2005

 Volume 12, Issue 1 Electrical and Computer Engineering
 Volume 12, Issue 2 Civil and Mechanical Engineering
 Volume 12, Issue 4 Civil and Mechanical Engineering
 Volume 12, Issue 3 Chemistry and Chemical Engineering
Volume 12, Issue 4, 2005
Civil and Mechanical Engineering

 Axisymmetric Radial Stagnation-Point Flow of a Viscous Fluid on a Rotating Cylinder with Time-Dependent Angular Velocity           A.B. Rahimi (PhD.) R. Saleh [PhD.] Preview   Download PDF The unsteady viscous flow in the vicinity of an axisymmetric stagnation point of an infinitely long rotating circular cylinder is investigated, when the angular velocity varies arbitrarily with time. The free stream is steady and with a constant strain rate of k. An exact solution of the Navier-Stokes equations is derived in this problem. The general self-similar solution is obtained when the angular velocity of the cylinder varies as certain functions. The cylinder may perform different types of motion: It may rotate with constant speed, with exponentially increasing/decreasing angular velocity, with harmonically varying rotation speed or with accelerating/decelerating oscillatory angular speed. For completeness, some sample semi-similar solutions of the unsteady Navier-Stokes equations have been obtained numerically using a finite-difference scheme. These solutions are presented for special cases when the time-dependent is step-function, linear and non-linear, with respect to time. All the solutions above are presented for Reynolds numbers, Re=ka^2/2\upsilon, ranging from 0.1 to 1000, where a is the cylinder radius and \upsilon is the kinematic viscosity of the fluid. Shear stresses corresponding to all cases increase with the Reynolds number. The maximum value of the shear-stress increases with an increase in oscillation frequency and amplitude. An interesting result is obtained, in which a cylinder, spun up from rest with a certain angular velocity function and at a particular value of Reynolds number, is azimuthally stress-free.
 Reclamation Potential of Urban Stormwater Runoff in Iran           N. Vaseli (PhD.) P. Monadjemi [PhD.] Preview   Download PDF Large volumes of potable water are imported into almost all urban areas of Iran at extremely high cost, while considerable volumes of urban stormwater are disposed of out of the cities and wasted, mostly into bodies of saltwater. In this paper, urban stormwater is examined as a potentially valuable and reclaimable resource. A model is introduced in which stormwater runoff is captured and stored behind a small dam of height $H$ with an overflow weir of length $L$ to waste excess flows. At the same time, the stormwater is diverted through a side weir of width W, to be conveyed to suitable recharge grounds for later reclamation and use. A particular watershed, in the arid and rapidly urbanizing city of Bandar Abbas in southern Iran, with 24 years of rainfall records, was chosen and used in the model. The rainfall from nine other arid, semiarid and wet regions were used as input to the same watershed. The results show that the amount of reclaimable water as a percent of total runoff is almost the same for all the regions. This study provides a relationship, which defines the reclaimable water as a function of W,L and H. The relationship may be used for planning urban stormwater reclamation projects. The normal parameters defining arid, semiarid and wet climate are not of significance in this relationship. The relationship, however, may be further refined if one incorporates the number of intense storms as an extra parameter.
 N-Junction Modeling in Perforate Silencers for Internal Combustion Engines           M.R. Modarres Razavi (PhD.) A. Faezian [PhD.] A. Onorati [PhD.] Preview   Download PDF In this work, boundary conditions of the T-junctions in engine silencers are modeled by the Constant Pressure Model (CPM) and the Pressure Loss Model (PLM). Initially, the mean flow velocity through the ducts is assumed to be zero. Two Benson CPM and Corberan CPM approaches are employed in perforate silencers simulation. For the silencer with more than one perforated pipe, in which N-branch junctions are formed, it is possible to apply the Benson CPM approach. Finally, when the mean flow velocity through the ducts is non-zero, the shortcoming of the CPM model and the ability of the PLM model in describing the T-junctions are shown."
 Simulation of Average Stress-Average Strain Relationship of Ship Unstiffened/Stiffened Plates Subject to in-Plane Compression           M.R. Khedmati (PhD.) Preview   Download PDF In this paper, a simple and efficient analytical method, combining elastic large deflection analysis and rigid plastic mechanism analysis, is presented for derivation of the average stress-average strain relationship of plates subject to in-plane longitudinal compression. By imposing equilibrium conditions of forces and bending moments and assuming proper stress and strain distributions in the stiffened plate cross-sections, the average stress-average strain relationship of the stiffened plates is also derived. The algorithm can be easily implemented in methods for the evaluation of ship hull girder strength, as well as in the estimation of the ultimate capacity of offshore structures.
 Fundamentals of Optimum Performance-Based Design for Dynamic Excitations           H. Moghaddam (PhD.) I. Hajirasouliha [PhD.] Preview   Download PDF This paper presents a new method for optimization of the dynamic response of structures subjected to seismic excitation. This method is based on the concept of uniform distribution of deformation. In order to obtain the optimum distribution of structural properties, an iterative optimization procedure has been adopted. In this approach, the structural properties are modified so that inefficient material is gradually shifted from strong to weak areas of a structure. This process is continued until a state of uniform deformation is achieved. It is shown that, in general, for a MDOF structure, there exists a specific pattern for distribution of structural properties that results in an optimum seismic performance. It has been shown that the seismic performance of such a structure is optimal and behaves generally better than those designed by conventional methods. The application of the proposed method for optimum seismic design of different structural forms, such as truss-like structures and shear-buildings, is presented. The effects of fundamental period, target ductility demand, damping ratio and seismic excitations on an optimum distribution pattern are investigated.
 A New Approach to Investigate Unsteady Aerodynamic Phenomena           M.R. Soltani (PhD.) A.R. Davari [PhD.] Preview   Download PDF A new approach, based on a Generalized Regression Neural Network (GRNN), has been proposed to predict the unsteady forces and moments of two different modelsa 70\degree swept delta wing in subsonic incompressible flow and a standard fighter model (SDM) in a compressible flow regime, both undergoing sinusoidal pitching motion. Extensive wind tunnel results were used for training the network and verification of the values predicted by this approach. GRNN was trained by the aforementioned experimental data and, subsequently, was used as a prediction tool to determine the unsteady longitudinal forces and moment of the two models under various conditions. Further, it was applied to extend the experimental data beyond the conditions tested in the tunnel. The results are in a good agreement with the experimental findings. This indicates that the present prediction and optimization tool provides sufficient accuracy with a modest amount of experimental data.
 A Convergent Genetic Algorithm for Pipe Network Optimization           M.H. Afshar (PhD.) M.A. Marino [PhD.] Preview   Download PDF A highly convergent Genetic Algorithm (GA) for pipe network optimization is presented in this paper. An artificial genotype passing mechanism, an alternative penalty cost calculation method, an iterative setting of the penalty parameters prior to the GA search and, more importantly, a new selection operator, are introduced in the proposed GA. The genotype passing mechanism leads to a monotonically decreasing convergence curve of the GA search and, therefore, paves the way for introducing a logical convergence criterion for genetic algorithms. The use of an alternative penalty cost calculation leads to a better distribution of the fitness function in the search space, compared to conventional methods and, therefore, helps the GA to locate useful genes. Penalty parameters used for the calculation of the penalty cost are determined prior to a GA search, via use of a mathematical programming method, eliminating the possibility of choosing too low or high parameter values. Finally, a new selection operator is designed in an attempt to simulate the process of natural mating more closely, leading to an improvement in the optimality and convergence characteristics of the method. The efficiency of the proposed GA is shown by applying the method to the optimal design of three well-known benchmark networks, namely two-loop, Hanoi and New York networks. The method produces results comparable to the best results presented in the literature with much less computational effort.