Cross‐shore migration of lunate megaripples during Duck94
Cross‐shore migration of lunate megaripples during Duck94
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Duck94 期间月状巨波纹的跨岸迁移
DOI：
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
A. Hay
中科院分区：
文献类型：
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作者：
A. Ngusaru;A. Hay
[1]在Duck 94近岸动力学试验期间，在沿岸流较弱（<20 cm/s）的时间段内，从两次风暴事件中对月状巨水怪迁移进行了远程声学观测。在这些时期，显着的波轨道速度为50-80厘米/秒; megaripple高度为0.05-0.5米; megaripple角指向岸边;波峰到波谷的斜率向岸边前进的涟漪面接近休止角;和迁移速度为10-40厘米/小时岸上。观测结果还表明，当第二场风暴期间的平均离岸流量超过20厘米/秒时，巨水纹停止了，并可能已经开始向离岸迁移。应力为基础的推移质输沙模型是适度成功的预测所观察到的依赖性迁移速度测得的流体速度分为零（平均电流），重力波，海和膨胀波频带。波浪和平均流摩擦系数，fw和fc，通过预测和观察到的迁移速度之间的最佳拟合，两个选择（3/2和5/2）的应力指数在推移质输运模型的一部分。净输运是使用从游程统计和逐波确定的波速振幅计算的。改进的协议与观测获得的波波的净运输预测和类波处理的亚重力带。协议的水平对价格的价值相对不敏感。当λ = 5/2和3/2时，最佳拟合的海流和波浪摩擦系数值分别为fc = 4.3 × 10−3和8.0 × 10−3，fw = 1.7 × 10−2和4.8 × 10−2。
[1] Remote acoustic observations of lunate megaripple migration are presented from two storm events during the Duck94 nearshore dynamics experiment for time periods during which longshore currents were weak (<20 cm/s). During these periods, significant wave orbital velocities were 50–80 cm/s; megaripple heights were 0.05–0.5 m; megaripple horns were directed shoreward; the crest-to-trough slope of the shoreward advancing ripple face was close to the angle of repose; and migration speeds were 10–40 cm/h onshore. The observations also indicate that the megaripples stalled, and may have begun to migrate offshore, when the mean offshore flow exceeded 20 cm/s during the second storm. Stress-based bed load sediment transport models are moderately successful in predicting the observed dependence of migration velocity on measured fluid velocities separated into zero (mean current), infragravity wave, and sea-and-swell wave frequency bands. Wave and mean current friction factors, fw and fc, are obtained by best fit between the predicted and observed migration velocities, for two choices (3/2 and 5/2) for the stress exponent ξ in the bed load transport part of the model. Net transport is computed using wave velocity amplitudes determined from both run length statistics and wave by wave. Improved agreement with observations is obtained for the wave-by-wave net transport predictions and for the wave-like treatment of the infragravity band. The level of agreement is relatively insensitive to the value of ξ. The best fit current and wave friction factor values, for ξ = 5/2 and 3/2 are fc = 4.3 × 10−3 and 8.0 × 10−3 and fw = 1.7 × 10−2 and 4.8 × 10−2, respectively.