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Floating offshore wind (FOW) holds the key to 80 % of the total offshore wind resources, located in waters of 60 m and deeper in European seas, where traditional bottom-fixed offshore wind (BFOW) is not economically attractive.
Many problems affecting floating offshore wind turbines (FOWT) were quickly overcome based on previous experience with floating oil rigs and bottom-fixed offshore wind. However, this technology is still young and there are still many challenges to overcome.
This paper shows that electrical failures are amongst the most significant errors of FOWT. The most common cause was corrosion. It is also stated that the control system is most often affected, and that the Generator is frequently involved. Material corrosion is also the key factor when it comes to the most common overall reason for failures.
A particular attention must be paid to mooring line fracture. Mooring lines are especially vulnerable to extreme sea conditions and the resulting fatigue, corrosion, impact damage, and further risks.
It must be stated that the primary challenge is that of economics. Over time technological costs will decline making FOW more competitive and hence attractive for greater depth.
Originally this article was supposed to be a comparison between the technological differences of bottom-fixed offshore wind turbines (BOWT) and floating offshore wind turbines (FOWT). However, several authors already contributed to this topic and came to the conclusion that the higher levelized costs of energy (LCOE) prevent FOWTs from successfully entering the energy market. Multiple sources seem to agree on this conclusion but often do not provide the reader with further information regarding the LCOE. This is the reason why this article understands itself as an in depth cost comparison between BOWTs and FOWTs. For this purpose, individual LCOE are calculated for the upcoming FOWT technologies such as spar-buoy (SPAR), tension-leg platform (TLP) and semi-submersible platform (semi-sub) as well as conventional BOWTs using the wind turbines hours of full utilization (HOFU). The resulting functions are visualized graphically in order to determine break-even points between BOWTs and FOWTs. Finally, a sensitivity analysis is carried out to determine the influence of the weighted average costs of capital (WACC).
With floating offshore wind turbines, new sources of wind energy can be used, which cannot be tapped into by bottom-fixed wind turbine systems. However, due to their design, they experience additional motion caused by wind and wave loads. The motions that are induced into the system have an oscillating course. This affects the aerodynamic properties of the wind turbine and leads to changes in the thrust force and power output of floating wind turbines compared to bottom-fixed wind turbines. Furthermore, the motions lead to an earlier breakdown of the helical wake structure behind the wind turbine and moreover lead to a decreased reliability of the rotor blades. Differences in the effects of wind and wave loads on the aerodynamic performance of floating offshore wind turbines supported by different platform systems were found.
A numerical analysis of laser resonators with aberrations is presented. {T}he analysis shows that aberrations lead to large diffraction losses of laser resonators which are laid out to produce diffraction-limited beam quality. {S}tatic or dynamic compensation of the aberrations is possible and would yield much higher output power.
Die Studie untersucht den didaktischen Mehrwert partizipativer Medien in der hochschulischen Lehrerbildung. Die hier entwickelten Gestaltungsgrundsätze für die Planung von Lernarrangements mit Social Media sollen dazu beitragen, die Besonderheiten dieser Medien in die didaktische Konzeption einzubinden. Auf diese Weise soll ein Beitrag dazu geleistet werden, den didaktischen Mehrwert von Social Media in Lernarrangements zu entfalten.
Adaptive laser resonators with deformable MOEMS mirrors under closed-loop control are discussed and experimental results are presented. The requirements for deformable mirrors and for closed-loop control systems of these mirrors are analyzed. Several deformable mirrors have been characterized and the results are presented. Currently available membrane mirrors deform under laser load and need further development before they can be used for aberration correction of solid state lasers above some tens of Watts. Nevertheless, the results are encouraging and the requirements are within reach of currently available technology. Finally, we demonstrate an Nd.YVO4-laser with a closed-loop adaptive resonator and more than 6 W of output power. The closed-loop system was able to compensate artificially introduced aberrations from a phase plate.
In order to avoid optical damage and non-linear effects, high-power, high-energy lasers of the petawatt class like PHELIX (petawatt high-energy laser for heavy-ion experiments) use large-aperture optics. Usually, chromatic aberration associated with these optical elements is neglected. By means of numerical simulations, we show how the chromatic aberration affects the focal intensity pattern. In particular, we make quantitative predictions of how chromatic aberration decreases the focused peak intensity. Furthermore, we prove the feasibility of a new interferometer that measures the temporal pulse front distortions which arise from expansion telescopes. We also propose a scheme that pre-compensates these distortions.