Abstract A numerical model of scour beneath subsea structures considering the effect of upward seepage in the seabed is proposed. A small seepage can cause significant changes to the hydrodynamic force on the bed surface and stability of bed particles, which can further affect the sediment transport processes and scour patterns around subsea structures. The present model is developed based on a fully-coupled hydrodynamic and morphologic sediment transport model. The unsteady Reynolds-averaged Navier-Stokes (URANS) equations are solved together with the k − ω turbulence closure. In the presence of seepage, the bed friction velocity, the bed shear stress, and the bed load transport rate will be changed as compared to conditions without seepage. The sediment particle stability is also affected and the critical Shields parameter is changed. In the presence of upward seepage forces, the repose angle of the sediment is also reduced. The present model is validated against existing experiments in terms of streamwise flow velocity distribution subjected to upward seepage. The fully-coupled hydrodynamic and morphologic model is validated against existing experiments of scour beneath a pipeline in the live-bed regime and clear-water regime, respectively. The validated model is then applied to investigate the scour development beneath a submarine pipeline subjected to different upward hydraulic gradients. It is found that the equilibrium scour width is increased with a large upward hydraulic gradient. The equilibrium scour depth stays in the range of 0.6–0.8 of the pipeline diameter for the live-bed cases. For the clear-water case, with a large upward hydraulic gradient, the equilibrium scour depth slightly decreases.

中文翻译：

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具有向上渗流作用的海底管道下方冲刷的CFD研究

摘要 提出了一种考虑海底向上渗流影响的海底结构下冲刷数值模型。小的渗流会导致床表面的水动力和床颗粒的稳定性发生显着变化，这会进一步影响海底结构周围的沉积物输送过程和冲刷模式。本模型是基于完全耦合的水动力和形态沉积物输送模型开发的。非定常雷诺平均 Navier-Stokes (URANS) 方程与 k − ω 湍流闭合一起求解。在存在渗流的情况下，与无渗流条件相比，床层摩擦速度、床层剪切应力和床层荷载传输速率将发生变化。沉积物颗粒稳定性也会受到影响，并且临界 Shields 参数会发生变化。在向上渗流作用下，沉积物的休止角也减小。本模型在受向上渗流影响的流向流速分布方面针对现有实验进行了验证。完全耦合的流体动力学和形态模型分别针对现有的活床状态和清水状态下管道下方的冲刷实验进行了验证。然后应用经过验证的模型来研究受到不同向上水力梯度的海底管道下方的冲刷发展。发现平衡冲刷宽度随着大的向上水力梯度而增加。对于活床情况，平衡冲刷深度保持在管道直径的 0.6-0.8 范围内。对于清水情况，向上的水力梯度很大，