Numerical simulations were conducted to investigate steady current scour around rectangular and square subsea caissons. The caissons, which are representative of subsea structures, have a submerged height ranging from 0.5 to several times their longest base dimension. The flow model used is based on the Reynolds Averaged Navier-Stokes equations, and the scour model simulates bed load and suspended load transport to predict the evolution of the seabed profile. The aim of this study is to investigate the mechanisms of local scour, specifically the contribution of the horseshoe vortex and the local streamline contraction near the caisson corners to local scour. The model is validated through comparisons with experimental measurements, indicating reasonable agreement. Based on the numerical model results, the mechanisms of local scour around square and rectangular caissons are found to be qualitatively similar. If the flow is directed perpendicular to one of the caisson faces, both the horseshoe vortex and the local streamline contraction contribute to scour. The maximum scour depth is located at the two upstream corners of the caisson due to the combined effects of the horseshoe vortex and streamline contraction. When the flow approaches the caisson with a diagonal attack angle of 45°, the two upstream faces act like a streamlined wedge that splits the incoming flow. The study found that the horseshoe vortex almost disappears and the scour is primarily caused by the local velocity amplification at the two side corners. If the flow attack angle is 45°, the scour does not initiate near the upstream corner without the contribution from the horseshoe vortex. These findings are expected to serve as a valuable theoretical foundation for the design of scour protection.

中文翻译：

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稳态水流条件下矩形、方形海底沉箱周围局部冲刷研究

通过数值模拟研究了矩形和方形海底沉箱周围的稳态水流冲刷。沉箱是海底结构的代表，其水下高度为最长基础尺寸的 0.5 至几倍。所使用的流动模型基于雷诺平均纳维-斯托克斯方程，冲刷模型模拟底床载荷和悬浮载荷传输，以预测海底剖面的演变。本研究的目的是研究局部冲刷的机制，特别是马蹄涡和沉箱角部附近的局部流线收缩对局部冲刷的贡献。该模型通过与实验测量的比较进行了验证，表明了合理的一致性。根据数值模型结果，发现方形和矩形沉箱周围的局部冲刷机制在性质上是相似的。如果水流垂直于沉箱面之一，马蹄涡和局部流线收缩都会产生冲刷。由于马蹄涡和流线收缩的共同作用，最大冲刷深度位于沉箱上游两个角部。当水流以 45° 的对角攻角接近沉箱时，两个上游面就像一个流线型楔子，将传入的水流分开。研究发现，马蹄涡几乎消失，冲刷主要是由两侧角部的局部速度放大引起的。如果水流攻角为 45°，则在没有马蹄涡的影响的情况下，冲刷不会在上游角附近开始。这些发现有望为冲刷防护设计提供有价值的理论基础。