共查询到20条相似文献，搜索用时 494 毫秒
1.
Laboratory study of the nonlinear transformation of irregular waves over a mild slope 总被引：1，自引：0，他引：1
This paper considers the nonlinear transformation of irregular waves propagating over a mild slope （1：40）. Two cases of irregular waves, which are mechanically generated based on JONSWAP spectra, are used for this purpose. The results indicate that the wave heights obey the Rayleigh distribution at the offshore location; however, in the shoaling region, the heights of the largest waves are underestimated by the theoretical distributions. In the surf zone, the wave heights can be approximated by the composite Weibull distribution. In addition, the nonlinear phase coupling within the irregular waves is investigated by the wavelet-based bicoherence. The bicoherence spectra reflect that the number of frequency modes participating in the phase coupling increases with the decreasing water depth, as does the degree of phase coupling. After the incipient breaking, even though the degree of phase coupling decreases, a great number of higher harmonic wave modes are also involved in nonlinear interactions. Moreover, the summed bicoherence indicates that the frequency mode related to the strongest local nonlinear interactions shifts to higher harmonics with the decreasing water depth. 相似文献
2.
The wavelet-based bicoherence, which is a new and powerful tool in the analysis of nonlinear phase coupling, is used to study the nonlinear wave–wave interactions of breaking and non-breaking gravity waves propagating over a sill. Two cases of mechanically generated random waves based on Jonswap spectra are used for this purpose. Values of relative depth, kph (kp is the wave number of the spectral peak and h is the water depth) for this study range between 0.38 and 1.22. The variations of wavelet-based total bicoherence for the test cases indicate that the degree of quadratic phase coupling increases in the shoaling region consistent with a wave profile that is pitched shoreward, relative to a vertical axis as seen in the experiments, but decreases in the de-shoaling region. For the non-breaking case, the degree of quadratic phase coupling continues to increase until waves reach the top of the sill. Breaking waves, however, achieve their highest level of quadratic phase coupling immediately before incipient breaking and the degree of phase coupling decreases sharply following breaking. In addition the wavelet-based bicoherence spectra provide evidence of the harmonics' growth which is reflected in the energy spectra. The bicoherence spectra also show that quadratic phase coupling between modes within the peak frequency as well as between modes of the peak frequency and its higher harmonics are dominant in the shoaling region, even though there are relatively high levels of quadratic phase coupling occurring between other frequencies. Furthermore, using the temporal resolution property of the wavelet-based bicoherence, we find that the quadratic wave interactions occur more readily during segments of time with large change of wave amplitude, rather than those segments having large wave amplitudes, but small gradients in amplitude. 相似文献
3.
《Coastal Engineering》2002,46(3):233-247
A field experiment, conducted on a sandy, barred beach situated on the southern part of the French Atlantic coastline, allowed us to investigate the formation of secondary waves when a moderate (significant wave height of about 0.8 m in 3.7-m water depth), long (11–14 s) narrowband swell propagated over an intertidal ridge and runnel system, in both breaking and nonbreaking conditions. Field evidence using higher spectral analysis is given for the sum interactions between pairs of waves at the primary spectral peak and the consequent energy transfer to nearly harmonic wave components. Although wave breaking appears to weaken the strength of nonlinear couplings, the generation of high-frequency energy is hardly affected by wave breaking. The phenomenon of harmonic decoupling, which takes place behind the bar, cannot be completely ascribed to the increase in water depth and the so-called deshoaling effect. Indeed, the variation in the values of the maximum bicoherence was very moderate when no breaking occurred. Finally, the doubling in the number of wave crests and the consequent decrease in the significant wave period delay the energy dissipation on the beach face. 相似文献
4.
响水近岸海域波浪特性研究 总被引：3，自引：0，他引：3
基于响水波浪站累计一整年的现场观测资料，分析了波高和波周期的年内变化特性，研究了波浪的统计特性和波谱特性，并总结归纳了该海域各特征波要素之间以及各波谱参数之间的转换关系。结果显示:响水海域全年有效波高的变化幅度在0.10~2.80 m之间，年平均值为0.56 m；最大波高的变化幅度在0.15~5.58 m之间，年平均值为0.93 m；平均波周期的变化范围为1.91~9.02 s，年平均值为3.90 s。夏季大波高发生频率明显要小于冬、春季节，波浪季节性变化较为显著。就波高和波周期分布而言，通过拟合得出的Weibull分布较为适合本海域实测波高分布和波周期分布。波谱特性方面，本海域双峰谱占到总数的62.5%，且低频谱峰值普遍高于高频谱峰值，其中低频谱峰出现在0.04 Hz左右，高频谱峰则出现在0.15~0.20 Hz之间，分别为本海域涌浪和风浪所集中的频率区间。采用回归分析方法进一步分析了各特征波要素之间以及各波谱参数之间的关系，发现多数波参数之间存在显著的相关性，但受波浪浅水变形影响，各参数之间的比值与理论深水关系有所区别。本文的研究成果可为沿海建筑物的设计以及防灾减灾提供参考和依据。 相似文献
5.
SWAN model predictions, initialized with directional wave buoy observations in 550-m water depth offshore of a steep, submarine canyon, are compared with wave observations in 5.0-, 2.5-, and 1.0-m water depths. Although the model assumptions include small bottom slopes, the alongshore variations of the nearshore wave field caused by refraction over the steep canyon are predicted well over the 50 days of observations. For example, in 2.5-m water depth, the observed and predicted wave heights vary by up to a factor of 4 over about 1000 m alongshore, and wave directions vary by up to about 10°, sometimes changing from south to north of shore normal. Root-mean-square errors of the predicted wave heights, mean directions, periods, and radiation stresses (less than 0.13 m, 5°, 1 s, and 0.05 m3/s2 respectively) are similar near and far from the canyon. Squared correlations between the observed and predicted wave heights usually are greater than 0.8 in all water depths. However, the correlations for mean directions and radiation stresses decrease with decreasing water depth as waves refract and become normally incident. Although mean wave properties observed in shallow water are predicted accurately, nonlinear energy transfers from near-resonant triads are not modeled well, and the observed and predicted wave energy spectra can differ significantly at frequencies greater than the spectral peak, especially for narrow-band swell. 相似文献
6.
A new technique in the analysis of wind–wave interaction, wavelet bicoherence, will be applied in this article. Wavelet bicohence has the ability to detect phase coupling and nonlinear interactions of the quadratic order with time resolution. It is used in this study to analyze wind–wave interaction during wave growth in a Mistral event. A selected record of simultaneously measured wind and wave data during Mistral is divided into five segments and the computations of the wavelet bicoherence are conducted for the whole record and for all divided segments. The results show that the phase coupling occurs between wind speed and wave height over a certain range of frequencies and that the range is different from one segment to another due to the non-stationary feature of the time series. 相似文献
7.
In this paper.the characteristics of laboratory wind waves under various wind speeds and wat-er depths are studied.It is found that either the real or the imaginary part of the bispectrum can be relatedto the asymmetry of the wave profile,and the bicoherence is related to the ratio of nonlinear to linear wavecomponent.Occasionally,these two categories of nonlinear index lead to opposite inferences,because eachof them has its own significance and functions.The applicability of linear wave spectral model in oceanwaves becomes questionable only when strong nonlinearity is indicated by both of these two indexes.Thelinear spectral representation of wave fields does not necessarily become inadequate as water depth de-creases,and its appropriateness can be examined through the characteristics of the bispectrum. 相似文献
8.
海洋波浪能平均功率的准确计算是波浪能开发和利用的基础。实践中，波浪能转换装置一般安装在有限水深区域。对于随机波，只有当详尽的波浪谱已知的时候，有限水深区的波能功率才能被准确计算出来。由于种种原因，实践中波浪的实测数据大多以散点图或有义波高和统计波周期的形式给出，而波浪谱信息有时则很难获得。基于这种情况，传统上人们利用无限水深条件下的相关公式来估算有限水深区域的波能功率，但这种做法会造成较大的误差。本研究显示，对于50 m水深的理论波谱JONSWAP谱来说该误差高达14.6%。为了提高波能功率计算的准确性，本文提出了一种基于能量频率的一阶和二阶近似算法，可以在未知波浪谱的情况下较为准确地计算不同水深时的波能功率。针对两种理论波浪谱的计算结果表明，本方法在计算有限带宽内的波能功率时计算误差低于2.8%。 相似文献
9.
《中国海洋工程》2021,(4)
The main objective of this paper is to examine the influences of both the principal wave direction and the directional spreading parameter of the wave energy on the wave height evolution of multidirectional irregular waves over an impermeable sloping bottom and to propose an improved wave height distribution model based on an existing classical formula. The numerical model FUNWAVE 2.0, based on a fully nonlinear Boussinesq equation, is employed to simulate the propagation of multidirectional irregular waves over the sloping bottom. Comparisons of wave heights derived from wave trains with various principal wave directions and different directional spreading parameters are conducted. Results show that both the principal wave direction and the wave directional spread have significant influences on the wave height evolution on a varying coastal topography. The shoaling effect for the wave height is obviously weakened with the increase of the principal wave direction and with the decrease of the directional spreading parameter. With the simulated data, the classical Klopman wave height distribution model is improved by considering the influences of both factors. It is found that the improved model performs better in describing the wave height distribution for the multidirectional irregular waves in shallow water. 相似文献
10.
基于激波捕捉类Boussinesq模型对岛礁地形上波浪传播的数值模拟 总被引：2，自引：2，他引：0
为了探究激波捕捉类Boussinesq模型在模拟岛礁地形上规则波和不规则波传播的可行性,采用基于完全非线性Boussinesq方程并具有激波捕捉能力的数值模型Funwave-TVD对规则波和不规则波在岛礁地形上的传播进行了数值模拟,通过与试验数据对比,分析模型中空间步长的影响,验证模型在模拟波高、平均水位分布以及波谱空间演变的能力,结果表明:采用合适的空间步长,模型能较好地模拟规则波和不规则波在岛礁地形上的传播和演化过程。对于规则波,较小的空间步长可改善破碎点处波高峰值的预测,并能更好地预测波浪破碎后波高的空间分布,相比结合经验破碎的Boussinesq模型,Funwave-TVD能更好地模拟规则波在岛礁地形上的破碎,以及破碎以后行进涌波的再生成过程;对于不规则波,Funwave-TVD总体而言能较好地模拟涌浪有效波高、次重力波的生成及空间演化和平均水位,但会低估礁坪上次重力波波高,较粗的空间步长也会低估礁坪上涌浪有效波高。 相似文献
11.
12.
Wave elevations and water particle velocities were measured in a laboratory surf zone created by the breaking of a narrow-band irregular wave train on a 1/35 plane slope. The incident waves form wave groups that are strongly modulated. It is found that the waves that break close to the shoreline generally have larger wave-height-to-water-depth ratios before breaking than the waves that break farther offshore. After breaking, the wave-height-to-water-depth ratio for the individual waves approaches a constant value in the inner surf zone, while the standard deviation of the wave period increases as the still water depth decreases. In the outer surf zone, the distribution of the period-averaged turbulent kinetic energy is closely correlated to the initial wave heights, and has a wider variation for narrow-band waves than for broad-band waves. In the inner surf zone, the distribution of the period-averaged turbulent kinetic energy is similar for narrow-band waves and broad-band waves. It is found that the wave elevation and turbulent kinetic energy time histories for the individual waves in a wave group are qualitatively similar to those found in a spilling regular wave. The time-averaged transport of turbulent kinetic energy by the ensemble-averaged velocity and turbulence velocity under the irregular breaking waves are also consistent with the measurements obtained in regular breaking waves. The experimental results indicate that the shape of the incident wave spectrum has a significant effect on the temporal and spatial variability of wave breaking and the distribution of turbulent kinetic energy in the outer surf zone. In the inner surf zone, however, the distribution of turbulent kinetic energy is relatively insensitive to the shape of the incident wave spectrum, and the important parameters are the significant wave height and period of the incident waves, and the beach slope. 相似文献
13.
在理论分析的基础上利用根、茎、叶均可量化的植物模型,开展波浪水槽实验。通过改变实验水深、入射波高、植物分布密度等因素,研究不规则波在植物群传播时沿程波高衰减特性,利用快速傅里叶变换对不规则波频谱变化情况进行分析。结果表明,各植物模型消波效果较好,但很少出现植物消波的边界效应,不规则波沿植物群的波高变化情况多数时与Mendez理论曲线不一致,植物群各部分的波能衰减情况并无固定的变化规律。此外,波能衰减集中在谱峰频率处,且入射波高越大,透射波与入射波之间的谱峰值差值越大,但透射波的频谱宽度与入射波相比无明显变化。本研究可为采用近岸植物消波护岸提供一定的理论依据。 相似文献
14.
利用大型水槽设计了在由深水到近岸不同坡度处海浪在变浅作用下诱导产生的长周期重力波的实验。正态随机海浪在深水生成并沿斜坡向浅水传播,记录了不同水深处波面高度随时间的变化过程并进行统计分析和谱分析。实验数据分析结果表明,长周期重力波的能量随着水深的变浅而增高,其谱锋频率位于0.2~0.3fp附近,这里fp是深水正态海浪过程的谱峰频率。长周期重力波的能量与入射波的能量比与波面高度分布的偏度密切相关。进一步分析了两种波动的能量谱峰值比和波面高度分布偏度的相关关系,获得了经验关系,为预测近岸浅水长周期重力波提供了科学依据。 相似文献
15.
洪广文 《海洋学报(英文版)》1982,1(1):144-154
Based on the perturbation method, a fourth order theory for nonlinear interactions among three dimensional gravity waves in water of any uniform depth is presented in this paper. Two cases are considered: ( i ) wave number vectors fixed, frequencies perturbed, and ( ii ) wave number vectors and frequencies both fixed. According to this solution, expressions of thesame order for progressive waves, short-crested waves and nonlinear interaction between wave and vertical wall are also derived' 相似文献
16.
The performance of the new wave diffraction feature of the shallow-water spectral model SWAN, particularly its ability to predict the multidirectional wave transformation around shore-parallel emerged breakwaters is examined using laboratory and field data. Comparison between model predictions and field measurements of directional spectra was used to identify the importance of various wave transformation processes in the evolution of the directional wave field. First, the model was evaluated against laboratory measurements of diffracted multidirectional waves around a breakwater shoulder. Excellent agreement between the model predictions and measurements was found for broad frequency and directional spectra. The performance of the model worsened with decreasing frequency and directional spread. Next, the performance of the model with regard to diffraction–refraction was assessed for directional wave spectra around detached breakwaters. Seven different field cases were considered: three wind–sea spectra with broad frequency and directional distributions, each coming from a different direction; two swell–sea bimodal spectra; and two swell spectra with narrow frequency and directional distributions. The new diffraction functionality in SWAN improved the prediction of wave heights around shore-parallel breakwaters. Processes such as beach reflection and wave transmission through breakwaters seem to have a significant role on transformation of swell waves behind the breakwaters. Bottom friction and wave–current interactions were less important, while the difference in frequency and directional distribution might be associated with seiching. 相似文献
17.
The covariance matrix of sound-speed variations is determined from yo-yo CTD data collected during the SWARM 95 experiment at a fixed station. The data covered approximately 2 h and were collected during a period when nonlinear solitary internal waves were absent or negligible. The method of empirical orthogonal functions (EOF) is applied to the sound-speed covariance matrix assuming that the internal wave modes are uncorrelated. The first five eigenvectors are found to agree well with the theoretically modeled eigenfunctions based on the measured buoyancy frequency and the internal wave eigenmode equation. The mode amplitudes for the first five modes are estimated from the corresponding eigenvalues. They agree with the Garrett-Munk model if j*=1 is used instead of j*=3. A second method is used to deduce the mode amplitudes and mode frequency spectra by projecting the sound-speed variation (as a function of time) onto the theoretical mode depth functions. The mode amplitudes estimated with this method are in agreement with the EOF results. A modified Garrett-Munk model is proposed to fit the frequency spectrum of linear internal waves in shallow water 相似文献
18.
本文分析了西太平洋实测的波高分布、同期分布、波高和周期的联合分布,以及波谱的分析。分析结果指出,大洋波浪的波高和周期都大于近海波浪的波高和周期。分布特征也不同于近海。波浪多属混合浪,会出现典型的双峰谱。 相似文献
19.