International Journal of Engineering
Volume:20 Issue: 2, Jun 2007

In this study, a white light particle image velocimetry (WL PIV) system which employs a light sheet generated with a flash was used. The system was developed in order to provide a cost-efficient and safe alternative to laser systems while keeping the accuracy limits required for hydraulic model tests. To investigate the accuracy of WL PIV method under different flow conditions, experiments were done at three different values of flow rates. Then the velocity vectors of each flow rate through the flume were calculated by means of cross-correlation of the two subsequent images. Flow velocity and Reynolds stress of each experiment were measured. The accuracy and integrity of the experiments were validated by comparison to the results which were obtained with empirical models of the mean velocity and Reynolds stress distribution in the boundary layer. Excellent agreement between the experimental and empirical results was observed. The whole flow field from the entrance of the experimental flume to its outlet was also modeled computationally using the Reynolds averaged Navier-Stokes equations and the k-e turbulence model of FLUENTTM code. It was found that the WL PIV measurements had a deviation of about 0.5 to 1.5% from the computational results which provides further evidence that WL PIV can be applied successfully in open channel flow analysis.

In the present paper simulation of tidal currents on three-dimensional geometry of the Persian Gulf is performed by the solution of the depth averaged hydrodynamics equations. The numerical solution was applied on two types of discritized simulation domain (Persian Gulf); with and without major islands. The hydrodynamic model utilized in this work is formed by equations of continuity and motion in two-dimensional horizontal plane. The effects evaporation and rainfall are considered in the source term of the continuity equation. The effects of bed slopes in x and y directions are considered in the partial differential terms representing the variation of hydrostatic pressure and the effects of bed friction, as well as the Coriolis effects are considered in algebraic terms of two equations of motion. The unstructured finite volume method is applied for solving the governing equations on overlapping control volumes formed by triangular cells. Using unstructured triangular meshes provides modeling of the geometrically complex flow domains, such as the Persian Gulf region. The results of the developed model for fluctuating flow on the variable bed elevation are compared with an available analytical solution of flow in a quadrant variable bed slope and Parshall flume. The accuracy of the finite volume flow solver is assessed by comparison between numerical results and the analytical solution and experimental measurements reported in the literature. The performance of the computer model to simulate tidal flow in the Persian Gulf domain is examined by imposing tidal fluctuations to the main flow boundary during a limited period of time and comparison of the computed results in an arbitrary location with available data from admiralty tide tables. Finally, a comparison was made between the model results of the two types of discritized simulation domain.

This paper describes a continuum model for analyzing the inelastic behavior of a single walled carbon nanotube (SWCNT) in different loading conditions. Because of limitations in using molecular dynamics (and other atomic methods) to model the failure load of the SWCNT, continuum mechanics methods are considered in this paper. Based on some experimental and theoretical results, an elasto-plastic model was used to analyze inelastic behavior of carbon nanotubes. 3D FEM model of SWCNT including the “Vander-Waals” interactions was developed with advanced capabilities. The results obtained by this model in different conditions have been compared with other numerical and experimental results. The comparison shows that this method is efficient and could be expanded for numerical modeling of nano-composites.

This paper presents a new time-frequency based EEG seizure detection method. This method uses the distribution of interspike intervals as a criterion for discriminating between seizure and nonseizure activities. To detect spikes in the EEG, the signal is mapped into the time-frequency domain. The high instantaneous energy of spikes is reflected as a localized energy in time-frequency domain. Histogram of successive spikes intervals is then used as a feature for seizure detection. In the presented technique the EEG data are segmented into 4-second epochs. A k-nearest neighbor algorithm is employed to classify the EEG epochs into seizure and nonseizure groups. The performance of the presented technique is evaluated using the EEG data of five neonates. The results indicate that the proposed technique is superior to the other existing methods with 92.4 % good detection rate and 4.9 % false detection rate.

In the present paper, the expressions for scalar and vector potentials in lossless isotropic chiral media are analyzed. Propagating eigenvalues of these potentials are then obtained. Furthermore by decomposition of sources and fields in a chiral medium, we introduce the auxiliary right-and left-handed potentials and find the associated fields. These potentials are used to solve the problem of a horizontal electric dipole (HED) above a chiral half space. Auxiliary right and left handed Hertzian vector potentials are introduced and and fields in terms of these potentials are obtained. The Hertzian potentials due to VED and/or VMD sources within a chiral half space are determined in terms of two-dimensional Fourier spectral domain and the expressions for EM fields with respect to these potentials are presented.

This investigation presents an economic production quantity (EPQ) model for deteriorating items with stock-dependent demand and shortages. It is assumed that a constant fraction of the on-hand inventory deteriorates and demand rate depends upon the amount of the stock level. Expression for various optimal indices as well as cost analysis are provided. By taking numerical illustration, sensitivity analysis has been carried out. For cost optimization, Newton’s method is employed.

The objective of this paper is to study the M/M/R machine repair queueing system with mixed standbys. The life-time and repair time of units are assumed to be exponentially distributed. Failed units are repaired on FCFS basis. The standbys have switching failure probability q (0≤q≤1). The repair facility of the system consists of R permanent as well as r additional removable repairmen. Due to impatience, the failed units may balk or renege, with a certain probability, on finding all repairmen busy. Transient probabilities of various states are obtained by solving the set of governing equations via Runge-Kutta method. Expressions for various performance measures are established in terms of transient probabilities of system states. By varying different parameters, the system behavior is examined with the help of numerical illustrations.

This paper presents a novel, integer-linear programming (ILP) model for an identical parallel-machine scheduling problem with family setup times that minimizes the total weighted flow time (TWFT). Some researchers have addressed parallel-machine scheduling problems in the literature over the last three decades. However, the existing studies have been limited to the research of independent jobs, and most classical optimization methods are focused on parallel-machine scheduling problems without considering setup times and relationship between jobs. This problem is shown to be NP-hard one in the strong sense. Obtaining an optimal solution for this type of complex, large-sized problems in reasonable computational time is extremely difficult. A meta-heuristic method, based on genetic algorithms, is thus proposed and applied to the given problem in order to obtain a good and near-optimal solution, especially for large sizes. Further, the efficiency of the proposed algorithm, based on various test problems, is compared with the Lingo 8.0 software.

This article has focused on evaluation and identification of effective parameters in positioning performance with an odometry approach of an omni-directional mobile robot. Although there has been research in this field, but in this paper, a new approach has been proposed for mobile robot in positioning performance. With respect to experimental investigations of different parameters in omni-directional mobile robots error, the effects of velocity, length of path, type of wheels and other parameters are analyzed with Gaussian error function estimation. A new approach for determining better characteristics in omni-directional mobile robots error is presented. With respect to arrangement of effective parameters by using statistical process control we have reached a model equation for assumed process (odometry errors). The results show statistical process control as a new trend for reduction of mobile robot error.