Large-scale laboratory observations of turbulence on a fixed barred beach
Large-scale laboratory observations of turbulence on a fixed barred beach
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DOI：
10.1088/0957-0233/16/10/004
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发表时间：
2005-10
影响因子：
2.4
通讯作者：
C. P. Scott;D. Cox;T. Maddux;J. W. Long
中科院分区：
文献类型：
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作者：
C. P. Scott;D. Cox;T. Maddux;J. W. Long
本文介绍了一个大型实验室试验的详细情况，该试验研究了波浪破碎在一个固定的栅栏式海滩上所产生的湍流。数据集包括一个随机和一个规则波情况下的自由表面位移和流体速度的综合测量。每单位质量的时间平均湍流动能的观察表明，由波浪破碎产生的湍流最大的酒吧顶部，并没有完全消散之前到达的床。这表明，即使在时间平均意义上，波浪破碎湍流可能是重要的近床过程。在岸边的酒吧，湍流一般局限于水柱的上部，并已消散，一旦波重组（约1.5波长岸上的酒吧波峰）。在随机波和规则波情况下，湍流结构相同;然而，尽管离岸波浪条件相似，但随机波情况下的幅度要小得多。此外，还采用了三种方法来分离波致速度和湍流速度分量：系综平均、高通滤波和由特罗布里奇（1998 J. Atmos.海洋Technol.15290 -8）。在这些方法中，振幅的变化高达5倍，但从质量上讲，跨岸和垂直结构与所使用的方法无关。差分法与系综平均法在时间平均量的大小和结构以及随时间变化的湍流动能的特征方面密切相关。鉴于这种协议，差分方法似乎是最适合应用于随机波，如在现场观察到的。
The details of a large-scale laboratory experiment to study the turbulence generated by waves breaking on a fixed barred beach are presented. The data set includes comprehensive measurements of free surface displacement and fluid velocity for one random and one regular wave case. Observations of the time-averaged turbulent kinetic energy per unit mass, , show that the turbulence generated by wave breaking was greatest at the bar crest and did not fully dissipate prior to reaching the bed. This indicates that, even in a time-averaged sense, wave breaking turbulence may be important for near-bed processes. Onshore of the bar, turbulence was generally confined to the upper part of the water column and had dissipated once the waves reformed (approximately 1.5 wavelengths onshore of the bar crest). The turbulent structure was the same in the random and regular wave cases; however, the magnitude of was much less in the random wave case, despite similar offshore wave conditions. Additionally, three methods were used to separate the wave-induced and turbulent components of velocity:. ensemble averaging, high-pass filtering and a differencing method proposed by Trowbridge (1998 J. Atmos. Ocean. Technol. 15 290–8). The magnitude of varied by as much as a factor of 5 among these methods, but qualitatively, the cross-shore and vertical structure were independent of the method used. The differencing method agreed closely with ensemble averaging in terms of the magnitude and structure of time-averaged quantities and in the signature of the time-dependent turbulent kinetic energy. Given this agreement, the differencing method appears to be the most suitable for application to random waves, such as those observed in the field.