Scanline Method Research Articles

Mechanical prediction of fracture aperture in layered rocks

Two types of opening‐mode fractures (joints) are commonly found in layered rocks. One is called unconfined because fracture heights are much less than the layer thickness and they behave like fractures in massive rocks. The other is called confined because the fractures terminate at the layer boundaries. We investigate the mechanical control on apertures in these systems using the theory of elasticity. An analytical solution demonstrates that the ratio of aperture to height (aspect ratio) of an unconfined fracture in a homogeneous, isotropic medium is linearly related to the average strain, the overburden stress, and the internal fluid pressure within the fracture. Numerical results based on of the finite element method (FEM) for an unconfined fracture in the central layer of a three‐layer model agree with the analytical result when the fractured layer and neighboring layers have the same elastic constants. The aspect ratio of the unconfined fracture is insensitive to the ratio of Young's modulus of the fractured layer to that of the neighboring layers and to the differences in Poisson's ratios. The FEM results for confined fractures show that their aspect ratio is linearly related to the average strain, the overburden stress, and the internal fluid pressure. However, the aspect ratio increases nonlinearly with increasing fracture spacing to layer thickness ratio because of the mechanical interaction between adjacent fractures. The interaction becomes insignificant when the spacing to layer thickness ratio is > ∼ 6.0. The aspect ratio of confined fractures depends on the ratio of Young's modulus of the fractured layer to that of the neighboring layers. This dependence is significant when the fracture spacing to layer thickness ratio is <1.3; otherwise, it is negligible. In all of these cases the aspect ratio of confined fractures is insensitive to variations in Poisson's ratios. Furthermore, the FEM results predict that fracture accommodated strain measured by the traditional scan line method may slightly overestimate the average normal strain when the spacing to layer thickness ratio is < ∼ 1.0, and may slightly underestimate this strain for greater ratios.

Estudo de fraturas nos taludes de corte, em rocha vulcânica, ao longo da BR 158, Santa Maria, RS

Weathering processes and jointing degree are the conditioning factors for rock falI.The fractured volcanic lithologies from Santa Maria, RS, Brazil, were studied along the BR 158 road. Data was gathered through the Scanline method from BRADY & BROWN (1985) and analyzed by vector statistics.Six main jointing groups were defined, associated to rock cooling and shrinking. Main attitudes are: Group 1: 348;83; Group 2: 174;82; Group 3: 85;76; Group 4: 265;75; Group 5: 300;42 and Group 6: 121 ;53.

Development of a new television set with personal computer capability

A prototype of a novel television set (TV) with personal computer (PC) capability is presented. In addition to fundamental TV functions, the system provides three PC functions: CD playing, teletext viewing and WWW (World Wide Web) browsing. This paper describes the user interface that the user can operate without knowledge of PC. Also, a scan-line conversion method to display clear PC images on a TV monitor is described.

The lazy z-buffer

This paper describes a new perspective on a fundamental algorithm of three-dimensional computer graphics, namely z-buffering. An implementation of the z-buffer method in a lazy functional language behaves in a manner quite different to its traditional imperative counterpart. The main result of this paper is to demonstrate that the lazy z-buffer is a scan-line method. The essential difference between scan-line methods and z-buffers is one of order of evaluation. A hybrid algorithm with properties common to both z-buffer and scan-line methods is also described.

Parallel data resampling and Fourier inversion by the scan-line method

Fourier inversion is an efficient method for image reconstruction in a variety of applications, for example, in computed tomography and magnetic resonance imaging. Fourier inversion normally consists of two steps, interpolation of data onto a rectilinear grid, if necessary, and inverse Fourier transformation. Here, the authors present interpolation by the scan-line method, in which the interpolation algorithm is implemented in a form consisting only of row operations and data transposes. The two-dimensional inverse Fourier transformation can also be implemented with only row operations and data transposes. Accordingly, Fourier inversion can easily be implemented on a parallel computer that supports row operations and data transposes on row distributed data. The conditions under which the scan-line implementations are algorithmically equivalent to the original serial computer implementation are described and methods for improving accuracy outside of those conditions are presented. The scan-line algorithm is implemented on the iWarp parallel computer using the Adapt language for parallel image processing. This implementation is applied to magnetic resonance data acquired along radial-lines and spiral trajectories through Fourier transform space.

Conditional simulations of fluid flow in three‐dimensional networks of discrete fractures

How to predict flow through a network of discrete fractures in a three‐dimensional domain is investigated. Fractures are modeled as circular discs of arbitrary size, orientation, transmissivity, and location. A fracture network is characterized by the statistical distributions of these quantities. Fracture traces observed on a wall form the basis for estimates of mean fracture radius, fracture orientation parameters, and fracture density. Fracture trace lengths are estimated with the scanline method and from areal sampling on circular regions. The traces observed on the wall can also be used to condition the network. This trace conditioning is achieved by forcing the network generator to always reproduce the observed traces. Conditioning might be a means of decreasing the variability of the fracture networks. A numerical simulation model has been developed which is capable of generating a fracture network of desired statistical properties and solving for the steady state flow. On each fracture disc the flow is discretized with the boundary element method. A series of hypothetical examples are analyzed. These examples consist of sets of Monte‐Carlo simulations of flow through a series of networks generated from the same statistical distributions. The examples lead to the following conclusions. Large fractures and high fracture density implies good connectivity in the networks. A high fracture density implies a small variance in the flow through the network. Trace conditioning decreases estimation variance only when the fracture network consists of large fractures. Fracture statistics can be estimated reasonably well from fracture traces observed on a wall.

A Scanline Method for Solid Model Display

AbstractThe modelling of solid objects is becoming increasingly important in the application of computer graphics to a wide variety of problems, such as CAD/CAM, simulation, and molecular modelling. A variety of methods for rendering solid objects exists, including 2‐Buffer, Scanline and Ray Tracing. This paper is concerned with a scanline method for the production of still images of complex objects. The implementation of a scanline algorithm is discussed, in conjunction with a consideration of its performance in relation to the z‐buffer method.Many scanline methods cater only for a restricted class of primitives, such as polygons or spheres, whereas this implementation is a general purpose scanline algorithm capable of being extended to handle a variety of primitives. The primitives currently available are polygons, spheres, spheres swept along straight‐line trajectories, and cylinders. Polygonal models of cubes, cones and cylinders are also available.The approach is capable of dealing with “positive” and “negative” volumes, allowing objects with holes to be modelled and displayed. It has further been extended to cater for the inclusion of transparent objects into a scene, and consequently allows the modelling of coloured “glass” objects.

A generalized scan line algorithm for the computer display of parametrically defined surfaces

A scan line method is presented for creating shaded pictures of parametrically defined curved surfaces of piecewise continuity class C 2. The algorithm uses a new subdivision technique to produce appropriate polygons for smooth shaded pictures. The approach results in smoothly curved silhouettes.