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1.
海浪破碎对海洋上混合层中湍能量收支的影响 总被引：3，自引：1，他引：2
海浪破碎产生一向下输入的湍动能通量,在近海表处形成一湍流生成明显增加的次层,加强了海洋上混合层中的湍流垂向混合。为了研究海浪破碎对混合层中湍能量收支的影响,文中分析了海浪破碎对海洋上混合层中湍流生成的影响机制,采用垂向一维湍封闭混合模式,通过改变湍动能方程的上边界条件,引入了海浪破碎产生的湍动能通量,并分别对不同风速下海浪破碎的影响进行了数值研究,分析了混合层中湍能量收支的变化。当考虑海浪破碎影响时,近海表次层中的垂直扩散项和耗散项都有显著的增加,该次层中被耗散的湍动能占整个混合层中耗散的总的湍能量的92.0%,比无海浪破碎影响的结果增加了近1倍;由于平均流场切变减小,混合层中的湍流剪切生成减小了3.5%,形成一种存在于湍动能的耗散和垂直扩散之间的局部平衡关系。在该次层以下,局部平衡关系与壁层定律的结论一致,即湍动能的剪切生成与耗散相平衡。研究结果表明,海浪破碎在海表产生的湍动能通量影响了海洋上混合层中的各项湍能量收支间的局部平衡关系。 相似文献
2.
Past studies have shown that there is a wave-enhanced, near-surface mixed-layer in which the dissipation rate is greater than
that derived from the “law of the wall”. In this study, turbulence in water columns under wind breaking waves is investigated
numerically and analytically. Improved estimations of dissipation rate are parameterized as surface source of turbulent kinetic
energy (TKE) for a more accurate modelling of vertical profile of velocity and TKE in the water column. The simulation results
have been compared with the experimental results obtained by Cheung and Street (1988) and Kitaigorodskii et al. (1983), with good agreement. The results show that the numerical full model can well simulate the near-surface wave-enhanced
layer and suggest that the vertical diffusive coefficients are highly empirical and related to the TKE diffusion, the shear
production and the dissipation. Analytical solutions of TKE are also derived for near surface layer and in deep water respectively.
Near the surface layer, the dissipation rate is assumed to be balanced by the TKE diffusion to obtain the analytical solution;
however, the balance between the dissipation and the shear production is applied at the deep layer. The analytical results
in various layers are compared with that of the full numerical model, which confirms that the wave-enhanced layer near the
surface is a diffusion-dominated region. The influence of the wave energy factor is also examined, which increases the surface
TKE flux with the wave development. Under this region, the water behavior transits to satisfy the classic law of the wall.
Below the transition depth, the shear production dominantly balances the dissipation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
Breaking wave induced nearsurface turbulence has important consequences for many physical and biochemical processes including water column and nutrients mixing,heat and gases exchange across air-sea interface.The energy loss from wave breaking and the bubble plume penetration depth are estimated.As a consequence,the vertical distribution of the turbulent kinetic energy(TKE),the TKE dissipation rate and the eddy viscosity induced by wave breaking are also provided.It is indicated that model results are found to be consistent with the observational evidence that most TKE generated by wave breaking is lost within a depth of a few meters near the sea surface.High turbulence level with intensities of eddy viscosity induced by breaking is nearly four orders larger than υwl(=κuwz),the value predicted for the wall layer scaling close to the surface,where uw is the friction velocity in water,κ with 0.4 is the von Kármán constant,and z is the water depth,and the strength of the eddy viscosity depends both on wind speed and sea state,and decays rapidly through the depth.This leads to the conclusion that the breaking wave induced vertical mixing is mainly limited to the near surface layer,well above the classical values expected from the similarity theory.Deeper down,however,the effects of wave breaking on the vertical mixing become less important. 相似文献
4.
继第部分之后研究了惯性内波和近惯性内波由f～的作用所致的剪切不稳定引起的破碎机制。物理上,该机制很象存在由风应力所致薄表面涡旋漂流层时表面波的破碎与饱和过程。惯性内波和近惯性内波的破碎产物与小尺度湍流一起形成了混合块,它与Gregg等人(1986)的持久混合观测结果一致。依据Thorpe(1973)实验的结果作者提出了一个估计湍流动能耗散率和消衰时间的方法。结果表明,在剪切不稳定中近惯性内波在湍动耗散中起了关键作用,而惯性内波引起非常弱的湍动耗散。使用内波能量谱的标准总能量密度估计出的近惯性内波的耗散率和消衰时间与PATCHEX测量结果非常一致。文中还讨论了几个与此破碎机制有关的问题。 相似文献
5.
Both microscale and finescale measurements were conducted along 20°N and 21°N in the northern South China Sea (SCS) during July 2007. Spatial variability of turbulent kinetic energy (TKE) dissipation rate was examined, and two finescale parameterizations were assessed and compared. TKE dissipation rates along the 21°N section were found to be much higher than those along 20°N; in particular, remarkably high TKE dissipation rates existed near the Luzon Strait and around the Dongsha Plateau, which were likely caused by internal tides and internal solitary waves, respectively. The Gregg–Henyey scaling does not work well in the northern SCS, while the MacKinnon–Gregg scaling with a modified parameter matches the observations in both magnitude and variability. One explanation is that the large-scale/low-mode shear mainly comes from low-frequency internal waves such as internal tides, which are not described well by the Garrett–Munk spectrum. 相似文献
6.
7.
Wave elevations and water particle velocities were measured in a laboratory surf zone created by the breaking of a narrow-band irregular wave train on a 1/35 plane slope. The incident waves form wave groups that are strongly modulated. It is found that the waves that break close to the shoreline generally have larger wave-height-to-water-depth ratios before breaking than the waves that break farther offshore. After breaking, the wave-height-to-water-depth ratio for the individual waves approaches a constant value in the inner surf zone, while the standard deviation of the wave period increases as the still water depth decreases. In the outer surf zone, the distribution of the period-averaged turbulent kinetic energy is closely correlated to the initial wave heights, and has a wider variation for narrow-band waves than for broad-band waves. In the inner surf zone, the distribution of the period-averaged turbulent kinetic energy is similar for narrow-band waves and broad-band waves. It is found that the wave elevation and turbulent kinetic energy time histories for the individual waves in a wave group are qualitatively similar to those found in a spilling regular wave. The time-averaged transport of turbulent kinetic energy by the ensemble-averaged velocity and turbulence velocity under the irregular breaking waves are also consistent with the measurements obtained in regular breaking waves. The experimental results indicate that the shape of the incident wave spectrum has a significant effect on the temporal and spatial variability of wave breaking and the distribution of turbulent kinetic energy in the outer surf zone. In the inner surf zone, however, the distribution of turbulent kinetic energy is relatively insensitive to the shape of the incident wave spectrum, and the important parameters are the significant wave height and period of the incident waves, and the beach slope. 相似文献
8.
S. N. Moshonkin V. B. Zalesny A. V. Gusev R. Tamsalu 《Izvestiya Atmospheric and Oceanic Physics》2014,50(1):49-60
A physical formulation of the problem is considered. A mathematical model and a numerical algorithm of the turbulence model as part of the ocean circulation model for simulations for decades are formulated. The model is based on the evolution equations for turbulent kinetic energy (TKE) and the frequency of its viscous dissipation. A numerical solution algorithm for both the circulation model and the turbulence model is based on implicit schemes of splitting with respect to physical processes and geometric coordinates. For the turbulence model, this provided analytical solutions at a splitting step related to TKE generation and dissipation. Numerical experiments have been performed with a model of the joint circulation of the North Atlantic, the Arctic Ocean, and the Bering Sea to reproduce the annual cycle and synoptic disturbances of ocean characteristics. The model has a resolution of 0.25° in latitude and longitude and 40 levels in the vertical, which are compressed toward the surface to reproduce the process of developed turbulence better. The results are compared with observations and with the results of simulations using traditional parameterizations of the upper ocean mixing. It is shown that the model reproduces ocean characteristics correctly, only slightly increasing the computation time in comparison with simple parameterizations. Spatial and temporal characteristics of turbulence are analyzed. 相似文献
9.
The parameter that describes the kinetics of the air-sea exchange of a poorly soluble gas is the gas transfer velocity which
is often parameterized as a function of wind speed. Both theoretical and experimental studies suggest that wind waves and
their breaking can significantly enhance the gas exchange at the air-sea interface. A relationship between gas transfer velocity
and a turbulent Reynolds number related to wind waves and their breaking is proposed based on field observations and drag
coefficient formulation. The proposed relationship can be further simplified as a function of the product of wind speed and
significant wave height. It is shown that this bi-parameter formula agrees quantitatively with the wind speed based parameterizations
under certain wave age conditions. The new gas transfer velocity attains its maximum under fully developed wave fields, in
which it is roughly dependent on the square of wind speed. This study provides a practical approach to quantitatively determine
the effect of waves on the estimation of air-sea gas fluxes with routine observational data. 相似文献
10.
《Coastal Engineering》2001,42(1):53-86
A numerical model is used to simulate wave breaking, the large scale water motions and turbulence induced by the breaking process. The model consists of a free surface model using the surface markers method combined with a three-dimensional model that solves the flow equations. The turbulence is described by large eddy simulation where the larger turbulent features are simulated by solving the flow equations, and the small scale turbulence that is not resolved by the flow model is represented by a sub-grid model. A simple Smagorinsky sub-grid model has been used for the present simulations. The incoming waves are specified by a flux boundary condition. The waves are approaching in the shore-normal direction and are breaking on a plane, constant slope beach. The first few wave periods are simulated by a two-dimensional model in the vertical plane normal to the beach line. The model describes the steepening and the overturning of the wave. At a given instant, the model domain is extended to three dimensions, and the two-dimensional flow field develops spontaneously three-dimensional flow features with turbulent eddies. After a few wave periods, stationary (periodic) conditions are achieved. The surface is still specified to be uniform in the transverse (alongshore) direction, and it is only the flow field that is three-dimensional.The turbulent structures are investigated under different breaker types, spilling, weak plungers and strong plungers. The model is able to reproduce complicated flow phenomena such as obliquely descending eddies. The turbulent kinetic energy is found by averaging over the transverse direction. In spilling breakers, the turbulence is generated in a series of eddies in the shear layer under the surface roller. After the passage of the roller the turbulence spreads downwards. In the strong plunging breaker, the turbulence originates to a large degree from the topologically generated vorticity. The turbulence generated at the plunge point is almost immediately distributed over the entire water depth by large organised vortices. Away from the bed, the length scale of the turbulence (the characteristic size of the eddies resolved by the model) is similar in the horizontal and the vertical direction. It is found to be of the order one half of the water depth. 相似文献
11.
A laboratory study on the turbulence and wave energy dissipations of spilling breakers in a surf zone is presented. Instantaneous velocity fields of propagating breaking waves on a 1/20 slope were measured using Particle Image Velocimetry (PIV). Due to the large region of the evolving wave breaking generated turbulent flow, seven PIV fields of view (FOVs) were mosaicked to form a continuous flow field in the surf zone. Mean and turbulence quantities were extracted by ensemble averaging 25 repeated instantaneous measurements at each FOV. New results for distribution and evolution of turbulent kinetic energy, mean flow energy, and total energy across the surf zone were obtained from analyzing the data. The turbulence dissipation rate was estimated based on several different approaches. It was found that the vertical distribution of the turbulence dissipation rate decays exponentially from the crest level to the bottom. The resulting energy budget and energy flux were also calculated. The calculated total energy dissipation rate was compared to that based on a bore approximation. It was found that the ratio of turbulence dissipation rate to total energy dissipation rate was about 0.01 in the outer surf zone and increased to about 0.1 after the breaking waves transformed into developed turbulent bores in the inner surf zone. 相似文献
12.
A comparison of weakly and fully non-linear models of the shoaling of a solitary internal wave 总被引：1，自引：0，他引：1
This study investigates the behaviour of internal solitary waves crossing a continental slope in the presence of a seasonal thermocline. Comparisons are made between a fully non-linear computational fluid dynamics (CFD) model, and weakly non-linear theory. Previous observations suggested that the amplitudes of solitary waves are capped as they pass across the continental slope, which may be due to laminar dynamics, or due to the effect of turbulence. Across the continental slope, CFD and second order variable depth KdV (vEKdV) predictions agree well with observations of a limited change in solitary wave amplitude. First order variable depth KdV theory overpredicts the final amplitude significantly. In terms of the wave shape, the CFD modeled wave changes from a KdV shape in deep water towards an EkdV solution in shallow water, as observations suggest. The phase speed of the CFD and vEKdV waves are similar to that observed in waters of 400–500 m deep, but are slightly lower than observed in 140 m depth. CFD predictions using a standard k, turbulence model showed that turbulence had little effect on the amplitude. These preliminary results indicate that in this situation wave capping is due to laminar, large amplitude solitary wave dynamics and is independent of turbulent mixing. 相似文献
13.
基于海浪模式WAVEWATCH Ⅲ模拟北太平洋海浪要素,结合NDBC浮标资料进行验证,发现模拟出的有效波高与浮标测量值具有很好的一致性。基于改进型白冠覆盖率耗散模型,利用海浪模式模拟出的有效波高、有效波周期和摩擦速度等海浪要素计算出单位面积水柱内因海浪破碎产生的湍动能通量。通过改变环流模式sbPOM湍动能方程的上边界条件,引入海浪破碎产生的湍动能通量,并探究海浪破碎对北太平洋海表面温度模拟的影响。研究表明,由于海浪破碎的引入,环流模式sbPOM对北太平洋海表面温度模拟的准确程度得到提升,这为大气模式提供一个准确的北太平洋下边界条件具有重要意义。 相似文献
14.
Large Eddy Simulation for Plunge Breaker and Sediment Suspension 总被引：1，自引：1，他引：1
Breaking waves are a powerful agent for generating turbulence that plays an important role in many fluid dynamical processes, particularly in the mixing of materials. Breaking waves can dislodge sediment and throw it into suspension, which will then be carried by wave-induced steady current and tidal flow. In order to investigate sediment suspension by breaking waves, a numerical model based on large-eddy-simulation (LES) is developed. This numerical model can be used to simulate wave breaking and sediment suspension. The model consists of a free-surface model using the surface marker method combined with a two-dimensional model that solves the flow equations. The turbulence and the turbulent diffusion are described by a large-eddy-simulation (LES) method where the large turbulence features are simulated by solving the flow equations, and a subgrid model represents the small-scale turbulence that is not resolved by the flow model. A dynamic eddy viscosity subgrid scale stress model has been used for the 相似文献
15.
Observational and numerical modeling methods for quantifying coastal ocean turbulence and mixing 总被引：6，自引：0，他引：6
Hans Burchard Peter D. Craig Hans van Haren H.E. Markus Meier Hartmut Prandke Eric D. Skyllingstad David J.S. Welsh Hemantha W. Wijesekera 《Progress in Oceanography》2008,76(4):399-442
In this review paper, state-of-the-art observational and numerical modeling methods for small scale turbulence and mixing with applications to coastal oceans are presented in one context. Unresolved dynamics and remaining problems of field observations and numerical simulations are reviewed on the basis of the approach that modern process-oriented studies should be based on both observations and models. First of all, the basic dynamics of surface and bottom boundary layers as well as intermediate stratified regimes including the interaction of turbulence and internal waves are briefly discussed. Then, an overview is given on just established or recently emerging mechanical, acoustic and optical observational techniques. Microstructure shear probes although developed already in the 1970s have only recently become reliable commercial products. Specifically under surface waves turbulence measurements are difficult due to the necessary decomposition of waves and turbulence. The methods to apply Acoustic Doppler Current Profilers (ADCPs) for estimations of Reynolds stresses, turbulence kinetic energy and dissipation rates are under further development. Finally, applications of well-established turbulence resolving particle image velocimetry (PIV) to the dynamics of the bottom boundary layer are presented. As counterpart to the field methods the state-of-the-art in numerical modeling in coastal seas is presented. This includes the application of the Large Eddy Simulation (LES) method to shallow water Langmuir Circulation (LC) and to stratified flow over a topographic obstacle. Furthermore, statistical turbulence closure methods as well as empirical turbulence parameterizations and their applicability to coastal ocean turbulence and mixing are discussed. Specific problems related to the combined wave-current bottom boundary layer are discussed. Finally, two coastal modeling sensitivity studies are presented as applications, a two-dimensional study of upwelling and downwelling and a three-dimensional study for a marginal sea scenario (Baltic Sea). It is concluded that the discussed methods need further refinements specifically to account for the complex dynamics associated with the presence of surface and internal waves. 相似文献
16.
The characteristics of wave and turbulence velocities created by a broad-banded irregular wave train breaking on a 1:35 slope were studied in a laboratory wave flume. Water particle velocities were measured simultaneously with wave elevations at three cross-shore locations inside the surf zone. The measured data were separated into low-frequency and high-frequency time series using a Fourier filter. The measured velocities were further separated into organized wave-induced velocities and turbulent velocity fluctuations by ensemble averaging. The broad-banded irregular waves created a wide surf zone that was dominated by spilling type breakers. A wave-by-wave analysis was carried out to obtain the probability distributions of individual wave heights, wave periods, peak wave velocities, and wave-averaged turbulent kinetic energies and Reynolds stresses. The results showed that there was a consistent increase in the kurtosis of the vertical velocity distribution from the surface to the bottom. The abnormally large downward velocities were produced by plunging breakers that occurred from time to time. It was found that the mean of the highest one-third wave-averaged turbulent kinetic energy values in the irregular waves was about the same as the time-averaged turbulent kinetic energy in a regular wave with similar deep-water wave height to wavelength ratio. It was also found that the correlation coefficient of the Reynolds stress varied strongly with turbulence intensity. Good correlation between u′ and w′ was obtained when the turbulence intensity was high; the correlation coefficient was about 0.3–0.5. The Reynolds stress correlation coefficient decreased over a wave cycle, and with distance from the water surface. Under the irregular breaking waves, turbulent kinetic energy was transported downward and landward by turbulent velocity fluctuations and wave velocities, and upward and seaward by the undertow. The undertow in the irregular waves was similar in vertical structure but lower in magnitude than in regular waves, and the horizontal velocity profiles under the low-frequency waves were approximately uniform. 相似文献
17.
The characteristics of turbulence created by a plunging breaker on a 1 on 35 plane slope have been studied experimentally in a two-dimensional wave tank. The experiments involved detailed measurements of fluid velocities below trough level and water surface elevations in the surf zone using a fibre-optic laser-Doppler anemometer and a capacitance wave gage. The dynamical role of turbulence is examined making use of the transport equation for turbulent kinetic energy (the k-equation). The results show that turbulence under a plunging breaker is dominated by large-scale motions and has certain unique features that are associated with its wave condition. It was found that the nature of turbulence transport in the inner surf zone depends on a particular wave condition and it is not similar for different types of breakers. Turbulent kinetic energy is transported landward under a plunging breaker and dissipated within one wave cycle. This is different from spilling breakers where turbulent kinetic energy is transported seaward and the dissipation rate is much slower. The analysis of the k-equation shows that advective and diffusive transport of turbulence play a major role in the distribution of turbulence under a plunging breaker, while production and dissipation are not in local equilibrium but are of the same order of magnitude. Based on certain approximate analytical approaches and experimental measurements it is shown that turbulence production and viscous dissipation below trough level amount to only a small portion of the wave energy loss caused by wave breaking. It is suggested that the onshore sediment transport produced by swell waves may be tied in a direct way to the unique characteristics of turbulent flows in these waves. 相似文献
18.
《Coastal Engineering》2004,51(1):53-80
In this paper, a two-dimensional multi-scale turbulence model is proposed to study breaking waves. The purpose of developing this model is to produce a relatively accurate model with moderate computer requirements. The free surface is tracked by the VOF technique, the log-law profile for the mean velocity is applied at the bottom. Comparing with the Reynolds-Averaged Navier-Stokes models (RANS), the present model shows improving agreement with experimental measurements in terms of surface elevations, particle velocities, wave height distributions and undertow profiles. The subgrid scale (SGS) turbulent transport mechanism is also discussed in the paper. It is found that turbulent production and dissipation are of the same order, but turbulent production is primarily located at the wavefront and above the wave trough, whereas turbulent dissipation is primarily located at the back face of a wave, indicating that in these regions, the assumption of equilibrium is not correct. Below the trough level, the local equilibrium assumption is reasonable. Turbulent convection and diffusion are of the same order at the trough level. Above the trough level, turbulent convection dominates. Under the spilling breaking wave, turbulent kinetic energy is continue to dissipate in the bore region, whereas under the plunging breaking wave, the turbulent kinetic energy is dissipated very rapidly within one wave period. 相似文献
19.
Rainfall effects on wind waves and turbulence are investigated through the laboratory experiments in a large wind-wave tank. It is found that the wind waves are damped as a whole at low wind speeds, but are enhanced at high wind speeds. This dual effect of rain on the wind waves increases with the increase of rain rate, while the influence of rainfall-area length is not observable. At the low wind speed, the corresponding turbulence in terms of the turbulent kinetic energy （TKE） dissipation rate is significantly enhanced by rain- fall as the waves are damped severely. At the high wind speed, the augment of the TKE dissipation rate is suppressed while the wind waves are enhanced simultaneously. In the field, however, rainfall usually hin- ders the development of waves. In order to explain this contradiction of rainfall effect on waves, a possibility about energy transfer from turbulence to waves in case of the spectral peak of waves overlapping the inertial subrange of turbulence is assumed. It can be applied to interpret the damping phenomenon of gas trans- fer velocity in the laboratory experiments, and the variation of the TKE dissipation rates near sea surface compared with the law of wall. 相似文献
20.
孙文心 《中国海洋大学学报(自然科学版)》1992,(4)
对几个参数化浅海流体动力学模型的耗散性和频散关系进行了理论分析,提出三点结论:1.深度平均(或积分)的浅海流体动力学模式不能充分表达湍耗散;2.浅海中的强耗散将对长波振荡具有本质的影响;3.几种不同的湍参数化动力模型将对长波产生不同的频散效应。 相似文献