共查询到20条相似文献，搜索用时 218 毫秒
1.
This is the first part of a publication that describes the generation of adaptive grids (this part), and simulations with vector-ocean-model (VOM) in unstructured grids resulting from the adaptation (part II). A static vertical adaptive grid in z-coordinates allows improving the approximation of topography and vertical resolution at slopes. Adaptive grids use elements from a set of grid sizes by multiplying a basic smallest cell size with powers of two, as in cell division. Grids with locally isotropic vertical resolution at surface, seabed, and slopes can be generated whereby resolution decreases towards the ocean interior. The adaptation to topography yields unstructured grids that are organised in a one-dimensional vector by column-wise storage of cells, discarding land cells. The vector storage suggested the model’s name. Grids are generated by an iterative procedure that relies on rules, i.e. criteria and directives to control the grid structure in favour of a good representation of physics and smooth numerical operations. The directives govern vertical resolution at sea surface and seabed, and at slopes. For the latter vertical resolution is extended in the horizontal. In the ocean interior horizontal distances between changes in grid size can be controlled for the sake of smooth numerics. The use of a z-grid that avoids transformation errors, the depth-independence of vertical resolution, and the lateral extension of vertical resolution at slopes towards the ocean interior are the most significant differences of adaptive grids in comparison to vertical coordinate transformations. Unstructured grids do not rely on a smoothing of topography and can be used within any of the horizontal Arakawa-grids. For the same topography directives allow creating various grids as demonstrated for a shelf-ocean topography. The number of cells per column in two unstructured grids generated for the North Atlantic may locally well exceed typical layer numbers in conventional model matrices. But the domain average is similar to layer numbers of today’s ocean models. Thus, with the same investment of cells per domain a higher resolution in slope regions can be achieved by unstructured grids as compared to conventional z-grids. 相似文献
2.
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
3.
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.
U. Raudsepp 《Estuarine, Coastal and Shelf Science》1998,47(6):715-730
High spatial resolution measurements of current velocity performed by the shipboard mounted Acoustic Doppler Current Profiler (ADCP) in the lateral boundary layer of the southern Gulf of Finland during two 5-day periods are described and analysed with a focus on the dominant dynamics. The measurement site represents a small (15×20 km), relatively deep (up to 100 m) bay opened to large-scale estuarine circulation. The measurement period was characterized by calm winds and a strong seasonal pycnocline (Brunt-Väisälä frequencyN=6–9*10−2 s−1). The quasi-steady velocity field revealed polarization of currents along the shore whereas an intensive baroclinic coastal jet was observed over a cross-shore scale of 1–2 km. The level of vertical separation of the alongshore flow coincided with the pycnocline at the coast, but was shifted below it in the offshore region. The cross-shore flow was considerably weaker and showed a three-layer structure with an opposite phase between the first and second surveys. It is suggested that the observed jet resembles a non-locally forced eastward propagating coastally trapped wave. In the offshore area the alongshore flow field satisfies local geostrophic balance quite well, except in the pycnocline where strong vertical stratification exerts considerable vertical stress. As vertical velocity shear is well correlated with vertical stratification, the horizontal advection prevails over vertical mixing. Horizontal inhomogeneities of density distribution are partly explained by vertical velocities with an estimated magnitude of less than 0·6 mm/s and the spatial pattern following bottom topography. 相似文献
5.
Coastal ocean hydrodynamic models are subject to a number of stability constraints. The most important of these are the Courant–Friedrichs–Levy (CFL) constraint on gravity waves, a Courant (Cr) number constraint on advection, and a time step constraint on the vertical component of viscous stresses. The model described here removes these constraints using a semi-implicit approximation in time and a semi-Lagrangian approximation for advection. The accuracy and efficiency of semi-Lagrangian methods depends crucially on the methods used to calculate trajectories and interpolate at the foot of the trajectory. The focus of this paper is on evaluation of several new and old semi-Langrangian methods. In particular, we compare 3 methods to calculate trajectories (Runge–Kutta (RK2), analytical integration (AN), power-series expansion (PS)) and 3 methods to interpolate (local linear (LL), global linear (GL), global quadratic (GQ)) on unstructured grids. The AN and PS methods are both efficient and accurate, and the latter can be expanded in a straightforward manner to treat time-dependent velocity. The GQ interpolation method provides a major step in introducing efficient and accurate semi-Lagrangian methods to unstructured grids. 相似文献
6.
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
7.
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
8.
《Deep Sea Research Part I: Oceanographic Research Papers》2003,50(1):53-71
Ventilation of the deep basins of the North Aegean Sea takes place during relatively scarce events of massive dense water formation in that region. In the time intervals between such events, the bottom waters of each sub-basin are excluded from interaction with other water masses through advection or isopycnal mixing and the only process that changes their properties is diapycnal mixing with overlying waters. In this work we utilize a simple one-dimensional model in order to estimate the vertical eddy diffusion coefficient Kρ based on the observed rate of change of density and stratification. Vertical diffusivity is estimated for each of three sub-basins of the North Aegean, one of convex shape of the seabed and the other two of concave topography. It is noteworthy that the convex sub-basin exhibited much higher vertical diffusivity than the two concave sub-basins, a fact consistent with theoretical predictions that internal-wave-induced mixing is higher over the former shape of seabed. Furthermore, the estimates of Kρ are exploited in computing the vertical transport of dissolved oxygen through diffusion and the rate of oxygen consumption by decaying organic matter. The different levels of the estimated diffusion and oxygen consumption rates testify to the dynamical and biogeochemical characteristics of each basin. 相似文献
9.
10.
Large eddy simulations of the flow around a circular cylinder at high Reynolds numbers are reported. Five Reynolds numbers were chosen, such that the drag crisis was captured. A total of 18 cases were computed to investigate the effect of gridding strategy, turbulence modelling, numerical schemes and domain width on the results. It was found that unstructured grids provide better resolution of key flow features, when a ‘reasonable’ grid size is to be maintained.When using coarse grids for large eddy simulation, the effect of turbulence models and numerical schemes becomes more pronounced. The dynamic mixed Smagorinsky model was found to be superior to the Smagorinsky model, since the model coefficient is allowed to dynamically adjust based on the local flow and grid size. A blended upwind-central convection scheme was also found to provide the best accuracy, since a fully central scheme exhibits artificial wiggles, due to dispersion errors, which pollute the solution.Mean drag, fluctuating lift Strouhal number and base pressure are compared to experiments and empirical estimates for Reynolds numbers ranging from 6.31 × 104 to 5.06 × 105. In terms of the drag coefficient, the drag crisis is well captured by the present simulations, although the other integral quantities (rms lift and Strouhal number) show larger discrepancies. For the lowest Reynolds number, the drag is seen to be more sensitive to the domain width than the spanwise grid spacing, while at the higher Reynolds numbers the grid resolution plays a more important role, due to the larger extent of the turbulent boundary layer. 相似文献
11.
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
12.
Masahiro Endoh 《Journal of Oceanography》1973,29(1):16-27
A numerical experiment is made using a barotropic model for the western boundary currents. The time-dependent, non-linear vorticity equation is integrated with and without the variable of bottom topography. The inertial and frictional boundary flow is resolved with a fine grid size of 10 km. Connection of the western boundary currents with the general circulation is facilitated by giving the fixed Sverdrup transport at the eastern boundary of the model (400 km offshore).For the flat bottom topography, steady flow forRe=35 shows dynamical balance essentially of a frictional model. The transient response leading to the formation of the western boundary currents in the model seems to support theLighthill's theory (1969). ForRe=350, unsteady features revealed byBryan (1963) is re-established. A phenomenon of barotropic instability is also observed with sufficient resolution. For the model with a continental slope the steady flow is also obtained forRe=35. The boundary currents flow over the continental slope, deviating offshore as they flow northward. 相似文献
13.
The parallel, finite-volume, unstructured-grid SUNTANS model has been employed to study the interaction of the tides with complex bathymetry in the macrotidal Snohomish River estuary. The unstructured grid resolves the large-scale, O(10 km) tidal dynamics of the estuary while employing 8 m grid-resolution at a specific region of interest in the vicinity of a confluence of two channels and extensive intertidal mudflats to understand detailed local intratidal flow processes. After calibrating tidal forcing parameters to enforce a match between free surface and depth-averaged velocities at several locations throughout the domain, we analyze the complex dynamics of the confluence and show that the exposure of the intertidal mudflats during low tide induces a complex flow reversal. When coupled with the longitudinal salinity gradient, this flow reversal results in a highly variable salinity field, which has profound implications for local mixing, stratification and the occurrence of fine-scale flow structures. This complex flow is then used as a testbed from which to describe several challenges associated with high resolution modeling of macrotidal estuaries, including specification of high resolution bathymetry, specification of the bottom stress, computation of the nonhydrostatic pressure, accurate advection of momentum, and the influence of the freshwater inflow. The results indicate that with high resolution comes the added difficulty of requiring more accurate specification of boundary conditions. In particular, the bottom bathymetry plays the most important role in achieving accurate predictions when high resolution is employed. 相似文献
14.
瓯江口是一个径流量变化剧烈的强潮河口。本文基于非结构网格FVCOM模型,建立瓯江口海域大范围三维数学模型,研究不同时间尺度（潮周期、大-小潮）的盐度变化,并利用势能异常动力方程对数值模拟结果分析了瓯江口层化过程的动力机制。同时,利用河口Ri数和层化参数△s/<s>研究了不同时间尺度的层化稳定性及其空间变化,得出决定层化状态的潮差和径流量的阈值。结果显示：瓯江北口上段、中段和口门在潮差分别超过3.8m、4.0m和4.6m时呈完全混合状态。当径流量小于280 m3/s或大于510 m3/s,北口上段持续完全混合;而在口门附近,完全混合和层化的临界径流量约为280 m3/s。研究认为瓯江河口北口存在周期性的层化,北口下段在落潮和涨潮初期呈部分混合状态,而其它时段为完全混合。上段只在落潮初期存在层化。层化增强主要是纵向对流与横向速度剪切导致,而湍混合和纵向潮应力是层化减弱的主要因素。 相似文献
15.
A new adaptive Cartesian-grid for the CIP (constrained interpolation profile) method is proposed and applied to two-dimensional numerical simulations of violent free-surface flows. The CCUP (CIP combined and unified procedure) method is employed and combined with this adaptive Cartesian-grid for robust and efficient computation. This adaptive grid is capable of tracking regions where flows vary violently, and a much finer grid is then concentrated automatically on these regions to adapt to the violent changing of the flow. Unlike the abacus-like Soroban grid which is an adaptive meshless grid with complicated algorithms and inefficiency of evaluation of frequently computed spatial derivatives, the present approach not only simplifies computational algorithm but also enhances efficiency of frequently-computed spatial derivatives. It is also different from most of the remeshing schemes that no additional CPU-time for the value-mapping from the old grid to the new grid is taken in this adaptive grid system provided that the advection velocity is interpolated, since the value-mapping process is accomplished simultaneously within the advection process. To validate the accuracy and efficiency of this newly-proposed CFD model, several two-dimensional benchmark problems are performed, and the results are compared with experimental measurements and other published numerical results. Numerical simulations show that the proposed numerical model is robust, accurate, and efficient for strongly nonlinear free-surface flows. 相似文献
16.
By ANDREA MOLOD 《地球，A辑:动力气象学与海洋学》2009,61(3):381-393
An 'alternate grid' (GridAlt) technique is presented, which allows the different components of a general circulation model's governing equations to be computed on distinct grids chosen for that component or process. In the implementation presented here, the tendencies of state variables from the physical parametrizations are computed on a vertical grid with very fine resolution near the surface, whereas the remaining terms in the equations of motion are computed using an Eta coordinate with coarser vertical resolution.
Results from a suite of aquaplanet experiments show that much of the benefit of increased vertical resolution in the whole model can be realized by enhancing the vertical resolution of the 'physics grid' using GridAlt. The benefit is realized in the fields which are computed directly in the physical parametrizations, and in the vertical structure of the relative humidity and mass streamfunction. Results from a suite of realistically configured simulations demonstrated an impact of GridAlt that was similar to its impact in the simplified simulations, as well as an improved response to El Niño Southern Oscillation forcing. It is concluded that the present implementation of GridAlt offers a practical way to allow GCMs to better capture the near-surface structure of the atmosphere. 相似文献
Results from a suite of aquaplanet experiments show that much of the benefit of increased vertical resolution in the whole model can be realized by enhancing the vertical resolution of the 'physics grid' using GridAlt. The benefit is realized in the fields which are computed directly in the physical parametrizations, and in the vertical structure of the relative humidity and mass streamfunction. Results from a suite of realistically configured simulations demonstrated an impact of GridAlt that was similar to its impact in the simplified simulations, as well as an improved response to El Niño Southern Oscillation forcing. It is concluded that the present implementation of GridAlt offers a practical way to allow GCMs to better capture the near-surface structure of the atmosphere. 相似文献
17.
MPAS-Ocean is used to simulate an idealized, density-driven overflow using the dynamics of overflow mixing and entrainment (DOME) setup. Numerical simulations are carried out using three of the vertical coordinate types available in MPAS-Ocean, including z-star with partial bottom cells, z-star with full cells, and sigma coordinates. The results are first benchmarked against other models, including the MITgcm’s z-coordinate model and HIM’s isopycnal coordinate model, which are used to set the base case used for this work. A full parameter study is presented that looks at how sensitive overflow simulations are to vertical grid type, resolution, and viscosity. Horizontal resolutions with 50 km grid cells are under-resolved and produce poor results, regardless of other parameter settings. Vertical grids ranging in thickness from 15 m to 120 m were tested. A horizontal resolution of 10 km and a vertical resolution of 60 m are sufficient to resolve the mesoscale dynamics of the DOME configuration, which mimics real-world overflow parameters. Mixing and final buoyancy are least sensitive to horizontal viscosity, but strongly sensitive to vertical viscosity. This suggests that vertical viscosity could be adjusted in overflow water formation regions to influence mixing and product water characteristics. Lastly, the study shows that sigma coordinates produce much less mixing than z-type coordinates, resulting in heavier plumes that go further down slope. Sigma coordinates are less sensitive to changes in resolution but as sensitive to vertical viscosity compared to z-coordinates. 相似文献
18.
19.
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
20.
夏季珠江口溶解氧垂向输运数值模拟研究 总被引：1，自引：1，他引：0
通过建立一个珠江口三维水质模型,对夏季珠江口溶解氧垂向输运进行研究。结果表明:潮汐、风及上升流间歇性破坏层化,令溶解氧垂向对流及扩散通量的方向和大小随潮汐发生周期性变化。在西四口门海域,由于水体层化稳定,垂向上对流及扩散作用产生的溶解氧输运通量都较小,且相互平衡;在伶仃洋内的深槽,径流与潮汐的相互作用强烈,层化被间歇性地打破,溶解氧的垂向对流通量大于扩散通量,导致底层溶解氧浓度产生波动;在伶仃洋内的西部浅滩上,层化相对稳定,溶解氧的垂向扩散通量大于对流通量。这表明在珠江口不同区域,垂向的对流扩散作用对溶解氧垂向输运起不同作用,从而影响表底层溶解氧的浓度。 相似文献