基于OpenGL的3维弯管线的衔接方法

三维管线的显示问题已取得了不少进展,直线部分已经成熟,但弯管的显示还不够光滑。从三维管线衔接处的光滑出发,借助OpenGL中的几何转换技术及剪切变换技术,巧妙地利用四串同直线上的圆台衔接两直线管。该方法不仅实现起来比较简单,而且视觉效果较好,不论从哪个角度观察,衔接处都很光滑。     

基于LOD的选取模型应用于电子地图多尺度显示的研究

从电子地图多尺度显示角度出发,提出了基于LOD的选取模型。在选取模型中将显示比例尺和地图比例尺的比值作为LOD算子,总结了LOD算子设置的3个层次,以及分类、分级、要素和空间几何特征等LOD算子的设置规则。     

Numerical modeling of the flow and transport of radionuclides in heterogeneous porous media

This paper is concerned with numerical methods for the modeling of flow and transport of contaminant in porous media. The numerical methods feature the mixed finite element method over triangles as a solver to the Darcy flow equation and a conservative finite volume scheme for the concentration equation. The convective term is approximated with a Godunov scheme over the dual finite volume mesh, whereas the diffusion–dispersion term is discretized by piecewise linear conforming triangular finite elements. It is shown that the scheme satisfies a discrete maximum principle. Numerical examples demonstrate the effectiveness of the methodology for a coupled system that includes an elliptic equation and a diffusion–convection–reaction equation arising when modeling flow and transport in heterogeneous porous media. The proposed scheme is robust, conservative, efficient, and stable, as confirmed by numerical simulations.      

Debris flows in the Swiss National Park: the influence of different flow models and varying DEM grid size on modeling results

In the Swiss National Park, debris flows are a frequent phenomenon and have repeatedly affected highways and hiking structures. In this study, we first investigated the main characteristics and dimensions of current debris flows by field work and empirical parameterization schemes. Additionally, we evaluated a topography-based flow-trajectory geographic information system model (MSF) and a flow-routing model (FLO-2D) in terms of debris flow-affected areas. Three generically different digital elevation models (DEM) with grid spacing of 25, 4, and 1 m were used in conjunction with the flow models. The evaluation of the DEM grid spacing shows that for both flow models the 25-m DEM can give an approximate estimation of the potential hazard zone. Four- and one-meter DEMs mostly confine the simulated debris flow to existing channels and are in accordance with observations of recent debris-flow events. The study shows that DEM quality and grid resolution are crucial for the resulting delineation of potentially affected areas and thus for hazard assessment and mapping.     

What controls the magnitude of the daytime heat sink in a desert city?

The aim of this study was to increase knowledge of the causes of cooling in desert cities. We used a time-series of Landsat images to characterize the changes in daytime land surface temperature during the period of rapid urbanization in Dubai. Changes in land cover and albedo were also quantified from Landsat data and the development of different land use types and variations in urban geometry were characterized. The results demonstrate that urban growth has promoted a heat sink and that all urban land use types contributed to this effect. Vegetation generated the largest cooling effect per unit surface area but impervious surfaces dominated the urban environment and are responsible for the majority of the heat sink created by the city. Changes in albedo were not causally related to the urban heat sink, however, variations in urban geometry, particularly the amount of shading cast by buildings, had some influence on the magnitude of cooling. This study provides evidence that the expansion of the heat sink during urbanization in a desert environment is influenced by the forms of land cover transition, the type of urban land use that is developed, the thermal properties of construction materials used and the geometry of the city environment that is constructed. Future research should concentrate upon understanding these mechanisms in order to plan future developments which maximize cooling and reduce the environmental impacts of desert cities.     

Reducing the grid orientation dependence of flow routing on square-grid digital elevation models

Topographical parameters derived from digital elevation models by employing flow routing algorithms may depend on the orientation of the square grid. Grid orientation dependence results from the insufficient isotropy of square grid and affects the flow directions and subsequent calculations based on flow routing. In this article, a systematic approach for analysing the rotational invariance of flow accumulation calculations is presented and applied. Computed flow accumulation maps are found to depend strongly on the grid orientation, especially if flow routing methods with low dispersion are used. It is also shown that isotropy of flow routing algorithms can be significantly improved by introducing a numerical parameter resulting in adjustable weighting for cardinal and diagonal directions in flow routing. The actual value of this parameter depends on the used flow routing method.     

南海海流和涡旋概况

 提要:本文综述了南海海流、涡旋和上升流研究等三个方面迄今所取得的一些成果和在某些问题(例如关于台湾海峡中的黑潮分支)上的不同观点。指出南海海流中、上层的基本流型、广东沿岸流的变化等方面都不同于东海、黄海;南海中珠江冲淡水和上升流都显示出自身的特色，在南海北部，中、上层海流主要有三支流系:广东沿岸流、南海暖流和南海黑潮分支。沿
岸流基本上呈sw向流动，南海暖流终年自sw流向NE，而南海黑潮分支则终年偏sw向流动，它们构成sw-irE--sw向相间分布状态。
        

Non-Linear Numerical Model Predictions of Flow Over an Isolated Hill of Moderate Slope

Non-linear model simulations of atmospheric boundary-layer flow over the hill called Blashaval have been compared with observations and linear model predictions. Previous studies have shown that linear models can give good predictions of wind speed at the summit and on the upwind slopes of Blashaval. The non-linear model provided wind speed predictions of similar accuracy when compared with the mean observed values at these locations.The published experimental data showed that on the lee-slope the wind speeds at 8m were reduced to approximately 10% of their upstream value at the same height. This was associated with an 180° change in wind direction compared with the upstream flow, suggesting that flow separation had occurred. The non-linear model predictions of lee-slope wind speed, when used with high-resolution topography data, were significantly better than linear model predictions. However, the non-linear model predicted lee-slope wind speeds that were still stronger than observed. The non-linear model simulated flow separation more readily with a 1 1/2-order turbulence closure than with a first-order, mixing-length closure. The configuration of the non-linear model that gave best agreement with observations predicted an 8m lee-slope wind speed that was around 50% of the upstream value.     

雁列构造的几何及其应力场的数值模拟

用数值模拟方法研究了几何、力学条件不同的雁列构造模型的应力场,探讨了几何参数对应力场的影响。模拟结果表明,在几何参数不同的情况下,雁列构造中局部断层扩展引起的应力扰动场会对相邻构造产生作用。围绕断层扩展部位剪应力增量场呈八瓣式分布,平均应力增量场呈四象限分布。在较小范围内同时存在几个断层扩展区的情况下,围绕这个弱化区仍可形成上述增量场图案     

脉状金矿床断裂容矿空间模拟

断裂几何学、运动学及控矿规律研究,是开展脉状金矿床深部矿体预测的前提。以断裂几何学控矿规律解析为基础,利用矿山勘探、生产过程中积累的大量地质勘探数据,模拟断裂运动及由此产生的容矿空间,为查明可能的断裂运动方式和控矿规律、进行深部盲矿体预测开辟了一条新的途径。