海上单桩风机结构冰激振动响应分析

针对冰区海上单桩风机易发生冰激振动的问题,以NREL5MW风机为对象,详细开展其在风-冰联合作用下的动力响应研究.基于叶素动量理论,考虑Prandtl叶尖损失修正和Grauert修正,利用MATLAB编程计算获得叶片空气动力载荷;基于M??tt?nen自激振动模型,采用APDL开发冰区风机自激振动分析程序;基于我国渤海...     

Interface behavior of grouted connection on monopile wind turbine offshore structure

The interface behavior of a concrete grouted connection is studied in a monopile wind turbine offshore structure. The grouted connection between transition piece and monopile is fixed by filling it with grout materials made of high-strength concrete. We observe a nonlinear equilibrium path from the grouted connection in experiments. For comparison with the experimental results, nonlinear finite element analysis of the grouted connection is performed, taking the effects of both material and geometrical nonlinearities into consideration. A finite element model of the grouted connection between the steel and concrete materials is realistically simulated using an interface element. The finite element results compares well with the experimental results. Thus, the finite element analysis showed that the numerical model based on the interface element is a good method for investigating the behavior of grouted connections of monopile offshore structures.     

Motion analysis of a floating offshore wind turbine considering rotor-rotation

Development of offshore wind energy is desired as a countermeasure against global warming. This article presents motion analysis of a floating offshore wind turbine during the rotor-rotation under wind loads. A 2 MW downwind turbine is mounted on a floating foundation of the spar-type. The wind loads acting on the rotor blades are calculated using the blade element momentum theory. The multibody dynamics system theory is employed to consider the effect of the rotor-rotation. As a result, the motion of yaw, sway and roll are generated due to the effect of the gyro-moment for the rotor-rotation.     

竖向水平向荷载共同作用下排桩模型试验研究

在实际工程中,排桩常常在承受竖向荷载的同时也承受水平向荷载的作用,在竖向、水平向荷载共同作用下的排桩,因受到桩距、桩长、荷载等因素的影响,其受力性状比较复杂[1～3]。国内外对该问题的研究,目前限于纵横向同时受荷时桩极限荷载的确定,且试验资料较少,并以单桩研究为主,而在实际工程中,基桩常常以排桩形式出现[4,5]。通过模型试验,本文主要研究了排桩在这些因素变化情况下的受力性状,分析总结了排桩在不同工况下的工作特性,从而得出一些对工程具有指导性意义的结论,供同类工程参考。     

Simulation of offshore wind turbine response for long-term extreme load prediction

When there is interest in estimating long-term extreme loads for an offshore wind turbine using simulation, statistical extrapolation is the method of choice. While the method itself is rather well-established, simulation effort can be intractable if uncertainty in predicted extreme loads and efficiency in the selected extrapolation procedure are not specifically addressed. Our aim in this study is to address these questions in predicting blade and tower extreme loads based on stochastic response simulations of a 5 MW offshore turbine. We illustrate the use of the peak-over-threshold method to predict long-term extreme loads. To derive these long-term loads, we employ an efficient inverse reliability approach which is shown to predict reasonably accurate long-term loads when compared to the more expensive direct integration of conditional load distributions for different environmental (wind and wave) conditions. Fundamental to the inverse reliability approach is the issue of whether turbine response variability conditional on environmental conditions is modeled in detail or whether only gross conditional statistics of this conditional response are included. We derive long-term loads for both these cases, and demonstrate that careful inclusion of response variability not only greatly influences such long-term load predictions but it also identifies different environmental conditions that bring about these long-term loads compared with when response variability is only approximately modeled. As we shall see, for this turbine, a major source of response variability for both the blade and tower arises from blade pitch control actions due to which a large number of simulations are required to obtain stable distribution tails for the turbine loads studied.     

循环荷载下海洋风机单桩基础简化分析模型

海洋风机单桩基础的控制荷载主要为风载荷、波浪载荷、地震载荷等水平循环荷载。而我国相关规范中对水平循环荷载作用下单桩分析模型与计算方法却论述较少。从3个方面深入分析了影响桩土相互作用的基本因素:土体非线性、土体极限抗力退化以及桩土脱开效应。考虑以上3点并用弹簧和阻尼串联来模拟桩周土体,提出了循环荷载作用下海洋风机单桩基础简化分析模型并编制了计算程序。通过与相关文献的试验数据比较,表明本文模型能较好地模拟循环荷载作用下水平受荷桩的性状。     

Numerical analysis of a laterally loaded shaft constructed within an MSE wall

Drilled shafts have been widely used to support lateral loads from superstructures. For typical applications, design methods are available to generate lateral load versus displacement curves and to estimate ultimate lateral capacity and displacement of the drilled shaft under a certain lateral load. However, occasionally drilled shafts have to be constructed within the reinforced zones of MSE walls, for instance drilled shafts supporting sound walls, traffic signs, billboards, and other superstructures. Under these circumstances, existing design methods are not applicable because of: (1) the limited horizontal extent of the soil mass; (2) the resistance from reinforcement; and (3) the influence of MSE wall facing. In this regard, a full-scale field study was conducted to investigate the behavior of shafts within the MSE wall, subjected to lateral loads. The test wall was 43 m long and 6 m high and constructed with layers of uniaxial geogrid and selected backfill. Three-dimensional numerical analyses were performed prior to the construction of this test wall (i.e., Class-A prediction) to guide its design and after the field test using the actual material properties (i.e., Class-C prediction). The selected test shaft for the analyses in this study was located at 1.8 m behind the wall facing. The numerical results from the Class-A and Class-C predictions are compared with the field data. The study showed that the Class-A prediction provided useful information for the design of the test wall and development of field test details. The Class-C prediction improved the overall accuracy of the calculations and could serve as a reference for future study.     

考虑部分埋入群桩基础阻抗的海上风机结构共振特性

海上风机结构一阶自振频率与风轮转动频率或叶片通过频率重合时,会产生共振现象,严重时会造成风机损坏。现有风机结构的共振研究多假设底部刚性固定,以定性分析为主,没有对基础的埋置深度和土层参数进行量化分析。以部分埋入群桩基础的海上风机结构为研究对象,基于风机结构水平–摇摆耦合简化方法,分析了群桩基础不同埋入比和土层弹性模量对风机结构共振特性的影响,建立了群桩埋入比与结构共振频率的关系。进一步开展了4组不同群桩埋深比的海上风机共振频率室内模型试验,验证理论分析结果的规律性是否合理。     

Comparison of the dynamic responses of monopiles and gravity base foundations for offshore wind turbines in sand using centrifuge modelling

Monopiles and gravity base foundations (GBF) are two of the most commonly used foundations for offshore wind turbines. As resonance can cause damage and even failure of wind turbines, understanding the difference between the dynamic responses of monopiles and GBFs under free vibration is important. However there is little experimental data regarding their natural frequency, especially from model tests carried out at correct stress levels. This paper presents the results of novel monopile and GBF tests using a centrifuge to directly determine the natural frequency (f_n) of the foundation-soil system. The natural frequencies of wind turbine monopiles and GBFs in centrifuge models were measured during harmonic loading using a piezo-actuator, with the results confirming that soil-structure interaction must be considered to obtain the system’s natural frequency as this frequency reduces substantially from fixed-base values. These results will contribute in preventing resonance induced damage in wind-turbines.     

大型海上风力发电高塔随机最优减震控制

考察了基于结构动力可靠度的调谐液体柱形阻尼器(TLCD)参数优化设计方法,并用于风-地震联合作用及地震作用下海上风力发电高塔系统的随机最优控制。文中,采用Kane动力学-有限元一体化模型,建立了TLCD-结构整体系统方程。基于概率密度演化理论的极值分布方法,给出了基于可靠度的TLCD参数优化设计方法及程序解答。在数值算例中,采用随机谐和函数和物理随机风场模型分别模拟随机地震动和随机风荷载,通过对优化的受控系统进行随机反应分析与可靠度分析,比较了不同控制准则和约束条件下TLCD的减震控制效果。研究表明基于可靠度的随机最优控制方法是可行的。     

Effect of structural nonlinearity on probabilistic risk assessment of offshore wind turbine including inelastic soil medium

This research intends to evaluate the influence of structural nonlinearity on the seismic risk of an offshore wind turbine with respect to linear analysis. The structural nonlinearity is presented into the structure, as materially nonlinear, by calibrating plastic hinge at the end of the elastic beam-element of the structure. To guarantee ideal circumstance for seismic analysis, this study includes inelastic soil stratum by using an equivalent linear approach. Monte Carlo simulation is performed by means of seismic vulnerability of the structural system. The research presents a study of a large amount of simulation over the nonlinear and linear structures considering the random character of basic variables of soil under selective earthquakes. The earthquakes having different source-to-site (STS) distances ranging from 7 to 145?km have consistency with the soil parameters. This rigorous implementation is done to accomplish site-specific dynamic analysis. Illustrative results obtained from nonlinear and linear dynamic analysis are compared. The overall finding shows that the nonlinear structure produces highest estimated uncertainty compared to the linear structure. Another termination can be addressed that the earthquake with less STS distance (7.29?km) causes the highest level of destruction to the structure.     

岩土质边坡水平受荷嵌岩桩受力性能研究

以贵州某一边坡支护中的桩基挡墙为例,采用ANSYS有限元软件,对水平受荷嵌岩桩的受力性能进行了数值模拟计算,将所得有限元解与传统解作了对比研究,在此基础上,分析了桩端约束情况、桩径等因素对基桩内力和变形的影响,以期为同类地区水平受荷桩的设计提供参考。     

Stiffening of laterally loaded coupled shear walls on elastic foundations

An investigation is made of the relative effectiveness of using either a top or bottom connecting beam to stiffen a pair of laterally loaded coupled shear walls supported on independent elastic foundations. By basing the analysis on the continuous medium approach, a closed solution to the problem is achieved. A numerical example for a typical structure illustrates the influence of the stiffening beams on the forces and deformations in the structure for two different soil conditions.     

Long-term fatigue analysis of multi-planar tubular joints for jacket-type offshore wind turbine in time domain

Long-term fatigue analysis of welded multi-planar tubular joints for a fixed jacket offshore wind turbine designed for a North Sea site in a water depth of 70 m is performed. The dynamic response of the jacket support structure due to wind and wave loads is calculated by using a decoupled procedure with good accuracy (Gao et al., 2010). Hot-spot stresses at failure-critical locations of each reference brace for 4 different tubular joints (DK, DKT, X-type) are derived by summation of the single stress components from axial, in-plane and out of plane action, the effects of planar and non-planar braces are also considered. Both a 2-parameter Weibull function and generalized gamma function are used to fit the long-term statistical distribution of hot-spot stress ranges by a combination of time domain simulation for representative environmental conditions in operational conditions of the wind turbine. A joint probabilistic model of mean wind speed U_w, significant wave height H_s and spectral peak period T_p in the northern North Sea is used to obtain the occurrence frequencies of representative environmental conditions (Johannessen, 2002). In order to identify the contributions to fatigue damage from wind loads, wave loads and the interaction effect of wind and wave loads, 3 different load cases are analyzed: wind loads only; wave loads only; a combination of wind and wave loads. The representative environmental condition corresponding to the maximum contribution to fatigue damage is identified. Characteristic fatigue damage of the selected joints for different models is predicted and compared. The effect of brace thickness on the characteristic fatigue damage of the selected joints is also analyzed by a sensitivity study. The conclusions obtained in this paper can be used as the reference for the design of future fixed jacket offshore wind turbines in North Sea.     

风-浪-流-RNA运行耦合作用下近海风电结构动态响应分析

近海风电结构不仅长期遭受风、浪、流等荷载的耦合作用,还需承担风轮-机舱组件(Rotor Nacelle Assembly,RNA)运行作用带来的额外动力影响,这不仅会加剧结构受载集中部位的损伤,还会影响甚至中断发电机组的正常运作。为探索近海风电结构关键部位的动力特性及振动模式,该文建立考虑风-浪-流-RNA运行的单桩风电塔的耦合分析模型,采用Von Karman风谱模型和叶素动量理论计算气动荷载,通过莫里森方程求取单桩基础结构的波浪及海流荷载,对NREL 5MW单桩塔的塔顶、叶根及单桩底部开展动力响应分析。基于频谱分析法探究结构各关键部位的响应激励源;研究了在3～30m/s风速范围内,近海风电结构动态响应随风速及海流流速的动力特性变化规律。结果表明：近海风电结构动态响应在不同工作状态下会呈现不同的频谱特征,其动态响应时程的均值与峰值随风速增加呈非线性的变化趋势。     

海上风机部分埋入群桩水平-摇摆振动与结构共振分析

对于海上风机部分埋入群桩基础,风机结构的高度将导致基础承受较大的倾覆力矩,因而在风机振动分析中需要考虑到基础的摇摆特性。为避免发生共振,风机结构第一阶自振频率应避开风轮转动频率（1P频率）和叶片通过频率（3P或2P频率）。目前关于风机结构动力特性的研究常常以底部刚性固定为假定,忽略了地基基础的影响,因而可能带来误差。结合既有研究成果,推导简化解析方法研究了部分埋入群桩基础的水平-摇摆耦合振动特性以及基础阻抗对风机结构共振特性的影响。首先,推导了采用动力Winkler地基模型的部分埋入群桩基础水平-摇摆动力阻抗,与精确解进行对比,验证了方法的正确性;其次,考虑基础阻抗的作用,推导了风机结构水平-摇摆振动方程;最后,通过简化方法和频域有限元方法对不同地基条件下某风机结构的共振特性及基础阻抗进行了计算和对比,研究了基础阻抗对结构共振特性的影响,并验证了简化方法的正确性。     

水平荷载单桩计算的综合刚度和双参数法杆系有限元数值解

 为提高水平荷载单桩设计计算的准确度和效率,建立基于综合刚度和双参数法原理的杆系有限元数值解。同时,从理论和对静载试验实例的分析上,指出我国现行规范建议的水平荷载桩设计计算m法存在的缺陷,建议改进方法。本文建立的杆系有限元法不像解析法那样存在参数取值的限制,避免了烦琐的查表计算,且无需对桩端约束条件进行假定及区分长桩、短桩和中长桩。实例计算比较表明,当采用与解析法相同的综合刚度和双参数时,杆系有限元解与解析解结果吻合很好,能保证桩顶位移和转角、桩身最大弯矩和及其作用位置与实测结果基本一致;当根据桩长范围内土层变化确定各土层比例系数m,通过若干次试算调整幂指数n和综合刚度EI可获得较解析法更好的计算结果。     

Numerical study on wind pressure characteristics of Chinese yurt building under downburst wind

Inner Mongolia is a high-frequency thunderstorm region in China, and the downburst caused by the thunderstorm weather is a severe threat to buildings. In order to study the influence of downburst on the wind pressure characteristics of the yurt building, the wind field model of the yurt building under downburst is established based on the computational fluid dynamics method, and the effect of the wall treatment method and turbulence model on the numerical simulation of wind pressure of the yurt building under downburst is analyzed. The results demonstrate that the maximum positive pressure at the windward side of the yurt building occurs at 3/4 of the yurt building height under downburst, and the maximum negative pressure at the roof of the yurt building appears at the center of the roof. Compared with the experimental results, the Shear Stress Transport (SST) k-ω model is suitable for simulating both sides of the yurt building, while the Reynolds Stress equation Model (RSM) is suitable for simulating the windward side, roof, and leeward of the yurt building. The enhanced wall treatment is appropriate for simulating the remaining sides of the yurt building while the standard wall function is appropriate for simulating both sides of the building.     

Stochastic seismic response analysis of offshore wind turbine including fluid‐structure‐soil interaction

This paper presents the stochastic seismic response analysis of offshore wind turbines subjected to multi‐support seismic excitation by using a three‐dimensional numerical finite element model considering viscous boundaries. The seawater‐offshore wind turbine‐soil interaction system is modelled by the Lagrangian (displacement‐based) fluid and solid‐quadrilateral‐isoparametric finite elements. The random seismic excitation is described by the filtered white noise model and applied to each support point of the three‐dimensional finite element model of the coupled interaction system. The research conducts a parametric study to estimate the effects of variable seawater level, different foundation soil types and support site conditions on the stochastic behaviour of the offshore wind turbine coupled interaction system. The finite element model of coupled interaction system was also analyzed to examine the effect of the surrounding ice sheet on the stochastic response of the coupled system with and without ice sheet. The results obtained for different cases are compared with each other. Copyright © 2010 John Wiley & Sons, Ltd.