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1.
A three-dimensional numerical model is developed in this study to investigate the problem of wave–current–body interaction. The model solves the spatially averaged Navier–Stokes equations. Turbulence effects are modeled by a subgrid-scale (SGS) model using the concept of large eddy simulation (LES). The model is employed to study the wave–current interaction with a square cylinder that is mounted on the bottom and vertically pierces the free surface. The force analysis demonstrates that the presence of waves can reduce both the strength and frequency of vortex shedding induced by a uniform current due to the nonlinear wave–current interaction. The free surface elevation, strain rates of the mean flow, and eddy viscosity are found to closely correlate with the mechanism of vortex shedding. It is also shown that when the vortex shedding is neglected in the calculation such as by the potential flow approach, one may significantly underestimate the magnitude of in-line force. The energy spectral analysis reveals that there exist initiating, growing, and decaying regions for shedding vortices around the cylinder. In the vortex initiating region, both coherent and turbulent structures are nearly two-dimensional that become three-dimensional in the vortex growing region. The kinetic energy of both coherent and turbulent motions is dissipated in the vortex decaying region, within which the mean flow gradually returns back to two-dimensional. 相似文献
2.
上混合中剪切湍流和朗缪尔环流动力特征差异 总被引：1，自引：0，他引：1
LI Guojing WANG Dongxiao CHEN Ju YAO Jinglong ZENG Lili SHU Yeqiang SUI Dandan 《海洋学报(英文版)》2015,34(5):1-11
Large eddy simulation(LES) is used to investigate contrasting dynamic characteristics of shear turbulence(ST)and Langmuir circulation(LC) in the surface mixed layer(SML). ST is usually induced by wind forcing in SML. LC can be driven by wave-current interaction that includes the roles of wind, wave and vortex forcing. The LES results show that LC suppresses the horizontal velocity and greatly modifies the downwind velocity profile, but increases the vertical velocity. The strong downwelling jets of LC accelerate and increase the downward transport of energy as compared to ST. The vertical eddy viscosity Km of LC is much larger than that of ST. Strong mixing induced by LC has two locations. They are located in the 2ds–3ds(Stokes depth scale) and the lower layer of the SML,respectively. Its value and position change periodically with time. In contrast, maximum Km induced by ST is located in the middle depth of the SML. The turbulent kinetic energy(TKE) generated by LC is larger than that by ST. The differences in vertical distributions of TKE and Km are evident. Therefore, the parameterization of LC cannot be solely based on TKE. For deep SML, the convection of large-scale eddies in LC plays a main role in downward transport of energy and LC can induce stronger velocity shear(S2) near the SML base. In addition, the large-scale eddies and S2 induced by LC is changing all the time, which needs to be fully considered in the parameterization of LC. 相似文献
3.
《Ocean Modelling》2007,16(1-2):106-140
Mixing in both coastal and deep ocean emerges as one of the important processes that determines the transport of pollutants, sediments and biological species, as well as the details of the global thermohaline circulation. Both the observations, due to their lack in space and time resolution, and most coastal and general circulation models due to inadequate physics, can only provide partial information about oceanic mixing processes. A new class of nonhydrostatic models supplemented with physically based subgrid-scale (SGS) closures, or so-called large eddy simulation (LES), is put forth as another tool of investigation to complement observational and large-scale modeling efforts.However, SGS models have been developed primarily for homogeneous, isotropic flows. Here, four SGS models based on Smagorinsky eddy viscosity and diffusivity are tested for stratified flows in the context of 2D dam-break problem in a rectangular enclosed domain. This idealized testbed leads to a number of simplifications about the initial conditions, boundary conditions and geometry, while exhibiting the dynamically complex characteristics of stratified flows involving the interaction of shear-induced mixing and internal waves. Direct numerical simulations (DNS) at high resolutions are taken as benchmark solutions. Under-resolved simulations without SGS terms (so-called DNS1) are used to quantify the impact of SGS stresses. The performance of LES is assessed by using the time evolution of the volume fraction of intermediate density water masses generated by mixing. The simulations are conducted using a nonhydrostatic high-order spectral element model Nek5000 developed to exhibit minimal numerical dissipation and dispersion errors, which is advantageous to quantify accurately the impact of SGS stresses.It is found that all tested SGS models lead to improved results with respect to those from DNS1. Also, SGS models allow for simulations with coarse resolutions that blow up in DNS1 due to lack of adequate dissipation where needed. The SGS model in which the vertical eddy diffusion is modulated via a function that depends on the Richardson number Ri shows the most faithful reproduction of mixed water masses at all resolutions tested.The sensitivity of the results to the tunable parameter of the SGS model, to changes in the Ri-dependent function and resolution of the turbulent overturning scales is shown. 相似文献
4.
Langmuir环流影响着海洋上层的能量输入,对海洋上混合层的形成和加深起着重要作用,对于海洋上混合层具有重要意义。近年来许多学者采用大涡模拟(LES)方法对Langmuir环流进行机制研究,并通过在雷诺平均模型中参数化Langmuir环流效应,将Langmuir环流过程引入到三维海洋环流或海洋耦合模式中,提出了一系列混合参数化方案。本文回顾了Langmuir环流在雷诺平均模式参数化中的研究进展,主要可分为以下几种方案:一种方法是用Langmuir数在KPP垂直混合参数化方案中引入湍流特征速度增强因子,并不断发展Langmuir数的定义;一种是在Mellor-Yamada2.5湍流闭合模型中增加斯托克斯漂流剪切效应项,此外还有通过修改模式中混合长方程来加入Langmuir效应等。通过在雷诺平均模式中应用的结果来看,现有的参数化方案在一定程度上改善了混合层深度和SST的模拟,肯定了Langmuir环流在加深混合等方面的作用,但仍存在一些问题需要在今后的研究中进一步改进。 相似文献
5.
A numerical model has been developed to study sloshing of turbulent flow in a tank with elastic baffles. The Moving-Particle Semi-implicit method(MPS) is a kind of meshless Lagrangian calculation method. The large eddy simulation(LES) approach is employed to model the turbulence by using the Smagorinsky Sub-Particle Scale(SPS)closure model. This paper uses MPS-FSI method with LES to simulate the interaction between free surface flow and a thin elastic baffle in sloshing. Then, the numerical model is validated, and the numerical solution has good agreement with experimental data for sloshing in a tank with elastic baffles. Furthermore, under external excitations,the MPS is applied to viscous laminar flow and turbulent flow, with both the deformation of elastic baffles and the wave height of the free surface are compared with each other. Besides, the impact pressure with/without baffles and wave height of free surface are investigated and discussed in detail. Finally, preliminary simulations are carried out in the damage problem of elastic baffles, taking the advantage of the MPS-FSI method in computations of the fluid–structure interaction with large deformation. 相似文献
6.
G. T. Csanady 《Journal of Oceanography》1997,53(1):67-80
A “slip law” connects the excess velocity or “slip” of a wind-blown water surface, relative to the motion in the middle of
the mixed layer, to the wind stress, the wind-wave field, and buoyancy flux. An inner layer-outer layer model of the turbulent
shear flow in the mixed layer is appropriate, as for a turbulent boundary layer or Ekman layer over a solid surface, allowing,
however, for turbulent kinetic energy transfer from the air-side via breaking waves, and for Stokes drift. Asymptotic matching
of the velocity distributions in inner and outer portions of the mixed layer yields a slip law of logarithmic form, akin to
the drag law of a turbulent boundary layer. The dominant independent variable is the ratio of water-side roughness length
to mixed layer depth or turbulent Ekman depth. Convection due to surface cooling is also an important influence, reducing
surface slip. Water-side roughness length is a wind-wave property, varying with wind speed similarly to air-side roughness.
Slip velocity is typically 20 times water-side friction velocity or 3% of wind speed, varying within a range of about 2 to
4.5%. A linearized model of turbulent kinetic energy distribution shows much higher values near the surface than in a wall
layer. Nondimensional dissipation peaks at a value of about eight, a short distance below the surface. 相似文献
7.
A recently developed fully explicit algebraic model of Reynolds stress and turbulent heat flux in a thermally stratified planetary atmospheric boundary layer without stratification has been used for a numerical study of the Ekman turbulent boundary layer over a homogeneous rough surface for different dimensionless surface Rossby numbers. A comparative analysis has been conducted for a closure model of the transport term in the prognostic equation of turbulent kinetic energy dissipation including third-order moments. Dependences of the total wind rotation angle on the Rossby number have been obtained. The calculated vertical profiles of mean velocity, turbulent stress, turbulent kinetic energy, surface-friction velocity, and boundary-layer height agree satisfactorily with observational and earlier obtained LES data. 相似文献
8.
Effects of Stokes production on summer ocean shelf dynamics 总被引：1，自引：0，他引：1
A two-dimensional numerical model,which is configured on the basis of Princeton ocean model（POM）,is used to study the effect of Stokes production（SP） of the turbulent kinetic energy on a density profile and Ekman transport in an idealized shelf region in summer.The energy input from SP is parameterized and included into the Mellor-Yamada turbulence closure submodel.Results reveal that the intensity of wind-driven upwelling fronts near the sea surface is weakened by the SP-associated turbulent kinetic energy input.The vertical eddy viscosity coefficient in the surface boundary layer is enhanced greatly owing to the impact of SP,which decreases the alongshore velocity and changes the distribution of upwelling.In addition,the SP-induced mixing easily suppresses the strong stratification and significantly increases the depth of the upper mixed layer（ML） under strong winds. 相似文献
9.
Three-dimensional liquid sloshing in a tank with baffles 总被引：1，自引：0，他引：1
Dongming Liu 《Ocean Engineering》2009,36(2):202-52
A numerical model has been developed to study three-dimensional (3D) liquid sloshing in a tank with baffles. The numerical model solves the spatially averaged Navier-Stokes equations, which are constructed on a non-inertial reference frame having six degree-of-freedom (DOF) of motions. The large-eddy-simulation (LES) approach is employed to model turbulence by using the Smagorinsky sub-grid scale (SGS) closure model. The two-step projection method is employed in the numerical solutions, aided by the Bi-CGSTAB technique to solve the pressure Poisson equation for the filtered pressure field. The second-order accurate volume-of-fluid (VOF) method is used to track the distorted and broken free surface. The baffles in the tank are modeled by the concept of virtual boundary force (VBF) method. The numerical model is first validated against the available analytical solution and experimental data for two-dimensional (2D) liquid sloshing in a tank without baffles. The 2D liquid sloshing in tanks with baffles is then investigated. The numerical results are compared with other results from available literatures. Good agreement is obtained. Finally, the model is used to study 3D liquid sloshing in a tank with vertical baffles. The effect of the baffle is investigated and discussed. 相似文献
10.
In this work, the large-wave simulation (LWS) method is adapted for application in spilling wave breaking over a constant slope beach. According to LWS, large scales of velocities, pressure and free-surface elevation are numerically resolved, while the corresponding unresolved scale effects are taken into consideration by a subgrid scale (SGS) model for wave and eddy stresses. The model may be not fully applicable in very shallow water, close to the shoreline, where the unresolved, turbulent, free-surface oscillation is of the same order with the water depth. Time integration of the Euler equations is achieved by a two-stage fractional scheme, combined with a hybrid scheme for spatial discretization, consisting of finite difference and pseudospectral approximation methods. Model parameters are calibrated by comparison to available experimental data of free-surface elevation and velocities in the surf zone for cross-shore incoming waves. The action of the wave SGS stresses in the outer coastal and surf zones initiates breaking and generates appropriate vorticity, in the form of an eddy structure (surface roller), at the breaking wavefront. At incipient breaking, both advection and gravity contribute to the vorticity flux at the free surface, while only after the full development of the surface roller, the effect of advection becomes stronger. The SGS model is also utilized to simulate propagation, refraction and breaking of oblique incoming waves. The gradual breaking and dissipation of wave crestlines and the surface roller structure along the breaking wavefront are automatically captured without any empirical input, such as data for the roller shape or the wave propagation angle at breaking. 相似文献
11.
A new three-dimensional numerical model is derived through a wave average on the primitive N-S equations, in which both the＂Coriolis-Stokes forcing＂ and the＂Stokes-Vortex force＂ are considered. Three ideal experiments are run using the new model applied to the Princeton ocean model （POM）. Numerical results show that surface waves play an important role on the mixing of the upper ocean. The mixed layer is enhanced when wave effect is considered in conjunction with small Langmuir numbers. Both surface wave breaking and Stokes production can strengthen the turbulent mixing near the surface. However, the influence of wave breaking is limited to a thin layer, but Stokes drift can affect the whole mixed layer. Furthermore, the vertical mixing coefficients clearly rise in the mixed layer, and the upper ocean mixed layer is deepened especially in the Antarctic Circumpolar Current when the model is applied to global simulations. It indicates that the surface gravity waves are indispensable in enhancing the mixing in the upper ocean, and should be accounted for in ocean general circulation models. 相似文献
12.
Liquid sloshing in storage tank is a fundamental problem of great engineering importance. Sloshing motion can be laminar or turbulent. However, the necessity for inclusion of turbulence in CFD simulation of sloshing flows has not yet been established. In this paper, three roll–induced sloshing cases are studied to assess the merits and shortcomings of the laminar model and three most–commonly used turbulence models (RANS k–ε, LES and Very LES). To overcome the deficiencies in the RANS and LES, the new Very LES (VLES) model, which combines the RANS k–ε and LES, is developed in this paper. The free surface profiles are reconstructed by a coupled Level–Set and Volume–of–Fluid (CLSVOF) method. To the authors’ knowledge, the comprehensive and systematical assessment of the effect of turbulence on sloshing simulation has not been reported in the literature. The numerical results are evaluated using experimental measurements from Delorme and Souto−Iglesias. The present study indicates that the inclusion of an appropriate turbulence model has a profound influence on the simulations of violent and non–violent sloshing flows. The VLES and LES models can provide accurate predictions of free surface profiles and impact pressures, whereas the laminar flow assumption and the RANS model cannot adequately capture the energy dissipation in the sloshing simulation and lead to the inaccurate flow predictions. 相似文献
13.
E.V. Stanev J. Staneva J.L. Bullister J.W. Murray 《Deep Sea Research Part I: Oceanographic Research Papers》2004,51(12):2137-2169
Data from field observations and numerical model simulations are used to understand and quantify the pathways by which passive tracers penetrate into the Black Sea intermediate and deep layers. Chlorofluorocarbon (CFC) concentrations measured during the1988 R.V. Knorr cruise show strong decrease with increasing density in the Black Sea and illustrate the very slow rate of ventilation of deep water in this basin. We develop a 3D numerical model based on the Modular Ocean Model (MOM), and calibrate it in a way to produce consistent simulations of observed temperature, salinity and CFCs. One important feature is the implementation of a special parameterization for convection, which is an alternative of the convective adjustment in MOM and handles the penetration of the Bosporus plume into the halocline. The model forcing includes interannually variable wind, heat and water fluxes constructed from Comprehensive Ocean–Atmosphere Data Set and ECMWF atmospheric analysis data and river runoff data. The analysis of observations and simulated data are focused on correlations between thermohaline and tracer fields, dynamic control of ventilation, and the relative contributions of sources at the sea surface and outflow from the Bosporus Strait in the formation of intermediate and deep waters. A simple theory is developed which incorporates the outflow from the strait along with the vertical circulation (vertical turbulent mixing and Ekman upwelling) and reveals their mutual adjustment. The analyses of simulated and observed CFCs demonstrate that most of the CFC penetrating the deep layers has its source at the sea surface within the Black Sea rather than from the Marmara Sea via the Bosporus undercurrent. Under present-day conditions, the surface CFC signals have reached only the upper halocline. Intrusions below 600 m are not simulated. The major pathways of penetration of CFCs are associated with cold-water mass formation sites, Bosporus effluent, as well as with the diapycnal mixing in the area of Rim Current. Future CFC sampling strategies coherent with the unique conditions in the Black Sea are discussed. 相似文献
14.
Large eddy simulation of turbulence in ocean surface boundary layer at Zhangzi Island offshore 总被引：1，自引：0，他引：1
This study uses a large eddy simulation （LES） model to investigate the turbulence processes in the ocean surface boundary layer at Zhangzi Island offshore. Field measurements at Zhangzi Island （39°N, 122°E） during July 2009 are used to drive the LES model. The LES results capture a clear diurnal cycle in the oceanic turbulence boundary layer. The process of the heat penetration and heat distribution characteristics are analyzed through the heat flux results from the LES and their differences between two diurnal cycles are discussed as well. Energy balance and other dynamics are investigated which show that the tide-induced shear production is the main source of the turbulence energy that balanced dissipation. Momentum flux near the surface shows better agreement with atmospheric data computed by the eddy correlation method than those computed by bulk formula. 相似文献
15.
In this paper, a two-fluid model of turbulent two-phase flow is used to simulate turbulent stratified flows. This is a unified multi-fluid model for the motion of each phase in the flow, whose turbulent transport is closed by a two-phase k– model. The exchanges of mass, momentum and energy between the two phases are fully accounted for in the simulation. For illustration, a case of turbulent stratified flow with strong buoyancy effects, for which extensive experimental data are available, is selected for examination. It is shown that the numerical results agree well with the experimental data. 相似文献
16.
《Coastal Engineering》2005,52(1):43-62
A vertical two-dimensional (2D) numerical model for time dependent local scour below offshore pipelines subject to unidirectional steady flow is developed. The governing equations for the flow and sediment transport are solved by using finite difference method in a general curvilinear coordinate system. The performance of two turbulence models, the standard k–ɛ model and Smagorinsky subgrid scale (SGS) model, on modeling time dependent scour processes is examined. Both suspended load and bed load are considered in the scour model. The suspended-load model is verified against two channel sediment transport cases. The change of bed level is calculated from the continuity equation of total sediment transport. A new time marching scheme and a sand slide scheme are proposed for the scour calculation. It is found that the proposed time marching scheme and sand slide model work well for both clear-water and live-bed scour situations and the standard k–ɛ turbulence closure is more preferable than the SGS model in the 2D scour model developed in this study. 相似文献
17.
In designing the coastal structures, the accurate estimation of the wave forces on them is of great importance. In this paper, the influences of the phase difference on wave pressure acting on a composite breakwater installed in the three-dimensional (3-D) wave field are studied numerically. We extend the earlier model [Hur, D.S., Mizutani, N., 2003. Coastal Engineering 47, 329–345] to simulate 3-D wave fields by introducing 3-D Navier–Stokes solver with the Smagorinsky's sub-grid scale (SGS) model. For the validation of the model, the wave field around a 3-D asymmetrical structure installed on a submerged breakwater, in which the complex wave deformations generate, is simulated, and the numerical solutions are compared to the experimental data reported by Hur, Mizutani, Kim [2004. Coastal Engineering (51, 407–420)]. The model is then adopted to investigate 3-D characteristics of wave pressure and force on a caisson of composite breakwater, and the numerical solutions were discussed with respect to the phase difference between harbor and seaward sides induced by the transmitted wave through the rubble mound or the diffraction. The numerical results reveal that wave forces acting on the composite breakwater are significantly different at each cross-section under influence of wave diffraction that is important parameter on 3-D wave interaction with coastal structures. 相似文献
18.
LI Yucheng CHEN Bing LAI Guozhang Professor Dept. of Civil Engineering Dalian University of Technology Dalian P. R. China.Ph. D. Candidate Dept. of Civil Engineering Dalian University of Technology Dalian P. R. China.Professor Dept. of Engineering Mechanics Dalian University of Technology Dalian P. R. China. 《中国海洋工程》1998,(2)
A three-step finite element method(FEM)together with Large Eddy Simulation(LES)is ap-plied to incompressible turbulent flow around seabed pipelines at relatively high Reynolds numbers.Bothtwo-dimensional and three-dimensional numerical simulation is carried out to determine thethree-dimensional effect.The results of numerical simulation agree quite well with the wave forces actingon pipeline models measured in physical model test. 相似文献
19.
《Coastal Engineering》2004,51(10):1021-1049
A numerical process-based model to forecast beach profile morphodynamics has been developed. In the present paper, an analysis of various modelling approaches and key parametrizations involved in the estimation of the wave-driven current and the suspended sediment concentration is carried out.Several resolution techniques for the 1DV horizontal (i.e., in the x-direction perpendicular to coastline) momentum equation governing the Mean Horizontal Velocity (MHV) are analysed. In the first kind of techniques, the mean horizontal velocity is computed from the momentum equation, whereas the Mean Water Level (MWL) is computed using a parametrization of the depth-averaged momentum equation. Two boundary or integral conditions are thus needed. In the second kind, both mean horizontal velocity and mean water level gradient in the x-direction are the unknowns of the momentum equation, thus, three boundary or integral conditions are needed. Various additional conditions are discussed. We show that using a technique of the first kind is equivalent to imposing the difference between the surface and the bottom shear stresses in the 1D vertical equation. Both techniques lead to results that are in good agreement with the Delta Flume experimental data, provided the Stokes drift flow discharge is imposed as an additional condition. The influence of the breaking roller model and of the turbulent viscosity parametrization are also analysed.Suspended sediment transport by the mean current and wave-induced bedload transport are taken into account in the sediment flux. Three turbulent diffusivity parametrizations are compared for suspended sediment concentration estimations. A linear profile for the turbulent diffusivity taking into account the wave bottom shear stress and the surface wave breaking turbulence production is shown to give the best results. Using experimental data, we put forward the poor estimation of the bottom sediment concentration given by the three implemented parametrizations. We thus propose a new parametrization relying on a Shields parameter based on the breaking roller induced surface shear stress. Using this new parametrization, the bottom profile used in the tests keeps its two bars which disappear otherwise. However, the morphodynamical model still overestimates the bars offshore motion, a bias already observed in other models. 相似文献
20.
P. C. Sinha Y. R. Rao S. K. Dube C. R. Murthy A. K. Chatterjee 《Estuarine, Coastal and Shelf Science》1999,48(6):649
This paper has two purposes. The first is to study the circulation and salinity in Hooghly Estuary, along the east coast of India and the second is to compare the performance of two turbulence closure schemes by modelling it. A breadth averaged numerical model using a sigma co-ordinate system in the vertical is briefly described. Vertical diffusion of momentum and salt are parameterized by a simple first-order turbulent closure or by a one equation model for turbulent kinetic energy (TKE) which uses a specified mixing length. The results are compared with the available neap and spring tide observations along the estuary for both low and high discharge periods.The computed elevations and currents are in reasonable agreement with the observations showing no major differences in vertical current profiles by both the turbulent schemes. However, there is a slight under-prediction of bottom currents. The salinity profiles predicted by TKE model show better matching with observations. Statistical tests are also conducted to study the comparative performance of the turbulent closure schemes. The maintenance of two layer structure in residual currents and salt variability are also studied by using the model. 相似文献