Dynamics of Mooring System for Floating Offshore Wind Turbine (FOWT)

在近海深水水域，系泊系统对系统的总成本有很大贡献。虽然对于利润非常巨大的海上石油和天然气行业来说，这可能不是一个令人信服的问题，但对于FOWTs来说，这是一个至关重要的因素，因为实现一个具有成本效益和盈利的系统是开发商面临的主要挑战之一。随着装机容量的增加和近岸浅水场地的枯竭，项目将需要在离海岸更远的地方和更深的水域开发，这将带来更大的技术挑战，并限制降低成本的努力。目前有许多浮风概念正在开发中，但由于其他想法的提出和研究，目前还没有明确的偏好哪个概念最有可能在未来工业规模上部署。在浮式海上风力机的技术开发方面，对结构在恶劣环境中的行为有一个清楚的了解，并考虑一个可持续、可靠和具有成本效益的系泊和锚定系统。这意味着，重要的是展示如何利用系统的系泊、锚定和布线元件，以提高统一能源成本(LCOE)和风力发电场的生命周期。因此，有必要提高对这些因素的理解，以推动大规模的开发。本项目致力于开发可靠的方法来解决系泊系统的静态和动态响应，以检验这些知识是如何根据定位系泊系统的设计和建造的技术要求和指南而转移到系泊系统设计中的。本研究将使用真实的海洋数据(海浪、风、流和岩土)，这些数据代表了适合于100多个浮动风力发电机组的风电场的浅水和深水场地。为了开发降低成本所需的创新技术，可以采用引领这一概念的行业的经验来建立FoWT的基本情况设计。该系泊系统的关键部件包括具有分离能力的悬链线和半张紧系泊索、顶载式吸力桩和锚地张拉系泊索，以研究系泊和平台动力的耦合动力学。更好地估计极限力和疲劳载荷的分布将能够找到更现实的，从而找到更经济的安全系数，满足可接受的故障概率。以下是本项目过程中解决的新的和创新的方面的简短总结。-对不同类型的10 MW FoWT系统在不规则波浪条件下的动态行为进行数值研究，通过在系统上应用气动、水动力和水流的组合作用力来面对非定常风。将对一系列运行条件进行耦合分析，并评估在生存条件下的系统安全性。-通过彻底调查材料特性、系泊布局和锚特性等各种关键方面及其对关键部件疲劳寿命的影响，确定FoWT的最佳系泊配置。-研究对称和非对称系泊系统，以评估发生故障时的关键安全方面，特别是对于紧密排列的阵列和共享锚的情况。-应用FoWT设计优化的分析方法，目的是研究各种设计约束(特征频率、极限载荷和疲劳载荷约束)对结构设计和性能优化程序的详细影响。-对一个10兆瓦的FoWT完整系统进行实验模型测试，包括非定常风、不规则波和海流。

In deep water offshore, mooring systems can contribute significantly to the total cost of the system. Whilst this may not be such a compelling issue with the offshore oil and gas industry where profit is very large, it is vital factor for FOWTs where accomplishing a cost effective and profitable system is the one of the main challenges facing developers. As installed capacity increases and shallow water near shore sites are exhausted, projects will need to be developed further from shore and in deeper water, which will pose greater technical challenges and constrain efforts to reduce costs. There are a number of floating wind concepts currently under development, but there is no clear favourite at this stage with regard to which concept is most likely to be deployed at industrial scale in the future as other ideas are being proposed and investigated.In terms of technology development of floating offshore wind turbine, it is essential to have a clear understanding about the structure behaviour in harsh environment as well as to consider a sustainable, reliable, and cost effective mooring and anchor system. This means, it is important to demonstrate how the mooring, anchoring and cabling elements of the system can be utilized aim for improving levelized cost of energy (LCOE) and the lifecycle of the wind farm. Therefore, there is a need for improved understanding of those factors to drive towards large scale development.This project concentrates on developing reliable methods to solve the static and dynamic response of mooring lines to examine how this knowledge transfers into the design of mooring system in terms of technical requirements and guidelines on design and construction of positioning mooring system.This study will use realistic met-ocean data (wave, wind, current and geotechnical) which represents shallow and deep water sites suitable for wind farms of more than 100 floating wind turbines. In order to develop the innovative technologies required to reduce the cost, experiences from industries leading this concept can be adapted for establishing a base case design of a FOWT. The key elements of the mooring system include catenary and semi taut mooring lines with disconnecting ability, top loaded suction piles and tensioning mooring line at anchor to investigate the coupled dynamics of the mooring and platform dynamics. Better estimation of extreme forces and the distribution of fatigue loads will enable to find more realistic, and thereby more economic safety factors that meet an acceptable probability of failure.The following presents a short summary of the new and innovative aspects addressed in the course of this project.- Numerical investigation of different types of 10MW FOWT system dynamic behaviour in irregular wave conditions, facing unsteady wind by applying combined aerodynamics, hydrodynamic, current forces on the system. Coupled analysis will be conducted for a range of operating conditions and to evaluate system safety in survival conditions. - Identify optimised mooring configurations for FOWT through a thorough investigation of various key aspects such as material properties, mooring layout and anchor properties and their influence on the fatigue life of key components.- Investigate symmetric and asymmetric mooring systems to evaluate critical safety aspects in case of failure, especially for closely spaced arrays and in case of anchor sharing.- Apply analytical methods of FOWT design optimization with the aim to study the detailed influence of various design constraints (eigenfrequency, extreme load and fatigue load constraints) on the structural design and the performance optimization procedure.- Conduct an experimental model test of a 10MW FOWT complete system including unsteady wind, irregular wave and current forces.