Severe Storm Wave Loads on Offshore Wind Turbine Foundations (SEA-SWALLOWS)

海上结构，包括海上风力涡轮机基础、海洋可再生能源装置支撑结构、桥梁桥墩和浮船，经常暴露在恶劣的环境载荷下。这些因素经常驱动设计。波-结构相互作用的物理和统计是复杂的，并且在最恶劣的条件下仍然没有完全理解强非线性载荷。这个项目的重点是固定的海上风力涡轮机。这些是最有前途的清洁能源之一；也是英国实现碳中和目标的核心。在过去十年中，海上风电的价格大幅下降。这种减少的部分原因是由于技术理解的改进导致不那么保守的设计。最近，有一种趋势是转向更暴露、更深的水域，那里有“更好”的风力资源。然而，这些地点容易受到更极端的浪高和随后更严重的载荷的影响。这些变化增加了波浪荷载模型的重要性，这些模型能够准确地预测基底剪切和弯矩时间序列。重要的是，这些模型不仅预测了载荷的大小，而且还预测了载荷的正确频率含量。例如，一个大的冲击荷载可能持续时间很短，荷载不会简单地传递到基础上。此外，建筑物的设计通常是为了避免风暴波的自然频率。然而，如果载荷发生在基波频率的高次谐波上，这些频率可能与结构的固有频率一致，因此大大增加了它们对设计的重要性。对于结构疲劳评估，需要很长的时间序列。因此，实验和高保真数值模型资源过于密集，无法直接用于实际工程计算。需要一种高效而又足够精确的替代方案。波浪荷载的物理特性通常分为非破断荷载和破断荷载。它们有不同的量级和时间尺度，因为它们受不同的物理现象支配。对于非破碎波，morrison方程传统上被广泛接受为大多数现代设计标准计算海上结构的波浪荷载的起点。对于惯性状态下的细长圆柱体，如用于海上风力的单桩，将波浪运动学作为输入，对莫里森模型进行了扩展。预测波浪的运动本身是一项困难的任务，特别是对于严重而随机的海况，其中标准的规则波流函数理论和二阶随机波理论都是不完善的模型。众所周知，由于流体力学和尺度问题的影响，破碎波很难进行数值模拟和实验测量。人们提出了各种模型来模拟荷载的时程。然而，在计算动力敏感结构的极端响应和基础反应时，通常只需要知道冲击荷载的总施加脉冲（及其作用位置）就足够了，而不是确切的时程。估计脉冲更可靠，更快，物理也更容易建模。我们的目标是利用新颖的流体力学来开发快速降阶工程模型，从而彻底改变海上结构的载荷计算。虽然这项工作的重点是研究极端波浪载荷对海上风力涡轮机基础的影响，但所产生的想法和工具将更广泛地适用。我们将开发一种计算快速的方法和开源工具，供工业实践工程师使用，以模拟长期循环载荷，从而更有效地设计海上结构，降低建筑成本，同时保持功能和可靠性。

Offshore structures, including offshore wind turbine foundations, marine renewable energy device support structures, bridge piers, and floating vessels, are routinely exposed to harsh environmental loads. These frequently drive the design. The physics and statistics of wave-structure interaction are complex and still not fully understood for strongly non-linear loads as experienced in the most severe conditions.The particular focus of this project is fixed offshore wind turbines. These are one of the most promising sources of clean energy; and central to the UK's ambitions to become carbon neutral. The price of offshore wind has fallen significantly over the past ten years. Part of this reduction has been due to improvements in technical understanding leading to less conservative designs. Recently, there has been a trend to move to more exposed and deeper water locations with 'better' wind resources. However, such locations are susceptible to more extreme wave heights and subsequently more severe loading. These changes have increased the importance of wave loading models able to give accurate predictions of base shear and moment time-series. It is important that such models predict not only the magnitude of the load but also the correct frequency content of the loading. For instance, a large slamming load may be of sufficiently short duration that the load is not simply transmitted to the foundation. Further, structures are typically designed so as to avoid the natural frequency of the storm waves. However, if loading was to occur at higher harmonics of the fundamental wave frequencies these may coincide with the structure's natural frequencies, thus greatly increasing their importance for design. For structural fatigue assessment very long time series are required. Therefore, experimental and high-fidelity numerical models are too resource-intensive to be directly useful for practical engineering calculations. A highly efficient yet still sufficiently accurate alternative is required.The physics of wave loading is typically split into non-breaking and breaking loads. These have different magnitudes and timescales as they are dominated by different physical phenomena. For non-breaking waves, traditionally the Morison equation has been widely accepted as the starting point for calculating wave loading on offshore structures by most modern design standards. For slender cylinders in the inertia regime such as the monopiles used for offshore wind, extensions have been made to the Morison model, taking wave kinematics as inputs. Predicting wave kinematics is itself a difficult task, particularly for severe yet random sea-states where both standard regular wave stream function theory and 2nd order random wave theory are imperfect models.Breaking waves are notoriously difficult to model numerically and to measure experimentally due to the violence of the hydrodynamics and scaling issues. Various models have been proposed to simulate the time history of the loading. However, when calculating extreme responses and foundation reactions for dynamically sensitive structures, it is generally sufficient to know the total applied impulse (and where it acts) for impact loads rather than the exact time-history. Estimating the impulse is far more robust, quicker and the physics can more easily be modelled. We aim to revolutionize load calculations on offshore structures using novel fluid mechanics to develop fast reduced-order engineering models. While the focus of this work will be examining the impact of extreme wave loading on offshore wind turbine foundations, the ideas and tools generated will be more broadly applicable. We will develop a computationally fast method and an open source tool to be used by practicing engineers in industry to model long-term cyclic loading, leading to more efficient designs of offshore structures, reducing construction cost whilst preserving function and reliability.