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51.
地理模型分布式集成是虚拟地理环境研究的主要内容之一。在分布式系统中多采用XML作为数据交换的统一标准,以解决多种信息在网络空间的表达和传输。本文在VisualC#.NET平台下开发了一个通用的模型数据定义编辑器,用XML来统一描述多源异构的地理模型数据,以实现模型的共享和集成。提供了直观式图形界面,可满足无程序背景的设计人员的需求,使智能化的模型集成成为可能。以地下水模型分布式调用为例,验证了此编辑器的有效性和易操作性。  相似文献   
52.
Precise, automatic and fast method for vanishing point detection   总被引:1,自引:0,他引:1  
A new automated approach for vanishing point detection in images of urban scenes is described. This method is based on the theorem of Thales. The main contribution of this paper is the automatic and simultaneous detection of all vanishing points of the image, achieved by converting this problem into the detection of circles in a complex cloud of points, in which each point corresponds to a segment and is associated with an uncertainty. This extraction of circles uses a RANSAC method, modified to improve its speed by using accumulation techniques (Hough transform or otherwise). This robust estimation is then refined by least squares error propagation using the individual variances of each segment. The algorithm is robust, its accuracy is optimised and it is entirely automatic. Its successful operation has been tested on a large number of images of varied urban scenes.  相似文献   
53.
露天煤矿数字地质模型的建立及在虚拟开采中的应用研究   总被引:1,自引:1,他引:0  
为了对露天煤矿剥、采、排和土地复垦的进行预控制,需要对露天矿生产进行预演,计算相关数据。采用层面模型建立露天矿的地质模型,以"多对角线交换循环算法"结合"凸包推进算法"建立约束TIN结构层面。根据露天矿开采推进的特点建立以台阶为单元的分层式开采模型,在地质模型和开采模型的基础上,根据露天矿实际生产情况建立开采模板,采用"人工交互式推进"实现露天矿的虚拟开采。  相似文献   
54.
后差分GPS测量则木河断裂地震微地貌特征   总被引:4,自引:0,他引:4  
任治坤  田勤俭  张军龙 《地震》2007,27(3):97-104
地震微地貌是研究古地震的重要证据。 发生在则木河断裂带上的1850年地震的地表破裂带在人类活动较少的地区得以保存完好。 研究区内地形起伏大, 断塞塘、 断层陡坎、 鼓包等微地震地貌特征明显, 在三维视图内可直观反映测量区内的这些地貌特征。 利用后差分GPS方法测量断裂活动形成的地震微地貌, 水平测量精度可达0.5 m, DEM精度可到一个像元1 m, 是定量化研究地震微地貌的一种新方法。 测量结果表明, 大箐梁子顶部七条干沟对应多次古地震事件; 大箐梁子顶部鼓包被断裂断错, 断塞塘沉积区向南迁移, 鼓包最新断错约4 m, 大箐村南山坡形成50 cm高断层陡坎。 说明大箐梁子一带地震活动性较强, 且以挤压构造为主。  相似文献   
55.
Thermal fracturing can play an important role in development of unconventional petroleum and geothermal resources. Thermal fractures can result from the nonlinear deformation of the rock in response to thermal stress related to cold water injection as well as heating. Before the rock reaches the final failure stage, material softening and bulk modulus degradation can cause changes in the thermo‐mechanical properties of the solid. In order to capture this aspect of the rock fracture, a virtual multidimensional internal bond‐based thermo‐mechanical model is derived to track elastic, softening, and the failure stages of the rock in response to the temporal changes of its temperature field. The variations in thermo‐mechanical properties of the rock are derived from a nonlinear constitutive model. To represent the thermo‐mechanical behavior of pre‐existing fractures, the element partition method is employed. Using the model, numerical simulation of 3D thermal fracture propagation in brittle rock is carried out. Results of numerical simulations provide evidence of model verification and illustrate nonlinear thermal response and fracture development in rock under uniform cooling. In addition, fracture coalescence in a cluster of fractures under thermal stress is illustrated, and the process of thermal fracturing from a wellbore is captured. Results underscore the importance of thermal stress in reservoir stimulation and show the effectiveness of the model to predict 3D thermal fracturing. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
56.
Propagation of fractures, especially those emanating from wellbores and closed natural fractures, often involves Mode I and Mode II, and at times Mode III, posing significant challenges to its numerical simulation. When an embedded inclined fracture is subjected to compression, the fracture edge is constrained by the surrounding materials so that its true propagation pattern cannot be simulated by 2D models. In this article, a virtual multidimensional internal bond (VMIB) model is presented to simulate three‐dimensional (3D) fracture propagation. The VMIB model bridges the processes of macro fracture and micro bond rupture. The macro 3D constitutive relation in VMIB is derived from the 1D bond in the micro scale and is implemented in a 3D finite element method. To represent the contact and friction between fracture surfaces, a 3D element partition method is employed. The model is applied to simulate fracture propagation and coalescence in typical laboratory experiments and is used to analyze the propagation of an embedded fracture. Simulation results for single and multiple fractures illustrate 3D features of the tensile and compressive fracture propagation, especially the propagation of a Mode III fracture. The results match well with the experimental observation, suggesting that the presented method can capture the main features of 3D fracture propagation and coalescence. Moreover, by developing an algorithm for applying pressure on the fracture surfaces, propagation of a natural fracture is also simulated. The result illustrates an interesting and important phenomenon of Mode III fracture propagation, namely the fracture front segmentation. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
57.
Abstract

Experimental investigations of the surface discharge of two-dimensional heated saline jets into surroundings with stable, constant salt gradients were carried out. The discharge conditions were parameterized with the densimetric Froude number, and the Reynolds number. The evolution of the discharge was monitored by flow visualization methods, and by the measurements of temperature and salinity distributions. For comparison, experiments of the surface discharge of heated water into homogeneous surroundings at the corresponding discharge conditions were also conducted. The results clearly showed that while in the former case, the region away from the vicinity of the discharge manifold was marked by the presence of salt-finger convection, in the latter case this region exhibited stable thermal stratification. Furthermore the occurrence of salt-finger convection considerably retarded the motion of the jet, and increased the penetration depth of temperature and salinity fields.  相似文献   
58.
位场DFT算法研究   总被引:5,自引:0,他引:5       下载免费PDF全文
本文推广了经典的抽样定理,并据此导出了函数有限离散傅里叶变换误差方程(简称DFT误差方程,下同)。该方程把有限离散傅里叶变换中固有的离散效应和有限效应表示为确切的数学形式。离散效应被表示为一个含整参变量(参变量取0,1,…,N-1)的复无穷级数;有限效应被表示为一个含整参变量(参变量取0,1,…,N-1)的复无穷级数的DFT。 基于DFT误差方程和位函数特点,作者提出了两种位场数值傅里叶变换新算法--移样法和等效源续尾叠样法。移样法可近百倍地提高位场数值傅里叶反变换的精度,等效源续尾叠样法可数十倍地提高正变换精度。两种算法都不需要增加资料长度和取样密度,因而基本不需要增加计算机时间和内存。文中给出了算例。  相似文献   
59.
To account for elastic and attenuating effects in the elastic wave equation, the stress-strain relationship can be defined through a general, anisotropic, causal relaxation function ijkl (x, ). Then, the wave equation operator is not necessarily symmetric (self-adjoint), but the reciprocity property is still satisfied. The representation theorem contains a term proportional to the history of strain. The dual problem consists of solving the wave equation withfinal time conditions and an anti-causal relaxation function. The problem of interpretation of seismic waveforms can be set as the nonlinear inverse problem of estimating the matter density (x) and all the functions ijkl (x, ). This inverse problem can be solved using iterative gradient methods, each iteration consisting of the propagation of the actual source in the current medium, with causal attenuation, the propagation of the residuals—acting as if they were sources—backwards in time, with anti-causal attenuation, and the correlation of the two wavefields thus obtained.  相似文献   
60.
Intriguing reciprocity relations exist between the static deformation excited by a point dislocation in a SNREI earth and those generated by external forces, such as tidal force, surface loading and surface shear forces. Coseismic deformations can be rewritten as follows: (1) potential change in terms of the tide deformation field, (2) radial displacement in terms of the load and tidal deformation fields, and (3) tangential displacement in terms of shear and torsional deformation fields. The relations greatly reduce the effort to compute the coseismic crustal deformation in a spherically symmetric earth.  相似文献   
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