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Issue 1, Volume 6,
January 2011
Title of the Paper:
Mitigation Assessment of Passive Seismic Protection
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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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