孔隙水压力对岩石裂纹扩展影响的数值模拟   总被引：1，自引：0，他引：1  

唐春安  杨天鸿  李连崇  梁正召  ThamL.G.  LeeK.K.  TsuiY. 《岩土力学》2003,(Z2)

应用岩石破坏过程渗流-应力-损伤(FSD)耦合分析软件F-RFPA2D,通过对孔隙水压作用下岩石试件加载破坏过程的数值模拟,对孔隙水压力大小和梯度对岩石试样中裂纹的萌生和扩展进行了数值模拟研究。模拟结果再现了孔隙水压力作用下裂纹萌生扩展的全过程,表明孔隙水压力大小和梯度对岩石中裂纹的萌生和扩展模式都有很大的影响。  相似文献   

Interaction of metamorphism, deformation and exhumation in large convergent orogens   总被引：11，自引：0，他引：11  

R. A. Jamieson  C. Beaumont  M. H. Nguyen  B. Lee 《Journal of Metamorphic Geology》2002,20(1):9-24

Coupled thermal‐mechanical models are used to investigate interactions between metamorphism, deformation and exhumation in large convergent orogens, and the implications of coupling and feedback between these processes for observed structural and metamorphic styles. The models involve subduction of suborogenic mantle lithosphere, large amounts of convergence (≥ 450 km) at 1 cm yr^?1, and a slope‐dependent erosion rate. The model crust is layered with respect to thermal and rheological properties — the upper crust (0–20 km) follows a wet quartzite flow law, with heat production of 2.0 μW m^?3, and the lower crust (20–35 km) follows a modified dry diabase flow law, with heat production of 0.75 μW m^?3. After 45 Myr, the model orogens develop crustal thicknesses of the order of 60 km, with lower crustal temperatures in excess of 700 °C. In some models, an additional increment of weakening is introduced so that the effective viscosity decreases to 10¹⁹ Pa.s at 700 °C in the upper crust and 900 °C in the lower crust. In these models, a narrow zone of outward channel flow develops at the base of the weak upper crustal layer where T≥600 °C. The channel flow zone is characterised by a reversal in velocity direction on the pro‐side of the system, and is driven by a depth‐dependent pressure gradient that is facilitated by the development of a temperature‐dependent low viscosity horizon in the mid‐crust. Different exhumation styles produce contrasting effects on models with channel flow zones. Post‐convergent crustal extension leads to thinning in the orogenic core and a corresponding zone of shortening and thrust‐related exhumation on the flanks. Velocities in the pro‐side channel flow zone are enhanced but the channel itself is not exhumed. In contrast, exhumation resulting from erosion that is focused on the pro‐side flank of the plateau leads to ‘ductile extrusion’ of the channel flow zone. The exhumed channel displays apparent normal‐sense offset at its upper boundary, reverse‐sense offset at its lower boundary, and an ‘inverted’ metamorphic sequence across the zone. The different styles of exhumation produce contrasting peak grade profiles across the model surfaces. However, P–T–t paths in both cases are loops where P_max precedes T_max, typical of regional metamorphism; individual paths are not diagnostic of either the thickening or the exhumation mechanism. Possible natural examples of the channel flow zones produced in these models include the Main Central Thrust zone of the Himalayas and the Muskoka domain of the western Grenville orogen.  相似文献   

Bearing capacity of strip foundation on geogrid-reinforced sand   总被引：1，自引：0，他引：1  

E. C. Shin  B. M. Das  E. S. Lee  C. Atalar 《Geotechnical and Geological Engineering》2002,20(2):169-180

Results of small-scale laboratory model tests to determine the ultimate bearing capacity of a strip foundation supported by sand with multiple layers of geogrid reinforcement are presented. Tests were conducted with only one type of geogrid and a sand compacted to one relative density. The embedment ratio of the foundation was varied from zero to 0.6. It is found that, for the given reinforcement-depth ratio, the bearing capacity ratio with respect to ultimate load increases with embedment. The relationship between the bearing capacity ratio at ultimate load and at limited levels of settlement (less than or equal to 5% of foundation width) is also presented. The bearing capacity ratio at limited levels of settlement is smaller than the value at ultimate load.  相似文献   

A Finite-Volume Method with Hexahedral Multiblock Grids for Modeling Flow in Porous Media     

S.H. Lee  P. Jenny  H.A. Tchelepi 《Computational Geosciences》2002,6(3-4):353-379

This paper presents a finite-volume method for hexahedral multiblock grids to calculate multiphase flow in geologically complex reservoirs. Accommodating complex geologic and geometric features in a reservoir model (e.g., faults) entails non-orthogonal and/or unstructured grids in place of conventional (globally structured) Cartesian grids. To obtain flexibility in gridding as well as efficient flow computation, we use hexahedral multiblock grids. These grids are locally structured, but globally unstructured. One major advantage of these grids over fully unstructured tetrahedral grids is that most numerical methods developed for structured grids can be directly used for dealing with the local problems. We present several challenging examples, generated via a commercially available tool, that demonstrate the capabilities of hexahedral multiblock gridding. Grid quality is discussed in terms of uniformity and orthogonality. The presence of non-orthogonal grid and full permeability tensors requires the use of multi-point discretization methods. A flux-continuous finite-difference (FCFD) scheme, previously developed for stratigraphic hexahedral grid with full-tensor permeability, is employed for numerical flow computation. We extend the FCFD scheme to handle exceptional configurations (i.e. three- or five-cell connections as opposed to the regular four), which result from employing multiblock gridding of certain complex objects. In order to perform flow simulation efficiently, we employ a two-level preconditioner for solving the linear equations that results from the wide stencil of the FCFD scheme. The individual block, composed of cells that form a structured grid, serves as the local level; the higher level operates on the global block configuration (i.e. unstructured component). The implementation uses an efficient data structure where each block is wrapped with a layer of neighboring cells. We also examine splitting techniques [14] for the linear systems associated with the wide stencils of our FCFD operator. We present three numerical examples that demonstrate the method: (1) a pinchout, (2) a faulted reservoir model with internal surfaces and (3) a real reservoir model with multiple faults and internal surfaces.  相似文献   

Bundle Adjustment with Self–Calibration Using Straight Lines     

Ayman F. Habib  Michel Morgan  & Young–Ran Lee 《The Photogrammetric Record》2002,17(100):635-650

Increased use of digital imagery has facilitated the opportunity to use features, in addition to points, in photogrammetric applications. Straight lines are often present in object space, and prior research has focused on incorporating straight–line constraints into bundle adjustment for frame imagery. In the research reported in this paper, object–space straight lines are used in a bundle adjustment with self–calibration. The perspective projection of straight lines in the object space produces straight lines in the image space in the absence of distortions. Any deviations from straightness in the image space are attributed to various distortion sources, such as radial and decentric lens distortions. Before incorporating straight lines into a bundle adjustment with self–calibration, the representation and perspective transformation of straight lines between image space and object space should be addressed. In this investigation, images of straight lines are represented as a sequence of points along the image line. Also, two points along the object–space straight line are used to represent that line. The perspective relationship between image– and object–space lines is incorporated in a mathematical constraint. The underlying principle in this constraint is that the vector from the perspective centre to an image point on a straight–line feature lies on the plane defined by the perspective centre and the two object points defining the straight line. This constraint has been embedded in a software application for bundle adjustment with self–calibration that can incorporate point as well as straight–line features. Experiments with simulated and real data have proved the feasibility and the efficiency of the algorithm proposed.  相似文献   

Interactive Analysis Using Voronoi Diagrams: Algorithms to Support Dynamic Update from a Generic Triangle-based Data Structure     

Ickjai Lee  & Mark Gahegan 《Transactions in GIS》2002,6(2):89-114

This paper describes a series of dynamic update methods that can be applied to a family of Voronoi diagram types, so that changes can be updated incrementally, without the usual recourse to complete reconstruction of their underlying data structure. More efficient incremental update methods are described for the ordinary Voronoi diagram, the farthest-point Voronoi diagram, the order- k Voronoi diagram and the ordered order- k Voronoi diagram. A discussion is also given of one case where incremental update is not practical, that of the multiplicatively weighted Voronoi diagram. Update methods rely on a previously reported generic, triangle-based data structure (Gahegan and Lee 2000) from which local topology can be dynamically reconstructed following changes to the underlying pointset. An application, which implements these ideas, is available for download via the Internet as proof of concept. Results show that the algorithmic complexity of dynamic update methods vary considerably according to the Voronoi type, but offer in all cases (except the multiplicatively weighted Voronoi diagram) a substantial increase in performance, enabling Voronoi methods to address larger pointsets and more complex modelling problems without incurring too great a computational burden.  相似文献   

Effect of boundary element details on the seismic deformation capacity of structural walls     

Young‐Hun Oh  Sang Whan Han  Li‐Hyung Lee 《地震工程与结构动力学》2002,31(8):1583-1602

The objective of this study is to investigate the effect of boundary element details of structural walls on their deformation capacities. Structural walls considered in this study have different sectional shapes and/or transverse reinforcement content at the boundaries of the walls (called boundary element details hereafter). Four full‐scale wall specimens (3000mm (h_w)×1500mm (l_w)×200mm (T)) were fabricated and tested. Three specimens are rectangular in section and the other specimen has a barbell‐shaped cross‐section (a wall with boundary columns). The rectangular wall specimens are reinforced according to the common practice used for reinforced concrete residence buildings in Korea and Chile. In this study, the primary variable for these rectangular specimens is the content of transverse reinforcement to confine the boundary elements of a wall. The barbell‐shaped specimen was designed in compliance with ACI 318‐95. The response of the barbell‐shaped specimen is compared with those of other rectangular specimens. The effective aspect ratio of the specimens is set to two in this study. Based on the experimental results, it is found that the deformation capacities of walls, which are represented by displacement ductility, drift ratio and energy dissipation capacities, are affected by the boundary element details. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

A Numerical Study Of Nocturnal Wavelike Motion In Forests     

Xinzhang Hu  Xuhui Lee  David E. Stevens  Ronald B. Smith 《Boundary-Layer Meteorology》2002,102(2):199-223

In this paper, we use a two-dimensional eddy-resolved model to investigate the instability of a parallel shear flow in a stably stratified boundary layer whose lower domain is occupied by a canopy. The results support our contention that wave motion in the canopy is initiated by shear in an air layer near the treetops. Significant modification by the wave motion of the mean velocity and temperature fields is found even before the wave reaches saturation. The wave fluxes of momentum and heat are not constant with height. Downwind tilting braids are found at the finite amplitude stage of the wave growth and could persist after wave breaking; these downwind tilting structures are believed to be the same as the temperature microfronts reported in the literature. We also present an analysis of the velocity and temperature fields of an observed wave event in the time-height domain and show that the simulation has captured the broad features of the observation.  相似文献   

Dissolved free and combined amino acids in nearshore seawater,sea surface microlayers and foams: Influence of extracellular hydrolysis   总被引：1，自引：0，他引：1  

Marina Kuznetsova  Cindy Lee 《Aquatic Sciences - Research Across Boundaries》2002,64(3):252-268

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Geologic,geomorphic, and meteorological aspects of debris flows triggered by Hurricanes Frances and Ivan during September 2004 in the Southern Appalachian Mountains of Macon County,North Carolina (southeastern USA)   总被引：3，自引：1，他引：2  

R. M. Wooten  K. A. Gillon  A. C. Witt  R. S. Latham  T. J. Douglas  J. B. Bauer  S. J. Fuemmeler  L. G. Lee 《Landslides》2008,5(1):31-44

In September 2004, rain from the remnants of Hurricanes Frances and Ivan triggered at least 155 landslides in the Blue Ridge Mountains of North Carolina. At least 33 debris flows occurred in Macon County, causing 5 deaths, destroying 16 homes, and damaging infrastructure. We mapped debris flows and debris deposits using a light-detecting and ranging digital elevation model, remote imagery and field studies integrated in a geographic information system. Evidence of past debris flows was found at all recent debris flow sites. Orographic rainfall enhancement along topographic escarpments influenced debris flow frequency at higher elevations. A possible trigger for the Wayah and fatal Peeks Creek debris flows was a spiral rain band within Ivan that moved across the area with short duration rainfall rates of 150–230 mm/h. Intersecting bedrock structures in polydeformed metamorphic rock influence the formation of catchments within structural–geomorphic domains where debris flows originate.  相似文献