Müller, Nathalie (Fraunhofer-Institut für Windenergie und Energiesystemtechnik (IWES)) | Kraemer, Peter (University of Siegen) | Leduc, Dominique (Research Institute of Civil Engineering and Mechanics (GeM)) | Schoefs, Franck (Research Institute of Civil Engineering and Mechanics (GeM))
A fatigue test has been conducted on a large-scale offshore wind turbine grouted connection specimen at the Leibniz University of Hannover. For detecting damages in the grouted joint, a structural health monitoring (SHM) system based on fiber optic sensor-type fiber Bragg grating (FBG) has been implemented. By extracting the features of the FBG signal responses using the Wigner–Ville distribution (WVD) and one of its marginal properties, the energy spectral density (ESD), it is possible to detect the occurrence and the global severity of the damage. Some information about the local severity of the damage has also been obtained.
The grouted connection consists of the high-performance grout-filled space between the two structural steel components of respectively the sleeve and the pile of offshore wind turbines (OWTs). For monopile OWTs, it is located around the water level between the transition piece and the pile, whereas for jacket and tripod OWTs, it is located just above the seabed, between substructure and foundation pile. While grouted joints for monopiles are exposed to bending moments, grouted joints for latticed substructures (tripods and jackets) are exposed to predominant axial loadings and low torsional moments (Schaumann and Böker, 2005; Schaumann, Lochte-Holtgreven et al., 2010). It is a critical structural part of OWTs. In 2009–2010, engineers reported grouted connection failures causing slight and progressive settlement of turbines. The problem affected approximately 600 of the 988 monopile wind turbines in the North Sea, requiring further investigations concerning the design of the grouted connection (Rajgor, 2012). Since then, two grouted connection designs reducing the axial forces in this area have been recommended by Det Norske Veritas (2014): using a conical grouted connection (first design) or a tubular connection with shear keys (second design).
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.
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 support structure of offshore wind turbines is working in harsh ocean environments, where uncertainties exist and affect the performance of the whole system. This work presents an efficient methodology for the Reliability Based Design Optimization (RBDO) of the support structure of offshore wind turbines considering uncertainties. Reliability analysis is a feasible option in the absence of field measurement data. Monte Carlo simulations are robust and used as reliability analysis benchmark, but they are very computationally demanding for offshore wind turbine cases. Efficient Fractional Moment reliability analysis method was proposed. The results show that the proposed methodology can obtain a reliable design with better dynamic performance and less weight. Compared with the deterministic optimization, the presented dynamic RBDO of offshore wind turbines is more practical, and this methodology can be applied in the design of other similar offshore structures.
The support structure of offshore wind turbines is working in harsh ocean environments, reliability analysis is a feasible option in absence of field measurement data (Yang et al., 2017). To ensure that the proposed offshore wind turbine design is cost effective, it is necessary to check whether the decided support structures provides optimal life cycle cost.
For a reliable design, it is essential to consider various uncertainties in the dynamic analysis of offshore wind turbine (Xiao and Yang, 2014; Zhang et al., 2017). Due to the random nature of environmental parameters, wave, wind and currents must be modelled as stochastic process (Zhang and Yang, 2014). Hence, there is a need of stochastic dynamic analysis on one hand and the need of developing performance assessment, maintenance and optimization of the offshore wind turbine system with uncertainties. We try to answer the following questions: a) Can we formulate an efficient and accurate method for reliability analysis to replace Monte Carlo simulations which are robust but too time consuming; b) How to overcome computational challenges associated with reliability-based optimization methodology of offshore wind turbine system?
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.
Wind power generation is gradually expanding from land to sea. In floating offshore wind turbine, the position of floater is maintained by the mooring line, and it is difficult to predict the behavior by the combined action of wind and wave forces. To create optimal design conditions of floater and mooring line, a combined analysis of aerodynamics and hydrodynamics should be performed. Therefore, in this study, we have analyzed the behavior of the floater under wind and wave loads considering the aerodynamic damping effects of rotating blade. We used FAST provided by NREL for numerical simulations. Experiments were carried out in the Ocean Engineering Wide Tank, University of Ulsan, using the reduced OC3 Spar type platform model.
Since the Paris Conference of the Parties in 2015, interest in renewable energy around the world is higher than ever. Among them, wind power generation has achieved remarkable growth so that power generation cost can compete with the coal-fired power plant. Wind turbines on the land has a disadvantage of making noise caused by the blades, and it is difficult to secure a tract of land. On the other hand, offshore wind turbine is relatively easy to secure a large area, and it is free from noise even in the enlargement of the turbine. Also, it can obtain more persistent and stronger wind than on land. Therefore, wind power generation is gradually expanding from land to sea. In floating offshore wind turbine, to create optimal design conditions of floater and mooring line, a combined analysis of aerodynamics and hydrodynamics should be performed. Therefore, in this study, we have analyzed the behavior of the floater under wind and wave loads considering the aerodynamic damping effects of rotating blade. There are several papers (Salzmann and Temple, 2005; Myers and Valamanesh, 2014) that have already been studied. In this paper, presents the estimated results from the numerical simulations and the model scale experiments of the OC3-Hywind 5-MW Floating Offshore Wind Turbine. With a 1/128 scale ratio, model tests were carried out in the Ocean Engineering Wide Tank of University of Ulsan. Numerical simulations done by NREL-FAST v8. FAST v8 was performed according to following FAST User's Guide (Buhl and Jonkman, 2005). The objective is to analyze motion of floater considering aerodynamic damping effect at the combined wind/wave conditions.
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).
Allseas Engineering's giant new offshore construction vessel has a new name, prior to its first job. What was once the Pieter Schelte is now the Pioneering Spirit. The change occurred in early February after Jewish groups protested that the original namesake, a pioneer in creating the heavy lift offshore business, supported the Nazi war effort by serving in the SS during World War II. The company said the vessel's new name, "reflects what she stands for: a new technological step in platform installation and decommissioning. It also fits the 30-year tradition of Allseas to pioneer and surpass technical boundaries."
The effects of oil price volatility on operators and service companies, technological advances, safety and environmental risks, economic and regulatory impacts, and sustainability were highlighted in the sessions and discussions during the annual Offshore Technology Conference (OTC) held 4–7 May in Houston. More than 94,700 attendees from 130 countries gathered to exchange ideas and opinions. It is the sixth largest attendance in the conference's 47-year history. This year's conference also had 2,682 companies exhibiting, up from 2,568 in 2014, representing 37 countries.
Wind power could be used to pump oil from remote offshore fields in the way windmills were once used to pump water from wells in arid West Texas. The offshore wind idea was offered by DNV GL, which did a study showing that the wind offshore Norway is strong and steady enough year round to provide the electric power needed to inject 45,000 B/D of water into a remote offshore field in water 200 m deep. The study, which is the product of a seven-company joint industry project (JIP) created by the Norwegian classification and standards setting body, examined ways to move the source of power close to where it is needed. It is a natural idea for the offshore Europe region, a leader in the growth of offshore wind capacity, which is rising 37% a year. The JIP is now talking to oil producers about working with them on the next stage, which will move from a tabletop test using available data to laboratory testing with a goal of preparing for an offshore test.