不规则波致沿岸流不稳定运动时空变化研究

Variation of Instabilities of Irregular Waves Induced Longshore Currents in Time and Spatial Domain

基于Morlet小波与沿岸流不稳定运动流速时间历程形态相似的原则,采用Morlet复小波作为基小波,得到沿岸流不稳定运动流速时间历程的小波功率谱,以此分析了1∶100和1∶40平直斜坡不规则波条件下观测到的沿岸流不稳定运动时空变化特性,并分析了坡度对沿岸流不稳定运动时空变化的影响.通过分析各个波况下距岸线不同位置处小波谱能量分布的变化,得到沿岸流不稳定运动随时间、空间的变化特性,同时通过分析在坡度不同其它波况相近的情况下小波谱中能量分布的不同,得到坡度对沿岸流不稳定运动的影响.结果表明沿岸流不稳定运动随着时间的变化不会和低频波以及其它模式的低频成分有能量交换;随着距岸线距离的增大,沿岸流不稳定运动获得能量的时间提前,在时均沿岸流最大值附近获得能量最早;从地形影响角度看,地形坡度增大使得沿岸流不稳定运动在垂直岸线和沿岸方向的作用增大.该研究结果可以应用于沿岸流不稳定运动对近岸泥沙、污染物输移影响等的经验参数的标定.

The Morlet wavelet transform was chose to obtain the wavelet power spectrum based on the similarity between the time series and the Morlet wavelet. The variations of Jinstabilities of irregular waves induced longshore currents were analyzed under plane beach slopes 1 ： 100 and 1 ： 40 in time and spatial domain, and the effects of slope on it were considered. The variations and effects were discussed by analysis of the wavelet energy distribution at different position from shore line for each wave condition. The results showed that the energy transfer hardly occured between the instabilities of longshore currents and other low frequency waves;and the instabilities grew earlier with the increase of distance from the shore line and occued earliest at the position of maximum mean longshore currents, and developed stronger in cross-shore and longshore directions with the increase of slope. These results could be used to estimate the experienced model parameters quickly and effectively at engineering analyses of sediment and dye transport.