层次分析法在长江源区生态地质环境质量(脆弱性)评价中的应用

以长江源区生态地质环境调查基础数据为契机,采用层次分析法(AHP)模型的方式,提出长江源区生态地质环境指标体系,最终划定本区域生态地质环境质量综合指数。在定性的基础上从一个崭新的角度定量化分析长江源头生态地质环境质量的变化,得出影响本区域生态环境的主要因素为动植物环境的改变,进而揭示长江源区生态地质环境发展的未来趋势,为今后研究长江源区生态地质环境质量及其合理发展做出了较为客观、准确的评价。     

混合式球面退化剖分模型的设计与编码

为了解决球面退化四叉树格网(DQG)模型孔径较大、格网单元面积分布不均匀以及三角格网单元应用不完全四叉树剖分的问题,通过控制单元面积的思路设计了一种格网单元孔径更小、分布更均匀的四边形(中低纬地区)与三角形(高纬地区)的混合格网模型——混合式球面退化格网模型(MSDG);并对所有格网单元利用四叉树进行编码。通过对格网单元的几何属性统计分析发现,该格网模型的几何属性与DQG模型相比,其单元面积变化更小、分布更加均匀稳定。     

基于改进二维离散希尔伯特变换的图像边缘检测方法

提出一种新的基于二维希尔伯特变换的边缘检测方法。对于频域信号而言,希尔伯特变换不改变信号的幅值,而仅仅改变其相位,即负频率的相位作+90°相移,而正频率作-90°相移。经由傅里叶变换后,边缘特征呈极值状态,因此本文利用二维离散希尔伯特变换实现边缘检测。由于二维离散希尔伯特变换结果具有方向性,提出利用两个呈正交性的二维离散希尔伯特变换的幅度平方和来检测图像边缘特征。此外将高斯核函数引入到希尔伯特变换中,以减少图像噪声对检测结果的影响,并根据PSNR(峰值信噪比)来确定最佳参数σ,从而得到理想的边缘检测效果。为验证该方法的检测结果,将所提方法与传统边缘检测算子的检测效果进行了比较分析,并将该方法运用于卫星遥感图像中,结果表明该方法可以有效地应用于边缘检测工作中。     

实数编码改进遗传算法的非线性最小二乘平差

遗传算法在处理测量领域中的非线性问题时,算法中的种群数目大小、个体中的参数分量的数量以及参数的取值区间都会对算法的效率产生影响。针对基本遗传算法在处理非线性问题时,容易陷入局部最优值、速度慢、收敛区间小等问题,本文采用了一种新的交叉策略,并对变异算子中的变异步长作动态的自适应改变。最后通过实例解算验证了这种改进的遗传算法比基本遗传算法更加稳定、精度更高、收敛速度更快、收敛区间更大。     

Operator splitting methods for degenerate convection–diffusion equations II: numerical examples with emphasis on reservoir simulation and sedimentation

We present an accurate numerical method for a large class of scalar, strongly degenerate convection–diffusion equations. Important subclasses are hyperbolic conservation laws, porous medium type equations, two-phase reservoir flow equations, and strongly degenerate equations coming from the recent theory of sedimentation–consolidation processes. The method is based on splitting the convective and the diffusive terms. The nonlinear, convective part is solved using front tracking and dimensional splitting, while the nonlinear diffusion part is solved by an implicit–explicit finite difference scheme. In addition, one version of the implemented operator splitting method has a mechanism built in for detecting and correcting unphysical entropy loss, which may occur when the time step is large. This mechanism helps us gain a large time step ability for practical computations. A detailed convergence analysis of the operator splitting method was given in Part I. Here we present numerical experiments with the method for examples modelling secondary oil recovery and sedimentation–consolidation processes. We demonstrate that the splitting method resolves sharp gradients accurately, may use large time steps, has first order convergence, exhibits small grid orientation effects, has small mass balance errors, and is rather efficient.     

Uncertainty of the numerical solution of a nonlinear system’s long-term behavior and global convergence of the numerical pattern

The computational uncertainty principle in nonlinear ordinary differential equations makes the numerical solution of the long-term behavior of nonlinear atmospheric equations have no meaning. The main reason is that, in the error analysis theory of present-day computational mathematics, the non-linear process between truncation error and rounding erroris treated as a linear operation. In this paper, based on the operator equations of large-scale atmospheric movement, the above limitation is overcome by using the notion of cell mapping. Through studying the global asymptotic characteristics of the numerical pattern of the large-scale atmospheric equations, the definitions of the global convergence and an appropriate discrete algorithm of the numerical pattern are put forward. Three determinant theorems about the global convergence of the numerical pattern are presented, which provide the theoretical basis for constructing the globally convergent numerical pattern. Further, it is pointed out that only a globally convergent numerical pattern can improve the veracity of climatic prediction.     

Zipf’s Law: A Viable Geological Paradigm?

Zipfs Law originally was proposed as a guide to a statistical distribution in social studies. The law describes a relationship between size and rank of discrete phenomena. It is a variant of Paretos 1927 Law known as the 80/20 rule and is similar to Bodes Law in concept. The relationship described by Zipfs Law is a succession of order data with the largest followed by half the size for the next largest, which in turn, the next is half that size, and so on. In geology, it has been used with moderate success in resource assessment of mining and petroleum. In essence, it predicts how many entities of a certain size may be left in a sequence of decreasing size assuming the largest has been ascertained. Examples of applications would be plotting the rank and size of ore deposits or oil fields to determine how many deposits remained undiscovered and their size. After a flurry of papers in the 1970s and 1980s, application of the law apparently either was successful and thus not reported in way the literature or was determined to be ineffectual and its use discontinued, but either way the law lapsed into obscurity. Examples of oil- and gas-field size in Kansas, the occurrence of historic earthquakes that affected the state, and size of anticlines (plains-type folds) are presented to illustrate application and limits of Zipfs Law.     

Discrete Element Modeling of Stress and Strain Evolution Within and Outside a Depleting Reservoir

Stress changes within and around a depleting petroleum reservoir can lead to reservoir compaction and surface subsidence, affect drilling and productivity of oil wells, and influence seismic waves used for monitoring of reservoir performance. Currently modeling efforts are split into more or less coupled geomechanical (normally linearly elastic), fluid flow, and geophysical simulations. There is evidence (from e.g. induced seismicity) that faults may be triggered or generated as a result of reservoir depletion. The numerical technique that most adequately incorporates fracture formation is the DEM (Discrete Element Method). This paper demonstrates the feasibility of the DEM (here PFC; Particle Flow Code) to handle this problem. Using an element size of 20 m, 2-D and 3-D simulations have been performed of stress and strain evolution within and around a depleting reservoir. Within limits of elasticity, the simulations largely reproduce analytical predictions; the accuracy is however limited by the element size. When the elastic limit is exceeded, faulting is predicted, particularly near the edge of the reservoir. Simulations have also been performed to study the activation of a pre-existing fault near a depleting reservoir.     

The Displacement and Strain Field of Three-dimensional Rheologic Model of Earthquake Preparation

Based on the three-dimensional elastic inclusion model proposed by Dobrovolskii, we developed a rheological inclusion model to study earthquake preparation processes. By using the Corresponding Principle in the theory of rheologic mechanics, we derived the analytic expressions of viscoelastic displacement U(r, t) , V(r, t) and W(r, t), normal strains ε_xx (r, t), ε_yy (r, t) and ε_zz (r, t) and the bulk strain θ (r, t) at an arbitrary point (x, y, z) in three directions of X axis, Y axis and Z axis produced by a three-dimensional inclusion in the semi-infinite rheologic medium defined by the standard linear rheologic model. Subsequent to the spatial-temporal variation of bulk strain being computed on the ground produced by such a spherical rheologic inclusion, interesting results are obtained, suggesting that the bulk strain produced by a hard inclusion change with time according to three stages (α, β, γ) with different characteristics, similar to that of geodetic deformation observations, but different with the results of a soft inclusion. These theoretical results can be used to explain the characteristics of spatial-temporal evolution, patterns, quadrant-distribution of earthquake precursors, the changeability, spontaneity and complexity of short-term and imminent-term precursors. It offers a theoretical base to build physical models for earthquake precursors and to predict the earthquakes.     

博斯腾湖湿地生态脆弱性评价研究

通过对博斯腾湖流域的水资源及其湿地现状分析,采取了定性与定量相结合的方法,对博斯腾湖湿地进行了评价。评价中依据湿地生态特性及演化规律建立评价指标体系,利用层次分析法(AHP)确定指标权重,利用综合指数法计算出湿地的脆弱度。结果显示博斯腾湖湿地生态系统为中度脆弱,在此基础上探讨了博斯腾湖湿地生态脆弱性的成因。指出人类活动通过叠加在自然变化背景上的影响程度日趋增强成为该区湿地生态环境的主导性脆弱因子。