共查询到20条相似文献，搜索用时 31 毫秒
1.
A static adaptive grid approximates the topography and defines the vertical resolution in Vector-Ocean-Model (VOM). The adaptation to topography creates unstructured grids, which are organised in a one-dimensional vector by column-wise storage of only wet cells. The model’s name reflects this data structure. The intention of VOM is better resolving flow and stratification near topographic boundaries in Z-coordinates. This is the second part of a publication that describes the generation of adaptive grids (part I), and simulations with VOM in unstructured grids (this part). Adaptive grids generated for a synthetic topography in part I include shelf, continental slope, and ocean. Three of those grids are here utilised in upwelling simulations. Under the same forcing increased vertical resolution at seabed and slopes yields a significant increase in flow energy as compared to coarser grids. Results allow explaining the surface intensification of a continental slope jet by vertical displacements of water masses in the seabed Ekman layer. Results in unstructured grids are almost identical to reference simulations in equidistant grids where the respective smallest grid size of unstructured grids was used. Negative effects of grids on predicted flow and stratification are absent also over particularly rough topography, as demonstrated by using vertical velocity as most sensitive indicator. In a further simulation an overflow governed by the advection of water mass properties is presented to demonstrate the conservation properties of the model. After 5 months of simulation the predicted domain average temperature deviated by 10−8 from the initial temperature field. Compared to equidistant grids the advection/diffusion scheme looses about one order of magnitude in accuracy when used in an unstructured grid. The results of VOM, being defined in Z-coordinates, are void of coordinate transformation errors. In an arbitrary topography unforced zero-flow remains quiescent in a stratification that only varies in the vertical. VOM due to its depth-independent vertical resolution appears particularly suitable for simulations of ocean-shelf exchange. 相似文献
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Sensitivity studies with a new generalized coordinate ocean model are performed in order to compare the behavior of bottom boundary layers (BBLs) when terrain-following (sigma or combined sigma and z-level) or z-level vertical grids are used, but most other numerical aspects remain unchanged. The model uses a second-order turbulence closure scheme that provides surface and BBL mixing and results in a quite realistic climatology and deep water masses after 100 year simulations with a coarse resolution (1° × 1°) basin-scale terrain-following grid. However, with the same turbulence scheme but using a z-level grid, the model was unable to produce dense water masses in the deep ocean. The latter is a known problem for coarse resolution z-level models, unless they include highly empirical BBL schemes.A set of dense water overflow experiments with high-resolution grids (10 and 2.5 km) are used to investigate the influence of model parameters such as horizontal diffusivity, vertical mixing, horizontal resolution, and vertical resolution on the simulation of bottom layers for the different coordinate systems. Increasing horizontal diffusivity causes a thinner BBL and a bottom plume that extends further downslope in a sigma grid, but causes a thicker BBL and limited downslope plume extension in a z-level grid. A major difference in the behavior of the BBL in the two grids is due to the larger vertical mixing generated by the turbulence scheme over the step-like topography in the z-level grid, compared to a smaller vertical mixing and a more stably stratified BBL in the sigma grid. Therefore, the dense plume is able to maintain its water mass better and penetrates farther downslope in the sigma grid than in the z-level grid. Increasing horizontal and vertical resolution in the z-level grid converges the results toward those obtained by a much coarser resolution sigma coordinate grid, but some differences remain due to the basic differences in the mixing process in the BBL. 相似文献
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A coastal ocean -coordinate model of Monterey Bay (MOB) with realistic bottom topography and coastlines is developed using the Princeton Ocean Model (POM) and grid generation technique (GGT) to study the horizontal pressure gradient errors associated with the MOB steep topography. The submarine canyon in MOB features some of the steepest topography encountered anywhere in the world oceans. The MOB grids are designed using the EAGEAL View and GENIE++ grid generation systems. A grid package developed by Ly and Luong (1993) is used in this study to couple grids to the model. The MOB model is tested with both orthogonal and curvilinear nearly-orthogonal (CNO) grids. The CNO grid has horizontal resolution which varies from 300 m to 2 km, while the resolution of the orthogonal grid is uniform with x = 1.25 km and y = 1.38 km. These grids cover a domain of 180 × 160 km with the same number of grid points of 131 × 131. Vertical resolutions of 25, 35 and 45 vertical sigma levels are tested. The error in the MOB are evaluated in terms of mean kinetic energy and velocity against various grids, vertical, horizontal resolution and distributions, and bottom topography smoothing. Simulations with various grids show that GGT can be used as another tool in reducing -coordinate errors in coastal ocean modeling besides increasing resolution and smoothing bottom topography. Topographical smoothing not only reduces topographic slope, but changes realistic topography. A CNO grid with a high grid density packed along steep slopes and Monterey Submarine Canyon reduces the errors by 40% compared to a rectangular grid with the same number of grid points. The CNO grid is more efficient than the rectangular grid, since it has most of its grids over water. The simulations show that the presented MOB -coordinate model can be used with a confidence regarding horizontal pressure gradient error. 相似文献
4.
Comparison of overflow simulations on different vertical grids using the Finite Element Ocean circulation Model 总被引：1，自引：0，他引：1
The Finite Element Ocean circulation Model (FEOM) is applied to study the sensitivity of density driven overflows to the vertical discretization and bottom topography representation using the dynamics of overflow mixing and entrainment (DOME) setup. FEOM allows for hybrid grids combining σ, z + σ, full cell, partly shaved cell and fully shaved cell grids within the same numerical kernel thus isolating as far as possible effects of mesh geometry from those of model numerics. The sensitivity of diapycnal mixing, entrainment, plume thickness and plume meridional distribution to vertical discretization and partly to the subgrid process parameterization is explored. It is shown that simulations on pure σ grids or the combination of z + σ resolve the overflow processes best in terms of downslope plume propagation, plume thickness and dilution, and also have the least resolution dependence. Grids using z-levels generate excessive spurious mixing when resolution is insufficient. Applying partial cells improves the plume representation, but still requires higher horizontal and vertical resolution to converge to the σ grid results. It is demonstrated that increasing lateral viscosity causes the plume thickness to reduce whereas increasing lateral diffusivity has opposite effect. When keeping the Prandtl number constant, the increase in diffusivity and viscosity leads to an increase in mixing and plume thickness on z-level grids and also on σ-grids when lateral dissipation is oriented along geopotential surfaces. Using the along σ- diffusion helped to obtain correct plume thickness and entrainment on σ grids. Increasing the vertical mixing coefficients leads to an increase in diapycnal mixing and in downslope penetration as well. 相似文献
5.
强潮河口盐水入侵对饮用水源地危害极大。基于平面二维水动力盐度模型, 对典型强潮河口—钱塘江的水动力及盐水入侵过程进行了数值模拟研究。结果表明枯水径流时盐度变化与潮位过程曲线类似, 潮差对盐度大小影响显著, 径流量的增加将逐渐减小其相似程度。当流量增加到一定程度后, 继续增加的一定径流量所产生的抑咸效果减弱, 水资源有效利用率降低, 此时允许水源地盐度超标并改从蓄淡避咸水库取水可有效节约水资源。盐度平面分布显示, 盐水入侵在强潮河口弯道处受涨潮流主流线影响明显, 靠近主流线一岸的盐度大于对岸, 单从盐水入侵角度考虑, 强潮河口弯道段的取水口应设置在远离涨潮流主流线一岸。钱塘江河口盐度数值模拟对于研究减轻盐水入侵对水源地危害的措施具有指导意义。 相似文献
6.
A new three-dimensional semi-implicit finite-volume ocean model has been developed for simulating the coastal ocean circulation, which is based on the staggered C -unstructured non-orthogonal grid in the horizontal direction and z -level grid in the vertical direction. The three-dimensional model is discretized by the semi-implicit finite-volume method, in that the free-surface and the vertical diffusion are semi-implicit, thereby removing stability limitations associated with the surface gravity wave and vertical diffusion terms. The remaining terms in the momentum equations are discretized explicitly by an integral method. The partial cell method is used for resolving topography, which enables the model to better represent irregular topography. The model has been tested against analytical cases for wind and tidal oscillation circulation, and is applied to simulating the tidal flow in the Bohai Sea. The results are in good agreement both with the analytical solutions and measurement results. 相似文献
7.
《Ocean Modelling》2008,20(2):170-182
Most ocean models in current use are built upon structured meshes. It follows that most existing tools for extracting diagnostic quantities (volume and surface integrals, for example) from ocean model output are constructed using techniques and software tools which assume structured meshes. The greater complexity inherent in unstructured meshes (especially fully unstructured grids which are unstructured in the vertical as well as the horizontal direction) has left some oceanographers, accustomed to traditional methods, unclear on how to calculate diagnostics on these meshes. In this paper we show that tools for extracting diagnostic data from the new generation of unstructured ocean models can be constructed with relative ease using open source software. Higher level languages such as Python, in conjunction with packages such as NumPy, SciPy, VTK and MayaVi, provide many of the high-level primitives needed to perform 3D visualisation and evaluate diagnostic quantities, e.g. density fluxes. We demonstrate this in the particular case of calculating flux of vector fields through isosurfaces, using flow data obtained from the unstructured mesh finite element ocean code ICOM, however this tool can be applied to model output from any unstructured grid ocean code. 相似文献
8.
Dmitry S. Dukhovskoy Steven L. Morey Paul J. Martin James J. O&#x;Brien Cortis Cooper 《Ocean Modelling》2009,28(4):250-265
Recent observations over the Sigsbee Escarpment in the Gulf of Mexico have revealed extremely energetic deep currents (near 1 m s−1), which are trapped along the escarpment. Both scientific interest and engineering needs demand dynamical understanding of these extreme events, and can benefit from a numerical model designed to complement observational and theoretical investigations in this region of complicated topography. The primary objective of this study is to develop a modeling methodology capable of simulating these physical processes and apply the model to the Sigsbee Escarpment region. The very steep slope of the Sigsbee Escarpment (0.05–0.1) limits the application of ocean models with traditional terrain-following (sigma) vertical coordinates, which may represent the very complicated topography in the region adequately, can result in large truncation errors during calculation of the horizontal pressure gradient. A new vertical coordinate system, termed a vanishing quasi-sigma coordinate, is implemented in the Navy Coastal Ocean Model for application to the Sigsbee Escarpment region. Vertical coordinate surfaces for this grid have noticeably gentler slopes than a traditional sigma grid, while still following the terrain near the ocean bottom. The new vertical grid is tested with a suite of numerical experiments and compared to a classical sigma-layer model. The numerical error is substantially reduced in the model with the new vertical grid. A one-year, realistic, numerical simulation is performed to simulate strong, deep currents over the Escarpment using a very-high-resolution nested modeling approach. The model results are analyzed to demonstrate that the deep-ocean currents in the simulation replicate the prominent dynamical features of the observed intense currents in the region. 相似文献
9.
斜压海洋动力学的一种三维数值模式 Ⅰ.动力学方程数值格式 总被引：1，自引：0，他引：1
依据自由海面海洋动力学原始方程建立了一种三维有限差分数值模式,可用于潮波、风暴潮和海流的数值模拟和预报。运动方程和连续方程的数值格式采用内、外模态分离的技术。外模态采用交替方向隐格式,用于计算海面高度和垂直平均流速,时间步长不受Ｃｏｕｒａｎｔ－Ｆｒｉｄｅｒｉｃｈｓ－Ｌｅｗｙ条件限制;内模态采用半隐格式,用于计算海流的垂直２颁布,其时间步长可大于外模态时间步长。模式的计算程度比一般显式模式可快１０倍 相似文献
10.
基于2000年8月在南海调查航次得到的水文资料,首次采用广义随底坐标形式的改进POM模式对南海夏季环流进行了数值研究.用正交曲线性水平网格覆盖观测区域,在垂向上对近表海面层次采用近似z坐标,而近底层则为随底坐标.在计算海区实际地形及假设的水平均匀而垂直层化的密度分布下,实施的两个数值计算试验表明,本模式采用的垂直坐标方案比传统的σ坐标方案优越,随底坐标模式因压力梯度项在起伏地形下产生的系统计算误差将变得十分的微小.在南海2000年夏季环流的实际计算中,首先对观测资料进行了60d的诊断计算,然后在诊断已得到的动力场结果基础上,又进行了10d左右的预报运行得到半诊断结果.从计算结果来看,它依赖于参数Cvis与Cdif的选择,特别是参数Cvis,文中取值为Cvis=Cdif=008.比较诊断与半诊断两个计算过程的结果,它们在定性上较为一致,在定量上有些差别.这是因为半诊断计算的方法对密度场作适当的动力调整,使其与地形、风场等更加匹配.在大尺度环流结构不受影响的情况下,尽可能地消除了小尺度噪声,可使计算得到的流场更为清晰.2000年8月南海计算区域环流的最大特点是多涡结构,其中有些反气旋暖涡和气旋式冷涡相间分布.在越南东南海域自表层至1000m水层稳定存在着一个显著的反气旋暖涡,其中心位置在11°51'N,112°07'E(诊断计算),水平尺度约为300km.此暖涡以东存在一个气旋式冷涡,这两个冷、暖涡是研究海区夏季环流的重要环流特征之一.在计算区域东北部夏季环流以反气旋环流系统为主;在计算区域东南部夏季环流以气旋系统为主;南海夏季环流分布,明显出现西部强化特征. 相似文献
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When a steep bottom slope exists, it is well known that conventional methods for calculating horizontal diffusion in sigma-coordinate coastal ocean models causes spurious transport (e.g. salinity, temperature, and sediments) and currents. In this study, a second-order accurate finite-difference algorithm and program have been developed to reduce the spurious numerical diffusion errors. In the proposed algorithm, the finite differencing is performed in the x–z coordinate system to approximate the horizontal gradient. Each variable in the finite differential formation is calculated in the sigma-coordinate grid cells using a second-order Lagrangian interpolation polynomial. In conjunction with a stepwise bottom boundary condition, numerical experiments show that the proposed finite-difference scheme considerably reduces numerical errors compared to conventional approaches when dealing with horizontal diffusion over steep topography, which often occurs in coastal oceans and navigation channels. 相似文献
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降低水平压力梯度误差的方法比较 总被引：1，自引：0，他引：1
由于坐标变换的关系,σ坐标海洋模式在处理陡峭地形时会产生较大的水平压力梯度误差.为减少水平压力梯度误差,前人提出了一系列改进的方法,这些方法可分为减去平均密度法、平滑地形法、网格变换法和水平压力梯度计算方程变换法4类.水平压力梯度计算方程变换法又可分为密度雅克比法、高阶精度法、有限体积法和转换到z坐标下计算水平压力梯度法.利用POM模式模拟理想海山来比较标准密度雅克比法、线性插值到z坐标法、四阶精度插值法、三次方多项式拟合法和权重密度雅克比法在计算水平压力梯度中出现的误差.模式初始时垂向分成,水平均匀,外模时间步长为12 s,内模时间步长为360 s,计算时间为360 d.从最大流速误差的结果可以看出,标准密度雅克比法得到的最大流速误差为0.45 m/s左右;线性插值到z坐标法得到的最大流速误差达到0.7 m/s;四阶精度方法计算得到的最大流速误差为0.3 m/s;权重密度雅克比方法和三次方多项式拟合法计算得到的最大流速误差相差不大,都只有0.2 m/s左右.标准密度雅克比法计算得到的单位质量平均动能最大,为9×10-4 m2/s2;四阶精度方法和线性插值到z坐标方法计算得到的单位质量平均动能差不多,为3×10-4 m2/s2;三次方多项式拟合法计算得到的单位质量平均动能为1.9×10-4 m2/s2;权重密度雅克比方法计算得到的单位质量平均动能最小,仅为1×10-4 m2/s2.标准密度雅克比法的计算耗时最短,为294 min;与其相比,三次方多项式拟合法的计算耗时增加了5.9%;权重密度雅克比法的计算耗时增加了8.8%;四阶精度插值法的计算耗时增加了23.6%.线性插值到z坐标法的计算耗时最长,需要384.5 min,相对于标准密度雅克比法的计算耗时增加了30.6%.因此,综合最大流速误差、平均动能和计算耗时的结果可知,线性插值到z坐标法的计算结果相对较差,采用权重密度雅克比法能较好地降低水平压力梯度误差. 相似文献
15.
《Ocean Modelling》2007,16(1-2):61-75
There is an increasing interest to move ocean codes from classical Cartesian staggered mesh schemes to unstructured staggered grids. By using unstructured grid models one may construct meshes that follow the coastlines more accurately, and it is easy to apply a finer resolution in areas of special interest.In this paper we focus on how to approximate the Coriolis terms in such unstructured staggered grid models using equivalents of the Arakawa C-grid for the linear equations governing the propagation of the inertia-gravity waves. We base the analysis on a Delaunay triangulation of the region in question and use the Voronoi points and the midpoints on the triangle edges to define a staggered grid for the sea elevation and the velocity orthogonal to the edges of the triangles. It is shown that a standard method for the Coriolis weighting may create unphysical growth of the numerical solutions. A modified Coriolis weighting that conserves the total energy is suggested.In real applications diffusion is often introduced both for physical reasons, but often also in order to stabilise the numerical experiments. The growing modes associated with the unstructured staggered grids and equal weighting may force us to enhance the diffusion more than we would like from physical considerations. The modified weighting offers a simple solution to this problem. 相似文献
16.
We present a porous medium approach to representing topography, and a new algorithm for the objective interpolation of topography, for use in ocean circulation models of fixed resolution. The representation and algorithm makes use of two concepts; impermeable thin walls and porous barriers. Impermeable thin walls allow the representation of knife-edge sub-grid-scale barriers that block lateral flow between model grid cells. Porous barriers permit the sub-grid scale geometry to modulate lateral transport as a function of elevation. We find that the porous representation and the resulting interpolated topography retains key features, such as overflow sill depths, without compromising other dynamically relevant aspects, such as mean ocean depth for a cell. The accurate representation of the ocean depth is illustrated in a simple model of a tsunami that has a cross-basin travel time very much less dependent on horizontal resolution than when using conventional topographic interpolation and representation. 相似文献
17.
SELFE: A semi-implicit Eulerian–Lagrangian finite-element model for cross-scale ocean circulation 总被引：1，自引：0，他引：1
Unstructured-grid models grounded on semi-implicit, finite-volume, Eulerian–Lagrangian algorithms, such as UnTRIM and ELCIRC, have enjoyed considerable success recently in simulating 3D estuarine and coastal circulation. However, opportunities for improving the accuracy of this type of models were identified during extensive simulations of a tightly coupled estuary–plume–shelf system in the Columbia River system. Efforts to improve numerical accuracy resulted in SELFE, a new finite-element model for cross-scale ocean modeling. SELFE retains key benefits, including computational efficiency of existing semi-implicit Eulerian–Lagrangian finite-volume models, but relaxes restrictions on grids, uses higher-order shape functions for elevation, and enables superior flexibility in representing the bathymetry. Better representation of the bathymetry is enabled by a novel, “localized” vertical grid that resembles unstructured grids. At a particular horizontal location, SELFE uses either S coordinates or SZ coordinates, but the equations are consistently solved in Z space. SELFE also performs well relative to volume conservation and spurious oscillations, two problems that plague some finite-element models. This paper introduces SELFE as an open-source code available for community use and enhancement. The main focus here is on describing the formulation of the model and on showing results for a range of progressively demanding benchmark tests. While leaving details to separate publications, we also briefly illustrate the superior performance of SELFE over ELCIRC in a field application to the Columbia River estuary and plume. 相似文献
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岛屿岛礁海域海浪能谱模型研究进展 总被引：2，自引：0，他引：2
波浪能谱模型在岛屿岛礁海域的波浪预报研究和海洋工程中应用广泛,但存在模式计算格点无法充分体现岛屿岛礁的复杂地形特征和很难刻画波浪受到岛屿岛礁影响发生变形物理过程等两个关键问题。多重网格嵌套方案、岛屿次网格地形效应计算方案以及非结构网格、无网格、动态自适应四叉树网格等技术在体现岛屿岛礁复杂地形方面取得了较好的效果;将相位解析模型与波浪能谱模型优势互补是提高能谱模型对岛屿近岸波浪变形物理过程计算能力的一个有效方法。开展球坐标系下波作用密度谱方程的自适应四叉树网格求解方法研究,借鉴相位解析模型最新成果完善能谱模式的绕射、反射、底摩擦等物理过程,是提高岛屿岛礁海域海浪精细预报技术水平的前沿性、探索性研究方向。 相似文献
20.
A three dimensional hydrostatic finite volume ocean model has been developed to solve the integral dynamical equations. Since the basic (integral) equations are solved for finite volumes rather than grid points, the flux conservation is easily enforced, even on arbitrary meshes. Both upwind and high-order combined compact schemes can be incorporated into the model to increase computational stability and accuracy. This model uses a highly distorted grid system near the boundary. The lateral boundaries of each finite volume are perpendicular to x and y axes and the two vertical boundaries are not purely horizontal. Four types of finite volumes are designed to follow the terrain with four (Type-A), three (Type-B), two (Type-C), and one (Type-D) vertices in the lower surface. Such a terrain-following grid discretization has superior features to z- and σ-coordinate systems. The accuracy of this model was tested. 相似文献