Offshore Wind Turbine Foundation

桩土分析(PISA)项目桩土分析项目是由Carbon Trust‘s Offshore Wind Accelerator计划运行的联合行业倡议。PISA的目的是研究和开发“专门为海上风电行业量身定做的改进的横向加载桩的设计方法”(牛津大学，北达科他州)。目前用于海上风电应用的单体桩是根据(API，2010)和(DNV，2014)中的指导设计的，这两个指南是几十年前编写的，用于石油和天然气行业，因为石油和天然气行业的桩又长又细，不会承受很大的横向载荷。问题是，为海上风能应用而设计的桩直径要大得多，也要短得多，因为它们需要抵抗更大的横向荷载，导致建造的桩过于保守，土壤响应与预期的不同。PISA项目已经在陆地上进行了大规模的现场测试，以收集数据(Byrne等人，2015年)。地点的选择使土壤与北海发现的土壤相似。为了验证实地测试的结果，在伦敦帝国理工学院(Zdravkovic等人，2015年)进行了计算分析。设计方法报告将于2016年初提交给工业界。为了更好地了解土体对横向荷载桩的响应，需要进一步的计算模型。其他可以考虑的领域包括地基响应：-根据更宽的参数空间-在由粘土和砂土组成的成层土壤中-在不同的荷载下。建模将使用帝国理工学院有限元程序(ICFEP)或另一种商业软件，如ABAQUSFEA。土壤将被模拟为类似于兹德拉夫科维奇等人所做的方法的“结构性土壤”。(2015)二.连续实时健康结构监测大多数已建成的涡轮机在转子组件中都有一个基本的数据采集系统，称为监控和数据采集(SCADA)。这些数据包括从风速到油温的一系列不同变量(Antoniadou等人，2015年)。这些数据还包括涡轮机的加速度，由此可以计算出结构的基频。最近在Duddon Sand离岸风电场进行的一项研究发现，风力涡轮机的设计基频和实际基频之间存在显著差异。低估基频的后果是，这可能会增加结构的使用寿命。另一项针对Walney Offshore Wind Farm中单个风力涡轮机的研究显示，该结构的运行寿命可能会增加88%(Kallehad等人，2015年)，以进一步改进风力涡轮机的优化，并使单极子能够更有把握地在不同地点使用。以下领域将需要进一步研究：-使用测量改进设计--使用收集的数据改进设计过程。除了查看SCADA收集的数据外，还应使用其他数据收集技术。-更准确地模拟土壤-结构相互作用-这与上文所述的PISA项目有关。-更好地理解涡轮机中的整体结构阻尼-整体结构阻尼是总阻尼减去空气动力阻尼。目前，很难准确确定单个阻尼对整体阻尼的贡献，特别是在运行期间(Kallehad等人，2015)。这项研究属于EPSRC Energy主题，由Mott MacDonald赞助。

I. The Pile Soil Analysis (PISA) projectThe Pile Soil Analysis project is a joint industry initiative which is run by the Carbon Trust's Offshore Wind Accelerator program. The aim of PISA is to investigate and develop 'improved design methods for laterally loaded piles, specifically tailored to the offshore wind sector' (University of Oxford, n.d.).Currently monopiles used in offshore winds applications are designed following the guidance found in (API, 2010) and (DNV, 2014), which were written many decades ago for use in the oil and gas industry,where piles are long and slender and do not experience large lateral loads. The issue is that piles designed for offshore wind applications have much larger diameters and are significantly shorter as theyneed to resist larger lateral loads, resulting in an overly conservative pile being built with the soil response being altered from what was expected.The PISA project has carried out 'large scale field tests' onshore to gather data (Byrne, et al., 2015). The locations were chosen such that the soil was similar to that found in the North Sea. In order to validatethe results of the field tests, computational analyses were carried out at Imperial College London (Zdravkovic, et al., 2015). The design methodology report is to be handed over to industry at the start of2016.In order to gain a better understanding of soil response with respect to laterally loaded piles further computational modelling is required. Other areas which may be looked at include foundation response:- depending on the wider parameter space- in layered soils, made up of both clay and sand-under varied loading.The modelling will be carried out either using Imperial College Finite Element Program (ICFEP) or another commercial software e.g. AbaqusFEA. The soil will be modelled as a 'constitutive soil' similar tothe method carried out by Zdravkovic, et al. (2015).II. Continuous real time heath structural monitoringThe majority of the turbines that have been built have a basic data collection system in the rotor assembly called the Supervisory Control And Data Acquisition (SCADA). This data includes a range of different variables ranging from wind speed to oil temperature (Antoniadou, et al., 2015). The data also includes acceleration of the turbine from which it is possible to calculate the fundamental frequency of the structure. A recent study carried out in the Duddon Sand Offshore Wind Farm has found that there is a significant difference between the designed and the actual fundamental frequency for the wind turbines. The consequence of underestimating the fundamental frequency is that this allows for the possibility of increasing the operational lifetime of the structure. Another study looking at a single wind turbine in theWalney Offshore Wind Farm showed the potential increase in the operational lifetime of the structure to be 88% (Kallehave, et al., 2015)In order to further improve the optimization of wind turbines and allow monopoles to be used in locations with greater confidence the following areas will require further research:- Improve design with the use of measurements - where the design process is refined using data that is gathered. In addition to looking at the data that is gathered with the SCADA, other data collection techniques should be utilised.- More accurate modelling of the soil-structure interaction - this is related to the PISA project see above.- Improved understanding of overall structural damping in the turbine - overall structural damping is the total damping minus the aerodynamic damping. Currently there is difficulty in accurately determining the individual damping contributions to the overall damping, especiallyduring operation (Kallehave, et al., 2015).The research falls within the EPSRC Energy theme and is sponsored by Mott MacDonald.