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61.
模糊面元素空间拓扑关系抽象化方法研究 总被引:7,自引:3,他引:4
空间拓扑关系的判定是地理信息系统中进行空间查询、空间分析、空间推理等操作的基础.在分析模糊区域空间拓扑关系的基础上,用空间关系向量定量描述这些拓扑关系.依据空间抽象的要求,通过计算向量之间的相关程度,对模糊区域的空间拓扑关系进行抽象,并根据空间拓扑关系的区域分布特征对抽象后的结果进行调整. 相似文献
62.
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
63.
三维体目标间拓扑关系与方向关系的混合推理 总被引:1,自引:1,他引:0
重点研究了三维空间中拓扑关系和方向关系间的混合空间关系推理。用Allen区间关系对描述基于投影的空间划分方法得到的方向区域和用九交矩阵描述的拓扑关系,用定义法研究混合空间关系推理,推理结果用组合推理表表示。 相似文献
64.
Internal erosion (IE) affects the stability of natural and reinforced materials by causing instability within their granular structure. The dislodgement and transport of eroded particles affect both the particulate concentration of eroding fluid and the pore network of eroded material. In this study, we examined these modifications using a transport model with a finite element code. First, IE tests on chemically reinforced sand columns were performed to obtain information about eroded material loss of mass, particulate concentration of effluent, porosity and permeability modifications, and existing IE stages. Second, based on experimental results, a mathematical one‐dimensional model has been formulated to monitor the evolution and spatial distribution of erodible solids, fluidized particles, porosity, permeability, and seepage stresses. The model consists of a set of coupled nonlinear differential equations solved in sequence. It provides valuable information about the extent and the dynamics of structural changes, which can be used to estimate an IE time for the hydraulic work to reach failure. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
65.
66.
P. F. Linden 《地球物理与天体物理流体动力学》2013,107(3-4):163-182
Abstract The flow of a two-layer flow in a rotating channel on an f-plane over topography with sinusoidal variation of height in a direction parallel to the flow is investigated. When the two layers flow in opposite directions a resonance is found when the topographic scale matches the free mode of the system. We examine the stability of the forced mode in the vicinity of this resonance by means of a perturbation expansion of the topographic height. Both subresonant and super-resonant instabilities are found and their equilibration is examined. For small values of the dissipation multiple equilibria are found. The topographic drag releases potential energy even when the flow is baroclinically stable. 相似文献
67.
A study of internal solitary waves observed on the continental shelf in the northwestern South China Sea 总被引:3,自引:1,他引:2
Based on in-situ time series data from the acoustic Doppler current profiler (ADCP) and thermistor chain in Wenchang area, a sequence of internal solitary wave (ISW) packets was observed in September 2005, propagating northwest on the continental shelf of the northwestern South China Sea (SCS). Corresponding to different stratification of the water column and tidal condition, both elevation and depression ISWs were observed at the same mooring location with amplitude of 35 m and 25 m respectively in different days. Regular arrival of the remarkable ISW packets at approximately the diurnal tidal period and the dominance of diurnal internal waves in the study area, strongly suggest that the main energy source of the waves is the diurnal tide. Notice that the wave packets were all riding on the troughs and shoulders of the internal tides, they were probably generated locally from the shelf break by the evolution of the internal tides due to nonlinear and dispersive effects. 相似文献
68.
S.C. Tripathy J. Ishizaka T. Fujiki T. Shibata K. Okamura T. Hosaka T. Saino 《Estuarine, Coastal and Shelf Science》2010
A comparative account of primary productivity (PP), in the characteristically turbid and highly dynamic waters of Ariake Bay, measured by 13C uptake and fast repetition rate fluorometer (FRRF) was conducted to ensure compatibility between the two methods. Estimates from both methods depicted strong linearity for both short-term (r2 > 0.90) and daily (r2 = 0.42–0.93) measurements, except in the near-surface (∼0 m) layer. 13C-based short-term (1 h; in situ) PP estimates showed similar magnitudes and trend with the instantaneous PP measured by FRRF concurrently. Whereas, unlike short-term measurements, the daily PP estimates from both methods showed large difference, with FRRF-based time integrated daily PP resulting in 1.09–1.82 times higher than the carbon-based daily (24 h; simulated in situ) PP. This difference between daily PP estimates was mainly due to: (1) the temporal variation of water column chlorophyll a (Chl a) because of frequent moving of water mass, and (2) the dissimilarity in ambient light field conditions between the two methods. Results revealed that considering the above two environmental factors invariable over a daylength, fairly close approximation of daily PP, compared to 13C-based daily PP, could be obtained from FRRF. Hence, FRRF-based daily PP can be considered as more realistic in this highly dynamic water body like Ariake Bay where water column parameters are subjected to strong temporal variation. The relationship between Chl a-specific photosynthetic rate (PB) and the corresponding photosynthetically active radiation (PAR) in the water column (PAR–PB relationship) was found to be linear for FRRF and curvilinear for 13C-based measurements in the near-surface layer, for the same intensities of incident PAR, and this is thought to be the primary basis for the higher difference in PP estimates at the near-surface layer. Considering the minor variations in FRRF-based time series of PAR–PB relationships, a combined and/or instantaneous PAR–PB relationship in combination with incubation Chl a and light field condition was used to obtain fairly close estimates of daily water column integrated PP from FRRF. 相似文献
69.
70.
随着深部岩体工程的发展,开挖卸荷导致的应力主轴旋转问题引起了广泛关注。首先,分析总结了岩体工程中存在的应力主轴旋转问题及其对岩体工程稳定性的影响;其次,介绍了土体空心圆柱扭剪仪的发展现状及其特点,从荷载的施加方式、试样尺寸两个方面指出了研制岩石空心圆柱扭剪仪的关键问题,并与土体空心圆柱扭剪仪进行了对比,提出了新的扭矩施加技术和合理的岩石空心圆柱试样尺寸;最后,总结概括了考虑应力主轴旋转的土体本构模型的研究成果,并对考虑应力主轴旋转的岩石本构关系的研究进行了展望。该工作将对岩石空心圆柱扭剪仪的研制和相关理论的研究提供一定的参考和指导。 相似文献