In this numerical study, sediment transport and bed evolution in the surf zone under plunging breakers are investigated; this is a challenging topic that involves complex hydrodynamics coupled with sediment dynamics. Here, a Eulerian–Eulerian multi-phase model for sediment transport, with the capability to capture the free surface, is used. Waves are generated using an open-source toolbox ‘waves2foam’, based on a relaxation method. The model is validated with published experimental results in three cases: (i) surf-zone hydrodynamics over a sloped-rigid bed, (ii) suspended sediment concentration over a sloped-sediment pit, and (iii) bed profile change of a sloped-mobile bed. The profiles of time-averaged velocity, concentration, sediment fluxes, and the time series of concentration are presented. The numerical results suggest that the undertow plays a key role in offshore sediment transport. The instantaneous flow fields show that the vortices under plunging breakers roll up the sediment layers originally near the bed; in such an event, the buoyancy provides a centripetal force to sediment particles. The vortices further transport the suspended sediment onshore and cause strong mixing in water column. This is marked as the underlying mechanism for significant wave-driven flux in the surf zone.

在这项数值研究中，研究了冲入式破碎机下海浪带的泥沙输移和河床演化；这是一个具有挑战性的主题，涉及复杂的流体动力学和沉积物动力学。在这里，使用了能够捕获自由表面的欧拉-欧拉多相沉积物输运模型。波浪是使用基于松弛方法的开源工具箱“waves2foam”生成的。该模型在三种情况下通过已发表的实验结果进行了验证：（i）倾斜刚性床上的冲浪带流体动力学，（ii）倾斜沉积物坑上方的悬浮沉积物浓度，以及（iii）倾斜的床剖面变化 -移动床。给出了时间平均速度、浓度、沉积物通量和浓度时间序列的剖面。数值结果表明暗流在近海沉积物输送中起关键作用。瞬时流场表明，下沉式破碎机下的涡旋卷起原来靠近床层的沉积层；在这种情况下，浮力为沉积物颗粒提供了向心力。涡流进一步将悬浮的沉积物输送到岸上，并在水柱中引起强烈的混合。这被标记为海浪区显着波浪驱动通量的潜在机制。涡流进一步将悬浮的沉积物输送到岸上，并在水柱中引起强烈的混合。这被标记为海浪区显着波浪驱动通量的潜在机制。涡流进一步将悬浮的沉积物输送到岸上，并在水柱中引起强烈的混合。这被标记为海浪区显着波浪驱动通量的潜在机制。