Wave-induced steady streaming,mass transport and net sediment transport in rough turbulent ocean bottom boundary layers   总被引：1，自引：0，他引：1  

Lars Erik Holmedal  Dag Myrhaug 《Continental Shelf Research》2009

The interaction between two important mechanisms which causes streaming has been investigated by numerical simulations of the seabed boundary layer beneath both sinusoidal waves and Stokes second order waves, as well as horizontally uniform bottom boundary layers with asymmetric forcing. These two mechanisms are streaming caused by turbulence asymmetry in successive wave half-cycles (beneath asymmetric forcing), and streaming caused by the presence of a vertical wave velocity within the seabed boundary layer as earlier explained by Longuet-Higgins. The effect of wave asymmetry, wave length to water depth ratio, and bottom roughness have been investigated for realistic physical situations. The streaming induced sediment dynamics near the ocean bottom has been investigated; both the resulting suspended load and bedload are presented. Finally, the mass transport (wave-averaged Lagrangian velocity) has been studied for a range of wave conditions. The streaming velocities beneath sinusoidal waves (Longuet-Higgins streaming) is always in the direction of wave propagation, while the streaming velocities in horizontally uniform boundary layers with asymmetric forcing are always negative. Thus the effect of asymmetry in second order Stokes waves is either to reduce the streaming velocity in the direction of wave propagation, or, for long waves relative to the water depth, to induce a streaming velocity against the direction of wave propagation. It appears that the Longuet-Higgins streaming decreases as the wave length increases for a given water depth, and the effect of wave asymmetry can dominate, leading to a steady streaming against the wave propagation. Furthermore, the asymmetry of second order Stokes waves reduces the mass transport (wave-averaged Lagrangian velocity) as compared with sinusoidal waves. The boundary layer streaming leads to a wave-averaged transport of suspended sediments and bedload in the direction of wave propagation.  相似文献   

The influence of El Niño-Southern Oscillation (ENSO) cycles on wave-driven sea-floor sediment mobility along the central California continental margin     

Curt D. Storlazzi  Jane A. Reid 《Continental Shelf Research》2010

Ocean surface waves are the dominant temporally and spatially variable process influencing sea floor sediment resuspension along most continental shelves. Wave-induced sediment mobility on the continental shelf and upper continental slope off central California for different phases of El Niño-Southern Oscillation (ENSO) events was modeled using monthly statistics derived from more than 14 years of concurrent hourly oceanographic and meteorologic data as boundary input for the Delft SWAN wave model, gridded sea floor grain-size data from the usSEABED database, and regional bathymetry. Differences as small as 0.5 m in wave height, 1 s in wave period, and 10° in wave direction, in conjunction with the spatially heterogeneous unconsolidated sea-floor sedimentary cover, result in significant changes in the predicted mobility of continental shelf surficial sediment in the study area. El Niño events result in more frequent mobilization on the inner shelf in the summer and winter than during La Niña events and on the outer shelf and upper slope in the winter months, while La Niña events result in more frequent mobilization on the mid-shelf during spring and summer months than during El Niño events. The timing and patterns of seabed mobility are addressed in context of geologic and biologic processes. By understanding the spatial and temporal variability in the disturbance of the sea floor, scientists can better interpret sedimentary patterns and ecosystem structure, while providing managers and planners an understanding of natural impacts when considering the permitting of offshore activities that disturb the sea floor such as trawling, dredging, and the emplacement of sea-floor engineering structures.  相似文献   

中纬度电离层f_oF₂潮汐的变化特性          下载免费PDF全文

周惟琦  余优  万卫星  刘立波 《地球物理学报》2018,61(1):30-42

本文通过对1960年以来全球磁纬度40°N至50°N内测高仪台站的观测数据进行研究，提取了电离层F₂层临界频率（f_oF₂）的潮汐，揭示了其变化特征及可能的形成原因.研究发现，周日和半日的迁移潮汐分量（即DW1和SW2）强度最大，并且显示出明显的年变化和半年变化.周日潮汐的3波分量（即DE3）作为典型的非迁移潮汐分量，相对较弱，显示出微弱的半年变化.在冬季，DW1和SW2与太阳活动指数（F₁₀₇）呈现正相关性，其相关系数分别大于0.88和0.65.相反，在夏季，DW1和SW2与太阳活动指数呈现负相关性，特别是SW2，其相关系数在6月份达到-0.72.在相对于纬向均值的归一化处理之后，上述潮汐强度和太阳活动指数之间的正/负相关性被显著增强/削弱.其中，归一化后的夏季DW1和SW2与太阳活动指数的相关系数达到-0.8.更加深入的讨论显示出上传的大气潮汐波动可能是电离层潮汐除了太阳辐射之外的重要驱动源，并且这种驱动机制在SW2中更加强烈.  相似文献   

1979-2018年间山东半岛沿海台风浪危险性分布的数值模拟研究     

王宁  侯一筠  李水清  莫冬雪  刘泽  李健 《海洋与湖沼》2020,51(4):861-868

台风浪灾害在山东半岛沿海时常发生，对人类生命财产和基础设施构成很大威胁，因此，对山东半岛海域台风浪的危险性分析具有重要的现实意义。本研究使用ADCIRC+SWAN耦合数值模式采用Holland模型风场与NCEP再分析风场组合的风场驱动，对1979—2018年36次台风过境期间的海浪过程进行了模拟。以台风过境时最大有效波高及历时频数作为危险性评价指标，给出了山东半岛近岸台风浪强度等级分布、历时频数分布以及危险性指数分布。研究结果显示，山东半岛北部为台风浪低危险区，台风浪强度等级低且历时短；南部二级强度（有效波高范围为1.3—2.5m）以上台风浪发生较为频繁，危险性高于北部；东部台风浪强度可以达到四级（有效波高4m以上），危险性最高。  相似文献   

Effects of waves on the initiation of headland-associated sandbanks     

Nicolas Guillou  Georges Chapalain 《Continental Shelf Research》2011,31(11):1202-1213

Linear sandbanks appear in the lee of coastal headlands where the hydrodynamics are dominated by strong tidal currents and the seabed is characterized by an abundance of sands. They may develop as symmetrical sandbanks on either sides of the headland or as an unique banner bank. The present study numerically investigates the combined effects of waves and tide on the initial development of headland-associated sandbanks. A morphological model based on the coupling of the wave propagation module SWAN (Simulating WAves Nearshore) with the three-dimensional circulation module COHERENS (COupled Hydrodynamical-Ecological model for REgioNal and Shelf seas) is applied to an idealized Gaussian shaped headland for waves conditions varying in heights and directions at the offshore boundary. The coupling considers the effects of the interactions between the wave and current bottom boundary layers, namely the enhanced levels of turbulence near the bottom and the increase of the total bottom shear stress. Waves substantially modify the initial development of sandbanks formed by suspension narrowing their width and reorienting them along the side of the headland. They weakly impact the morphogenesis of sandbanks by bedload favoring on a short-time scale the growth of symmetric circular-shaped features and a central depositional spit prolonging the headland tip. Waves of transverse directions toward the tip of the headland contribute to the initiation by suspension of a well-developed feature in the headland side of low energy limiting the seabed evolution in the exposed area.  相似文献   

Scour and burial mechanics of conical frustums on a sandy bed under combined flow conditions     

Yovanni A. Cataño-Lopera 《Ocean Engineering》2011,38(10):1256-1268

The scour and burial of conical frustums placed on a sandy bed under waves alone (WA) and combined flows (CF) conditions was investigated. The observations indicate that equilibrium burial depth is smaller than burial of other objects such as short cylinders laying on a sand bed under equivalent hydrodynamic conditions. Truncated cone offers less resistance to the flow field due to its more round shape when compared to a horizontally placed short cylinder characterized by sharp edges. A smaller disruption to the flow field translates to less turbulent intensity and to smaller sediment transport capacity of the flow around the object and less burial. The equilibrium burial depth shows a significantly weaker dependency on the Shields parameter than on the Keulegan-Carpenter number, contrary to the case of finite short cylinders. A new empirical predictor based on the relative strength of the wave to the wave plus current velocity, the Keulegan-Carpenter number, and the Shields parameter is proposed for estimating the equilibrium burial of truncated cones under combined flows. Both the Keulegan-Carpenter number and the Shields parameter determine the width of the scour hole around the cone. The former however, is the most dominant parameter influencing the length of the scour hole.  相似文献   

SWAN predictions of waves observed in shallow water onshore of complex bathymetry   总被引：1，自引：0，他引：1  

L. Gorrell  B. Raubenheimer  Steve Elgar  R.T. Guza 《Coastal Engineering》2011

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   

Wave-ice interaction in the North-West Barents Sea     

《Applied Ocean Research》2019

The results of field work on drift ice during wave propagation are analyzed and presented. The field work was performed in the Barents Sea, and the main focus of the paper is on wave processes in the MIZ. A model of wave damping in broken ice is formulated and applied to interpret the field work results. It is confirmed that waves of higher frequencies are subjected to stronger damping when they propagate below the ice. This reduces the frequency of most energetic wave with increasing distance from the ice edge. Difference of wave spectra measured in two relatively close locations within the MIZ is discussed. The complicated geometry and dynamics of the MIZ in the North-West Barents Sea allow waves from the Atlantic Ocean and south regions of the Barents Sea to penetrate into different locations of the MIZ.  相似文献   

A two layer model for wave dissipation in sea ice     

《Applied Ocean Research》2019

Sea ice is highly complex due to the inhomogeneity of the physical properties (e.g. temperature and salinity) as well as the permeability and mixture of water and a matrix of sea ice and/or sea ice crystals. Such complexity has proven itself to be difficult to parameterize in operational wave models. Instead, we assume that there exists a self-similarity scaling law which captures the first order properties. Using dimensional analysis, an equation for the kinematic viscosity is derived, which is proportional to the wave frequency and the ice thickness squared. In addition, the model allows for a two-layer structure where the oscillating pressure gradient due to wave propagation only exists in a fraction of the total ice thickness. These two assumptions lead to a spatial dissipation rate that is a function of ice thickness and wavenumber. The derived dissipation rate compares favourably with available field and laboratory observations.  相似文献   

风暴潮与盐沼相互作用研究进展          下载免费PDF全文

张振伟  刘贞文  刘必劲 《海洋开发与管理》2019,36(7):42-48

文章对沿海风暴和盐沼之间动态相互作用的研究所取得的进展进行了综述。包括:极端水位和风浪在盐沼区域的耗散,风暴对盐沼的地貌影响,沉积记录对风暴潮和沉积物的保留,以及海平面上升对盐沼长期存活的重要性。盐沼能够有效地消散波浪能和风暴增水,特别是当沼泽植被较高并且连续时。地貌形态学观点认为盐沼通常能够抵御风暴而不会崩溃,风暴只会造成长期盐沼侵蚀的一小部分。风暴作用的结果可能影响盐沼系统在随后的暴风雨期间对正常天气条件的响应。  相似文献