فصلنامه مدل سازی در مهندسی
پیاپی 40 (بهار 1394)

This paper consider flexible jobshop scheduling problem with minimizing maximum completion time of orders(Cmax), maximum workload of machines(Wmax) and total workloads (WT). The problem is known as Np-Hard. So finding the optimal solution in a reasonable time is impossible. A genetic algorithm named 2 part genetic algorithm is proposed for solving the problem. For evaluating the problem, we used 2 test data sets and proposed genetic algorithm is compared with other algorithms in the literature. Results show proposed genetic algorithm has higher performance for solving the problem in comparison with other algorithms.

The present paper deals with the parametric simulation and economic analysis of a CHP system based on an industrial microturbine to produce combined electricity and heat energy. The compressor pressure ratio and turbine inlet gas temperature have been chosen as design and optimization parameters for the current CHP system. In the present investigation, the simple and TRR model have been applied for estimation of the electricity price and other costs. The results show that the optimal performance of the system is obtained by the compressor pressure ratio in the range of 5 to 7 bar and decreasing of the turbine inlet temperature causes the reduction of the optimal pressure ratio. Also, the economical investigation results confirms that the system electricity price in an optimum case is about 20 to 25 cents, while the installation and preparation cost is about 500- 600 dollar per kilowatt. Comparative analysis between two applied economical models proves that the TRR model shows the better accurate results in comparison to simple model with about 9-12 percent.

Highway construction projects, due to the frequent repetition of many of the activities and buildings during the execution process, are known as linear-repetitive projects. In this projects work Interruptions and resources unemployment is causing time and cost waste. So scheduling as result to reduce time and cost waste, is extremely important. The proposed method in this study to scheduling optimization of highway construction projects is based on one of the principles of lean thinking in removal of the wastes (Muda). And Genetic Algorithm and NSGAII approach has been used to solve scheduling problems. Given that in many cases because of uncertainties in terms of project, time and cost of the activity can not determine conclusively, thus it is seen based on fuzzy approach to this problem too. The main advantage of this method is the special attention the continuity of work between units, so that work interruptions and the resources unemployment reduced to the lowest possible. Thus reducing of wastes, project will be closer to lean construction.

Flare tips usually suffer from high temperature that causes more maintenance. By controlling and decreasing the temperature it is possible to reduce the maintenance cost and reduce the emission. Considering numerical simulation technique for combustion, flare tip wall temperature and emission have been studied. Three different geometries include of cylindrical, conical shape and reverse cone shape for flare tip under several wind velocities have been simulated in a 3D space. This study shows that for parameter that have been studied in the research a cone shape can provide better situation such as less pollution or wall temperature.

In finite element analysis of flexible pavement, general characteristics’ layers usually are used. This issue does not specify effects of micromechanical behavior and its impact on the overall behavior of pavement. In this study has tried to obtain more accurate results using micromechanical approach and entering components’ properties of road in modeling. For this purpose, distribution of stress and strain and interaction between layers with micromechanical model in Abaqus is been discussed. With review of layers’ interaction the ability has obtained to design road according to independently or connected performance of layers compared to load Distribution as a design parameter. With this parameter, depth of soil sub grade suggested with modeling was in the range of 2 meters. Then with sensitivity analysis of independent layers’ interface compared to contact type of layers determined that strain compared to interface roughness has little sensitivity. But in the stress distribution, this issue not happened and interface roughness can influence the stress results.

This paper presents a design of fuzzy power system stabilizer (FPSS) using Harmony Search Algorithm (HSA) to damp low frequency oscillation in multi-machine power system where the parameters of proposed controller are optimized offline automatically by the proposed techniques. This newly proposed controller is more efficient because it cope with oscillations and different operating points. In this strategy the controller is tuned on line from the knowledge base and fuzzy interference. Two eigenvalue-based objective functions to enhance system damping of electromechanical modes are considered. This newly developed control strategy mixed the advantage of HSA and Fuzzy controller with simple structure while is easy to implement. The New England 10-unit 39-bus standard power system and 9 buses IEEE power system, under various system configurations and loading conditions, is employed to illustrate the performance of the proposed method. The effectiveness of proposed controller is compared with other techniques. Eigenvalue analysis and nonlinear simulation results show the effectiveness of the proposed controller.

Dynamic stress intensity factor determination on crack tip under impact loading is widely investigated. The history of impact loading in analytical researches is considered to be step function but experimental tests show that in impact loading, a small time is needed to the loading rise from zero to ultimate amount. This interval time is called rise time. In this research, Firstly, Dynamic stress intensity factor for a semi- infinite crack on a plate under impact loading is determined analytically but the history of loading is considered as a ramp function. Then a comparison between the analytical solution in this paper and the last results and also with finite element is done. Finally, the experimental method for changing the rise time on impact loading is presented and the effect of it in dynamic stress intensity factor is researched.

Creation and growth of vapor film in contact between hot objects and liquids is possible in many industries, including nuclear reactors, metals casting industries and paper production. Due to severe heat transfer from a hot objects (as droplets of molten metal) in contact with a coolant and relatively volatile matter (like water), the pressure inside vapor film formed on hot sphere increases at very short time and result in, sudden pressure wave inside related substance storage structure is created and so this wave may lead to destruct the storage structure. In this paper First, the mathematical model of problem is obtained and then conclusion of numerical solution and previous studies is compared. Then, the effects of changing various pressures in vessels On the vapor film radius, vapor film pressure is investigated and finally this model is developed for contact between reactor coolant and hot objects in such nuclear power plants in which pressurized water is 60 to 150 bars. Results show that in case of high pressure inside vessel, the pressure inside vapor film increases to high values in a very short time.

This paper is concerned with the effects of Nield number on heat transfer in a straight channel occupied by a porous medium. Investigation of force convective heat transfer of nanofluids in a porous channel has not been considered completely in the literature and this challenge is generally considered to be an open research topic that may require more study. The present work is an extension to our previous paper (see Maghrebi et al. [24]); such that three-equation energy model, for fluid/particle/solid phases, is employed in the porous channel. Moreover, one heat flux model is proposed. The fully-developed flow and steady Darcy-Brinkman equation is employed in the porous channel. The local thermal nonequlibrium model is assumed between fluid, particles and solid phases. It is assumed that the nanoparticles are distributed non-uniformly inside the channel. As a result, the volume fraction distribution equation is also coupled with other governing equations. The effects of Nield number and modified thermal capacity ratio on the heat transfer are completely studied.

EEG signals are usually contaminated with some interference like eye electrical activity. Ocular interference; is produced by eye electrical activity that propagates through the head volume conductor and contaminates the scalp EEG electrodes. Therefore, ocular artifact is stronger in frontal EEG recording channels. Removal of Ocular artifact is necessary in many applications such as BCI (Brain- Computer Interface) and EEG diagnostic usages. In order to remove ocular artifact, many methods have been proposed. Most of these methods have some problems especially in modeling of the mixture of EEG and Ocular artifact in the head volume conductor. In this research in addition to literature review and analysis of old methods, a new validation method based on modeling of EEG signal, Ocular artifact and the mixture of EEG and ocular artifact in the head volume conductor is presented in order to validate the methods of removal of ocular artifact.

The cold-formed steel stud framed shear wall using steel sheet sheathing is a lateral force resisting system for residential and low-rise commercial buildings. The current design specifications such as AISI Lateral Design 2007 Edition provides nominal shear strength for a limited range of sheet steel sheathed CFS shear wall configurations in terms of the sheathing thickness and the wall aspect ratio (height divided by width). Considering the ever increasing construction of buildings with cold formed steel and industrialization of the construction process, a need for shear strength of wall for wide range of wall geometrical dimensions seems to be inevitable. In this study, shear wall panels have been analyzed using the finite element method and the ABAQUS software and a method for modeling the screw connection of steel sheathing to frame has been presented so that the simulation of possible damage in connection locations resulting in displacements will be possible. Available experimental data has been used for validation of the model. After verification of finite element model, the effect of the various parameters of shear wall including height of wall, yield stress properties, frame member and sheeting thickness, and the method of connecting frame to the steel sheathing on the lateral behavior of wall was evaluated. At the end, some methods have been presented for increasing the lateral strength of these types of shear walls.

Abstract Isogeomteric Analysis is a newly developed method with some features that can be considered as ‎a potential substitute to other numerical methods such as finite elements and meshless approaches. ‎The NURBS technique, that allows precise geometrical modeling, plays an important role in this ‎method. However, similar to other numerical methods, existence of errors in the approximation of ‎the unknown function is inevitable. This paper is devoted to finding points with higher accuracy in ‎stress recovery by the isogeometric analysis. It can be shown that these points are coincident with ‎the Gauss quadrature points. By making use of these superconvergent points together with the ‎NURBS technique and the least square method, a surface is constructed for each component of ‎the stress tensor that represents the improved stresses. For this purpose, three examples with ‎available analytical results has been solved. The comparison of the obtained improved stresses ‎with the exact solution is used for the sake of verification of the proposed method. It is concluded ‎that the superconvergent points location in the isogeometric analysis are the same as the minimum ‎required Gauss points for the integration of a square element.‎