通过理论计算及实测数据定量分析了长江口海域潮汐对波浪的影响。考虑潮流及潮位变化, 计算了波数沿波向线的变化, 在计算过程中采用数据库查询方式避免了公式简化引起的误差。将计算出的波数带入由波作用量守恒推导出的波高变化公式, 其中只考虑反映潮汐影响的多普勒效应项和浅滩效应项, 由此得到顺流低潮位、顺流高潮位、逆流低潮位和逆流高潮位4种情况下某一周期的波浪其波高随水深和流速的变化以及相应的波长和陡度变化。通过个例分析将计算结果与长江口的实际观测比较, 并统计潮汐对波高贡献值占总波高之比以及潮汐对波高作用中多普勒效应项和浅滩效应项分别对波高的贡献率。结果表明, 理论计算值能很好地反映实际波浪的特征, 多普勒效应项和浅滩效应项能够基本解释波高的半日变化; 对于所分析的个例, 潮汐对波高的平均贡献值为负, 理论计算及观测数据分析得到的值分别为-8%及-6%; 多普勒效应项和浅滩效应项对波高的影响中后者是主要的; 另外理论计算及实测均反映出潮位变化对波高的影响不及相对流速对波高的影响明显。

Using theoretical calculations, tidal effects on waves in the Yangtze River estuary were analyzed quantitatively. Considering variations of tidal current and tidal level, wavenumber changing along a wave ray was calculated. In order to avoid errors produced by formula simplification during the calculation, database query method was used. The wavenumbers were used in wave height changing formula, which was deduced based on wave action conservation and in which only Doppler coefficient and shoaling coefficient terms reflecting effects of tide were considered. Then, wave height variation for different water depths and different current speeds of a certain periodic wave along-a-wave ray was obtained, and four examples under different situations were shown. These situations were downstream with low tide, downstream with high tide, upstream with low tide, and upstream with high tide. Their corresponding wavelengths and steepness were also calculated. Through a case study, theoretical results were compared with observations, percentages of tide-induced wave height to total wave height and contribution values of Doppler coefficient and shoaling coefficient to wave height were calculated. The results show that theoretical calculations and observations have good relationship and Doppler coefficient and shoaling coefficient can basically explain wave height’s semidiurnal change. For the study case, tidal effect on wave height is negative, namely, -8% for theoretical calculation and -6% for observation. Effect of shoaling coefficient on wave height is much more important than that of Doppler coefficient. Both theoretical calculation and observation reveal that influence of tidal level on wave height is inferior to that of relative current.