A tile-based method for geodesic buffer generation in a virtual globe

Geometric buffers are important for spatial analysis in many applications of geographic information systems (GISs), such as environmental measurement and management, human health, urban planning, etc. Geometric buffer generation algorithms are well studied in the Euclidean space where the buffer distance is measured by Euclidean metrics; however, very few algorithms are available for generating geometric buffers on the terrain surface in a virtual globe where the buffer distance is measured by geodesic metrics. This paper proposes a tile-based method for geodesic buffer generation according to the characteristics of a virtual globe. It extends the vector tile model (VTM) to organize terrain and vector data, and the XYH algorithm is improved to build geodesic distance fields for terrain meshes. Based on the data organization and the improved XYH algorithm, a geodesic buffer is generated via three main steps: selecting and assembling tiles, updating geodesic distance fields and tracing the boundaries of buffer zones. This method is implemented with multi-scale terrain and vector data, and the experimental results show that it is valid and exact and can be applied in practical applications.     

多边形直角房屋外墙体一半面积计算模型的研究

在不动产测量中,计算外墙体一半面积的数学模型,只有针对四边形直角房屋的数学模型,而对于多边形直角房屋计算外墙体一半面积的数学模型还没有发现,这给分析多边形直角房屋外墙体一半面积的精度带来困难,本文通过研究分析,推导出了多边形直角房屋外墙体一半面积的数学模型,供研究面积精度者参考。     

整体式折线重力坝的深层抗滑稳定及加固研究

分别采用三维弹塑性有限元法和分项系数法,对非整体式和整体式折线重力坝的应力和深层抗滑稳定性进行了计算分析,得出整体式折线重力坝有效地改善了坝体的应力和变形状态,但对提高抗滑稳定性不一定有效的结论,并通过拱梁分载法解释了上述结论。采用高压旋喷灌浆进行加固,并提出了较优的加固范围。     

Timing and duration of hydrological transitions in Arctic polygonal ground from stable isotopes

Land surface models and Earth system models that include Arctic landscapes must capture the abrupt hydrological transitions that occur during the annual thaw and deepening of the active layer. In this work, stable water isotopes (δ²H and δ¹⁸O) are used to appraise hydrologically significant transitions during annual landscape thaw at the Barrow Environmental Observatory (Utqiaġvik, Alaska). These hydrologically significant periods are then linked to annual shifts in the landscape energy balance, deduced from meteorological data and described by the microclimatic periods: Winter, Pre-Melt, Melt, Post-Melt, Summer, and Freeze-Up. The tight coupling of the microclimatic periods with the hydrological transitions supports the use of microclimatic periods as a means of linking polygonal surface water hydrology to meteorological datasets, which provides a mechanism for improving the representation of polygonal surface water hydrology in process-based models. Rayleigh process reconstruction of the isotopic changes revealed that 19% of winter precipitation was lost to sublimation prior to melting and that 23% of surface water was lost to evaporation during the first 10 days post-melt. This agrees with evaporation rates reported in a separate study using an eddy covariance flux tower located nearby. An additional 17% was lost to evaporation during the next 33 days. Stable water isotopes are also used to identify the dominant sources of surface water to various hydrogeomorphological features prevalent in polygonal terrain (a lake, a low centre polygon centre, troughs within the rims of low centre polygons, flat centre polygon troughs, a high centre polygon trough, and drainages). Hydrogeomorphologies that retained significant old water or acted as snow drifts are isotopically distinct during the Melt Period and therefore are easily distinguished. Biogeochemical changes related to the annual thaw are also reported and coupled to the hydrological transitions, which provides insight into the sources and sinks of these ions to and from the landscape.     

A continuum mechanics‐based framework for boundary and finite element mesh optimization in two dimensions for application in excavation analysis

The determination of the optimum excavation sequences in mining and civil engineering using numerical stress analysis procedures requires repeated solution of large models. Often such models contain much more complexity and geometric detail than required to arrive at an accurate stress analysis solution, especially considering our limited knowledge of rock mass properties. This paper develops an automated framework for estimating the effects of excavations at a region of interest, and optimizing the geometry used for stress analysis. It eliminates or simplifies the excavations in a model while maintaining the accuracy of analysis results. The framework can equally be applied to two‐dimensional boundary and finite element models. The framework will have the largest impact for non‐linear finite element analysis. It can significantly reduce computational times for such analysis by simplifying models. Error estimators are used in the framework to assess accuracy. The advantages of applying the framework are demonstrated on an excavation‐sequencing scenario. Copyright © 2005 John Wiley & Sons, Ltd.     

Simulation of localization failure with strain‐gradient‐enhanced damage mechanics

Strain gradient implies an important characteristic in localized damage deformation, which can be observed in the softening state of brittle materials, and strain gradients constitute the basic behaviours of localization failure area of the materials. The most important point in strain gradient is its damaging function including an internal length scale, which can be used to express the scale effects of mechanical responses of brittle rock mass. By extending the strain gradient theory and introducing an intrinsic material length scale into the constitutive law, the authors develop an isotropic damage model as well as a micro‐crack‐based anisotropic damage model for rock‐like materials in this paper. The proposed models were used to simulate the damage localization under uniaxial tension and plain strain compression, respectively. The simulated results well illustrated the potential of these models in dealing with the well‐known mesh‐sensitivity problem in FEM. In the computation, elements with C₁ continuity have been implemented to incorporate the proposed models for failure localization. When regular rectangle elements are encountered, the coupling between finite difference method (FDM) and conventional finite element method (FEM) is used to avoid large modification to the existing FEM code, and to obtain relatively higher efficiency and reasonably good accuracy. Application of the anisotropic model to the 3D‐non‐linear FEM analysis of Ertan arch dam has been conducted and the results of its numerical simulation coincide well with those from the failure behaviours obtained by Ertan geophysical model test. In this paper, new applications of gradient theories and models for a feasible approach to simulate localized damage in brittle materials are presented. Copyright © 2002 John Wiley & Sons, Ltd.     

WENO格式与虚拟单元浸入边界法在笛卡尔网格中的应用

高精度有限差分WENO格式在结构网格上处理具有复杂几何外形绕流问题时较困难,而虚拟单元浸入边界法却是一种较新颖且对网格的要求较低的方法,适用于复杂几何外形边界的处理.为此,在笛卡尔网格上采用WENO格式以求解Euler守恒律方程,试图将两者有效结合起来,希望能在笛卡尔网格上处理具有复杂几何外形的物体绕流问题.最后,几个经典数值算例的结果验证了该方法的有效性.     

CINRAD/SA雷达对Parsivel激光粒子谱仪的干扰及处理技术

针对黄山光明顶的Parsivel激光降水粒子谱仪在实际观测中出现的问题,给出了可行的解决方法.仪器自动连续观测以来每天09:00-16:00采样数据均出现异常谱,经排查发现这个时段恰好是CINRAD/SA雷达观测时段,所以考虑异常数据由雷达电磁辐射或周围电磁场的影响造成,并简要探索了其影响原因.根据金属可以屏蔽电磁波的性质,在确保钢丝网完全屏蔽雷达的电磁辐射下,考虑尽量不影响仪器周围的流场结构且易于固定等因素,经过多次试验,最终选定在雷达方向靠近雨滴谱仪器约3 m处安放钢丝网,完全屏蔽了雷达观测时对仪器的辐射,保障了观测资料的可靠性.     

渤海典型温带风暴潮数值模拟及改进实验

分析了2010年渤海两次典型温带风暴潮过程及规律,发现沿岸的最大增水基本由北沿渤海西岸向南传播且各站出现最大增水时间有较稳定的滞后,利用一套基于非结构网格的高分辨率风暴潮模式(ADCirc)和NMEFC温带风暴潮模式(CES)分别对“20101212”强温带风暴潮过程进行数值模拟,对比分析其结果的优劣后提出基于测站风场...     

The numerical modelling of advective transport in the presence of fluid pressure transients

Conventional modelling of transport problems for porous media usually assumes that the Darcy flow velocities are steady. In certain practical situations, the flow velocity can exhibit time‐dependency, either due to the transient character of the flow process or time dependency in the boundary conditions associated with potential flow. In this paper, we consider certain one‐ and three‐dimensional problems of the advective transport of a chemical species in a fluid‐saturated porous region. In particular, the advective flow velocity is governed by the piezo‐conduction equation that takes into account the compressibilities of the pore fluid and the porous skeleton. Time‐ and/or mesh‐refining adaptive schemes used in the computational modelling are developed on the basis of a Fourier analysis, which can lead to accurate and optimal solutions for the advective transport problem with time‐ and space‐dependent advective flow velocity distributions. Copyright © 2006 John Wiley & Sons, Ltd.