There is a lack of research in the existing literature regarding the scour around foundations for offshore wind turbines under tidal currents, which primarily relies on laboratory experiments with simplified flow velocity hydrographs like square tidal currents. To improve the prediction accuracy of scour development under tidal currents, a series of experiments were conducted to investigate the local scour process around a pile foundation under two typical tidal velocity hydrographs (sinusoidal and square tidal currents) in a specially designed fluid-structure-soil coupling flume. The results demonstrate that reciprocating tidal currents lead to a continuously evolving process of sediment erosion and backfilling around the pile. Although the shapes of the scour holes are similar between sinusoidal and square tidal currents, there are significant differences in the evolving process of the scour depth, presenting a short-platform shape and serrated shape, respectively. A consistent relationship is found between the dimensionless scour depth and the dimensionless effective flow work (DFW) under both tidal and unidirectional currents. An equivalent velocity expression for sinusoidal and square tidal currents is proposed and verified using existing experimental data. Furthermore, an empirical expression for the scour depth reduction coefficient between square tidal currents and unidirectional currents is proposed. These outcomes not only establish a theoretical approach for simplifying tidal currents hydrographs in laboratory experiments, but also provide practical guidance for assessing the tidal currents-induced scour development around pile foundations for in-situ offshore wind turbines.

中文翻译：

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潮流引起的桩基周围冲刷发展：流速过程线的影响

现有文献中缺乏关于潮汐流作用下海上风电机组基础周围冲刷的研究，主要依赖于实验室实验，采用简化的流速过程线（如方形潮汐流）。为了提高潮流下冲刷发展的预测精度，在特殊设计的流体-结构-土中，进行了一系列实验，研究了两种典型潮流速度过程线（正弦和方形潮流）下桩基周围的局部冲刷过程。耦合水槽。结果表明，往复的潮流导致桩周围沉积物侵蚀和回填的过程不断演变。虽然正弦潮流和方潮流的冲刷孔形状相似，但冲刷深度的演变过程却存在显着差异，分别呈现短台状和锯齿状。在潮汐流和单向流下，无量纲冲刷深度与无量纲有效流动功（DFW）之间存在一致的关系。提出了正弦和方潮流的等效速度表达式，并使用现有的实验数据进行了验证。此外，还提出了平方潮流和单向潮流之间冲刷深度折减系数的经验表达式。这些成果不仅为简化实验室实验中的潮流过程线建立了理论方法，而且为评估现场海上风力涡轮机桩基周围潮流引起的冲刷发展提供了实践指导。