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1.
Considering the deficiencies of the traditional monopile foundation for offshore wind turbines (OWTs) in severe marine environments, an innovative hybrid foundation is developed in the present study. The hybrid foundation consists of a traditional monopile and a wide–shallow bucket. A series of numerical analyses are conducted to investigate its behavior under the static and dynamic loading, considering various loading eccentricities. A traditional monopile with the same steel volume is used as a benchmark. Although the monopile outperforms the hybrid foundation in terms of the ultimate moment capacity under each loading eccentricity, the latter can achieve superior or the same performance with nearly half of the pile length in the design loading range. Moreover, the horizontal load and moment are mainly resisted by the bucket and the single pile in the hybrid foundation respectively. The failure mechanism of both the hybrid foundation and the monopile is excessive rotation. In the rotation angle of 0.05 rad, the rotation center is located at the depth of approximately 0.6–0.75 times and 0.65–0.75 times the pile length for the hybrid foundation and the monopile respectively. The increasing loading eccentricities can lead to increasing moment bearing capacity, increasing initial stiffness and upward movement of the rotation center of the two foundations, while decreasing load sharing ratio of the single pile in the hybrid foundation. Three scenarios are considered in investigating the dynamic loading behavior of the hybrid foundation. Dynamic response results reveal that addition of the bucket to the foundation can restrain the rotation and lateral displacement effectively. The superiority of the hybrid foundation is more obvious under the combined wave and current loading. 相似文献
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Foundations for Offshore Wind Turbines (OWTs) are designed following the limit state philosophy. One of the considered states is the Serviceability Limit State (SLS), which verifies that the permanent rotation of the foundation generated from accumulated strains in the soil is below a project specific criterion. Despite design codes requiring an estimation of the permanent rotation, there is not clear guidance on how to implement this. This paper describes a methodology to estimate the monopile permanent rotation for SLS and discusses its advantages and limitations. The methodology combines an accumulation method with results from 3D Finite Element Analyses (FEA) and a soil model that accounts for strain accumulation as a function of the number of cycles, relative density and load characteristics. The performance of the proposed methodology is compared against experimental centrifuge tests and results from advanced 3D FEA, indicating that it can predict the permanent rotation with satisfactory accuracy, and with a considerable reduction in computational effort. This is important for the design of OWTs, where different load histories might be required to be checked – often under tight time constraints – to find which load history leads to the largest permanent rotation, and therefore is more critical to SLS design. 相似文献
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This paper presents experimental assessment of crack growth rates of S355J2+N steel in a corrosion fatigue environment similar to what is experienced on offshore wind farm monopile structures under various cyclic load frequencies in order to assess the effect of cyclic frequency of the applied loading within a frequency range pertinent to the structure. Fatigue crack propagation behaviour in this test programme is evaluated through fatigue tests on six compact tension test specimens in air and in laboratory simulated seawater under free corrosion condition. Fatigue crack lengths were monitored by back face strain (BFS), DCPD and ACPD. A regression model was derived through the BFS method to express strain values as a function of crack length to width ratio. The effectiveness of BFS method is particularly demonstrated in the simulated marine environment. Within the range of test frequencies, crack growth rates in simulated seawater when compared to the equivalent air test revealed environmental reduction factors of 2 and 4 at lower and higher values of stress intensity factors respectively. Significant difference in the results of the seawater test frequencies is discussed. 相似文献
4.
Today, an important challenge for offshore wind energy is to design efficient and reliable offshore wind turbines (OWTs). The overall damping of OWTs plays an important role in the design process as it limits the amplitude of the OWT dynamic response at frequencies near resonance. Therefore, an accurate estimation of OWTs damping is necessary for the efficient design of these systems. The foundation damping is one of the main sources overall turbine damping and is the least well understood. This paper presents a critical review of recently published studies on foundation damping for OWTs on monopiles and explains how soil damping contributes to the total damping of OWTs. It also reviews the main methods that have been used for the estimation of foundation damping in numerical and experimental studies. In addition, the importance of damping to the OWTs fatigue life is discussed. Finally, a discussion is provided on the challenges to be overcome and recommendations for the accurate estimation of foundation damping. 相似文献
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For offshore structures such as offshore wind turbines (OWT), typhoon is usually considered one of the most critical threats to structural safety performances and service life due to its heavy wind, wave, and even coexisted storm surge. Meanwhile, it is challenging to obtain the systematic data from the environmental conditions, structural dynamic vibrations and the SCADA record, when typhoon passes by the offshore wind farm. Taking into account these situations, a real-time multi-source monitoring system enabling the investigation of the typhoon impact on the performances of OWT, has been firstly established and implemented to a 4.0 MW mono-pile OWT in Rudong, Jiangsu, China. One of the major contributions in this work is to develop the monitoring system using a unique environment of real-world data that has been synchronously obtained from waves, winds, vibrational accelerations, inclinations of towers and SCADA data during the typhoon “In-fa” passing by the wind farm, and provide the scientific community with the underlying standards and technical recommendations. To investigate the influence caused by “In-fa”, comparison results of the measured data in the range of June to August have been analysed. It is worth noting that two conclusions have been obtained: (1) the region near the nacelle is not always the most critical vibrational area. Actually, the change of the maximum structural response in the position under different external loads should be applied to effectively evaluate the structural safety; (2) the measured accelerations exhibit an obvious decay process in the presence of the turbine rotor-stop, but not the yaw rigid-body motion. This observation promotes the accurate identification of modal parameters for the long-term monitoring. Consequently, these valuable findings to facilitate the assessment of structural operational conditions have been developed into two guide-lines. All the data and analyses presented in this paper provide a valuable insight into the design, energy efficiency, safety monitoring and damage diagnosis of OWT structures. 相似文献
6.
在阐述海上风机基础的种类和特性的基础上,介绍风机基础的设计要点,包括设计流程,设计的外部环境分析以及风机基础的选型等,分析各个设计阶段的要求及注意事项。 相似文献
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Loads from storm waves can in some cases be dimensioning for offshore wind turbine substructures. Accurate determination of nonlinear wave loads is therefore important for a safe, yet economic design. In this paper, the fully nonlinear waves, realized by a fully nonlinear potential wave solver OceanWave3D, are incorporated into coupled aero-servo-hydro-elastic simulations for a reduced set of wave-sensitive design load cases, in comparison with the widely used linear and constrained waves. The coupled aero-elastic simulations are performed for the DTU 10 MW reference wind turbine on a large monopile at 33 m water depth using the aero-elastic code HAWC2. Effect of the wave nonlinearity is investigated in terms of the ultimate sectional moments at tower bottom and monopile mudline. Higher ultimate moments, 5% at tower bottom and 13% at monopile mudline as maximum, are predicated when the nonlinear waves are used. It could be explained by the fact that the extreme nonlinear waves, that are close to the breaking limit, can induce resonant ringing-type responses, and hereby dominate the ultimate load responses. However, the constrained wave approach shows marginal difference compared to the standard linear wave approach. It can be concluded at least for the present configuration that the industry standard approaches (linear and constrained wave approach) underestimate the ultimate load responses on offshore wind turbines in severe sea states. 相似文献
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This paper reports the lateral – moment bearing capacity of bucket foundations under lateral loading in sand. The Modified Mohr-Coulomb (MMC) model is adopted to capture the hardening – softening behaviour in medium dense and dense sands within a finite element (FE) modelling framework. The FE model performance is assessed against available field test data as well as analytical solutions showing a relatively good agreement. A series of parametric study is conducted to investigate the effects of bucket aspect ratio, bucket diameter, load eccentricity, vertical load and relative density of sand on the lateral - moment bearing capacity of the bucket. Comparisons are drawn between the conventional Mohr-Coulomb (MC) model and the stress dependent MMC model highlighting the role of sand dilatancy in mobilising the lateral moment capacity. Based on the FE results, a simple stepwise calculation framework is proposed for two scenarios: (i) to predict the lateral - moment bearing capacity of the bucket if the bucket dimensions are known, and (ii) to design the bucket dimensions for a known required bucket capacity. 相似文献
10.
We present an optimization study for the conceptual design of wind turbine floaters of the TetraSpar type. The optimization variables include all geometric dimensions of the floater, keel, mooring lines and tower design. A gradient based optimization method is applied to a mass proportional objective cost function. The objective function accounts for the different weight components of the floater, including secondary steel, the wind turbine tower, and the mooring system. A frequency domain response method is utilized, so that each design evaluation also takes into account the dynamic response for 12 wind speeds with associated wave conditions. Nineteen constraints are applied for static and dynamic response, natural frequencies, and fatigue at the bottom of the tower. Two reference designs are presented, namely one with a soft–stiff tower and one with a stiff–stiff tower. Due to the anti-phase coupling of the floater pitch and tower vibration, the soft–stiff tower needs a stronger floater stiffness in pitch. This design thus has a larger water plane area moment than the more compact stiff–stiff floater, which is found to be the least economical. A constraint analysis is next presented based on Lagrange multipliers and a relative cost index. We find that the strongest cost influence is exerted by the 3P tower frequency constraint for the stiff-stiff and soft-stiff designs. Finally, a third design variant with a free optimizable tower frequency is introduced. This design is found to be 11% cheaper than the soft–stiff design and highlights the potential cost savings of tower designs within the 3P region. 相似文献
11.
In this study corrosion-fatigue tests have been conducted on fracture mechanics specimens extracted from an S355 G10+M structural steel welded plate. The tests have been performed on compact tension specimens with the crack tip located in the heat affected zone. The corrosion-fatigue test results from this study have been compared with the data available on the base metal as well as air tests on the same material. Moreover, the obtained results have been compared with the corrosion-fatigue data available in the literature on a wide range of steels and also the fatigue trends for welded joints in free-corrosion condition recommended in the BS7910 Standard. The effect of the specimen orientation, with respect to the weld region, is also examined in this study and it has been found that higher corrosion-fatigue crack growth rates are generally observed in the tests with 0° orientation. The results have also shown that the corrosive environment has significant effects on the fatigue crack growth acceleration at the beginning of the tests; however, as the crack propagates, the environmental damage effect on crack growth behaviour becomes less pronounced. The results presented in this study are discussed in terms of improvement in the structural integrity assessment of offshore wind turbine monopiles. 相似文献
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海上风电是最有前途的清洁能源之一,在概念设计时,海上风机的支撑结构选型优化非常重要。选型优化是一个多属性决策问题,本文将广泛应用的多因素、多层次模糊优选理论引入支撑结构的选型决策中。针对环境等影响因素复杂、确定隶属函数主观因素较强的问题, 成功引入因素的优先关系法来确定优选矩阵的隶属度,较好地减少了确定隶属函数的人为影响。通过此优选模型成功地将四种优选方案(单桩,三脚架,五桩,高桩门架)和影响支撑结构选型的8种因素(施工难度,维护成本,CO2排放量,海水浑浊度,珊瑚礁形成,强度,刚度,耐久性)进行了多级模糊综合优选决策,得到了比较科学的决策结果,本研究为海上风机支撑结构的方案选型决策提出了一种量化分析的手段。 相似文献
13.
Several floating wind turbine designs whose hull designs reflect those used in offshore petroleum industry have emerged as leading candidates for the future development of offshore wind farms. This article presents the research findings from a model basin test program that investigated the dynamic response of a 1:50 scale model OC3 spar floating wind turbine concept designed for a water depth of 200 m. In this study the rotor was allowed to rotate freely with the wind speed and this approach eliminated some of the undesirable effects of controlling wind turbine rotational speed that were observed in earlier studies. The quality of the wind field developed by an array of fans was investigated as to its uniformity and turbulence intensity. Additional calibration tests were performed to characterize various components that included establishing the baseline wind turbine tower frequencies, stiffness of the delta type mooring system and free decay response behaviour. The assembled system was then studied under a sequence of wind and irregular wave scenarios to reveal the nature of the coupled response behaviour. The wind loads were found to have an obvious influence on the surge, heave and pitch behaviour of the spar wind turbine system. It was observed from the experimental measurements that bending moment at the top of the support tower is dominated by the 1P oscillation component and somewhat influenced by the incoming wave. Further it was determined that the axial rotor thrust and tower-top shear force have similar dynamic characteristics both dominated by tower’s first mode of vibration under wind-only condition while dominated by the incident wave field when experiencing wind-wave loading. The tensions measured in the mooring lines resulting from either wave or wind-wave excitations were influenced by the surge/pitch and heave couplings and the wind loads were found to have a clear influence on the dynamic responses of the mooring system. 相似文献
14.
The assembly and installation costs account for a large share in the overall expenditures of an offshore wind farm project. Single blade installation is suitable for large scale wind turbines due to the lower crane capability requirement and lower transportation time. By introducing active tension control on the tugger lines, an automatic single blade installation approach can accomplish operations in higher sea states, reduce the waiting-on-weather time, and improve the operational efficiency. Compared to early research, a more complicated control objective is achieved in this paper, i.e., a two-tugger-line configuration is applied to stabilize the suspended blade in three degrees of freedom during crane rotation and blade root-hub mating processes. The pulleys on the crane boom, i.e., the ends of the tugger lines, are assumed to be fixedly placed, resulting in tugger line time-varying inclinations. A novel backstepping-like controller is designed and proved. It is able to stabilize the blade around its equilibrium and make it track the desired path. Sensitivity studies are conducted to evaluate the influence of the tugger line inclinations. In addition, the influence of the installed blades on a three-blade horizontal wind turbine with a monopile foundation is discussed. The proposed active control setup improves the installation success rate and reduces the risks for blade impacts that may occur during mating. 相似文献
15.
海上风电开发中随着水深增加,传统的固定式风机基础的劣势逐步显现,建造成本也显著增加。本文提出了一种适用水深范围广、结构简单、刚度可调的新型牵索锚固式海上风机基础结构。结合海上风电场设计实践和经验,归纳了牵索锚固式海上风机基础的设计重点。以3MW海上风力发电机组为例,分析不同牵索结构设计参数对基础结构的影响,通过计算发现,索缆根数、夹角对结构位移影响显著,而对应力影响微弱,索缆牵拉位置对结构应力位移影响都很显著。分析牵索锚固式风机基础结构在工作荷载和环境荷载耦合作用下的力学性能,计算结果显示,牵索锚固式海上风机基础结构不会发生强度破坏,但位移可能超过使用限制。 相似文献
16.
This paper presents a preliminary technical feasibility study on a new methodology proposed for installing a monopile-based bottom supported offshore wind turbine structure. The concept is developed to address the problem of “waiting for a suitable weather window” which is commonly faced by the existing installation methods that uses a typical jack-up platform. In the methodology, a floating vessel along with a floatable subsea structure fitted with a hull on the top, hereafter named SSIP (subsea structure for installing a pile), is proposed first to install a monopile. Then the same structure is used to carry an FIUS (fully integrated upper structure) of an offshore wind turbine, which is characterized by a telescopic tower, and install it over the monopile by using an FOP (float-over-pulling) arrangement. Here, the installation methodologies are first briefly described along with the critical load cases associated with them. These load cases are then numerically studied for a significant wave height (HS) of 2.5 m, and the results are summarized. For installing a fully integrated offshore wind turbine upper structure on a monopile foundation by the FOP method, two installation schemes are presented, and their dynamic characteristics are compared. It is shown that the proposed methodologies have potential to provide installation solutions which can be environmentally more robust compared to the existing method for installing an offshore wind turbine. 相似文献
17.
The composite bucket foundation (CBF) is a new and environmentally-friendly foundation for offshore wind turbines. This foundation can be prefabricated in batches onshore followed by integrated transport and installation at sea. The structure itself has a subdivision air cushion structure that enables the foundation to float stably on the water surface and realize long-distance towing of the foundation. The mechanism of this air-liquid-solid coupling towing process is complicated, and the influence of the bulkheads on the towing resistance is not clear. In this paper, the influence of the subdivision structure on the towing resistance of the CBF is compared with the tow test in hydrostatic water. The structural motion characteristics and the change of the cushion pressure are also analysed. Experiments are used to verify numerical calculation results. The flow field difference between the CBF with bulkheads, the CBF without bulkheads and the real floating structure was analysed. The dynamic pressure coefficient was used to analyze the force at surfaces of different CBF's. For the tow test and numerical calculation of multiple CBFs, the optimal multi-CBF tow distance and towage number are obtained through the calculation of energy consumption rate. 相似文献
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从分析风机基础可能遭遇的船舶撞击的风险出发,提出了船舶撞击风机基础的概率计算方法。在此基础上提出通过防护成本和撞击损失的比较分析确定撞击标准的方法。进而提出了海上风机基础防撞设计的基本思路,并就风机基础防撞设计所涉及的船舶撞击力的计算方法和风机基础防撞设施的设计和使用进行了阐述。初步阐明了海上风机基础防撞标准的确定方法和海上风机基础防撞设计的思路,可供海上风机基础设计参考。 相似文献
20.
Grouted connections (GCs) are widely used to connect superstructures and driven piles in offshore wind turbine structures. They resist fatigue loading in marine splash zones and even submerged environments. In this paper, six GC segment specimens were designed and tested under fatigue loading in both the air and water ingression conditions. The results in the air condition showed that for the specimens with lower loading ranges, the strain distributions and residual displacements stabilized after 20 thousand load cycles. These conditions persisted until the end of the test with two million cycles, with only a few tiny cracks appearing on the grout material surface. Meanwhile, wide cracks and grout material exfoliation were found in specimens with higher loading ranges. The residual displacement accumulated gradually, which eventually caused the termination of the test when it reached 5 mm after 1.3 million cycles. The results in the water ingression condition showed that the water had entered into the micro-cracks of the grout material, which severely degraded the fatigue behavior of the GC specimens. Even in lower loading ranges, specimens W-1 and W-2 only endured 0.264 million and 64 thousand load cycles before the displacement of the top clamp reached −10 mm. Compared with two specimens tested in the air, with a total displacement of less than −0.7 mm after two million load cycles, the severe deteriorating effect of water ingression on the fatigue behavior of GCs was apparent. 相似文献