reached the location hydrophone, a wide band pulse sound was generated with a level as high as 120 dB. In the analysis of each frequency (1k, 2k, 3k, 4k, 5k Hz), due to the oscillating effects air bubbles after breaking wave, the noise level at 2~5k Hz were higher as compared to that without breaking wave passing the hydrophone. The last result was also validated by the time integral of the noise energy through out the wave evolution. In addition to the process of breaking waves and residual air bubbles under breaking waves contributing to the breaking wave source, for example discussed in the study breaking wave¡¦s period and breaking wave height, the results from these two studies found, when the longer the breaking wave period , the breaking wave SPL will be bigger with the longer the breaking wave period. And in the breaking wave height, when the breaking wave height much higher, breaking wave SPL will be much bigger too. And learned from these two conclusions , breaking wave periods and height will make the breaking waves source level caused by changes.

In this thesis,I discuss the wave pass on submerged bweakwater,and theheight of submerged breakwater,different slope of submerged breakwater with breaking wave relations.I do experiment to find the regular between breaking wave and the design of submerged breakwater.I use different submerged breakwater,there are two slope.There are 1/2 and 1/5.The height of submerged breakwater is 45 cm,the wide of submerged breakwater is 75 cm.the water deep is from 50cm to 90 cm,Wave cyclical is from 1.2 sec to 2.7 sec,I use H L to choose wave height,and save the data of incident wave.and then I analysis the data to get t K and energy.I also memorize the site of breaking wave and breaking type. From the experiment ,we know that wave do not be broken, be broken, and the regular of breaking wave and breaking type ,so we can use the regular to design the height of submerged breakwater, the slope of submerged breakwater. So we can use the least costs to protect the seacoast. When we know local wave condition, we can design the height of submerged breakwater to break wave that is dangerous for seacoast ,or we want to break wave when the wave height at 1 m or 2 m or others design the height of submerged breakwater. When £m^2h/g is between 0.3 and 2.5,we can find that when R/H0¡¦ is smaller than 1,the wave will break¡CWhen wave break bysubmerged breakwater ,we can find the slope of 1/5 is better than the slope of 1/2 to reduce the wave.Both slope of 1/2 and slope of 1/5 are effective to reduce wave energy at Hi/R=2.

The simulation of breaking wave has a computationally intensive application. In order to reduce the computation, this thesis presents a slice-based water simulation method for ocean breaking waves on natural simulation by generating the 2D simulations and then integrating these 2D simulation results into a 3D shape. We first simulate a 2D wave by a 2D Navier-Stokes solver to obtain the varying of ocean. Then, we combine VOF (Volume of fluid) with a new reconstruct free surface method that is a fast 2D simulation. We use linear interpolation with noise function to construct a complete 3D ocean simulation from these 2D simulations. By doing these, one can reduce the computation time and achieve better efficiency.

Yes / The paper employs a Reynolds-averaged Navier¿Stokes (RANS) approach to investigate the time-dependent wave breaking processes. The numerical model is the smoothed particle hydrodynamic (SPH) method. It is a mesh-free particle approach which is capable of tracking the free surfaces of large deformation in an easy and accurate way. The widely used two-equation k¿¿ model is chosen as the turbulence model to couple with the incompressible SPH scheme. The numerical model is employed to reproduce cnoidal wave breaking on a slope under two different breaking conditions¿spilling and plunging. The computed free surface displacements, turbulence intensities and undertow profiles are in good agreement with the experimental data and other numerical results. According to the computations, the breaking wave characteristics are presented and discussed. It is shown that the SPH method provides a useful tool to investigate the surf zone dynamics.

The major purpose of this study is focused on the characteristics of the breaker and the impulse caused by wave breaking. Two-dimensional surface regular gravity water waves propagating on a gentle sloping bottom are considered and the consecutively temporal-spatial evolution of wave traveling form deep water to shallow water is also investigated. Two perturbation parameters, bottom slope and the deep water wave amplitude , proposed by Chen et al.(1992~2005), are introduced in this problem. Also, two different systems in fluid mechanics are used and the theoretical results are corrected to order , including nonlinear quantities, in both of Eulerian and Lagrangian systems. Considering the point of view that the horizontal velocity of a specified fluid particle is equal to the wave celerity while the wave begins to break, some important physical phenomena, such as the evolution of wave profile, the trajectory of fluid particle, and the water wave pressure, are described in this analytical analysis. Furthermore, the wave length, wave height, water depth and wave steepness of breaking wave are solved. To modify the insufficiency of former semi-empirical formula for the impulse due to wave breaking, a theoretical formula is proposed by integrating the resulting water wave pressure form mean still water level to free surface. Previous experimental studies are employed to verify the theoretical results. For wave for a further verification on the characteristics of wave breaking, some measurements on the movement of fluid particle, wave force and impulse wave conducted. Reasonable agreements can be found from the comparisons. It is concluded that consideration of wave nonlinearity is necessary while dealing with wave breaking problem.

A laboratory experiment was performed to investigate the three-dimensional turbulence and kinematic properties that develop due to a breaking solitary and an irregular shallow water bathymetry. A large basin equipped with a piston-type wavemaker was used to generate the wave, while the free surface elevations and fluid velocities were measured using wave gauges and three-dimensional acoustic-Doppler velocimeters (ADVs), respectively. From the free surface elevations, the evolution and runup of the wave was revealed; while from the ADVs, the velocity and turbulent energy was determined to identify specific turbulent events and coherent structures. It was found that shoaling was confined to areas with gentler sloping bathymetry near the basin side walls and the runup shoreward of the still water shoreline was not uniform. The runup was characterized by a jetting mechanism caused by the convergence of water mass near the basin centerline as the wave refracted during breaking. The jetting mechanism caused the greatest cross-shore velocities to be located near the basin centerline. The greatest turbulent events were well correlated to borefronts, resembling hydraulic jumps, where the greatest shear and fluid accelerations occurred. Because of an abrupt change in the bathymetry, a coherent structure developed which was found to have a three-dimensional flow field. It was proposed that variations in the internal flow with depth were due to the orientation of multiple vortex rings.

¡@¡@The main purpose of this paper is to analyze the surface progressive gravity waves propagating on a gentle sloping beach in two dimension. Instead of using the method of Eulerian system by the previous investigators, we introduce the governing equations completely in the Lagrangian system directly. All the characteristics of the wave system is expressed by a suitable perturbation expansion in the bottom slope under linearizing the problem in wave amplitude, then all the governing equations are systematically expanded to order. The solution of the wave system is to be solved to second order , even to high order could also be obtained. Based on the obtained results, the velocity potential, pressure and motion of the fluid particle in the wave system in time and space is therefore presented, and we can see that the bottom slope is a main factor to screw the wave field to deform to break. Finally, the experimental result is cited to compare and verify.

In the present study, a fifth-order weighted essentially non-oscillatory (WENO) scheme was built for solving the surface-capturing level-set equation. Combined with the level-set equation, the three-dimensional Reynolds averaged Navier-Stokes (RANS) equations were employed for the prediction of nonlinear wave-interaction and wave-breaking phenomena over sloping beaches. In the level-set finite-analytic Navier-Stokes (FANS) method, the free surface is represented by the zero level-set function, and the flows are modeled as immiscible air-water two phase flows. The Navier-Stokes equations for air-water two phase flows are formulated in a moving curvilinear coordinate system and discretized by a 12-point finite-analytical scheme using the finite-analytic method on a multi-block over-set grid system. The Pressure Implicit with Splitting of Operators / Semi-Implicit Method for Pressure-Linked Equation Revised (PISO/SIMPLER) algorithm was used to determine the coupled velocity and pressure fields. The evolution of the level-set method was solved using the third-order total variation diminishing (TVD) Runge-Kutta method and fifth-order WENO scheme. The accuracy was confirmed by solving the Zalesak's problem. Two major subjects are discussed in the present study. First, to identify the WENO scheme as a more accurate scheme than the essentially non-oscillatory scheme (ENO), the characteristics of a nonlinear monochromatic wave were studied systematically and comparisons of wave profiles using the two schemes were conducted. To eliminate other factors that might produce wave profile fluctuation, different damping functions and grid densities were studied. To damp the reflection waves efficiently, we compared five damping functions. The free-surface elevation data collected from gauges distributed evenly in a numerical wave tank are analyzed to demonstrate the damping effect of the beach. Second, as a surface-tracking numerical method built on curvilinear coordinates, the level-set RANS model was tested for nonlinear bichromatic wave trains and breaking waves on a sloping beach with a complex free surface. As the wave breaks, the velocity of the fluid flow surface became more complex. Numerical modeling was performed to simulate the two-phase flow velocity and its corresponding surface and evolution when the wave passed over different sloping beaches. The breaking wave test showed that it is an efficient technique for accurately capturing the breaking wave free surface. To predict the breaking points, different wave heights and beach slopes are simulated. The results show that the dependency of wave shape and breaking characteristics to wave height and beach slope match the results provided by experiments.