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

在深水海上，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油气行业来说，这可能不是一个引人注目的问题，但对于fowt来说，实现成本效益和盈利系统是开发商面临的主要挑战之一，这是至关重要的因素。随着装机容量的增加和近海浅水的枯竭，项目将需要在远离海岸和更深的水域进行开发，这将带来更大的技术挑战，并限制降低成本的努力。目前有许多漂浮风概念正在开发中，但在现阶段，关于哪个概念最有可能在未来以工业规模部署，没有明确的偏爱，因为其他想法正在被提出和研究。在海上浮式风力发电机组的技术开发中，必须明确结构在恶劣环境下的性能，并考虑可持续、可靠、经济的系泊和锚系统。这意味着，重要的是要展示如何利用系统的系泊、锚定和布线元素，以提高能源平准化成本（LCOE）和风电场的生命周期。因此，有必要增进对这些因素的了解，以推动大规模发展。本项目专注于开发可靠的方法来解决系泊线的静态和动态响应，并根据定位系泊系统的设计和建造的技术要求和指南，研究如何将这些知识转移到系泊系统的设计中。这项研究将使用真实的海洋气象数据（波浪、风、水流和岩土），这些数据代表了适合100多个浮动风力涡轮机的风力发电场的浅水和深水地点。为了开发降低成本所需的创新技术，可以将行业领先的这一概念的经验用于建立FOWT的基本案例设计。系泊系统的关键要素包括具有分离能力的悬链线和半紧系泊线、顶载吸力桩和锚固处的张拉系泊线，以研究系泊与平台动力学的耦合动力学。更好地估计极端力和疲劳载荷的分布将能够找到更现实的，从而更经济的安全系数，满足可接受的失效概率。以下是对该项目过程中涉及的新方面和创新方面的简短总结。-对不同类型的10MW FOWT系统在面对非定常风时的不规则波浪条件下的动力学行为进行数值研究，通过对系统施加空气动力学、水动力学和电流联合力。将对一系列操作条件进行耦合分析，并评估系统在生存条件下的安全性。-通过对材料性能、系泊布局和锚的性能及其对关键部件疲劳寿命的影响等各个关键方面的深入研究，为FOWT确定优化的系泊配置。-研究对称和非对称系泊系统，以评估故障情况下的关键安全方面，特别是在紧密间隔阵列和锚共享的情况下。-应用FOWT设计优化的分析方法，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过程的详细影响。-对一个10MW的FOWT完整系统进行了包括非定常风、不规则波浪和水流力的实验模型试验。

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.