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Cyclic Behaviour of Monopile Foundations for Offshore Wind Farms

海上风电场单桩基础的循环行为

基本信息

批准号：
EP/H013857/1
负责人：
Santana Madabhushi
金额：
$ 41.42万
依托单位：
University of Cambridge
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2010
资助国家：
英国
起止时间：
2010 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FH013857%2F1
关键词：
Cyclic Behaviour Monopile Foundations Offshore

项目摘要

Offshore wind farms are gaining popularity in the UK due to the current interest in the need for greener energy sources, security of energy supply and to the public's reluctance to have wind farms on-shore. Offshore wind farms often contain hundreds of turbines supported at heights of 30m to 50m. The preferred foundations for these tall structures are large diameter monopiles due to their ease of construction in shallow to medium water depths. These monopiles are subjected to large cyclic, lateral and moment loads in addition to axial loads. It is anticipated that each of these foundations will see many millions of cycles of loading during their design life. In coastal waters around the UK, it is common for these monopiles to pass through shallow layers of soft, poorly consolidated marine clays before entering into stiffer clay/sand strata. One of the biggest concerns with the design of monopiles is their behaviour under very large numbers of cycles of lateral and moment loads. The current design methods rely heavily on stiffness degradation curves for clays available in the literature that were primarily derived for earthquake loading on relatively small diameter piles with relatively small numbers of cycles of loading. Extrapolation of this stiffness deterioration to large diameter piles with large numbers of cycles of loading represents the key risk factor in assessing the performance of offshore wind turbines. Further research is therefore required. The proposed project aims to understand the behaviour of large diameter monopiles driven through clay layers of contrasting stiffness and subjected to cyclic lateral and moment loading. Centrifuge model tests will be conducted taking advantage of recent developments at the Schofield Centre that include a computer-controlled 2-D actuator that can apply both force or displacement controlled cyclic loading to monopiles in-flight. In addition it is possible to carry out in-flight installation of the monopiles to simulate the insertion of these monopiles into the seabed. New equipment will be developed for the in-flight measurement of soil stiffness and dynamic response comparative to the state-of-the-art equipment which is now used in the field. The main outcome of the project will be a better understanding of the response of the monopiles in layered soil systems to large number of loading cycles (lateral and moment loads). The results will be directly compared to the current design practices and guidelines for improved design will be developed. The outcome of this project will allow an accurate estimation of the behaviour of offshore monopile foundations under very large numbers of cycles of loading, thus leading to a confident estimation of the life cycle of the foundation. This is critical in determining the economic viability of an offshore wind farm given that the capital costs are high and the revenue stream is relatively low but continues for the life of the wind farm.

海上风电场在英国越来越受欢迎，原因是目前人们对更绿色能源的需求、能源供应的安全感兴趣，以及公众不愿将风电场建在岸上。海上风力发电场通常包含数百台涡轮机，支撑高度在30米至50米之间。这些高层结构的首选基础是大直径单桩，因为它们易于在浅水到中水深度施工。除了轴向载荷外，这些单桩还承受较大的循环载荷、横向载荷和弯矩载荷。预计每个基础在其设计寿命内都将经历数百万次加载循环。在英国各地的沿海水域，这些单体膜在进入更坚硬的粘土/砂层之前，通常会穿过浅层柔软、固结较差的海相粘土。单桩设计最大的顾虑之一是它们在非常大量的横向和力矩载荷循环下的行为。目前的设计方法在很大程度上依赖于文献中提供的粘土的刚度退化曲线，这些曲线主要是针对相对较小的直径桩和相对较少的加载循环次数的地震荷载而推导的。将这种刚度退化外推到大直径桩在大量循环加载的情况下，是评估海上风力涡轮机性能的关键风险因素。因此，需要进一步的研究。这项拟议的项目旨在了解大直径单桩在刚性反差的粘土层中的行为，并受到循环的横向和弯矩载荷。将利用斯科菲尔德中心的最新发展进行离心机模型测试，其中包括计算机控制的2-D执行器，该执行器可以对飞行中的单层施加力或位移控制的循环载荷。此外，还可以进行单管柱的飞行安装，以模拟将这些单管柱插入海床。将开发新的设备，用于在飞行中测量土壤硬度和动态响应，与目前现场使用的最先进设备相比。该项目的主要成果将是更好地了解层状土壤系统中的单桩对大量载荷循环(横向和力矩载荷)的反应。结果将直接与目前的设计实践进行比较，并将制定改进设计的指导方针。该项目的结果将使人们能够准确地估计海上单体桩基础在非常大的载荷周期下的行为，从而对基础的生命周期作出有把握的估计。这对于确定海上风电场的经济可行性至关重要，因为资本成本很高，收入流相对较低，但在风电场的整个生命周期内都会持续下去。