CableDyn: Subsea Power Cable Dynamics Under Complex Ocean Environment

预计未来浮动海上风力涡轮机（FOWT）部署将增加，并且展望未来10年全球将建造6.2 GW的FOWT（https：//tinyurl.com/camyybxk）。高度动态的自由悬挂电力电缆将这些FOWT产生的电力输送到变电站和陆上电网。考虑到这些电缆的安装和更换非常昂贵，并且涡轮机电力输出的任何停机时间都会导致巨大的收入损失，因此这种电力电缆的安全关键设计是极其重要的，以便使它们在海洋中无故障地运行。在FOWT中，从浮式基础的基部到海床的大长度的电力电缆直接暴露于由海浪、水流和湍流引起的动态载荷。波浪移动浮动基础，水流产生由旋涡脱落产生的电缆振荡。在水柱中，缆索经受增强的动态载荷并经历复杂的运动。当动态电缆安装在深水中时，电缆的上部暴露于高机械负载和疲劳，并且下部暴露于相当大的静水压力。浮式基础在纵荡、摇摆和垂荡中的运动导致电力电缆经历振荡运动，这反过来又促进涡激振动（VIV）-这类似于海上石油和天然气平台中使用的长海洋电缆所经历的振动。结果，电缆的大的和复杂的偏转发生在沿其长度的各个位置沿着，改变其机械性能和强度，并最终导致疲劳引起的故障。动态力产生缆索的周期性运动，并且在这些运动和载荷朝向刚性连接点集中的情况下，预期缆索刚度的急剧转变。重复上述过程和过度弯曲也会导致电缆的疲劳损坏。到目前为止，几乎没有任何研究已经进行调查的三维性质的涡激振动，动态载荷，和运动的电力电缆受到组合波，流和湍流。此外，在海上风电行业的设计标准中没有给出关于如何预测、评估和抑制波浪-水流-湍流条件下动态电缆疲劳失效的详细指导。本基础研究旨在探讨海底电缆在三维波浪、海流和湍流共同作用下的动力载荷、运动响应、涡激振动的影响及其抑制机理、疲劳破坏等问题。这项研究将接近电力电缆的响应的数值和物理模型。将在爱丁堡大学的FloWave波流设施中对电力电缆的比例模型进行受控实验测试，在该设施中可以产生幅度，频率和方向的各种组合的多向波和电流。先进的新型唯象尾流振荡器模型，校准和FloWave实验结果验证，将用于模拟电力电缆的流体动力学行为。由此产生的软件工具，实验数据，电缆动力学和涡激振动特性的分析技术，疲劳分析建立的方法，以及本研究的其他成果将提高成本效益的电力电缆的设计。通过减少不确定性，我们的研究将提高海上电力电缆的可靠性，有利于电力电缆制造业。

Floating offshore wind turbine (FOWT) deployments are predicted to increase in the future and the outlook is that globally, 6.2 GW of FOWTs will be built in the next 10 years (https://tinyurl.com/camyybxk). Highly dynamic, free hanging power cables transport power generated by these FOWTs to substations and the onshore grid. Safety critical design of such power cables in order for them to operate in the ocean without failure is of utmost importance, given that these cables are highly expensive to install and replace and any down-time of turbine electrical output results in huge revenue loss. In FOWTs, a large length of the power cable, from the base of the floating foundation to the seabed, is directly exposed to dynamic loading caused by ocean waves, currents, and turbulence. Waves move the floating foundation, and currents produce cable oscillations generated by vortex shedding. In the water column a cable experiences enhanced dynamic loads and undergoes complicated motions. When a dynamic cable is installed in deep water, the upper portion of the cable is exposed to high mechanical load and fatigue, and the lower part to substantial hydrostatic pressure. Motion of the floating foundation in surge, sway, and heave causes the power cable to undergo oscillatory motions that in turn promote vortex-induced vibration (VIV) - which is analogous to the vibration experienced by long marine risers used in offshore oil and gas platforms. As a result, large and complex deflections of the cable occur at various locations along its length, altering its mechanical properties and strength, and eventually leading to fatigue-induced failure. The dynamic forces produce cyclical motions of the cable, and a sharp transition in cable stiffness is expected in cases where these motions and loads concentrate toward a rigid connection point. Repetition of the foregoing process and over-bending can also lead to fatigue damage to the cable. To date, hardly any research has been undertaken to investigate the 3-dimensional nature of VIV, dynamic loads, and motion of power cables subject to combined waves, currents, and turbulence. Moreover, no detailed guidance is given in design standards for the offshore wind industry on how to predict, assess, and suppress fatigue failure of dynamic cables under wave-current-turbulence conditions. Power cable failure is much more likely to occur if the design of such cables is based on poor understanding of the hydrodynamic interactions between cables and the ocean environment.This fundamental scientific research aims to investigate the dynamic loading, motion response, impact of vortex induced vibration and its suppression mechanism, and fatigue failure of subsea power cables subjected to combined 3-dimensional waves, currents, and turbulence. This research will be approached by both numerical and physical modelling of power cable's response. Controlled experimental tests on scale models of power cables will be undertaken in Edinburgh University's FloWave wave-current facility where multi-directional waves and currents of various combinations of amplitudes, frequencies, and directions can be generated. Advanced novel phenomenological wake oscillator models, calibrated and validated with FloWave experimental results, will be used to simulate the hydrodynamic behaviour of power cables. The resulting software tools, experimental data, analysis techniques for characterising cable dynamics and VIV, methodologies established for fatigue analysis, and other outcomes of this research will enhance the design of cost-effective power cables. By reducing uncertainty, our research will lead to increased reliability of offshore power cables, of benefit to the power cable manufacturing industry.