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

在深水近海，系泊系统对系统总成本的贡献很大。虽然对于利润非常大的海上石油和天然气行业来说，这可能不是一个引人注目的问题，但对于FOWT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能力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海岸附近浅水区的枯竭，项目将需要从海岸和更深的水域进一步开发，这将带来更大的技术挑战，并限制降低成本的努力。目前有许多浮式风力涡轮机概念正在开发中，但在现阶段，由于正在提出和研究其他想法，因此对于哪种概念最有可能在未来以工业规模部署，没有明确的偏好。必须清楚地了解恶劣环境下的结构行为，并考虑可持续、可靠和具有成本效益的系泊和锚系统。这意味着，重要的是要证明如何利用系统的系泊、锚定和电缆元件，以提高风电场的平准化能源成本（LCOE）和生命周期。因此，有必要提高对这些因素的理解，以推动大规模的发展。本项目集中于开发可靠的方法来解决系泊缆的静态和动态响应，以研究如何根据定位系泊系统设计和施工的技术要求和指南将这些知识转移到系泊系统的设计中。本研究将使用现实的海洋数据（波浪、风、流和岩土），其代表适合于100多个浮动风力涡轮机的风力发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，可以借鉴领先这一概念的行业的经验，以建立FOWT的基本案例设计。系泊系统的关键元件包括悬链线和具有断开能力的半张紧系泊缆、顶部加载吸力桩和锚处的张紧系泊缆，以研究系泊系统和平台动力学的耦合动力学。更好地估计极限力和疲劳载荷分布将能够找到更现实的，从而更经济的安全系数，以满足可接受的故障概率。以下是该项目过程中提出的新的和创新的方面的简短总结。数值研究了不同类型的10MW FOWT系统在不规则波条件下的动态行为，通过在系统上施加组合的空气动力学、水动力学和水流力来面对非定常风。将对一系列操作条件进行耦合分析，并评价系统在生存条件下的安全性。- 通过对材料特性、系泊布局和锚特性及其对关键部件疲劳寿命的影响等各个关键方面进行全面调查，确定FOWT的优化系泊配置。调查对称和非对称系泊系统，以评估故障情况下的关键安全问题，特别是对于密集排列和共用锚的情况。应用FOWT设计优化的分析方法，旨在研究各种设计约束（特征频率，极端载荷和疲劳载荷约束）对结构设计和性能优化过程的详细影响。进行10MW FOWT完整系统的实验模型试验，包括非定常风、不规则波和流力。

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.