一维全非线性Green-Naghdi水波方程数值模型

建立了求解一维全非线性Green-Naghdi水波方程的中心有限体积/有限差分混合数值格式。采用结构化网格对守恒形式的控制方程进行离散和积分,界面数值通量采用有限体积法计算,剩余项则采用中心有限差分格式求解。其中,采用中心迎风有限体积格式计算控制体界面数值通量,并结合界面变量的线性重构方法,使其在空间上具有四阶精度,通过引入静压重构技术和波浪破碎指标使模型具备处理海岸水-陆动边界及波浪破碎的能力。时间积分则采用具有总时间变差减小(Total Variation Diminishing,TVD)性质的三阶龙格-库塔法进行。应用该模型对孤立波在常水深和斜坡海岸上的传播过程及规则波跨越潜堤传播的实验进行了数值模型研究,数值计算同解析解及实验数据吻合良好。     

Controlling spatial oscillations in bed level update schemes

A frequent problem with process-based coastal morphological models is the appearance of high wave number spatial oscillations in the simulated bed levels with time. After a sufficiently long time, these oscillations become dominant and mask the large-scale features of the bed level evolution.The equation for conservation of sediment mass is used to show that the spatial oscillations are generated by the dependence of the bed celerity (celerity of the bed level oscillations) with bed levels, which is due to the non-linear relationship between sediment transport and bed levels. This breeds higher spatial harmonics of the bed level oscillations with time. In this situation, using a Finite Difference (FD) scheme that does not damp oscillations with high wave numbers leads to the generated harmonics being kept in the solution. These generate further harmonics until the entire solution is dominated by high wave number oscillations.In this paper, a finite difference scheme, in combination with a filtering procedure, is used to dissipate high wave number oscillations. Analysis of the amplification portraits show that the filtering procedure in combination with a Lax–Wendroff scheme does not affect oscillations with lower wave numbers (larger scale features resolved with seven or more grid points). Some examples are also presented to illustrate these features.     

Seasonal-scale nearshore morphological evolution: Field observations and numerical modeling

A coupled waves–currents-bathymetric evolution model (DELFT-3D) is compared with field measurements to test hypotheses regarding the processes responsible for alongshore varying nearshore morphological changes at seasonal time scales. A 2001 field experiment, along the beaches adjacent to Grays Harbor, Washington, USA, captured the transition between the high-energy erosive conditions of winter and the low-energy beach-building conditions typical of summer. The experiment documented shoreline progradation on the order of 10–20 m and on average approximately 70 m of onshore sandbar migration during a four-month period. Significant alongshore variability was observed in the morphological response of the sandbar over a 4 km reach of coast with sandbar movement ranging from 20 m of offshore migration to over 175 m of onshore bar migration, the largest seasonal-scale onshore migration event observed in a natural setting. Both observations and model results suggest that, in the case investigated here, alongshore variations in initial bathymetry are primarily responsible for the observed alongshore variable morphological changes. Alongshore varying incident hydrodynamic forcing, occasionally significant in this region due to a tidal inlet and associated ebb-tidal delta, was relatively minor during the study period and appears to play an insignificant role in the observed alongshore variability in sandbar behavior at kilometer-scale. The role of fully three-dimensional cell circulation patterns in explaining the observed morphological variability also appears to be minor, at least in the case investigated here.     

The occurrence of irregular frequencies in forward speed ship seakeeping numerical calculations

This study investigates the occurrence of irregular frequencies in a seakeeping analysis of a ship moving with forward speed. This is achieved by formulating the interior virtual flow Dirichlet or Neumann eigenvalue problem. A theoretical analysis of a rectangular box travelling and oscillating in waves reveals that in the forward speed case, apart from the singular irregular frequency at zero encounter frequency, no irregular frequencies exist whilst at zero forward speed multiple irregular frequencies are observed confirming previous findings. These theoretical predictions are further verified by numerical calculations involving the rectangular box and a Series 60, C_B=0.70, hull.     

Three-dimensional numerical calculations of currents east of Taiwan Island in December 1997

numerical calculationsI~IOXAInong the numerical studies Of the circulation east of Taiwan Island, there were some studies, such as Yuan et al. (1998a, b), Wang et al. (1998). In their work, the Kuroshio east ofTaiwan Island and the currents southeast of Rgukyu-guntO were computed by using three-dimensional diagnOStic, semidiagnostic and prognostic model, respectively, based on the wind and hydrographic data obtained from two cruises, i. e., one cruise during October 1995, and the otherin…     

基于不规则矩形划分的高效海洋环流数值模式并行算法

使用序列化和不规则矩形划分的方法,开发了基于消息传递接口(MPI)的环流数值模式并行算法,并通过邻近点交换策略(NPES)进一步提升了计算效率。在HP C7000刀片系统上设计了两个实验,数值结果表明,使用了NPES的并行版本(PVN)的计算效率要高于原并行版本(PV)。在第二个实验中当进程数为100时PVN的计算效率仍可达到0.9以上,然而此时PV的计算效率已迅速下降至0.39。并用环流模式的PVN版本对一个高分辨率的区域进行了模拟,效果较好。该算法具备普适性,可用于其它环流模式的高效并行。     

A numerical model of beach morphological evolution due to waves and currents in the vicinity of coastal structures

A numerical model was developed of beach morphological evolution in the vicinity of coastal structures. The model includes five sub-models for random wave transformation, surface roller development, nearshore wave-induced currents, sediment transport, and morphological evolution. The model was validated using high-quality data sets obtained during experiments with a T-head groin and a detached breakwater in the basin of the Large-scale Sediment Transport Facility at the Coastal and Hydraulics Laboratory in Vicksburg, Miss, USA. The simulations showed that the model reproduced well the wave conditions, wave-induced currents, and beach morphological evolution in the vicinity of coastal structures. Both salient and tombolo formation behind a T-head groin and a detached breakwater were simulated with good agreement compared to the measurements.     

Modeling meso- and sub-mesoscale circulation along the eastern Crimean coast using numerical calculations

A numerical experiment has been carried out using a hydrodynamical model with nonlinear equations of motion and heat and salt advection to reconstruct the fields of hydrophysical parameters taking into account the real atmospheric forcing for the autumn season along the southern coast of the Crimean Peninsula. The studied part of the coast is situated at 44.25°N 33.95°E/44.72°N 34.55°E. High spatial resolution is used for modeling: 350 m in the horizontal plane with 38 layers in the vertical; the bottom topography is described in detail with ~500 m resolution. Detected and studied meso- and sub-mesoscale structures in the current field agree well with the observational data, which is impossible or hard to identify in numerical experiments with coarser resolution. Their kinematic characteristics and the lifetime are defined and some mechanisms of their origin are suggested.     

一种冰-海洋模式的热力耦合方案

冰与海洋的热力耦合对冰与海洋环流的模拟有极其重要的影响,是冰-海洋相互作用的一个重要方面.对其精确确定需要详细考虑冰-海洋界面附近的湍流过程,这在长时期的模拟特别是气候模拟中,常受到技术条件的限制.过去的研究常常假设冰下海洋混合层的温度为冰点,特别是在单纯冰模式的模拟中,但考虑海冰漂移和冰点变化的效应时,这一假设是不精确的.因此,弱化冰下海洋混合层温度为冰点的约束,不考虑详细的冰-海洋界面和海洋混合层的湍流过程,根据冰-海洋耦合系统的能量收支关系,设计了一个简化的冰-海洋热力耦合方案.对该方案引起的海洋混合层适应、热力结构和海冰发展的影响进行了分析,并将其用于全球冰海洋耦合模式的数值试验,结果表明,在大气热力强迫下该耦合方案既可使冰区混合层海水温度向冰点适应,又使冰边缘带海水温度与冰点保持明显差异,能够较好地反映冰-海洋热力相互作用.利用该耦合方案构造的全球冰-海洋耦合模式模拟的海冰范围及季节变化与实际观测非常接近.     

LAGFD-WAM numerical wave model-Ⅱ. Characteristics inlaid scheme and its application

In this paper the parameterizational approach of nonlinear source function and the implicit scheme of the model are discussed in detail. The matching problem is solved between time and space steps using the characteristics inlaid scheme with very strong physical meaning. The computational comparison in typical winds shows some improvements to the WAM model. That the hindcast results of the model for typhoon cases are in good agreement with real data illustrates its applicability to wave forecast and engineering study.     

一种新型三维水流数值模型

以不可压缩流体的N-S方程为基本控制方程,用快速粒子level set方法(FPLS)追踪自由表面,提出了一种新的三维水流数值模型。在自由表面处应用虚拟压力法来封闭压力泊松方程,同时用速度等值外插的方法构造自由表面外侧的虚拟速度分布。通过模拟水波振荡、水柱崩塌、水滴滴落和空箱注水过程证明了模型的有效性。     

A simple numerical dynamic-stochastic model of the ocean's synoptic variability closed at the second moment level

The results of numerical experiments involving a dynamic-stochastic model closed at the second moment level are reported. Specific features of the model are the possibility of using it neglecting viscosity coefficients, as well as in energy and enstrophy conservation at the prediction stage. The model is fairly effective in saving computer time. The model prognostic fields are less smoothed than those produced by a model with similar characteristics of the computed grid area and with biharmonic viscosity.Translated by Vladimir A. Puchkin.     

马尔代夫海域水位、海流数值预报研究

基于无结构有限体积法海洋模式(FVCOM),建立了马尔代夫双重嵌套的水位、海流预报模式,并实现了业务化运行。利用三角网格提高重点区域(马尔代夫大桥及岛屿附近海域)的分辨率,最高网格分辨率达到45 m。垂向分层采用σ-s混合坐标的方式划分,分为31层,分别在表层和底层进行加密。采用GFS预报的风场、气压场和热通量结果制作模式表面强迫场文件。在开边界处与HYCOM预报结果进行嵌套,在斜压条件下,采用热启动的方式,业务化模拟了马尔代夫海域2020年的水位流场过程。结果表明,模式能够较好地再现计算海域内天文潮和综合水位的预报,模式预报的水位值与潮位站实测值非常接近。     

A hybrid Lagrangian-Eulerian numerical model for sea-ice dynamics

A hybrid Lagrangian-Eulerian(HLE) method is developed for sea ice dynamics,which combines the high computational efficiency of finite difference method(FDM) with the high numerical accuracy of smoothed particle hydrodynamics(SPH).In this HLE model,the sea ice cover is represented by a group of Lagrangian ice particles with their own thicknesses and concentrations.These ice variables are interpolated to the Eularian gird nodes using the Gaussian interpolation function.The FDM is used to determine the ice velocities at Eulerian grid nodes,and the velocities of Lagrangian ice particles are interpolated from these grid velocities with the Gaussian function also.The thicknesses and concentrations of ice particles are determined based on their new locations.With the HLE numerical model,the ice ridging process in a rectangular basin is simulated,and the simulated results are validated with the analytical solution.This method is also applied to the simulation of sea ice dynamics in a vortex wind field.At last,this HLE model is applied to the Bohai Sea,and the simulated concentration,thickness and velocity match the satellite images and the field observed data well.     

A numerical study of sea level and current responses to Hurricane Frederic using a coastal ocean model for the Gulf of Mexico

A three-dimensional, nonlinear, primitive equation ocean general circulation model is used to study the response of the Gulf of Mexico to Hurricane Frederic. The model has free surface dynamics and a second order turbulence closure scheme for the mixed layer. Realistic coastlines, bottom topography and open boundary conditions are used in the study. The model has a vertical sigma coordinate with 18 levels, and a horizontal resolution of 0.2°×0.2° for the entire Gulf. The study focuses on hurricane generated sea level, current, and coastally trapped wave (CTW) responses of the Gulf. Time series of sea levels from U.S. coastal tide gauge stations and the numerical model simulation of sea levels and currents on the shelf are used to study sea level, current and CTW responses. Both model sea levels and observations from tide gauge stations show a westward progression of the surge as a CTW response. The results of the study of sea levels and currents indicate that CTW propagate to the west with phase speeds of 7–10 m s^–1. There is also a strong nonlinear interaction between the Loop Current and hurricane induced currents. The surface current attains a maximum of 200 cm s^–1 in the eastern Gulf. The model surface elevation at several locations is compared with tide gauge data. The current meter data at three moorings are also compared with the model currents. The model simulations show good agreement with observed data for the hurricane induced coastally trapped wave, storm surge, and current distribution in the Gulf.     

BOM的动边界改进及其应用

针对河口海岸数值模拟的动边界问题,使用了一个简便的干湿网格法,对BOM(Burgen Ocean Model)模型进行了动边界改进。并将该模型应用于瓯江口海域进行数值模拟计算,计算结果表明实测值与计算值吻合良好,模型能够较好的模拟岸边界随潮位涨落的变动。     

海洋格点数据的无损压缩新方法

格点数据是海洋科学资料存储交换的重要形式,资料量的爆炸性增长给数据的存储、传输带来了巨大压力.海洋格点资料与大气格点资料的最大区别在于陆地格点上不存在海洋要素值.本文分析了海洋格点数据的基本特点,综合了行程编码(RLE)和增量编码的特性,设计了海洋格点数据的无损压缩方案.试验表明,该方案具有较高的压缩比,而且在有效精度...