فهرست مطالب

Engineering - Volume:25 Issue: 3, Jul 2012

International Journal of Engineering
Volume:25 Issue: 3, Jul 2012

  • Transactions A : Basics
  • تاریخ انتشار: 1391/05/01
  • تعداد عناوین: 10
  • M. S. Fallah Nezhad, M.B. Fakhrzad Page 197
    In this paper, we introduce a new sampling plan based on the defective proportion of batch. The proposed sampling plan is based on the distribution function of the proportion defective. A continuous loss function is used to quantify deviations between the proportion defective and its acceptance quality level (AQL). For practical purpose, a sensitivity analysis is carried out on the different values of the required sample sizes that allow practitioners to design near optimal inspection plans. A numerical example is presented to illustrate how the proposed procedure can be applied to design acceptance plans.
    Keywords: Loss function, Beta distribution, Acceptance sampling plan
  • S. Bensallam, L. Bahi, H. Ejjaaouani, V. Shakhirev Page 203
    In order to study the shrinkage process of clayey soil, we perform a modified laboratory test allowing to measure simultaneously and continuously the vertical displacement and the weight of natural state specimen. The experiment was conducted on undisturbed clayey specimen. Using the experimental results, and on the basis of the existing relation between the soil water content and its structural evolution, we propose an analytical model allowing the analysis of the soil shrinkage curve.
    Keywords: clayey soil, expansive soil, shrinkage curve, analytical model
  • K. Boussouara, A. Merabet M. Kadja Page 211
    When looking at the effects of diesel engine exhaust on the environment, it is important to first look at the composition of the exhaust gases. Over 99.5% of the exhaust gases are a combination of nitrogen, oxygen, carbon dioxide, and water. With the exception of carbon dioxide, which contributes about 5% of the total volume, the diesel engine exhaust consists of elements which are part of the natural atmosphere and are not harmful to the environment. Carbon dioxide emissions are directly related to the efficiency of the combustion unit. The higher efficiency obtained with lower amount of CO2 emissions. In this study we are interested in the effects of exhaust gas recirculation (EGR) on combustion and emissions direct injection diesel engine. In particular, the effects of carbon dioxide (CO2), water (H2O), carbon monoxide (CO), some different quantities of EGR, analysed and quantified numerically. Other parameters tha affect the rate of oxides of carbon in the bowl shape, the Mexican hat and spherical geometry are analyzed in this work. Therefore, A modified version of the computational fluid dynamics (CFD) Code KIVA-3V has been used for modelling combustion process and engine emission, in particular carbon oxides emission and its control. Simulation was carried out by using a two-stroke single-cylinder direct injection diesel engine.
    Keywords: simulation, EGR, Carbon oxides, Emissions, Kiva 3v
  • S. Kumar, R. Devi Page 221
    A global nonlinear stability analysis is performed for a couple-stress fluid layer heated from below saturating a porous medium with temperature-pressure dependent viscosity for different conducting boundary systems. Here, the global nonlinear stability threshold for convection is exactly the same as the linear instability boundary. This optimal result is important because it shows that linearized instability theory has captured completely the physics of the onset of convection. The eigenvalue problems for different conducting boundary systems are solved by using Galerkin method. The effects of couple-stress parameter, Darcy-Brinkman number and variable viscosity parameter on the onset of convection are also analyzed. The use of Darcy-Brinkman model makes the system thermally more stable than the Darcy model for all the different conducting boundary systems, couple-stress parameter and medium permeability promotes stabilization, and the variable viscosity destabilizes the system.
    Keywords: Couple, Stress Fluid Porous Medium Global Stability Temperature, Pressure Dependent Viscosity Different Conducting Boundaries (Free, Free, Rigid, Free, Rigid, Rigid)
  • A. B. Rahimi Page 231
    Numerical methods are not always convergent especially in higher velocities when shock waves are involved. A comparison analysis is performed to study the supersonic flow over conical bodies of three different cross sections circular, elliptic and squircle (square with rounded corners) shaped using Perturbation techniques to find flow variables analytically. In order to find lift and drag forces the pressure force on the body is found, the component along x is drag and the component along z is lift. Three equations are obtained for lift to drag ratio of each cross section. The graphs for L/D show that for a particular cross section an increase in angle of attack, increases L/D. Comparing L/D in the three mentioned cross sections depicted that L/D is the greatest in squircle then in ellipse and the least in circle. The results are efficient in design of flying objects.
    Keywords: Supersonic flow, conical bodies, lift to drag ratio, squircle cross, section, Euler equations, perturbation techniques
  • N. Amanifard, S. M. Mahnama, S. A. L. Neshaei, M. A. Mehrdad, M. H. Farahani Page 239
    This paper presents an incompressible smoothed particle hydrodynamics (SPH) model to simulate wave propagation in a free surface flow. The Navier-Stokes equations are solved in a Lagrangian framework using a three-step fractional method. In the first step, a temporary velocity field is provided according to the relevant body forces. This velocity field is renewed in the second step to include the viscosity effects. A Poisson equation is employed in the third step as an alternative for the equation of state in order to evaluate pressure. This Poisson equation considers a trade-off between density and pressure which is utilized in the third step to impose the incompressibility effect. The computations are compared with the experimental as well as numerical data and a good agreement is observed. In order to validate proposed algorithm, a dam-break problem is solved as a benchmark solution and the computational results are compared with the previous numerical ones.
    Keywords: Smoothed Particle Hydrodynamics (SPH), Lagrangian method, wave propagation, free surface
  • H. Sayyaadi, M. R. Zakerzadeh Page 249
    There are two different ways of using SMA wires as actuators for shape control of flexible structures; which can be either embedded within the composite laminate or externally attached to the structure. Since the actuator can be placed at different offset distances from the beam, external actuators produce more bending moment and, consequently, considerable shape changes with the same magnitude of the actuation force comparing to the embedded type. Such a configuration also provides fast convection which is very important in shape control applications that require a high-frequency response of SMA actuators. Although combination and modeling of externally-attached SMA actuator wires and strips have been considered by many researchers, these studies have some weaknesses neglecting them yields a number of errors between theoretical and experimental results. In this work, the aforementioned limitations of attaching actuators to the smart structures have been removed and a flexible beam actuated by two active SMA actuators is nonlinearly modeled. The Brinson constitutive equations and thermoelectric equations for SMA materials are coupled with the nonlinear beam behavior and the coupled system of equations is numerically solved for some particular practical cases. The analysis method done in this paper can be easily extended to the complicated smart structure with externally-attached SMA wires.
    Keywords: Nonlinear Modeling, Flexible Beam, SMA Actuators
  • S. Pourzeynali, M. Malekzadeh, F. Esmaeilian Page 265
    Semi-active fluid viscous dampers as a subset of control systems have shown their ability to reduce seismic responses of tall buildings. In this paper, multi-objective optimization of the performance of this group of dampers in reducing the seismic responses of buildings is studied using multi-objective genetic algorithms. For numerical example, two 7 and 18 stories buildings are chosen and modeled as 3D frames. The equation of motion for each building, subjected to earthquake accelerations, is written in presence of semi-active fluid dampers and resolved in state-space. The optimal number and position of dampers are considered as decision variables while the structural responses such as displacement of top floor, base shear and etc. are considered as the objective functions to be minimized. The objective functions are taken part in multi-objective optimization as a group of three functions, and the goal is finding so called Pareto-optimal solutions that are non-dominated to each other and can optimize whole objectives as best as possible, simultaneously. In this case, any Pareto-optimal solution will be in fact, a certain configuration of some dampers in specific places of the structure. In this study, a fast and elitist non-dominated sorting genetic algorithm (NSGA-II) has been used.
    Keywords: Semi, active control, Multi, objective optimization, NSGA, II, Pareto solution
  • B. Golami Bazehhour, J. Rezaeepazhand Page 277
    In this paper a method is presented for torsional analysis of non-homogeneous tubes with arbitrarily shaped cross-sections. A previously presented method based on Bredt’s theory is extended to achieve formulas for torsional analysis. Shear modulus varies through the thickness according to a power law distribution. To validate the accuracy of the presented formulas for angle of twist and shear stress, calculated results are compared with available analytical and numerical data. Moreover, the effects of thickness, bluntness of corners and cross-sectional shape are investigated. The presented formulas are relatively accurate, simple and applicable to thin to moderately thick cross-sections with constant wall thickness. Based on the method presented herein, one can achieve desirable maximum shear stress and angle of twist for a polygonal non-homogeneous tube using a proper bluntness. The presented formulas quickly converge and can be implemented in optimization programs.
    Keywords: Torsion, Non, homogeneous, Polygonal cross, section, Bluntness
  • M. R. Jahanshahi, R. Rahgozar, M. Malekinejad Page 289
    In this paper, an efficient technique is presented for static analysis of tall buildings with combined tube-in-tube and outrigger-belt truss system while considering shear lag effects. In the process of replacing the discrete structure with an elastically equivalent continuous one, the structure is modeled as two parallel cantilevered flexural-shear beams that are constrained at the outrigger-belt truss location by a rotational spring. Based on the principle of minimum total potential energy, simple closed form solutions are derived for stress and displacement distributions. Standard load cases, including uniformly distributed loads, triangularly distributed loads and point loads at top of the structure are considered. Results obtained from the proposed method for a 50-story tall building are compared to those obtained using a standard finite element computer package. The approximate analyses are found to yield reasonable results and give a fairly good indication of actual structure’s response.
    Keywords: Tube, in, Tube, Outrigger, Belt Truss, Equivalent Continuum Model, Shear Lag, Stress Functions, Displacement Functions