DESIGN AND IMPLEMENTATION OF DYNAMIC SYMBOLS IN DYNAMIC GIS

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求解二阶解耦弹性波方程的低秩分解法和低秩有限差分法

时间域的波场延拓方法在本质上都可以归结为对一个空间-波数域算子的近似.本文基于一阶波数-空间混合域象征,提出一种新的方法求解解耦的二阶位移弹性波方程.该方法采用交错网格,连续使用两次一阶前向和后向拟微分算子,推导得到了解耦的二阶位移弹性波方程的波场延拓算子.由于该混合域象征在伪谱算子的基础上增加了一个依赖于速度模型的补偿项,可以补偿由于采用二阶中心差分计算时间微分项带来的误差,有效地减少模拟结果的数值频散,提高模拟精度.然而,在非均匀介质中,直接计算该二阶的波场延拓算子,每一个时间步上需要做N次快速傅里叶逆变换,其中N是总的网格点数.为了减少计算量,提出了交错网格低秩分解方法;针对常规有限差分数值频散问题,本文将交错网格低秩方法与有限差分法结合,提出了交错网格低秩有限差分法.数值结果表明,交错网格低秩方法和交错网格低秩有限差分法具有较高的精度,对于复杂介质的地震波数值模拟和偏移成像具有重要的价值.

     

Estimating Heat Sources And Fluxes In Thermally Stratified Canopy Flows Using Higher-Order Closure Models

Over the past two decades, several inverse methods have been proposed to estimatescalar source and sink strengths from measured mean concentration profiles withinthe canopy volume (hereafter termed the `inverse' problem). These inverse methodscommonly assumed neutral atmospheric stability conditions for the entire canopyvolume. For non-neutral conditions, atmospheric stability corrections in inverseschemes were limited to adjusting the integral time scale or other flow statistics tomatch well-established surface-layer similarity relations above the canopy. Suchstability corrections do not explicitly consider the local stability effects within thecanopy volume. Currently, there is no satisfactory inverse scheme that explicitlyaccounts for local atmospheric stability for canopy turbulence. A Eulerian inversemethod that explicitly accounts for local atmospheric stability within the canopy isdeveloped using second-order closure principles. Field testing the method is conductedusing temperature measurements from two field experiments collected in an even-ageduniform loblolly pine forest. It is demonstrated that by accounting for local atmospheric stability in the inversion scheme, the agreement between modelled sensible heat flux calculations and measurements improve by 60% for stable conditions, 10% for near-neutral conditions and 20% for unstable conditions     

Numerical analysis of a one‐dimensional infiltration problem in unsaturated soil by a seepage–deformation coupled method

A multiphase coupled elasto‐viscoplastic finite element analysis formulation, based on the theory of porous media, is used to describe the rainfall infiltration process into a one‐dimensional soil column. Using this framework, we have numerically analyzed the generation of pore water pressure and deformations when rainfall is applied to the soil. A parametric study, including rainfall intensity, soil–water characteristic curves, and permeability, is carried out to observe their influence on the changes in pore water pressure and volumetric strain. From the numerical results, it is shown that the generation of pore water pressure and volumetric strain is mainly controlled by material parameters α and n′ that describe the soil–water characteristic curve. A comparison with the laboratory results shows that the proposed method can describe very well the characteristics observed during the experiments of one‐dimensional water infiltration into a layered unsaturated soil column. Copyright © 2010 John Wiley & Sons, Ltd.     

Surface temperature history determination from borehole measurements

All methods proposed to date for the determination of surface temperature history from temperature profiles measured in boreholes are based on the assumption that the borehole is a hole in a semiinfinite homogeneous earth of constant diffusivity , and more or less ignore the fact that the mathematical formulation for this problem is improperly posed. This assumption, which frequently represents a gross oversimplification of the situation, was originally introduced as a computational expedient. We propose a computational procedure which is independent of this assumption and takes the improperly posed nature of the problem into account. The essence of the method is: (a) determine the set of borehole profiles corresponding to a given set of linearly independent surface temperature history functions, and then (b) take the coefficients of the least-squares fit of these borehole profiles to the given borehole data as the coefficients in the linear combination of surface temperature history functions which defines the required approximation to the surface temperature history. An analogous procedure can be used to determine the lower boundary condition for the heat-flow problem if the surface-temperature history is assumed to be known. Results of numerical experimentation are used to indicate the extent to which the method is viable in practice.     

3-D wave propagation in fluid-filled irregular boreholes in elastic formations

Different seismic testing techniques rely on the propagation of acoustic waves in fluid-filled boreholes from sources placed within the borehole and in the solid media. The interpretation of the signals recorded relies on understanding how waves propagate in the borehole and its immediate vicinity. It is known that very complex wave patterns can arise, depending on the distance between the source and the receiver, and their placement and orientation relative to the axis of a circular borehole. The problem becomes more complex if the cross-section is not circular, conditions for which analytical solutions are not known. In this work, the Boundary Element Method (BEM) is used to evaluate the three-dimensional wave field elicited by monopole sources in the vicinity of a fluid-filled borehole. This model is used to assess the effects of the receiver position on the propagation of both axisymmetric and non-axisymmetric wave modes when different borehole cross-sections are used. Both frequency vs. axial-wave number responses and time-domain responses are calculated.     

农牧交错区城市可持续发展问题与对策

农牧交错区是我国重要商品粮基地和畜牧业基地的衔接区,集中了我国大部分贫困县（市）,在我国经济重心转移和农村经济发展和生态建设中扮演重要角色。该地区的生态环境的脆弱性孕育着城市生态环境问题,是制约城市可持续发展的“瓶颈”。随着西部大开发和社会经济可持续发展战略的实施,迫切要求作为区域增长极的城市走可持续发展之路。本文对城市可持续发展研究背景、内涵和理论框架进行探讨,并剖析农牧交错区生态环境的特殊性和城市生态环境问题（如水资源短缺、城市基础设施严重落后、城市环境污染较严重、城市产业结构单一,城市间产业关联度较低等）的基础上,提出实现城市可持续发展的针对性对策。