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A Structure Based Synthesis Method for Disturbance Rejection

IFAC Proceedings Volumes 1998年第18期31卷 691-696页

作者： Jean-François Camart Basilio Del-Muro-Cuellar Michel Malabre Institut de Recherche en Cybernétique de Nantes UMR GNRS 6597 1 rue de la Noë B.P. 92101 44321 Nantes Gedex 03 France. Phone: (+33) 2 40 37 16 51. Fax: (+33) 2 40 37 25 22. ITESM-GEM Depto. de Ingeniera Mécanica Apdo. Postal 6-3 Atizapan Estado de México GP 52926 México

A new method for the synthesis of compensators which solve the disturbance rejection problem (either by state feedback or by output feedback) is presented. This method, based on structural and geometric approaches, provides solutions to the problem with the minimal number of unassignable poles (i.e. poles that are fixed due to the fact that this particular problem is been solved). Moreover, all the poles that remain assignable are relocated to values selected by a non expert user, without any required knowledge of the proposed programs. Une nouvelle méthode de synthèse de compensateurs solutions du problème du rejet de perturbation, soit par retour d'état soit par retour de mesure, est proposée. Cette méthode, basée sur les approches géométrique et structurelle, permet de résoudre le problème (s'il est soluble) avec le minimum de pôles imposés par cette résolution. De plus tous les autres pôles sont placés aux valeurs indiquées par un utilisateur non expert de ces méthodes.

关键词： Linear Systems Disturbance Rejection Dynamic Output Feedback State Feedback Geometric Approach Fixed Poles Pole Assignment numerical algorithms

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Computation of Solutions of the DAP Using Optimization Methods

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IFAC Proceedings Volumes 1998年第20期31卷 859-864页

作者： M. Mitrouli J. Leventides N. Karcanias E. Milonidis Department of Mathematics University of Athens Panepistimiopolis Kaisariani 15784 Athens Greece Department of Economics University of Athens Pesmazoglou 8 Athens Greece Department of Electrical Electronic and Information Engeneering Control Engineering Center City University Northampton Square London ECl V 0HB U.K

Linear Control Theory problems such as those of pole assignment by state, output feedback (centralised or decentralised), and zero assignment by input, or output squaring down may be reduced to a standard common problem known as the Determinantal assignment Problem (DAP) Giannakopoulos (1985). The aim of this paper is to develop and compare optimization algorithms for the computation of solutions of DAP. The developed numerical approaches may be used as a basis of a design technique centered around the frequency assignment problems.

关键词： Determinantal Assignment Problem Optimization techniques numerical algorithms

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On convergence of "divide the best" global optimization algorithms

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Optimization 1998年第3期44卷 303-325页

作者： Sergeyev, Yaroslav D. ISI-CNR c/o DEIS University of Calabria Rende - Cosenza Italy Nizhni Novgorod State University Nizhni Novgorod Russian Federation

In this paper a new class of multidimensional global optimization algorithms (called "divide the best" algorithms) is proposed. The class unifies and generalizes the classes of the characteristic methods and the adaptive partition algorithms introduced by Grishagin and Pinter respectively. The new scheme includes also some methods which do not fit either the characteristic or the adaptive partition families. A detailed convergence study is presented. A special attention is paid to cases where sufficient conditions of everywhere dense, local and global convergence are fulfilled only over subregions of the search domain. © 1998 OPA (Overseas Publishers Association) N.V. Published by license under the Gordon and Breach Science Publishers imprint.

关键词： Convergence Global optimization numerical algorithms

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General numerical scheme for heat exchanger thermal analysis and design

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Computer Applications in Engineering Education 1998年第4期5卷

作者： Robert J. Ribando Gerald W. O'Leary Susan Carlson-Skalak Department of Mechanical Aerospace and Nuclear Engineering School of Engineering and Applied Science University of Virginia Charlottesville Virginia 22903-2442

This article describes two personal computer–based teaching modules designed to instruct engineering students in the more fundamental thermal aspects of the analysis and design of heat exchangers. One module applies to shell-and-tube exchangers; the other applies to cross-flow types. Enhanced numerical algorithms solve discretized forms of the governing differential energy-conservation equations. Graphical user interfaces display temperature distributions along with traditional design and performance measures. © 1997 John Wiley & Sons, Inc. Comput Appl Eng Educ 5: 231–242, 1997

关键词： heat exchangers engineering education design performance numerical algorithms graphical user interface

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A spectral method for numerical elastodynamic fracture analysis without spatial replication of the rupture event

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JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 1997年第8期45卷 1393-1418页

作者： Cochard, A Rice, JR HARVARD UNIV DEPT EARTH & PLANETARY SCICAMBRIDGEMA 02138

Perrin et al. (1995) and Geubelle and Rice (1995) have introduced a spectral method for numerical solution of two- and three-dimensional elastodynamic fracture problems. The method applies for ruptures confined to a plane separating homogeneous elastic half spaces. In this method, the physical variables, such as the traction components of stress and displacement discontinuity on the rupture plane, are represented as Fourier series in space with time-dependent coefficients. An analytical solution is found for each Fourier mode, in that each Fourier coefficient for stress is expressed by the time convolution of the corresponding coefficient for displacement with a convolution kernel specific to the rupture mode. Once the 2D formulation of the method is known, the method is readily generalizable to 3D problems in that it involves only linear combinations of the convolution kernels found for each rupture mode in 2D. This conceptual simplicity has, however, a major drawback: due to the Fourier series representations of the physical variables, the problem solved is in fact an infinite and periodic replication of rupture events on the fracture plane. So, in order to study the evolution of a single rupture, one has to use a spatial period large enough in order that the waves coming from the replication cracks do not enter the zone of interest during the time duration studied, or provide negligible stress alteration when they do arrive. We show here how to rigorously offset this defect while retaining the modal independence. Once expressed in the spatial domain, the method amounts to truncating in space the space-time convolution kernels, in a manner that provides an exact evaluation for all positions within the rupture domain (where the constitutive law between stress and displacement discontinuity is to be imposed), but not outside. In order for the method to be identical in structure to the method of Perrin er al. (1995) and Geubelle and Rice (1995), the period of the Fou

关键词： dynamic fracture crack mechanics fault dynamics numerical algorithms

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Representative volume element size for elastic composites: A numerical study

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JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 1997年第9期45卷 1449-1459页

作者： Gusev, AA Departement Werkstoffe Institut für Polymere ETH Zentrum CH-8092 Zürich Switzerland

Monte Carlo (MC) runs are employed to generate statistically independent realizations of a periodic elastic composite with a disordered unit cell made up of 8, 27, and 64 nonoverlapping identical spheres. In the limit of an infinite number of spheres in the disordered unit cell, this periodic composite obeys the Percus-Yevick hard-sphere statistics. By construction, the MC realizations studied have the same inclusion fraction. A constant-strain-tetrahedra displacement-based finite element code with an iterative solver is used to calculate the overall elastic constants of these periodic MC realizations. It appears that the scatter in the individual elastic constants already obtained with a few dozen spheres in the disordered unit cell is remarkably small and the averages obtained with varying numbers of spheres are practically stationary. (C) 1997 Elsevier Science Ltd.

关键词： microstructures constitutive behavior elastic material inhomogeneous material numerical algorithms

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General numerical scheme for heat exchanger thermal analysis and design

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COMPUTER APPLICATIONS IN ENGINEERING EDUCATION 1997年第4期5卷 231-242页

作者： Ribando, RJ OLeary, GW CarlsonSkalak, S UNIV VIRGINIA SCH ENGN & APPL SCIDEPT MECH AEROSP & NUCL ENGNCHARLOTTESVILLEVA 22903

This article describes two personal computer-based teaching modules designed to instruct engineering students in the more fundamental thermal aspects of the analysis and design of heat exchangers. One module apples to shell-and-tube exchangers;the other applies to cross-flow types. Enhanced numerical algorithms solve discretized forms of the governing differential energy-conservation equations. Graphical user interfaces display temperature distributions along with traditional design and performance measures. (C) 1997 John Wiley & Sons, Inc.

关键词： heat exchangers engineering education design performance numerical algorithms graphical user interface

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Multiprocessing ocean circulation: Modeling, implementation, and performance on the Intel Paragon

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JOURNAL OF SUPERCOMPUTING 1997年第4期10卷 349-369页

作者： Ahmad, I Leung, KC Hsu, HM NATL CTR ATMOSPHER RES BOULDERCO 80307

In this paper we present the modeling and implementation of a grand challenge problem in the field of scientific computation: the primitive-equation numerical ocean circulation model. We present the mathematical formulation of the model and propose a scheme for its parallel implementation. Optimizations are made through collective communications and various partitioning schemes. In our experiments, which use up to 100 processors on the Intel Paragon parallel computer, the proposed strategy yields an encouraging speedup and exhibits a sustained scalability with increasing problem and machine sizes. We consider barotropic continental shelf waves in a periodic channel as a test problem. The model has numerous applications in environmental studies and ocean sciences.

关键词： high-performance computing parallel applications partial differential equations partitioning numerical algorithms numerical ocean circulation scientific computation

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Assessing the impact of the new Athens airport to urban air quality with contemporary air pollution models

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ATMOSPHERIC ENVIRONMENT 1997年第10期31卷 1497-1511页

作者： Moussiopoulos, N Sahm, P Karatzas, K Papalexiou, S Karagiannidis, A ARISTOTELIAN UNIV THESSALONIKI LAB HEAT TRANSFER & ENVIRONM ENGN THESSALONIKI 54006 GREECE

The new airport of Athens will be constructed in the Spata area to the east of the Athens basin. In an attempt to study how the airport operation influences air quality in Athens, the wind how and pollutant transport in the Athens basin and the Spata area are studied by applying a set of contemporary models, all constituents of the EUMAC Zooming Model (EZM): (1) the nonhydrostatic prognostic mesoscale model MEMO for simulating air flow and the dispersion of inert pollutants, and (2) two photochemical dispersion models, the three-dimensional model MARS and the three-layer model MUSE for describing the dispersion of reactive pollutants. Simulations were performed for meteorological conditions favouring the occurrence of air pollution episodes. Emphasis is put on the influence of the airport emissions on air quality assuming that the airport is operating either at its old location (Hellenikon) or at Spata Comparison of simulation results for one selected scenario achieved with all three models reveals similar diurnal variation's of nitrogen oxides in the Athens basin and the Spata area. The model results show that under conditions favoring air mass penetration from Athens to the Spata area the resulting pollutant transport causes an increase in air pollution levels without, however, leading to the exceedance of air quality standards. In the opposite case, the pollutant transport cannot have a noticeable adverse influence on the Athens air quality because of both the relatively high urban air pollution levels and the fact that the penetration depth is small. (C) 1997 Elsevier Science Ltd.

关键词： air pollution modeling numerical algorithms airport emissions comparison with measurements

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Mode III stress intensity factor ahead of a rough crack

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JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 1997年第5期45卷 853-872页

作者： Vandembroucq, D Roux, S ECOLE SUPER PHYS & CHIM IND VILLE PARIS LAB OPT PHYSUPR 05 CNRSF-75231 PARIS 05FRANCE

The static stress field in the vicinity of a rough crack in mode III is studied via a conformal mapping technique. This purely geometrical method (friction effects are not studied) proves a direct and efficient way of solving the displacement field numerically for any prescribed geometry. It also leads to an analytical framework which is suited to a perturbation expansion for a small roughness amplitude. It is shown that the local stress intensity factor (SIF) at the crack tip differs from the ''far field'' SIF by a correction term which depends quadratically on the roughness amplitude. The Leading correction term, which is derived analytically, consists of two parts: (i) a local systematic term, which decreases the local SIF, is directly related to the orientation of the crack tip compared to its mean orientation;(ii) a second contribution which is non-local. In the case of a self-affine geometry, the second term has a non-zero average that also contributes to decrease the local SIF. Hence the mean local SIF is smaller than the far-field value, which induces a ''strengthening'' effect. The fluctuation amplitude due to both terms has the same dependence as the mean systematic decrease. Both effects are controlled by the lower scale cut-off of the self-affine regime. (C) 1997 Elsevier Science Ltd.

关键词： stress intensity factor crack mechanics elastic material analytic functions numerical algorithms

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