The problem of finding the response of a moored floating breakwater is examined with particular reference to the effect of the moorings on breakwater motions. A computer program has been developed in which hydrodynamic coefficients are calculated using the finite element method. The complete breakwater-mooring system is modelled using the techniques of plane-frame structural analysis. The importance of the second-order drift force in the mooring analysis is noted. Comparison is made between the motions of an unrestrained floating body and those of a body restrained by slack moorings. A simple approximation for high-frequency motions is proposed. / Applied Science, Faculty of / Civil Engineering, Department of / Unknown

Methods and equipment for the measurement of ocean waves were reviewed and their suitability assessed for the aim of this project: field measurement of sea waves near a reflective coastal structure such as a breakwater. None was found to be suitable. The functional and performance objectives are set out for a new system. The evolution of the final design, based on an array of pressure sensors, is described. The whole system is intended to be deployed on the sea-bed. It is fully self contained and independent of shore based services. Located away from the surf zone it is well placed to survive storm conditions and unauthorised interference. Theoretical methods for the re-construction of surface elevation records from measured sub-surface pressures, and the experimental findings of other workers, are presented. Available methods of estimating the wave directional spectrum from a spatial array of surface elevation records are reviewed, and the most appropriate one implemented. The system has given extensive service at a number of coastal defence sites. The results of subsequent analysis of selected data sets are presented in detail. They show the pronounced nodal structure in amplitude expected in the presence of wave reflection, clearly demonstrating that a single point measurement is likely to give misleading estimates of incident wave height. For near-calm to moderate, shore-normal incident wave conditions the results were found to agree with theoretical predictions both of wave height as a function of distance offshore, and of the structure's frequency-dependent reflection coefficient. For rougher conditions, in which both theoretical and physical models are less applicable, the results agreed with visual observations.

A numerical model is developed to estimate wave forces on A-Jacks armor units. The forces include drag, inertia, buoyancy, and slamming as the unit penetrates the free surface. The wave force model is used to determine the rigid body motions of the units. Bulk forces on a matrix of units are also estimated. Wave flume tests are used to provide preliminary verification of the wave force model. The wave force model discretizes the A-Jacks into a number of small elements. The Morison equation is used for submerged elements with stretch linear wave theory employed for wave kinematics. For elements that penetrate the free surface, slamming force calculations are based on the von Karman method. The calculated wave forces are used to determine the rigid body rotation of a single, unrestrained A-Jacks. The axes of rotation are defined by the three contacts between the unit and the under layer. The model allows for an individual A-Jacks unit to rotate with one degree of freedom about the axis of rotation with the minimum stability. Adjacent units do not restrain the rotation and interactions with other units in the matrix are not included. The equation of motion is integrated in time to determine the rotation. This technique is used to determine the incipient motion conditions for a single, unrestrained A-Jacks. This is verified with experimental observations. The wave force model is found to be in agreement with the incipient rotational motion experiment results. The angular velocity at the instant when a lea of the unit rocks back and impacts the under layer can also be used to determine the impact force on the leg. A single, unrestrained A-Jacks is a simplistic idealization. In reality, there is a high degree of interaction among the units. The interaction results in partial sheltering from wave forces and additional motion restraint. The bulk forces on a matrix of A-Jacks units are estimated by applying an empirical factor to the calculated forces to account for the sheltering effects among units. A calibration and preliminary verification of the bulk force models is obtained by measuring forces exerted on a matrix of units mounted on a load-frame. The A-Jacks were subjected to a variety of wave conditions in a 10 m wave flume. The measured bulk force on a matrix of units was fit with the numerical model output using a consistent set of sheltering coefficients. / Graduation date: 2000

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

This study is to simulate a detached breakwater that offers not only a good shelter region for aquaculture cages in its lee but also cost effective. At the first step, a relatively simple 2-D boundary element method had been adopted to simulate the waves passing around various upright detached breakwaters. Based on the results of shelter effect, an opening with angle shape upright breakwater was determined and chosen for further study. Then a 3-D boundary element method is applied to simulate the shelter effect for various heights of breakwater in z-direction in order to achieve the optimal effect. According to the floating breakwater model, it shows that the average diffraction coefficient in the cage region is 0.387 with smaller material volume 9000 m3, which is far bellow 27000 m3 for the upright breakwater. Therefore, it suggests that floating breakwaters with angle should be used in cage aquaculture if the shelter region is required.

Thesis (Ph.D.) - University of Glasgow, 2008. / Ph.D. thesis submitted to the Department of Naval Architecture and Marine Engineering, Faculty of Engineering, University of Glasgow, 2008. Includes bibliographical references. Print copy also available.

Thesis (Ph. D.)--University of Hong Kong, 1998. / Includes bibliographical references (leaf 102-108).

Several theoretical models of the wave-induced current circulation in the vicinity of a breakwater extending from shore are presented. The models,which are patterned after a local field site, include several numerical models which take into account variable sea-floor topography and which compare the effects of linear and non-linear bottom friction as well as an analytical model characterized by semi-infinite beaches and uniform sea-floor topography. In general (for a given angle of wave incidence) the circulation patterns show two counter-rotating cells driven by wave-induced longshore currents which flow along both the breakwater and natural beaches toward their common intersection corner, with an offshore return flow in the form of a rip current. The qualitative features of the models are consistent with observations of sediment transport taken at the study site. Differences in the linear and non-linear bottom friction models do not become apparent until an off-shore trench parallel to the breakwater is introduced to the sea-floor topography. The non-linear model shows a deflection of the off-shore return flow into the trench in agreement with preliminary analysis based on a one-dimensional model. The linear results, however, differ considerably from those of the non-linear model and are difficult to interpret, showing an inordinate increase in transport over the trench. During the development of the analytical model difficulties were encountered due to the complexities of the analysis which necessitated that part of the solution be solved numerically. The results, while showing the same general features as the numerical models, exhibit a much more strongly divergent off-shore return flow. This difference, while unresolved, appears to be one of scale rather than of form. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Thesis (Masters Diploma (Engineering))--Cape Technikon, 1997 / The idea for this study occurred when movement of the caisson extension to the breakwater was observed. The major concern was, what would happen if the caisson breakwater extension failed? What would the financial implications be to the port? The CSIR have carried out a number of studies with regards to the safety of the structure. The consequences of caisson failure and the possible effects on the port were however not investigated. When it was determined that settlement was taking place, information concerning the condition of the caisson structure and factors influencing the structure were gathered. Investigations on the following were done: (a) Extent of caisson settlement. (b) Sediment movement around the structure. (c) Foundation condition. (d) Wave impacts of long and short period waves on the Ben Schoeman Dock in the event of caisson failure. (Refraction and diffraction). (e) Financial implications due to possible container operation downtime at Ben Schoeman Dock in the event of caisson failure. (f) The tourist potential of the structure. The conclusion reached in this study was that the Ben Schoeman Dock would not be adversely effected if partial or complete failure of the main breakwater should take place. One could even question the length of the extension and whether it was actually required. The recommendations of this study would be as follows follows: Maintain the caisson extension in good condition as it will be important for possible future extensions to the port. Develop the breakwater as it is an asset which has potential for tourism to Cape Town.

Two dimensional experimental and numerical modeling of wave transmission and wave-induced current over detached submerged breakwaters has been carried out in this thesis. Two preliminary 3D and a comprehensive series of 2D laboratory experiments have been conducted in the wave basin and 3 m wide wave flume. The preliminary 3D experimental tests qualitatively investigated the flow behavior behind a submerged breakwater and confirmed the validity of the 2D tests. The 2D laboratory tests examined wave breaking, reflection, transmission as well as wave-induced set-up and currents over submerged breakwater/reef structures. Different approaches to experimental data processing are examined in producing reliable application of the 2D laboratory measurements. Sensitivity of wave transmission coefficient, wave-induced set-up and wave-induced discharge over submerged breakwaters to other dimensional and non-dimensional parameters are comprehensively investigated. Previously published analytical/experimental studies for predicting/calculating wave breaking, wave transmission, wave-induced set-up and current are discussed and compared with the present experimental results. Improved equations/models are presented. Numerical modeling of the hydrodynamic effects of wave breaking and flow over a submerged breakwater is investigated using Delft3D. The capability of the Delft3D numerical model to simulate wave height transformation and wave-induced current over submerged breakwaters is provided. Four different approaches using combinations/options within the two main modules of Delft3D (SWAN and FLOW) are tested in the numerical simulations and the results are compared to the laboratory experimental data. Guidance is provided as to the most appropriate application of WAVE/FLOW/ROLLER modules in Delft3D for the reliable prediction of discharge and wave height over different width submerged breakwaters.