共查询到20条相似文献，搜索用时 640 毫秒
1.
《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
2.
《Ocean Modelling》2011,40(3-4):248-261
Accurate representation of geostrophic and hydrostatic balance is an essential requirement for numerical modelling of geophysical flows. Potentially, unstructured mesh numerical methods offer significant benefits over conventional structured meshes, including the ability to conform to arbitrary bounding topography in a natural manner and the ability to apply dynamic mesh adaptivity. However, there is a need to develop robust schemes with accurate representation of physical balance on arbitrary unstructured meshes. We discuss the origin of physical balance errors in a finite element discretisation of the Navier–Stokes equations using the fractional timestep pressure projection method. By considering the Helmholtz decomposition of forcing terms in the momentum equation, it is shown that the components of the buoyancy and Coriolis accelerations that project onto the non-divergent velocity tendency are the small residuals between two terms of comparable magnitude. Hence there is a potential for significant injection of imbalance by a numerical method that does not compute these residuals accurately. This observation is used to motivate a balanced pressure decomposition method whereby an additional “balanced pressure” field, associated with buoyancy and Coriolis accelerations, is solved for at increased accuracy and used to precondition the solution for the dynamical pressure. The utility of this approach is quantified in a fully non-linear system in exact geostrophic balance. The approach is further tested via quantitative comparison of unstructured mesh simulations of the thermally driven rotating annulus against laboratory data. Using a piecewise linear discretisation for velocity and pressure (a stabilised P1P1 discretisation), it is demonstrated that the balanced pressure decomposition method is required for a physically realistic representation of the system. 相似文献
3.
The wind-induced sea-level variations at Hakata tidal station in winter are reproduced realistically using a one-way nested
model. This nested model is constructed with a structured finite-difference Princeton Ocean Model (POM) for the Tsushima-Korea
Straits, and an unstructured Finite Volume Coastal Ocean Model (FVCOM) for Fukuoka Bay divided into triangular-cell grids.
The correlation coefficient and root-mean-square error between observed and modeled results are 0.742 and 1.88 [cm], respectively.
Moreover, the results show that the nested model with FVCOM is more accurate than the model in which FVCOM is replaced with
a high-resolution POM for Fukuoka Bay. This indicates that the nested model constructed with structured and unstructured models
works effectively in hindcasting the wind-induced sea-level variations. 相似文献
4.
《Ocean Modelling》2003,5(1):37-63
A stabilized finite-element (FE) algorithm for the solution of oceanic large scale circulation equations and optimization of the solutions is presented. Pseudo-residual-free bubble function (RFBF) stabilization technique is utilized to enforce robustness of the numerics and override limitations imposed by the Babuška–Brezzi condition on the choice of functional spaces. The numerical scheme is formulated on an unstructured tetrahedral 3d grid in velocity–pressure variables defined as piecewise linear continuous functions. The model is equipped with a standard variational data assimilation scheme, capable to perform optimization of the solutions with respect to open lateral boundary conditions and external forcing imposed at the ocean surface. We demonstrate the model performance in applications to idealized and realistic basin-scale flows. Using the adjoint method, the code is tested against a synthetic climatological data set for the South Atlantic ocean which includes hydrology, fluxes at the ocean surface and satellite altimetry. The optimized solution proves to be consistent with all these data sets, fitting them within the error bars.The presented diagnostic tool retains the advantages of existing FE ocean circulation models and in addition (1) improves resolution of the bottom boundary layer due to employment of the 3d tetrahedral elements; (2) enforces numerical robustness through utilization of the RFBF stabilization, and (3) provides an opportunity to optimize the solutions by means of 3d variational data assimilation. Numerical efficiency of the code makes this a desirable tool for dynamically constrained analyses of large datasets. 相似文献
5.
William A. Prothero Jr. 《Marine Geophysical Researches》1977,3(1):119-141
The ocean bottom seismometer capsule contains a 1 Hz. vertical seismometer and triggerable or programmable digital recording system. The output of the seismometer is continuously digitized at a preselected rate of 64, 128, or 256 samples/sec. The digital data words are mixed with a time code and synchronization characters, serialized and passed through a 1536 sample shift register which acts as a delay line. The serial output bits are then encoded and recorded on a SONY TC800B tape recorder which is turned on when a seismic event occurs. The event trigger occurs when the seismic signal jumps to 8 times the time averaged input signal. A memory may be programmed to run the recorder on a schedule so that small amplitude signals from refraction shots are sure to be recorded. Data are recovered using the same recorder for playback and a decoder which provides an analog output for field data interpretation or a digital output for computer analysis. An acoustic transponder allows precise ranges between the capsule and ship to be determined. In addition, commands for the capsule to release or to transmit diagnostic data may be given from the surface ship. The capsule falls freely to the ocean bottom. After a predetermined time or when a release command is received, it is released from a 68 kg steel tripod and floats to the surface. A dual timer and explosive bolt system is used to increase recovery reliability.The first capsules were designed and constructed between October 1972 and October 1973. Good results were obtained from 38 out of 43 launchings made on six expeditions in 1974, 1975, and 1976. Four capsules have been lost. 相似文献
6.
G.J. Gorman M.D. Piggott C.C. Pain C.R.E. de Oliveira A.P. Umpleby A.J.H. Goddard 《Ocean Modelling》2006,12(3-4):436-452
A method for generating high quality unstructured computational meshes for applications in geophysical, and specifically ocean, modelling is presented. The method generates a three-dimensional mesh which is optimised to approximate the bathymetry to a user-specified accuracy, which itself may be defined as a function of space and bathymetry. To do this a mesh optimisation method is employed which allows the formation of highly anisotropic elements aligned with bathymetric variations of high curvature. In addition a coastal recovery algorithm, based upon feature decimation and edge recovery, is described. 相似文献
7.
我国主要海洋产业发展规模预测分析 总被引：1，自引：0，他引：1
通过收集整理1952—2002年50a的海洋经济统计数据,结合计量经济学手段进行时间序列分析。依样本空间和分析对象的不同,运用趋势外推法分别建立了线性模型、抛物线模型、生长曲线模型3种预测外延模型结构。并对预测外延模型结构进行了数据拟合与相关参数分析,总结出了适合预测海洋经济发展的线性模型和抛物线模型。根据海洋渔业、海洋油气业、海滨砂矿业、海洋盐业、海洋船舶工业、海洋交通运输业、滨海国际旅游业等7个主要海洋产业各自发展特点,用预测模型分别进行拟合,建立适合各海洋产业的预测模型。最终对2010年全国6个主要海洋产业、分产业总产值进行了预测。 相似文献
8.
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
9.
Wave-tide-surge coupled simulation for typhoon Maemi 总被引：1，自引：0，他引：1
The main task of this study focuses on studying the effect of wave-current interaction on currents, storm surge and wind wave as well as effects of current induced wave refraction and current on waves by using numerical models which consider the bottom boundary layer and sea surface roughness parameter for shallow and smooth bed area around Korean Peninsula. The coupled system (unstructured-mesh SWAN wave and ADCIRC) run on the same unstructured mesh. This identical and homogeneous mesh allows the physics of wave-circulation interactions to be correctly resolved in both models. The unstructured mesh can be applied to a large domain allowing all energy from deep to shallow waters to be seamlessly followed. There is no nesting or overlapping of structured wave meshes, and no interpolation is required. In response to typhoon Maemi (2003), all model components were validated independently, and shown to provide a faithful representation of the system’s response to this storm. The waves and storm surge were allowed to develop on the continental shelf and interact with the complex nearshore environment. The resulting modeling system can be used extensively for prediction of the typhoon surge. The result show that it is important to incorporate the wave-current interaction effect into coastal area in the wave-tide-surge coupled model. At the same time, it should consider effects of depth-induced wave breaking, wind field, currents and sea surface elevation in prediction of waves. Specially, we found that: (1) wave radiation stress enhanced the current and surge elevation otherwise wave enhanced nonlinear bottom boundary layer decreased that, (2) wind wave was significantly controlled by sea surface roughness thus we cautiously took the experimental expression. The resulting modeling system can be used for hindcasting (prediction) the wave-tide-surge coupled environments at complex coastline, shallow water and fine sediment area like areas around Korean Peninsula. 相似文献
10.
Victoria J. Hill Richard C. Zimmerman 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(10):1243-1254
The Arctic Ocean, including its regional shelf seas, is assumed to play an important role in the global carbon cycle. However, the true magnitude of annual production is unknown, as in situ data are sparse in time and space. Remote sensing technology has the potential to provide large scale estimates of phytoplankton biomass at much higher frequency and spatial coverage than shipboard observations in this remote region. Subsurface peaks in both biomass and primary production (PP), which are the characteristics of the Arctic, are shown to limit the reliability of ocean color based integrated PP (IPP) models in the Chukchi Sea. Here we report that the retrievals of IPP from remotely sensed ocean color data were accurate only when limited to 1.2 optical depths, which severely constrains the utility of ocean color remote sensing for the assessment of Arctic Ocean dynamics.Active sensors such as LIDAR, can, in combination with passive ocean color, dramatically improve our ability to estimate IPP for the Arctic. IPP retrievals were improved to within a factor of 2–3 of the measured values, when the vertical distribution of Chl a was determined to a resolution of 1 m using modeled LIDAR retrievals of the beam attenuation coefficient. This was far better than models using only passive ocean color. The instrument specifications of the current NASA spaceborne LIDAR (CALIOP) allow for the retrieval of Kd at a depth resolution of 23 m. Even with this constraint, however, the accuracy of the modeled IPP was improved over passive ocean color retrievals to approximately a factor of 3. The Arctic is a perfect location to merge ocean color and LIDAR measurements as the polar orbit of CALIOP provides complete grid coverage of the area every 8 days, crossing the horizontal gradients in Chl a already known to exist from passive ocean color observations. 相似文献
11.
《Ocean Modelling》2008,20(3):223-239
A turbulence closure for the effect of mesoscale eddies in non-eddy-resolving ocean models is proposed. The closure consists of a prognostic equation for the eddy kinetic energy (EKE) that is integrated as an additional model equation, and a diagnostic relation for an eddy length scale (L), which is given by the minimum of Rhines scale and Rossby radius. Combining EKE and L using a standard mixing length assumption gives a diffusivity (K), corresponding to the thickness diffusivity in the [Gent, P.R., McWilliams, J.C. 1990. Isopycnal mixing in ocean circulation models. J. Phys. Oceanogr. 20, 150–155] parameterisation. Assuming downgradient mixing of potential vorticity with identical diffusivity shows how K is related to horizontal and vertical mixing processes in the horizontal momentum equation, and also enables us to parameterise the source of EKE related to eddy momentum fluxes.The mesoscale eddy closure is evaluated using synthetic data from two different eddy-resolving models covering the North Atlantic Ocean and the Southern Ocean, respectively. The diagnosis shows that the mixing length assumption together with the definition of eddy length scales is valid within certain limitations. Furthermore, implementation of the closure in non-eddy-resolving models of the North Atlantic and the Southern Ocean shows consistently that the closure has skill at reproducing the results of the eddy-resolving model versions in terms of EKE and K. 相似文献
12.
《Ocean Modelling》2002,4(3-4):249-267
During the course of developing new numerical algorithms for a terrain-following ocean modeling system (TOMS), different numerical aspects have been evaluated through a comparison between two widely used community ocean models, the Princeton ocean model (POM) and the regional ocean modeling system (ROMS). While both models aim at modeling coastal to basin-scale problems using similar grids, their numerical algorithms, code structure, and parameterization options are very different. Sensitivity studies with an idealized channel flow and a steep seamount configuration demonstrate how different algorithms in the two models may affect numerical errors, the stability of the code and the computational efficiency. For example, new pressure gradient schemes using polynomial fits and new time stepping algorithms may reduce numerical errors and allow using longer time steps than standard schemes do. However, the new schemes may require more careful choices of time steps and the use of higher order advection schemes to maintain numerical stability. 相似文献
13.
A new approach to detecting ocean eddies automatically from remote sensing imageries based on the ocean eddy's eigen-pattern in remote sensing imagery and "force field-based shape extracting method" is proposed. First, the analysis on extracting eddies' edges from remote sensing imagery using conventional edge detection arithmetic operators is performed and returns digitized vector edge data as a result. Second, attraction forces and fusion forces between edge curves were analyzed and calculated based on the vector eddy edges. Thirdly, the virtual significant spatial patterns of eddy were detected automatically using iterative repetition followed by optimized rule. Finally, the spatial form auto-detection of different types of ocean eddies was done using satellite images. The study verified that this is an effective way to identify and detect the ocean eddy with a complex form. 相似文献
14.
An unstructured-grid, finite-volume, nonhydrostatic, parallel coastal ocean simulator 总被引：4，自引：4，他引：4
A finite-volume formulation is presented that solves the three-dimensional, nonhydrostatic Navier–Stokes equations with the Boussinesq approximation on an unstructured, staggered, z-level grid, with the goal of simulating nonhydrostatic processes in the coastal ocean with grid resolutions of tens of meters. In particular, the code has been developed to simulate the nonlinear, nonhydrostatic internal wave field in the littoral ocean. The method is based on the formulation developed by Casulli, in that the free-surface and 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 with the second-order Adams–Bashforth method, while the pressure-correction method is employed for the nonhydrostatic pressure in order to achieve overall second-order temporal accuracy. Advection of momentum is accomplished with an Eulerian discretization which conserves momentum in cells that do not contain the free surface, and scalar advection is discretized in a way that ensures consistency with continuity, thereby ensuring local and global mass conservation using a velocity field that conserves volume on a local and global basis. The nonhydrostatic pressure field is solved efficiently using a block-Jacobi preconditioner, and while stability is limited by the internal gravity wave speed and vertical advection of momentum, applications requiring relatively small time steps due to accuracy or stability constraints are run efficiently on parallel computers, since the present formulation is written entirely with the message-passing interface (MPI). The ParMETIS libraries are employed in order to achieve a load-balanced parallel partitioning that minimizes interprocessor communication, and the grid is reordered to optimize per-processor performance by limiting cache misses while accessing arrays in memory. Test cases demonstrate the ability of the code to efficiently and accurately compute the nonhydrostatic lock exchange and internal waves in idealized as well as real domains, and we evaluate the parallel efficiency of the code using up to 32 processors. 相似文献
15.
16.
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
17.
基于采用无结构网格和有限体积方法的FVCOM陆架模式,考虑8个主要的天文分潮,建立胶州湾三维高分辨率数值模型来重现和研究其潮汐潮流变化状况。与实测资料对比验证表明,模拟结果与实测值吻合较好。在此基础上,根据模拟结果计算得到了较以往更为精细的同潮图和潮汐、潮流、余流分布特征。研究结果揭示,最大可能潮流和最大余流都发生在团岛附近,流速分别可达2.14和0.43 m/s;除了湾口附近前人报道过的4个余流系统外,还在中部首次揭示了2个相对较弱的余流系统;潮流能通量在内外湾口呈"左进右出"的结构;胶州湾的平均纳潮量为8.31亿m3;染色试验表明,胶州湾30 d的水交换率为36.8%。 相似文献
18.
Large eddy simulation of stratified mixing in a three-dimensional lock-exchange system 总被引：1，自引：1，他引：0
Accurate and computationally-efficient modeling of stratified mixing processes are of paramount importance in both coastal and large-scale ocean circulation. In this study, our main objective is to investigate the feasibility and accuracy of large eddy simulation (LES) as a possible tool to study small-scale oceanic processes. To this end, LES is evaluated in a 3D lock-exchange problem, which contains shear-driven mixing, internal waves, interactions with boundaries and convective motions, while having a simple domain, initial and boundary conditions, and forcing.Two general classes of LES models are tested, namely eddy viscosity (EV) models based on constant–coefficient and dynamic Smagorinsky models, and an approximate deconvolution (AD) model. By noting that the dynamic Smagorinsky and AD models have different strengths in that the former is good in providing appropriate dissipation while the latter in preserving the detail of coherent structures on coarse resolution meshes, a hybrid approach combining EV and AD models is also evaluated. A direct numerical simulation (DNS) is performed as the benchmark solution, and all LES models are tested on three coarse meshes. The main measure of mixing is taken as the temporal evolution of background potential energy.It is found that constant-coefficient Smagorinsky models can only provide a marginal improvement over under-resolved simulations, while both dynamic Smagorinsky and AD models lead to significant improvements in mixing accuracy. The primary accomplishment of this study is that it is shown that the hybrid approach attains the best agreement with the mixing curve from DNS, while being computationally approximately a thousand times faster. 相似文献
19.
Andrew M. Moore Hernan G. ArangoGregoire Broquet Brian S. PowellAnthony T. Weaver Javier Zavala-Garay 《Progress in Oceanography》2011,91(1):34-49
The Regional Ocean Modeling System (ROMS) is one of the few community ocean general circulation models for which a 4-dimensional variational data assimilation (4D-Var) capability has been developed. The ROMS 4D-Var capability is unique in that three variants of 4D-Var are supported: a primal formulation of incremental strong constraint 4D-Var (I4D-Var), a dual formulation based on a physical-space statistical analysis system (4D-PSAS), and a dual formulation representer-based variant of 4D-Var (R4D-Var). In each case, ROMS is used in conjunction with available observations to identify a best estimate of the ocean circulation based on a set of a priori hypotheses about errors in the initial conditions, boundary conditions, surface forcing, and errors in the model in the case of 4D-PSAS and R4D-Var. In the primal formulation of I4D-Var the search for the best circulation estimate is performed in the full space of the model control vector, while for the dual formulations of 4D-PSAS and R4D-Var only the sub-space of linear functions of the model state vector spanned by the observations (i.e. the dual space) is searched. In oceanographic applications, the number of observations is typically much less than the dimension of the model control vector, so there are clear advantages to limiting the search to the space spanned by the observations. In the case of 4D-PSAS and R4D-Var, the strong constraint assumption (i.e. that the model is error free) can be relaxed leading to the so-called weak constraint formulation. This paper describes the three aforementioned variants of 4D-Var as they are implemented in ROMS. Critical components that are common to each approach are conjugate gradient descent, preconditioning, and error covariance models, which are also described. Finally, several powerful 4D-Var diagnostic tools are discussed, namely computation of posterior errors, eigenvector analysis of the posterior error covariance, observation impact, and observation sensitivity. 相似文献
20.
Fast dynamical spin-up of ocean general circulation models using Newton–Krylov methods 总被引：2，自引：2，他引：0
Numerical models of the ocean play an important role in efforts to understand past climate variability and predict future climate changes. In many studies, ocean models are driven by forcings that are either time-independent or vary periodically (seasonally) and it is often highly desirable or even essential to obtain equilibrium solutions of the model. Existing methods, based on the simple, expedient idea of integrating the model until the transients have died out, are too expensive to use routinely because the ocean takes several thousand years to equilibrate. Here, we present a novel approach for efficiently computing equilibrium solutions of ocean models. Our general approach is to formulate the problem as a large system of nonlinear algebraic equations to be solved with a class of methods known as matrix-free Newton–Krylov, a combination of Newton-type methods for superlinearly convergent solution of nonlinear equations, and Krylov subspace methods for solving the Newton correction equations. As an initial demonstration of the feasibility of this approach, we apply it to find the equilibrium solutions of a quasi-geostrophic ocean model for both steady forcing and seasonally-varying forcing. We show that the matrix-free Newton–Krylov method converges to the solutions obtained by direct time integration of the model, but at a computational cost that is between 10 and 100 times smaller than direct integration. A key advantage of our approach is that it can be applied to any existing time-stepping code, including ocean general circulation models and biogeochemical models. However, effective preconditioning of the linear equations to be solved during the Newton iteration remains a challenge. 相似文献