海上风电单桩式支撑结构冰激振动及参数敏感性分析

针对渤海湾某风电场的海上固定式风机支撑结构,采用适用于大直径单桩结构的PSI曲线模拟桩土相互作用,并采用SACS软件建立支撑结构的动力分析模型。首先对支撑结构进行模态分析;其次考虑海冰结构的随机振动作用模式,根据适用于渤海湾的随机冰力谱构造随机冰载荷时程曲线,基于半耦合的时域方法,采用SACS软件对支撑结构进行冰激振动分析,输出塔筒顶部加速度、单桩基底剪力及倾覆力矩等响应参数的时程曲线和响应功率谱;最后针对冰厚、冰速和海冰强度等海冰参数对支撑结构的冰激振动进行敏感性分析。研究结果表明,在随机振动模式下,冰载荷及结构动力响应对冰厚和海冰强度较为敏感,在进行冰激振动分析时应合理确定冰厚和海冰强度等参数。     

Impact of climate change on dynamic behavior of offshore wind turbine

Global warming is expected to change the wind and wave patterns at a significant level, which may lead to conditions outside current design criteria of monopile supported offshore wind turbine (OWT). This study examines the impact of climate change on the dynamic behavior and future safety of an OWT founded in clay incorporating dynamic soil–structure interaction. A statistical downscaling model is used to generate the time series of future wind speed and wave height at local level. The responses and fatigue life of OWT are estimated for present and future periods and extent of change in design is investigated at offshore location along the west coast of India. Wind speed, wave height, and wave period data are collected from the buoy deployed by Indian National Centre for Ocean Information Services and the future climate for the next 30 years is simulated using the general circulation model corresponding to Special Report on Emission Scenarios A1B scenario. The OWT is modeled as Euler–Bernoulli beam and soil–structure interaction is incorporated using nonlinear p-y springs. This study shows that changes in design of OWT are needed due to increased responses owing to the effect of climate change. Fatigue life is found to be decreased because of climate change.     

海上风电单桩基础土相互作用特性影响因素分析

采用有限元软件ABAQUS建立了海上风电单桩基础与土相互作用数值计算模型,将波浪、洋流及风荷载等效成双向对称循环荷载,研究了水平循环荷载作用下不同因素对桩身水平位移、剪力和弯矩的影响规律。研究表明,随着循环荷载比的增加,桩身位移零点和桩身剪力反弯点沿埋深逐渐下移,桩身弯矩最大值点位于浅层土体;不同荷载频率时桩身位移在零点以上变化较大,桩身弯矩随着频率的增加逐渐增大;单向循环荷载作用下桩身位移最大,双向对称循环荷载作用下桩身位移最小;壁厚较小时对桩身水平位移影响较大;在位移零点之上范围内可以考虑设计"上厚下薄"的钢管桩,以减小桩身水平位移;不同桩壁厚时桩身剪力曲线在埋深约6D处出现交点,且泥面处桩身弯矩变化不明显。     

Uncertainty analysis of soil-pile interactions of monopile offshore wind turbine support structures

The objective of this work is to study the uncertainties involved in the modelling of the soil-pile interaction concerning their influence on the prediction of the dynamic structural response of monopile offshore wind turbine support structures. Two main issues are identified and addressed: the adequacy of the method used to deal with the soil-pile interactions and the adequacy of the soil properties reflecting the behaviour of the soil. The present study develops an approach that defines the penetrated pile length depending on the soil profile. Also, a parameter is defined to avoid the excessive usage of steel for the penetrated pile structure. The uncertainties are included in the probabilistic free vibration analysis and the contribution of each random variable to the scatter of the response is estimated by performing a sensitivity analysis. The results indicate that the uncertainty involved in the modelling of the soil profile has a significant effect on the coefficient of variance of the natural frequency, which is a serious issue to be considered in the fatigue life assessment of offshore wind turbine support structures.     

风、浪荷载作用下海上风机单桩结构灌浆连接段疲劳性能评价

灌浆连接段的疲劳性能对于海上风机单桩支撑结构至关重要。基于385种工况下的某实际5 MW单桩风机支撑结构在风、浪荷载作用下的动力响应分析,获取了灌浆连接段荷载边界条件时程。建立灌浆连接段精细化有限元子模型,将荷载边界条件转化为应力时程。对于剪力键采用"热点应力"方法进行疲劳性能评价。对于灌浆材料,选取剪力键附近灌浆材料单元积分点处的第三主应力进行疲劳性能评价。采用Palmgren-Miner线性损伤累计准则和雨流计数方法进行疲劳损伤的累计。在某实际灌浆连接段20年的设计寿命周期内,最大剪力键总疲劳损伤为1.35×10~(-10);最大灌浆材料总疲劳损伤为1.54×10~(-3)。由此可见,灌浆连接段的疲劳性能由灌浆材料控制,且损伤值远小于限值1/3,在现有的荷载条件下,灌浆连接段不会发生疲劳破坏。分析产生损伤较大的几种工况可知,风速对现有单桩结构灌浆连接段疲劳的损伤起控制作用。     

台风对海上风电单桩基础累积变形影响试验研究

文中主要采用小比尺模型试验,研究了台风对海上风电单桩基础累积变形的影响。通过在模型槽中进行桩的水平静力和循环加载试验,得到了不同工况下桩的累积转角与循环加载次数之间的关系曲线。随后对曲线进行分析,拟合出无台风工况下累积转角的计算公式,然后运用叠加法,得出了有台风工况下累积转角的计算公式。试验结果表明,单独作用一种循环荷载时,桩的累积转角是循环次数的幂函数。台风引起的大幅值循环荷载会导致转角的陡升,且增加幅度与小幅值循环荷载的幅值负相关。当将台风荷载设置在加载过程的开头时,对于疲劳设计工况,台风荷载产生的累积转角占总的累积转角的99%以上,因而可以忽略小幅值循环荷载产生的累积转角,直接用台风荷载产生的累积转角代表桩的长期累积转角,实现简化设计。     

Wave run-up on cylindrical and cone shaped foundations for offshore wind turbines

During the last decade, several offshore wind-farms were built and offshore wind energy promises to be a suitable alternative to provide green energy. However, there are still some engineering challenges in placing the foundations of offshore wind turbines. For example, wave run-up and wave impacts cause unexpected damage to boat landing facilities and platforms. To assess the forces due to wave run-up, the distribution of run-up around the pile and the maximum run-up height need to be known. This article describes a physical model study of the run-up heights and run-up distribution on two shapes of foundations for offshore wind turbines, including both regular and irregular waves. The influence of wave steepness, wave height and water depth on run-up is investigated. The measured run-up values are compared with applicable theories and previous experimental studies predicting run-up on a circular pile.     

海上风电基础结构动力分析

针对单桩、三桩、四桩导管架3种常规海上风电基础结构型式动力特性展开研究。以模态分析为基础,获得结构整体固有频率和振型;进而综合运用谐响应分析、瞬态分析、谱分析等方法,对基础结构在简谐荷载、冲击荷载、地震荷载及波浪荷载作用下的动力响应特性进行了数值模拟计算和分析。结果显示:本设计中的单桩、三桩、四桩基础结构刚度依次增大,一阶固有频率递增;对于相同的动力荷载激励,基础结构动力响应递减;基础结构设计中既要保证结构具有足够的刚度以满足荷载作用下的变形控制要求,还要使基础刚度适中以避免共振。为海上风电基础结构动力分析提供了参考。     

气流喷射模拟海上浮式风电结构风机载荷实验技术初探

随着海上风电技术的快速发展,海上风电逐渐由浅海走向深海,海上风电基础结构型式将逐渐由固定式发展到漂浮式。在浮式风电结构的模型实验中,风机载荷的模拟是保证实验效果的重要因素。针对浮式风电结构模型实验中风机载荷的模拟问题,提出了一种新型的基于气流喷射、利用气流反作用力模拟风机载荷的实验方法并进行了初步验证。通过标定得到气流控制信号与反作用力的关系,将数值模拟得到的原型风机载荷时程转换为相应的控制信号,同时针对实验装置对气流变化的响应特性,对控制信号进行频域和时域修正,驱动气流喷射以模拟风机作用力和力矩。经过实验验证,载荷模拟装置产生的载荷在时域和频域上都能与模型实验所需风机载荷保持较好的一致性,证明该方法可行。     

海上风机支撑结构设计分析

介绍海上风机支撑结构的一般失效形式,提出了适合工程实践的设计分析方法,并以某一单立柱三桩的海上风机支撑结构为例,进行了最终强度计算、动力特性分析以及疲劳强度分析。计算结果表明:1)疲劳工况是结构设计的控制工况;2)支撑结构振动频率在风机工作频率1P和3P之间;3)风机工作时的气动阻尼可有效减少支撑结构振动和疲劳损伤。     

波浪荷载及土体特性对风电单桩基础水平变形影响规律

大直径单桩基础是海上风电应用广泛的一种基础形式,严格控制桩基泥面处的位移是保证基础稳定和风机安全运营的关键因素.通过数值方法建立了单桩—海床的三维模型,将可以描述海洋砂土超固结性和结构性的弹塑性本构模型通过UMAT子程序嵌入有限元软件ABAQUS中,桩基承受的波浪荷载通过Morison方程进行计算模拟.针对无波浪荷载、仅作用于海床的波浪荷载、同时作用于桩基和海床的波浪荷载三种情况,分析了海床土的动力响应以及桩基的水平位移之间的差异,探讨了海床土体参数对桩基水平变形的影响.研究结果表明海床土体液化会导致桩基水平变形增加,海床土渗透性、超固结性、结构性对桩基水平位移影响显著,研究成果可为海上风电单桩基础的设计与运维提供参考.     

Dynamic analysis of tension leg platform for offshore wind turbine support as fluid-structure interaction

Tension leg platform (TLP) for offshore wind turbine support is a new type structure in wind energy utilization.The strong-interaction method is used in analyzing the coupled model,and the dynamic characteristics of the TLP for offshore wind turbine support are recognized.As shown by the calculated results:for the lower modes,the shapes are water’s vibration,and the vibration of water induces the structure’s swing;the mode shapes of the structure are complex,and can largely change among different members;the mode shapes of the platform are related to the tower’s.The frequencies of the structure do not change much after adjusting the length of the tension cables and the depth of the platform;the TLP has good adaptability for the water depths and the environment loads.The change of the size and parameters of TLP can improve the dynamic characteristics,which can reduce the vibration of the TLP caused by the loads.Through the vibration analysis,the natural vibration frequencies of TLP can be distinguished from the frequencies of condition loads,and thus the resonance vibration can be avoided,therefore the offshore wind turbine can work normally in the complex conditions.     

Numerical investigations of soil plugging effect inside large-diameter,open-ended wind turbine monopiles driven by vibratory hammers

Abstract

This study established a Couple Eulerian–Lagrange model to simulate monopile vibratory penetration for the investigation of soil plugging effect during high-frequency penetration of monopiles for wind turbine. Simulation analysis is focused particularly on soil plugging effect of a large diameter monopile during vibratory penetration into sand, clay, or layered soil. The results of the numerical simulation show that soil plugging effect is unlikely to occur during monopile penetration into the clay soil, while partial soil plugging may occur during the sand penetration. Penetration resistance at the pile toe is transferred to the radial stress around the pile wall. At a critical point penetration process, internal shaft friction becomes larger than external shaft friction. Moreover, radial pressure factors increase during partial soil plugging effect. For layered soil, the topsoil not only has great influence on the soil plugging effect, but also affects shaft friction in the subsoil during monopile penetration.     

Dynamic response of a monopile wind turbine in waves: Experimental uncertainty analysis for validation of numerical tools

The responses of a monopile offshore wind turbine subjected to irregular wave loads are investigated numerically and experimentally, considering a range of sea states. An extensive experimental campaign was carried out on a fully flexible model, representative of a 5 MW offshore wind turbine, at 1:40 scale. An assessment of the experimental results for the response amplitude operator for regular waves and the 90th percentile seabed bending moment in long-crested irregular waves is carried out using two models (analytical and numerical) for uncertainty propagation, suggesting that bias errors in the model properties and in the wave elevation contribute the most to the total uncertainty. The experimental results are also compared to a numerical model using beam elements and Morison-type wave loads with second order wave kinematics. The numerical model does not capture all of the responses within the level of uncertainty of the experiments, and possible reasons for the discrepancies are discussed.     

半潜型风机浮式基础设计及幅频运动特性研究

针对5MW海上风机,进行了半潜型浮式基础的概念设计,研究了其幅频运动特性。考虑风机浮式基础的稳性和运动要求,对浮式基础的构件进行设计,并进行舱室划分;考虑叶片产生的气动载荷影响以及风载荷作用,计算分析风机浮式基础的完整稳性及破舱稳性;考虑浮式基础构件及压水板的粘性阻尼,计算浮式基础的幅频运动响应特性。计算结果表明,设计的浮式基础运动性能满足风机发电作业的要求。     

A simplified calculation method for axial cyclic degradation of offshore wind turbine foundations in clay

Abstract

Pile foundation is the most popular option for the foundation of offshore wind turbines. The degradation of stiffness and bearing capacity of pile foundation induced by cyclic loading will be harmful for structure safety. In this article, a modified undrained elastic–plastic model considering the cyclic degradation of clay soil is proposed, and a simplified calculation method (SCM) based on shear displacement method is presented to calculate the axial degradated capacity of a single pile foundation for offshore wind turbines resisting cyclic loadings. The conception of plastic zone thickness R_p is introduced to obtain the function between accumulated plastic strain and displacement of soil around pile side. The axial ultimate capacity of single piles under axial cyclic loading calculated by this simplified analysis have a good consistency with the results from the finite element analysis, which verifies the accuracy and reliability of this method. As an instance, the behavior of pile foundation of an offshore wind farm under cyclic load is studied using the proposed numerical method and SCM. This simplified method may provide valuable reference for engineering design.     

海上风电基础下放通过浪溅区响应特性研究

多筒型导管架基础下放安装过程筒顶开口,筒内气—水自由置换,浪溅区下放过程由于浮力、冲击载荷、附加质量、阻尼效应等因素影响具有很强的非线性。开展模型试验研究波浪荷载下外界控制因素对四筒导管架基础下放过程气垫响应、基础运动和吊缆张力响应的影响机理,探究气垫结构对基础下放过程附加质量和固有周期的影响。结果表明：初始下放过程,筒内气体积聚,气垫压力非线性增长,随着下放深度增大,气垫压力趋于稳定;气垫压力响应趋势与基础下放速度和开孔率相关,波浪荷载仅影响气垫响应幅值;筒型基础下放穿越浪溅区阶段受到砰击荷载作用,气垫结构对砰击荷载产生缓冲效果;考虑气垫—水柱耦合作用时,顶盖即将入水阶段,气弹簧和水弹簧耦合作用下整体刚度增大,基础固有周期出现减小趋势。     

单向荷载作用下海上风机多桶基础承载特性数值分析

作为一种新型的深水海上基础型式,桶形基础在海上风机设施设计与建设中逐步得到了发展和应用。以三桶基础为例,采用大型有限元软件ABAQUS对海上风机多桶基础的承载特性进行了三维有限元数值分析。根据海上风机的荷载受力特点,分别探讨了三桶基础在竖向荷载、水平荷载和力矩作用下的极限承载力,得出荷载作用方向及桶间距对极限承载力的影响程度,研究成果为复合加载模式下海上风机多桶基础的承载特性分析奠定了基础。     

V⁃H荷载作用下海洋平台吸力式桩桶桩土承载特性研究

用于海洋平台的吸力式桩桶基础作为一种新型平台基础正逐渐成为人们研究的重点。为研究吸力式桩桶单桩基础的受力特性,对V-H（竖向—水平）联合荷载作用下的吸力式单桩基础桩土的承载特性进行了数值模拟,并将数值模拟的有限元解通过与API规范中对p-y曲线的计算方法进行对比来验证有限元模型的可行性,最后采用分级作用力的加载方式对其破坏包络曲线进行绘制,并推导出相应的函数表达式。研究表明,采用ABAQUS有限元分析软件对吸力式桩桶进行数值模拟是可行的,随着对吸力式桩桶所施加V-H联合荷载的不断增大,吸力式桩桶所能体现的应力和弯矩极限值也在随之增大,其位移变化主要在施加荷载的区域附近,最后在联合荷载作用下所体现的极限承载状态,即包络曲线大致呈四分之一的椭圆形状。     

海上风机稳桩施工平台吊装过程中的多船水动力干扰特性与动力响应分析

建立双臂起重船从运输船上起吊大型稳桩施工平台的吊装系统模型,其中,起重船与运输船呈T型布置。首先基于势流理论,采用专业水动力分析软件AQWA开展了双船系统的频域水动力分析,分析双船起吊系统的水动力干扰特性和遮蔽效应,并对双船间隙自由液面进行黏性修正从而提高频域多体水动力分析的精度。进一步采用频域—时域方法对起吊耦合系统进行参数分析,探究起吊速度、波浪周期等对吊索张力和起重船运动的影响规律。分析多个工况下运输船的遮蔽效应对起吊系统的影响。结果表明,对间隙流体施加阻尼自由液面边界条件可以一定程度提高计算模型的精度,在某些周期的迎浪条件下运输船对起重船的遮蔽效应可以降低吊装系统的响应;起吊速度对时域动力响应的影响较小;周期为8 s的规则波引起过大的动力响应。