Showing 37 results for S.
M.r. Modarres Razavi, S.h. Seyedein, P.b. Shahabi , S.h Seyedein,
Volume 17, Issue 3 (IJES 2006)
Abstract
In this paper hemodynamic wall parameters which play an important role to diagnose arterial disease were studied and compared for three different rheology models (Newtonian, Power law and Quemada). Also because of the pulsatile behavior of blood flow the results were obtained for three Womersley numbers which represent the frequencies of the applied pulses. Results show that Quemada model always located between Newtonian and Power law models however its behavior is closer to Power law model. Concerning this behavior and better agreement between Quemada and experimental blood viscosity, it can be expected that Quemada results are more realistic and accurate.
M. Nikian, , M. Naghashzadegan, S. K. Arya ,
Volume 17, Issue 3 (IJES 2006)
Abstract
The cylinder working fluid mean temperature, rate of heat fluxes to combustion chamber and temperature distribution on combustion chamber surface will be calculated in this research. By simulating thermodynamic cycle of engine, temperature distribution of combustion chamber will be calculated by the Crank-Nicolson method. An implicit finite difference method was used in this code. Special treatments for piston movement and a grid transformation for describing the realistic piston bowl shape were designed and utilized. The results were compared with a finite element method and were verified to be accurate for simplified test problems. In addition, the method was applied to realistic problems of heat transfer in an Isuzu Diesel engine, and gave good agreement with available experimental.
M.r. Alirezaee, S.a Mir-Hassani,
Volume 17, Issue 4 (IJES 2006)
Abstract
In the evaluation of non-efficient units by Data Envelopment Analysis (DEA) referenced Decision Making Units (DMU’s) have an important role. Unfortunately DMU’s with extra ordinary output can lead to a monopoly in a reference set, the fact called abnormality due to the outliers' data. In this paper, we introduce a DEA model for evaluating DMU’s under this circumstance. The layer model can result in a ranking for DMU’s and obtain an improving strategy leading to a better layer.
A. Azaron , S.m. Fatemi Ghomi,
Volume 18, Issue 3 (International Journal of Engineering 2007)
Abstract
Abstract : In this paper , we apply the stochastic dynamic programming to approximate the mean project completion time in dynamic Markov PERT networks. It is assumed that the activity durations are independent random variables with exponential distributions, but some social and economical problems influence the mean of activity durations. It is also assumed that the social problems evolve in accordance with the independent semi-Markov processes over the planning horizon. By using the stochastic dynamic programming, we find a dynamic path with maximum expected length from the source node to the sink node of the stochastic dynamic network. The expected value of such path can be considered as an approximation for the mean project completion time in the original dynamic PERT network.
S.m. Seyed-Hosseini, M. Sabzehparvar, S. Nouri ,
Volume 18, Issue 3 (International Journal of Engineering 2007)
Abstract
Abstract: This paper presents an exact model and a genetic algorithm for the multi-mode resource constrained project scheduling problem with generalized precedence relations in which the duration of an activity is determined by the mode selection and the duration reduction (crashing) applied within the selected mode. All resources considered are renewable. The objective is to determine a mode, the amount of continuous crashing, and a start time for each activity so that all constraints are obeyed and the project duration is minimized. Project scheduling of this type occurs in many fields for instance, predicting the resources and duration of activities in software development projects. A key feature of the model is that none of the typical models can cope with the continuous resource constraints. Computational results with a set of 100 generated instances have been reported and the efficiency of the proposed model has been analyzed.
H. Ahmadian, S. Nazari , H. Jalali ,
Volume 18, Issue 4 (International Journal of Engineering 2007)
Abstract
Abstract: The governing equations of motion for a drill string considering coupling between axial, lateral and torsional vibrations are obtained using a Lagrangian approach. The result leads to a set of non-linear equations with time varying coefficients. A fully coupled model for axial, lateral, and torsional vibrations of drill strings is presented. The bit/formation interactions are assumed to be related to the following parameters: bit motion, effects of gyroscopic moments, contact with the borehole wall, axial excitation due to bit/formation interactions, and hydrodynamic damping due to the presence of drilling mud. Simulation results show that parametric resonance and whirling may occur simultaneously within the range of operating conditions of drilling. The contact force between collar and borehole wall is calculated and its behavior is investigated. The dynamic behavior is quite complicated and may become non-periodic, suggesting a chaotic behavior.
F. Sanati , S.m. Seyedhoseini,
Volume 19, Issue 1 (International Journal of Engineering 2008)
Abstract
Abstract: At the last decade of the 20th century, Womack et. Al introduced Lean concept to the industrial world. Since 1990 up to now, existed studies mostly have focused on lean production in the step of manufacturing, but in this research leanness concept has developed in the plant life cycle. In this paper leanness concept will be described as elimination of wastes in the phases of investment, plant design & construction(hardware), organization & systems design (software) and these three steps will be added to, elimination of previously described seven wastes in production step. For this purpose at first, the types of wastes in the above mentioned phases are defined by using Axiomatic Design methodology. After defining the types of wastes, a model for assessment of leanness is submitted. In this quantitative model, amount of leanness in each phase will be determined and combined to make a unique measure for total leanness. Dimensions of leanness are shown for quick understanding, by using a spider diagram. In the last section of the paper, the results of an example of the application of this model in fan industry are brought. This example shows the simplicity and powerfully of the model to determine the leanness in before production phases. © 2008 Authors all rights reserved.
M. Jahir Bin Alam, M.a. Ansery, R.k Chowdhuary, J. Uddin Ahmed, S. Islam , S. Rahman ,
Volume 19, Issue 3 (International Journal of Engineering 2008)
Abstract
Abstract: Sylhet is the northeastern region of Bangladesh and probability of earthquake in Sylhet is higher than other areas of this zone. Among 27 wards, Ward no. 14 is one of the important largest Wards in Sylhet city and a densely populated one. It was clear from the survey works, 42.8% buildings are belongs to Building with RCC frame 54.03% buildings are Masonry buildings. Another interesting finding is 325 houses fall in the category of Houses with resident 1-10. The occurrence of an earthquake of PGA value 0.9g on ward no. 14 causes massive loss of lives and damage to buildings. Depending on the time of the day 147 to 603 people may be killed due to structural collapse and the buildings of worth approximately TK.32.00 core may be damaged.
A. Nicknam, S. Yaghmaei Sabegh, A. Yazdani,
Volume 19, Issue 3 (International Journal of Engineering 2008)
Abstract
Abstract : The main objective of this study is estimating the strong motion for the Bam region using the stochastically based seismological models. The two widely used synthetic techniques namely point-source and finite-fault were utilized incorporating the source-path and site parameters into simple function. The decay factor kappa was estimated based on the data obtained from recorded strong motions to be used as an appropriate factor for the region. The results were validated against those of the recorded data during the destructive 26 December 2003 Bam earthquake in south east of Iran. The efficiency of these methods and estimating the appropriate regional model parameters are the main objectives of this study. The results of the synthesized ground motion, such as acceleration time history, PGA and elastic response spectra were compared /assessed with those of observed data. The Bias model (MB) is used to assess the validation of the simulated earthquakes against recorded horizontal acceleration time histories. The %90 confidence interval of the means averaged over the whole stations using t-student distribution was evaluated and it was shown to be in an acceptable range. The elastic response spectra of the simulated strong motion are showed to be in a good agreement between the recorded waveforms confirming the acceptability of the selected/evaluated source-path-site model parameters. The sensitivity of the simulated PGA and response spectra against kappa factor as well as the path-averaged frequency-dependent quality factor Q, is studied and discussed.
A. Amid, S.h. Ghodsypour,
Volume 19, Issue 4 (IJIE 2008)
Abstract
Supplier selection is one of the most important activities of purchasing departments. This importance is increased even more by new strategies in a supply chain, because of the key role suppliers perform in terms of quality, costs and services which affect the outcome in the buyer’s company. Supplier selection is a multiple criteria decision making problem in which the objectives are not equally important. In practice, vagueness and imprecision of the goals, constraints and parameters in this problem make the decision making complicated. Simultaneously, in this model, vagueness of input data and varying importance of criteria are considered. In real cases, where Decision- Makers (DMs) face up to uncertain data and situations, the proposed model can help DMs to find out the appropriate ordering from each supplier, and allows purchasing manager(s) to manage supply chain performance on cost, quality, on time delivery, etc. An additive weighted model is presented for fuzzy multi objective supplier selection problem with fuzzy weights. The model is explained by an illustrative example.
S.k. Charsoghi, A. Sadeghi,
Volume 19, Issue 4 (IJIE 2008)
Abstract
In this paper, a two-echelon supply chain, which includes two products based on the following considerations, has been studied and the bullwhip effect is quantified. Providing a measure for bullwhip effect that enables us to analyze and reduce this phenomenon in supply chains with two products is the basic purpose of this paper. Demand of products is presented by the first order vector autoregressive time series and ordering system is established according to order up to policy. Moreover, lead-time demand forecasting is based on moving average method because this forecasting method is used widely in real world. Based on these assumptions, a general equation for bullwhip effect measure is derived and there is a discussion about non-existence of an explicit expression for bullwhip effect measure according to the present approach on the bullwhip effect measure. However, bullwhip effect equation is presented for some limited cases. Finally, bullwhip effect in a two-product supply chain is analyzed by a numerical example.
F. Sereshki, S.a. Hosseini, N. Aziz , I. Porter ,
Volume 19, Issue 5 (IJES 2008)
Abstract
The Outburst can be defined as a sudden release of coal and rock accompanied by large quantities of gas into the underground coal mine workings which represents a major hazard in underground coal mines. Gas drainage has been proven to be successful in reducing outburst hazards by decreasing the in-situ gas pressure. One of aspect of gas drainage from coal seams is coal matrix volume changes. Current study is primarily concerned with experimental studies related to coal volume change (coal shrinkage) under various gas types and pressures. Two types of tests were conducted on each sample, the adsorption test for coal swelling and the desorption test for coal shrinkage. The gases used in the study were CH4, CO2, CH4/CO2 (50-50% volume), and N2. In this research, tests were conducted with respect to volumetric change behavior in different gases and their corresponding comparative results were presented.
S. Rastegari, Z. Salehpour , Bakhshi , H. Arabi,
Volume 19, Issue 5 (IJES 2008)
Abstract
Formation mechanism of silicon modified aluminide coating applied on a nickel base super alloy IN-738 LC by pack cementation process was the subject of investigation in this research. Study of the microstructure and compositions of the coating was carried out, using optical and scanning electron microscopes, EDS and X-ray diffraction (XRD) techniques. The results showed that due to low partial pressure of silicon halide in Pack process, the amount of soluble silicon in the coating can not exceed 1 wt % of the total coating composition, although the Si content of the particles present within the outer coating sub-layer could reach as far as 5 wt%. Thus, the small amount of soluble Si within the coating could not provide the necessary conditions for formation of any intermetallic and it seems that the formation and growth behavior of various sub-layers in Si-modified aluminide coating is similar to that of simple aluminide coating. Three sub-layers were detected in the coating structure after being subjected to diffusion heat treatment. They were an outer Ni-rich NiAl sub-layer a middle Ni-rich NiAl and an inter diffusion sub-layers. The details of formations and growth mechanism of these sub-layers has been discussed in this research.
H. Arabi, M.t Salehi, B. Mirzakhani, M.r. Aboutalebi , S.h. Seyedein , S. Khoddam,
Volume 19, Issue 5 (IJES 2008)
Abstract
Hot torsion test (HTT) has extensively been used to analysis and physically model flow behavior and microstructure evolution of materials and alloys during hot deformation processes. In this test, the specimen geometry has a great influence in obtaining reliable test results. In this paper, the interaction of thermal-mechanical conditions and geometry of the HTT specimen was studied. The commercial finite element package ANSYS was utilized for prediction of temperature distribution during reheating treatment and a thermo-rigid viscoplastic FE code, THORAX.FOR, was used to predict thermo-mechanical parameters during the test for API-X70 micro alloyed steel. Simulation results show that no proper geometry and dimension selection result in non uniform temperature within specimen and predicted to have effects on the consequence assessment of material behavior during hot deformation. Recommendations on finding proper specimen geometry for reducing temperature gradient along the gauge part of specimen will be given to create homogeneous temperature as much as possible in order to avoid uncertainty in consequent results of HTT.
A. Golbabai, M. Mammadov , S. Seifollahi ,
Volume 19, Issue 6 (IJES 2008)
Abstract
A new learning strategy is proposed for training of radial basis functions (RBF) network. We apply two different local optimization methods to update the output weights in training process, the gradient method and a combination of the gradient and Newton methods. Numerical results obtained in solving nonlinear integral equations show the excellent performance of the combined gradient method in comparison with gradient method as local back propagation algorithms.
L. Garooci Farshi, A. H. Mosafa , S. M. Seyed Mahmoudi ,
Volume 19, Issue 7 (IJES 2008)
Abstract
The exhaust gases of gas turbine power plant carry a significant amount of thermal energy that is usually expelled to the atmosphere this causes a reduction in net work and efficiency of gas turbine. On the other hand, the generated power and efficiency of gas turbine plants depend largely on the temperature of the inlet air, So that they both increase as the inlet air temperature decreases. The mentioned two problems can be solved by installing an absorption refrigeration cycle (ARC) at gas turbine inlet, working with thermal energy of exhaust gases. In this research, effect of inlet air cooling on gas turbine performance is studied. The work shows that, the net work and the efficiency will increase by 6-10% and 1-5% respectively for every 10°C decrease of inlet temperature. Since, coefficient of performance (COP) of ARC is low, with high pressure ratios in simple gas turbine (SGT) and with low pressure ratios in regenerative gas turbine (RGT), thermal energy of exhaust gases can not supply all the needed thermal energy for refrigeration cycle. The results show that, when an ejector is included in refrigeration cycle, the need for external energy source required for refrigeration cycle is reduced .
M.h. Sadegh, S. Jafari , B. Nasseroleslami ,
Volume 19, Issue 7 (IJES 2008)
Abstract
Modal parameter extraction of high speed shafts is of critical importance in mechanical design of turbo-pumps. Due to the complex geometry and peripheral components of turbo-pumps, difficulties can arise in determination of modal parameters. In this study, modal properties of a turbo-pump shaft, was studied by experimental modal analysis, and using different excitation techniques. An innovative suspending method is proposed to reduce noise-to-signal ratio, resulting from classic suspensions. Comparison of the experimental results obtained from the proposed suspension method and the traditional ones shows that the proposed approach was a promising method, when classic methods fall short of expectations in analysis of complex structures. To validate the experimental results, numerical solution was carried out using simplified geometric modeling combined with the Finite Element Method. The simplified modeling approach can be considered as a reliable theoretical method for numerical modal analysis of similar structures. Comparison of experimental and numerical results shows that there is a good conformity between the results of two approaches .
A. Jafari, S.h. Seyedein , M. Haghpanahi ,
Volume 19, Issue 7 (IJES 2008)
Abstract
Microcasting Shape-Deposition-Manufacturing is an approach to Solid-Freeform-Fabrication (SFF) process which is a novel method for rapid automated manufacturing of near-net-shape multi-material parts with complex geometries. By this method, objects are made by sequentially depositing molten metal droplets on a substrate and shaping by a CNC tool, layer by layer. Important issues are concerned with remelting dept of substrate, cooling rate and stress build up. In the present study attempts were made to numerically model the heat transfer and phase change within the droplet/substrate, making a better understanding of process performance. Thus, making a brief literature review, a 2-D transient heat transfer Finite Element Analysis was carried out by the use of ANSYS multiphysics, in which solidification is handled using apparent capacity method. Verification was done by available experimental data in the open literature to ensure model predictions. The model was run under various process parameters and obtained results presented in the form of temperature fields, solidification profiles, cooling curves and remelting history curves. Solidification profile studies predict a columnar dendritic solidified structure in the vertical orientation which was in agreement with metallographic sections published earlier. Parametric studied were also carried out under different boundary conditions, initial temperature of the droplet and Substrate temperature. It was concluded that 1) the process is not sensitive to convection/radiation effects from the surface. 2) the main parameter that can control the maximum remelting dept is initial temperature of the droplet. the more drop temperature, the more remelting dept. This parameter also affects cooling rate during solidification. 3) Increasing substrate temperature showed a decreased cooling rate in solid, which can be used to reduce residual stresses, but it had a minor effect on the cooling rates during solidification .
, , ,
Volume 20, Issue 1 (IJIEPR 2009)
Abstract
The problem of lot sizing, sequencing and scheduling multiple products in flow line production systems has been studied by several authors. Almost all of the researches in this area assumed that setup times and costs are sequence –independent even though sequence dependent setups are common in practice. In this paper we present a new mixed integer non linear program (MINLP) and a heuristic method to solve the problem in sequence dependent case. Furthermore, a genetic algorithm has been developed which applies this constructive heuristic to generate initial population. These two proposed solution methods are compared on randomly generated problems. Computational results show a clear superiority of our proposed GA for majority of the test problems.
S.m. Mohammad Seyedhoseini , M. Ali Hatefi,
Volume 20, Issue 1 (IJIEPR 2009)
Abstract
Selecting an effective project plan is a significant area in the project management. The present paper introduces a technique to identify the project plan efficient frontier for assessing the alternative project plans and selecting the best plan. The efficient frontier includes two criteria: the project cost and the project time. Besides, the paper presents a scheme to incorporate Directed Acyclic Graph (DAG) into the project risk analysis.
This scheme is used to estimate the expected impacts of the occurrence of the project risks on the project cost and the project time. Also, a theoretical model is defined to provide integration between project risk analysis and overall project planning using the breakdown structures. We believe that applying the proposed technique helps the company’s managers in most effective manner dealing with his complicated project plan assessment and selection problems. The application of the technique was implemented in the companies in construction industry in which represented a considerable cost and time improvements.