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International Review on Modelling and Simulations - August 2008 - Preface and acknowledgments
International Review on Modelling and Simulations - August 2008 - Papers
International Review on Modelling and Simulations - Preface and acknowledgments
by the Editor-in-Chief Santolo Meo
International Review on Modelling and Simulations - Papers
by A. Messabhia, N. Hassounet, J. Dufau
Abstract - A correct diagnosis is a key- step during the evaluation of the real causes leading to concrete works degradation. This task requires specific evaluation of the concrete behavior phenomenon, especially, when the structure is exposed to an aggressive environment. Understanding the causes of an unspecified deterioration of the concrete remains a complex subject as it is related to the interaction between various pathologies. In the present investigation an attempt is made to develop a Knowledge base that will organizes, rationalizes and optimizes the process of decision-making during a diagnosis on concrete works, by providing to the user the information, the reasoning and the most recent know-how related to the material’s behavior that leads to structural degradations. The proposed Knowledge base is based on sets of rules which can be exploited directly by the user or coupled to an inference engine incorporated in an expert system, which makes use of an integrated and systematic approach based on the artificial intelligence techniques. The decision making process could also be enhanced by a recommendation’s module that proposes the most appropriate solution to the defined degradation. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Concrete degradation, Knowledge base, Expert system.
Abstract - The paper deals with a new Maximum Power Point Tracking (MPPT) algorithm for photovoltaic power systems. The proposed MPPT is based on temperature measurement and is implemented on a quasi-resonant boost converter to maximize the photovoltaic output power. The proposed MPPT algorithm shows better stability in steady-state conditions and improved dynamic response, respect to the classical MPPT methods. The power obtained from the PV generator is also increased. At end, the suggested algorithm presents intrinsic self-starting capability. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Photovoltaic energy, converter, MPPT, ZVS.
Abstract - The aim of this work is to diagnosis of mixed eccentricity in the squirrel cage asynchronous machine. These machines are well known to be tough, and adapted for high power applications. However, it is not unusual that these machines present some failures from premature aging. The study of the phenomena created on the various sizes in time of the machine by such defect, and more particularly the order harmonics appearing during the failure to define them as identifier such analyses have been lacking. The contribution to this work, the calculation of inductances is derived from the stored magnetic energy in the air gap assuming an infinite permeability iron. Simulation result confirms the validity of proposed method. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Diagnosis, Eccentricity, Asynchronous Machine, Simulations.
Abstract - This paper presents an analytical approach to modelling radial magnetic force acting on stator surface of induction motors, this model covering the most important causes of magnetic noise such as saturation, eccentricity, slots and winding distribution. The study of magnetic noise due to eccentricity is given, which demonstrate the adverse effect of this phenomena, often occurring due to production. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Magnetic noise, Eccentricity, Permeance, Magnetomotive force, Radial force, Modes, natural frequency.
Abstract - Transmission network expansion is an important part of power system planning. Uncertainties in the procedures of planning are rapidly increasing within new restructured power systems. As a result, new methodologies of Transmission Expansion Planning should be developed. In this paper a Hybrid Method along with four other algorithms, namely, Union method, Substitution Method, Generalized Backward Method, and Genetic Algorithm Method are proposed. It is demonstrated that the plans developed under these schemes are robust for all scenarios in spite of the uncertainties observed in all cases. Moreover, the solution is economical and applicable to large scale systems. The proposed methods have been successfully tested for three typical power systems, namely, a 6-bus and an 87-bus test system as well as the Iranian Power Grid, as a practical and large scale transmission. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Uncertainties, Transmission Augmentation, Genetic Algorithm, Scenario Approach.
Abstract - In this paper, we have investigated the impact of the dynamic magnetic hysteresis on the induced currents. The method used combines a finite element method and a numerical procedure capable of analyzing dynamic hysteresis in axial-symmetric problems. The ferromagnetic hysteresis is described by Jiles-Atherton model. This model is integrated in finite element method (FEM) in order to resolve magneto-dynamic problems. The interface between the Jiles-Atherton model and the finite element magnetic vector potential formulation is introduced through the fixed-point iterative technique. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Finite element, Hysteresis, Magnetodynamic, Jiles–Atherton model.
Abstract - An exact solution to the boundary value problem of multiple scattering by M parallel two-layer elliptic cylinders, based on the separation of variable technique and the addition theorem for Mathieu function is presented. It is expressed in terms of a system of simultaneous linear equations of infinite order. Numerical results for the special case of two parallel two-layer cylinders are presented and discussed for several geometrical cases and material parameters. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Scattering, Parallel Two-Layer Elliptic Cylinders, Metamaterials.
Abstract - Artificial neural networks are becoming increasingly popular in engineering applications due to their exceptional abilities in solving non-linear problems, a field where conventional computational techniques under-perform or even fail. In power electronics in particular, neural networks have been employed in a range of adaptive control, optimisation and estimation tasks. This paper presents a novel method for the optimal control of full-bridge DC-to-AC converters, based on a fully digital feed-forward neural network structure. The aim is to produce a set of switching patterns that control the fundamental of the output voltage, while suppressing a selected set of harmonics. A simple neural network is initially presented with a very small set of examples, partly describing the required behaviour. After a brief training period, the structure of the network is transferred to the pulse width modulator. The circuit can easily be adapted to suit different requirements, even during operation and can be implemented in a variety of different methods, such as using gate array integrated circuits, conventional microprocessors or digital signal processing hardware. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: PWM, DC-AC Converters, Neural Network applications.
Abstract - This paper presents a fast algorithm to compute the 8x8 Discrete Cosine Transform (DCT), using a new lossless encoding which partially overcomes the quantization error of digital implementation due to finite-precision effect. The proposed encoding scheme, Algebraic Integer Quantization (AIQ), is achieved by obtaining the exact representation of the irrational matrix elements with algebraic integers, allowing “error-free map¬ping” of the transcendental functions. As a result, the Discrete Cosine transform can be realized as an Integer transform. It also capitalizes the symmetry of the transform matrix resulting in very fast, hardware-efficient, parallel, and multiplication-free archi¬tectures. A comparative study with the simplified integer transform, adopted in H.264, is also presented, and the results show that using the proposed encoding scheme, we can achieve comparably better performance with reduced hardware cost. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Discrete Cosine Transform, Advanced Video Coding, H.264, Error-Free Computation.
Abstract - The paper presents a solution for increasing the efficiency of the photovoltaic conversion. The aim is to design the tracking system that adjusts the position of the PV module for maximizing the incident solar radiation. The energetic efficiency is evaluated considering also the energy consumption for orientation. The design of the tracking system is approached as a mechatronic concept, integrating the mechanical model with the electronic control system at the virtual prototype level. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Photovoltaic Module, Tracking Mechanism, Control System, Virtual Prototype.
Abstract - Elevated liquid-storage tanks are commonly built with a combined vessel consisting of a truncated cone and a superimposed top cylindrical cap. As a result of the inclination of the walls of the conical segment, compressive meridional stresses are induced in the shell by the hydrostatic pressure of the contained fluid and the hydrodynamic pressure associated with vertical ground excitation. The current paper aims at identifying the dynamic characteristics of liquid-filled combined tanks subjected to vertical ground excitation. Numerical analysis is conducted based on a coupled finite-boundary element formulation that accounts for the fluid-structure interaction associated with this type of analysis. A mechanical analog is developed to simulate the seismic response of liquid-filled combined vessels to vertical base excitation. The mass of the contained fluid is idealized as rigid and flexible components connected by a linear spring that represents the flexibility of the vessel walls. The proposed analog provides a simplified tool to predict seismically-induced shell forces due to the vertical component of earthquake excitation. In addition, the analog can be used to evaluate the maximum overall forces acting on the supporting structure. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Combined Shells, Axisymmetric, Hydrodynamic, Seismic, Fluid-Structure Interaction.
by Y. Benlalli, A. E. Hadjadj, D. Khalfa
Abstract - The lubrication is an essential element for the good working of the rolling. It has for objective to interpose a lubricant between the rolling bodies and the runway, in order to avoid the wear of the elements made of contact metal / metal between stationary and mobile parts that generate fast grippages of the surfaces in look whose repercussions are always catastrophic. The objective of this research is to put in evidence the optimal quantity of oil in a rolling and it impact on its life span. Tests of simulation are elaborated as well as the experiences on the rolling. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Ball-bearing, Movie of oil, Lubrication Elastohydrodynamic, Life span, Viscosity.
by A. F. Boudjabi, A. Bellaouar, M. Lachi, M. Bensouici
Abstract - The present study relates to the numerical simulation of biphasic flow in continuous casting machine. Molten steel and non–metallic inclusions constitute in the tundish, a nonreactional state of the two phases liquid and solid. Two approaches can be applied to study the removal phenomena of harmful particles. A physical approach based on a water modelling method with respect to some important similarity conditions between molten steel and water. The second one is a numerical approach which is often considered in order to take account of certain phenomena not elucidated by physical modelling. The numerical code “Fluent “is applied. Non-metallic inclusions are the Al2O3 alumina and they are considered in this study to be of spherical form. Their trajectories in the tundish are calculated for various diameters from 10 to 150 m. They are simulated in the case of the water model by a tracer. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Biphasic flow, numerical simulation, convective transfer, continuous casting, molten steel, water model, inclusion removal.
Abstract - In this paper a comprehensive model of a tracker system including derive subsystem is presented. Since the main part of the under consideration system consists a two Degree-Of-Freedom (DOF) gimbal subsystem, at first, the model of a two-axis gimbal is considered. For this purpose, after introducing the coordinate systems and different transformation matrices, the related equations of pitch and yaw axes by considering the friction torques, mass unbalances and cable restraint torques are derived. Moreover, all disturbance terms and the methods for their reduction or elimination are investigated. Then, the derive system of the gimbal including a DC motor with a gear is modeled and governing overall equations of the whole system is obtained. In order to have a model with practical considerations, the model of rate gyro which is used for measuring the angular velocities is also included. Finally, the simulation results of the under consideration case study by using the derived comprehensive dynamical equations of this paper are provided. Analysis of these results are used to synthesis the behavior of the practical system and choosing the suitable control structure in order to achieve stabilization and tracking objectives. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Tracker system, Two DOF gimbal system, Euler equations, Stabilizer.
Abstract - This paper deals with the behavior of an idealized multilayer structure representing an idealized pavement, observed using a numerical simulation. The investigated layered structure is constituted by the asphalt layer commonly called the road made of bituminous material, a layer of clean aggregate (gravel) and a foundation layer of soil mass. The numerical model was developed with respect to the geometry, dimensions, boundary and loading conditions of a physical model investigated by a previous researcher. After validation, the numerical model was used in a parametric study to show the effect of different parameters as the Young’s modulus of the materials, the temperature effect and the type of loading. Emphasis was put upon the behavior of the structures when subjected to static and cyclic loadings induced by the normalized stress of a wheel. The irreversible deformation of the road surface, usually called rutting was investigated. Out of this numerical exercise it was found that the deflection associated with rutting, considered as a residual displacement, is mainly due to the effect of the cyclic loading of the structure. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Pavement, Numerical model, Interface, rutting.
Abstract - This paper presents a new formulation based on generalized benders decomposition approach to solve thermal unit commitment problem. This new approach decomposes the problem into a master problem and a sub-problem. The master problem is an integer program and sub-problem is a nonlinear program. The master problem applies the integer programming method to solve (Unit Commitment) UC and finds proper on/off states of the units. In the proposed approach, the sub-problem is modeled as a nonlinear problem and it uses the outputs of master problem to form appropriate cuts and adds them to the master problem for solving the next iteration of UC. Appropriate formulations of constraints for both parts of problem are presented. The results obtained, considering a commonly used system, show the efficiency of this approach in comparison with other methods. Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords: Benders decomposition, mixed integer programming, unit commitment.
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