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Sun, Xiao-Qian (Zhong Neng Power-tech Development Co. Ltd.) | Cao, Shu-Gang (Zhong Neng Power-tech Development Co. Ltd.) | Chi, Yan (Zhong Neng Power-tech Development Co. Ltd.) | Zhu, Zhi-Cheng (Zhong Neng Power-tech Development Co. Ltd.)
This study investigated a vibration and tilt monitoring system for an offshore wind turbine constructed using a high-rise-pile- cap supporting foundation, which is the first offshore wind power project in South China with a batholith seabed. The analysis of data collected by the system during the 2016 typhoon Meranti showed that the typhoon significantly affected vibration and instantaneous tilt of the supporting system without any significant change to the first natural frequency. Additionally, it did not produce any permanent inclination, indicating that no serious structural failure occurred under the influence of the typhoon. However, during the typhoon, the vibration acceleration, vibration intensity, and the effective inclination of the high-rise-pile-cap supporting system using rock-socketed piles were smaller than those with driven frictional piles, indicating that the former is better than the latter in terms of resistance to vibration and tilt.
The construction of offshore wind power plants in China faces many challenges, including the raging typhoons in the East and South Seas. Each year, the Guangdong province experiences typhoons three times on average, accounting for 33% of the annual typhoons in China’s coastal areas. The proportions of typhoon episodes in Taiwan, the Hainan province, the Fujian province, and the Zhejiang province are 19%, 17%, 16%, and 10%, respectively (Wu and Li, 2012). The extreme vibration and abnormal inclination of the offshore wind turbine supporting system as a result of typhoons sometimes lead to structural failures and can even result in the collapse of the wind turbine structure into the ocean.
The development of new technologies for clean, reliable renewable energy is a key challenge for modern society. Tidal energy is an important renewable energy source with significant advantages over competing sources, including predictability and repeatability (Uihlein and Magagna, 2016). This paper is concerned with establishing the optimum operating performance of a range of novel vertical axis tidal turbines for micro-hydro power through analytical modelling. The development of wind turbine technology is significantly more progressed in this area, leading to potential technology transfer opportunities for tidal turbine developers. Roberts et al. (2016) have recently assessed a number of state-of-the-art tidal turbines and identified key challenges faced by these emerging technologies.
Wind turbine towers are being planned in ice covered regions subject to pressure ridges (e.g. the Great Lakes). Conical collars are often employed to reduce ice loads from level ice and their associated dynamics. For level ice, downward breaking cones have some advantages. It is not clear if this is the case for pressure ridges. This paper presents an improved method for ridge loads on wind turbines with downward breaking cones and makes comparisons with upward breaking cones.
First year pressure ridges can be formidable ice features and usually control design ice loads in the sub-Arctic. Important components of a ridge creating ice loads are the consolidated layer at the surface (which is considered as solid ice) and the ridge keel below consisting of ice rubble, but much thicker. The load due to the consolidated layer is usually derived as if it is thick level ice. On a cone, methods for level ice assume it can be idealized as a plate on an elastic foundation (the water) and equations have been developed for upward and downward breaking cones. But for a ridge on a downward cone, to break the consolidated layer downwards requires it to be pushed into the keel rubble below. This will have a different foundation modulus than water buoyancy. A method is developed to account for this difference. The method uses an iterative approach to determine the point of breaking of the consolidated layer (and associated load) accounting for the ridge geometry, keel rubble shear strength, the flexural strength of the consolidated layer and the buoyancy forces. The keel loads on the vertical shaft below the conical collar are based on the method currently in ISO 19906 (2010) but modified to add the effect of additional rubble in the keel from breaking the consolidated layer downwards.
In examples, it is shown that the breaking force can be about twice that of breaking the consolidated layer without the keel present. This might be seen as a disadvantage for downward breaking cones vs upward breaking. However, it is also shown that the clearing forces on an upward cone are higher; which tends to balance out the lower breaking force. Example loads are given on typical wind turbine bases due to typical ridges. Upward and downward breaking configurations are compared.
The paper provides new methods for ice loads due to ridges acting on wind turbine structures not currently covered by existing methods.
Wind turbine, an efficient way to sustainably generate electricity, of which the noise problem would affect the living environment adversely. This paper presents the results of the aerodynamic and aero-acoustic calculation of a vertical axis wind turbine. The IDDES technique and FW-H acoustic analogy are adopted to conduct all simulations. The results indicate that the combination of thickness and loading noise are the dominant noise sources at tonal peak frequency, and quadrupole noise has negligible influence. Rotational speed and receiver distance will significantly affect noise level. This work can be exploited to design quieter vertical axis wind turbines.
In recent years, the demands of renewable energy have attracted more public attention. As a clean and sustainable renewable energy, offshore wind energy has been utilized by wind turbines to generate electricity. However, one offensive problem, noise pollution, would affect the living environment of nearby creatures. Especially in several offshore wind turbine farms, birds and other animals, have left for new habitats. Therefore, it is an important issue to simulate and evaluate wind turbine noise.
According to the direction of rotation, wind turbines can be divided into two major categories: horizontal axis wind turbines (HAWT) and vertical axis wind turbines (VAWT) (Borg, Collu and Brennan, 2012). Since the wind turbines require further performance optimization to be competitive with other energy devices, the geometrical design, aerodynamic performance and optimal solutions are continuing to be investigated. Bae et al. (Y.H. Bae, M.H. Kim and H.C. Kim, 2017) studied a floating offshore wind turbine with broken mooring line. The power production and structural fatigue life were checked respectively, and some risk assessments were conducted. Rezaeiha et al. (Rezaeiha, Kalkman and Blocken, 2017) conducted researches on the effects of pitch angle on power performance and aerodynamics of a vertical axis wind turbine. A 6.6% increase in power coefficient could be achieved using a pitch angle of 2 degree at a tip speed ratio of 4 was shown in the results. MirHassani and Yarahmadi( MirHassani and Yarahmadi, 2017) investigated the wind farm layout optimization under uncertainty. A mixed integer quadratic optimization model is developed based on the interaction matrix for multi-turbine wake effects considering different hub height wind turbines. Compared to the conventional HAWTs, the VAWTs show many superiorities, including universal wind exposure, relatively simple blade structure, lower maintenance costs and lesser aerodynamic noise (Tjiu, Marnoto, Mat, Ruslan and Sopian, 2015).Although the noise generated by VAWT is lesser than that caused by HAWT, VAWT's noise is not negligible. Noise generated by operating wind turbines can be divided into mechanical noise and aerodynamic noise. Mechanical noise is generated by different machinery parts. Aerodynamic noise is produced from the moving blades and is mainly associated with the interaction of turbulence with the blade surface (Ghasemian, Ashrafi, and Sedaghat, 2017). Mechanical noise can be decreased by some engineering methods, while the reduction of aerodynamic noise is still a problem.
The next large scale exploitation of wind energy will gradually move to the seas with the depth of 30-100m, in which only the semi- submersible and barge type foundation are suitable. Compared with the semi-submersible foundation, the barge type has simpler structure and is more adaptable to water depth, however, suffers larger seakeeping motions in waves. In order to improve the seakeeping performance of the barge foundation for offshore wind turbines, the present work proposes a concept of Air-cushion Supported Floating Platform (ASFP), and integrates the air cushion into barge foundations, which can buffer the wave loads acting on the foundation and reduce the motions. The air cushion makes the new floating foundation very different, and this paper presents a method to estimate the initial stability of the air- cushioned floating offshore wind turbine foundation
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The next generation of wind energy exploitation in China will move to the seas with the depth of 30-100m. Generally, the fixed offshore wind turbine is used in shallow water, and the cost increases very quickly with the increase of water depth. It is considered that the fixed one is not suitable for the water of depth more than 30m (Zhou, 2013), in which the floating one should be considered. Besides, the floating one could be built and assembled in shipyard, which is very useful to reduce the cost. So the floating offshore wind turbine should be used when the water depth is within 30-100m.
Some types of platforms have been employed for floating offshore wind turbines (Ewea, et al, 2013), which can mainly be classified into four types (Wang, et al, 2010): Spar-buoy type, Tension-leg platform (TLP) type, Semi-submersible type and Pontoon type (Barge type). The Spar-buoy type needs a long body to lower the center of gravity and the required water depth should be more than 100m. The TLP type needs a certain water depth to adapt the tidal range and the required water depth should be more than 70m. So only the Semi-submersible and Barge type platforms are suitable for the seas with depth of 30-100m. Compared with the Semi-submersible platforms, the Barge type is more adaptable to water depth, and the simpler structure makes it possible to be built by concrete, which can reduce the cost and overcome the seawater corrosion effectively. But it suffers larger seakeeping motions in waves. So if the motion response of Barge type platforms in waves can be reduced, it will be very desirable to be used in the seas with depth of 30-100m.
Based on the CFD-CSD (Computational Fluid Dynamics-Computational Structure Dynamics) coupled model, the antiliquefaction effect of stone layers on liquefiable seabed is studied. Under the extreme waves, the dynamic response of the seabed around the wind turbine in the Xiangshui area of Jiangsu Province was simulated. By comparing the seabed response results of four tests with cover stones under the same wave conditions, it shows that the thickness and porosity of the cover stones are two important parameters of anti-liquefaction capacity.
The stability of composite bucket foundation of offshore wind turbine under wave action is very important for the development of offshore wind power technology (Zhang et al., 2016). Under the action of wave, the seabed liquefaction occurs due to periodic changes in pore water pressure and effective stress in the seabed. It is of great scientific significance and great engineering value to study the liquefaction and anti-liquefaction measures of the seabed soil under the action of waves for the stability of the offshore wind turbines, especially for the steady development of the offshore wind power foundation.
Based on the analytical method, experimental study and numerical simulation, the study of liquefaction and stability of seabed under wave action is mainly concentrated on three aspects: (1) the pore water pressure in the time and space, the effective stress state and shear strength in the seabed are analyzed (Hsu and Jeng, 1994; Jeng, 1997; Jeng, 2013; Ye et al., 2018); (2) the wave- structure-seabed interaction is investigated (Sumer, 2014; Ye et al., 2015; Zhang et al., 2016; Sui et al., 2017); (3) in order to accurately analyze the liquefaction of seabed, a series of seabed liquefaction standards have been put forward (Ye, 2012), and a series of anti-liquefaction methods have been studied (Yang et al., 2004; Susana and Rafeal, 2006; Sumer et al., 2010; Zhang et al., 2014; Huang et al., 2015).
Currently, the development of renewable energy has become a trend with the increasing demand for energy. Wind energy, as a renewable source of energy, is also getting more attention. Increasing effort is devoted to developing floating offshore wind turbines in deep water. In this paper, a V-shaped semisubmersible floating wind turbine was adopted to investigate the dynamic response of the system. Numerical simulations are conducted using aero-hydro coupled analysis in a time domain. The performance of the V-shaped semisubmersible floating wind turbine with respect to global platform motion, mooring line tensions and tower base moment is evaluated in this study. It turns out that the V-shaped semisubmersible offshore wind turbine is a promising concept that provides a good practice for the application of wind energy in deep water in the future.
Currently, due to energy deficiency, many countries are devoted to developing renewable energy to meet energy demands. According to the Chinese 13th renewable energy development five year plan, by 2020, total electric from renewable energy will grow to up to 27% of the total electricity generated(NDRC, 2017). Wind energy, one of the promising renewable energies, has attracted more and more attention because of its low environmental pollution. Compared with onshore wind energy, offshore wind energy has better wind condition, unlimited sites and negligible environmental impact. Especially in China, the area with rich onshore wind resource is far from the energy consumption center, which is located near the eastern coastline (Li et al., 2012). A number of studies have been carried out for offshore wind turbine analysis (Jiang et al., 2015; Shi et al., 2016; Shi et al., 2014). The bottom-fixed wind turbine is not suitable for deep water due to increase in cost (Shi, 2015). Therefore, the floating offshore wind turbine (FOWT) is becoming one of the promising solutions.
According to the offshore oil and gas industry, several different foundations are suitable for FOWT: spar buoy, tension leg platform (TLP), semi-submersible platform and barge. In particular, the semisubmersible platform, compared with spar buoy and TLP, has more feasibility in various water depth, seabed conditions and low installation costs due to the simpler installation (it is fully constructed onshore). The semi-submersible platform can also avoid the main energy range of the waves because of its relatively large natural period. The OC4 semi-submersible offshore wind turbine was simulated by Bayati (2014) to focus on the impact of second-order hydrodynamics on semi-submersible platforms. Moreover, the second-order hydrodynamic force can stimulate the oscillation of the platform and further cause fatigue damage to the structure. How the mooring systems influence the motion of the FOWT (Masciola and Robertson, 2013) determined by using coupled and uncoupled model on DeepCwind semi-submersible FOWT. Luan et al. (2016) employed a braceless semi-submersible platform to establish a numerical model and performed extreme sea states analysis on a braceless semi-submersible platform. The results showed that the platform has good stability under extreme sea and is a good design concept. A 5 WM wind turbine was employed by Kim et al. (2017), and WindFloat and OC4 floating platform were carried out to focus on the motion of FOWT and evaluating the mooring system force by using FAST (Jonkman, 2005) code.
This paper presents the application of a risk- and reliability-based inspection planning framework for the InnWind 20 MW reference wind turbine jacket substructure. A detailed fracture mechanics-based fatigue crack growth model is developed and used as a basis to derive optimal inspection plans for the jacket substructure. Inspection plans for different inspection techniques are proposed, and recommendations on how to optimize inspection intervals are discussed.
Upscaling current wind turbines to very large wind turbines is considered as one of the important ways to decrease the levelized cost of energy (LCoE) of wind energy. Steel jacket structures are one possible type of support structure for very large offshore wind turbines and have been considered in the EU InnWind project, INNWIND.EU (http://www.innwind.eu). Reliability with respect to fatigue failure is generally driving the design of offshore wind turbine jacket structures and is being considered in this paper in combination with applications of reliability-based inspection planning.
Haji, Maha N. (Massachusetts Institute of Technology) | Kluger, Jocelyn M. (Massachusetts Institute of Technology) | Carrus, Justin W. (Massachusetts Institute of Technology) | Sapsis, Themistoklis P. (Massachusetts Institute of Technology) | Slocum, Alexander H. (Massachusetts Institute of Technology)
With conventional sources of uranium forecasted to be depleted within a century, developing methods to cost-effectively harvest uranium from seawater, which is estimated to contain 1,000 times more uranium than land does, is crucial to the continued viability of nuclear power generation. Studies have shown that coupling a uranium harvester system with an existing offshore structure, such as a floating wind turbine (FWT), could greatly reduce the cost of harvesting uranium from seawater as it eliminates the need for dedicated moorings and increases the overall energy-gathering ability of the offshore wind farm. This paper explores the hydrodynamic effects of adding a uranium harvester to an offshore FWT. The experimentally determined hydrodynamic responses of two designs of a symbiotic machine for ocean uranium extraction (SMORE) are compared with that of an unmodified FWT. Both SMORE designs utilize adsorbent filament that is enclosed in a hard permeable shell to decouple the mechanical and chemical requirements of the device. It was found that neither SMORE design significantly shifted the resonant peaks of the FWT.