Thesis (MEng)–Stellenbosch University, 2014. / ENGLISH ABSTRACT: The Port of Durban is forecasted to reach its capacity in terms of container handling soon, which necessitates the investigation of an alternative port in the vicinity. The old Durban Airport site has been identified as a potential location to develop a new deep water container harbour. This is driven by a demand for deep water berth capacity as a result of shipping liners preferring the benefits of scale in their operations, leading to the use of larger ships with deeper drafts. To protect the new port from wave energy penetrating inside the basin as well as from sedimentation from the adjacent beaches, the design and construction of breakwaters are required. The proposed main breakwater for this dig-out port is expected to extend 1 200m into the sea, up to depths of 30m at the seaward roundhead. The deeper parts of the breakwater face wave onslaught in a different manner than a conventional breakwater in shallower waters. At these larger depths, the breakwater has to dissipate the energy of non-breaking waves. In this thesis, the wave climate nearshore, adjacent to the proposed breakwater is studied and extreme wave events are simulated with a SWAN numerical model. The results for a range of wave conditions, corresponding to selected events up to a return period of one in 100 years, are presented. A study of deep water breakwaters was undertaken to investigate other examples of similar structures. This indicated a clear distinction between vertical wall type breakwaters and the more traditional rubble-mound type breakwaters. For this thesis, a rubble-mound breakwater was chosen as the breakwater type for testing under conditions of the Durban Dig-Out Port (DDOP). Focussing on a deep water trunk section of the proposed main breakwater, a concept cross-section was designed using deterministic design methods. The formulae incorporated in this method did however not take into account the packing density of the armour layer and only assumed the recommended values. The hypothesis is thus put forward that the breakwater will still be hydraulically stable for packing densities below the recommended values. This would decrease material consumption and save on cost over the entire breakwater. A physical model was designed to experiment with different armour layer configurations of single- and double layer Cubipod arrangements. The unit was chosen for its massive shape and structural integrity even during impact. A physical model study was performed at the facilities of the CSIR in Stellenbosch. It entailed setting up a fixed-bed two-dimensional physical model in a glass wave flume. Measuring wave heights, wave reflection, overtopping, wave transmission and armour damage, the hydraulic stability and operational performance were analysed for several tests. Based on the results of the first few test series, alterations were made to the breakwater geometry and armouring. The results confirmed the hypothesis that lower packing densities were still hydraulically stable under 1 in 100 year return period wave conditions without inhibiting operational performance. A final cross-section is presented as concept design for the deep section of the proposed DDOP main breakwater. / AFRIKAANSE OPSOMMING: Volgens vooruitsigte gaan Durban hawe binnekort sy kapasiteit bereik wat die hantering van skeepshouers betref. Hierdie verwikkeling noodsaak die ondersoek na ‘n alternatiewe hawe in die nabye omgewing. Die voormalige Durban lughawe is intussen geïdentifiseer as ‘n potensiële perseel waar ‘n diep water houervrag hawe ontwikkel kan word. Dit word gedryf deur die aanvraag na diep water kaai kapasiteit as gevolg van skip operateurs wat skaalvoordele verkies, sodat groter skepe met diep rompe meer populêr word. Die ontwerp en konstruksie van breekwaters word dus benodig, om te verhoed dat beide golwe, sowel as sediment van aangrensende strande, die hawe binnedring. Die voorgestelde hoof breekwater vir hierdie hawe sal na verwagting tot 1200m in die see in strek, waar dit tot 30m diep is naby die seewaartse hoof van dié breekwater. Die dieper gedeeltes van só ‘n breekwater sal blootgestel word aan ‘n ander soort golf aanslag as ‘n soortgelyke konvensionele breekwater in vlakker water. In hierdie waterdiepte is die breekwater verantwoordelik vir die energie verbreking van ongebreekte golwe. In hierdie tesis word die golfklimaat langs die kus, naby aan die voorgestelde breekwater bestudeer. Die uiterste golf gebeurtenisse word gesimuleer met ‘n SWAN numeriese model. Die resultate van ‘n reeks golf kondisies, ooreenstemmend met bepaalde gebeurtenissemet herhaal periodes van tot 100 jaar, word aangebied. ‘n Studie van diep water breekwaters is onderneem om voorbeelde van soortgelyke strukture te ondersoek. Die studie toon ‘n definitiewe onderskeid tussen vertikale muur breekwaters en die meer tradisionele “rubble-mound” breekwater tipes. Vir hierdie tesis is die “rubble-mound” breekwater tipe gekies vir toetsing, onderhewig aan die kondisies van die “Durban Dig-Out Port” (DDOP). ‘n Konsep deursnit is ontwerp vir ‘n diep water romp gedeelte van die voorgestelde hoof breekwater, deur van deterministiese metodes gebruik te maak. Die formules soos vervat in hierdie proses maak egter nie voorsiening vir die pakdigtheid van die bewapeningslaag nie, maar aanvaar slegs die voorgestelde waardes. Die hipotese word dus aangevoer dat die breekwater steeds hidrolies stabiel sal wees vir pakdigthede wat laer as die voorgestelde waardes is. Dit sal die verbruik van materiale verlaag en lei tot koste besparings vir die breekwater. ‘n Fisiese model is ontwerp om te eksperimenteer met verskillende opstellings van die bewapeningslaag. Dit sluit enkel- en dubbel laag bewapening met Cubipod eenhede in. Hierdie eenheid is gekies vir sy massiewe vorm en strukturele integriteit, selfs tydens impak. ‘n Fisiese model studie is uitgevoer by die fasiliteite van die WNNR in Stellenbosch. Dit het die opstel van ‘n vaste-bodem, twee-dimensionele fisiese model in ‘n glas golftenk (“wave flume”) behels. Hidroliese stabiliteit en operasionele werksverrigting is geanaliseer deur golf hoogtes, -weerkaatsing, -oorslag, -deurlating, en skade aan die bewapening te meet vir verskeie toetse. Gebasseer op die resultate van die eerste paar toetsreekse, is veranderinge gemaak aan die breekwater se geometrie en bewapening. Die resultate het die hipotese bevestig dat laer pakdigthede steeds hidrolies stabiel is tydens golf kondisies met ‘n 1 in 100 jaar herhaal periode, sonder om die werksverrigting van die breekwater te belemmer. ‘n Finale deursnit word voorgestel as ‘n konsepontwerp vir die diep water deursnit van die DDOP se hoof breekwater.

Thesis (Ph. D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 2000. / Includes bibliographical references (leaves 134-141). / by Nicole Marie Suoja. / Ph.D.

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 (PhD (Civil Engineering))--University of Stellenbosch, 1989. / ENGLISH ABSTRACT: Several aspects related to the estimation and selection of design wave conditions were investigated. An analysis program which includes strict quality control routines was developed for digital Waverider data. All available Waverider data from deepsea records were analysed with this program. A remarkable similarity in simultaneously recorded wave heights between Cape Town and Port Elizabeth was found. This similarity was used to compile a near continuous wave record over an eight year period for the Southern Cape coast. The 10537 values of significant wave height (Hmo) which made up the record for the Southern Cape were found to give a good visual fit to the Extreme I and Log-normal distributions over the entire range of Hmo values. Design wave heights derived from the Extreme I distribution were found to be insensitive to assumptions regarding the independence and identical distribution of the wave height samples and the method used for parameter estimation. Design wave heights for the coastline between Oranjemund and Port Elizabeth were found to be strongly correlated to the latitude of the recording site. High waves along these coasts are invariably caused by the passage of cold fronts past the southern tip of the continent. Wave heights reduce as the distance from the west to east route of these cold fronts increase, thus the reason for the abovementioned correlation. No deepwater wave records are available east of Port Elizabeth. Shallow water records indicate that a reduction in wave height can be expected between Port Elizabeth and East London.

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2006. / This research provides and overview of sea storms around the South African Coast in terms of weather types, characteristic wave statistics, storm processes and wave energy. Sea Storm Profiles are unique to the particular storm events causing them, but they can be associated with Equivalent Wave Energy (EWE) Storm Profiles, which are representative of them and have a linear, symmetric, “Capital Lambda” ( Λ ), shape. The actual storm profile and the EWE Profile are equivalent in wave energy, and the benefit of the EWE is that it is regular and can be can be readily compared with another EWE Storm Profile for analysis, and for the comparison of impacts. The ability to compare the impacts of Sea Storms from different areas, on the basis of characteristic Equivalent Wave Energy (EWE) Storm Profiles within the South African Coastal Regions, is considered to be advantageous. This will allow Engineers to apply the knowledge gained in one area to another with a similar EWE Storm Profile, with more confidence. There will always be the need for site-specific investigations, data recording, data analysis and interpretations in Coastal Engineering Work, but one needs to start with an understanding of the general nature of the coastal region in which one is working. This research adds to the background “Body of Knowledge” relating to the character of the sea storms in the Regions around South Africa. The study is based on a literature survey of atmospheric weather, sea wave theory and wave climates, as well as the analysis of weather and sea state data at selected recording stations around the South African Coastline.

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.

In the present dissertation, the hydrodynamic and hydro-elastic characteristics of ship hull and plate vibrations are analyzed using theoretical and numerical methods. The wave forces are determined using a suite of methods which include the Froude-Krylov method for incident wave forces, Wagner's method and ABS rules for the slamming wave force, and numerical methods for nonlinear wave radiation forces. Finite difference methods are developed to determine the wave forced vibrations of ship hull plates which are modeled using a range of plate theories including nonlinear plate theory with and without material damping and orthotropic plate theory for stiffened hull plates. For small amplitude deformation of thin plates, a semi-theoretical superposition method is used to determine the free and forced vibrations. The transient ship hull vibration due to whipping is also analyzed using the finite difference method. Results, in the form of deformations and stress distributions, are obtained for a range of scantling and wave parameters to identify key parameters to consider in ship structural design. / by Fnu Lakitosh. / Thesis (Ph.D.)--Florida Atlantic University, 2012. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2012. Mode of access: World Wide Web.

Thesis (S.M.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 148-152). / Wind waves in the ocean are a product of complex interaction of turbulent air flow with gravity driven water surface. The coupling is strong and the waves are non-stationary, irregular and highly nonlinear, which restricts the ability of traditional phase averaged models to simulate their complex dynamics. We develop a novel phase resolving model for direct simulation of nonlinear broadband wind waves based on the High Order Spectral (HOS) method (Dommermuth and Yue 1987). The original HOS method, which is a nonlinear pseudo-spectral numerical technique for phase resolving simulation of free regular waves, is extended to simulation of wind forced irregular broadband wave fields. Wind forcing is modeled phenomenologically in a linearized framework of weakly interacting spectral components of the wave field. The mechanism of wind forcing is assumed to be primarily form drag acting on the surface through wave-induced distribution of normal stress. The mechanism is parameterized in terms of wave age and its magnitude is adjusted by the observed growth rates. Linear formulation of the forcing is adopted and applied directly to the nonlinear evolution equations. Development of realistic nonlinear wind wave simulation with HOS method required its extension to broadband irregular wave fields. Another challenge was application of the conservative HOS technique to the intermittent non-conservative dynamics of wind waves. These challenges encountered the fundamental limitations of the original method. Apparent deterioration of wind forced simulations and their inevitable crash raised concerns regarding the validity of the proposed modeling approach. The major question involved application of the original HOS low-pass filtering technique to account for the effect of wave breaking. It was found that growing wind waves break more frequently and violently than free waves. / (cont.) Stronger filtering was required for stabilization of wind wave simulations for duration on the time scale of observed ocean evolution. Successful simulations were produced only after significant sacrifice of resolution bandwidth. Despite the difficulties our modeling approach appears to suffice for reproduction of the essential physics of nonlinear wind waves. Phase resolving simulations are shown to capture both - the characteristic irregularity and the observed similarity that emerges from the chaotic motions. Energy growth and frequency downshift satisfy duration limited evolution parameterizations and asymptote Toba similarity law. Our simulations resolve the detailed kinematics and the nonlinear energetics of swell, windsea and their fast transition under wind forcing. We explain the difference between measurements of initial growth driven by a linear instability mechanism and the balanced nonlinear growth. The simulations validate Toba hypothesis of wind-wave nonlinear quasi-equilibrium and confirm its function as a universal bound on combined windsea and swell evolution under steady wind. / by Alexander G. Kalmikov. / S.M.

Thesis (S.M.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), February 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 327-334). / In the present work, we study the statistics of wavefields obtained from non-linear phase-resolved simulations. The numerical model used to generate the waves models wave-wave interactions based on the fully non-linear Zakharov equations. We vary the simulated wavefield's input spectral properties: directional spreading function, Phillips parameter and peak shape parameter. We then investigate the relationships between a wavefield's input spectral properties and its output physical properties via statistical analysis. We investigate surface elevation distribution, wave definition methods in a nonlinear wavefield with a two-dimensional wavenumber, defined waves' distributions, and the occurrence and spacing of large wave events. / by Legena Albertha Henry. / S.M.

This study reports on a new formulation of the spectral dissipation source term Sds for wind-wave modelling applications. This new form of Sds features a nonlinear dependence on the local wave spectrum, expressed in terms of the azimuthally integrated saturation parameter B(k)=k^4 F(k). The basic form of this saturation-dependent Sds is based on a new framework for the onset of deep-water wave breaking due to the nonlinear modulation of wave groups. The new form of Sds is succesfully validated through numerical experiments that include exact nonlinear computations of fetch-limited wind-wave evolution and hindcasts of two-dimensional wave fields made with an operational wind-wave model. The newly-proposed form of Sds generates integral spectral parameters that agree more closely with observations when compared to other dissipation source terms used in state-of-the-art wind-wave models. It also provides more flexibility in controlling properties of the wave spectrum within the high wavenumber range. Tests using a variety of wind speeds, three commonly-used wind input source functions and two alternative full-development evolution limits further demonstrate the robustness and flexibility of the new saturation-dependent dissipation source term. Finally, improved wave hindcasts obtained with an implementation of the new form of Sds in a version of the WAM model demonstrate its potential usefulness in operational wind-wave forecasting applications.