Selective omission of road features based on mesh density for automatic map generalization

Selection of roads is an intractable generalization operation due to the difficulty in retaining the density difference and connectivity of a road network. This paper proposes a novel approach of selective omission for roads based on mesh density. The density of a road network and its local variations are calculated using meshes as units. Since maps at different scales usually reveal different densities, different density thresholds for road networks are determined on the basis of theoretical analysis and empirical study of mesh densities on maps at different scales. The selection process starts with the identification of the meshes that have a density beyond the threshold. The mesh with the largest density is first treated. Its bounding road segments are ordered according to their relative importance. The least important segment is eliminated. The remaining segments are then merged with the adjacent mesh, thus forming a new mesh. The selection procedure is repeated until none of the meshes has a density beyond the threshold. Such a process of eliminating road segments and merging meshes can ensure the road network connectivity. In this study, the meshes are classified depending on the types of road segment. For the different mesh types, their density thresholds are set to be different, which can be used as an indicator for the preservation of the density difference. This proposed approach considers topological, geometric and semantic properties of the road network. It was applied to two sets of road networks, and the results of selection are convincing. This methodology has now been adopted for the updating of 1:50,000 maps of China.     

A hybrid optimization approach for efficient calibration of computationally intensive hydrological models

ABSTRACT

The calibration of hydrological models is formulated as a blackbox optimization problem where the only information available is the objective function value. Distributed hydrological models are generally computationally intensive, and their calibration may require several hours or days which can be an issue for many operational contexts. Different optimization algorithms have been developed over the years and exhibit different strengths when applied to the calibration of computationally intensive hydrological models. This paper shows how the dynamically dimensioned search (DDS) and the mesh adaptive direct search (MADS) algorithms can be combined to significantly reduce the computational time of calibrating distributed hydrological models while ensuring robustness and stability regarding the final objective function values. Five transitional features are described to adequately merge both algorithms. The hybrid approach is applied to the distributed and computationally intensive HYDROTEL model on three different river basins located in Québec (Canada).     

Demonstration and application of NMM‐based fractured porous medium flow model

In natural rock masses, the shapes of three‐dimensional (3‐D) blocks cut by arbitrary fracture networks may be very complex. Owing to the geometric complexity and difficulty of mesh discretization of 3‐D blocks and fracture facets, explicit consideration of fracture networks in flow analysis of fractured porous medium (FPM) is very challenging. Using the numerical manifold method based on independent covers (NMMIC), an FPM flow model was proposed that can deal with very complex 3‐D fracture networks. In this paper, the convergence of NMMIC was first demonstrated. The theoretical basis of the arbitrary refinement of computational meshes was proven. Moreover, three peculiarities of NMMIC meshes, that is, arbitrary shape, arbitrary connection, and arbitrary refinement of independent covers, were concluded. Finally, some two‐dimensional (2‐D) tunnel flow examples were analyzed and the numerical results were compared with the analytical results. 3‐D examples with complex fracture distributions were also analyzed. In addition, the computational scale of the developed program was tested by increasing the number of computational elements. The results show that our model can accurately analyze the groundwater flow of rocks surrounding tunnels with complex fracture distributions.     

武汉市轨道交通运行对地磁观测的影响

对武汉市轨道交通一号线附近进行了地磁干扰测试,测试结果表明轨道交通的运行对周边地磁观测产生了干扰,干扰距离为10km左右,其干扰主要来自轨道泄露电流产生的磁场和输电线路产生的磁场。     

Calculation of significant wave height using the linear mean square estimation method

Significant wave height is an important criterion in designing coastal and offshore structures. Based on the orthogonality principle, the linear mean square estimation method is applied to calculate significant wave height in this paper. Twenty-eight-year time series of wave data collected from three ocean buoys near San Francisco along the California coast are analyzed. It is proved theoretically that the computation error will be reduced by using as many measured data as possible for the calculation of significant wave height. Measured significant wave height at one buoy location is compared with the calculated value based on the data from two other adjacent buoys. The results indicate that the linear mean square estimation method can be well applied to the calculation and prediction of significant wave height in coastal regions.     

Air–water two-phase flow modeling of turbulent surf and swash zone wave motions

Wave breaking and wave runup/rundown have a major influence on nearshore hydrodynamics, morphodynamics and beach evolution. In the case of wave breaking, there is significant mixing of air and water at the wave crest, along with relatively high kinetic energy, so prediction of the free surface is complicated. Most hydrodynamic studies of surf and swash zone are derived from single-phase flow, in which the role of air is ignored. Two-phase flow modeling, consisting of both phases of water and air, may be a good alternative numerical modeling approach for simulating nearshore hydrodynamics and, consequently, sediment transport. A two-phase flow tool can compute more realistically the shape of the free surface, while the effects of air are accounted for. This paper used models based on two-dimensional, two-phase Reynolds-averaged Navier–Stokes equations, the volume-of-fluid surface capturing technique and different turbulence closure models, i.e., k–ε, k–ω and re-normalized group (RNG). Our numerical results were compared with the available experimental data. Comparison of the employed method with a model not utilizing a two-phase flow modeling demonstrates that including the air phase leads to improvement in simulation of wave characteristics, especially in the vicinity of the breaking point. The numerical results revealed that the RNG turbulence model yielded better predictions of nearshore zone hydrodynamics, although the k–ε model also gave satisfactory predictions. The model provides new insights for the wave, turbulence and means flow structure in the surf and swash zones.     

北京城市广场及校园表土(灰尘)中重金属水平与健康风险

通过对北京市城市广场和学校表层土壤与相应的地表灰尘中重金属含量调查,探讨土壤与灰尘之间元素分布的差异及来源,评估青少年在校期间通过灰尘摄入重金属的健康风险。研究表明:城市广场和校园土壤中Cu、Pb和Zn、灰尘中As、Cu、Pb、Zn和Cd显著高于北京市土壤重金属背景值,土壤(灰尘)中As、Ni、Cu、Pb、Zn和Cd超过背景值的样本比率分别为67%(27%)、13%(63%)、83%(100%)、73%(100%)、83%(100%)和53%(100%)。土壤中Cu、Pb和Zn存在一定积累,灰尘中Cd、Cu、Pb和Zn积累较重。灰尘中Cu、Pb和Zn显著高于土壤。校园土壤中Ni显著高于城市广场土壤,其他元素两者之间差异不大;校园灰尘中Ni、Pb和Zn显著高于城市广场。中学生通过校园灰尘摄入没有导致明显的健康风险。     

地电阻率资料日常处理软件研制

地电阻率观测在地震前兆观测中具有重要的地位,大量的观测资料表明,多数中强地震前地电阻率出现了异常变化,而快速地发现、甄别地电阻率的变化是地震前兆信息还是干扰,高效率地做好地电阻率资料日常处理工作是前提。由此,依据地电阻率理论和有关规定,基于V isualC＋＋6.0平台,开发了一款关于ZDSB或ZD8B I地电仪产出的地电阻率资料日常处理软件,旨在介绍本软件算法的理论原理、设计思路及实现方法,并结合陇南中心地震台地电阻率观测资料给出了相应的应用实例。应用表明,研发的该软件可以将地电阻率资料日常处理工作系统化,将日常处理工作中大量繁杂的手工操作自动化,能及时地对资料的异常变化做出初步判定,快速地为地震预测部门提供依据。     

基于导电孔隙的中基性火山岩储层含气饱和度解释模型

由于中基性火山岩储层的特殊性,很难利用传统的导电模型求准含气饱和度。为准确计算储层含气饱和度,对研究区中基性火山岩储层孔隙类型、特征及岩电实验资料进行了研究,结果表明:储层孔隙类型主要有气孔、溶蚀孔及微缝,且具有超高孔喉半径比,储层中存在不导电孔隙和导电背景;对Maxwell导电模型进行分析推导,将总孔隙分为导电孔隙和不导电孔隙,引入孔隙联通因子,得到导电孔隙度;应用电导率叠加原理,建立了基于导电孔隙的原始含气饱和度模型,该模型处理的含气饱和度与毛管压力分析饱和度相比,平均绝对误差小于3％,且与试气资料具有较好的一致性。