Wave attenuation by the deltaport floating breakwater

• Main Author: Yetman, Richard D.
• Other Authors: Memorial University of Newfoundland. Faculty of Engineering and Applied Science
• Format: Thesis
• Language: English
• Published: 1988
• Subjects: Breakwaters; Mobile; Breakwater; The Breakwater; Newfoundland studies; University of Newfoundland
• Online Access: http://collections.mun.ca/cdm/ref/collection/theses2/id/249288

Thesis (M.Eng.)--Memorial University of Newfoundland, 1989. Engineering and Applied Science Bibliography: leaves 79-80. Deltaport is basically a large floating breakwater intended for use in the Hibernia region. This thesis describes an exploratory investigation into its wave attenuation characteristics. The breakwater portion of its structure is porous like and consists of a staggered array of tubes. When wave energy impinges on such a structure, some of it is reflected back, some is transmitted through, under and around the structure, and the rest is dissipated. Initially, we had hoped to completely isolate the contributions to this energy balance. However, because of the complex nature of the Deltaport Structure, we found this goal to be extremely difficult, if not impossible, to attain. To simplify, we decided to consider only two dimensional sections of the structure and concentrate on the effect of porosity. A two dimensional section of the breakwater structure was installed in the wave tank at Memorial University of Newfoundland, and its attenuation characteristics for several levels of porosity were measured. As expected, it was found that porosity greatly reduces attenuation. -- Two theoretical procedures were developed for the two dimensional setup. One, known as Dean's method, assumes the structure to be a nonporous vertical thin plate and is based on a potential flow description of the water motion. It gives very simple expressions for reflection and transmission and allows one to get a rough but quick look at performance. The other procedure is basically a finite difference numerical simulation based on the Navier-Stokes equations. It allows for wave energy dissipation, something not considered in a potential flow formulation. It also has a feature by which the porous nature of the structure can be accounted for. We believe we are the first to use this in a study of breakwater performance. Comparisons of the latter with the experiment show reasonable agreement. -- Numerical schemes are available that can handle three dimensional bodies interacting with waves; however, they can only deal with nonporous structures. One of these schemes, known as the Panel Method, accounts for wave diffraction and is based on a distribution of potential flow singularities over the wetted surface of the body. This technique was also applied to the Deltaport geometry. Obviously, because it ignores porosity, it represents an ideal. The two dimensional setup suggests that it overpredicts attenuation. -- The report also gives some suggestions for future work. For example, it might be possible to develop correction factors for the Panel Method based on the two dimensional setup.