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在近岸缓坡浅水海岸,波浪破碎产生沿岸流是近岸海域流场的重要组成部分,它对污染物输移扩散规律的影响重大,在高阶近似抛物化缓坡方程求解大面积波浪场基础上,建立了波浪作用下污染物输移扩散数学模型.计算结果与不同坡度均匀斜坡地形上具有不同波高、周期的规则波及不规则波浪作用下污染物输移扩散实验结果进行了比较,分析了各种因素对波浪作用下沿岸流分布规律影响,所得结论认为地形坡度及入射波高对污染物输移扩散的影响较大,波浪作用将使缓坡海滩上污染物的输移扩散平行岸线方向. 相似文献
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破波带内外都有质量输移流存在，其对破波带内污染物输移有怎样的影响，需要进一步深入研究。本文基于实验以及考虑质量输移流的对流扩散数学模型研究了平直斜坡上破波带内质量输移流对污染物输移影响。数学模型包括波浪模型、近岸流模型以及对流扩散模型。首先建立了破波带内污染物输移数学模型，其中波浪场基于波能守恒方程来计算，波导流场基于Longuet-Higgins提出的辐射应力模拟，污染物对流扩散方程中考虑了质量输移流的影响，并利用算例验证该数学模型。其次简要介绍了平直斜坡上破波带内污染物输移实验，并分析了污染物输移特性。连续投放污染物会形成污染带，本文分析了两种波况下不同时刻污染带与岸线夹角的变化，以及污染物在垂直岸线和沿岸线方向的输移速度，结果表明对两种波况来说在初始10-40s污染团向岸线方向输移速度分别约为0.05m/s、0.017m/s，之后速度分别减小为0.001m/s、0.011m/s。数值模拟结果与实验结果比较表明：考虑质量输移流的模拟结果与实验更为吻合。因而，通过实验以及数模研究表明破波带内质量输移流对破波带内污染物在垂直岸线方向的输移有重要影响，而对沿岸方向的输移则影响较小。 相似文献
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波浪作用下渤海湾近岸海域污染物的输移扩散规律 总被引：10，自引：3，他引：10
用物理模型实验和数学模型计算相结合的方法，研究了均匀缓坡岸滩上，规则波及不规则波浪作用下形成的沿岸流及其对岸边排放污染物输移扩散的影响。针对渤海湾的地形和主要波浪方向，研究了渤海湾主要排污口附近单纯波浪以及波浪、潮流共同作用下近岸海域内流动速度分布与相应污染物输移扩散规律。结果表明，在渤海湾近岸海域(一定范围内)，污染物输移扩散受到波浪作用的影响，表现为平行岸线方向。波浪作用使得远离污染物排放口的滩涂受污染的影响增大。 相似文献
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沿岸流不稳定运动目前已成为一个研究热点,对于沿岸流不稳定的研究对于近岸泥沙、污染物输移以及海岸养护等都有很重要的意义。本文详细介绍了沿岸流不稳定运动的研究进展,具体包括沿岸流不稳定运动现场以及实验室实验研究进展,沿岸流线性不稳定理论,非线性不稳定理论以及沿岸流不稳定运动产生的其它理论分析。结果表明国外对于该问题的研究(主要是有关不稳定理论方面)已经取得很多成果,但国内目前很少,并且现在对沿岸流不稳定研究比较成熟的理论基础是不稳定理论,该理论都假定增长率最大的不稳定模式决定着沿岸流的波动特性。但对于多模式不稳定运动的研究还基本没有,对于沿岸流不稳定运动三维特性的研究(包括数值研究及实验研究)也基本没有报道。所以这两个方面可能是以后对该问题研究的重要方向。 相似文献
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沿岸流不稳定运动属于超低频运动,研究它的传播特性,有助于深入理解其对岸滩演变、污染物、鱼卵等输移、迁移的影响。本文基于小波相干谱对所选实验波况进行了研究,分析了规则波、随机波入射情况下沿岸流不稳定运动传播特性,并讨论了入射波高、周期、坡度等对其的影响。结果表明,不规则波更易诱导出沿岸流不稳定运动,且在不规则波情况下,不稳定运动在沿岸方向相距4 m的两个断面上产生的相位差都约为±30°,与波浪入射角相近;随着入射波高的增加,非线性随之增强,更易诱导出不稳定运动,生成的沿岸流不稳定运动周期范围将增大;入射波周期对沿岸流不稳定运动的传播特性影响较小;坡度越陡越易诱导出超低频的不稳定运动。 相似文献
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中国近岸海区沿岸流和海岸流对沉积物的搬运 总被引：4，自引：0，他引：4
中国近岸海区存在两种海流:沿岸流和海岸流。前者是波浪产生的,主要搬运破波带以内的沉积物。后者是中国边缘海环流系统的一部分,位于破波带外,主要搬运粉砂和黏土细粒沉积物。在一些中文文献中两者都称作"沿岸流"。这容易形成概念上的混乱和分析问题上的错误。为了避免混淆,属于边缘海环流系统一部分的"沿岸流"应该称作海岸流,对于具体的"沿岸流"如"渤莱沿岸流"可以直接称呼为渤莱海流。两种海流的方向可以相同、相反或者呈一定角度。山东北部海岸沉积物的空间分布明显地受波浪、近岸环流系统(沿岸流、裂流)及海岸流控制。 相似文献
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珊瑚礁破碎带附近波浪演化和波生流实验研究 总被引：2，自引：0，他引：2
为了研究珊瑚岸礁破碎带附近波浪演化和波生流特性,通过水槽实验对规则波浪作用下珊瑚岸礁上沿礁分布的水位和流速进行了详细的测量。在典型卷破波条件下,测试了礁冠存在与不存在的两种情况。实验结果表明,多重波浪反射作用引起岸礁上形成不完全驻波,而破碎带附近的浅化作用则产生高次谐波,波浪破碎所耗散的波能主要来源于主频波,礁坪上透射波成分中二次谐波与主频波的能量相当;礁冠的存在引起破碎带宽度减小、礁坪上增水变大以及礁坪上各次谐波变小;礁冠不存在时,岸礁上波生流的沿礁分布与平直海岸相似,而礁冠的存在一定程度上阻碍了礁坪上水体向外海的回流。研究成果将丰富和发展珊瑚礁水动力学理论,并为岛礁工程的建设和维护提供一定的理论参考。 相似文献
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A laboratory experiment on alongshore currents is conducted for two plane beaches with slopes 1:40 and 1:100 to investigate the instability of alongshore currents.The dye release experiment is also performed synchronously in surf zone.Complicated and strongly unstable motions of alongshore currents are observed in the experiment.To examine the spatial and temporal variations of the shear instabilities of longshore clearly,dye batches are released in surf zone.The deformation of the dye patch is observed efficiently and effectively with charge coupled device(CCD) system.Some essential characteristics of the shear instability are validated from the results of image analyses of the temporal variation of the dye patch.The influences of alongshore currents,Stokes drift,large-scale vorticity and the shear instabilities on the transport of dye are analyzed using the collected images.The spatial structure of the instabilities of longshore currents is studied by analyzing collected images of the dye patch.And the phase velocity of the meandering movements is obtained through measuring the movement distances of the oscillations of dye patch in alongshore direction with time.The results suggest that the propagation speed of the shear instability is approximately 50%-75% of maximum of mean alongshore currents for irregular and regular waves.The calculated propagation speed using a linear instability analysis theory is compared with the experimental results.The comparison shows agreements between them. 相似文献
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《Coastal Engineering》2006,53(5-6):419-439
The flow on a plane beach with a random, directionally spread wave field was simulated with a Boussinesq model. The random wave spectra were directionally symmetric with their central direction perpendicular to the beach, so no constant longshore current was generated. Variable wave-averaged currents were generated because of the spatially variable wave field, and sometimes formed offshore directed rip currents that appear in variable longshore locations. The rip currents are associated with a vortex pair which is generated within the surfzone and subsequently propagates offshore. Analysis of the vorticity balance show that the main vorticity input occurs within the inner surfzone. Three different beach slopes and four different wave spectra are simulated. The frequency, duration, and intensity of the transient rips depend on both the beach slope and the incident wave spectra. The results have important engineering implications for the transport of material in the nearshore zone, in particular on longshore uniform beaches. 相似文献
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A well-established 3D phase-averaged beach morphodynamic model was applied to investigate the morphodynamics of a typical artificial beach,and a series of discussions were made on the surfzone hydro-sedimentological processes under calm and storm events.Model results revealed that the nearshore wave-induced current presents a significant 3D structure under stormy waves,where the undertow and longshore currents exist simultaneously,forming a spirallike circulation system in the surfzone.Continuous longshore sediment transport would shorten the sediment supply in the cross-shore direction,subsequently suppress the formation of sandbars,showing that a typical recovery profile under calm waves does not necessarily develop,but with a competing process of onshore drift,undertow and longshore currents.Sediment transport rate during storms reaches several hundreds of times as those under calm waves,and two storm events contribute approximately 60%to the beach erosion.Sediment transport pattern under calm waves is mainly bed load,but as the fine sands underneath begin to expose,the contribution of suspended load becomes significant. 相似文献
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David R. Basco 《Coastal Engineering》1983,7(4):331-355
Investigations of surfzone currents including longshore currents, rip currents and nearshore circulations have been conducted worldwide for over sixty years. The motivation is understanding and prediction of sediment transport and coastal pollution processes. This article summarizes a recent state-of-the-art review of theory and experiments conducted since 1967 (Basco, 1982, with Volume II including over 350 annotated bibliographic entries). Emphasis is on the now generally accepted, time-averaged theory based upon radiation stress principles. The newly emerging Boussinesq-type theory, which follows the instantaneous water surface and current variations within each wave period, is also briefly considered. Both approaches assume uniform currents with depth, rely upon empirical wave breaking and surfzone energy empiricism, and suffer from a limited data base for verification. Emphasis throughout is on needed areas for further research. 相似文献
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Longshore currents of regular waves on different beaches 总被引：1，自引：0，他引：1
The experiment and numerical computations of longshore currents produced by regularwaves on the two beaches with the slopes of 1:100 and 1:40 are made. The cross-shore distributions of longshore current velocities and wave heights are given and the influences of wave heights, wave periods and beach slopes on the longshore currents are discussed. The discussion is also made for the influences of different eddy viscosity coefficients on the numerical results of longshore current velocities. 相似文献
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The laboratory experiment and numerical simulations of wave-driven longshore currents by random waves on barred beaches with slopes of 1:100 and 1:40 were conducted to investigate the bimodal feature of mean longshore currents, with emphasis on the location and ratio of two peaks of longshore currents. The location and ratio of two peaks are controlled by the sand bar. The influences of wave heights and beach slopes on the longshore currents are discussed. Numerical simulations were also performed to compute the measured velocity profile, with the emphasis on the effect of lateral mixing, bottom friction and surface rollers on numerical results. 相似文献
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《Coastal Engineering》1999,36(3):171-195
A morphological stability analysis is carried out for a long straight coast with a longshore bar. The situation with oblique wave incidence and a wave-driven longshore current is considered. The flow and sediment transport are described by a numerical modelling system. The models comprise: (i) a wave model with depth refraction, shoaling and wave breaking, (ii) a depth integrated model for wave driven currents and (iii) a sediment transport model for the bed load transport and the suspended load transport in combined waves and current. The direction of the sediment transport is taken to be parallel to the depth integrated mean current velocity, neglecting the effects of a bed slope and secondary currents. An instability is found to develop around the bar crest. The instability is periodic in the alongshore direction, and tends to form rip channels and to steepen the offshore face of the bar between the rip channels. The alongshore wave length of the most unstable perturbation is determined for different combinations of the wave conditions and the geometry of the profile. 相似文献
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沿岸流流速垂向分布的实验研究 总被引：1，自引：0，他引：1
进行了沿岸流模型实验,测量沿岸流流速的垂向分布.采用Faria等(1996)的方法对实验结果进行了分析,将水深分为上层和下层两部分:下层采用对数分布来表达沿岸流的垂向分布;上层考虑了波浪引起的自由表面的波动,使流速分布包括了修正的对数分布和质量输移速度两部分.对实验结果得到的相对粗糙度与sleath(1991)的经验公式结果进行了对比,也对摩阻流速结果与已有经验公式计算结果的进行了对比. 相似文献
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A laboratory experiment on alongshore currents was conducted for two plane beaches, with gradients 1:40 and 1:100, to investigate the instability of alongshore currents. Complicated and strongly unstable alongshore current motions were observed. In order to clearly examine the spatial and temporal variations of the shear instability of the currents, digital images from a charge-coupled device (CCD) recorded the deformations of dye batches released in the surf zone. Some essential characteristics of the shear instability were obtained from analyses of images showing the temporal variation of the dye patches.A high-resolution spectral analysis technique (the maximum entropy method, or MEM) was used to analyze the dominant frequency of the observed oscillation, along with the trigonometric regression method for determining the variations of the oscillation strength in the cross-shore direction. The propagation speed of the dye patch was obtained by tracking the movement over time of fixed locations in the dye patch, such as its peak, in the longshore direction. This data was then fitted linearly.Alongshore and cross-shore velocity time series acquired from sensors showed clearly that large-amplitude, long-period (about 50 s or 100 s) oscillations were present for all sensors deployed in the cross-shore direction under regular and irregular wave conditions. The analysis found that the maximum shear wave amplitude was approximately one-sixth of the maximum for the mean alongshore current, and occurred approximately at the position of the maximum of the mean alongshore current for irregular waves. The spatial structure of the shear waves was studied by analyzing collected images of the dye patches. The phase velocity of the meandering movements was obtained by measuring the magnitude of the oscillations of the dye patches in the alongshore direction with respect to time. The results suggest that the propagation speed of the shear instability was approximately one-half to three-quarters of the maximum mean longshore current for both regular and irregular waves.Linear instability analysis theory was applied to the characteristics of alongshore current instability, which suggested that there are two instability modes related to the observed oscillations: the frontshear mode observed for the 1:100 slope, and the backshear mode observed for the 1:40 slope. Theoretical analyses agreed with the experimental results in both cases. The velocity profile of the mean longshore current was found to affect the instability mode significantly, leading to further investigations on the influence of the velocity profiles and to provide support for the above conclusions. 相似文献