A gradient plasticity model for lüders band propagation

At the onset of plastic deformation some materials exhibit non-monotonic behaviour in that after initially yielding the flow stress decreases with continuing strain, passing through a minimum. Strain softening destabilizes homogeneous configurations and results in the formation of bands of localized deformation. Within these bands the macro and microscales of the deformation overlap and accordingly terms have to be included in the evolution equation for the plastic strain to provide the necessary information on the material's behaviour at the next smaller scale. In the model chosen here the evolution equation has the form of a reaction diffusion equation, whereby physically the diffusion term accounts for the nonlocal interaction between dislocations on neighbouring slip planes. The model predicts the band propagation velocity, the width of the propagation front and the strain profile.     

考虑震相清晰度时的最优化定位方法

在文献[1]的基础上详细讨论了各台站直达波初动震相清晰度存在差异时如何利用井下和地面观测资料联合确定震源位置、发震时刻及区域平均波速的最优化方法。理论和实际检验表明,对于一个台网而言,考虑各台站震相清晰度间的差异,会使定位主要依赖于震相清晰的台站的资料,而震相不太清晰的台站的资料只对定位起参考作用。从而提高了整个台网定位的可信度。     

Localized spectral analysis of global satellite gravity fields for recovering time-variable mass redistributions

A spatiospectral localization method is discussed for processing the global geopotential coefficients from satellite mission data to investigate time-variable gravity. The time-variable mass variation signal usually appears associated with a particular geographical area yielding inherently regional structure, while the dependence of the satellite gravity errors on a geographical region is not so evident. The proposed localization amplifies the signal-to-noise ratio of the (non-stationary) time-variable signals in the geopotential coefficient estimates by localizing the global coefficients to the area where the signal is expected to be largest. The results based on localization of the global satellite gravity coefficients such as Gravity Recovery And Climate Experiment (GRACE) and Gravity and Ocean Circulation Explorer (GOCE) indicate that the coseismic deformation caused by great earthquakes such as the 2004 Sumatra–Andaman earthquake can be detected by the low-low tracking and the gradiometer data within the bandwidths of spherical degrees 15–30 and 25–100, respectively. However, the detection of terrestrial water storage variation by GOCE gradiometer is equivocal even after localization.     

Ideal Case Study of Adaptive Localization in Storm-scale Ensemble Kalman Filter Assimilation

This study explores the use of the hierarchical ensemble filter to determine the localized influence of ob-servations in the Weather Research and Forecasting ensemble square root filtering (WRF-EnSRF) assimilation system. With error correlations between observations and background field state variables considered, the adaptive localization approach is applied to conduct a series of ideal storm-scale data assimilation experiments using simulated Doppler radar data. Comparisons between adaptive and empirical localization methods are made, and the feasibility of adaptive locali-zation for storm-scale ensemble Kalman filter assimilation is demonstrated. Unlike empirical localization, which relies on prior knowledge of distance between observations and background field, the hierarchical ensemble filter provides con-tinuously updating localization influence weights adaptively. The adaptive scheme improves assimilation quality during rapid storm development and enhances assimilation of reflectivity observations. The characteristics of both the observation type and the storm development stage should be considered when identifying the most appropriate localization method. Ultimately, combining empirical and adaptive methods can optimize assimilation quality.     

Spatial localization of closeness and betweenness measures: a self-contradictory but useful form of network analysis

Closeness and betweenness are forms of spatial network analysis grounded in a long-standing tradition of measuring accessibility and flow potential. More recently, these measures have been enhanced by the concept of spatial localization, producing effective models for the prediction of pedestrian and vehicle driver behaviour.

A contradiction arises where the distance metric used to define locality does not match the distance metric used to define shortest paths for closeness and betweenness. A typical case is the use of angular shortest paths within a Euclidean buffer as a pedestrian flow model. Such a model assumes that people make a mode choice based on distance, but a route choice based on least angular change – even when this results in an excessively long ‘problem route’, which conflicts with their criterion for mode choice.

This study examines the prevalence of problem routes and the magnitude of their effect on some pedestrian and vehicle models. We show that while in a weighted analysis, pathological cases could invalidate an entire model, in the models presented the effect of this contradiction is minor. We do this by comparing model predictions to real flow data, using four strategies for handling problem routes: ignore, discard, reroute and strict locality. Strict locality is justified on the grounds of bounded rationality. We find all strategies to give broadly similar results, although the reroute and strict strategies give marginally better simulation accuracy. We also present a discussion of the characteristics of each strategy, and findings on computational efficiency.

We conclude that it is prudent in any computation of localized closeness and betweenness to consider the impact of problem routes; however, they do not necessarily invalidate these forms of analysis, which remain useful.     

A Runge–Kutta,Taylor–Galerkin scheme for hyperbolic systems with source terms. Application to shock wave propagation in viscoplastic geomaterials

This paper presents an alternative formulation of Solid Dynamics problems based on (i) a mathematical model consisting of a system of hyperbolic PDEs where the source term is originated by the viscoplastic strain rate and (ii) a splitting scheme where the two‐step Taylor–Galerkin is used for the advective part of the PDE operator while the sources are integrated using a fourth‐order Runge–Kutta. Use of the splitting scheme results in a higher accuracy than that of the original two‐step Taylor–Galerkin. The scheme performs well when used with linear triangle or tetrahedra for (i) bending‐dominated situations (ii) localized failure under dynamic conditions and keeps the advantages of the two‐step Taylor–Galerkin concerning numerical dispersion and damping of short wavelengths. Copyright © 2006 John Wiley & Sons, Ltd.     

Analytical and numerical investigation of uniqueness and localization in saturated porous media

This paper presents first the applications of uniqueness and strain localization analysis of saturated porous media, where localization of deformation into well defined narrow zones in a saturated porous medium is studied in terms of discontinuous bifurcation theory. A generalized plasticity constitutive model and a Mohr–Coulomb model are used in both the theoretical and numerical analyses of shear band formations. The critical hardening moduli and shear band angle for localization are computed, and quantitative results are given for both constitutive models. Numerical results previously obtained and new ones are confirmed by this analytical and numerical investigation. Copyright © 2002 John Wiley & Sons, Ltd.     

三星星座对地定位的最佳构形研究

用数值方法对三星星座几何构形与定位精度的关系进行了仿真计算，结果表明对满足较高定位精度的区域进行定位，三星的几何构形呈等边三角形时，定位精度最高。     

EnKF局地化算法对雷达资料同化的影响研究

分级集合滤波(Hierarchical Ensemble Filter,HEF)和采样误差修正(Sampling Error Correction,SEC)局地化算法能够使采样误差取得极小值,且不需要给出距离的定义。为了检验其理论优势,基于集合卡尔曼滤波(Ensemble Kalman Filter,En KF)方法同化模拟雷达资料,通过与Gaspari-Cohn(GC)局地化算法对比,分析不同局地化算法对En KF同化效果的影响。结果表明,HEF和SEC局地化算法的雷达回波在水平和垂直方向上均强于GC局地化算法。HEF局地化算法各个变量的离散度最高,均方根误差最低;SEC局地化算法离散度略低,均方根误差略高;GC局地化算法离散度最低,均方根误差最高。相比于GC局地化算法,HEF和SEC局地化算法的冷池强度减弱,面积减小,下沉气流的速度和范围增大,雹霰混合比的大小和覆盖面积增大。通过模拟发现,HEF局地化算法模拟的北侧对流中心最强,SEC局地化算法模拟的南侧对流中心最强,且模拟出(40 km,60 km)处的强对流中心。HEF局地化算法模拟的冷池强度最强,HEF和SEC局地化算法基本上模拟出北侧的雹霰混合比高值区。这表明HEF局地化算法有效地改进了基于GC局地化算法的En KF雷达资料同化效果,SEC局地化算法减小了计算量,是HEF局地化算法较好的近似。     

中西生态旅游解说系统差异化研究进展及本土化路径

解说是生态旅游实现其环境教育责任的重要手段,在西方其研究和行业发展已积累了大量成功的理论和实践经验。本文从解说方程式中资源、受众和媒介3个关键要素入手,依据地域分异规律、生态学原理、地理环境决定论等理论,梳理中西方解说系统差异的根源所在。结果发现：西方受“人地分立”价值取向的影响,保持着生态旅游的“纯自然性”,西方的海洋外向型思维延续了注重空间拓展、关注自然客体奥秘的传统,媒介设计鼓励多方利益相关者参与,强调长期公益性;中国人受“天人合一”的审美价值的影响,接受生态旅游自然与人文资源的结合,大陆内向型思维形成了求稳好静的性格,探索未知事物的兴趣较弱,媒介的物造形式胜过内容要求,短期功利性突出。最后,本文提出中国生态旅游解说本土化路径,包括确定可行的解说目标、挖掘双重价值的资源、定位受众特征与类型、标准化规范引导媒介设计等。