Mooring analysis and design for offshore WEC survivability and fatigue (MoorWEC)

全球波浪能的潜在平均功率略低于风能，但到目前为止还没有得到开发。这里我们关注的是近海的波能转换器(WEC)，在能源被浅水效应减少之前，它将适合于电网规模的发电。单个WEC的容量被认为比风力涡轮机小得多，而能源成本(COE)要大得多。然而，对于多模式、多浮子系统，在某些位置的容量可能类似于或大于风，而COE估计类似于海上风能。需要建立在极端海浪中的生存能力，以及部件的可靠性。系泊是海上波能转换器中最脆弱的结构部件。在极端波浪和影响疲劳的中间波浪中，冲击载荷是一个特别的问题。在波浪能源界有一个广泛的共识，即系泊系统的设计和建模是需要克服的主要挑战。虽然传统海洋工程应用的文献和设计指南很多，但总的来说，它们没有考虑到波能转换的要求，即系泊不应抑制平台运动导致的能量产生。系泊系统的设计、优化和评估需要高效的水动力和动力系泊模型，它们应该完全耦合以表示所有的相互作用。有多种系泊选择：悬链式松弛系泊、弹性拉紧系泊、单点(浮标)系泊组合，以及尼龙/聚酯绳索提供了一种经济的选择，同时减少了卡扣载荷。虽然点吸波体的非线性水动力WEC加载模型已经取得了一些进展，但目前还没有一个有效的考虑波浪破碎的多体非线性水动力加载模型。计算流体动力学(CFD)模拟需要在多个处理器上运行数天甚至数周，对于复杂的动力学问题是不可靠的。这里的目的是通过包括由波浪中的压力场引起的完全非线性的力分量，即众所周知的弗劳德-克雷洛夫力，来推广有效的线性水动力载荷模型。这改善了对响应和系泊载荷的预测，在某些情况下尤其明显。这将通过与实验波盆测试进行比较来推进，并通过系统识别来正式推广，适用于具有代表性的、通常是多方向的波场和水流中具有一系列系泊配置的单体和多体。还将利用由系统识别确定的修正力公式来评估线性波输入的方便简化。这些力公式将与考虑动态和材料特性的通用行业标准系泊模型Oraflex相结合，从而使用多目标遗传算法进行设计优化。这将使生存能力、疲劳和可靠性分析成为可能。

Wave energy globally has potential average power slightly less than wind but this has been unexploited to date. We are concerned here with wave energy converters (WECs) offshore, before the energy resource is reduced by shallow-water effects, which would be suitable for grid scale electricity generation. Individual WEC capacity has been considered to be much smaller than for wind turbines and cost of energy (COE) considerably larger. However, with multi-mode, multi-float systems, capacity may be similar to or greater than wind in some locations and COE has been estimated to be similar to offshore wind. Survivability in extreme waves needs to be established, along with reliability of components. The mooring is the most vulnerable structural component of an offshore wave energy converter. Snap loads are a particular problem in extreme waves, and also in intermediate waves affecting fatigue. There is a widespread consensus in the wave energy community that mooring system design and modelling is a major challenge that needs to be overcome. Although literature and design guidelines for conventional ocean engineering applications are abundant, in general they do not account for the requirements of wave energy conversion, where the mooring should not inhibit platform motion causing the energy generation. Design, optimization, and assessment of mooring systems require efficient hydrodynamic and dynamic mooring models, which should be fully coupled to represent all interactions. There are various mooring options: catenary slack moored, elastic taut moored, combinations with single point (buoy) moorings, and nylon/polyester ropes offer an economic option while reducing snap loads. While some progress has been made with nonlinear hydrodynamic WEC loading models for point absorbers, an efficient general nonlinear hydrodynamic loading model for multi-bodies, accounting for wave breaking, is presently not available. Computational fluid dynamics (CFD) simulations require days, even weeks, to run on multiple processors and is unreliable for complex dynamic problems. The intention here is generalise efficient linear hydrodynamic load models by including the fully nonlinear force component due to the pressure field in the waves, known as the Froude-Krylov force. This has improved predictions of response and mooring load, markedly in some cases. This will be advanced through comparison with experimental wave basin tests and formally generalised through system identification, for single and multi-bodies with a range of mooring configurations in representative, generally multi-directional wave fields and currents. The convenient simplification of linear wave input will also be assessed with a revised force formulation determined by system identification. These force formulations will be coupled with the general industry-standard mooring model Orcaflex accounting for dynamic and material properties enabling design optimization using multi-objective genetic algorithms. This will enable survivability, fatigue and reliability analyses.