A novel video observational method for the space-time stereoscopic reconstruction of dynamic surfaces representable as graphs, such as ocean waves, is developed. Variational optimization algorithms combining image processing, computer vision and partial differential equations are designed to address the problem of the recovery of the shape of an object's surface from sequences of synchronized multi-view images. Several theoretical and numerical paths are discussed to solve the problem. The variational stereo method developed in this thesis has several advantages over existing 3-D reconstruction algorithms. Our method follows a top-down approach or object-centered philosophy in which an explicit model of the target object in the scene is devised and then related to image measurements. The key advantages of our method are the coherence (smoothness) of the reconstructed surface caused by a coherent object-centered design, the robustness to noise due to a generative model of the observed images, the ability to handle surfaces with smooth textures where other methods typically fail to provide a solution, and the higher resolution achieved due to a suitable graph representation of the object's surface. The method provides competitive results with respect to existing variational reconstruction algorithms. However, our method is based upon a simplified but complete physical model of the scene that allows the reconstruction process to include physical properties of the object's surface that are otherwise difficult to take into account with existing reconstruction algorithms. Some initial steps are taken toward incorporating the physics of ocean waves in the stereo reconstruction process. The developed method is applied to empirical data of ocean waves collected at an off-shore oceanographic platform located off the coast of Crimea, Ukraine. An empirically-based physical model founded upon current ocean engineering standards is used to validate the results. Our findings suggest that this remote sensing observational method has a broad impact on off-shore engineering to enrich the understanding of sea states, enabling improved design of off-shore structures. The exploration of ways to incorporate dynamical properties, such as the wave equation, in the reconstruction process is discussed for future research.

Investigations into the characteristics and underlying mechanism of the circulation of water near the shore are reported. The two main types of circulation, one a cellular system resulting from Haves propagated nearly normally to the shore, and the other an essentially alongshore flow associated with oblique waves, are treated separately. The cellular circulation studies were made in the field at Virginia Beach and more extensively in wave tanks. From the field experiments data were collected about the dimensions of the cells, the way in which the Hater circulated, the rate of exchance of surf zone water and the extent of recycling. A method for measuring the changes in the mean sea level over intervals of time greater than those of the wave periods, was developed. The model experiments carried out in uniform wave tanks showed that the cellular circulations could be well simulated. Measurements were made of the cell dimensions, the velocity of the longshore and rip currents, and of the recycling regime. A finding from the wave tank studies Has the presence of standing waves formed by transverse edge waves. The interaction of these standing waves with the gene rated waves normal to the shore could be the initial cause of rip currents and the cellular circulation. Studies of the alongshore system were made in the field only. A method for measuring the volume of flow of longshore currents was developed, tested, and applied. Calculated volumes of flow using a theory based on continuity and the solitary wave theory (as proposed by Inman and Bagnold) compared tolerably well with the field observations. The calculations of volume of flow required a knowledge of the wave height spectra in the surf. This was established by making wave height recordings in the between-breaker zone . It was found that the characteristics of the spectra compared reasonably well with those pr e dict ed by the Longuet-Higgins theory, previously assumed to apply to deep water waves only. A mechanism for the transition from cellular to alongshore system is proposed. / Thesis (Ph.D.)-University of Natal, 1967.

La mangrove de Guyane est caractérisée par un dynamisme spatial exceptionnel. Ce caractère découle de processus hydro-sédimentaires côtiers très intenses. Les objectifs de la thèse ont été de : (1) quantifier la dynamique spatiale de l'écosystème mangrove à l'échelle régionale et multi-décennale par l'analyse de données d'archives issues de la télédétection ; (2) tester l'hypothèse selon laquelle le climat océanique serait à l'origine de cette dynamique en évaluant les corrélations avec des séries temporelles de données atmosphériques et d'états de surface de l'océan ; (3) quantifier les conséquences de cette dynamique spatiale sur le stockage du carbone en mangrove. Les résultats ont montré qu'environ 15 000 ha de mangrove fluctuent à l'échelle multi-décennale en opposition avec les phases de l'Oscillation Nord Atlantique (NAO), principal mode de variabilité atmosphérique en Atlantique Nord. Le lien est opéré par l'intermédiaire des vagues océaniques dont l'énergie est modulée par les phases de la NAO. L'étude suggère que la diminution des surfaces de mangrove est la conséquence de périodes où les vagues sont puissantes (phase NAO+), ce qui favorise l'érosion côtière, la remise en suspension des sédiments et leur transport le long de la côte. Au contraire, les périodes où les vagues sont faibles (phase NAO-) favorisent le dépôt des sédiments, ce qui est à l'origine de l'expansion des surfaces de mangrove. Les résultats montrent que l'alternance entre des périodes d'expansion et de retrait génère une mosaïque d'âges de mangrove qui détermine la capacité de stockage du carbone par l'écosystème. A partir de ce dernier résultat, l'étude suggère qu'au cours du temps la mangrove puisse alternativement passer d'une fonction de puis à celle de source de carbone pour l'océan côtier et l'atmosphère. / Mangroves in French Guiana are characterized by their spatial dynamism. This specificity is the result of intense coastal sedimentary processes. The goals of this study are to: (1) quantify mangrove spatial dynamics on a regional level and a multi-decadal timescale using archives of remote sensing images; (2) test the hypothesis of the role played by the atmosphere using correlations with time series of atmospheric and ocean surface reanalysis datasets; (3) quantify consequence of this spatial dynamism on coastal carbon storage. Results showed that approximatively 15 000 ha of mangroves fluctuate on a multi-decadal timescale in opposition to the North Atlantic Oscillation (NAO) phases, the main mode of atmospheric multi-decadal variability in the North Atlantic. This relation is operated by ocean waves whose energy is modulated by NAO phases. The study suggests that, on the one hand, decrease of mangrove surface areas is due to periods of high wave energy (NAO+) which favour coastal erosion and mangrove retreat, sediment resuspension and transport. On the other hand, the study suggests that periods of low wave energy (NAO-) favour sediment deposition on the coast and is at the origin of mangrove surface area expansion. Results also showed that alternation between phases of retreat and expansion generates the demographic structure of mangrove ages, which determines the mangrove carbon storage capacity. The study finally suggests that through time mangrove can switch from a source to a sink of carbon, and vice and versa, for the ocean and the atmosphere.

Thesis (S.M.)--Joint Program in Oceanographic Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering, and the and Woods Hole Oceanographic Institution), 2000. / Includes bibliographical references (p. 100-101). / A finite difference computer model is developed to simulate the exposure statistics of a radio frequency buoyant antenna as it is towed in a three-dimensional random seaway. The model allows the user to prescribe antenna properties (length, diameter, density, etc.), sea conditions (significant wave height, development of sea), tow angle, and tow speed. The model then simulates the antenna-sea interaction for the desired duration to collect statistics relating to antenna performance. The model provides design engineers with a tool to predict antenna performance trends, and to conduct design tradeoff studies. The floating antenna envisioned is for use by a submarine operating at modest speed and depth. / by Sam R. Geiger. / S.M.

Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Civil and Environmental Engineering; and the Woods Hole Oceanographic Institution), 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references. / To understand how waves and sea level shape sandy shoreline profiles, I use existing energetics-based equations of cross-shore sediment flux to describe shoreface evolution and equilibrium profiles, utilizing linear Airy wave theory instead of shallow-water wave assumptions. By calculating a depth-dependent characteristic diffusivity timescale, I develop a morphodynamic depth of shoreface closure for a given time envelope, with depth increasing as temporal scale increases. To assess which wave events are most important in shaping the shoreface in terms of occurrence and severity, I calculate the characteristic effective wave conditions for both cross-shore and alongshore shoreline evolution. Extreme events are formative in the cross-shore shoreface evolution, while alongshore shoreline evolution scales linearly with the mean wave climate. Bimodal distributions of weighted wave heights are indicative of a site impacted more frequently by tropical storms rather than extra-tropical storms. To understand how offshore wave climate and underlying geometry of a carbonate reef platform shapes evolution of atolls, I simulate the hydrodynamics of a simplified reef flat, using XBeach, a two-dimensional model of infragravity wave propagation. The reef flat self-organizes to a specific width and water depth depending on the offshore wave climate and characteristics of the available sediment. Formation of a sub-aerial landmass, like a motu, can be initiated by a change in offshore wave climate (like a storm), which can create a nucleation site from mobilization and deposition of coarse sediment on the reef flat. Once a motu is present, the shoreline should prograde until reaching a critical reef-flat width. Our conceptual model of reef-flat evolution and motu formation is governed by understanding the hydrodynamics of the system and subsequent response of sediment transport. / by Alejandra C. Ortiz. / Ph. D.

Thesis: S.M., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 119-122). / The scattering of low-mode internal tides by ocean-floor topography is extensively studied through analytical models and field observations at the Line Islands Ridge (LIR). An existing Green function method is utilized to examine the generation of internal tides by idealized topographic shapes as well as realistic transects of the LIR. The method is also applied to examine the scattering of a mode-1 internal tide at these topographies to determine the relative high mode energy flux due to generated and scattered internal tides at the realistic transects. A method of determining the modal content of an internal wave field is advanced to account for arbitrary stratification and rotation. It is then adjusted to allow for image loss as is common to oceanographic studies. Its performance is compared to the existing regression method widely used by oceanographers to determine the modal content of internal tides. The results from this comparison are used to inform the analysis of the field observations. This thesis concludes by examining the modal content of the LIR as determined from measurements taken during the 150-day EXperiment on Internal Tide Scattering (EXITS) NSF field study. Motivated by satellite altimetry data and three-dimensional numerical model studies, the EXITS cruise sought to observe the internal tide scattering process in the ocean for the first time. The data from three moorings equipped with moored profilers, spanning total depths of 3000-5000 m is analyzed to determine the modal content of the southward propagating internal tide before and after it encounters the ridge for evidence of topographic scattering. / by Maha Niametullah Haji. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology and Physical Oceanography, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN. / Bibliography: leaves 118-120. / by Randall J. Patton. / M.S.

This thesis details the design and optimization of a buoy used to collect renewable energy from ocean waves. The proposed buoy is a point absorber—a device that transforms the kinetic energy of the vertical motion of surface waves into electrical energy. The focus of the research is on the mechanical system used to collect the energy, and methods to improve it for eventual use in an actual wave energy harvester. A flywheel energy storage system was utilized in order to provide an improved power output from the system, even with the intermittent input of force exerted by ocean waves. A series of laboratory prototypes were developed to analyze parameters that are important to the success of the point absorb mechanical system. By introducing a velocity-based load control scheme in conjunction with flywheel energy storage, it was seen that the average power output by the prototype was increased. The generator load is controlled via a relay switch that removes electrical resistance from the generator—this sacrifices time during which power is drawn from the system, but also allows the buoy to move with less resistance. A simulation model was developed in order to analyze the theoretical wave absorber system and optimize the velocity threshold parameters used in the load control. Results indicate that the power output by the system can be substantially improved through the use of a flywheel energy storage control scheme that engages and disengages the electrical load based on the rotational velocity of the flywheel system. The results of the optimization are given for varying-sized generator systems input into the simulation in order to observe the associated trends.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: When a sailing ship passes a moored ship the moored ship experiences forces and moments. These forces and moments cause the moored ship to move. The resulting ship motions due to the passing ship can sometimes be more severe than the ship motions due to ocean waves and can cause serious accidents at moorings such as the failing of mooring lines or even the total break away of the ship from the berth. Since bulk carriers and tankers were traditionally the largest seafaring ships, passing ship studies have focused mainly on these vessels, but recently container ships have grown to a comparable size. In this study an existing numerical model “Passcat” is validated with physical model measurements for a Post Panamax container ship passing a Panamax bulk carrier. Other existing mathematical formulae are also evaluated by comparison with these model tests. In the physical model tests the passing speed (V), passing distance (G), depth draft ratio (d/D) and the presence of walls and channels were varied. It was found that the passing ship forces are proportional to the passing speed to the power of 2.32. This is slightly higher than the generally accepted quadratic relationship for passing ship induced forces. Similar relationships were found for the other variables. The numerical model results were compared to the physical model measurements by determining agreement ratios. A perfect agreement between the numerical and physical models would result in an agreement ratio of 1. Agreement ratio boundaries, wherein agreement would be regarded as good, were drawn between 0.7 and 1.3. The numerical model, Passcat, was found to under predict the passing ship forces. It was found that Passcat is valid for a wide range of sensitivities and remains within the agreement ratio limits as long as passing speed is limited to 10 knots (kt), depth draft ratio to more than 1.164, passing distance to less than four times the moored ship beam (Bm) for surge and sway estimation and passing distance to less than three times the moored ship beam for yaw estimations. These limits are true for no structures in the water. For structures in the water only the passing speed limits are different. When quay walls are present, the surge and sway forces will only provide acceptable answers at passing speeds below 9kt. When 9Bm or 12Bm channels are present, the sway force will only provide acceptable answers at passing speeds below 7kt. When a 6Bm channel is present, the yaw moments will only provide acceptable answers at passing speeds below 6kt. From the mathematical model evaluation study it was found that empirical or semi empirical methods can not provide answers with good agreement to the physical model when walls or channels are present. For the open water case, it is only the Flory method that can provide answers with good agreement to the physical model for surge, sway and yaw forces. The Flory method can provide answers with acceptable agreement within narrow boundaries of passing distance (1 to 2 times the beam of the moored ship), passing speed (4 kt to 14 kt) and depth draft ratio (less than 1.7). The numerical model, Passcat can be used with little effort to provide answers with better agreement to the physical model for a larger range of variables. / AFRIKAANSE OPSOMMING: Wanneer ’n skip verby ‘n vasgemeerde skip vaar, ondervind die vasgemeerde skip kragte en momente. Hierdie kragte induseer beweging van die vasgemeerde skip. Die beweging kan soms groter wees as die effek van wind of golwe. Indien die bewegings groot genoeg is kan dit van die vasmeer lyne van die skip laat breek, of al die lyne laat breek sodat die skip vry in die hawe ronddryf. Aangesien erts skepe en tenk skepe vir jare die grootste skepe in the wêreld was, het die meeste van die skip interaksie studies op daardie skepe gefokus. Die grootte van behouering skepe het egter in die onlangse tye gegroei om dimensies soortgelyk aan die van erts en tenk skepe te hê. In hierdie studie word ’n bestaande numeriese model “Passcat” gestaaf met fisiese model metings op ’n Post Panamax behoueringskip wat verby ‘n Panamax erts skip vaar. Bestaande wiskundige formules is ook getoets deur dit met dieselfde fisiese model metings te vergelyk. In die fisiese model studie is die spoed van die skip (V), tussenafstand (G), diepte diepgang verhouding (d/D) en die teenwoordigheid van kaai mure en kanale in die water getoets. Daar is gevind dat die kragte op die vasgemeerde skip direk eweredig is aan die spoed van die skip tot die mag 2.32. Dit is effens meer as die algemeen aanvaarde kwadratiese verhouding tussen vloeistof sleurkrag en vloeisnelheid asook tussen skip interaksie kragte en vaar snelheid. Soortgelyke verhoudings is vir al die veranderlikes bereken. Numeriese model resultate is vergelyk met die fisiese model om die verhouding van ooreenstemming te bepaal. ’n Perfekte ooreenstemming word voorgestel deur ’n verhouding van ooreenstemming van 1. Grense waarbinne die verhouding van ooreenstemming as goed beskou word is getrek tussen 0.7 en 1.3. Daar is gevind dat die numeriese model, Passcat, kragte oor die algemeen onderskat. Passcat is geldig vir 'n breë reeks van veranderlikes en sal geldig bly solank die skip spoed tot 10 knope, diepte diepgang verhouding tot meer as 1.164, tussenafstand tot minder as vier skipwydtes (Bm) vir 'surge' en 'sway' kragte en tot minder as drie skipwydtes vir 'yaw' momente beperk word. Hierdie grense is opgestel vir geen strukture in die water. Vir strukture in die water word slegs die skip spoed aangepas. Wanneer daar mure in die water is sal 'surge' en 'sway' slegs geskikte antwoorde gee as die skip spoed tot 9 knope beperk word. Vir 9Bm of 12Bm kanale sal geskikte antwoorde vir 'sway' kragte slegs voorkom met 'n skip spoed minder as 7 knope. Vir 6Bm kanale sal geskikte antwoorde vir 'yaw' momente slegs voorkom met 'n skip spoed van minder as 6 knope. Van die wiskundige model evaluasie studie is gevind dat empiriese of semi empiriese metodes nie resultate met goeie ooreenstemming tot the fisiese model metings kan gee, wanneer daar kaai of kanaal mure in die water is nie. Vir die oopwater geval is dit slegs die Flory metode wat antwoorde kan voorsien wat goed ooreenstem met die fisiese model vir 'surge', 'sway', en 'yaw' kragte. Die Flory metode voorsien hierdie resultate binne noue grense vir tussenafstand (1 tot 2 wydtes van die vasgemeerde skip), verbyvaar spoed (4 knope tot 14 knope) en diepte diepgang verhouding (minder as 1.7). Die numeriese model, Passcat, kan met min moeite antwoorde bereken wat beter ooreenstemming vir 'n groter reeks veranderlikes gee.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Sea-level rise due to climate change results in deeper water next to existing coastal structures, which in turn enables higher waves to reach these structures. Wave overtopping occurs when wave action discharges water over the crest of a coastal structure. Therefore, the higher waves reaching existing structures will cause higher wave overtopping rates. One possible solution to address increasing overtopping, is to raise the crest level of existing coastal structures. However, raising the crest level of a seawall at the back of a beach, will possibly obstruct the view to the ocean from inland. Alternatively, recurves can be incorporated into the design of both existing and new seawalls. The recurve wall reduces overtopping by deflecting uprushing water seawards as waves impact with the wall. The main advantage of seawalls with recurves is that their crest height can be lower, but still allow for the same wave overtopping rate as vertical seawalls without recurves. This project investigates the use of recurve seawalls at the back of a beach to reduce overtopping and thereby reducing the required wall height. The objectives of the project are twofold, namely: (1) to compare overtopping rates of a vertical seawall without a recurve and seawalls with recurves; and (2) to determine the influence that the length of the recurve overhang has on the overtopping rates. To achieve these objectives, physical model tests were performed in a glass flume equipped with a piston type wave paddle that is capable of active wave absorption. These tests were performed on three different seawall profiles: the vertical wall and a recurve section with a short and a long seaward overhang, denoted as Recurve 1 and Recurve 2 respectively. Tests were performed with 5 different water-levels, while the wall height, wave height and period, and seabed slope remained constant. Both breaking and non-breaking waves were simulated. A comparison of test results proves that the two recurve seawalls are more effective in reducing overtopping than the vertical seawall. The reduction of overtopping can be as high as 100%, depending on the freeboard and wave conditions. Recurve 2 proves to be the most efficient in reducing overtopping. However, in the case of a high freeboard (low water-level at the toe of the structure), the reduction in overtopping for Recurve 1 and Recurve 2 was almost equally effective. This is because all water from the breaking waves is reflected. Even for the simulated lower relative freeboard cases, the recurve walls offer a significant reduction in overtopping compared with the vertical wall. A graph is presented which shows that the length of the seaward overhang influences the overtopping performance of the seawall. As the seaward overhang length increases, the wave overtopping rate decreases. However, for high freeboard cases the length of the seaward overhang becomes less important. The graph gives designers an indication of how recurves can be designed to reduce seawall height while retaining low overtopping. It is recommended that further model tests be performed for additional overhang lengths. Incorporation of recurves into seawall design represents an adaptation to problems of sea-level rise due to global warming / AFRIKAANSE OPSOMMING: Stygende seevlak as gevolg van klimaatverandering, veroorsaak dat dieper water langs bestaande kusstrukture voorkom. Gevolglik kan hoër golwe hierdie strukture bereik. Golfoorslag vind plaas wanneer water oor die kruin van ‘n kusstruktuur, hoofsaaklik deur golfaksie, spat of vloei. Dus sal hoër golfhoogtes tot verhoogde golfoorslag lei. Een moontlike oplossing vir hierdie verhoogde golfoorslag is om die kruinhoogte van bestaande kusstrukture te verhoog. In die geval van ‘n seemuur aan die agterkant van ‘n strand, kan hoër strukture egter die see-uitsig na die see vanaf die land belemmer. Om hierdie probleem te vermy, kan terugkaatsmure in die ontwerp van bestaande en nuwe seemure ingesluit word. Terugkaatsmure verminder golfoorslag deurdat opspattende water, afkomstig van invallende golwe terug, na die see gekaats word. Die grootste voordeel van ‘n terugkaatsmuur is dat hierdie tipe muur ‘n laer kruinhoogte as die vertikale seemuur sonder ‘n terugkaatsbalk, vir dieselfde golfoorslagtempo kan hê. Hierdie projek ondersoek dus die gebruik van terugkaatsmure aan die agterkant van ‘n strand met die doel om golfoorslag te verminder en sodoende die vereiste muurhoogte te verminder. Die doelwit vir die projek is tweeledig: (1) om die golfoorslagtempo van terugkaatsmure te vergelyk met dié van ‘n vertikale muur sonder ‘n terugkaatsbalk; en (2) om die invloed van die terugkaatsmuur se oorhanglengte op die golfoorslagtempo te bepaal. Om bogenoemde doelwitte te bereik, is fisiese modeltoetse in ‘n golfkanaal, wat met ‘n suiertipe golfopwekker toegerus is en wat aktiewe golfabsorbering toepas, uitgevoer. Hierdie toetse is op drie verskillende seemuurprofiele, naamlik ‘n vertikale muur en ‘n terugkaatsmuur met ‘n kort en lang oorhang, genaamd “Recurve 1” en “Recurve 2” onderskeidelik, uitgevoer. Die muurhoogte, die seebodemhelling asook die golfhoogte en –periode is tydens al die toetse konstant gehou. Vir elke profiel is toetse by 5 verskillende watervlakke vir beide brekende en ongebreekte golwe uitgevoer. Uit die toetsresultate is dit duidelik dat terugkaatsmure meer effektief as vertikale mure is om golfoorslag te beperk. Die vermindering van golfoorslag kan tot 100% wees, afhangende van die vryboord en golftoestande. Daar is bevind dat “Recurve 2” golfoorslag die effektiefste verminder. In die geval van hoë vryboord (lae watervlak by die toon van die struktuur) is daar egter gevind dat “Recurve 1” en “Recurve 2” die golfoorslag feitlik ewe goed beperk. Dit is die geval aangesien alle water van die brekende golwe weerkaats word. In die geval van ‘n lae vryboord, word die voordeel van die terugkaatsmuur teengewerk deurdat daar ‘n kleiner verskil in golfoorslagtempo’s tussen die drie profiele is. ‘n Grafiek is voorgelê wat wys dat die lengte van die terugkaatsmuur se oorhang golfoorslag beperk. ‘n Groter oorhanglengte van die terugslagmuur veroorsaak ‘n groter vermindering in golfoorslag. Vir gevalle met ‘n hoë vryboord, is daar egter gevind dat die oorhanglengte van die terugslagmuur minder belangrik is. Hierdie grafiek gee ontwerpers ‘n aanduiding van hoe terugslagmure ontwerp kan word met ‘n lae hoogte terwyl ‘n lae oorslagtempo behou word. Die gebruik van terugslagmure bied ‘n aanpassing vir die probleme van seevlakstyging, as gevolg van klimaatverandering.