Wave-formed rippled sediment beds are extremely important to the processes that act on or across the sediment-water interface. Ripples increase the exchange of materials between the sediment and the water column, enhance sediment transport rates, and act to increase the dissipation of waves by increasing the hydraulic roughness of the seafloor. Previous research has, however, failed to take into account the substantial spatial and temporal variation rippled beds display when formed under real sea conditions. Based on a set of laboratory experiments a spectral method to predict and model rippled beds has been developed. Through the use of the rippled surface's spectral density function the spatial and temporal variability of the rippled surface can be taken into account with greater efficiency. A prediction method for the equilibrium ripple spectrum was developed based on a nondimensional spectral form, which utilised the peak orbital excursion diameter and the 50th percentile grain size diameter of the sediment bed. The method provided an effective technique to predict ripple parameters with the same degree of accuracy achievable at small scale as more accepted ripple prediction methods. A new method was derived to model the changes a rippled bed undergoes as it actively evolves between two given equilibrium states due to a change in surface wave conditions. The evolution of a rippled bed can be described mathematically in exactly the same way as a rippled bed growing from a flat bed condition. The method allows any bed to be modelled through time if the flow conditions and sediment properties are known. There is little advantage in using the spectral method to predict rippled beds when they are in equilibrium with the flow conditions. The main benefit of the spectral method comes when attempting to model rippled beds evolving under changed flow conditions. In the same way as the parameterisation of surface waves in terms of their spectral density function has increased the ability to model wind generated wave fields, studies of rippled beds would benefit from the increased detail and ease the spectral method brings. / Thesis (Ph.D.)--School of Civil and Environmental Engineering, 2005.

Thesis (M.Sc. Earth and Ocean Sciences)--University of Waikato, 2008. / Title from PDF cover (viewed September 18, 2008) Includes bibliographical references (p. 121-123)

Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

Tendo em vista a importância das obras portuárias e costeiras no desenvolvimento do país e a complexidade dos fenômenos que regem os Processos Litorâneos, torna-se relevante a utilização de modelos físicos, como os canais de ondas, para otimização destes projetos. Neste sentido, os principais objetivos desta Tese são o desenvolvimento de um sistema de controle para o gerador de ondas do Laboratório de Hidráulica da Escola Politécnica da Universidade de São Paulo - LHEPUSP, capaz de gerar ondas irregulares, baseadas em espectros de energia da agitação, bem como, a partir de um estudo com caso de um molhe de berma, avaliar do ponto de vista técnico o procedimento de dimensionamento de quebra-mares com base no ensaio da estrutura frente a ondas regulares com as características da onda significativa de projeto. Uma das contribuições desta Tese é o novo sistema de controle da geração de ondas do LHEPUSP, que é capaz de gerar ondas regulares, irregulares e randômicas. A outra contribuição, referente ao estudo de caso, permitiu concluir que o emprego de ondas regulares na otimização em modelo físico de projetos de quebra-mares pode levar a dimensionamentos conservadores, e portanto de custo mais alto, principalmente no dimensionamento de obras dispostas em profundidades inferiores aos 10 m, onde foram encontradas diferenças para mais no recuo da estrutura, comparativamente com a ação de ondas irregulares de mesma altura significativa. / Considering the harbour and coastal structures significance for the Country development and the complex Littoral Processes phenomena, is an important requirement the physical models use, like wave flumes, to improve these designs. Following this context, the Thesis main purposes are to develop a wave maker control system for the Laboratório de Hidráulica da Escola Politécnica da Universidade de São Paulo - LHEPUSP wave fume able to generate irregular waves, based on wave energy spectra, and also, from a berm jetty case study, evaluate, from the technical point of view, the breakwater design procedure based on structure tests with design significative regular waves. One of the Thesis contribution is the new wave maker control system for the LHEPUSP wave fume able to generate regular, irregular and randomic waves. The other contribution, about the case study, showed as conclusion that the regular waves use for breakwaters design physical model improvement may suggest conservative results, inducing high cost structures, mainly for those ones in depths lower than 10 m, being observed larger structural backward response differences, comparing with irregular waves action with the same significative height.

This thesis describes experiments that were carried out using focused wave groups in the UK Coastal Research Facility (UKCRF). Considerable effort was put into calibrating the UKCRF to determine the relationship between the input signals sent to the paddles and the waves generated in the facility. Focused wave groups of various sizes and phases, based on NewWave theory were generated, and measurements were made of the resulting surface elevation data, water particle kinematics, wave runup and overtopping volumes. NewWave theory models the profile of extreme waves in a Gaussian (random) sea. The thesis describes the first time this model has been applied in the context of coastal wave transformation. A method for the separation of the underlying harmonic structure of a focused wave group is described and results presented. This technique has been used in relatively deep water but is shown to work successfully in the coastal zone until wave overturning. A method has been devised to provide a theoretical Stokes-like expansion of the free and bound waves to model the surface elevation and water particle kinematics of the focused wave groups. Satisfactory agreement is achieved between the theoretical predictions of UKCRF measurements. Suggestions are made for an improved model. The underlying harmonic structure of the focused wave groups is presented as stacked time histories that give insight into the wave transformation process from deep to shallow water. Particular attention is paid to the low frequency wave generated as the wave group interacts with the beach. This is compared to the low frequency wave that is generated by a solitary wave in the UKCRF. Runup and overtopping measurements are in reasonable agreement with predictions based on certain empirical formulae, but not others. These comparisons are useful in identifying those formulae able to predict runup and overtopping of extreme waves in the coastal zone.

With a continuing and rising demand for hydrocarbons, the energy companies are installing infrastructure ever further offshore, where such infrastructure is often exposed to extreme waves. This thesis explores some aspects of wave-structure interaction, particularly the maximum water surface elevation increase in severe storms due to these local interactions. The effects on wave-structure interactions of column cross-sectional shape are investigated using linear and second-order wave diffraction theory. For multi-column structures, the excitation of locally resonant wave modes (near-trapping) is studied for several column cross-sectional shapes, and a simple method for estimating the surface elevation mode shape is given. The structure of the quadratic transfer functions for second-order sum wave elevation is investigated and an approximation assuming these QTFs are flat perpendicular to the leading diagonal is shown to be adequate for the first few lowest frequency modes. NewWave-type focused wave groups can be used as a more realistic model of extreme ocean waves. A Net Amplification Factor based on the NewWave model is given as an efficient tool for finding the incident frequencies most likely to cause a violent wave-structure interaction and where these violent responses are likely to occur. Statistics are collected from Monte Carlo type simulations of random waves to verify the use of the Net Amplification Factor. Going beyond linear calculations, surface elevation statistics are collected to second-order and a `designer' wave is found to model the most extreme surface elevation responses. A `designer' wave can be identified at required levels of return period to help to understand the relative size of harmonic components in extreme waves. The methods developed with a fixed body are then applied to an identical hull which is freely floating, and the responses between the fixed and moving cases are compared. The vertical heave motion of a semi-submersible in-phase with the incident wave crests is shown to lead to a much lower probability of water-deck impact for the same hull shape restrained vertically. The signal processing methods developed are also applied to a single column to allow comparison with experimental results. Individual harmonic components of the hydrodynamic force are identified up to at least the fifth harmonic. Stokes scaling is shown to hold even for the most violent interactions. It is also shown that the higher harmonic components of the hydrodynamic force can be reconstructed from just the fundamental force time history, and a transfer function in the form of a single phase and an amplitude for each harmonic. The force is also reconstructed well to second-order from the surface elevation time history using diffraction transfer functions. Finally, possible causes of damage to a platform high above mean water level in the North Sea are investigated.

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Calculation of longshore sediment transport rates is a typical part of coastal engineering work. One of the important inputs to such calculations is the sediment grain size. A single, representative grain size is typically required. The inter-tidal beach is the most convenient and common area from which grain size data can be obtained. Yet only a fraction of the longshore transport occurs at the beach, with the bulk of the transport occurring in the surf zone, where sampling is difficult. Sediment transport calculations can be improved if the representative grains size is also characteristic of this area. A better understanding how the grain size in the longshore transport zone compares to the beach grain size is required. A review of relevant literature indicates that limited attention has been given to quantifying the grain size in the longshore transport zone. No previous investigations were found that tried to link the longshore transport zone grain size to that found on the beach. A comprehensive analysis of beach and longshore transport zone grain sizes was therefore undertaken and is described in this thesis. Beach grain sizes were compared to those in the longshore transport zone for three different locations around the world: Published grains size information, together with detailed wave and profile data, was obtained from the US Army Field Research Facility at Duck; a second data set was obtained from measurements done at Bogenfels in Namibia; a third dataset was compiled from sampling undertaken by the author in Table Bay, South Africa. A total of 189 samples were collected at four sampling lines in Table Bay between September 2005 and September 2006. Samples were collected across the entire profile from the primary dune to a water depth of 10 m. Samples were collected by grab in the offshore, and by swimming and diving in the surf zone. The location of the four Table Bay sampling lines was chosen so as to obtain data from beaches with different wave and grain size characteristics. Together with the Duck and Bogenfels data, data from six different beaches was therefore available for study. A settling tube was used to determine the grain sizes. Verification of the settling tube analyses against conventional sieving indicated a good comparison. However, the settling tube proved unsuitable for processing of samples with coarse to very coarse material, for which sieving was conducted instead. The grain size at the mid-tide level has been used to characterise the beach. The limits of the longshore transport zone were defined by calculating the cross-shore distribution of longshore transport with the Unibest model. Simpler methods, such as the depth of closure, either overestimated or underestimated it, depending on which wave condition was used in the depth of closure formula. It was found that the beaches with steeper mid-tide beach slopes, such as Bogenfels and northern Table Bay, had coarser median grain sizes than more gently sloping beaches such as found in the south of Table Bay. On energetic beaches, the mid-tide beach grain sizes were significantly coarser than those in the surf zone, by more than twice. At less exposed locations, such as Duck and the central Table Bay beaches, this difference was less. At sheltered locations, such as the southern sampling lines in Table Bay, the mid-tide beach grain sizes are virtually the same as those found in the surf zone. The surf similarity parameter was used to compare the characteristics of the different sites. This parameter was defined using the average wave height seaward of breaking, and the mid-tide beach slope. The ratio between the longshore transport zone grain size and the mid-tide beach grain size was found to be similar to the inverse of the surf similarity parameter for the six beaches that were studied. These findings have led to an improved understanding of the grain size in the longshore transport zone and allow a better characterisation of the representative grain size to use for sediment transport calculations. / AFRIKAANSE OPSOMMING: In kusingenieurswese word langstrandse sedimentvervoer (langsvervoer) gereeld bereken. Belangrike invoer vir sulke berekeninge is die verteenwordigende korrelgrootte van die sand. Die sandkorrelgrootte van die benatte strand is die maklikste om te bepaal, al vind net ‘n klein gedeelte van die langsvervoer op die benatte strand plaas. Die grootste gedeelte van die langsvervoer kom in die brandersone voor, waar dit moeilik is om monsters te neem. Sedimentvervoerberekeninge kan verbeter word as die korrelgrootte ook hierdie sone verteenwoordig. Dit is dus van belang om te verstaan hoe die korrelgrootte van die benatte strand met die gemiddelde korrelgrootte oor die algehele langsvervoersone vergelyk. ‘n Literatuursoektog dui aan dat min aandag al gegee is aan hoe die korrelgrootte op die benatte strand met dié in die langsvervoersone vergelyk. ‘n Ontleding van sandkorrelgroottes op die benatte strand en in die langsvervoersone is dus onderneem en word in die tesis uiteengesit. Strandkorrelgroottes word met dié in die langsvervoersone vergelyk vir drie verskillende gebiede in die wereld : (1) Gepubliseerde data oor korrelgroottes, sowel as strandhellings en golwe, is van die Field Research Facility by Duck in die VSA verkry ; (2) ‘n tweede stel data is van opmetings by Bogenfels in Namibie verkry; (3) die derde stel data is saamgestel deur die skrywer tydens opmetings in Tafelbaai, Suid-Afrika. ‘n Totaal van 189 monsters is tussen September 2005 en September 2006 by vier verskillende opmetingslyne in Tafelbaai geneem. Monsters is geneem van die duin tot in 10 m waterdiepte. In dieper water is grypmonsters geneem, terwyl dié in the brandersone verkry is deur te duik. Die posisie van die vier Tafelbaaise opmetingslyne is gekies om strande met verskillende golftoestande en korrelgroottes te dek. Tesame met die data van Duck en Bogenfels is dus ses datastelle vir ontleding beskikbaar. ‘n Valbuis is gebruik om die korrelgroottes te bepaal. Die valbuismetode het goed met gewone sifresultate vergelyk, behalwe vir monsters met baie growwe korrels. Hiervoor is sifwerk gebruik. Die korrelgrootte van die benatte strand is gebruik om die strand te karakteriseer. Die grense van die langsvervoersone is bepaal deur die dwarsstrandse verdeling van die langsvervoer met die Unibest-model te bereken. Eenvoudiger metodes, soos die berekening van die sluitingsdiepte, het minder betroubare resultate gelewer. Daar is gevind dat steiler benatte strande, soos Bogenfels en Noord-Tafelbaai se strande, groter gemiddelde korrelgroottes as platter benatte strande, soos dié in suidelike Tafelbaai, het. Op blootgestelde strande is die benatte strand se korrelgrootte tot meer as twee keer groter as dié in die brandersone. By gedeeltelik beskutte strande, soos Duck en Sentraal- Tafelbaai se strande, was die verskil minder. Op beskutte strande, soos die Suid-Tafelbaai se strande, is gevind dat die benatte strand se korrelgrootte amper dieselfde as dié in die brandersone is. Die brandergelyksoortigheidsfaktor is gebruik om die verskillende strande te vergelyk. Die golfhoogtes net buite die branderlyn en die benatte strandhelling is gebruik om die veranderlike te bereken. Daar is gevind dat by die ses strande wat ondersoek is, die verhouding van die korrelgrootte in die langsvervoersone en dié van die benatte strand ongeveer gelyk aan die omgekeerde brandergelyksoortigheidsfaktor is. Die bevindings het tot ‘n beter begrip van die wisseling van die korrelgroottes in die langsvervoersone gelei. Gevolglik kan ‘n akkurater verteenwoordigende sandkorrelgrootte bepaal word.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: On the 9th September 2009, the 178 m Panamanian bulk carrier, the Seli One, ran aground off the coast of Blouberg in Table Bay, South Africa. Due to failed salvage attempts, the vessel has remained stranded approximately 500 m off the Blouberg beachfront. Since the vessel ran aground, a gradual change in the Blouberg beach shape in the lee of the wreck has been observed. The local coastline, which has traditionally been fairly uniform, has assumed a curved shape, with significant sediment accretion being observed in the wave shadow of the wreck. Initially, the Seli One wreck remained intact. However, during a storm on the 4th September 2011, the vessel split up into three separate pieces. The impact that the wreck is having on the local wave, current and sediment transport dynamics remains undefined. This lack of knowledge results in significant risks, relating to shoreline stability and beach amenity. The objective is this study was therefore the determination of the long-term impact of the Seli One shipwreck on the Blouberg beachfront. A review of existing literature has indicated that no empirical relationships are available which could be used to calculate the impact of a shipwreck on nearby coastal processes. Numerous methods are available which can be used to determine the net longshore transport rates, but these cannot be used to quantify the impacts of shipwrecks on the local sediment transport regime. Numerical models were therefore used to determine the impact of the Seli One shipwreck. Through the analysis of simulation results, it was concluded that, as expected, the shipwreck has resulted in a significant reduction in the net longshore sediment transport rate in her lee, resulting in sediment deposition in this area. It was further concluded that the vessel does not result in the complete blockage of longshore sediment transport, and that sediment is able to periodically pass through the lee of the vessel. The simulated beach salient on the 3rd July 2011 was compared to results of a beach survey, performed on the same date specifically for this study. The simulated accretion of approximately 27 m in the lee of the shipwreck agrees well with the measured salient. It has been shown that approximately 75% of the salient accretion occurred within the first two months of the vessel’s arrival. Furthermore, shoreline erosion on the northern side of the salient resulting directly from the shipwreck has been shown to be approximately 15 m. This too occurs relatively rapidly, within approximately two months of the vessels arrival. Following the initial impact of the wreck in its intact configuration, the long-term potential impact of the vessel in its broken-up configuration was determined. This included the assumption that the vessel does not undergo any additional breaking-up, and remains in its three-piece configuration indefinitely. This has shown that the salient width resulting from the shipwreck is reduced to approximately 20 m, compared to the initial 27 m. However, shoreline erosion on the northern side of the wreck has increased from approximately 15 m initially to approximately 18 m in the long-term, which is caused by the continuous sedimentation between the vessel and the beach. A two-dimensional coupled wave, current and sediment transport model has been developed and has shown that the wave shelter resulting from the Seli One results in the formation of a submerged salient between the vessel and the shoreline. It was found that shipwrecks have the potential of significantly altering local longshore sediment transport characteristics in general. Depending on local conditions, this may pose serious risks, both in terms of jeopardizing local seaside infrastructure, as well as creating dangerous swimming conditions. Considering the impact that a shipwreck can have on local shoreline changes, with special regard to the rate at which these shoreline changes can occur, it is recommended that the results obtained from the current study be used to estimate the impact of potential future shipwreck scenarios in Table Bay. / AFRIKAANSE OPSOMMING: Op die 9de September 2009 het die 178 m lange Panamese vragskip, die Seli Een, aan die kus van Bloubergstrand in Tafelbaai, Suid Afrika, gestrand. Weens mislukte reddingspogings, het die skip ongeveer 500 m van die kuslyn gestrande gebly. Sedertdien, is ‘n geleidelike verandering in die vorm van Bloubergstrand se kuslyn waargeneem. Die kuslyn, wat tradisioneel redelik uniform en reguit was, het onlangs ‘n aansienlike geboë vorm aangeneem, met ‘n beduidende hoeveelheid sand wat in die skip se lykant neerset. Aanvanklik het die Seli Een wrak ongeskonde gebly, maar tydens ‘n storm op die 4de September 2011, het die skip in drie afsonderlike stukke opgebreek. Die impak wat die wrak op die golf, strome en sediment vervoer dinamika het,bly ongedefinieërd. Hierdie gebrek aan kennis veroorsaak ‘n aansienlike hoeveelheid risiko’s met spesifieke betrekking tot kuslyn stabiliteit en strand gerief. Die doel van hierdie studie was dus om die langtermyn-impak van die Seli Een skeepswrak op Bloubergstrand te bepaal. 'n Hersiening van bestaande literatuur het aangedui dat geen empiriese verhoudings beskikbaar is wat gebruik kan word om die impak van 'n skeepswrak op die nabygeleë kustelike prosesse te bereken nie, maar wel versekeie metodes wat gebruik kan word om die netto langsstroom sediment vervoer te bepaal. Hierdie verhoudings kan egter nie gebruik word om die impak van ‘n skeepswrak op die sediment vervoer meganisme te kwantifiseer nie, dus is numeriese modelle gebruik om die impak van die Seli Een skeepswrak te bepaal. Die skeepswrak het ‘n aansienlike vermindering in the netto langsstroom sediment vervoer veroorsaak, wat tot die afsetting van sediment in hierdie gebied lei. Dit is ook verder bepaal dat die Seli Een nie die volledige verstopping van langsstroom sedimentvervoer veroorsaak nie, maar dat sediment van tyd tot tyd in staat is om deur die lykant van die skeepswrak te beweeg. Die gesimuleerde strand aanwas van die 3de Julie 2011 is vergelyk met resultate van ‘n strand-opmeting, wat uitgevoer is op dieselfde datum, spesifiek vir hierdie studie. Die gesimuleerde aanwas, van ongeveer 27 m in die lykant van die skeepswrak, stem saam met die gemete aanwas. Ongeveer 75% van die aanwas het binne twee maande van die aankoms van die Seli Een plaasgevind. Verder is dit getoon dat aan die noordelike kant van die aanwas, ongeveer 15 m van die kuslyn weggespoel het as gevolg van die Seli Een. Na die aanvanklike impak van die wrak in sy ongeskonde konfugirasie, is die potensiële langtermyn impak van die skip in sy opgebreekte konfugirasie bepaal. Dit sluit die aanname in dat die skip nie enige bykomende breke ondergaan nie, en in sy drie-stuk konfigurasie bly. Dit het getoon dat die breedte van die aanwas, wat veroorsaak is deur die skip, verminder tot ongeveer 20 m in vergelyking met die aanvanklike 27 m. Verder is dit getoon dat die erosie aan die noordelike kant van die Seli Een vermeerder het van die aanvanklike 15 m na ongeveerder 18 m in die langtermyn. Die oorsaak hiervaan is die aaneenlopende sedimentasie tussen die wrak en die strand. 'n Twee-dimensionele gekoppelde golf, stroom en sediment vervoer model is ontwikkel en het getoon dat die golf skuiling, as gevolg van die Seli Een, sedimentasie tussen die skip en die kuslyn veroorsaak. Daar is gevind dat skeepswrakke die potensiaal het om aansienlike veranderinge aan die nabygeleë langstroom sediment vervoer stelsel te veroorsaak. Afhangende van die plaaslike omstandighede, kan hierdie ernstige risiko’s veroorsaak, beide in terme van die gevaar vir plaaslike kustelike infrastruktuur, sowel as die generasie van gevaarlike swem toestande. Met inagneming van die impak wat 'n skeepswrak op plaaslike kuslyn veranderinge kan hê, met spesiale verwysing na die tempo waarteen hierdie kuslyn veranderinge kan plaasvind, word dit aanbeveel dat die resultate wat verkryg is vanuit die huidige studie, gebruik word om die impak van moontlike, toekomstige skeepswrakke in Tafelbaai te bepaal.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Innovative and versatile coastal protection structures made of Geotextile Sand Containers (GSCs) are increasingly being incorporated into coastal management solutions because of their cost effective and environmentally friendly characteristics. This is as opposed to conventional ‘hard’ coastal protection solutions that utilise rocks and or concrete units to protect the coastline. With GSC structures being a relatively new coastal protection solution, few design and construction guidelines are available. Research into the behaviour of GSC structures under wave attack is on-going with particular emphasis on the hydraulic processes that affect GSC structures and cause them to fail. The use of GSC revetments as coastal protection solutions has become more popular in South Africa during recent times, particularly along the coastline of KwaZulu-Natal. However, the chosen design of these GSC revetments falls outside the range of applicability of the available design charts and stability equations. Therefore the hydraulic stability of these structures is largely unknown. The primary objective of this study is to investigate the effect of structure slopes and packing arrangements on the hydraulic stability of GSC revetments. The application of available design charts and stability equations was also evaluated. Two-dimensional physical modelling was undertaken and a total of 12 GSC revetment permutations were tested during the physical modelling test series. The results of the physical modelling showed that the structure slope had the most significant effect on the hydraulic stability. Steeper structure slopes were more hydraulically stable than gentler structure slopes. The packing arrangements of the GSCs had less of an effect on the hydraulic stability of the GSC revetments. Single layer GSC armour revetments matched or out-performed the equivalent double layer GSC revetments; while GSC revetments with GSCs orientated with the long axis perpendicular to the wave attack performed marginally better than the equivalent GSC revetments with GSCs orientated with the long axis parallel to the wave attack. The available design charts and stability equations were assessed against the results of the physical modelling and showed varying degrees of correlation. The stability equation proposed by Recio (2007) proved to be particularly accurate. / AFRIKAANSE OPSOMMING: Innoverende en veelsydige kusbeskermingstrukture wat van geotekstielsandhouers (GSH’s) gemaak is, word al hoe meer by kusbestuursoplossings ingesluit weens die kostedoeltreffendheid en omgewingsvriendelike aard daarvan. Dít is in teenstelling met konvensionele ‘harde’ kusbeskermingsoplossings, wat van rotse en/of betoneenhede gebruik maak om die kuslyn te beskerm. Aangesien GSH-strukture ’n betreklik nuwe kusbeskermingsoplossing is, is weinig ontwerp- en konstruksieriglyne beskikbaar. Navorsing oor die werkverrigting van GSH-strukture onder golfaanslag duur voort, met bepaalde klem op die hidrouliese prosesse wat GSH-strukture beïnvloed en die werking daarvan benadeel. Die gebruik van GSH-bedekte hellings as kusbeskermingsoplossings het in die laaste tyd al hoe gewilder geword in Suid-Afrika, veral langs die kus van KwaZulu-Natal. Tog val die gekose ontwerp van hierdie GSH-bedekte hellings buite die toepaslikheidsbestek van die beskikbare ontwerpriglyne en stabiliteitsvergelykings. Die hidrouliese stabiliteit van hierdie strukture is dus grotendeels onbekend. Die hoofoogmerk van hierdie studie was om ondersoek in te stel na die effek van struktuurhellings en pakformasies op die hidrouliese stabiliteit van GSH-bedekte hellings. Die toepaslikheid van beskikbare ontwerpriglyne en stabiliteitsvergelykings is ook geëvalueer. Tweedimensionele fisiese modellering is onderneem en altesaam 12 GSH-bedekte hellings is gedurende die fisiese-modelleringstoetsreeks getoets. Die resultate van die fisiese modellering toon dat die struktuurhelling die beduidendste effek op hidrouliese stabiliteit het. Steiler struktuurhellings was hidroulies meer stabiel as platter hellings. Die pakformasies van die GSH’s blyk ’n kleiner effek op die hidrouliese stabiliteit van die GSH-bedekte hellings te hê. GSH-bedekte hellings wat met ’n enkele laag GSH’s versterk is, het ewe goed of beter presteer as die keermure met ’n dubbele laag GSH’s, terwyl GSH-bedekte hellings met die lang-as van die GSH’s loodreg op die rigting van die golfaanslag effens beter presteer het as dié met die lang-as parallel met die golfaanslag. Die beskikbare ontwerpriglyne en stabiliteitsvergelykings is geëvalueer aan die hand van die resultate van die fisiese modellering, en het ’n wisselende mate van korrelasie getoon. Veral die stabiliteitsvergelyking van Recio (2007) blyk besonder akkuraat te wees.

Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: The port of Ngqura is situated on the east coast of South Africa. Since its first operational winter excessive vessel motions have interrupted container shipping operations and lead to mooring line failure. A major component contributing to the excessive motions is the presence of seiching in the port, resonating long waves. This study investigates the long wave generation, penetration into the port and subsequent resonance in the vicinity of the problem berths. An extensive literature review identified two predominant types of long waves along the coast of South Africa. Long waves with periods over 12 min generated by resonant air-water coupling and then shorter long waves between 30 s and 6 min attributed to bound long wave energy and broadly speaking, surf beat. A review of the state of the art long wave modelling techniques was included and contributed to the methodology in this study. Analysis of simultaneous measurements from the outside and inside of the port confirmed the generating mechanism of the long waves to be storm systems also responsible for generating short waves. Long waves outside the port were found to be on average 8% of the height of the short waves. On average 90% of the long wave height outside the port penetrated the port. The measurements further identified distinct resonating periods of the long wave energy inside the port. Calibrated Boussinesq wave models allowed for identification of how long waves penetrated the port and subsequently resonated. Both surface elevation measurements and white noise spectra were used as inputs. The penetration mechanisms were attributed to direct diffraction around the main breakwater as well as reflection off the beach south of the port leading to refraction and reflection off the lee side of the main breakwater. Tests with both free and bound long waves proved that at least for some period intervals the long wave energy was indeed bound to short waves. The excessive vessel motions are attributed to berths positioned in line with nodes created by the resonating long waves; nodes are characterized by strong horizontal currents which can induce surge motions in vessels. Various long waves between the period intervals of 45 s to 125 s resonate in the port to generate nodes at the berths of interest. In conclusion, the port of Ngqura is susceptible to a range of long wave periods resulting in significant basin oscillations which present nodes at mooring places. As a result of the analyses in this study the mechanisms of interaction between the port, port basins and the long waves penetrating into the port directly, or via the surf zone as surf beats, have been modelled, documented and better understood. This provides the potential for better prediction of severe long wave events and for the investigation of feasible mitigation measures to prevent damage to moored ships in the port. / AFRIKAANSE OPSOMMING: Die Ngqura hawe is aan die ooskus van Suid-Afrika geleë. Sedert die hawe se eerste operasionele winterseisoen, het oormatige skeepsbewegings operasies van behoueringskepe onderbreek en gelei tot faling van vasmeertoue. Die teenwoordigheid van langgolf resonansie is ‘n groot bydraende faktor tot die oormatige skeepsbewegings. Hierdie studie ondersoek die opwekking, penetrasie en gevolglike resonansie van langgolwe in die areas aangrensend tot die problematiese kaaie. ‘n Uitgebreide literatuurstudie het twee tipes langgolwe aan die Suid-Afrikaanse kus geïdentifiseer, naamlik langgolwe met periodes langer as 12 minute wat deur resonante lug-water koppeling opgewek word en korter langgolwe met periodes tussen 30 s en 6 min wat aan gebonde langgolfenergie of, meer algemeen, surf beat toegeskryf word. Verder is ‘n studie rakende die jongste langgolfmodelleringstegnieke ook uitgevoer waaruit die metodiek van hierdie studie bepaal is. ‘n Analise van gelyktydige opmetings binne en buite die hawe het bevestig dat kortgolwe wat deur stormsisteme gegenereer word, die opwekkingsmeganisme van lang golwe is. Daar is bevind dat langgolwe buite die hawe gemiddeld 8% so hoog soos kort golwe is. ‘n Gemiddeld van 90% van die langgolfhoogte het die hawe penetreer. Die opmetings het ook verder duidelike resonansieperiodes van langgolfenergie binne die hawe aangedui. Gekalibreerde Boussinsq-golfmodelle is gebruik om te indentifiseer hoe langgolwe die hawe binnedring en gevolglik resoneer. Beide oppervlakmetings en wit geraas spektra is as invoerwaardes vir die model gebruik. Die penetrasiemeganismes is toegeskryf aan diffraksie rondom die hoof hawemuur asook refleksie vanaf die strand, suid van die hawe, wat lei tot refraksie en refleksie teen die lykant van die hoof hawemuur. Toetse met vry langgolwe het bewys dat die langgolfenergie, vir ten minste sommige periode intervalle, aan die kort golwe vebonde is. Die oormatige skeepsbewegings is toegeskryf aan die kaaie wat in lyn met nodes van die langgolfresonansie geposisioneer is. Nodes word gekarakteriseer deur sterk horisontale strome wat surge bewegings in skepe kan veroorsaak. Verskeie langgolwe met periode intervalle tussen 45 s tot 125 s resoneer in die hawe en vorm nodes by die kaaie van belang. Ten slotte, die Ngqura hawe is vatbaar vir ‘n reeks langgolfperiodes wat ossilasies in die bekkens van die hawe veroorsaak en nodes naby kaaie vorm. As gevolg van die analises in hierdie studie is die meganismes van interaksie tussen die hawe, sy bekkens en langgolwe wat die hawe direk of via die brandersone binnedring gemodelleer, gedokumenteer en beter verstaan. Hierdeur is die potensiaal vir beter voorspelling van ernstige langgolftoestande verhoog en is dit moontlik gemaak om lewensvatbare oplossings vir skade aan vasgemeerde skepe te ondersoek.