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 Volume 6, 2011
Print ISSN: 1991-8747
E-ISSN: 2224-3429








Issue 1, Volume 6, January 2011

Title of the Paper: Mitigation Assessment of Passive Seismic Protection


Authors: Ioana Ladar, O. Prodan, P. Alexa

Abstract: The intended contribution proposes a versatile approach of assessing the efficiency of seismic mitigation of passive seismic protection – via supplemental damping - of steel multi storey type structures. The efficiency of seismic mitigation is expressed in terms of reduction in the amplitudes of kinematical parameters (top lateral displacements, in this case) associated to seismically induced vibratory motion of the analyzed structures. The proposed approach may be applied to other parameters (story drifts, induced velocities and accelerations, ductility coefficients) describing static and kinematical states of steel skeletal structures seismically acted upon. The proposed parameter for assessing efficiency of seismic protection is associated to the mitigation interval of steel frame type structures equipped with passive protection (viscous dampers). This interval is expressed in terms of both, time and fundamental natural period of vibrations of the structure and is considered from the moment when the vibratory motion is initiated till the moment the motion reaches its (approximate) steady state. During this time interval, a clear picture of vibratory motion is exhibited: length of the interval, number of vibratory cycles, amplitudes, their variation / decrease in time, the end of transitory motion and the beginning of the (short, nevertheless) induced pseudo - steady state motion. The intended contribution proposes a time variable parameter that synthesizes all these features of the transitory motion. The length of this interval is expressed in number of natural fundamental periods of vibrations and together with its descending slope emphasizes the effectiveness of seismic protection. The shorter is the interval and the greater is its descending slope, the more effective is the associated seismic protection. Time history type analyses have been carried out on several sets of skeletal steel structures. The structures are analyzed in two cases: without seismic protection (reference structure) and equipped with passive seismic protection (viscous dampers). The numerical results of time history analyses refer to the variation of top lateral displacements ant the top lateral (induced) accelerations. The results are presented and discussed with reference to the proposed parameter assessing seismic mitigation. The time variation of the proposed parameter is presented graphically for a better and immediate “physical” perception. The effectiveness of the seismic passive protection is discussed in terms of proposed parameter.

Keywords: Steel skeletal structures, viscous dampers, time history analysis, seismic mitigation curves

Title of the Paper: Dynamic Behavior of a Valve Train System in Presence of Camshaft Errors


Authors: M. Tounsi, F. Chaari, L. Walha, T. Fakhfakh, M. Haddar

Abstract: In this paper a dynamic model of cam-follower-rocker-valve system is presented. The lumped parameters model is with 8 degrees of freedom. Camshaft eccentricity and cam profile errors are also modeled and can be introduced in the model to observe their influence. The numerical simulation shows a fluctuation on the acceleration of the valve induced by the motion law exerted by the cam follower mechanism. The presence of eccentricity on camshaft showed a slight influence on the dynamic behavior whereas the cam profile error showed a substantial increase in the vibration levels.

Keywords: Cam follower , valve train , dynamic behavior, eccentricity, profile error

Title of the Paper: Vibration Response of Sandwich Plate Under Low-Velocity Impact Loading


Authors: M. Wali, M. Abdennadher, T. Fakhfakh, M. Haddar

Abstract:The vibration response of sandwich panels, under low-velocity impact, is presented by using finite element method (FEM) and Hertz contact low. The vibrations on the sandwich plate under the impact are evaluated using the Wigner-Ville distribution. As a result, by formulating a simple model involving the motion of a rigid impactor combined with dynamic equation of sandwich plate, the effect of initial impact velocity and the geometric properties of plate are identified. This numerical simulation that determine the impact force and estimate the behaviour under impact would be very helpful during the sandwich structures design.

Keywords: Low-velocity, Impact, Hertz contact law , Impact force, Wigner-Ville distribution, Indentation

Title of the Paper: Parallel-Sparse Symmetrical/Unsymmetrical Finite Element Domain Decomposition Solver with Multi-Point Constraints for Structural/Acoustic Analysis


Authors: Siroj Tungkahotara, Willie R. Watson, Duc T. Nguyen, Subramaniam D. Rajan

Abstract: Details of parallel-sparse Domain Decomposition (DD) with multi-point constraints (MPC) formulation are explained. Major computational components of the DD formulation are identified. Critical roles of parallel (direct) sparse and iterative solvers with MPC are discussed within the framework of DD formulation. Both symmetrical and unsymmetrical system of simultaneous linear equations (SLE) can be handled by the developed DD formulation. For symmetrical SLE, option for imposing MPC equations is also provided. Large-scale (up to 25 million unknowns involving complex numbers) structural and acoustic Finite Element (FE) analysis are used to evaluate the parallel computational performance of the proposed DD implementation using different parallel computer platforms. Numerical examples show that the authors’ MPI/FORTRAN code is significantly faster than the commercial parallel sparse solver. Furthermore, the developed software can also conveniently and efficiently solve large SLE with MPCs, a feature not available in almost all commercial parallel sparse solvers.

Keywords: Domain Decomposition Solver, Multi-Point Constraints, Parallel Computation, Symmetrical / Unsymmetrical Simultaneous Linear Equation, Finite Element Analysis, Acoustic/Structural Engineering Applications, Iterative Algorithms, Sparse Assembly, Sparse Factorization

Issue 2, Volume 6, April 2011

Title of the Paper: Dynamic Analysis of Cracks Running at a Constant Velocity in a Strip


Authors: Jia-Yen Huang

Abstract: The scattering of a time-harmonic anti-plane shear (SH) wave by finite length cracks with constant velocity in an elastic medium is considered. In the first case, cracks are assumed to propagate in an infinite elastic space. In the second case, the problems of propagation of subsurface crack and edge crack propagating with uniform velocity in a half-space are treated. In the third case, based on the extension of the dislocation model and images method for the free surface, an analysis of the scattering of SH waves by cracks moving in a strip is carried out. The effects of the wave number, crack velocity and relative position of the cracks are presented. The dynamic stress intensity factors (SIFs) are numerically computed and the results are shown graphically.

Keywords: Finite length moving cracks, Antiplane shear waves, Galerkin numerical method, Colinear cracks, Half-space, Strip

Title of the Paper: Numerical Simulation Analysis for Thermal Optimization of Heat Affected Zone (HAZ) in GMAW Process


Authors: Ali Moarrefzadeh

Abstract: In this paper, the Gas Metal Arc Welding is studied and temperature field is gained in this process. Thermal effects of Gas Metal Arc (GMA) and temperature field from it on workpiece (copper) and shielding gas type, is the main key of process optimization for GMAW. Energy source properties of GMA strongly depend on physical property of a shielding gas. In this paper, carbon dioxide (CO2) was used as an alternative gas for its low cost. The basic energy source properties of CO2 GMA were numerically predicted ignoring the oxidation of the electrodes. It was predicted that CO2 GMA would have excellent energy source properties comparable to that of He, Ar GMA. The numerical results show the time-dependant distributions of arc pressure, current density, and heat transfer at the workpiece surface are different from presumed Gaussian distributions in previous models.

Keywords: Finite-Element, Copper, Shielding gas, Argon, Helium, CO2, GMAW/MIG

Title of the Paper: The Nature of Instabilities in Blocked Media and Seismological Law of Gutenberg-Richter


Authors: B. P. Sibiryakov, B. I. Prilous, A. V. Kopeykin

Abstract: This paper studies properties of a continuum with structure. The characteristic size of the structure governs the fact that difference relations do not automatically transform into differential ones [1]. It is impossible to consider an infinitesimal volume of a body, to which we could apply the major conservation laws, because the minimal representative volume of the body must contain at least a few elementary microstructures. The corresponding equations of motions are the equations of infinite order, solutions of which include, along with sound waves, the unusual waves propagating with abnormal low velocities, not bounded below. It is shown that in such media weak perturbations can increase or decrease outside the limits. The variance of structure sizes plays a double role. The intensity of instabilities decreases due to dispersion, thereby stabilizing the media, while the frequency range of unstable solutions expands, and disasters can occur at very low frequencies. The equation of equilibrium is not satisfied at any point in the medium. It is true only at an average. Hence there is a possibility to have a lot of micro-dynamic acts, in spite of static macroscopic state in average. This paper describes some of the conditions under which the possible occurrence of usual wave motion in media in the presence of certain dynamic phenomena. The number of complex roots of the corresponding dispersion equation, which can be interpreted as the number of unstable solutions, depends on the specific surface cracks and is an almost linear dependence on a logarithmic scale, as in the seismological law of Gutenberg-Richter.

Keywords: Specific surface, Operator of continuity, Equation of motion, Catastrophes, Structured media, Gutenberg–Richter law

Title of the Paper: Ahead Prediction of Kinematics of Vehicles under Various Collision Circumstances by Application of ARMAX Autoregressive Model


Authors: Witold Pawlus, Hamid Reza Karimi, Kjell G. Robbersmyr

Abstract: In this paper we present the application of regressive models to simulation of a full-scale vehicle-topole impact as well as virtual vehicle-to-barrier collision. The capability of an ARMAX model to reproduce vehicle kinematics was examined. Regressive model parameters were established by minimizing a weighted sum of squares of prediction errors. The prediction horizon was assigned to evaluate model’s robustness and verify its time series data forecasting performance. It was found that the ARMAX model does not only reproduce the signal which was used for its establishment (i.e. real vehicle’s acceleration) but it predicts another signal as well (i.e. virtual vehicle’s acceleration). Moreover, such estimation technique preserves all characteristic information relevant for a given collision, since integration of the estimated acceleration pulse yields plots of velocity and displacement which closely follow the reference ones.

Keywords: ARMAX model, prediction horizon, vehicle crash, vehicle kinematics

Issue 3, Volume 6, July 2011

Special Issue: Numerical Methods in Mechanics

Editors: Olga Martin, Nikos Mastorakis

Title of the Paper: Formulation of Elastodynamic Infinite Elements for Dynamic Soil-Structure Interaction


Authors: Konstantin Kazakov

Abstract: The paper is devoted to formulations of decay and mapped elastodynamic infinite elements, based on modified Bessel shape functions. These elements are for Soil-Structure Interaction problems, solved in time or frequency domain and can be treated as a new form of the recently proposed Elastodynamic Infinite Elements with United Shape Functions (EIEUSF) infinite elements. The formulation of 2D horizontal type infinite elements (HIE) is demonstrated here, but by similar techniques 2D vertical (VIE) and 2D corner (CIE) infinite elements can also be formulated. Using elastodynamic infinite elements is the easier and appropriate way to achieve an adequate simulation including basic aspects of Soil-Structure Interaction. Continuity along the artificial boundary (the line between finite and infinite elements) is discussed as well and the application of the proposed elastodynamical infinite elements in the Finite Element Method is explained in brief. Finally, a numerical example shows the computational efficiency of the proposed infinite elements.

Keywords: Soil-Structure Interaction, Wave propagation, Infinite Elements, Finite Element Method, Bessel functions

Title of the Paper: Implementation of Numerical Non-Standard Discretization Methods on a Nonlinear Mechanical System


Authors: Patete Anna, Velasco Maria, Rodriguez-Millan Jesus

Abstract: In this work, we shortly review the mathematical concepts of the well known numerical standard disctretization methods: Approximate, Exact and Truncated discretization methods and, the numerical nonstandard discretization methods, named: Euler, Euler-Picard and Euler-Taylor-Picard discretization methods. The standard discretization methods are applicable to continuous linear dynamics and a very limited class of nonlinear continuous dynamics; while the non-standard discretization methods are applicable to linear and nonlinear dynamics in general. The non-standard discretization methods theory was developed recently and only simulated results were presented. Our contributions in this work are to show the obtained results and analysis from the digital implementation of linear and nonlinear control laws on a nonlinear control mechanical system: the simple pendulum, using the numerical standard and non-standard discretization methods to discretize the continuous dynamics. Through the implementation we analyze the real validation of the numerical non-standard discretization methods. The results show that better approximation to the real data, obtained from the controlled real system, is given when the numerical non-standard discretization methods are used to dicretize the nonlinear dynamics. Also we validated the advantages of using digital nonlinear control laws on nonlinear control systems.

Keywords: Nonlinear control, nonlinear discretization, nonlinear state feedback, numerical method, mechanical system, simple pendulum

Title of the Paper: Effects of Turbulence Model in Computational Fluid Dynamics of Horizontal Axis Wind Turbine Aerodynamic


Authors: Kamyar Mansour, Mohsen Yahyazade

Abstract: The present paper report the numerical solution of horizontal axis wind turbines (HAWTs) of the aerodynamics by using computational fluid dynamics, CFD with three turbulence model, and compare these turbulence model results with experimental data to validate and determine which one is more reliable for numerical solution. Computational domain was divided in two zones; rotating and stationary .The numerical solution was carried out in the rotation zone, by solving conservation equations in a rotating reference frame. The blades have fixed 12° pitch angle and the computational results for different turbulent models such as standard k-a, RNG k-a &Spalart- Allmaras has been reported and compare with the experimental data of The National Renewable Energy Laboratory (NREL), for two wind speeds. It seems that the one-equation Spalart-Allmaras model is the suitable for turbulence closure, in low wind speed, and RNG k-a model is more reliable for higher wind speed.

Keywords: Wind turbine, HAWT, turbulence model, CFD, NREL, blade torque

Issue 4, Volume 6, October 2011

Title of the Paper: Developing an Innovative Design Processes of Su-Field Modeling


Authors: Chang-Tzuoh Wu, Chang-Shiann Wu, Hung-Jen Yang, Hsueh-Chih Lin

Abstract: TRIZ is a systematic method for providing valid suggestions to meet the requirements of inventive steps. Su-Field analytic method, deduced from TRIZ method, is one of the inventive problem solving tools that can be used to analyze and improve the efficacy of the technological system. By possessing a symbolic system and transformation rules, the Su-Field analysis model can assist designers to diagnose and solve most design problems. This study proposes an innovative design and problem-solving process, based on Su-Field modeling method integrated with extension of matter-element. This research tries to develop a innovative process by introducing “transformation and extension methods of matter-elements“ into the Su-Field modeling procedure to improve the efficiency and extent of concept evolutions. We make use of extensibility of matter-element to exchange the descriptions of design problems and solutions into creative fields. The concrete result includes, Proposed the flowchart of extensible innovative design process. The differences and benefits between Su-Field modeling procedure and matter-element modeling procedure are also evaluated. Assess possibility and advantage to combine construction of symbolic system in Su-Field model and the transformation and extension of matter-elements. Introducing concept extension and transformation of matter-element into symbolic developments, more creative solutions can be derived. Besides, some interrogative sentences are proposed to provide the designer facilitate tools while operating transformation methods. Two innovative design cases, staple free stapler and manpower-drive vehicle, successfully demonstrates that the proposed design process is feasible and efficient.

Keywords: TRIZ, Su-Field, Matter-Element, Extension theory

Title of the Paper: Numerical-Analytical BEM for Elliptic Problems


Authors: V. P. Fedotov

Abstract: This work is devoted to the development of the algorithms of solutions of boundary problems of mathematical physics based on the boundary elements method (BEM). The main advantages of the boundary elements method are decrease of dimension of a problem on unit, carrying discretization on the border of investigated area, and also obtaining a continuous decision in the interior of domain. As a result the quantity of calculations is reduced and accuracy of the decision rises. Distinctive features of the approach offered by the author are a use of analytical integration and ideology of parallel calculations at algorithm level.

Keywords: Boundary Elements Method, theory of elasticity, strain, stress, integral equation

Title of the Paper: Hysteresis Identification Methodology for the SAS Rotational MR Damper


Authors: Y. Iskandarani, G. A. Moslatt, E. Myklebust, J. P. Kolberg, L. L. Solberg, H. R. Karimi

Abstract: Vibrations is an extremely important issue to consider when designing various systems. It may lead to discomfort and malfunction or in some cases collapse of structures. To compensate for these vibrations different types of damping devices can be introduced and applied. The main scope which the following work addresses has been to look at standard methodology which enables determining the hysteresis from predefined steps for range of measurements which will be applied later on specific system integrated with Magnetorheological damper.The mathematical equations that lie behind the Bingham, Dahl, Lugre and Bouc-Wen have been studied to describe the behavior of the MR damper. The hysteresis equations of Bouc-Wen, Lugre, and Dahl have been modeled and simulated in Matlab/Simulink. The different parameters in the models have been manipulated and analyzed to determine the effects on the outcome. The hysteresis models of Bouc-Wen, Dahl and LuGre have been analyzed and compared analytically to show the difference in the models. At last the Bouc-Wen model was implemented together with the SAS(Semi Active Suspension) experimental system. The model parameters were tuned manually to fit the response of the system. This paper introduces the methodology flowchart which can be implemented and generalized for any kind of dampers, in the following work, the methodology was used to find hysteric behavior of MR damper with different mathematical models.

Keywords: Bouc-Wen model, Dahl model, Hysteresis methodology, Lugre model, Magnetorheological damper,Semi-Active Suspension System

Title of the Paper: Effect of Transition Stresses in a Disc Having Variable Thickness and Poisson’s Ratio Subjected to Internal Pressure


Authors: Pankaj Thakur

Abstract: Elastic-plastic transitional stresses in an annular disc having variable thickness and variable passion’s ratio subjected to internal pressure has been derived by using Seth’s transition theory. It is seen that thickness and passion’s ratio variation influence significantly the stresses and pressure required for initial yielding. The thickness variation reduces the magnitude of the stresses and pressure needed for fully plastic state. It is seem for fully plastic state that circumferential stresses is maximum at the outer surface.

Keywords: Disc, thickness, pressure, stresses, transitional, elastic, plastic

Title of the Paper: Numerical Simulation of Workpiece Thermal Profile in Plasma Arc Cutting (PAC) Process


Authors: Ali Moarrefzadeh

Abstract: Plasma arc cutting (PAC) is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch. In this process, an inert gas (in some units, compressed air) is blown at high speed out of a nozzle; at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut, turning some of that gas to plasma. The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut. The thermal effect of Plasma Arc that specially depends on the plasma, gas type and temperature field of it in workpiece, is the main key of analysis and optimization of this process, from which the main goal of this paper has been defined. Numerical simulation of process by ANSYS software for gaining the temperature field of workpiece, the effect of parameter variation on temperature field and process optimization for different cases of plasma Arc are done. The numerical results show the time-dependant distributions of arc pressure, current density, and heat transfer at the workpiece surface are different from presumed Gaussian distributions in previous models.

Keywords: Numerical simulation, workpiece, plasma, Machining, PAC

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