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.

Background: This research work takes a strong sustainability approach with the focus on renewable energy technology (RET) diffusion to meet the multifold and complex challenges with CO2 emission targets and geopolitical energy challenges. Global warming, sustainability issues and significant energy crises, suggests that RET is seen as one of the most important solutions to deal with these challenges. Wind energy has been identified to have a leading role in achieving a low-carbon or completely carbon-free energy sector. Sweden is in the forefront of an energy transition having ambitious goals, and the lack of renewable energy sources may potentially become a problem. Diffusion of new technology may facilitate access to new resources at non-exploited areas, why the challenges to implementation of Floating Offshore Wind Technology (FOWT) and how the technology will diffuse in Sweden is the focus of this research study. Objectives: The purpose and aim of this study is to establish an understanding of diffusion and its drivers and challenges related to FOWT in Sweden and contribute with new knowledge in the field of renewable energy sources. FOWT may facilitate access to new wind resources at deep water conditions, why this study research the challenges to implementation of FOWT and how the technology will diffuse in Sweden. Methodology: The research area is limited to Sweden where main drivers and challenges are identified and framed by literature review of Porter’s Diamond model competitiveness factors and interviewing experts within the Offshore Wind Energy (OWE) industry. The qualitative interview results are applied in the Technology Acceptance Model (TAM) framework, where Innovation Diffusion Technology (IDT) model is used as theoretical framework to build up an understanding of the level of FOWT diffusion in Sweden and how it will diffuse. We use the concept of TAM in combination with IDT to explain how FOWT as a new technology is perceived to be used in the OWE industry with a particular focus on the challenges related to the implementation of FOWT in Sweden. Results: We provide guidance for the OWE industry stakeholders and valuable information of what need to be in focus to resolve challenges for implementation, and the diffusion of FOWT in Sweden. Our general assessment show that the market is positive about the technology. On the other hand, we find that the challenges are multifold and further complicates the implementation phase. Although FOWT has support from climate and environmental impact, the technology has limitations that can negatively affect the Behavioral Intention to Use (BIU). Conclusions: The challenges to implementing FOWT are multifold and concluded to be high risk premium for investors with limited scale effects due to substantiated grids and infrastructure. Collaboration issues between investors and government agencies are obvious, this in terms of inefficient permit processes and general understanding of the impact of the technology for decision-makers within the FOWT value chain. The interview results and IDT analysis direct that FOWT is in the stage of persuasion and will from this stage progress further to the decision and implementation phase of diffusion. Our arguments are based on the identified level of knowledge maturity present among the interviewed stakeholders, and the fact that policy and specialist reports include FOWT when evaluating RET alternatives for new areas. The IDT framework is concluded to be a good tool to further understand what can be done to facilitate diffusion. The study conclude that TAM can be used to identify challenges related to stakeholder perspective and perception also for non-information technology related technologies. Our study suggest that collaborative approach is needed in Sweden to resolve challenges for implementation. Recommendations for future research: The data is collected during a relatively short time period and limited number of interviews are conducted, therefore further studies are needed in the same area to bring more clarity to the FOWT diffusion mechanisms. We identify an opportunity for future research to further focus on the negative aspects of why the Swedish OWE industry perceives these factors as strong obstacles affecting the BIU. In parallel further of interest is to look at FOWT from a larger perspective such as Scandinavia and the understanding if cooperative activities can accelerate FOWT diffusion.

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 paper compares electricity production between the semi-submersible and the spar-buoy floating wind turbine systems under normal, stochastic and extreme wind conditions at Utsira Nord site located on the Norwegian continental shelf in the North Sea. The analysis of complex behavior of the floating wind turbine system and the fluid-structure interaction is performed in aero-servo-hydro-elastic code ASHES. The results indicate a slightly better energy performance of the semi-submersible than the spar in all load cases but one. The pitch and heave degrees of freedom are evaluated as the most relevant for the power output. It is shown that pitch and heave platform motions have smaller displacement in the semi-submersible floater than in the spar under average environmental conditions and at the rated wind speed operating range. The simulation also confirmed that the energy yield is very sensitive to the magnitude of the loads: the spar performed best under mild environmental conditions, while the semi-submersible was better under medium environmental conditions. Small difference in energy yield is attributed to the same baseline blade and external controller properties used for both floaters where generator torque was kept constant to limit the power excursions above the rated power. The method proposed under this paper has demonstrated that a good approximation of the energy performance of the floating wind turbine system can be performed in a fast and effective manner.

The ocean has tremendous potential in terms of energy generation, and wave energy is especially promising. However, wave energy technology is still non-commercial. Along with ambitious renewable energy targets and investments, much is happening within the field and the wave energy converter developers CorPower Ocean intend to have their technology proven in the upcoming years. This study aims at investigating the value of commercial wave energy in an energy system. This is fulfilled by the possibilities of achieving 24/7 Carbon-free Energy with the wave energy technology from CorPower Ocean at the stage of commercialization. An energy system is modeled with wave energy, floating offshore wind energy, lithium-ion battery storage and the Portuguese national grid, supplying Northvolt’s and Galp’s future lithium conversion facility in Portugal. Different system configurations are compared based on three Key Performance Indicators: 24/7 Carbon-free Energy performance, system emission, and cost for the electricity consumer. In addition, a review of available financial support mechanisms for renewable energy technologies and especially wave energy is done to understand how such mechanisms can affect the economic feasibility of the energy system modeled. The wave energy technology from CorPower Ocean shows to have a high power output and 24/7 carbon-free Energy performance in this study. Although a combination of wave and floating offshore wind energy better ensure energy security with generation profiles that peak at different times, the modeling shows that a system with wave energy alone is preferred for supplying the facility with electricity both from an environmental and economic perspective. The economic feasibility of Lithium-ion battery storage in the system is uncertain and to achieve 24/7 Carbon-free Energy supply of the facility a longer duration storage solution is needed. The price for wave energy in this study is higher than for other commercial renewable energy technologies such as solar PV. However, based on the available financial support structures from governments and other stakeholders, wave energy technology has the potential to be competitive as soon as the technology is proven. / Energigenerering från våra hav har stor potential, inte minst från vågkraft. Trots att vågkraftstekniken ännu inte har nått ett kommersiellt stadie händer det mycket inom området i takt med fler ambitiösa miljökrav och investeringar. CorPower Ocean utvecklar vågkraftsteknik och planerar att ha sin teknik bevisad inom några år. Den här studien syftar till att undersöka värdet av kommersiell vågkraft, vilket uppfylls genom möjligheterna till förnybar el 24 timmar om dygnet med CorPower Ocean’s vågenergiomvandlare. Ett energisystem modelleras med vågkraft, flytande vindkraft, litium-jon batterier och det portugisiska elnätet för att försörja Northvolts och Galps planerade anläggning för litiumkonvertering i Portugal. Olika systemkonfigurationer är jämförda utifrån tre parametrar: 24/7 förnybar el prestation, systemutsläpp och elkostnad för konsumenten. I tillägg utförs en studie om vilka finansiella supportmekanismer som finns för hållbar energiteknik och speciellt för utvecklingen av vågkraft. Detta för att få insikt i om vågkraft kan få finansiellt stöd och konkurrera med andra förnybara energitekniker. Studien visar att vågkraftstekniken presenterar bra utifrån de tre parametrarna. Trots att en kombination av våg och flytande vindkraft ger bättre elsäkerhet med alternerande produktionskurvor visar modelleringen att ett system med endast vågkraft är att föredra både från ett ekonomiskt och ett miljöperspektiv. En investering av litium-jon batterier i energisystemet är tveksam och för att uppnå förnybar elförsörjning av anläggningen 24 timmar om dygnet krävs en energilagringsteknik som möjliggör lagring över längre perioder. Priset för vågkraft i studien är högre än för andra kommersiella förnybara energitekniker så som solpaneler. Baserat på det finansiella stöd som finns från myndigheter och andra intressenter så är det möjligt för vågkraften att bli konkurrenskraftig så fort tekniken är bevisad.

Multiline anchors are a novel way to reduce the cost of arrays of floating offshore wind turbines (FOWTs), but their behavior is not yet fully understood. Through metocean characterization and dynamic simulations, this thesis investigates the effects of wind-wave misalignment on multiline anchor systems. Four coastal U.S. sites are characterized in order to develop IEC design load cases (DLCs) and analyze real-world misaligned conditions. Stonewall Bank, Oregon showed the highest 500-year extreme wave height, at 16.6 m, while Virginia Beach, Virginia showed the highest 500-year wind speed, at 56.8 m/s. Misalignment probability distributions, at all sites, are found to converge towards zero (aligned conditions) and become less variable as wind speed increases. This indicates that high misalignment angles are unlikely at high wind speeds. A simulation parameter study, spanning a range of wave directions, misalignment angles, and DLCs, is run in OpenFAST to explore how misalignment affects multiline anchor loading. The simulated anchor is connected to three IEA 15 MW FOWT models via a taut mooring system. The force on the multiline anchor is calculated by summing the three tension vectors from the mooring lines. The mean direction of this force is found to align closely with the wind; each mean is within 5.5° of the wind direction. Higher misalignment angles cause increases to the amount of directional variation about this mean. The magnitude of the multiline force is also examined. Mean force level is found to be nearly unaffected by misalignment. However, maximum force decreases significantly as misalignment angle increases, dropping as much as 23.3% in extreme conditions. This confirms current anchor design practice, which treats aligned metocean conditions as the peak load an anchor experiences. Standard deviation of multiline force also decreases with misalignment. The operational load case, DLC 1.6, shows a slight trend towards this, but the extreme case, SLC, shows a more pronounced drop of 32.4%. This suggests that anchor cyclic loading analyses could benefit from considering misalignment. Doing so could lead to lower estimates of the cyclic loading amplitudes that anchor designs must withstand, thus leading to smaller, cheaper anchors.

Durch Umwandlung unterschiedlichster Formen von Energie in mechanische oder elektrische Energie wird die Menschheit seit Jahrhunderten bei der Umsetzung von Arbeitsprozessen im Alltag und bei der industriellen Nutzung unterstützt. Strömende Medien wie Wasser oder Wind gelten dabei als die ältesten Energielieferanten. Im Rahmen der Dissertation wird das Konzept einer zugspannungsverankerten Plattform für Offshore Windenergieanlagen (WEA) vorgestellt, wobei neben den, für diesen Plattformtyp typischen, vertikalen auch geneigte Verankerungselemente Verwendung finden. Diese Art der Verspannung einer zugspannungsverankerten Plattform, respektive ’Tension Leg Platfrom’ (TLP) ist bisher von keiner Quelle bekannt und stellt ein Alleinstellungsmerkmal dar. Folglich sollen Untersuchungen zum dynamischen Verhalten schwimmender Gründungen für Offshore WEA, im Speziellen zu einer TLP mit vertikalen und geneigten Ankerelementen, im Rahmen dieser Arbeit erstmalig vorgestellt werden. Die Plattform ist ein modular gestaltetes Tragwerk bestehend aus großen Rohren und mit integrierten zylindrischen Auftriebskörpern. Diese erzeugen im Transportzustand der Plattform vom Hafen zum Einsatzort und im Betriebszustand innerhalb eines Windparks den nötigen Auftrieb. Infolge der speziellen Art der Verspannung werden die Bewegungen der TLP durch die, aus den Belastungen resultierenden, Seildehnungen dominiert. Damit stellte die TLP im Vergleich zu anderen schwimmenden Gründungen ein bewegungsarmes System dar. Inhalt der hier vorgelegten Arbeit sind Untersuchungen zum dynamischen Verhalten schwimmender Offshoregründungen, im speziellen einer TLP für Windenergieanlagen. Es wurden unterschiedliche Tragstrukturen für TLP-Systeme entwickelt und im Rahmen von Modellversuchen getestet. Den Kern der Arbeit bildet der Vergleich des dynamischen Tragverhaltens der unterschiedlichen Plattformen unter Berücksichtigung der geometrischen und strukturellen Randbedingungen.

Floating offshore wind power is a relatively new technology that enables wind turbines to float above the sea level, tied by anchors at the seabed. The purpose of this work is to develop an economic model for the technology in order to calculate the total cost of a planned wind farm. Cost data are retrieved from reports and academic journals available online. Based on these data, a model in Microsoft Excel is developed which calculates the Levelized cost of energy (LCOE) for floating wind power plants as a function of several input values. As an addition to this model, financing offshore projects are described using literature study and by doing interviews with three major companies, currently investing in offshore wind. As a result, the model allows the user to calculate Capital expenditures, Operating expenditures and LCOE for projects at any given size and at any given site. The current LCOE for a large floating offshore wind farm is indicated to be in the range of 138-147 £/MWh. The outline from interviews was that today there is no shortage of capital for funding wind projects. However, in order to attract capital, the governmental regulatory of that market has to be suitable since it has a crucial impact on price risks of a project.

Durch Umwandlung unterschiedlichster Formen von Energie in mechanische oder elektrische Energie wird die Menschheit seit Jahrhunderten bei der Umsetzung von Arbeitsprozessen im Alltag und bei der industriellen Nutzung unterstützt. Strömende Medien wie Wasser oder Wind gelten dabei als die ältesten Energielieferanten. Im Rahmen der Dissertation wird das Konzept einer zugspannungsverankerten Plattform für Offshore Windenergieanlagen (WEA) vorgestellt, wobei neben den, für diesen Plattformtyp typischen, vertikalen auch geneigte Verankerungselemente Verwendung finden. Diese Art der Verspannung einer zugspannungsverankerten Plattform, respektive ’Tension Leg Platfrom’ (TLP) ist bisher von keiner Quelle bekannt und stellt ein Alleinstellungsmerkmal dar. Folglich sollen Untersuchungen zum dynamischen Verhalten schwimmender Gründungen für Offshore WEA, im Speziellen zu einer TLP mit vertikalen und geneigten Ankerelementen, im Rahmen dieser Arbeit erstmalig vorgestellt werden. Die Plattform ist ein modular gestaltetes Tragwerk bestehend aus großen Rohren und mit integrierten zylindrischen Auftriebskörpern. Diese erzeugen im Transportzustand der Plattform vom Hafen zum Einsatzort und im Betriebszustand innerhalb eines Windparks den nötigen Auftrieb. Infolge der speziellen Art der Verspannung werden die Bewegungen der TLP durch die, aus den Belastungen resultierenden, Seildehnungen dominiert. Damit stellte die TLP im Vergleich zu anderen schwimmenden Gründungen ein bewegungsarmes System dar. Inhalt der hier vorgelegten Arbeit sind Untersuchungen zum dynamischen Verhalten schwimmender Offshoregründungen, im speziellen einer TLP für Windenergieanlagen. Es wurden unterschiedliche Tragstrukturen für TLP-Systeme entwickelt und im Rahmen von Modellversuchen getestet. Den Kern der Arbeit bildet der Vergleich des dynamischen Tragverhaltens der unterschiedlichen Plattformen unter Berücksichtigung der geometrischen und strukturellen Randbedingungen.

Previous research has displayed that multi-source farms provide an opportunity to reduce the cost of energy and improve the energy output quality. This thesis assesses the cost competitiveness of co-located wind-wave farms, specifically floating offshore wind (FLOW) turbines and CorPower’s wave energy converters (WEC). This research was conducted in collaboration with CorPower, a Swedish WEC developer. A cost model is generated, which calculates the levelized cost of energy (LCOE) utilizing a life-cycle cost analysis. The model is developed by combining CorPower’s existing cost model with an agglomeration of FLOW cost models from previous studies. An in depth literature research informs about synergies, which are translated into shared costs within the model. The cost model is applied to a site on the Northern coast of Portugal; the location of a FLOW farm project under development. Including wave energy, improves the annual energy production of the farm by up to 10%. However, the effects on power smoothing are negligible, due to the high seasonal variability of the wave resource and the minimal complementarity of the two energy sources. The LCOE of a 1GW 50% wind - 50% wave farm is 63€/MWh. The high initial investment costs of the wind farm results in the standalone wind LCOE of 73€/MWh. The strong capacity factor of the WECs cause the LCOE to reduce to 55€/MWh, when evaluating a standalone wave farm. In all co-location configurations, savings for FLOW and wave farm developers are exhibited. The highest savings are identified for small wind/wave arrays co-located in large farms. This results in an LCOE reduction of up to 4.5% for both wind and wave farm developers. The largest relative savings are found in the DEVEX costs and the electrical transmission installation costs. The identified cost calculations and savings are inline with previous studies. The savings are in the lower range compared to other studies, due to the conservative estimations of the degree of shared costs. The cost model provides a tool, that can be continuously updated with the most recent findings of cost inputs and wind-wave synergies, i.e. shared cost opportunities. This thesis’ results reflect how co-locating wind and wave farms can improve the cost-competitiveness of both technologies. Nevertheless, more in depth research is required to comprehend the full potential of co-located wind-wave farms. There is a necessity of collaboration between wind and wave industry members to ensure that the synergies and shared cost-opportunities identified, are fully exploited. / Tidigare forskning har visat att parker med flera källor ger möjlighet att minska energikostnaderna och förbättra energiproduktionens kvalitet. I den här avhandlingen utvärderas kostnadskonkurrenskraften hos samlokaliserade vind- och vågkraftsparker, särskilt flytande havsbaserade vindkraftverk (FLOW) och CorPowers vågenergiomvandlare (WEC). Denna forskning genomfördes i samarbete med CorPower, en svensk WEC-utvecklare. En kostnadsmodell genereras, som beräknar den nivellerade energikostnaden (LCOE) med hjälp av en livscykelkostnadsanalys. Modellen är utvecklad genom att kombinera CorPowers befintliga kostnadsmodell med en agglomeration av FLOW-kostnadsmodeller från tidigare studier. En djupgående litteraturstudie ger information om synergier, som översätts till delade kostnader i modellen. Kostnadsmodellen tillämpas på en plats på Portugals norra kust, där ett FLOW-anläggningsprojekt är under utveckling. Genom att inkludera vågenergi förbättras parkens årliga energiproduktion med upp till 10%. Effekterna på effektutjämningen är dock försumbara, på grund av vågresursens stora säsongsvariationer och de två energikällornas minimala komplementaritet. LCOE för en 1GW 50% vind - 50% vågkraftspark är 63€/MWh. De höga initiala investeringskostnaderna för vindkraftsparken resulterar i en LCOE för fristående vindkraft på 73 €/MWh. Den starka kapacitetsfaktorn för WECs gör att LCOE minskar till 55€/MWh, vid utvärdering av en fristående vågkraftspark. I alla samlokaliseringskonfigurationer uppvisas besparingar för FLOW och vågparksutvecklare. De största besparingarna identifieras för små vind-/vågkraftsparker som samlokaliseras i stora parker. Detta resulterar i en minskning av LCOE med upp till 4,5% för både vind- och vågparksutvecklare. De största relativa besparingarna finns i DEVEX-kostnaderna och installationskostnaderna för elektrisk överföring. De identifierade kostnadsberäkningarna och besparingarna är i linje med tidigare studier. Besparingarna ligger i det lägre intervallet jämfört med andra studier, på grund av de konservativa uppskattningarna av graden av delade kostnader. Kostnadsmodellen är ett verktyg som kontinuerligt kan uppdateras med de senaste rönen om kostnadsingångar och synergier mellan vind och våg, dvs. möjligheter till delade kostnader. Resultaten i denna avhandling visar hur samlokalisering av vind- och vågkraftsparker kan förbättra kostnadskonkurrenskraften för båda teknikerna. Det krävs dock mer djupgående forskning för att förstå den fulla potentialen hossamlokaliserade vind- och vågparker. Det finns ett behov av samarbete mellanvind- och vågkraftsindustrin för att säkerställa att de identifierade synergierna ochgemensamma kostnadsmöjligheterna utnyttjas fullt ut.