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海洋水文(如海流、潮流、潮汐、水位、海浪等)信息和海上天气信息在沿海存在广泛需求,拥有大量用户。例如,海上航运业需要有关水位、海流、海浪、风和海雾等信息,以保证航行安全,提高航运效率;为了有效地清除海面油膜和其他污染物,需开展海面油膜及污染物运动预报,并获得污染海域海流和海浪数据;因为幼鱼 相似文献
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海流信息在海上航行、海洋资源勘探等方面有着重要的应用,传统的现场和遥感观测方式不能满足大面积、实时观测海流的要求。基于无人机平台的光学海洋遥感技术具有机动灵活、成本低、分辨率高的特点,近年来在海洋环境监测中得到应用。然而,由于小型无人机容易受飞行姿态、太阳耀斑等因素的影响,目前在海流观测方面还不成熟。本文提出了利用小型无人机获取高分辨率海面流场的方法,并分析不同因素对观测结果的影响。首先,对无人机获取的光学海面图像做预处理,消除几何成像和图像噪声等因素的影响,并通过分析图像灰度值均值的变化,减小太阳耀斑对图像的影响;然后,基于三维傅里叶变换和海浪的频散关系反演海流,并将反演结果与浮标实测的海流数据进行对比,验证了该方法的可靠性。其次,结合实验数据详细分析了不同因素对海流反演的影响:在本文的实验条件下(有效波高0.2～1.5m,波浪主波周期3.8～5.7s),当图像空间分辨率为0.15m、反演子图尺寸在波浪主波波长的2～3倍时,海流的反演误差较小;增加图像幅数和提高时间分辨率也有利于提高海流的反演精度。现场观测实验的结果表明,本文提出的无人机观测海流技术可以有效获取海流信息。 相似文献
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近二、三十年来,由于军事、海上航运、海洋资源开发和利用等方面的需要,海浪观测仪器和技术得到了迅速发展。现在,海洋应用卫星遥感已从试用阶段逐步成熟起来,一些先进的海洋国家正在形成以观测浮标为主的卫星、飞机、浮标、船舶和沿岸观测相结合的综合海浪观测系统。我国从1956年起,首先在青岛附近的小麦岛海浪站开始使用岸用光学测波仪观测海浪。目前,我国已基本上形成了以岸用光学测波仪为主的沿海波浪观测网,并积累了大量资料。这些资料在我国的海浪研究和社会主义建设中起了很大作用。在海浪观测仪器方面,与一些 相似文献
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海岸沙坝近底悬移质通量实验研究 总被引：1，自引：0，他引：1
为了研究海岸沙坝的产生和演化机理,对不规则波和波群作用下沙坝上方的近底悬移质通量进行了实验研究。分析了短波、长波和平均水流对悬移质通量的影响。结果表明:各种波况下平均水流和长波的作用始终使泥沙向离岸方向输移,而短波的作用使泥沙向岸方向运动;平均水流引起的泥沙输移始终占主要成分,长波的次之。不规则波情况下平均水流的影响较规则波的情况相对较弱,三种成分对泥沙输运的贡献属于同一量级。波群情况下长波的影响随着波浪群性的增强而加大,短波的不明显,而平均水流的影响则随着波浪群性的增强而减弱。 相似文献
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Computation of wave kinematics at or near offshore structures is a vitally important consideration in the design of offshore structures. Design waves often include breaking and near-breaking storm waves in the presence of currents. It is important to predict the kinematics of these steep waves. Experiments were carried out in a wave tank with simulated steep waves with and without in-line current in which the wave profiles and the corresponding kinematics were simultaneously measured. The simulated waves represent shallow-water Gulf of Mexico storm waves. Many of these waves broke at or near the measuring instruments. Irregular stream-function theory was used to compute the wave kinematics and was found to generally predict the measured wave-current kinematics well. The differences found between the two are noted. Some of the noteworthy features of the breaking waves are also discussed. 相似文献
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Based on the shear effect of internal wave currents in stratified fluid, the necessary condition for the possible existence of an internal wave and the sufficient condition under which there will be no internal wave are deduced starting from the continuity equation of incompressible fluid. The above two conditions are verified by the measured results from vertical current meter arraies at some observation stations in the Bohai Sea and the South Huanghai Sea. In the treatment of measured results, first of all, the tidal period components are separated from the measured currents by Fourier-analysis method, and then the internal wave currents of tidal period from the tidal period components in the light of some considerations. The analytical results of observed currents are well consistent with theoretical analysis. Furthermore, one can also deduce some features of internal waves therefrom. Consequently, it is concluded that the observation from a vertical current meter array is an important means to verif 相似文献
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The continuous research and improvement of ocean modelling helps to provide a more sustainable development of coastal and offshore regions. This paper focuses on ocean modelling at the NW Mediterranean using the POLCOMS–WAM model with new developments. The Stokes’ drift effect on currents has been included and the distribution of surface stress between waves and currents has also been considered. The system is evaluated in the NW Mediterranean and an evaluation of different forcing terms is performed. The temperature and salinity distributions control the main patterns of the Mediterranean circulation. Currents are typically small and therefore the modification of waves due to the effect of currents is minimal. However, the wave induced currents, mainly caused by a modified wind drag due to waves, produce changes that become an important source of mass transport. POLCOMS was able to reproduce the main Mediterranean features, its coupling with WAM can be a very useful tool for ocean and wave modelling in the Mediterranean and other shelf seas. 相似文献
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Field measurements of cross-shore currents 0.25 m from the bed were made on two natural beaches under a range of incident wave conditions. The results indicated the presence of a relatively strong, offshore-directed mean current, both within and seaward of the surf zone. Typical velocities within the surf zone were of the order of 0.2–0.3 m/s. This bed return flow, or “undertow”, represents a mass conservation response, returning water seaward that was initially transported onshore in the upper water column, primarily above the trough of the incident waves. The measurements demonstrated that the bed return flow velocity increases with the incident wave height. In addition, the crossshore distribution of the bed return flow is characterised by a mid-surf zone maximum, which exhibits a strong decrease in velocity towards the shoreline and a more gradual decay in the offshore direction. Several bed return flow models based on mass continuity were formulated to predict the cross-shore distribution of the bed return flow under an irregular wave field and were compared with the field data. Best agreement was obtained using shallow water linear wave theory, after including the mass transport associated with unbroken waves. The contribution of the unbroken waves enables net offshore-directed bottom currents to persist outside the region of breaking waves, providing a mechanism, other than rip currents, to transport sediment offshore beyond the surf zone. 相似文献
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《Coastal Engineering》2006,53(2-3):157-170
Influence of various factors affecting the longshore currents induced by obliquely incident random waves is examined through numerical calculation. Seven numerical models for random wave breaking process are found to yield large differences in the wave heights in the surf zone and longshore current velocities. The turbulent eddy viscosity formulation by Larson and Kraus [Larson, M. and Kraus, N.C. (1991): Numerical model of longshore current for bar and trough beaches, J. Waterway, Port, Coastal, and Ocean Eng., ASCE, 117 (4), pp. 326-347.] functions almost equal to that by Battjes [Battjes, J.A. (1975): Modeling of turbulence in the surf zone, Proc. Symp. Modeling Techniques, pp. 1050–1061.], but the formulation by Longuet-Higgins [Longuet-Higgins, M.S. (1970): Longshore current generated by obliquely incident sea waves, 1 and 2, J. Geophys. Res., 75 (33), pp. 6779–6801.] produces excessive diffusion of longshore currents into the offshore zone. The generation and decay process of the surface roller is indispensable in the longshore current analysis. The random wave transformation model called PEGBIS (Parabolic Equation with Gradational Breaker Index for Spectral waves) by Goda [Goda, Y. (2004): A 2-D random wave transformation model with gradational breaker index, Coastal Engineering Journal, JSCE and World Scientific, 46 (1), pp. 1–38.] produced good agreement with several laboratory and field data of longshore currents. 相似文献
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A field experiment on the nature of rip currents was conducted on the Dutch coast, which differs from previous rip current study sites because it is a wind-sea dominated environment with mostly obliquely incident waves and tidally-driven longshore currents. During the experiment three distinct flow patterns, obtained with GPS tracked drifter instruments, were observed: (1) a locally governed circulation cell, (2) an offshore current that is deflected shore parallel outside the surf zone and (3) a meandering longshore current. The transition from rip currents (flow patterns 1 and 2) to meandering longshore currents (flow pattern 3) occurred gradually within the tidal cycle with longshore currents prevalent at mid to high tide. Rip currents at this site appeared at depressions in the surf zone bar and typically occurred when the water level fell below NAP (equivalent to MSL), even in the presence of obliquely incident waves and tidally driven longshore currents. Hindcast simulations of the drifter experiments were performed with the numerical model XBeach and showed good agreement with field observations. The model was subsequently used to investigate the influence of tidal water level fluctuations, longshore currents and obliquely incident waves on rip currents.Rip currents were initiated when the water level dropped below a specific threshold with the magnitude of the rip current associated with the water level. The strength of the tidal current and its orientation with respect to the incident waves governed the offshore extent and orientation of the rip current. In contrast to other studies that suggest that rip currents solely occur under shore normal (or slightly oblique waves), in this study both observations and numerical model simulations indicate that rip currents can exist under large angles of wave incidence, when the rip channel is sufficiently wide and the wave height is small. 相似文献
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Lou Jing P.V. Ridd C.L. Mayocchi M.L. Heron 《Estuarine, Coastal and Shelf Science》1996,42(6):787-802
Waves propagating from deep water into shallow coastal areas produce oscillatory currents near the sea bottom. The magnitude of these currents depend upon the period and amplitude of the incoming waves, and the dissipation mechanism such as wave breaking and bottom friction. Field experiments in a gently shoaling bay, i.e. Cleveland Bay, Northern Australia, showed that there is a broad band of water at around 6 m depth, where the benthic surge velocities are maximum. Both further inshore and offshore, the bottom velocities were less than at 6 m depth, contrary to the normal expectation that the velocities should increase as the water becomes shallower. A new and computationally efficient wave model was developed and was able to reproduce experimental results for waves above 50 cm wave height, but not for small waves (wave height about 30 cm). One implication of this higher band of benthic surge velocities may be to produce high water turbidities in this region. Turbidity data from Cleveland Bay is consistent with this hypothesis. 相似文献
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An offshore shoal or bar refracts ocean surface waves and causes wave focusing/defocusing on the adjacent beach.Wave focal patterns characterized by alongshore variations in wave height, wave angle, and breaking location induce alongshore non-uniformities of wave setup and nearshore circulation, e.g., rip currents and alongshore currents, in the surfzone. A simplified analytic model for nearshore circulation generated by focused/defocused waves on a planar beach is developed and theoretical solutions are obtained using transport stream function and perturbations in alongshore distributions of wave height and wave angle at the breaker line. The analytic model suggests that alongshore currents are strongly affected by a pair of counter-rotating vortices generated shoreward of the wave focal zone. The vortices are persistent, and their strengths depend on the amplitudes of alongshore variations in wave height and wave angle. The alongshore gradient in wave height tends to intensify the vortices while the convergence of wave angle tends to weaken the vortices. Divergent flows associated with the vortices in the surfzone are intense,strengthening alongshore currents in the downstream of the wave focal zone and weakening alongshore currents or causing flows reversal in the upstream. Alongshore currents are modulated by rip currents associated with the wave focusing/defocusing patterns. 相似文献