The nature of British Columbia coastal and inland waterways affords many locations where floating breakwaters are or could be used to protect small-craft harbours from wave action. A field survey of many of the current breakwater sites is undertaken in order to establish qualitative performance criteria of various designs. A two-dimensional numerical model is developed to predict the oscillatory response and wave transmission characteristics for a number of common breakwater designs. Finally, experiments with two configurations of breakwater models were carried out in the Hydraulics Laboratory at the University of British Columbia. The experiments were designed to validate the numerical model and to estimate viscous damping coefficients required in the numerical solution. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Seagrass is a key stone component for the Indian River Lagoon (IRL) ecosystem, and therefore it is an important topic for many studies in the lagoon. This study focuses on the effects of seagrass beds on the hydrodynamics in the IRL. A hydrodynamic model based on the Delft3D modeling system has been developed for the southern IRL including the St. Lucie estuary, Ft. Pierce and St. Lucie Inlets, and adjacent coastal waters. The model is driven by freshwater inputs from the watershed, tides, meteorological forcing, and oceanic boundary forcing. The model has been systematically calibrated through a series of numerical experiments for key parameters, particularly the bottom roughness, and configuration including heat flux formulation and bottom bathymetry. The model skills were evaluated with quantitative metrics (point-to-point correlation, root-mean-square difference, and mean bias) to gauge the agreements between model and data for key variables including temperature, salinity, and currents. A three-year (2013-2015) simulation has been performed, and the results have been validated with available data including observations at HBOI Land-Ocean Biogeochemistry Observatory (LOBO) stations and in situ measurements from various sources. The validated model is then used to investigate the effects of 1) model vertical resolution (total number of model vertical layers), 2) spatial variability of surface winds, and 3) seagrass beds on the simulated hydrodynamics. The study focuses on the vicinity of Ft. Pierce Inlet, where significant seagrass coverage can be found. A series of numerical experiments were performed with a combination of different configurations. Overall, the experiment with 2-dimensional (2-D) winds, ten vertical layers and incorporating seagrass provided the most satisfactory outcomes. Overall, both vertical resolution and spatial variability of surface winds affect significantly the model results. In particular, increasing vertical resolution improves model prediction of temperature, salinity and currents. Similarly, the model with 2-D winds yields more realistic results than the model forced by 0-D winds. The seagrass beds have significant effects on the model results, particularly the tidal and sub-tidal currents. In general, model results show that both tidal and sub-tidal currents are much weaker due to increase bottom friction from seagrass. For tidal currents, the strongest impacts lie in the main channel (inter-coastal waterway) and western part of the lagoon, where strong tidal currents can be found. Inclusion of seagrass in the model also improves the simulation of sub-tidal currents. Seagrass beds also affect model temperature and salinity including strengthening vertical stratification. In general, seagrass effects vary over time, particularly tidal cycle with stronger effects seen in flood and ebb tides, and seasonal cycle with stronger effects in the summer than in winter. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

L’interface air-eau est un milieu où la tension de surface intervient en permanence pour minimiser l’énergie de la surface. Cette force est à l’origine des phénomènes capillaires que les organismes semi-aquatiques exploitent. L’objectif de cette thèse est d’étudier l’importance de ces phénomènes dans l’écologie des organismes semi-aquatiques en prenant les gyrins comme modèle. Les résultats montrent que le ménisque bipolaire produit par les gyrins est responsable d’auto-assemblables statiques entre individus immobiles. Les gyrins utilisent également différents types de nage pour minimiser les forces de résistance qu’ils rencontrent, notamment la force liée à la production d’onde. L’étude expérimentale de la perception d’objets immobiles suggère la perception des ménisques par les gyrins. L’écholocation grâce aux ondes de surface, supposée dans la littérature, ne peut cependant être exclue. / The surface tension at the air-water interface is responsible for capillary phenomena minimizing surface energies. Semi-aquatic organisms have evolved to exploit this capillarity. The purpose of this thesis is to study the importance of capillary phenomena in the ecology of semi-aquatic organisms using whirligig beetles as a model. Results show that the bipolar meniscus produced around whirligig beetles is responsible for static self-assembly between individuals. These insects use different types of swimming to minimize resistance forces, especially the wave drag. The experimental study of the detection of immobile objects suggests that whirligig beetles perceive the menisci. Echolocation using surface waves, assumed in literature, cannot however be excluded.

Dans cette thèse, nous calculons la forme d’un objet immergé d’aire donnée qui minimise la résistance de vague. Le corps, considéré lisse, avance à vitesse constante sous la surface libre d’un fluide qui est supposé parfait et incompressible. La résistance de vague est la traînée, c’est-à-dire la composante horizontale de la force exercée par le fluide sur l’obstacle. Nous utilisons les équations de Neumann-Kelvin 2D, qui s’obtiennent en linéarisant les équations d’Euler irrotationnelles avec surface libre. Le problème de Neumann-Kelvin est formulé comme une équation intégrale de frontière basée sur une solution fondamentale qui intègre la condition linéarisée à la surface libre. Nous utilisons une méthode de descente de gradient pour trouver un minimiseur local du problème de résistance de vague. Un gradient par rapport à la forme est calculé par la méthode de variation de frontières. Nous utilisons une approche level-set pour calculer la résistance de vague et gérer les déplacements de la frontière de l’obstacle. Nous obtenons une grande variété de formes optimales selon la profondeur de l’objet et sa vitesse. / In this thesis, we compute the shape of a fully immersed object with a given area which minimises the wave resistance. The smooth body moves at a constant speed under the free surface of a fluid which is assumed to be inviscid and incompressible. The wave resistance is the drag, i.e. the horizontal component of the force exerted by the fluid on the obstacle. We work with the 2D Neumann-Kelvin equations, which are obtained by linearising the irrotational Euler equations with a free surface. The Neumann-Kelvin problem is formulated as a boundary integral equation based on a fundamental solution which handles the linearised free surface condition. We use a gradient descent method to find a local minimiser of the wave resistance problem. A gradient with respect to the shape is calculated by a boundary variation method. We use a level-set approach to calculate the wave-making resistance and to deal with the displacements of the boundary of the obstacle. We obtain a great variety of optimal shapes depending on the depth of the object and its velocity.

With steadily increasing computational power, computational fluid dynamics (CFD) can be applied to unsteady problems such as seakeeping simulations. Therefore, a good balance between accuracy and computational speed is required. This thesis investigates the application of CFD to seakeeping performance predictions and aims to propose a best-practice procedure for efficient seakeeping simulations. The widely used KVLCC2 research vessel serves as a test case for this thesis and FINEŠ/Marine software package is used for CFD computations. In order to validate the simulations, results are compared to recent experimental data from SSPA as well as predictions with potential ˛ow code SHIPFLOW® Motions. As for the calm water simulations, both inviscid and viscous ˛ow computations are performed in combination with three mesh refinement levels. Seakeeping simulations with regular head waves of different wavelengths are set-up correspondingly. Furthermore, different strategies for time discretization are investigated. With the given computational resources, it is not feasible to complete seakeeping simulations with a ˝ne mesh. However, already the coarse meshes give good agreement to experiments and SHIPFLOW® Motions' predictions. Viscous ˛ow simulations turn out to be more robust than Euler ˛ow computations and thus should be preferred. Regarding the time discretization, a fixed time discretization of 150 steps per wave period has shown the best balance between accuracy and speed. Based on these findings, a best-practice procedure for seakeeping performance predictions in FINEŠ/Marine is established. Taking the most efficient settings obtained from head wave simulations, the vessel is subjected to oblique waves with 160° encounter angle. Under similar wave conditions, CFD predictions of a similar thesis show close agreement in terms of added wave resistance. Compared to the previous head wave conditions of this study, added resistance in 160° oblique waves is found to be significantly higher. This underlines that oblique bow quartering waves represent a relevant case for determining the maximum required power of a ship. CFD and potential ˛ow show similar accuracy with respect to ship motions and added wave resistance, albeit potential ˛ow outperforms CFD in terms of computational speed. Hence, CFD should be applied in cases where viscous effects are known to have large influence on a vessel's seakeeping behavior. This can be the case if motion control and damping devices are to be evaluated, for instance. / Tack vare den stadigt ökande beräkningskraften kan beräkningsuiddynamik (CFD) idag användas på beräkningsintensiva problem som sjöegenskapssimulationer. Den här rapporten undersöker användning av CFD på sjöegenskapsprestanda och syftar till att foreslå ett best-practice förfaringssätt för effektiv sjöegenskapssimulationer. Forskningsskrovet KVLCC2 fungerar som ett testfall för denna rapport och FINE—/Marine-mjukvarupaketet används för CFD-beräkningar. Viktiga parametrar, såsom ödestyp, beräkningsnät och tidssteg varierars systematiskt. Resultaten jämförs med experiment gjorda vid SSPA. Baserat på resultaten förelås en best-practice. Den föreslagna best-practice användas vidare för berökningar av sjöegenskaper i sneda vågor. Jämförelse av resultaten med liknande studier visar god överensstämmelse. Genom att använda det föreslagna förfarandet för best-practice kan CFD-sjöegenskapssimulationer användas på fall där viskösa krafter måste beaktas, till exempel rörelseregleringsanordningar.

This thesis investigates reasons for significant uncertainties in added wave resistance predictionsand how wave conditions can potentially affect the design of RoPax ferries. The objectiveis to find a suitable prediction method of added wave resistance for the RoPax ferry designapplication. Furthermore, the wave environment on the route strongly influences this delicateand complex phenomenon. Thus, the emphasis is to understand the added wave resistancethrough a case study with a probabilistic wave environment.The fast transition into decarbonization and regulations regarding energy-efficient ship designhave ramped up the awareness of the influence of seaways. For lower speeds, the addedresistance becomes a more significant part of total resistance, with concerns regarding minimumpropulsion power and safe maneuvering in adverse sea conditions. Consequently, the demandhas rocketed for profound insight and accurate prediction methods of added wave resistance. Inaddition, with new larger ships, added wave resistance domain for short waves becomes essentialand an additional challenge regarding predictions. Nevertheless, added wave resistancepredictions are complex and contain many pitfalls, so accurate estimations of the ship’s addedwave resistance response and wave environment are crucial. In addition, added wave resistanceis very ship-specific, and published research for RoPax ferries is rare.Due to significant uncertainties for general numerical methods, the study investigates a new(modified NTUA) semi-empirical method refined for ships with a large beam-to-draft ratio.In addition, a realistic wave environment is included by selecting relevant wave spectra forconditions on the route.The study shows that significant variances of added wave resistance predictions arise fromselecting prediction methods beyond the range of applicability and rough assumptions of waveconditions and spectra. The case study discovered that errors might also be introduced bythe classification society definitions, which gives reasons to rethink the applied definition of"average BF 8" wave conditions for Safe Return to Port (SRtP) assessments. This can causea false illusion of the ship’s performance and safety in waves. Only the misjudgment ofthe most critical peak period resulted in a rough underestimation (> 40%) of mean addedwave resistance. The error corresponded to 215% of the still water resistance for the SRtPassessment. In addition, the nature of added wave resistance is very ship specific. Therefore, theauthor emphasizes caution when selecting the prediction method, especially for semi-empiricalmethods. Despite the first promising glance of the applied semi-empirical method, it appearsthat the ship database correlates poorly for RoPax ferries. Reliability for the method is weak forshort waves, with a tendency to large overestimations. The lack of references of RoPax vesselsfor validations, accident statics in adverse sea conditions and recent insight into nonlinear effectsrequest further research on added wave resistance for modern hull shapes. / Den här studien undersöker orsaker till stora osäkerheter i adderade vågmotståndsberäkningaroch hur vågförhållanden eventuellt kan påverka designen av RoPax-färjor. Målet är att hittaen tillämpbar beräkningsmetod för adderat vågmotstånd för RoPax-designapplikationer. Dettakänsliga och komplexa fenomenet påverkas starkt av vågmiljön längs med rutten. Därför ärtyngdpunkten att förstå det adderade vågmotståndet genom en fallstudie med en probabilistiskvågmiljö.Den snabba övergången av minskat koldioxidutsläpp och designriktlinjerna för energieffektivafartyg har drivit fram förståelsen av sjövägarna inverkan. För lägre hastigheter utgör de adderademotstånd en mer betydande del av det totala motståndet, vilket har skapat oro för otillräckligframdrivningskraft och förlust av manövreringsförmåga under ogynnsamma sjöförhållanden.Därmed har efterfrågan ökat för djupare förståelse och noggranna beräkningsmetoder föradderat vågmotstånd. Dessutom, för allt större fartyg, blir också den adderade vågmotstånds-domänen för korta vågor dominerande och ytterligare en utmaning för beräkningsmetoderna.Eftersom adderade vågmotståndsberäkningarna är komplexa och omfattar många fallgropar,så därför är noggranna uppskattningar av fartygetsresponsen för adderad vågmotstånd ochvågmiljön avgörande. Dessutom är adderade vågmotståndet väldigt fartygsspecifikt, och publi-cerad forskning för RoPax-färjor är sällsynta.På grund av betydande osäkerheter för allmänna numeriska metoder utforskar studien enny (modifierad NTUA) semi-empirisk metod anpassad för fartyg med ett stort skeppbredd-djupgående förhållande. Dessutom inkluderas en realistisk vågmiljö genom att välja relevantavågspektra baserat på ruttens förhållanden.Studien visar att omfattande variationer av adderade vågmotståndsberäkningar uppstår genomatt välja beräkningsmetoder utanför dess tillämpningsområde, och grova antaganden om våg-förhållanden och vågspektra. Fallstudien upptäckte att fel också kan introduceras genomklassificeringssällskapets definitioner, vilket ger skäl att överväga den tillämpade definitionen av”genomsnittliga Beauforts 8"vågförhållanden för Safe Return to Port (SRtP) utredningar. Dettakan orsaka en falsk illusion av fartygets prestanda och säkerhet i vågor. Endast felbedömningenav den kritiska pik-perioden resulterade i en grov underskattning (> 40%) av den genomsnittligaadderade vågmotståndet. Felet motsvarade 215% av lugnvatten motståndet för SRtP-utredningen.Dessutom är karaktären av adderat vågmotstånd mycket fartygsspecifik. Därför framhållerförfattaren försiktighet för val av beräkningsmetoden, speciellt för semi-empiriska metoder.Trots en lovande första anblicken av det tillämpade semi-empiriska metoden, verkar det somom fartygsdatabasen korrelerar dåligt för RoPax-fartyg. Tillförlitligheten för metoden är svagför korta vågor, med en tendens till stora överskattningar. Bristen på RoPax-referenser förvalidering, olycksstatistiken för RoPax-fartyg och den senaste tidens insikt i icke-linjära effekterger anledning för vidare forskning om adderat vågmotstånd för moderna skrovformer.