Fully nonlinear investigation on energy transfer between long waves and short-wave groups over a reef
Fully nonlinear investigation on energy transfer between long waves and short-wave groups over a reef
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DOI：
10.1016/j.coastaleng.2022.104240
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发表时间：
2022-10
影响因子：
4.4
通讯作者：
Ye Liu;Yueying Yao;Zhiling Liao;Shaowu Li;Chi Zhang;Q. Zou
中科院分区：
文献类型：
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作者：
Ye Liu;Yueying Yao;Zhiling Liao;Shaowu Li;Chi Zhang;Q. Zou
长波在短波群冲滩和冲礁过程中被放大，对海岸淹没、结构稳定和泥沙输移有重要影响。本文利用非静力模式SWASH对模拟结果进行完全非线性分析，研究了长波与短波群能量交换的跨礁变化。其目的是阐明机制下的非线性短波群强迫下的长波转换的珊瑚礁，并评估在这个问题中的线性和弱非线性分析的简化的后果。短波和长波之间的能量传递是波辐射应力对长波所做的功，它是辐射应力梯度和长波速度的乘积。与传统的线性和弱非线性分析不同，全非线性分析中考虑了Stokes输运和局部水深的长波调制。结果发现，只有长波能量通量梯度预测的完全非线性分析所做的工作，由波辐射应力在浅礁平衡。完全非线性分析表明，严格的质量守恒必须使用适当的长波速度提取。相反，在线性和弱非线性分析中，长波速度是从单点速度测量中提取的。完全非线性分析表明，来波断点强迫长波的产生和增长克服了碎波带中束缚长波的耗散，导致来波长波能通量的放大。这一现象甚至发生在短波主要破碎在水平的礁滩与大淹没，表明长波的演变不是局部控制，而是依赖于波的空间演化历史。由于大量的能量转移到传入的短波，尽管它们都是自由波，但在前礁的去浅滩过程中，传出的断点强迫长波被大量消散。在断点处的所有频率上都发生了长波和短波的相位耦合，这是能量传递的主要驱动机制。根据完全非线性分析，礁滩淹没可能以复杂的方式影响长波，即，减小淹没度可以增强短波向长波的能量传递，或者同时通过增加长波的摩擦耗散来抑制长波的增长。
Long waves are amplified as short-wave groups shoal and break over reefs, therefore, having significant impacts on coastal inundation, structure stability, and sediment transport. This study investigated the cross-reef variation of long-wave energy exchange with short-wave group over a reef using fully nonlinear analysis of simulation results by the non-hydrostatic model SWASH. The objective was to elucidate the mechanisms of long-wave transformation under nonlinear short-wave group forcing over a reef, and to assess the consequences of simplifications in linear and weakly nonlinear analyses in this problem. The energy transfer between short and long waves is the work done by wave radiation stress on long waves, which is the product of radiation-stress gradient and long-wave velocity. Unlike conventional linear and weakly nonlinear analysis, the Stokes transport and long-wave modulation of local water depth are included in the fully nonlinear analysis. It was found that only the long-wave energy flux gradient predicted by the fully nonlinear analysis was balanced by the work done by wave radiation stress over a shallow reef. The fully nonlinear analysis showed that strict mass conservation has to be used to extract long wave velocity properly. In contrast, in linear and weakly nonlinear analysis, the long-wave velocity is extracted from single-point velocity measurements. The fully nonlinear analysis demonstrated that the generation and growth of incoming breakpoint-forced long waves overcame the dissipation of bound long waves in the surf zone, leading to amplification of incoming long-wave energy flux. This phenomenon occurred even when short waves mainly broke over the horizontal reef flat with large submergence, indicating that long-wave evolution is not locally controlled but dependent on wave spatial evolution history. Outgoing breakpoint-forced long waves were dissipated considerably during de-shoaling over the forereef due to substantial energy transfer to incoming short waves, though both of them are free waves. The phase coupling between outgoing long waves and incoming short-wave groups occurred at all frequencies at the breakpoint, which was found to be the main driving mechanism for the energy transfer. According to the fully nonlinear analysis, the reef-flat submergence may affect the long wave in a complex fashion,i.e., reducing the submergence may enhance the energy transfer from short waves to long waves or suppress long-wave growth by increasing its frictional dissipation at the same time.