[Truncated abstract] The demand for offshore wind turbines is increasing in densely populated areas, such as Europe. These constructions are typically founded on a gravity foundation or a large 'mono pile'. Gravity foundations can only be used at locations where strong soils exist and water depths are limited. Costs associated with a 'mono pile' type foundation contribute to a very large percentage of the total investment costs. This research, therefore, focuses upon a different foundation for offshore wind turbines, namely suction caissons beneath a tripod. This foundation can be used in all kinds of soil types and is cheaper than the 'mono pile' foundation, both in the amount of steel used and installation costs. Cheaper foundations can contribute to a more competitive price for offshore wind energy in comparison with other energy resources. To date, there have been relatively few studies to investigate the behaviour of this type of foundation during the installation process and during operational and ultimate loading for seabed conditions comprising dense sand. Two types of investigations were performed during this research to determine the behaviour of suction caissons beneath a tripod. Firstly, an existing computer program was extended to predict the typical loading conditions for a tripod foundation. Secondly, centrifuge tests on small scale suction caissons were performed to investigate the behaviour during the installation and loading phases. The computer program developed helped to quantify the likely ranges of environmental loading on an offshore wind turbine. For a typical 3 MW wind turbine of 90 m height, the vertical load is low at around 7 MN. During storm conditions the horizontal hydrodynamic load can be in the order of 4 MN. During normal working conditions the horizontal aerodynamic loads can reach 0.4 MN, but can increase to 1.2 MN when the pitch system malfunctions and gusts reach 30 m/s. This aerodynamic load will result in a very large contribution to the overturning moment, due to the high action point of this load. When the wind turbine is placed on top of a tripod, these large moments are counteracted by a push-pull system. ... The development of differential pressure was found to depend on the soil permeability, the extraction speed and a consolidation effect. During cyclic loading no obvious signs of a decrease in resistance were observed. During very fast cyclic loading differential pressures developed, which could increase the drained frictional resistance by approximately 40%. All centrifuge tests results were used to develop methods to predict or back calculate the installation process of suction caissons in sand and layered soil, and the behaviour during tensile and cyclic loading. These methods all use the cone resistance as the main input parameter and predict the force (or required suction) as a function of time, for a given rate of pumping or uplift displacement, in addition to the variation of suction with penetration (or force with uplift displacement). These new methods provide a useful tool in designing a reliable foundation for offshore wind turbines consisting of a tripod arrangement of suction caissons embedded in dense sand.

A comparison between a traditional fixed high voltage direct current energy transmission system and a mobile transmission system utilizing vanadium redox flow batteries has been conducted in this degree work.  The purpose of this comparison was to evaluate if a mobile energy transmission system could be competitive in terms of energy efficiency and cost-effectiveness for use in offshore wind power applications. A literary study was made to fully grasp the various technologies and to create empirical ground of which cost estimation methods and energy calculations could be derived. A specific scenario was designed to compare the two transmission systems with the same conditions. To perform the comparison, a model was designed and simulated in MATLAB. The results from the model showed that the flow battery system fell behind in energy efficiency with a total energy loss of 33.3 % compared to the 11.7 % of the traditional system, future efficiency estimations landed it at a more competitive 17.5 %. The techno-economic results proved that a mobile flow battery system would be up to nine times more expensive in comparison to a traditional transmission system, with the best-case scenario resulting in it being roughly two times more expensive. The main cause of this was found out to be the expensive energy subsystem, specifically the electrolyte, used in the flow battery system. Several environmental risks arise when using a flow battery system with this electrolyte as well which could harm marine life severely. In conclusion; with further development and cost reductions, a case could be made for the advantages of a truly mobile energy transmission system. Specifically, in terms of the pure flexibility and mobility of the system, allowing it to circumvent certain complications. The mobility of the system gives the possibility of selling energy where the spot prices are at their highest, providing a higher revenue potential compared to a traditional fixed system. As for now though, it is simply too expensive to be a viable solution.

Made available in DSpace on 2014-12-17T13:53:37Z (GMT). No. of bitstreams: 1 JoaoPCM_DISSERT.pdf: 2393754 bytes, checksum: f95d47c17e14c0db5625ca5a0ae4656d (MD5) Previous issue date: 2014-01-21 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Offshore wind power emits low amounts of gases, is renewable and has better performance than onshore due to its greater stability and higher wind power density, less visual and noise impact, among others. Brazil has a high capacity of generation, but has not yet developed any offshore projects. High costs are a strong impediment. This study is an effort towards pricing offshore resources through Livelized Cost of Energy - LCOE, which represents the minimum return to cover the costs of development, production and maintenance of a wind project. Initially LCOE was calculated for all Brazilian onshore wind farms listed at Bloomberg New Energy Finance R?, accounting for 71 farms. Then hypothetical offshore wind farms were created from the onshore farms, tripling the cost of generation, which is consistent with the literature, and estimating the offshore energy for two locations off the Brazilian coast using satellite data extracted from National Oceanic and Atmospheric Administration. The results demonstrate that offshore resources have the potential to significantly reduce the energy price due to the better performance of the wind at sea / A fonte de energia e?lica offshore emite baixas quantidades de gases causadores do efeito estufa, ? renov?vel e apresenta melhor desempenho do que a fonte onshore em quesitos como maior estabilidade e densidade de pot?ncia dos ventos, menor impacto visual e sonoro, dentre outros. O Brasil possui uma capacidade de gera??o offshore substancialmente elevada, mas ainda n?o desenvolveu nenhum projeto nessa modalidade. Os custos elevados s?o um forte empecilho. Esse estudo ? um esfor?o em dire??o ? explora??o desse campo, precificando a fonte offshore atrav?s do Livelized Cost of Energy LCOE, que representa o retorno m?nimo para cobrir os custos de desenvolvimento, produ??o e manuten??o de um projeto e?lico. O LCOE foi primeiramente calculado para todos os parques e?licos onshore brasileiros listados no Bloomberg New Energy Finance R?, contabilizando 71 parques. Em seguida foram criados parques e?licos offshore hipot?ticos a partir dos parques onshore, triplicando os custos de gera??o, o que est? em conformidade com a literatura especializada, e estimando-se a energia offshore para dois pontos da costa brasileira atrav?s de dados de sat?lite extra?dos do National Oceanic and Atmospheric Administration. Os resultados demonstram que a fonte offshore tem o potencial de reduzir significativamente o pre?o da energia devido ? melhor performance do vento no mar

Reef habitats built by the tubiculous polychaete Sabellaria spinulosa have been identified as a habitat with significant conservation importance, based on their historic decline across Europe and the assumption that, like many other biogenic reef systems, S. spinulosa reefs enhance biodiversity. Despite the high conservation status of this habitat very little work has been undertaken to explore the role that S. spinulosa reefs play in marine ecosystems, or their sensitivity to anthropogenic disturbance. Observations of the reproductive ecology and population dynamics of the reef building organism indicate that S. spinulosa exhibit life-history traits typically associated with r-strategists, indicating that this species is likely to have the ability to recover quickly following most anthropogenic disturbance events. A series of surveys on S. spinulosa reefs identified at the Thanet Offshore Wind Farm site, where the extent of the reef habitat was found to have increased between the pre-construction and post construction survey despite extensive cable laying and turbine installation, corroborates these findings. Detailed investigations into the macrofauna associated with S. spinulosa reefs in the eastern English Channel revealed that S. spinulosa reefs support macrofaunal communities that are comparable to those associated with adjacent muddy sandy gravel and gravelly muddy sand in terms of species composition, taxonomic breadth and beta-diversity. A consistent enhancement in species richness, abundance and biomass was identified in samples collected from S. spinulosa reefs when compared with adjacent sedimentary deposits, as well as a corresponding reduction in the equitability of species, indicating that some macrofauna are able to exist in higher densities within this habitat. The increase in macrofaunal biomass associated with S. spinulosa reefs was found to influence the diet of demersal fish species, with some species feeding on the reef organism itself while others feed on species found in high densities on the reefs. The high abundance of juvenile flatfish associated with this habitat also suggests that S. spinulosa reefs may provide an important nursery habitat.

This master thesis deals with study of properties pick-up generators for wind power. First part of thesis studies wind turbines, its structure, generators and describes advantages and disadvantages of ashore and offshore location. The next part presents description of parts of sliding contact. The main part assesses the impact of sea environment on sliding contact in generators at offshore wind turbines.

No description available.

Offshore wind is rapidly growing and optimised grid connections are crucial for its success. Generally, costs and losses are higher for HVDC at short distances due to the converters, while HVAC costs and losses increase more rapidly with distance due to the ac cables. Hence, there is a breaking point over which HVDC becomes beneficial, which is important knowledge for grid connection design. Recent research and practice indicate increasing distances for the breaking point, enabled by the introduction of offshore reactive compensation substations (RCS) for HVAC. In the study, steady-state models of HVAC and modular-multilevel converter (MMC) based VSC HVDC systems up to 260 km have been simulated in the Matlab/Simulink based program EeFarm-II. For base case assumptions, the average loss breaking point is 80 km and the levelised cost breaking point is 229 km. The resulting breaking point with respect to levelised cost of energy (LCOE) is 205 km and with respect to net present value (NPV) 186 km, agreeing with the trend of increasing breaking points. Given the range of distances in literature, it is of interest to also investigate how the breaking point depends on assumptions on technical, practical and economic parameters. For the NPV breaking point: lifetime and interest rate have no impact, availability and cost of RCSs have low impact, electricity price has moderate impact, operation and maintenance (O&M) cost has high impact while investment cost and lead time have very high impact. This could be taken into consideration in offshore projects and in future research.

Offshore wind turbines have the potential to be an important part of the United States' energy production profile in the coming years. In order to accomplish this wind integration, offshore wind turbines need to be made more reliable and cost efficient to be competitive with other sources of energy. To capitalize on high speed and high quality winds over deep water, floating platforms for offshore wind turbines have been developed, but they suffer from greatly increased loading. One method to reduce loads in offshore wind turbines is the application of structural control techniques usually used in skyscrapers and bridges. Tuned mass dampers are one structural control system that have been used to reduce loads in simulations of offshore wind turbines. This thesis adds to the state of the art of offshore wind energy by developing a set of optimum passive tuned mass dampers for four offshore wind turbine platforms and by quantifying the effects of actuator dynamics on an active tuned mass damper design. The set of optimum tuned mass dampers are developed by creating a limited degree-of-freedom model for each of the four offshore wind platforms. These models are then integrated into an optimization function utilizing a genetic algorithm to find a globally optimum design for the tuned mass damper. The tuned mass damper parameters determined by the optimization are integrated into a series of wind turbine design code simulations using FAST. From these simulations, tower fatigue damage reductions of between 5 and 20% are achieved for the various TMD configurations. A previous study developed a set of active tuned mass damper controllers for an offshore wind turbine mounted on a barge. The design of the controller used an ideal actuator in which the commanded force equaled the applied force with no time lag. This thesis develops an actuator model and conducts a frequency analysis on a limited degree-of-freedom model of the barge including this actuator model. Simulations of the barge with the active controller and the actuator model are conducted with FAST, and the results are compared with the ideal actuator case. The realistic actuator model causes the active mass damper power requirements to increase drastically, by as much as 1000%, which confirms the importance of considering an actuator model in controller design.

Recent events regarding energy policies throughout the globe and advances in technology are making offshore wind farms become a reality. Most offshore wind farms are still, however, built close to land masses, and need to be rigidly attached to the seabed in one way or another. In many countries, both public and private entities are developing new concepts of floating platforms to overcome the thirty to thirty-five-metre depth limit. Some of these new platforms use and adapt previous Oil and Gas platform concepts, while others are built up from scratch. This Master Thesis covers a hydrodynamic and structural analysis of a new concrete floating platform concept developed for medium to deep waters. This work is based on data from experimental model-scale tests performed in a wave tank and from numerical models using linear potential theory, limited here only to regular wave trains. The study focused on the behavior of the heave plates attached to the platform: test data was analyzed in order to find indicators of the largest dynamic pressures on the plates when only motion data was available, and the structural behavior of the plates was studied under different static pressure distributions using a commercial Finite Element Method software. The results from these analyses show that the normal accelerations of the plates -assumed rigid- strongly correlate with the dynamic pressures measured; and that the general structural behavior of the plate, in terms of deformations and bending moments, is well captured when the hydrodynamic load distribution is simplified into a uniformly distributed load of the same magnitude. The results obtained will help reduce the computational effort currently needed in the design of these floating structures, especially at some stages, when numerous scenarios, load cases and combinations need to be studied.

No description available.