A discrete global grid system for earth system modeling

To support Earth system modeling, we propose a discrete global grid system that expresses multi-resolution spatial data. Specifically, a unified coding model that expresses a grid of nodes, edges, and cells is constructed for a triangular discrete global grid system. To fulfill the requirements of practical applications, we design a code-based topological query method for this grid system and an algorithm to transform between grid codes and geographic coordinates. We evaluate the Global Finite Volume Community Ocean Model (Global-FVCOM) on the triangular discrete global grid system in the proposed uniform coding model. The ocean tidal waves simulated by the Global-FVCOM running on the coded grid are then compared with results obtained using a traditional irregular spherical grid system, and the results display comparable accuracy. The uniform coding model proposed in this paper provides a triangular discrete global grid system that can represent multi-resolution spatial data and can be used in Earth system models. This unified coding model can also be applied to the geographic coordinate system made up of latitudes and longitudes, as well as diamond and hexagonal grids.     

Synchronising geometric representations for map mashups using relative positioning and Linked Data

Map mashups, as a common way of presenting geospatial information on the Web, are generally created by spatially overlaying thematic information on top of various base maps. This simple overlay approach often raises geometric deficiencies due to geometric uncertainties in the data. This issue is particularly apparent in a multi-scale context because the thematic data seldom have synchronised level of detail with the base map. In this study, we propose, develop, implement and evaluate a relative positioning approach based on shared geometries and relative coordinates to synchronise geometric representations for map mashups through several scales. To realise the relative positioning between datasets, we adopt a Linked Data–based technical framework in which the data are organised according to ontologies that are designed based on the GeoSPARQL vocabulary. A prototype system is developed to demonstrate the feasibility and usability of the relative positioning approach. The results show that the approach synchronises and integrates the geometries of thematic data and the base map effectively, and the thematic data are automatically tailored for multi-scale visualisation. The proposed framework can be used as a new way of modelling geospatial data on the Web, with merits in terms of both data visualisation and querying.     

城市新区作为“家”的表征与实践——以鄂尔多斯康巴什新区为例

本文基于表征与非表征的研究视角,分析了以鄂尔多斯康巴什为代表的中国城市新区作为“家”的表征与实践过程。研究发现：针对康巴什新区,外部媒介与地方政府以表征手段建构了截然不同的“家”的意象。其中,BBC、Times等外媒将康巴什新区描绘成充满荒凉景观的“鬼城”和不健康的中国城市居住空间,而在地方政府的重构中,康巴什新区则充满了生态栖居必备的城市景观并成为了先进的城市文化空间。而作为“家”中的居住者,康巴什居民“家”的营建经历了从陌生到认同的渐进过程,这一过程包含了日常生活实践中的空间转换与情感边界的构建。不同行动者共同塑造了康巴什新区多元的、充满矛盾意义的“家”的空间身份。本文旨在丰富中国快速城市化背景下“家”的地理学研究视角与类型,回应“鬼城”话语对地方政府主导的城市化“无家”的质疑,亦是城市新区社会文化研究的有益拓展与补充。     

Single phase water flow through rock fractures

Flow analysis plays a major role in various geotechnical applications, and the understanding of flow mechanisms is essential for the development of a hydro-mechanical flow model suitable for underground excavations in rock. Discrete flow analysis through discontinuities is reviewed including empirical and analytical flow models. The influence of external loading on joint deformation and single-phase flow show that the surface roughness and aperture size are the prime factors influencing flow rate. Nevertheless, the idealization of natural fractures as smooth parallel plate joints is still followed in many numerical models, because of the simplicity of the cubic law when applied to fracture networks. A numerical study of water flow through a network of joints employing Universal Distinct Element Code (UDEC) is used to quantify the effects of joint orientation and external stress acting on idealized joints.It is found that, for the same joint spacing, the flow rate into an excavation depends on the boundary block size (A_b) relative to the excavation size (A_e). The inflow becomes excessive if A_b/A_e is less than 4, but becomes very small if A_b/A_e exceeds 8.     

基于稀疏表示的地面磁共振信号提取方法

在多孔隙含水层中地面磁共振（surface nuclear magnetic resonance,SNMR）信号呈现多弛豫衰减特性,常规盲源分离方法和单指数拟合方法引起信号严重失真和信息缺失等问题.本文提出了基于稀疏表示的随机噪声背景下多弛豫SNMR信号的提取方法.根据SNMR信号的衰减特征,设计了精确刻画SNMR信号且与随机噪声不相关的离散衰减余弦冗余字典.其次,针对多弛豫SNMR信号稀疏度未知的问题,通过设置合理的残差比阈值控制迭代次数,改进了广义正交匹配追踪（generalized orthogonal matching pursuit,gOMP）算法,使得该方法应用于SNMR信号的提取时,具有更好的自适应性和普适性.再次,鉴于SNMR测量数据为多次独立重复采集的结果,提出了基于数据流的SNMR信号提取策略,在提高算法鲁棒性的同时,保证了信号提取结果的唯一性.最后,通过仿真和实测数据证明了基于gOMP算法的稀疏表示方法可以显著地提升多弛豫SNMR信号的提取质量,降低随机噪声对含水层反演结果的影响,提高SNMR探测能力.     

正二十面体六边形全球离散格网编码运算

全球离散格网系统是指把地球表面按照一定规则离散分割成多分辨率层次结构的格网单元,广泛应用于海量多源空间数据的组织、管理和分析中。六边形全球离散格网具有优良的几何特性,非常适合于空间数据的处理,如何进一步提高六边形全球离散格网编码运算的效率仍是当前研究的重点。本文采用正二十面体施耐德投影四孔径六边形全球离散格网模型,基于六边形三轴坐标与编码的二进制数的对应关系构建四孔六边形的基础编码结构,将二十面体划分为32个基础六边形,并将之分为3种基础六边形剖分瓦片,在每个六边形剖分瓦片采用基础编码结构进行编码,建立了四孔六边形全球离散格网编码,同时设计了并实现了四孔六边形编码与六边形三轴坐标之间的快速转换,基于此构建了一种高效的四孔六边形全球离散格网编码运算方案,包括编码的算数运算、空间拓扑运算和邻域检索运算及跨面运算。与现有的六边形全球离散格网编码运算方案相比,本文的方案进一步提高了编码算数运算、空间拓扑运算和邻域检索运算的效率,编码加法运算是HLQT的2～3倍,邻域检索运算分别是HLQT的3～5倍和H3的2～3倍,且受格网编码层次的影响较小,编码的跨面邻域检索运算时间略高于面内的运算,可以为全...     

Using the applied element method for modelling calcium silicate brick masonry subjected to in‐plane cyclic loading

The response of calcium silicate unreinforced masonry construction to horizontal cyclic loading has recently become the focus of experimental and numerical research, given its extensive use in some areas of the world that are now exposed to induced earthquakes (eg, north of the Netherlands). To assess the seismic behaviour of such construction, a relatively wide range of modelling methodologies are available, amongst which the discrete elements approach, which takes into account the intrinsic heterogeneity of a brick‐mortar assembly, can probably be deemed as the most appropriate computational procedure. On the other hand, however, since discrete elements numerical methods are based on a discontinuum domain, often they are not able to model every stage of the structural response adequately, and because of the high computational burden required, the analysis scale should be chosen carefully. The applied element method is a relatively recent addition to the discrete elements family, with a high potential for overcoming the aforementioned limitations or difficulties. Initially conceived to model blast events and concrete structures, its use in the earthquake engineering field is, of late, increasing noticeably. In this paper, the use of the applied element method to model the in‐plane cyclic response of calcium silicate masonry walls is discussed and scrutinised, also through the comparison with experimental results of in‐plane cyclic shear‐compression tests on unreinforced masonry walls.     

离散元法模拟吸力锚施工中生成的土塞研究

吸力锚是近年来在海洋工程中出现并得以迅速发展的一种新型基础形式。然而吸力锚施工中产生的土塞现象对顺利施工和安全使用构成了严重的威胁。文章采用了离散单元法来研究吸力锚施工中的土塞现象,并得到了一些结论。圆形刚性颗粒模型是文章中所采用的基本模型,同时动态松弛法成为基本的求解方法。     

CALCULATING THE DYNAMIC STIFFNESS MATRIX OF 2-D FOUNDATIONS BY DISCRETE WAVE NUMBER INDIRECT BOUNDARY ELEMENT METHODS

Apart from some special cases, calculating the dynamic stiffness matrix of foundations on a layered half-space, especially for embedded foundations, is computationally expensive. An efficient method for two-dimensional foundations in a horizontally layered soil media is presented in this paper. This method is based on indirect boundary element methods and uses discrete wave number solution methods for calculating Green's functions for displacements and analytical methods for the integrations over the boundary. For surface foundations, the present method applies at all frequencies. For embedded foundations or for constructing energy transmitting boundaries, because the free-field part is modelled by boundary elements and the excavated part is modelled by finite elements, the present method applies only at low frequencies for the spring coefficients (the real parts of the dynamic stiffness matrix) but applies at all frequencies for the damping coefficients (the imaginary part of the dynamic stiffness matrix) for undamped sites. The novelty of the method can be used for three-dimensional foundations. © 1997 by John Wiley & Sons, Ltd.     

Evaluation of sensitivity of land surface hydrology representations with and without land–atmosphere feedback

This paper compares various ways of quantifying the importance of land–atmosphere feedback. A widely used land surface hydrology model is used in coupled (to a planetary boundary layer model) and uncoupled modes to compare the adequacy of different feedback indices. It is found that existing feedback indices are primarily based on ‘one factor at a time’ sensitivity analysis and cannot adequately capture the interaction between land and atmosphere. A new index is used which combines factorial design concepts and traditional sensitivity analysis. This index is shown to capture and quantify the strength of interaction between land surface parameters and atmosphere. To assess the effects of forcing characteristics on the stand alone model sensitivity, several ways to specify near-surface atmospheric conditions are evaluated. It is found that commonly used forcing conditions (e.g. model generated or observed time-series of near-surface atmospheric variables) may not be adequate to mimic the coupled model environment for evaluating the land surface representations. The partially coupled model sensitivity is shown to capture a major feedback loop related to water holding capacity, surface fluxes and near-surface atmospheric processes. These results suggest that sensitivity from the stand alone model should be interpreted with caution and future evaluations should strive to incorporate land–atmosphere feedback, at least within a partially coupled model. © 1997 John Wiley & Sons, Ltd.