INTERNATIONAL JOURNAL OF INDUSTRIAL ENGINEERING AND PRODUCTION MANAGEMENT (IJIE) (INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE) (PERSIAN)
Year:2006 | Volume:16 | Issue:4|Papers Count:18

Contractor selection is a critical activity that plays a vital role in the overall success of any construction project. In this study, first, criteria for determining the qualification and selection of the contractor were set given the finding of the studies and researches. Considering the fact that prequalification is primarily determinate based on filtering and ranking methods, two limits called veto and cut-off were identified for these criteria and these limits were also set following the consultation national experts. Finally, a computerized mathematical decision-making model was offered with can direct the process of setting the prequalification in terms of the important of the criteria determination.

An overview on some meshless methods, and a meshless procedure for solving linear convection-diffusion equation in steady state and nonlinear burgear equation in transient are presented in this paper. The approach termed generically the "Element Free Galerkin method" is based on a weighted moving least square (MLS) interpolation of point data for evaluating the approximation integral. EFG meshless method uses a background mesh to introducing the Guossian points for solution of the integral equation. In this paper we develop EFG meshless procedure for linear and nonlinear convection-diffusion equation problems in steady and transient forms. A one dimensional example by different values of peclet number is solved using MATLAB, V6.5 programming and the results are compared with the exact solution. The method is tested for shock wave propagation in example no two.

The rates of both road accidents' frequency and severity are high in Iran and the economical results put a great burden on the nation. Among these, the accidents which are caused by hitting roadside obstacles or are rolled over after an exit from road surface, account for 25-30 percent of fatal accidents. Considering the scarce resources available to tackle the problem, the necessity for efficient use is obvious. A powerful new software named RSAP for the analysis of such problems is recently (2003) introduced. The sub-models of deviation, accident forecast, and severity forecast; combined with geometric and traffic characteristics of the road, as well as economic indices of the society; altogether provide the ability for the system to analyze the complicated decision-making situations. Forecasting the vehicles' deviation risks and estimating the severities of the potential future accidents, then the optimized solutions in different economical conditions might be determined.In this research-work, considering the special case of the roadway in Iran, and performing different analyses using RSAP model; various charts and diagrams are developed. Using these, the planners and engineers in highway planning, construction, maintenance, and rehabilitation sections; will be able to make optimized decisions whether to select the guardrails and cushions or to choose the next alternative; which is flatting the embankment slopes. The provided tool is also capable to forecast the potential future accidents' severities. This is also beneficial for making necessary corrections and modifications in the current standards practiced in Iran.

In this paper, one of the common specimens for mode II fracture tests called the E-shape specimen is studied. The specimen is simulated using the finite element method and its stress intensity factors are calculated. Previous investigators have assumed that the specimen can provide pure mode II deformation. However, the results obtained in this research reveal that there are significant mode I effects in the specimen. The maximum tangential stress criterion is then used to study brittle fracture in the E-shape specimen. It is shown that the value of fracture toughness resulting from a standard fracture test can be noticeably inaccurate unless the mode I effects are also taken into account. Finally, a modification in the test method is proposed such that pure mode II is achieved from the E-shape specimen.

A numerical method for shape optimisation in forging is presented. The goal of the optimisation is to eliminate work-piece defects that may arise during the forging process. A two dimensional finite element code has been developed for the simulation of the mechanical process. The material is incompressible and it follows the Norton-Hoff law. To deal with contact constraint the velocity projection algorithm is used. The optimisation method considers a genetic algorithm supported by an elitist strategy. A new genetic operator called adaptive mutation has been developed in order to increase the efficiency of the search. The developed scheme is used to design optimal pre-form shapes for several axisymmetric examples. Comparing the obtained optimal results with the literature validates the proposed optimisation method.Continuous and discrete design variables are considered.

In this paper, a new type of gas-to-gas heat exchanger that operates based on energy conversion between gas enthalpy and thermal radiation is developed. This system consists of one high temperature section and two recovery sections. In high temperature section, the enthalpy of hot gas flow converts to thermal radiation by porous layer in this section and the reverse direction of this process occurs in recovery sections. A theoretical analysis is conducted for the one-dimensional system where convection and radiation take place simultaneously in three porous layers. In order to obtain the thermal characteristics of this type of heat exchanger, the coupled energy equations for the gas and porous mediums based on two-flux radiation model are solved numerically using iterative method. Computational results show that this type of heat exchanger works effectively especially when the porous layers with large optical thicknesses and small scattering factors are used in the system. In order to validate the numerical results, a comparison between theory and experiment is made for a system of heat recovery and a good agreement is found.

In this research work, a new turbulence model, introduced as turbulent potential model, is used to predict the onset of transition from laminar to turbulent and also to estimate transition length in flat plate flows. Analysis is carried out for both the zero and non-zero pressure gradients under different free stream turbulence intensities. In contrast to most of traditional turbulence models, no assumptions are used to establish any constitutive relations between averaged flow variables with governed turbulence quantities. Comparison made between final results with those obtained through experiments show a good capability of present model in analysis of non-equilibrium flows, such as transition from laminar to turbulent.

Neodymium doped silicate base Nd:BKS glasses were obtained from high-purity materials using ceramic crucibles and steel moulds. The powder XRD patterns correspond well to the calculations based on the theory of nucleation and generally present any crystalline local structure and/or the phase-separation in these fabricated glasses.Based on the XRF results, almost all of the physical properties of Nd:BKS glasses were directly calculated and/or approximated in a reasonable range of the error. The absorption/transmition spectra of the fine-polished Nd:BKS cross-sections, compared to the Nd:YAG single crystal spectra, led to the approximation of the laser characteristics of Nd:BKS glasses. The present computational methods may be regarded as a general algorithm for approximation of the laser-active amorphous materials' physical properties.

Some Micro structural Aspects of Explosive Welding Interface between Aluminum and Steel which welded in Different Conditions have been studied. Wavelength, amplitude and Interlayer Phase Dimensions Formed in the Welding Interface have been measured by means of an Optical Microscope. By Comparing Welded Samples, it is Determined that the Greater Stand off Distance, the Larger Interface Dimensions, But Interface Wavelength and Amplitude have not been Changed with Stand off Distance Variations. It has been concluded which an Increase in Explosive Mass and a Decrease in Flyer Tube Thickness, Will Result in Increase in Wavelength and Amplitude and Interlayer Phase Dimensions.

In this investigation physical properties and characterizations of 3 Iranian silica ramming mixes were studied and compared with a foreign sample. Nowadays silica ramming monolithics have a high consumption in Iranian foundry industries and many attempts for local production of these products have been made. Characterization of the samples was based on physical (porosity & density), mechanical (CCS), thermal (STA) behavior and phase, chemical and microstractural studies. The results showed that using high purity silica raw materials with low free iron content and adding proper amount of boron compounds have special effects on physical and mechanical Properties. However expansion phenomenon caused by quartz-crystoballite phase transformations at about 1200°C and the shrinkage related to borosilicate containing phases is the most important factor on silica ramming products at high temperatures.

Wrought aluminum 7075 alloy is hardened by precipitation hardening heat treatment. This alloy is one of the AI-Zn-Mg series with high strength and mechanical properties which is used in military and aerospace industries. This alloy has a long time heat treatment process. Therefore decreasing the heat treatment time is an important factor from economical view. The main objective of the present work is to reduce heat treatment time by the process which is a combination of duplex ageing and deformation (rolling). This regime involves T-AHA type treatment which is called FTMT process. First and second stages of ageing temperatures are different in this process and rolling is carried out at room temperature. Effective parameters of the process have been studied. The experimental results showed that this kind of thermo-mechanical treatment has not increased the hardness of alloy 7075 compared with conventional T6 treatment but, this process has reduced the heat treatment time about 58%, increased yield strength about 9% and increased ultimate tensile strength about 5.5%. The elongation of the alloy has not been changed by using this kind of thermo mechanical process.

World class manufacture is one of the influential terms and fundamental concepts which has evolved during these years. It is said, that it is the only term which signifies the expansion and required fundamental changes currently occurring in the industrial complexes, consequently WCM is a significant concept in the world of today for maintaining and also helping the existence of organizations as the world moves toward globalization. Attaining production opportunities in line with WCM specifications is one of the strategic objectives envisaged by production centers, entrepreneurial and service concerns. One of the objectives undertaken by this research is to survey production envisaged by WCM and to present a unified strategic model in order to obtain production opportunities according to WCM specifications.To implement WCM-SSM model, proper alignment and coordination between the two models had to be actualized.This resulted in the development of a WCM-SSM viable model, upon which the entire implementation process in the factory was based. Ultimately, based on the results of this new model, it became apparent that this model enjoys credible exactness and can be used effectively by manufacturing organizations seeking WCM compatibility. Organizations seeking access to WCM can utilize the WCM-SSM model; especially it can be used by developing countries that encounter challenging vague and unpredictable environments. This model can be effectively deployed not only in manufacturing concerns but also in organizations that provide all kinds of services, including cultural and media facilities.

In this paper, a mathematical programming model for set covering problems (SCPs) is presented and developed which is close to real-world cases. In this proposed model, m customers are covered by n facilities in such a way that the distance between facilities must not be less than the available defined limit Due to nonlinearity of the model, the traditional optimization methods cannot solve large-sized problems in a reasonable amount of computational time. Thus in this paper, a genetic algorithm is proposed as a well-known metaheuristic method to solve such a hard problem. To show the efficiency the proposed algorithm, 36 test problems classified into 9 groups are generated at random and then they are solved by genetic algorithms. The associated results are compared with the Lingo 6 software package. These results show the efficiency and validation of the proposed algorithm.

These paper discuses a model for performance evaluation of research projects, based on project triangle, which includes three parameters: time, cost and scope. Some models for performance evaluation of projects have been proposed in literature, such as checklist, scoring model, analytic hierarchy process and engineering economy techniques. Here, a different measurements criterion has been developed for evaluating performance of projects as; deviation of time, cost and quality based on project triangle. Then the relevant function was developed from the concept of quadratic loss function in quality engineering. The developed model needs defined conditions for evaluating projects performance. At first conditions are defined and their deviation from established criteria calculated. The calculated deviations are used to measure project performance.The developed model tested with data, which was generated at an engineering research institute and compared with the actual performance data. The generated results are satisfactory.

In this paper, extension of quiet zones in Active Noise Control (ANC) systems is considered. First, according to the coherency of input signals, an estimate of the accessible noise attenuation is calculated for a 1*1*2m enclosure. Then, the effects of important factors in extension of quiet zones such as location and number of error microphones and secondary speakers as well as the secondary signals powers are investigated. For this purpose, single and multi-channel ANC systems are implemented in the same enclosure. The noise attenuation levels around the error microphones are compared to the corresponding theories at different places of the enclosure.

This paper presents a sequential based Newton-Raphson power flow algorithm for reliable and efficiently handling power systems with embedded FACTS (Flexible AC Transmission Systems) devices. Computation and control of power flow in power systems with embedded FACTS devices appear to be fundamental for power system analysis and planning purposes. A power injection model for conventional FACTS devices such as SVC (Static Var Compensator) and TCSC (Thyristor Controlled Series Capacitor) as well as modem FACTS devices such as STATCOM (Static Series Compensator) SSSC (Static Synchronous Series Compensator) and UPFC (Unified Power Flow Controller) is derived. Also a power injection model of conventional HVDC (High Voltage Direct Current) is obtained. Then a sequential power flow algorithm (two step algorithm) is adopted. The proposed injection models and sequential power flow algorithm have been programmed and systematically tested in a number of systems. The results of Ward-Hale network are reported which clearly illustrates the Capabilities and generalization of the proposed algorithm.