Shaking Table Tests of Four-Bucket Jacket Foundation for Offshore Wind Turbines

As the offshore wind turbine foundation,the four-bucket jacket foundation has a large stiffness and the structure is difficult to be damaged under seismic load.Nevertheless,the saturated subsoil of the four-bucket jacket foundation tends to be liquefied under earthquake,which greatly affects the safety of offshore wind turbine.Therefore,the seismic performance of four-bucket jacket foundation is mainly reflected in the anti-liquefaction capacity of foundation soil.In this paper,the liquefaction resistance of sandy soil of four-bucket jacket foundation for offshore wind turbine is studied.The liquefaction and dynamic response of sandy soil foundation of four-bucket jacket foundation under seismic load are obtained by carrying out the shaking table test,and the influence mechanism of four-bucket jacket foundation on the liquefaction resistance of sandy soil foundation is analyzed.

Hydrodynamic Characteristics of Three-Bucket Jacket Foundation for Offshore Wind Turbines During the Lowering Process

The three-bucket jacket foundation is a new type of foundation for offshore wind turbine that has the advantages of fast construction speed and suitability for deep water. The study of the hoisting and launching process is of great significance to ensure construction safety in actual projects. In this paper, a new launching technology is proposed that is based on the foundation of the three-bucket jacket for offshore wind turbine. A complete time domain simulation of the launching process of three-bucket jacket foundation is carried out by a theoretical analysis combined with hydrodynamic software Moses. At the same time, the effects of different initial air storage and sea conditions on the motion response of the structure and the hoisting cable tension are studied. The results show that the motion response of the structure is the highest when it is lowered to 1.5 times the bucket height. The natural period of each degree of freedom of the structure increases with the increase of the lowering depth. The structural motion response and the hoisting cable tension vary greatly in the early phases of Stages Ⅰ and Ⅲ, smaller in Stage Ⅱ, and gradually stabilize in the middle and late phases of Stage Ⅲ.

Experimental Study on Tilt Adjustment Technique of Tripod Bucket Jacket Foundation for Offshore Wind Turbine in Sand

For the tripod bucket jacket foundations used in offshore wind turbines, the probable critical tilt angles should be avoidedduring tilt adjustment operation. Thus, these critical values must be identified by engineers, and remedial techniques mustbe established prior to the occurrence of the problem. Model tests were carried out for typical tilting conditions of tripodbucket foundations, which were allowed to tilt freely at various penetration depths without interruption by manualoperation. After the foundation ceased its tilting, some measures, such as water pumping, water injection, air injection, or acombination of the above methods, were enabled for adjustment. The research results showed two critical values in thetilting state of the tripod bucket jacket foundation, namely the terminal and allowable angles. In the installation condition,the terminal angle was negatively correlated with the initial penetration depth, but the opposite was observed with theremoval condition. The allowable angle was less than or equal to the terminal angle. The allowable angle in the installationwas related to the terminal angle. The critical angles all varied linearly with the initial penetration depth. When tiltingduring installation, adjustment measures can be used in the order of high drum pumping, low drum water injection, highdrum pumping and low drum water injection, air injection, and exhaust. When tilting during removal, the sequential use oflow drum water injection, air, and exhaust was applied. For buckets that were sensitive to angle changes, adjustmentmeasures of the “point injection” mode can be selected.

Shaking Table Tests and Seismic Response of Three-Bucket Jacket Foundations for Offshore Wind Turbines

The seismic response characteristics of three-bucket jacket foundations for offshore wind turbines(OWTs)and the liquefaction of the surrounding soil are particularly important for the development and application of this type of structure for offshore use.Using the shaking table test and three-dimensional finite element analysis,different magnitudes of simulated earthquake waves were used as inputs to the shaking table to model seismic excitations.The resulting changes in the excess pore water pressure and acceleration response of the soil under horizontal earthquake are compared in this paper.Calculations of the anti-liquefaction shear stress and equivalent shearing stress during the earthquake,determination of the areas prone to liquefaction,and identification of the effect of the three-bucket jacket foundation on the soil liquefaction resistance were conducted by developing a soil-structure finite element model.The development law of the soil’s amplification effect on seismic acceleration and the seismic response of the foundation soil under various magnitude earthquake waves were also discussed.Results indicate that liquefying the soil inside the bucket of the foundation is more difficult than that outside the bucket during the excitation of seismic waves due to the large upper load and the restraint of the surrounding hoop.This finding confirms the advantages of the three-bucket jacket foundations in improving the liquefaction resistance of the soil inside the bucket.However,the confinement has a barely noticeable impact on the nearby soil outside the skirt.The phenomenon of soil liquefaction at the bottom of the skirt occurred earlier than that in other positions during the seismic excitation,and the excess pore water pressure slowly dissipated.The acceleration amplification coefficient of the sand outside the bucket increases with depth,but that of the sand inside the bucket is substantially inhibited in the height range of the bucket foundation.This result proves the inhibition effects of the three-bucket jacket foundations on the seismic responses of soils.The liquefied soil layer has a significant effect in absorbing a certain amount of seismic wave energy and reducing the amplification effect.The numerical simulation results are consistent with the phenomenon and data measured during the shaking table test.The current study also verifies the feasibility of the excess pore water pressure ratio and the anti-liquefaction shear stress method for judging soil liquefaction.

剪切模式对砂-钢界面特性的影响

针对海上风机导管架基础在安装过程中发生的桩土界面单向剪切行为和服役过程中发生的持续循环剪切行为,分别采用常应力和等刚度边界条件对石英砂/钙质砂开展单向和循环剪切试验,研究不同剪切模式下界面强度发挥的细观作用。结果发现:随着单向剪切距离的增加,土样破碎带厚度逐渐增大,钢界面粗糙度下降;循环剪切幅值越大,颗粒排布重塑越充分,产生的法向位移越大。在大位移单向剪切和循环剪切过程中,破碎带的存在会改变土体的初始结构,使其具有强烈方向性。由于钙质砂的硬度较低,同等粒径下其形状相比石英砂颗粒更不规则,因此其在同等剪切距离下会产生更大的破碎量,引起较大体缩,而破碎后的石英砂棱角较多,在钢界面扰动下更易发生旋转,引起大位移单向剪切后的循环剪切过程中土样剪胀增加。

海上风电三筒导管架基础的湿拖耦合动力响应研究

[目的]为提高海上风电多筒导管架基础的湿拖运输安全性,需探究其湿拖运输过程的稳性和动态响应问题。[方法]基于海工分析软件MOSES构建水动力模型,对湿拖运输过程分别进行频域和时域分析,并定量分析波浪载荷、拖航方式等参数对三筒导管架基础拖航特性的影响。[结果]计算结果表明,三筒导管架具有良好的湿拖稳性,在吃水深度8~10 m范围内的正浮态均可满足完整稳性校核;三筒导管架基础的拖缆力、纵摇角、垂荡加速度、筒气压的幅值与波高呈正比关系,与吃水深度呈线性变化关系但影响较小;拖缆力和筒气压的幅值与波浪周期无明显关系,但波浪周期将影响该基础的纵摇和垂荡响应幅值;拖缆力与航速的平方近似呈正比关系;顺浪条件下三筒导管架基础的纵摇运动比逆浪条件更为剧烈。[结论]研究成果对于提高多筒导管架基础的湿拖运输安全性具有重要的指导意义。

复合加载模式下四筒导管架基础承载特性分析

针对海上风电四筒导管架基础在砂土中的复合承载特性,采用数值模拟的方法,计算5种不同荷载组合下的四筒导管架基础的极限承载力。为分析不同加载模式下筒基长径比和筒间距对基础极限承载力的影响,分别改变筒高和吸力筒圆心距离进行计算并绘制破坏包络线。结果表明,在竖向荷载作用下,基础的水平极限承载力先增大后减小;抗扭承载力随竖向荷载的增大而增大,随水平荷载的增大而减小;不同竖向荷载的作用下,水平和弯矩极限承载力基本呈线性相关。

海上风机基础定位吊装系统研发及应用

为了提升海上风机“先桩法”导管架基础的施工效率,减少安全事故发生的可能性,研发了海上风机基础定位吊装系统,该系统包含:形象进度模块、三维模型展示模块、视频监控模块、基础结构物监测模块,通过对导向平台及导管架(后统称为结构物)上传感器实时传输数据的相关理论计算及可视化,实现对风机基础吊装施工全过程的定位、监控,以指导施工过程有序、快速地进行。该系统成功运用于粤电阳江沙扒海上风电工程项目。吊装过程中结构物平台上的倾角角度始终在3°以内且最终达到稳定时小于0.2°,满足倾斜度0.5%以内的要求;GNSS定位数据异常值较少,不影响整体判断结构物的位置,且最终GNSS测值均趋于目标坐标。应用结果表明:在该系统辅助下,基础结构物吊装过程平稳且高效,能够实现基础结构物吊装厘米级定位精度。

分体式导管架灌浆连接段承载力数值分析

分体式导管架是一种降低深海风机导管架施工难度的新型结构形式。为了解分体式导管架结构灌浆连接段的受力情况,采用有限元方法对连接段隔离体进行数值模拟分析,研究剪力键高距比、灌浆层径厚比及横撑作用力大小对连接段承载力的影响,并分析灌浆料应力大小的分布规律。结果表明:灌浆段极限承载力随剪力键高距比减少而下降;灌浆段极限承载力随横撑作用力的增加而增加;灌浆段极限承载力不随着灌浆厚度的增加而单调增加,灌浆厚度存在最优值使承载力达到最大值。为分体式风机导管架连接段的优化设计提供参考。

海上工程吸力筒导管架基础沉贯理论与实证分析研究

为了验证美国石油学会(American Petroleum Institute,API)规范的理论计算分析结果同现场实证试验数据的一致性以及调平新技术的有效性,以大唐大连市庄河海上风电场址Ⅰ(100 MW)海上风电项目吸力式三筒导管架基础为研究对象,运用API规范的静力平衡法、屈曲分析、土塞理论,以及SACS与ANSYS有限元分析软件进行吸力筒导管架沉贯的土塞、沉贯可行性、贯入屈曲、竖向承载力及吊装适应能力的一系列力学分析,通过将吸力式三筒导管架沉贯过程实际监测的土塞高度、负压、承载力、屈曲变形数据同理论计算结果进行比对分析,验证了API规范的理论计算分析结果与现场实证试验数据之间具有良好的拟合度。而“水上星站差分定位+姿态监测及定向的测量+无线网桥通讯组合”和“吸力筒吸力贯入装备一体化系统智能控制系统”两种新技术的应用,成功达成了吸力筒导管架基础功能性的实现。本研究证明了API规范理论分析的准确性和新调平技术的有效性,同时本研究的创新吸力筒式基础可以大幅节约钢材,能显著降低海上风电项目投资成本,经济价值高,有望成为未来海上风电项目的主要基础型式之一。

大型海上风机导管架基础大直径钢管桩承载力与疲劳性能分析

导管架基础钢管桩是支撑上部风机、承受风浪流荷载的关键结构。以某深水区海上风电场大兆瓦风机为例,对不同桩径的导管架基础模型进行动力特性分析,提炼出了频率随桩径变化的发展规律;同时,结合SACS软件分别对主体结构、主体与桩连接段的受力性能进行敏感性分析,综合对比不同桩径导管架基础对嵌岩的影响程度;在此基础上,对桩顶连接段的过渡段开展疲劳性能研究,分别获取不同桩径下过渡段的应力集中系数,系统地评估不同桩径的导管架基础对疲劳损伤的影响;最终,形成一种适用于浅覆盖海域、大兆瓦海上风机的新型大直径避免嵌岩的导管架桩基础。研究结果表明:结构受力对桩径变化的敏感性由强至弱分别为:灌浆连接段强度>桩顶过渡段强度>导管架基础强度>桩顶过渡段疲劳性能>桩长>频率;在满足规范要求的前提下,该场址地区增大1.5 m桩径可减小桩长4 m,大幅降低了桩端打入岩层的概率。

考虑建设角度的植入式嵌岩导管架风机基础风振响应分析

基于广西防城港海上风电三桩导管架基础结构原型数据与地勘资料,采用ABAQUS建立相关有限元模型,选取3种建设角度施加风荷载,分析了结构整体的应力、位移响应情况。研究结果表明:不同建设角度下,结构最大应力均位于法兰连接段,且建设角度与主风向呈45°时最危险;建设角度与主风向平行时导管架应力较大,桩基础的应力较小且桩顶应力水平最大;嵌岩部分桩基础水平位移几乎可以忽略,导管架的2层横杆交界处水平合位移最大,水平方向位移最大值出现在法兰连接段顶部。工程建设中应该避免三桩导管架基础建设角度与主风向平行或垂直,45°方向建设相对更安全。

分体式吊装对导管架基础竖向承载特性影响的数值模拟

以庄河海域3000吨级海上升压站为例,基于Abaqus有限元软件建立海上升压站导管架基础模型,进行海上升压站上部组块分体式吊装对导管架基础竖向受荷特征影响规律的数值模拟研究。结果表明:采用分体式吊装方案后,升压站基础总沉降量比整体加载方案小,但基础沉降不均匀;升压站基础承受的竖向载荷与整体加载方案相比差别不大;升压站基础桩身变形略大于整体加载方案,相对容易导致桩周土体发生破坏。虽然分级加载方案与整体加载方案相比对导管架基础的承载特性有一定的不利影响,但考虑到施工成本,可采用分体吊装方式进行施工。研究成果可为海上风电类似工程提供参考。

高强灌浆材料结合卡箍在导管架受损构件加固中的应用

以南海某海域一施工船与四桩导管架基础发生碰撞为背景,结合当前研究对导管架受损区域的承载力进行分析,计算得到受损截面凹陷处的轴向承载力和极限弯矩。简述海洋工程领域中受损构件的加固修复方法,探讨卡箍技术的理论研究现状及其在实际工程中的应用现状。基于典型灌浆卡箍修复技术提出一种采用80 MPa高强度灌浆材料结合卡箍技术进行加固修复的新方案,并采用有限元软件对加固后的组合结构进行数值模拟。仿真结果表明,该组合结构可有效改善导管架受损区域受力状况,提高结构的承载力。简述该方案的施工流程,以期为实际工程提供参考。

砂土中长径比对三筒基础水平承载特性的影响

The tripod foundation(TF)is a prevalent foundation configuration in contemporary engineering practices.In comparison to a single pile,TF comprised interconnected individual piles,resulting in enhanced bearing capacity and stability.A physical model test was conducted within a sandy soil foundation,systematically varying the length-to-diameter ratio of the TF.The investigation aimed to comprehend the impact of altering the height of the central bucket on the historical horizontal bearing capacity of the foundation in saturated sand.Additionally,the study scrutinized the historical consequences of soil pressure and pore water pressure surrounding the bucket throughout the loading process.The historical findings revealed a significant enhancement in the horizontal bearing capacity of the TF under undrained conditions.When subjected to a historical horizontal loading angle of 0°for a single pile,the multi-bucket foundation exhibited superior historical bearing capacity compared to a single-pile foundation experiencing a historical loading angle of 180°under pulling conditions.With each historical increment in bucket height from 150 mm to 350 mm in 100 mm intervals,the historical horizontal bearing capacity of the TF exhibited an approximately 75%increase relative to the 150 mm bucket height,indicating a proportional relationship.Importantly,the historical internal pore water pressure within the bucket foundation remained unaffected by drainage conditions during loading.Conversely,undrained conditions led to a historical elevation in pore water pressure at the lower side of the pressure bucket.Consequently,in practical engineering applications,the optimization of the historical bearing efficacy of the TF necessitated the historical closure of the valve atop the foundation to sustain internal negative pressure within the bucket.This historical measure served to augment the historical horizontal bearing capacity.Simultaneously,historical external loads,such as wind,waves,and currents,were directed towards any individual bucket within the TF for optimal historical performance.

深水海上风机吸力桶导管架基础承载特性

针对海洋深水环境,设计适应70 m水深的四桶导管架结构形式,并在此基础上设计相同高度和主腿斜度的三桶导管架基础。采用Abaqus有限元软件建立导管架结构-吸力桶-土体整体有限元模型,通过对比分析探究海上风电深水吸力桶导管架基础的承载力特性。研究发现:吸力桶与土体的位移一致性程度可反映基础水平极限承载力大小,四桶导管架基础的综合承载特性优于三桶导管架基础;加载高度对四桶导管架基础的水平承载特性有重要影响,基础水平承载力随着加载高度增加逐渐减小;加载方向对四桶导管架基础水平承载力影响较小。

大兆瓦级海上风机导管架基础新型过渡段疲劳性能分析

导管架基础过渡段是连接上部塔筒和下部导管架主体结构、确保上部风机载荷有效传递到下部导管架主体结构上的关键结构,具有承上启下的作用,是整个导管架基础设计的重点和难点。以相同海域大、小兆瓦级海上风机为研究对象,采用大型通用有限元软件ANSYS建立基准模型进行分析,提炼出结构频率随结构型式的变化规律。基于不同兆瓦级风机过渡段结构,分别进行强度及屈曲稳定性能分析;同时,结合等效静力荷载方法选用适用于该结构型式的疲劳曲线,计算不同工况下不同兆瓦级风机导管架基础过渡段结构的累积疲劳损伤。在此基础上,对新型大兆瓦级过渡段结构进行疲劳敏感性分析,对不同型式的过渡段结构进行对比计算,最终确定可用于大兆瓦级海上风机导管架基础的新型过渡段结构.

海洋工程钢结构不规则防沉板基础承载力数值模拟

防沉板基础是海洋工程结构物中常用的浅基础形式,由于结构功能布置需要可能会导致其具有不规则的形状,同时海洋结构物的土壤条件和载荷条件较为复杂,要求防沉板基础具备可靠的承载能力。针对某海洋平台导管架结构的不规则防沉板基础,采用浅层土壤参数根据规范中推荐的理论公式以及面积和惯性矩等效的方法得到承载力;结合深层土壤条件,采用有限元方法和用户子程序对不同空间载荷作用下的极限承载力进行数值模拟。通过两种方法分析并验证了防沉板基础的承载力,结果表明:不规则形状的防沉板基础承载力计算可采用面积和惯性矩等效方法等效为长方形基础,浅层深度范围以内的土壤采用线性变化的承载力计算公式,与三维空间载荷作用下的有限元模型分析结果基本吻合。

海上风机基础与网箱融合系统静力计算

[目的]随着海上风电场不断增加,海域使用矛盾也越来越严重,海上风电和渔业养殖融合发展吸引越来越多的关注,并陆续提出了不同类型的风机基础融合养殖网箱的结构设计。这些设计多数处于概念设计阶段,距离工程应用还有比较遥远的距离。[方法]文章基于网衣质量相等、网衣附加海生物质量相等、网衣水动力性能等效的要求,提出高效的网箱等效载荷计算方法。根据14 MW风机设计载荷和海洋水文条件,设计适用于14 MW海上风机的导管架基础结构,并融合内网箱和外网箱,设计出2种导管架基础与海洋养殖网箱融合系统。基于Morison模型,考虑非线性波的影响,根据提出的网箱等效建模方法在SACS对不同设计进行静力分析。[结果]研究表明,内外网箱与导管架融合设计对整机频率一二阶影响较小可忽略不计,对三阶频率影响较大;转角工况是控制工况,增加内外养殖网箱后需对导管架基础进行局部加强,14 MW海上风机导管架基础与内网箱或外网箱融合的设计方案的计算结果均满足规范设计要求。[结论]研究结果可为海上风机基础与海洋养殖网箱融合系统设计的工程应用提供参考。

Reliability-Based Design for Jacket Platform Under Extreme Loads

In this paper, reliability analysis for the offshore jacket platform with the interaction of structure- pile- soil under extreme environmental loads is carried out. The inherent uncertainties of the environmental load, foundation soil, platform itself, and calculating models are evaluated. The action of extreme loads on the offshore platform is modeled as a function of extreme wave height. The system capacity of the whole platform is determined by nonlinear pushover analysis, and the relevant probability property is obtained by the simulation method. The reliability model for the whole jacket platform is described as the relationship between the load and resistance based on the offshore design codes. The reliability of whole platform is calculated by the analytical method and the importance sampling method on the basis of a case study for a tripod jacket platform.