Experimental studies of rip current systems induced by the intersecting waves near a groin
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摘要: 裂流是狭窄而集中的离岸方向水流,对海岸水底变形、物质输移和游泳者安全有重要影响。波浪在垂直海岸建筑物(如丁坝、航道挡沙堤等)上产生的反射会导致沿岸驻波,在驻波节点区域由于波高很小会产生裂流,这是海岸出现裂流原因之一。本研究通过物理模型实验给出了沙坝海岸上建筑物附近裂流系统不同于开敞水域交叉波裂流系统的特征,讨论了波高沿岸变化对裂流系统的各裂流单元流量平衡的影响。结果表明:建筑物的存在引起了沙坝和海岸之间背离建筑物方向的沿岸流动,这导致了裂流系统中各裂流单元之间存在着流量的交换,对各单元裂流流量大小和分布产生了直接影响;各单元侧向流流量对裂流的贡献依赖于单元距建筑物的距离。Abstract: Rip currents are narrow and concentrated seaward-directed flows and play an important role on coastal morphodynamics, mass transport and swimmer safety. As the intersecting wave field caused by wave reflection of coastal structures is not uniform alongshore, the flow characteristics and spatial distribution of rip currents are different from those of uniform intersecting waves on an open coast. The reflection of waves on cross-shore coastal structures will lead to longshore standing waves, and rip currents will occur in the area of standing wave nodes because of the small wave height, which is one of the generation mechanisms for rip currents. In this study, the characteristics of rip current systems near a coastal structure on a barred beach are given by a laboratory experiment. The influence of the longshore variation of wave height on the flow balance of each rip current unit is discussed. The results showed that the existence of structure drives a longshore current away from the structure and causes the water exchange between each rip current unit. The lateral currents between rip current units are found to make contributions to the rip current transport of each rip current unit and the contributions mainly depend on the relative position of the unit to the structure.
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Key words:
- rip current system /
- intersecting waves /
- barred beach /
- coastal structures /
- physical experiments
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图 9 坝顶波高Hbar(a)和破碎点处波高Hb(b)沿岸变化(波况RH2)
○:测量值; —:插值后的曲线。b中也标出了各节、腹点测量的破碎点位置xb
Fig. 9 The alongshore variation of wave height at bar crest (a) and maximum wave height at breaking point (b) (Case RH2)
○: Measured data; —: interpolated curves. The locations of breaking point xb at the node and anti-node lines are also given in b
图 11 各裂流单元上流量成分直方图(波况RH2)
Qrip:裂流流量;Qon:向岸环流流量;Ql:侧向流流量;Qr:水滚流量;Qs:Stokes质量输移流流量
Fig. 11 The histogram of flow transport for each rip current unit (Case RH2)
Qrip: rip current transport; Qon: onshore Eulerian transport; Ql: lateral current transport; Qr: surface roller transport; Qs: Stokes mass transport
表 1 实验波况
Tab. 1 Wave parameters of experiment
波况 周期T /s 入射波高Hi /cm RH1 1.5 2.61 RH2 1.5 4.16 RH3 1.5 5.87 -
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