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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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在坡度为1:40的平面斜坡上进行了单向不规则波的沿岸流不稳定运动实验,观测到了沿岸流的周期性波动(波动周期约为100 s)。利用最大熵方法和三角函数回归法求得这种波动的主频率以及幅值,分析了波动幅值在垂直岸线方向的变化,结果表明该变化与沿岸流变化类似,即在沿岸流最大值附近这种波动强度最大。为了分析波动的机理,利用线性沿岸流不稳定模型对模型实验结果进行了分析,求得了不稳定运动增长模式和波动周期,并与对应实测结果进行了比较,结果表明,计算结果与实测值符合,从而说明实验中观测到的这种周期性波动为沿岸流不稳定引起的剪切波。 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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本文以沿岸流不稳定运动实验中流速仪采集到的不规则波的流速时间历程为基础,利用相关性分析,得到两个不同位置处对应流速时间历程的最大相关系数和延迟时间,进而分析沿岸流不稳定运动在1∶40和1∶100平直斜坡上的传播方向,并且分析了其随入射波高、周期的变化。结果表明沿岸流不稳定运动在海岸垂向环流系统的作用下,其传播方向会向海方向偏移,与岸线角度大约在0°到45°之间,且在1∶40和1∶100坡情况下,沿岸流不稳定运动的偏移角分别随入射周期和波高的增加而增加,但1∶100坡的增加幅值较小,大约为1∶40坡情况下的1/2。 相似文献
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探讨一种基于完全非线性Boussinesq方程的波浪破碎模型在沿岸流计算中的应用问题。针对控制方程中的完全非线性项对沿岸流成长过程的影响进行了深入讨论。数学模型计算结果表明,完全非线性项有使平均流局部化的作用;通过数模实验还发现,垂向高阶涡度项可以有效抑制破波区外回流;运用Visser的实验室沿岸流实测资料从沿岸流速度、波高和平均水位几方面对所提模型进行了验证,并给出了紊动参数的计算结果。 相似文献
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采用完全非线性Boussinesq方程建立的FUNWAVE模型进行波生沿岸流数值模拟研究,通过对不同斜坡地形和波浪入射条件下波生流的物理模型实验结果进行比较,验证了该数值模型能较准确地计算沿岸流;通过改变波浪的不同入射条件,对不同入射条件的沿岸流数值模拟得出:当其他条件不变时,仅入射波高增大时,沿岸流的流幅和幅值增大,幅值位置向深水移动;仅增大入射周期时,沿岸流的流幅显著增加,幅值的增加较小;斜坡地形坡度的改变能显著影响波生沿岸流的流幅和幅值,但对沿岸流幅值位置的水深影响不大。采用窄缝法处理动边界时,选择合适的窄缝起始水深对沿岸流的准确计算是十分必要的。 相似文献
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基于2014-2018年NOAA/AVHRR遥感数据，在山东半岛海域选取6条剖面，结合海表温度和表层悬浮体的时空变化特征，详细研究了山东半岛沿岸流的年周期变化规律与移动路径。研究结果表明，山东半岛沿岸流年周期变化可分为4个阶段：成长期（10-12月）时开始形成于黄河口附近，沿莱州湾南部向东运移；强盛期（次年1-3月）时山东半岛沿岸流完全成型，扩散带最宽，鼎盛时期北部可以至38°N附近，东部可以至123°E附近，在35°～36°N附近分成NE-SW向的2个分支，主干部分最远可到达胶州湾东部海域，余流沿岸向西南方向转折；衰退期（4-6月）时沿岸流强度减弱，只在山东半岛北部和东部小范围内有微弱的显示；消亡期（7-9月）时基本消失。山东半岛沿岸流在冬季时对悬浮体扩散具有强烈的驱动作用，使其在黄河口南侧与山东半岛北岸-成山头东部海域分别形成呈“弧形”和“条带状”分布的2个高浓度区域。 相似文献
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为了解极端波浪非线性特征,明确波群在演化过程中的水动力学特性,针对一系列高斯波群进行了深水物理试验分析。试验结果显示,增加波陡或波群宽度,均可使波面偏度Sk发生明显变化,尤其当波浪发生破碎后,在破碎区域内,波面偏度变化范围剧烈增大,说明该偏度极大值可能作为判断破碎的一个指标。波陡和波群宽度对波面不对称度影响程度不同:当波陡或波群宽度增加后,波峰不对称度所受影响最大,波峰前端波谷不对称度次之,波峰后端波谷不对称度所受影响最小,但仍不可忽略。在波浪演化过程中,幅值谱出现不同程度频带下移,波浪破碎后,会出现永久频带下移;当调制不稳定发生时,随着调制不稳定指数增加,频带下移量呈现快速增长趋势。 相似文献
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Numerical study of wave and longshore current interaction 总被引：1，自引：0，他引：1
Wave and longshore current interaction was examined based on the numerical models.In these models,water waves in the presence of longshore currents were modeled by parabolic mild slope equation,and wave breaking induced longshore currents were modeled by shallow water equation.Water wave provided the radiation stress gradients to drive current.Wave and longshore current interactions were considered by cycling the wave and longshore current models to a steady state.The experiments for regular and irregular breaking wave induced longshore currents by Hamilton and Ebersole（2001） and Reniers and Battjes（1997） were simulated.The numerical results indicate that the present models are effective for simulating the interaction of wave and breaking wave induced longshore currents,and the numerically simulated longshore current at wave breaking point considering wave and longshore current interaction show some disagreement with those neglecting the wave-current interaction,and the breaking wave induced longshore current effect on wave transformation is not obvious. 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
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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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G. D. Aburjania 《Izvestiya Atmospheric and Oceanic Physics》2011,47(4):491-502
The generation and further linear and nonlinear dynamics of planetary magnetized Rossby waves (MRWs) in the rotating dissipative ionosphere are studied in the presence of a zonal wind (shear flow). MRWs are caused by interaction with the spatially nonuniform geomagnetic field and are ionospheric manifestations of ordinary tropospheric Rossby waves. A simplified self-consistent set of model equations describing MRW-shear flow interaction is derived on the basis of complete equations of ionospheric magnetohydrodynamics. Based on an analysis of an exact analytical solution to the derived dynamic equations, an effective linear mechanism of MRW amplification in the interaction with nonuniform zonal wind is ascertained. It is shown that operators of linear problems are non-self-adjoint in the case of shear flows, and the corresponding eigenfunctions are nonorthogonal; therefore, the canonically modal approach is of little use when studying such flows; a so-called nonmodal mathematical analysis is required. It is ascertained that MRWs effectively get shear flow energy during the linear stage of evolution and significantly increase (by several orders of magnitude) their energy and amplitude. The necessary and sufficient condition of shear flow instability in an ionospheric medium is derived. Nonlinear self-localization begins with the development of shear instability and an increase in the amplitude, and the process ends with the self-organization of strongly localized isolated large-scale nonlinear vortex structures. Thus, a new degree of freedom and a way for perturbation evolution to occur appear in medium with shear flow. The nonlinear systems can be a pure monopole vortex, a vortex streets, or vortex chains depending of the shape of the sheared flow velocity profile. The accumulation of such vortices in the ionospheric medium can produce a strongly turbulent state. 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