EXTREME WAVE LOADING ON OFFSHORE WAVE ENERGY DEVICES USING CFD: A HIERARCHICAL TEAM APPROACH

海上波浪能装置的一个主要设计考虑因素是极端波浪载荷下的生存能力。本项目的目的是使用CFD（计算流体动力学）来预测两个漂浮式波浪能装置在极端波浪中的载荷和响应，其中包括流体粘性、波浪破碎以及Navier-Stokes方程和连续性方程的完全非线性。将考虑两类设备：Pelamis（Ocean Power Delivery Ltd.），该原型已经成功地将电力输送到电网中，以及一个浮动浮标装置，称为曼彻斯特Bobber（曼彻斯特大学），正在以1/10的比例进行测试。这两类设备被认为与其他可再生能源具有竞争力，在经济上大致相当于陆上风能。计算流体动力学模拟将通过三种方式进行：通过商业代码、CFX和COMET（STAR-CD）;通过最近的先进表面捕获代码;以及通过新颖的SPH（平滑粒子流体动力学）方法。为了解决计算流体动力学方法中的不确定性，如预测的准确性和所需计算机资源的数量，将采用逐步增加计算机需求的分层方法：数学公式（从无粘性单流体到双流体粘性/湍流方法）;波描述（从规则的周期性到包括NewWave在内的聚焦波群）;以及结构的复杂性（从平行于波峰的固定水平圆柱到Pelamis的六个自由度）。在每个阶段，数值计算结果将与实验数据进行比较。因此，将对极端条件下的无粘性与粘性公式、波浪非线性、非破碎与破碎条件以及物体动态响应的重要性进行评估。因此，应更好地评估生存能力设计。由此产生的计算流体力学方法也将有利于分析极端波浪与船舶，其他海上车辆和结构的相互作用。例如，与畸形波的相互作用和“绿色”水的问题还有待解决。

A major design consideration for offshore wave energy devices is survivability under extreme wave loading. The aim of this project is to predict loading and response of two floating wave energy devices in extreme waves using CFD (computational fluid dynamics), in which fluid viscosity, wave breaking and the full non-linearity of Navier-Stokes and continuity equations are included. Two classes of device will be considered: Pelamis (of Ocean Power Delivery Ltd.), the prototype having already successfully generated electricity into the grid, and a floating buoy device responding in heave, known as the Manchester Bobber (Manchester University), which is being tested at 1/10th scale. Both classes of device are thought to be competitive with other renewable energy sources, being economically roughly equivalent to onshore wind energy. The CFD simulations will be undertaken in three ways: by commercial codes, CFX and COMET (STAR-CD); by recent advanced surface-capturing codes; and by the novel SPH (smoothed particle hydrodynamics) method. In order to address the uncertainties in the CFD approaches, such as the accuracy of prediction and the magnitude of computer resources required, a staged hierarchical approach of increasing computer demand will be taken in: mathematical formulation (from an inviscid single fluid to a two-fluid viscous/turbulence approach); wave description (from regular periodic to focussed wave groups including NewWave); and complexity of structure (from a fixed horizontal cylinder parallel to wave crests to the six degrees of freedom of Pelamis). At each stage, numerical results will be compared with experimental data. The significance of the inviscid v. viscous formulations, wave nonlinearity, non-breaking v. breaking conditions, and the dynamic response of the body will thus be assessed for extreme conditions. Designs for survivability should thus be better evaluated. The resulting CFD methodology will also benefit analysis of extreme wave interaction with ships, other marine vehicles and structures in general. For example interaction with freak waves and the 'green' water problem have yet to be resolved.