Spectral Characteristics of Wind-Waves in Laboratory

Spectral characteristics of wind-generated waves in labortaory are presented on the basis of a systematic measurement in a large-scale wind-wave channel and compared with those in the field. A marked characteristics of the measured spetra is the existence of secondary spectrum-peak. The dependence of spectral peak-frequency, peak-value and zeroth-order moment on wind speed and fetch are presented and found roughly similar to those in the field represented by the JONSWAP spectrum, regardless of the differences in coefficient. The spectral slope beta at high-frequencies are found somewhat greater than those of field wind-waves in both cases of deep and shallow waters. Except for the low-frequency part, the spectral forms measured in different wind conditions are similar and fit for the JONSWAP spectrum with gamma = 6 and beta = 5.5. Some relevant problems are discussed.

长江口南汇潮滩的波浪特征及其影响因素

波浪是塑造开敞型潮滩动力地貌的重要因素,但目前对潮滩波浪特征研究仍较少。该文以长江口南汇潮滩为例,通过对固定平台声学多普勒流速仪(Acoustic Doppler Velocimeter,ADV)获得的流速和水压等高频数据进行反演,获得了波浪特征参数和波浪谱参数,进而分析了它们在潮周期内的变化规律和影响机制。研究表明,观测期间南汇潮滩3个站位波浪的常浪向和强浪向以SE向为主,由长周期涌浪占主导。3个站位的有效波高与水深均成正相关关系,但各站位在涨、落潮期间的拟合系数不同。波浪轨道流速受浅水效应和潮流流向的影响明显,如在涨潮初期达到最大,在转流时期出现谷值。落潮期间波浪频谱以双峰谱为主,明显受到潮汐水位和地形的综合影响,期间峰值能量不断衰减且逐渐分散,并伴随出现了峰频转移现象。

JONSWAP谱和N谱的几个对应特征量间的关系

研究了风浪频谱JONSWAP谱的峰度因子γ、尖度因子PJ和N谱的尖度因子PN，参变量p，q间的关系；并在此关系上给出了由这两种谱计算的几个对应谱参量间的关系，如JONSWAP谱峰值A2（ω0）、零阶矩m0，J，平均频率，平均周期和对应于N谱的峰值S（ω0）、零阶矩m0，N，平均频率，平均周期间的关系；指出这些关系均与风浪的成长状态有关，在使用不同的谱形进行特征量的计算时，应注意不同频谱间的成长因子的一致性，以免引起计算结果的错误。