Numerical simulation of the hydrodynamic process of rip current hazard
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摘要: 离岸流是近岸流的重要组成部分，当波浪受到特殊海滩地形的影响，会形成一股沿着离岸方向运动的高速水流，能够迅速将人带离海岸，对海滨安全造成威胁。为了深入探究离岸流的形成机理及水动力学特性，本文基于二阶Stokes波浪理论，采用了更为光滑的变截面沙坝模型，通过流体体积法捕捉自由液面，对离岸流进行三维数值模拟探究。本文重点分析了离岸流产生时流场的瞬时速度、时均速度、压强等不同参量的分布规律，结果显示在沙坝和海岸线之间，有一对方向相反的水循环体系；对比不同流层离岸流的速度，了解到波浪与离岸流的耦合作用；并探究了入射波波高对离岸流强度及分布区域的影响，深化了对离岸流水动力学过程的认识。Abstract: Rip current is an important part of nearshore current. Affected by special beach topography, waves will form a high velocity flow moving along the offshore direction, which can quickly take people away from the shore and pose a threat to beach safety. In order to further explore the formation mechanism and hydrodynamics characteristics, three-dimensional numerical simulation of rip current was carried out. In this paper, based on the second-order Stokes wave theory, a typical sandbar model with variable cross-section is adopted and used to generate rip current. The free liquid surface is captured by volume of fluid method. The rip current flow field distribution laws of instantaneous velocity, time-averaged velocity and pressure are analyzed and made some discoveries: there is a pair of opposite water circulation systems between the bar and the shoreline. By comparing the velocity distribution of rip current a different depth, the interaction between waves and rip currents is understood. Furthermore, the influence of incident wave height on intensity and distribution of rip current is also studied, which deepens the understanding of the hydrodynamic process of rip current.
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图 2 可产生离岸流的典型海滩计算模型
Fig. 2 Typical beach calculation model which can produce rip current
图 4 1个周期内离岸方向（X）速度云图
Fig. 4 Velocity cloud distribution of offshore direction (X) velocity in a period
图 5 1个周期内沿岸方向（Z）速度云图
Fig. 5 Velocity cloud distribution of coastal direction (Z) velocity cloud map in a period
图 8 不同等压面上
$\bar u $ 分布Fig. 8 The velocity distribution of
$\bar u $ under different isobaric surfaces
图 9 不同流层
$\bar u $ 随离岸方向变化Fig. 9 The velocity distribution of
$\bar u $ at different flow layer along the offshore direction
图 10 流颈附近
$\bar u $ 随水位变化Fig. 10 The velocity distribution of
$\bar u $ near the neck of ripcurrent varies with the water level
图 11 速度u沿离岸方向X的分布
Fig. 11 The velocity distribution of ualong the offshore direction X
图 13 时均速度
$\bar u $ 在沿岸方向Z的分布Fig. 13 The mean velocity distribution of
$\bar u $ along the coastal direction Z表 1 不同波高的Ursell数
Tab. 1 Ursell number of different wave heights
波高/m 0.25 0.3 0.35 0.4 Ur 5.35 6.42 7.49 8.56 
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