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1.
Numerical simulations are performed to investigate the influence of variable front slopes on flow evolution and waveform inversion of a depression ISW (internal solitary wave) over an idealized shelf with variable front slopes. A finite volume based on Cartesian grid method is adopted to solve the Reynolds averaged Navier-Stokes equations using a k-ε model for the turbulent closure. Numerical results exhibit the variations of several pertinent properties of the flow field, in the case with or without waveform inversion on the horizontal plateau of an obstacle. The clockwise vortex is stronger than the counterclockwise one, almost throughout the wave-obstacle interaction. Analysis of the turbulent energy budget reveals that the turbulent production term in the governing equations dominates the wave evolution during a wave-obstacle interaction; otherwise the buoyancy production term and the dissipation term due to viscosity within turbulent eddies play a major role in energy dissipation. In addition, the front slope affects mainly the process and reflection of the wave evolution but has less influence than other physical parameters. Moreover, total wave energy of the leading crest is smaller than that of the leading trough even in the cases with waveform inversion on the plateau. 相似文献
2.
内孤立波具有振幅尺度大、能量集中的特点,其引起流场和密度场的迅速变化可能对海洋工程结构物以及水下潜体造成严重威胁。因此研究不同造波条件下生成的内孤立波运动的流场特征具有重要的学术意义和实际应用价值。采用直接数值模拟方法和给定的初始密度场密度跃迁函数,对重力塌陷激发内孤立波的运动过程进行研究,探讨了不同造波条件下,激发产生的内孤立波波型、涡度、振幅和水平速度等流场特征。结果表明:(1)直接模拟数值方法能够模拟内孤立波传播过程中的密度界面波型反转现象;(2)从定性和定量的角度,证实了不稳定内孤立波传播过程中存在能量的向后传递;(3)对于相同的台阶深度(水闸两侧初始密度界面的高度差),初始涡流保持相同,但是随着上下层水深比的减小,其强度下降显著;(4)台阶深度对初始涡流的垂直结构的影响要大于上下层水深比,且台阶深度对内孤立波的振幅、水平速度的影响显著。 相似文献
3.
4.
本文通过实验室水槽实验,讨论内孤立波经过凹陷地形的演化过程。实验在两层流体中进行,上下水层的厚度和密度被定量地控制,改变凹陷地形的宽度,并对每种地形分别进行了不同分层结构下具有不同初始振幅的内孤立波对照实验,研究内孤立波与凹陷地形的作用过程。研究发现,本文实验环境下凹型内孤立波实验波形与mKdV(Korteweg-deVries)理论波形更符合;而上凸型内孤立波实验,当非线性参数ε≤0.22时,KdV理论波形与实验波形符合较好,当非线性参数ε≥0.27时.mKdV理论与实验波形符合较好。下凹型内孤立波经凹陷地形过程中波形变化轻微,主波振幅有先减小后增大的趋势,且障碍比越大,变化趋势越明显。本实验结果可作为研究海洋中内孤立波与海底凹陷地形作用情况的参考。 相似文献
5.
Sperry B.J. Lynch J.F. Gawarkiewicz G. Ching-Sang Chiu Newhall A. 《Oceanic Engineering, IEEE Journal of》2003,28(4):729-749
During July and August of 1996, the summer component of the New England shelfbreak front PRIMER experiment was fielded in the Mid-Atlantic Bight, at a site due south of Martha's Vineyard, MA. This study produced acoustic transmission data from a network of moored sources and receivers in conjunction with very-high-resolution oceanography measurements. This paper analyzes receptions at the northeast array receiver from two 400 Hz acoustic tomography sources, with the transmission paths going from the continental slope onto the continental shelf. These data, along with forward acoustic-propagation modeling based on moored oceanographic data, SeaSoar hydrography measurements, and bottom measurements, reveal many new and interesting aspects of acoustic propagation in a complicated slope-shelf environment. For example, one sees that both the shelfbreak front and tidally generated soliton internal wave packets produce stronger mode coupling than previously expected, leading to an interesting time-and-range-variable population of the acoustic normal modes. Additionally, the arrival time wander and the signal spread of acoustic pulses show variability that can be attributed to the presence of a frontal meander and variability in the soliton field. These and other effects are discussed in this paper, with an emphasis on creating a strong connection between the environmental measurements and the acoustic field characteristics. 相似文献
6.
The experimental investigation of the run-up of periodic internal waves in a two-layer fluid on the coastal slope is performed
in an open hydrochannel at the Physical Department of the Lomonosov Moscow State University. The waves are produced by a wave
generator. We study the transformation of waves, the vertical structure of the field of velocities of mass transfer, and the
behavior of the parameters of internal waves propagating over the sloping bottom. It is shown that the run-up and breaking
of internal waves are accompanied by periodic emissions of portions of the heavier fluid from the bottom layer upward along
the slope. The Stokes drift velocity changes its sign as a function of depth. Moreover, both the wave length (the horizontal
distance between the neighboring crests) and the height of waves over the sloping bottom (the elevation of the crest over
the slope along the vertical) decrease as the wave approaches the coast. 相似文献
7.
A series of experimental studies about the force of internal solitary wave and internal periodic wave on vertical cylinders have been carried out in a two-dimensional layered internal wave flume. The internal solitary waves are produced by means of gravitational collapse at the layer thickness ratio of 0.2, and the internal periodic waves are produced with rocker-flap wave maker at the layer thickness ratio of 0.93. The wave parameters are obtained through dyeing photography. The vertical cylinders of the same size are arranged in different depths. The horizontal force on each cylinder is measured and the vertical distribution rules are researched. The internal wave heights are changed to study the impact of wave heights on the force. The results show that the horizontal force of concave type internal solitary wave on vertical cylinder in the upper-layer fluid has the same direction as the wave propagating, while it has an opposite direction in the lower-layer. The horizontal force is not evenly distributed in the lower fluid. And the force at different depths increases along with wave height. Internal solitary wave can produce an impact load on the entire pile. The horizontal force of internal periodic waves on the vertical cylinders is periodically changed at the frequency of waves. The direction of the force is opposite in the upper and lower layers, and the value is close. In the upper layer except the depth close to the interface, the force is evenly distributed; but it tends to decrease with the deeper depth in the lower layer. A periodic shear load can be produced on the entire pile by internal periodic waves, and it may cause fatigue damage to structures. 相似文献
8.
Dynamical analysis of mesoscale eddy-induced ocean internal waves using linear theories 总被引：3，自引：1，他引：2
This study aims to explore generation mechanisms of the ocean internal wave using the dynamical analysis methods based on linear theories. Historical cruise measurements and recent synthetic aperture radar （SAR） observations of mesoscale eddies with diameter of several tens of kilometers to hundreds of kilometers show that the internal wave packets with wavelength of hundreds of meters to kilometer exist inside the mesoscale eddies. This coexistence phenomenon and inherent links between the two different scale processes are revealed in the solutions of governing equations and boundary conditions for the internal wave disturbance with a horizontally slowly variable amplitude in a cylindrical coordinate system. The theoretical solutions indicate that the instability of eddy current field provides the dynamical mechanism to internal wave generation. The derived dispersion relation indicates that the internal wave propagation is modified by the eddy current field structure. The energy equation of the internal waves clearly shows the internal wave energy increment comes from the eddy. The theoretical models are used to explain the observation of the mesoscale eddy-induced internal waves off the Norwegian coast. The two-dimensional waveform solution of the anticyclonic eddy-induced internal wave packet appears as ring-shaped curves, which contains the typical features of eddy stream lines. The comparison of theoretical solutions to the structure of the internal wave packets on SAR image shows a good agreement on the major features. 相似文献
9.
南海北部陆坡区内孤立波的垂向热量输送 总被引：1，自引：0，他引：1
An integrated analysis of internal solitary wave(ISW) observations obtained from two moorings over the continental slope in the northern South China Sea(SCS) leads to an assessment of the vertical heat transport of the ISWs. The clusters of ISW packets are phase-locked to the fortnightly cycle of the semidiurnal tide. The ISWs appear during large semidiurnal tides, and there is a period of 5–6 d when no ISWs are observed. The effect of the ISWs on the continental slope heat budget is observed. The ISWs can modify a local temperature field in which the temperature in the upper layer can be changed by O(100) °C after the ISWs passed the mooring. Both ISWinduced diffusion and ISW-induced advection contribute to the temperature variation. The estimates imply an average vertical heat flux of 0.01 to 0.1 MW/m~2 in the ISWs in the upper 500 m of the water column. The vertical heat transport ranges from 0.56 to 2.83 GJ/m~2 with a mean value of 1.63 GJ/m~2. The observations suggest that the vertical heat transport is proportional to the maximum vertical displacement. 相似文献
10.
The continental margin of Western Australia is a rifted or “Atlantic”-type margin, with a complex physiography. The margin comprises a shelf, an upper and lower continental slope, marginal plateaus, a continental rise, and rise or lower slope foothills. Notches or terraces on the shelf reflect pre-Holocene deposition of prograded sediment, whose seaward limit was determined by variations in relative sea level, wave energy, and sediment size and volume. The upper continental slope has four physiographic forms: convex, due to sediment outbuilding (progradation) over a subsiding marginal plateau; scarped, due to erosion of convex slopes; stepped, due to deposition at the base of a scarped slope; and smooth, due to progradation of an upper slope in the absence of a marginal plateau. Lying at the same level as the upper/lower slope boundary are two extensive marginal plateaus: Exmouth and Scott. They represent continental crust which subsided after continental rupture by sea-floor spreading. Differential subsidence, probably along faults, gave rise to the various physiographic features of the plateaus. The deep lower continental slope is broken into straight northeasterly-trending segments, that parallel the Upper Jurassic/Lower Cretaceous rift axis, and northwesterly-trending segments that parallel the transform direction. The trends of the slope foothills are subparallel to the rift direction. The four abyssal plains of the region (Perth, Cuvier, Gascoyne and Argo) indicate a long history of subsidence and sedimentation on Upper Jurassic/Lower Cretaceous oceanic crust. 相似文献
11.
Masaki Kawabe 《Journal of Oceanography》1982,38(3):115-124
Properties of coastal trapped waves when the pycnocline intersects a sloping bottom are studied using a two-layer model which has slopes in both layers. In this system there is an infinite discrete sequence of modes, and four different sorts of waves exist: the barotropic Kelvin wave, the upper shelf wave, the lower shelf wave and the internal Kelvin-type wave. They all propagate with the coast to their right in the Northern Hemisphere. The upper and lower shelf waves are due to the topographic-effect on the upper-layer and lower-layer slopes, respectively. Their motions are dominant in the respective layers being accompanied by significant interface elevations. The properties of the upper (lower) shelf wave are almost unaffected by the existence of a lower-layer (upper-layer) slope. The motion of the internal Kelvin-type wave is confined to the region around the line where the density interface intersects the bottom slope.The modes, except that with the fastest phase speed (the barotropic Kelvin wave), are assigned mode numbers in order of descending frequency. Characteristics of Mode 1 change with wavenumber; the upper shelf wave for small wavenumbers and the internal Kelvin-type wave for large wavenumbers (high frequencies). The higher modes of Mode 2 and above can be classified into the upper and lower shelf waves. 相似文献
12.
经验模态分解(empirical mode decomposition,简称EMD)是反演海洋内波参数的有效方法之一,但由于EMD存在模态混叠等问题,对海洋内波进行参数反演时会产生一定误差。相比较于EMD,变分模态分解(variational mode decomposition,简称VMD)能够有效地抑制模态混叠现象。为了更好地对海洋内波进行参数反演,提出了一种基于VMD对合成孔径雷达(synthetic aperture radar,简称SAR)遥感图像中的内波参数进行自动反演的方法。该方法先对SAR图像进行Canny处理,获取图像中的内波条纹信息,再根据内波传播方向自动选取灰度剖面;然后利用集合经验模态分解(ensemble empirical mode decomposition,简称EEMD)信号特征自适应分解模态函数的特点,再将分解得到的有效模态数作为VMD中参数K的参考值;最后利用VMD分解后的数据进行内波参数反演。试验结果表明:通过对Canny预处理后的条纹信息进行灰度剖面自动选取,解决了人为选取剖面所可能导致的误差;通过对剖面信号进行VMD处理不仅解决了EMD模态混叠的问题,成功地反演出内波的前导波振幅,而且所反演的结果与EEMD反演参数以及实测资料数据吻合得很好。 相似文献
13.
为获取南海北部陆坡海区第一模态内孤立波的动力结构及时间变化特征,本文利用该海区1套内孤立波浮标观测数据,对陆坡海区的内孤立波现场观测数据分析,识别判定了2021年5月5日至6月3日共30 d的179次第1模态内孤立波过程,并进行了内孤立波的特征分析。南海北部陆坡海区第1模态内孤立波剖面流场为双层结构,上层主要为西偏北向流动,下层流向与之相背,流速转向发生在100～150 m深度处。内孤立波期间,最大流速多发生于上层,流速为60～120 cm/s,底层流增强,上层流与下层流流向相反。受内潮影响,研究区域内孤立波存在半日和全日2个周期,主要以20～30 min间隔的波列形式向西偏北方向传播。本文关于南海北部陆坡海区第一模态内孤立波的分析研究有助于提升对该海区内孤立波时空变化特征的认识,为工程水下施工提供参考和依据。 相似文献
14.
将置于大尺度密度分层水槽上下层流体中的两块垂直板反方向平推,以基于MCC理论解的内孤立波诱导上下层流体中的层平均水平速度作为其运动速度,发展了一种振幅可控的双推板内孤立波实验室造波方法,并对内孤立波作用下浮式生产储油系统(FPSO)的载荷特性开展了系列实验。结果表明,无因次内孤立波水平力和力矩幅值均与先导内孤立子无因次振幅之间呈线性关系,其斜率与上下层流体深度比有关;在各种上下层流体深度比下,无因次内孤立波垂向力幅值与先导内孤立子振幅之间近似呈幂函数关系。 相似文献
15.
Numerical modeling on the interaction of internal solitary wave with slope-shelf and modal analysis 总被引：1，自引：0，他引：1
On the basis of a nonhydrostatic numerical model,the interaction of internal solitary wave with slope-shelf was studied.The breaking and polarity transformation were analyzed.A "kink" structure,due to shoaling topography and higher nonlinear effect,was found to be generated by the leading wave before breaking.Coherent vortex shedding behind the leading wave was presented.The evolution characteristics of the modal structure were analyzed based on the empirical orthogonal function method.The modal structure was complicated due to the effect of the variable topography,especially when breaking occurred.In the performed experiments,the contributions to the total variance from higher mode jumped from no more than 20% to over 40%. 相似文献
16.
Toshiyuki Hibiya 《Journal of Oceanography》2004,60(3):637-643
The generation process of internal waves by strong tidal flow over a continental shelf slope is reproduced using a multi-level
numerical model. On the basis of the numerical results, the crucial role of the tidal advection effect in the generation process
of internal waves is demonstrated. The close relation between the resulting internal waveform and the strength of the tidal
advection effect is also examined. The barotropic forcing on the internal wave actually works within a relatively small horizontal
scale over the top of the continental shelf slope. When the maximum internal Froude number at the shelf break (Frm) is less than about 0.6, the amplitude of the resulting internal wave is almost proportional to Frm. When Frm is more than about 0.6, however, the amplitude of the resulting internal wave becomes larger than predicted by linear theory.
In particular, when Frm is more than unity, the time period during which the shoreward propagating internal wave stays in the barotropic forcing
region becomes much longer. Consequently, the internal wave is significantly amplified with the horizontal scale approaching
that of the barotropic forcing, which concentrates in a relatively small region over the top of the continental shelf slope.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
为研究内孤立波质量源数值造波方法,本文采用两个点源形式的质量源,分别放置于两层流体的上下层中作为内孤立波激发源。推导源项表达式,从不可压缩流体的Navier-Stokes方程出发,结合内孤立波Kd V、e Kd V理论,基于商业软件FLUENT发展了一种内孤立波质量源数值造波方法。通过数值模拟,分析了质量源造波过程中内孤立波的生成过程,并将数值模拟结果同理论及实验作对比。结果表明:基于此方法生成的内孤立波波形、波高及波致水平速度与理论及实验吻合度较好,该方法是可行的,并且耗时短、效率高。 相似文献
18.
《Oceanic Engineering, IEEE Journal of》2004,29(4):1182-1199
In a recent study, satellite images have shown that internal solitons are active in the northern South China Sea (SCS). During the Asian Seas International Acoustic Experiment (ASIAEX) pilot studies, current profiler and thermistor chain moorings were deployed in the spring of 1999 and 2000 to investigate internal solitons northeast of Tung-Sha Island on the continental slope of the northern SCS. Most of the observed internal solitons were first baroclinic mode depression waves. The largest horizontal current velocity, vertical displacement, and temperature variation induced by the internal solitons were around 240 cm/s, 106 m, and 11/spl deg/C, respectively, while the estimated nonlinear phase speed was primarily westward at 152 /spl plusmn/ 4 cm/s. The observed internal solitons could be categorized as four types. The first type is the incoming wave from deep water and can be described reasonably well with the KdV equation. The second and third types are in the transition zone before and close to the turning point (where the upper and lower layer depths are equal), respectively. These two types of solitons were generally near the wave-breaking stage. The fourth type of soliton is a second baroclinic mode and probably was locally generated. The time evolutions are asymmetric, especially at the middle depths. A temperature kink following the main pulse of the soliton is often seen. Higher order nonlinear and shallow topographic effects could be the primary cause for these features. The appearance/disappearance of internal solitons coincides mostly with spring/neap tide. The internal soliton is irregularly seen during the neap tide period and its amplitude is generally small. The time interval between two leading solitons is generally around 12 h. The first baroclinic mode of the semidiurnal tide has a larger amplitude than the diurnal tide and could redistribute its energy into the soliton. 相似文献
19.
The transfer function of a differential wave slope meter having the form of a two-element resonance array is determined. The measured spectrum depends on the coherence of the wave field and on the differential wave gauge's measuring base. Theoretical calculations of the transfer function are supported by experimentally derived data. Some recommendations are suggested on how to conduct measurements in the field and under laboratory conditions. Measurement accuracies are compared and limits of applicability are defined for a method of measuring sea surface slope by means of the differential wavemeter. The results presented may be effectively used to perform measurements of surface and internal waves, turbulence, etc.Translated by V. Puchkin. 相似文献
20.
利用2014年3–4月北象海豹携带的自动温盐深仪（CTD-SRDL）在阿拉斯加湾东部陆坡海域上采集到的温盐剖面数据,分析了该海域逆温现象的空间分布和演变过程。结果显示,研究海域存在明显的逆温现象,逆温幅度和逆温厚度范围分别介于0.2~1.6?C和20~280 m之间,前者沿陆坡向北幅度逐渐增大,后者在50?~58?N间往北逐渐变厚,在58?N以北海域平均厚度较薄。3月25日至4月22日,逆温层处于衰退阶段。逆温层下界温度不断下降,逆温幅度呈变弱趋势,逆温厚度呈变薄趋势。一维扩散模型模拟结果表明,湍扩散作用下,观测期间海表受热导致混合层上部位温升高,但底部仍保持低温,因此逆温层上界温度变化并不明显。次表层由于具有强的位温梯度,湍扩散导致逆温层下界温度显著降低,是观测期间逆温衰退的主要原因。湍扩散作用导致次表层水体温盐属性趋于均匀,这一过程对于阿拉斯加湾逆温现象的形成及演变研究具有重要意义。 相似文献