Numerical Estimation (numerical + estimation)

Distribution by Scientific Domains

Selected Abstracts

Numerical estimation of REV and permeability tensor for fractured rock masses by composite element method

S.-H. Chen
Abstract The Monte Carlo method is used to generate parent stochastic discrete fracture network, from which a series of fractured rock samples of different sizes and orientations are extracted. The fracture network combined with a regular grid forms composite element mesh of the fractured rock sample, in which each composite element is composed of sub-elements incised by fracture segments. The composite element method (CEM) for the seepage is implemented to obtain the nodal hydraulic potential as well as the seepage flow rates through the fractured rock samples. The application of CEM enables a large quantity of stochastic tests for the fractured rock samples because the pre-process is facilitated greatly. By changing the sizes and orientations of the samples, the analysis of the seepage characteristics is realized to evaluate the variation of the permeability components, the existence of the permeability tensor and the representative element volume. The feasibility and effectiveness are illustrated in a numerical example. Copyright 2008 John Wiley & Sons, Ltd. [source]

Asymptotic Back Strain Approach for Estimation of Effective Properties of Multiphase Materials

A. Gusev
Estimation of the effective properties of composite materials from those of the constituents and the material's morphology is a classical problem of both theoretical and technological interest. In this work, the authors have introduced an asymptotic back strain finite element approach for numerical estimation of effective properties of multiphase materials. The proposed approach should open an appealing pathway to rational and effective computer aided design of random microstructure composite materials. [source]

A numerical estimation of the effects of a cylindrical hole and imperfect bonding on stability of a fibre in an elastic matrix

Yuri N. Lapusta
Abstract A simple numerical model based on three-dimensional analytical considerations is proposed for an estimation of the local effects of a cylindrical hole in the matrix as well as of fibre,matrix interface imperfections on compressive stability of fibres in fibre-reinforced composites. The geometry of the model includes an inclusion (a fibre) in a matrix with the assumption of an imperfect bonding at the interface and a cylindrical hole in the closest neighbourhood. Then the problem formulation is idealized in two directions, providing a possibility of establishing lower and upper bounds for critical loads for the case of a matrix with a cylindrical hole of a non-circular cross-section as well as for the case of interface imperfections with the possibility of sliding without discontinuity of the displacements normal to the interface. The model takes into account the distinct difference in the properties of the fibre and the matrix and the spatial character of the problem at the microlevel. It is based on individual consideration of the fibre and the matrix with a hole with the necessity of satisfying certain idealized bonding conditions between them. Copyright 2001 John Wiley & Sons, Ltd. [source]

Robust estimation of the normal to a curve using optimal control

J. Fehrenbach
Abstract We propose an optimal control problem whose optimal command approximates the normal vector field to a given curve. This problem is obtained by studying a partial differential equation satisfied by a map that jumps across the given curve. The gradient of the cost function is then estimated by an adjoint method, and an explicit algorithm is proposed to obtain the optimal command. Examples show that this numerical estimation of the normal is robust, in the sense that when the curve is not a simple closed curve, or when it is incomplete (dashed), the solution is still a good approximation of the normal. As applications, we show how the optimal state can help closing discontinuous curves and improve image restoration; it also provides a coloring of simple planar maps. Copyright 2007 John Wiley & Sons, Ltd. [source]

Modelling the geography of economic activities on a continuous space,

Giuseppe Arbia
Birth-death processes; economic geography; geographical concentration; Markov fields; regional economic growth Abstract In the present article we propose a spatial micro econometric approach for studying the geographical concentration of economic activities. We analyse the incentives to use this approach rather than the traditional one based on regional aggregates. As an example, we present our prototypical theoretic model , to be seen as a continuous space version of Krugman's concentration model , that includes birth, survival and growth components. We present a numerical estimation of the birth model for a set of data referring to the concentration of the manufacturing industries in the San Marino Republic. [source]

Comparison of analytical and numerical solution for optimal vortex diffuser design

Andreas H. Mehrle
The contribution deals with optimization of wing tip devices, so called vortex diffusers. A comparison is given between an analytical approach for obtaining the optimal circulation loading and the results of a numerical investigation using a lifting line method. The purpose of most wing tip devices is to reduce the induced drag of the main wing by converting vortex energy into thrust. In order to achieve an optimal design, a variational formulation originally proposed by Betz and Prandtl for air screws is applied to the circulation distribution of the diffuser blades. In extension to the inviscid formulation, a viscous correction is applied in order to account for frictional forces. In an effort to validate the analytical results, a comparison is given with numerical solutions from a lifting line method. The loading of the diffuser blades is parametrized and optimized with respect to resulting thrust by use of a quasi-Newton gradient method. Comparison shows that, knowing the velocity distribution in the near wake of the wing, considerable decrease of induced drag may be achieved making use of vortex diffusers. Although actual circulation loading may differ between the analytical and numerical estimation, resulting thrust agrees within a few percent. ( 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The use of generalizability theory to estimate data reliability in single-subject observational research

Pui-Wa Lei
Direct observation of behaviors is a data collection method customarily used in clinical and educational settings. Repeated measures and small samples are inherent characteristics of observational studies that pose challenges to the numerical estimation of reliability for observational data. In this article, we review some debates about the use of Generalizability Theory in estimating reliability of single-subject observational data. We propose that it could be used but under a clearly stated set of conditions. The conceptualization of facets and object of measurement for a common design of observational research is elucidated under a different light. We provide two numerical examples to illustrate the ideas. Limitations of using Generalizability Theory to estimate reliability of observational data are discussed. 2007 Wiley Periodicals, Inc. Psychol Schs 44: 433,439, 2007. [source]