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International Review of
Mechanical Engineering - Papers
 Model of Chatter Vibrations and Stability Analysis of a Non-linear Wiper System
by S. Berger, P. Ragot, JJ. Sinou, E. Aubry
Abstract
- This paper presents a two dimensional phenomenological non-linear model of a windscreen wiper system. This non-linear model describes the instabilities arising from the frictional contact between the glass and the rubber. The objective of this paper is to illustrate the fact that a very simple non-linear phenomenological system may be used to model and simulate chatter vibrations for wiper systems stability analysis.
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords:
Friction, limit cycles, mechanical system, stability analysis, vibration.
Numerical Investigation of Moisture Diffusion Effects on Underfill within Flip-Chip Packages
by S. Ghosh, B. H. Dennis, Zhen-xue Han
Abstract
- In flip chip packages, the underfill between the solder and the package is generally used to improve the thermal performance and increase the thermal fatigue life. The underfill reduces the shear stresses induced in the package at reflow that is due to the thermal expansion coefficient mismatch between die and substrate. However, the underfill can be a significant source of stress when moisture is present. Prediction of the moisture concentration and resulting hygroscopic stresses are of particular importance for manufacturing processes that require high temperatures, such as lead free soldering. We numerically investigate the absorption process by solving a mathematical model for the time-dependant transport of moisture into the package through diffusion. Once the moisture concentration is known, we calculate the hygroscopic stresses due to the expansion of the underfill. The model is discretized using standard finite element analysis (FEA). We use the model to investigate the moisture sensitivity of two types of flip chip packages with underfill, the Flip Chip Ball Grid Array (FCBGA) and Flip-Chip on Board (F-COB). Also, we investigate the effects of the underfill amount on the package stresses, both for normal and shear stresses on the UBM (Underside Bump Metallurgy). Maximum stresses in the FCBGA package are determined by FEA for various amounts of underfill, for both hygroswelling loads during PCT (Pressure Cooker Test) and thermal loads that occur during reflow.
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords:
Moisture Diffusion, Hygroswelling, Electronic Package, Flip-Chip Package.
by M. Bouanini, A. Youcefi, B. Mebarki, L. Rahmani, O. Hami, B. Draoui
Abstract
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A large number of chemicals, biochemical or petrochemical industry operations are performed in stirred tanks or in mechanically agitated vessels. The optimum operating mode of these equipments requires a detailed knowledge of the hydrodynamic behaviour induced by the agitator. In this piece of work the characterization of the laminar viscous fluid flow fields in a cylindrical stirred tank is agitated by inclined blades anchor agitator studied. The computational fluid dynamic (CFD) model based on an implicit fractional step scheme and control volume method was developed for the spatial discretization of the Navier-Stokes, formulated in cartesian coordinates primitives variables (u, v, p, T) on unstructured triangular mesh. Some simulations of the flow around an anchor with straights blades allowed validating the used method. We have analyzed the influence of the tilt blades degree on the hydrodynamic flow behaviours, such as the stream function, the velocity field, the velocities components, and the power consumption. The comparison between some of the obtained results with literature data, have
showed a satisfactory agreement.
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords:
Agitated vessel, 2D modeling, Newtonian fluid, Laminar flow, Inclined blades anchor, Fractional step method, Finite volume.
Experimental and Numerical Analysis of the Scratch Behaviour of Steels: Description of the Effect of Work Hardening
by M. Mendas, M. Ben Tkaya, S. Benayoun, H. Zahouani, Ph. Kapsa
Abstract
- The scratch behaviour of three kind of steels witch one was work-hardened by uniaxial tensile tests until a three different values of deformation. In order to get rid of the indenter geometry effect, the representative deformation and the rheological factor X were used. To compare the results with analytical models, the hardness ratio was presented in function of the attack angle. In the aim of studying the effect of work hardening on the scratch behaviour of C45 steel, numerical simulations using ABAQUS/Explicit code were carried out for two cases of work-hardening. Furthermore, an examination by scanning electronic microscopy and optical interferometer of the ridges were performed. We show that, for steels slightly work-hardened, the shape ratio versus the factor X increase with a logarithmic law before being stabilized, towards a value of about 2.2 for X > 60. Lower values are observed for C45 steel with the annealed state. For attack angles between 0 and 30° the ratio of the normal hardness, Hn, with the indentation hardness, H, of these steels remains close to 1, except for C45 steel in the annealed state where for the weak ones b, Hn/H ~1.6. The ratio of the tangential hardness to the normal hardness is largely greater than 1 and decreases for the steels studied to reach 1,6 – 1,9. The apparent friction coefficient will be decomposed to the sum of three times the representative deformation plus the adhesive friction coefficient. The model developed made it possible to interpret the phenomena of microcutting observed on the scratch of strongly work-hardened C45 steel.
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords:
Scratch test, steels, hardness, friction, finite elements, damage.
Mechanical and Physico-Chemical Characterization of Ceramic-Metal Composites (kaolinite-aluminium)
by A. Ghorbel, J. Bouaziz, M. Fourati
Abstract
- The present work focuses on the study of the process of preparation and characterization of ceramic–metal composites. All the samples have been prepared from Kaolin and Aluminium powder. According to the study, it is shown that the experimental conditions revealed the effect on the mechanical properties and microstructure of composites: (the strength pressure, the percentage Aluminium doped on the Kaolinitic matrix and the sintering temperature). Sintered products are characterized by Electron Scanning Microscopy (SEM), MAS-NMR, X-Ray diffraction, Infrared Spectroscopy (IR); these have revealed the formation of new phases such as Silicon (Si), Corundum (α-Al2O3) and Mullite. The results of mechanical characterization have shown that the composites are hard and tenacious. Moreover, compression resistance of the composites is 6 times higher than that of the Kaolin sintered in the same conditions. Indeed, the flexural strength measured at room temperature is found to fall as Aluminium percent is decreased. Microstructure of the sintered also depends on the Kaolin/Aluminium ratio.
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords:
Composites, Mechanical and physico-chemical properties, Microstructure, Nuclear magnetic resonance (NMR), Sintering.
Turbulence Intensity Modeling of In-Cylinder Swirl Flow Using GA/SVD Designed Polynomial Neural Network
by K. Atashkari, N. Nariman-zadeh, A. Jamali
Abstract
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Some aspects of in-cylinder swirl flow in reciprocating internal combustions engine have been investigated employing Laser Doppler Velocimetry (LDV) and modelled using generalized GMDH-type (Group Method of Data Handling) neural networks. Genetic Algorithm (GA) and Singular Value Decomposition (SVD) are applied simultaneously for optimal design of both connectivity configuration and the values of coefficients involved in GMDH-type neural networks to model turbulence intensity of the swirl flow. In particular, the aim of such modelling is to show how the turbulence intensity changes with the variation of important parameters involved in the swirl flow. In this way, a new encoding scheme is presented to genetically design the generalized GMDH-type neural networks in which the connectivity configuration in such networks is not limited to adjacent layers. Such generalization of network's topology provides optimal networks in terms of hidden layers and/or number of neurons so that a polynomial expression for the turbulence intensity can be achieved consequently.
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords:
Swirl Flow, LDV, Genetic Algorithms (GAs), GMDH, SVD.
The Investigation of Flame Speed and Temperature in Flames of Aluminum Micro and Nano-Particle Clouds
by M. Bidabadi, N. Moallemi, A. Armin, I. Shafieenejad
Abstract
- In this paper, the effects of heat losses and particle size and on the flame speed and temperature profile in micro and nano dust combustion have been studied. The present work extended previous results by bridging the theories of the non-adiabatic stationary dust flame and the propagation of premixed flames in one-dimensional channels accounting for heat-losses to particles and environment. The results showed that the effects of heat losses played an important role in flame regimes and flame transition. Furthermore, it was found that convective heat losses significantly decreased the velocity of flame propagation and temperature in post-flame zone. Comparisons between the analytical solutions and the experiment results showed a good agreement.
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords:
Dust combustion, heat loss, nano particle, flame speed, non-adiabatic flame.
The Surface Morphology, Mechanical Characteristics and Corrosion Resistance of Plasma Sprayed Titanium Dioxide Nanostructured Coatings
by Z. Ahmad, M. Ahsan
Abstract
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Nanostructured titanium dioxide plasma sprayed coatings are the focus of attention because of their outstanding combination of properties. Most of the important information on their processing parameters and properties is proprietary and not reported. In this work, important information on mechanical properties, processing parameters and surface morphology combined with the new information arising out of the investigations on surface morphology, powder processing, corrosion and erosion studies is presented. The surface morphology and properties of nanostructured plasma sprayed coatings are high highly dependent upon critical spraying parameters. The surface morphology of nanostructured titanium dioxide coatings dictates their properties. The conventional titanium dioxide coatings showed a distinct layered structure and an uneven surface morphology compared to a more spherical morphology shown by nanostructured coatings. The nanostructured coatings showed a higher resistance to abrasion resistance, crack propagation and erosion resistance. The distribution of splats, intersplat spacing and volume of the fully melted zone and porosity controlled the properties as shown by scanning electronic microscopy and atomic force microscopy. The nanostructured coatings exhibited a high resistance to corrosion in 3.5% NaCl. Powder processing showed a significant effect on corrosion and erosion corrosion. Coatings employing densified powders showed a higher resistance to erosion corrosion than sintered and dried powders. The erosion corrosion resistance of nanostructured titanium dioxide coatings was controlled by surface morphology. Lower spraying temperatures favored increase photocatalytic activity.
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords:
Nanostructured coatings Air plasma spray, APS HVOF, splats, corrosion resistance.
Bucklewaves in Piezoelectrics with Cantor like Structure
by V. Chiroiu, L. Munteanu, M. Beldiman
Abstract
- The purpose of this paper is to study the bucklewaves in the piezoelectric plates with Cantor-like structure. The buckewaves are produced as a coupling between the buckling and the subharmonic axial waves in both phonon and fracton vibration regimes.
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords:
Bucklewave, Subharmonic waves, Photon and fracton vibration regimes.
Numerical Investigation of Internal Turbulent Flow Generated by A Flat-Blade Turbine and A Pitched-Blade Turbine in A Vessel Tank
by H. Kchaou, Z. Driss, G. Bouzgarrou, W. Chtourou, M. S. Abid
Abstract
- The hydrodynamic behaviours induced by a flat-blade turbine and a pitched-blade turbine in a stirred vessel were numerically predicted by considering a computational fluid dynamic model. Solutions of the Naviers-Stokes equations in conjunction with the standard k–ε turbulence model were developed using a control volume discretization method. In this paper, the result obtained by our code, such as average velocity and turbulent flow characteristics, were presented in different vessel planes. The comparison of the flow pattern has been presented to be compared with ones found by other researchers. The good agreement between the numerical results and the experimental data of agitated tank validate our proposed model.
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords:
CFD, 3D modelling, Turbulent, Flow, Flat-Blade, Pitched-Blade, Turbine.
Free Vibration of Helical Springs Using A Dynamic Finite Element Mesh Reduction Technique
by S. M. Hashemi, A. Roach
Abstract
- A Dynamic Finite Element (DFE) is developed to analyze the vibration characteristics of helical springs. The Dynamic Trigonometric Shape Functions (DTSF’s) of approximation space are developed from the exact solutions to the uncoupled equations governing axial and torsional vibrations of the system. By exploiting the principle of virtual work and the DTSF’s, the Dynamic Stiffness Matrix (DSM) of a uniform spring element is produced. The element matrices, exhibiting both mass and stiffness properties, are then assembled and the boundary conditions are applied to form the eigenproblem of the system. Based on the Sturm Sequence properties of the overall stiffness matrix, the well-known Wittrick-Williams algorithm is then used to evaluate the natural frequencies and modes of vibration of the system. Numerical checks are performed to confirm the accuracy and to ensure confidence for practical applicability and the performance of the DFE technique. The vibration characteristics of a uniform, cylindrical, helical spring with different boundary conditions are investigated. Numerical results on natural frequencies and convergence tests demonstrate the higher accuracy and superconvergent characteristics of the DFE and its superiority over the classical Finite Element Methods (FEM). Based on the numerical results, the DFE formulation can be justifiably called a Mesh Reduction Method (MRM).
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords:
Extension-Torsion Couplings, Dynamic Finite Element (DFE), Dynamic Stiffness Matrix (DSM), Finite Element Method (FEM), Geometrically Coupled Vibrations, Helical Springs.
An Explicit Triangular Shell Element
by L. T. Tenek
Abstract
- The present study introduces a 3-node triangular shell element, the element ET10, for the analysis of plates and shells. The triangular element is a flat element with 6 degrees of freedom at each node; three displacements and three rotations. The formulation is based on the Explicit Finite Element Method (E-FEM). All quantities, matrices, etc., are explicitly derived. We apply to the triangular shell element a number of modes and derive the diagonal Modal Stiffness Matrix, the diagonal Modal Mass Matrix and the diagonal Modal Geometric Matrix. The physical meaning of the diagonal modal matrices is that the modes are uncoupled. Temperature is accounted as an initial load. Numerical simulations are provided. Stress Wave Patterns are found in deforming plates and shells. Due to the explicit theory, the triangular element is suited for efficient computer implementation.
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords:
Triangular shell element, modes, modal matrices, stress wave patterns, computing.
Finite Element Model for Hyperelastic Axisymmetric Shells
by S. Abid, M. Ben Maatoug, A. Dhieb, F. Dammak
Abstract
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A finite element formulation is presented for the nonlinear analysis of axisymmetric thin shells in presence of two types of nonlinearities: geometric (large displacements and rotations) and material. As example of nonlinear material behavior, incompressible hyperelastic model in terms of principal stretches or invariants is considered. The finite element formulation is based on the cylindrical description. The element is validated by comparing the present results with the numerical and experimental solutions available in the literature.
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords:
Axisymmetric shells, Finite element method; Hyperelstic material, Nonlinear behavior.
Experimental Study of Synthetic Jets with Cross Flow in Boundary Layer
by F. Aloui, A. Kourta, S. Ben Nasrallah
Abstract
- The synthetic jet actuator is a low power, highly compact fluidic device which has potential application in boundary layer flow control. In this study, we have shown how synthetic jets work without cross flow and how effectively they modify the flow structure in the boundary layer. This paper describes the electrodynamics synthetic jet actuator used in our experiments. The experimental set-up for flow control using this type of actuator is detailed. The flowfield resulting from the interaction of a synthetic jet actuator and a quiescent environment and of synthetic jet actuator and a turbulent, flat-plate, zero pressure gradient boundary layer were examined via Particle Image Velocimetry (PIV) . The synthetic jet actuator was tested and two forcing amplitudes were investigated. Inspection of the phase-averaged velocity revealed that spanwise large-scale vortices are generated downstream of the slot and were persisting farther downstream.
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords:
Synthetic jet, vortex, turbulence,control.
Comparison of Optimum Finite Element Method vs. Differential Quadrature Method in Two-dimensional Heat Transfer Problem
by Md. Moslemuddin Fakir, S. Basri, R. Varatharajoo, A. A. Jaafar, A. S. Mohd. Rafie, D. L. A.Majid
Abstract
-
Among various numerical solution techniques, finite element method (FEM) and differential quadrature method (DQM) are two important of those. Usually elements are sub-divided uniformly in FEM (conventional FEM, CFEM) to obtain temperature distribution behavior in a fin or plate. Hence, extra computational complexity is needed to obtain a fair solution with required accuracy. In this paper, non-uniform sub-elements are considered for FEM (optimum FEM, OFEM) solution to reduce the computational complexity. Then this OFEM is applied for the solution of two-dimensional heat transfer problem in a rectangular thin fin. The obtained results are compared with CFEM and optimum DQM (ODQM, with non-uniform mesh generation). It is found that the OFEM exhibit more accurate results than CFEM and ODQM showing its potentiality.
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords:
Optimum finite element method, Optimum differential quadrature method, Heat transfer problem.
Numerical Flow and Heat Transfer in a Channel with Various Shaped Ribs
by M. Kanoun, M. Baccar, M. Mseddi
Abstract
-
A numerical investigation of convective heat transfer between a fluid and some physical obstacles (ribs) mounted on the lower wall (12 ribs) and on the upper wall (13 ribs) of a channel was conducted. This technique is used in the internal cooling of turbine blades. The governing equations have been solved in a two-dimensional domain using a control volume method and the SIMPLE algorithm for the velocity-pressure coupling is employed. Computation was made for three shaped ribs, rectangular, triangular and semicircular cross-sections. The flow Reynolds number for this numerical study is varied between 200 and 1000 and the Prandtl number is equal to 0.71. The rib height-to-channel hydraulic diameter, width-to channel hydraulic diameter and pitch-to-height ratio are fixed at h=0.214, w=0.74 and p=10, respectively. The grid is non uniform and is highly concentrated close to the rib to capture high gradient velocity, pressure and temperature. A uniform temperature through the ribs and all walls was assumed. We have determined distributions of velocity, friction factor, temperature and Nusselt number according to the shaped ribs and Reynolds numbers.
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords:
Forced convection, Heat transfer enhancement, Grooved channel, Finite volume method, Shaped ribs.
Multidisciplinary Optimization of a Structure with Temperature Dependent Material Characteristics, Subjected to Impact Loading
by F. J. Szabó
Abstract
- A macro has been developed for the analysis of structural behaviour for impact loads and has been integrated into a multidisciplanary optimization program written under the COSMOS/M finite element system. This macro makes possible to solve special types of multidisciplinary optimisation problems which could be very difficult or impossible to solve in any other program system. By using this method, it is possible to enlarge the application field of a finite element program system for the analysis of damages caused by winds, tornados, hurricanes, hails, traffic accidents, gun shots, etc. and for the optimization of special protection products (helmets, walls, covers, etc) against traffic or workplace accidents, natural disasters or terrorist attacks. Since during the usage of the macro all the features of the original finite element program system remain usable, it is possible to combine the impact loading with many special problems (nonlinear behaviour, electric or magnetic analysis, heat or fluid analysis, etc) and these problems can be integrated into a multidisciplinary optimization process. For the optimisation the author developed his new algorithm, the Random Virus Algorithm (RVA Algorithm), based on the simulation of reproduction process of biological or computer viruses. A numerical example of a wall subjeced to heating and impact load is presented.
Copyright © 2008 Praise Worthy Prize S.r.l. - All rights reserved
Keywords:
Multidisciplinary optimization, temperature dependent material characteristics, impact load, disasters, accidents.
 Pulsating Flows of Inelastic Fluids in Anisotropic Porous Viscoelastic Tubes
by K. Gueraoui, M. Taibi, A. Ghouli, A. Mrabti, G. Zeggwagh, Y. M. Haddad
Abstract
- A theoretical study concerning pulsatile flow of an inelastic fluid within anisotropic porous viscoelastic pipes is presented. The objective is to investigate the effects of porosity, transversal rotation and viscoelasticity of pipe wall material for a generalized Bingham fluid. An implicit difference method is used to solve the equations, and to determine the axial and radial velocity profiles, the pressure, the flow rate and the flow rate filtration distributions, the transversal rotation and the wall axial and radial displacement.
This study, considered as a step in modeling of flow in blood vessels, may also contribute to other important fields such as water desalination or gel filtration.
Copyright © 2008 Praise Worthy Prize S.r.l. -
All rights reserved
Keywords:
Pulsatile flow, implicit difference method, generalized Bingham fluid, anisotropic porous viscoelastic pipes.
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