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Prediction Techniques (prediction + techniques)

Distribution by Scientific Domains

Engineering	75%

Selected Abstracts

An overview of the damage approach of durability modelling at elevated temperature

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 6 2001
J.-L. Chaboche
Lifetime prediction techniques for components working at elevated temperature are revisited. Two damage approaches in which time effects at high temperature are introduced in different ways are discussed in greater detail. First, a creep,fatigue damage model considers the interaction of the two processes during the whole life before macrocrack initiation; and second, a creep,fatigue,oxidation model separates the fatigue life into two periods: during initiation the environment-assisted processes interact with fatigue, although bulk creep damage only interacts during the micropropagation period. The second model is illustrated by its application to a coated single-crystal superalloy used in aerojet turbine blades. Its capabilities are illustrated in a number of isothermal and thermomechanical fatigue tests. Anisotropy effects are also briefly discussed and a special test, introducing cyclic thermal gradients through the wall thickness of a tubular component, demonstrates the predictive capabilities for actual engine conditions. [source]

Toward accurate hybrid prediction techniques for cavity flow noise applications

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2009
W. De Roeck
Abstract A large variety of hybrid computational aeroacoustics (CAA) approaches exist differing from each other in the way the source region is modeled, in the way the equations are used to compute the propagation of acoustic waves in a non-quiescent medium, and in the way the coupling between source and acoustic propagation regions is made. This paper makes a comparison between some commonly used numerical methods for aeroacoustic applications. The aerodynamically generated tonal noise by a flow over a 2D rectangular cavity is investigated. Two different cavities are studied. In the first cavity (L/D=4, M=0.5), the sound field is dominated by the cavity wake mode and its higher harmonics, originating from a periodical vortex shedding at the cavity leading edge. In the second cavity (L/D=2, M=0.6), shear-layer modes, due to flow-acoustic interaction phenomena, generate the major components in the noise spectrum. Source domain modeling is carried out using a second-order finite-volume large eddy simulation. Propagation equations, taking into account convection and refraction effects, are solved using high-order finite-difference schemes for the linearized Euler equations and the acoustic perturbation equations. Both schemes are compared with each other for various coupling methods between source region and acoustic region. Conventional acoustic analogies and Kirchhoff methods are rewritten for the various propagation equations and used to obtain near-field acoustic results. The accuracy of the various coupling methods in identifying the noise-generating mechanisms is evaluated. In this way, this paper provides more insight into the practical use of various hybrid CAA techniques to predict the aerodynamically generated sound field by a flow over rectangular cavities. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Prediction of the gap of electromagnetic band gap structures in a parallel-plate waveguide environment

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 8 2010
Shahrooz Shahparnia
Abstract In this article the design, fabrication, and testing of several electromagnetic band gap (EBG) structures used to mitigate switching noise in high speed printed circuit boards is presented. Some features of these surfaces are considered as variables and results from different band gap prediction techniques are compared to actual fabricated parallel plate waveguides. The strength and weaknesses of these prediction techniques is shown and the power of full wave analysis to predict the band gap of these EBG structures and the limitation of simple L - C models are discussed. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1792,1795, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25327 [source]