Offshore wind in the United States is a rapidly growing industry. The development of both fixed bottom and floating platforms is important for the success of the industry. While monopiles are common substructures in Europe, the Atlantic Coast has a much greater risk for hurricanes. It is necessary to understand how extreme weather events will impact the structures. Meanwhile, floating offshore wind will be key for offshore wind development along the Pacific Coast, Hawaii, and Gulf of Maine. Before these projects can come to fruition, the cost of development must first decrease. A taut mooring system with multiline anchors may be able to reduce costs, specifically when deployed in deep water locations. This thesis considers these concerns for both the fixed bottom and floating wind developments. A parametric study is completed using OpenFAST for a variety of mooring systems. A taut multiline mooring system is designed for water depths ranging from 850 to 2000 meters. Further 850-meter designs explore how changing line properties impact the mooring line and multiline loading. Using these mooring designs, preliminary suction anchors are designed, focusing on the potential savings of decreasing the number of anchor installations from 3 single line anchors per turbine to 1 multiline anchor per turbine. Anchors are designed for a range of soil conditions to observe their impacts on anchor dimensions. For monopile design, four Atlantic Coast wind developments are chosen for design of monopiles at each site, using 50-year and 500-year storm conditions in the design process. These monopiles are designed using primarily hand calculations, with the assistance of OpenFAST to create a hub thrust power curve. The loads are then used to design monopile for a constant diameter and thickness from the transition piece to the mudline. The constant diameter monopiles are compared to a design that was complete for fatigue loading. In general, the fatigue loaded monopiles were required to be much larger, providing capacities larger than the monopiles designed for extreme storm conditions.

This thesis presents an innovative approach to enhance the stability of floating offshore wind turbine (FOWT) platform through mooring actuation. First, an OC3- Hywind spar-buoy floating platform is modeled utilizing the Control-oriented, Reconfigurable, and Acausal Floating Turbine Simulator (CRAFTS) with a specific focus on predicting hydrodynamic and mooring line loads while intentionally excluding consideration of aerodynamic forces. The accuracy of this model is validated against the industry standard OpenFAST simulator through various test cases. The central objective of this study revolves around achieving robust stabilization of the spar buoy platform, primarily focusing on X-Z symmetric planar motions, including surge, pitch, and heave degrees of freedom (DOFs). To accomplish this, two linearization techniques are employed: one transforms the inherently complex nonlinear model from CRAFTS into a linear Mass-Spring-Damper (MSD) system, particularly targeting surge and pitch motions, while the other method involves the conversion of the nonlinear model from CRAFTS into the Functional Mockup Interface (FMI) within MATLAB/Simulink for linearization. The analysis utilizing Bode plots derived from these lin- earized models yields crucial insights into the system's response to mooring actuation. Notably, it emphasizes the inherent challenge in pitch control, characterized by lower gain compared to surge at relevant frequencies, necessitating substantial mooring actuation or cable length modifications for effective pitch stabilization. Then, a Linear Quadratic Regulator (LQR) controller is designed to mitigate surge and pitch motions. Numerical simulations conducted across diverse scenarios reveal the inherent challenge in simultaneously mitigating surge and pitch motions using the original platform configuration. To address this challenge, a control co-design strategy is proposed, leading to the development of an optimized mooring line configuration that effectively stabilizes both motions with minimal adjustments. In summary, this thesis introduces a control-oriented modeling approach and an innovative control strategy to enhance the stability of the floating wind turbine platform through mooring actuation. The results emphasize the potential for broader application of this approach to various floating platforms for FOWTs and the extension of stabilization efforts to address all six DOFs in future research, where aerodynamic loads are also incorporated.

The objective of this thesis is to generate and enhance technical specifications for mooring equipment designated for the Swedish Navy, as commissioned by the Swedish Defence Materiel Administration. The technical specifications will primarily emphasize the capacity to endure various load scenarios imposed by the Swedish Defence on the mooring equipment. This technical report constitutes a preliminary investigation in collecting technical requirements where the mechanical characteristics will be of focus. The investigation assessed the elasticity characteristics of mooring ropes, considering their dependence on length and loading rate. As the mooring ropes are exposed to large forces and environmental circumstances, this study focused on investigating the impact of a used and worn rope, with the conclusive finding that the worn rope exhibited a substantial decline in its strength characteristics.  The thesis work will examine the different load cases, encompassing both slow and shock loadings, with the result that Young's modulus does depend on the loading rate and that the magnitude of damping in the rope holds notable significance. The mooring goods must also endure extreme conditions without failing prematurely while still conforming to the performance requirements of the personnel handling the ropes. Therefore, a study is included regarding how much impact the weather conditions may have on the mooring ropes and which parameters are important. The thesis also outlines the importance of considering similar handling standards for new mooring goods, given the expectation of future procurement. It is crucial to avoid certain mistakes during handling, which can severely damage personnel and equipment. Therefore, it is necessary to ensure that the new mooring ropes meet the current handling standards to maintain safety and avoid costly accidents. This report emphasizes the significance of adhering to proper handling standards in procuring and deploying mooring goods for the Swedish marine. / Syftet med detta arbete är att utveckla samt förbättra de tekniska specifikationer som FMV idag besitter angående de tampar \& förtöjningsgods som är avsedda för den svenska flottan, på uppdrag av Försvarets Materielverk, FMV. Denna rapport är en förstudie för samlandet av tekniska krav där fokuset främst ligger på de mekaniska egenskaperna ur ett hållfasthetsmässigt perspektiv. Undersökningen bedömde elasticitetsegenskaperna hos förtöjningsrep med hänsyn till deras beroende av längd och belastningshastighet. Eftersom dessa förtöjningsrep utsätts av diverse stora krafter och miljöförhållanden så undersöktes även vilken påverkan detta har på repen. Detta undersöktes genom att jämföra ett nytt mot ett gammalt och slitet rep. Båda av samma modell och tillverkare. Denna jämförelse ledde till slutsatsen att det använda repet besatt en betydande nedgång i samtliga sina egenskaper ur ett förtöjningsperspektiv. Avhandlingen kommer undersöka repens, främst amfibiebataljonens, olika belastningssituationer, inklusive både långsamma och plötsliga belastningar för att utvärdera de olika lastfallen de kan tänkas utsättas för. Detta resulterade i att elasticitetsmodulen verkar ha ett beroende av lastningshastigheten och visar på viskoelastiska egenskaper samt att dämpningsfaktorn har en betydande storlek hos tampen. Förtöjningsutrustningen måste även klara en rad olika miljöförhållanden utan att plötsligt ge vika, samtidigt som de uppfyller prestandakraven hos besättningen. Därför följer även en utredning kring hur mycket väderförhållandena kan påverka repen samt vilka parametrar som är viktiga att ta hänsyn till. Rapporten syftar även till att betona vikten av standardisering för ny förtöjningsutrustning med tanke på eventuell framtida upphandling. Det kan vara avgörande att undvika misstag vid hantering, vilket kan resultera i skador på besättning och utrustning. Därför är det viktigt att se till att nya förtöjningsrep uppfyller och upprätthåller de aktuella standarder som finns.

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.

Purpose: The purpose of this study is to increase the understanding of what makes Swedish millennials follow and unfollow influencers on Instagram.   Metod: This study had a deductive and qualitative approach and has collected data through twelve semi-structured interviews.   Conclusion: This study concludes that millennials mainly follow influencers on Instagram to get inspiration for their own lives. One of the most common reasons why millennials are unfollowing influncers on Instagram is that influencers tend to publish too much content, which leads to information overload. Millennials also unfollow influencers due to the fact that their posts no longer appeal to them because they changed preferences or because influencers shift the focus of their content. This study also concluded that there is nothing that inhibits a millennial from unfollowing an influencer on Instagram other than the fact that it takes a little bit of effort to visit the account and press the unfollow button. / Syfte: Syftet är att öka förståelsen för vad som får svenska millennials att följa respektive avfölja influencers påInstagram. Metod: Den här studien har haft en deduktiv och kvalitativ karaktär och har samlat in data genom tolv semi-strukturerade intervjuer. Slutsats: Den här studien drar slutsatsen av att millennials främst följer influencers på Instagram för att få inspiration till sina egna liv. En av de vanligaste orsakernatill att millennials avföljer influncers på Instagram äratt influencerstenderar att publicera för mycket inlägg vilket leder till en informationsöverbelastning.Millennials avföljer också influencers för att deras inlägg inte längre tilltalar dem på grund av att de bytt preferenser eller att influencers bytt inriktning på sitt innehåll. Den här studien drar också slutsatsen att det finns egentligen inget som hämmar en millennial från att avfölja en influencer på Instagram annat än att de upplever det som tids-och energikrävande att gå in och avfölja.

Um projeto portuário adequado deve garantir a segurança dos navios atracados e a eficiência das atividades de carga e descarga. Para isso, é preciso boa combinação entre condições de abrigo (natural ou artificial), e sistemas de amarração e defensas. Em geral, os problemas mais sérios de atracação estão relacionados a efeitos de ressonância. Nesse contexto, as obras de abrigo são pouco eficazes porque elas não alteram significativamente os períodos dos fenômenos hidrodinâmicos, e a restrição dos movimentos dos navios atracados depende principalmente dos sistemas de linhas de amarração e de defensas. Analisar um sistema de amarrações e defensas implica estudar a dinâmica do sistema de um navio atracado (navio/amarração/defensas), as ações aplicadas (principalmente as ações ambientais), e as características dos componentes desse sistema. Propõe-se, dessa forma, um estudo para elaboração de modelos que ajudem na compreensão do comportamento dinâmico desse sistema e uma comparação dos resultados obtidos nos modelos com as exigências de documentos técnicos. Partido de análises de modelos estáticos simples até a introdução de não linearidades geométricas e de perda de contato, esta dissertação discute, inicialmente, métodos convencionais de obtenção de esforços de amarração. Em seguida, o sistema é avaliado por meio de modelos dinâmicos que permitem uma compreensão maior sobre o comportamento de um navio amarrado. / An appropriate harbour project should ensure the safety of moored ships and the efficiency of loading and unloading activities. For these reasons, a good combination of (natural or artificial) shelter conditions, mooring systems and fenders is necessary. In general, the most serious mooring problems are related to resonance effects. In this context, shelter structures are not very effective because they do not significantly alter the periods of hydrodynamic phenomena, and the restriction of the moored ships\' movements depends mainly on mooring lines and fenders. Analysing a system of mooring lines and fenders involves studying the dynamics of a moored ship\'s system (ship / mooring / fenders), the actions applied (mainly environmental actions) and the characteristics of the components of that mooring system. Therefore, this study carries out models that help in the understanding of the dynamic behaviour of this system; and makes a comparison of the results obtained in the models with the requirements of technical documents. From the analysis of simple static models to an introduction of geometric nonlinearities and contact loss, this dissertation discusses, initially, conventional methods of obtaining mooring efforts. Then, the system is evaluated by dynamic models that allow a greater understanding of the behaviour of a moored ship.

The search for new solutions for the generation of energy is becoming more and more important for our future. Big arguments and disagreements on e.g. the questions of gas transport or the dependence on energy supplied by other countries raise demands on the development of new forms of alternative energy resources. Wave power is one of the main sources of renewable energy due to the high power density stored in ocean waves. Nevertheless, the dynamic forces of waves are so large that serious questions popped up on how to design a system which could work even in an unfavourable wave climate or could at least retain working capabilities after big storms without significant damages. This thesis studies the reliability of the mechanical parts of a linear direct driven permanent magnet generator. The results of offshore experiment where strain gauge sensors instrumented on the capsule and the inner framework structure are presented. Stress estimation analyses using strain gauges are carried out. A method for measuring forces and moments in the mechanical structure of the WEC is developed. Evaluation of the lateral force acting on the outer structure is a key factor for the design and construction of the WEC. A method for the measurement of the lateral force acting on the capsule has been developed. A study of the inclination angle between the Wave Energy Converter and the floating buoy has been carried out. The aim of this work is to contribute to the development of wave energy conversion system, and especially to the estimation of structural loads which are important for the survivability of the system under hard sea states. This work is a step that may influence future design of wave energy devices in terms of material aspect, survivability in a hard wave climate and cost-effective renewable energies.

The trajectory and capacity are key components of the design of drag embedment anchor and drag-in vertically loaded anchors. This experimental testing program quantifies two factors that describe the anchor trajectory and capacity: the equilibrium bearing factor (Ne) and the tangential bearing factor (Ne). These factors can aid in the development of a numerical model of anchor behavior. A magnetometer device is used to track the orientation and location of the anchor during drag embedment. The results of the experimental testing program were compared with the results from a predictive model. The experimental program consisted of drag embedment tests with various testing conditions including different anchor line diameters and different initial pitch orientations. The results with the different anchor lines indicated that thinner anchor lines cause the anchor to dive deeper in the soil. The different initial pitch results indicate that regardless of the initial pitch of the anchor, the anchor rotates to a unique pitch trajectory within 2 fluke lengths. / text

In the present study, a numerical simulation tool has been developed for the rotor-floater-tether coupled dynamic analysis of Multiple Unit Floating Offshore Wind Turbine (MUFOWT) in the time domain including aero-blade-tower dynamics and control, mooring dynamics and platform motion. In particular, the numerical tool developed in this study is based on the single turbine analysis tool FAST, which was developed by National Renewable Energy Laboratory (NREL). For linear or nonlinear hydrodynamics of floating platform and generalized-coordinate-based FEM mooring line dynamics, CHARM3D program, hull-riser-mooring coupled dynamics program developed by Prof. M.H. Kim’s research group during the past two decades, is incorporated. So, the entire dynamic behavior of floating offshore wind turbine can be obtained by coupled FAST-CHARM3D in the time domain. During the coupling procedure, FAST calculates all the dynamics and control of tower and wind turbine including the platform itself, and CHARM3D feeds all the relevant forces on the platform into FAST. Then FAST computes the whole dynamics of wind turbine using the forces from CHARM3D and return the updated displacements and velocities of the platform to CHARM3D. To analyze the dynamics of MUFOWT, the coupled FAST-CHARM3D is expanded more and re-designed. The global matrix that includes one floating platform and a number of turbines is built at each time step of the simulation, and solved to obtain the entire degrees of freedom of the system. The developed MUFOWT analysis tool is able to compute any type of floating platform with various kinds of horizontal axis wind turbines (HAWT). Individual control of each turbine is also available and the different structural properties of tower and blades can be applied. The coupled dynamic analysis for the three-turbine MUFOWT and five-turbine MUFOWT are carried out and the performances of each turbine and floating platform in normal operational condition are assessed. To investigate the coupling effect between platform and each turbine, one turbine failure event is simulated and checked. The analysis shows that some of the mal-function of one turbine in MUFOWT may induce significant changes in the performance of other turbines or floating platform. The present approach can directly be applied to the development of the remote structural health monitoring system of MUFOWT in detecting partial turbine failure by measuring tower or platform responses in the future.

O desenvolvimento de pesquisas relativas ao comportamento das estruturas offshore são de fundamental importância para as atividades de exploração de petróleo a fim de permitir uma análise mais precisa do desempenho do sistema de ancoragem. Neste sentido, o presente trabalho tem como objetivo analisar o comportamento das linhas de ancoragem submetidas a esforços de tração bem como avaliar e quantificar a atenuação das cargas ao longo do trecho enterrado determinando assim as forças que efetivamente chegam à estaca torpedo. Inicialmente foram projetados e construídos os equipamentos, em modelo reduzido, para a realização dos ensaios experimentais de carregamento estático conduzidos na escala de 1:40. As argilas empregadas nos ensaios foram produzidas em laboratório com o objetivo de obter um solo com propriedades físicas similares à da argila típica do leito marinho, a partir da mistura caulim, bentonita e água, sendo definida a composição em massa seca de 85% de caulim, 15% de bentonita e teores de 100% de umidade para a mistura denominada como argila A, e 120% de umidade para a mistura referida como argila B. Após a caracterização geotécnica concluiu-se que a argila B se assemelha às condições de campo. A força que chega ao ponto de ancoragem, equivalente ao que seria o ponto de fixação da amarra ao torpedo, foi medida experimentalmente através de uma célula de carga para duas componentes (vertical e horizontal) instalada no piso do tanque. A catenária invertida formada pela amarra foi registrada em alguns pontos não visíveis através de um sensor por ultrassom. O carregamento da linha de ancoragem foi produzido para diferentes ângulos de incidência, em ciclos de carga e descarga. Os resultados mostram que, mesmo em uma abordagem estática, flutuações de carga na linha de ancoragem não são inteiramente transmitidas ao ponto de ancoragem (torpedo), sendo parcialmente absorvidas ao longo do trecho enterrado da amarra. A atenuação de carga na argila A foi de 24%, enquanto que a atenuação apresentada na argila B variou entre 14 %, 6% e tendendo a 0 nos ensaios realizados respectivamente nas alturas de solo de 72 cm, 48 cm e 24 cm. Verificou-se também que a qualidade dos critérios de similaridade inicialmente adotados foi satisfatória. / The research development on the behavior of offshore structures is fundamentaly important for the exploration of oil in order to allow a more precise analysis of the performance of offshore mooring systems. In this sense, the present work aims to analyze the behavior of embedded mooring lines subjected to tensile stresses and to evaluate and quantify the attenuation of loads along the stretch buried thus determining the forces that effectively reach the torpedo pile. Initially, the equipment were designed and built, in a reduced model, so the experimental tests of conducted static load on the scale of 1:40 could be conducted. The clays used in the tests were produced in the laboratory in order to obtain a soil with similar physical properties to the typical clay seabed, from mixing kaolin, bentonite and water, the composition being set on dry matter of 85% kaolin 15% bentonite content and 100% humidity for mixing clay called as A, and 120% humidity for mixing said clay as B. After geotechnical characterization, it was found that the clay B is similar to field conditions. The force that reaches the anchor point, equivalent to what would be the point of attachment of mooring the torpedo, was experimentally measured by a load cell for two components (vertical and horizontal) installed on the floor of the tank. The reverse catenary formed by the embedded mooring line was recorded in some not visible spots through an ultrasound sensor. The load of the anchor line has been produced for different incidence angles, in loading and unloading cycles. The results show that, even in a static approach, load fluctuations in the anchor line are not fully transmitted to the anchor point (torpedo). Partially absorbed along the stretch of mooring buried. The attenuation of the load on the clay A was 24%, while the attenuation shown in clay B ranged from 14%, 6% and approaches 0 in the tests performed respectively on the ground heights of 72 cm, 48 cm and 24 cm. It was also found that the quality of similarity criteria adopted initially was satisfactory.