فصلنامه مدل سازی در مهندسی
پیاپی 50 (پاییز 1396)

In recent years, the various usage of fuel cells in vehicles has absorbed attention in industry and academic area. The fuel cells, are considered as a modern power sources in transportation. Compared with the internal combustion engines, fuel cells have the advantages of high energy efficiency and near zero emissions which is important to reduce global warming. However, vehicles powered only by fuel cells have some disadvantages, such as low power density, long start-up time, and slow power response. Hybridization of the fuel cell system with a secondary peaking power source is an effective approach to overcome the disadvantages of the fuel-cell-alone-powered vehicles. One of the possible combination is fuel cell/ battery composition. Obviously, the performance of the drive train relies mainly on control quality. This work presents an enhanced method for distributing power demand through the hybrid power sources. Fuzzy logic control and operation mode control have considered for this purpose. Genetic algorithm has implemented for tuning these strategies by means of off-line simulation in two combined driving cycle. Multiple objective fitness function deals with effective parameters (such as equivalent consumption, fuel cell and energy storage efficiency, state of charge variation, dynamic response…) for getting reliable and acceptable results from optimization process. Finally, these optimized strategies present a fully-advanced method for energy management system of fuel cell hybrid vehicles.

The low-dispersion and low-confinement loss waveguides are used in optical communication systems. The photonic crystal fibers (PCFs) can be used as waveguide. The several advantages of photonic crystal fibers cause to use these waveguides compared to the conventional fibers. In this paper, two structures of PCFs are designed and modeled. In the first design, a hexagonal photonic crystal fiber is presented which has nearly-zero dispersion at 1.55µm and 2.2w-1km-1 nonlinearity. In the improved structure, the dispersion reaches about zero and negative values and the confinement loss is obtained as small as 1×10-10dB/cm. The nonlinearity of the improved structure is also less than 9.31w-1km-1 and the negative dispersion in the wavelengths longer than 1.55 µm is obtained.

In this paper, the problem of scheduling and sequencing of multi-objective two-stage flexible flow shop with dedicated assembly lines, which produce various products during multiple planning periods, is proposed. The objectives of the proposed model are minimizing maximum completion time of products and total average weighted tardiness of production products. The first stage of the proposed flexible flow shop involves of several different parallel machines in site I and one machine in site II, and the second stage involves of two specific dedicated assembly lines. Each product has a specific bill of materials as well as has its own specific configuration which leading to difference processing times to assemble. Products composed of only single-process components are assigned to the first assembly line and products composed of at least a two-process component are assigned to the second assembly line. Components are placed on the associated dedicated assembly line in the second phase after completion of production process on the assigned machines in the first phase and final products will be produced by assembling the components. Uncertainty of demand of final products is handled via robust optimization technique based on the concept of uncertainty budget. The main contribution of this paper is development of a new mathematical model in flexible flow shop scheduling problem with dedicated assembly lines under uncertainty and presentation of a novel hybrid meta-heuristic for solving the proposed model. Due to the NP-hard nature of the proposed multi-objective problem, a hybrid evolutionary metaheuristic based on the strange Pareto evolutionary algorithm II is developed that incorporates a customized adaptive large neighborhood search as its local search heuristic. Extensive computational results illustrate the efficiency of the proposed model and solution algorithm in dealing with robust multi-objective flexible flow shop problem.

Solar pond is the one of the important ways for collecting and storing solar energy in the world. The salinity gradient solar ponds included the three layers of water-salt with different densities. In this study, the effect of the silica nanoparticles in the middle layer of the salt gradient solar pond was investigated for four different solar radiation zones in Iran. The nanoparticles volume concentrations, which were used in this study, were 1, 2, 5 and 10%. The results showed that nanoparticles improved solar pond efficiency and it increased with nanoparticles concentration. The temperature of the lower layer and efficiency of solar pond increased by 10% and 18 %, respectively. The nanoparticles were more efficient at cold zone.

Investigation of the radiation and natural convection heat losses from two finite concentric cylinders with radiation shields is performed numerically. The enclosure consists of two concentric cylinders with hotter inner cylinder and radiation shields with three different materials (aluminum, copper and steel) are inserted between the cylinders at different radial positions. The effects of physical properties (material), geometrical effects of radiation shields, inner cylinder temperature, and enclosure pressure on the heat losses have been investigated. The calculations were performed for two different inner temperatures as 473.15, and 673.15 K, and at two enclosure pressures of 0.2 and 1.0 atm. Results showed that the enclosure pressure and radiation shield emissivity together reduce the total heat loss from the inner cylinder.

In the present work, the experimental Study of the radiation and natural convection heat losses from two finite concentric cylinders with radiation shields is investigated. The enclosure consists of two concentric cylinders with hotter inner cylinder and radiation shields with three different materials (aluminum, copper and steel) are inserted between the cylinders at different radial positions. The effects of physical properties (emissivity), geometrical effects of radiation shields, inner cylinder temperature, and enclosure pressure on the heat losses have been investigated. The calculations were performed for two different inner temperatures as 200, and 400ºC, and at two enclosure pressures of 0.2 and 1.0 atm. Results showed that the enclosure pressure and radiation shield emissivity together reduce the total heat loss from the inner cylinder.

In this research, Si and nanowires with different lengths between 0.5 to 20 nm and thicknesses between 1 to 4 nm, are investigated by using structural mechanics approach and numerical method by ABAQUS software. DREIDING force field is used for force field. In this analysis critical buckling load are calculated. The results of this study show that critical load in ratio of the length of the nanowire thickness less than 10 will be diverted from the Euler equation. The same thickness and length, Si nanowires had the maximum critical buckling load. this method in comparison of other than methods such as molecular dynamics has higher analyzing speed and suitable accuracy.

This study deals with developing a dynamic model with capacity for use in aero-Thermodynamic real-time performance modeling of turbojet engines in MATLAB/Simulink environment. The elements of the engine are modeled by means of non-linear equations and using the inter component volume dynamics method. Through the use of the design point variables in the simulation, the model is capable to adapting with the characteristics of a particular engine. The three factors including, rotor dynamic, volume dynamic and heat soakage are considered in the dynamic model. To validate the modeling approach, the rotational speed and net thrust are compared with the results of the GSP program. The results show the ability of the model to simulate the transient performance such that the maximum error is estimated less than 4 percent. Then a new method to reduce the computational time and create a real-time performance capabilities, was studied. The results indicate that it is possible to select a fixed time step for solver and time scaling the smallest volume (from specified control volumes in the model), the real-time ability to be achieved. In these circumstances, the error in calculation of basic parameters of the engine is less than 0.5 percent.

The goal of this paper is to minimize self-excited vibration in the micro-milling process. This goal is achieved by using passive linear and nonlinear vibration absorbers. By reducing this unwanted vibration the final surface will have better surface quality. In this paper the micro-milling process is modelled as a two degree of freedom system and the effect of the cutting tool eccentricity is considered. To have stability for the larger depth of cut the optimal parameters for the passive vibration absorber is defined by a developed algorithm. The effects of vibration absorber on the stability and time response are investigated. The results show that using an optimal vibration absorber the vibration amplitude decreased and stability zone enlarged sensibility.

In this paper, parametric analysis and optimization of the transcritical ejector refrigeration cycle using different working fluids have been proposed which can be employed in the parts of solar energy processes. The main advantages of using ejector in the refrigeration cycles, which often use instead of the compressor, are simplicity in construction and maintenance, high reliability and low cost. In this study, the transcritical ejector refrigeration cycle is modelled using EES software and the effects of different parameters such as temperature and pressure of different parts of cycle on the coefficient of performance and entrainment ratio are investigated. In continued, the coefficient of performance of the transcritical ejector refrigeration cycle for four different working fluids is optimized using the combination the Artificial Neural Network and Particle Swarm Optimization algorithm.

In this work, the fluid flow and heat transfer and entropy generation of mixed convection in "Γ" -shaped cavity filled with Al2O3-Water-EG have been studied. For this propose, we used from a FORTRAN program based on finite volume method (FVM) and SIMPER algorithm. This investigation have done for volume fraction from 0 to 0.04, Richardson number between 0.01 and 100, and Grashof number equal to 104 for two situation, moving top wall with velocity of U from right to left and moving left vertical wall equal to V from up to bottom. In all cases average Nusselt number increase with adding of nanoparticle or decreasing of Richardson number. This phenomenon is sensitive with reduction of Richardson number. In addition for all Richardson number and for two cases total entropy generation and entropy generation due to conduction increase with nanoparticle volume fraction.

Topology optimization methods enable designers to find the best structural layout for required structural performances. Most papers in this area have been concerned with the optimization of structures with linear material. However, there are several structures involving nonlinear material.Evolutionary structural optimization (ESO) is based on the simple concept of systematically removing inefficient material from the structure after each finite element analysis, so that the resulting design is gradually evolved to an optimum. This method has been successfully applied to optimum material distribution problems for continuum structures and has been extended to a wide range of structural optimization problems.
This paper is concerned with optimization of elastic and elasto-plastic bodies, based on the von Misses stress criterion using two method.Several examples are presented to verify the proposed optimization methods. Results are compared for these two criteria and against elastic and elasto-plastic material and also with that of the adaptive method. It is concluded that for elastic and elasto-plastic bodies, the behavior of the both criteria is more or less the same and they can be used alternatively.

In this study, closed-form relations are obtained for the frequency equations of radial (in-plane) and transverse (out-of–plane) free vibration of a circular plate with free, simply-support, and clamped boundary conditions. Governing equations are obtained using Hamilton's principal. In the case of radial vibration, governing equations are coupled to each other. So, they are decoupled using Helmholtz decomposition technique and solved using separation of variables method. In the case of transverse vibration, governing equations are analytically solved using separation of variables method. Finally, natural frequencies obtained from the frequency equations are compared with finite element results for an isotropic homogeneous circular plate with various boundary conditions.

The vehicle routing problem (VRP) involves routing a fleet of vehicles for serving to a number of customers, with the objective of minimizing the total distance traveled by all the vehicles. In this Problem, the vehicles are required to return to the depot after completing service. The open vehicle routing problem (OVRP) is different from most variants of vehicle routing problems from the literature in that the vehicle does not return to the depot after serving the last customer. The constraints considered in this problem are the following: all the vehicles have the same capacity the traveling time of each vehicle should not exceed a given threshold, which is defined by the drivers_ legal traveling time the total demand of all the customers on a route must not exceed the capacity of the vehicle each customer is visited just once by one of the vehicles, and its requirements must be completely fulfilled. The ant colony system (ACS) is one of the most famous metaheuristic algorithms that differs from the other ant colony optimization (ACO) instances due to its transition rule and updating pheromone. Aimed at the disadvantages existed in the current ACS algorithms for solving the OVRP, two effective modificitions including heuristic information and transition rule are proposed in this paper. Furthermore, this algorithm is mixed with lin-kernigan local search for improving solutions of the ants and exploites more strong solutions. Computational results on sixteen standard benchmark problem instances show that the proposed algorithm is comparable in terms of solution quality to the best performing published heuristics.

Seismic events all over the world have shown that ground motions in vicinity of causative faults (within a distance of 15 km from the fault) may be categorized as large-velocity pulse and large-displacement fault which have the potential to cause considerable structural damage. Consequently, the main cause of long-period pulse formation is the cumulative effect of shear wave propagation along the fault rupture according to seismological investigations. Near-fault ground motions are severely affected by fault mechanism, rupture propagating direction relative to site and finally the permanent deformation of ground these parameters will cause two significant effects called directivity and fling step which should be taken into account in estimating the ground motions in vicinity of causative faults. The forward-directivity depends on rupture mechanism and slip direction relative to the site and is characterized by a large pulse occurring at the initiation of the record and oriented in a perpendicular direction relative to the fault plane but in contrast, the fling-step is affected by tectonic deformation in the fault and commonly generates permanent static displacement which happens parallel to the strike of the fault for strike-slip events, and normal-to-fault direction for dip-slip earthquakes. Because of the unique characteristics of the near-fault ground motions and their potential to cause severe damage to structures designed to comply with the criteria mostly based on far-field earthquakes, it is necessary to characterize and parameterize these special types of ground motions by simple and reliable mathematical models having input parameters which have clear physical meaning and scale to the earthquake magnitude. One of the newest models is the one proposed by Hoseini Vaez (Hoseini Vaez & el, 2013). The main objective of this study is to investigate capable of predicting the response of MDOF systems by model proposed by Hoseini Vaez. Generic frame models with 3 different heights and three levels of design ductility have been used to evaluate their response to 11 actual near-fault ground motions and the corresponding pulses calibrated to them. It has been found that the equivalent mathematical model being evaluated in this work is capable of estimating, fairly accurately, the height-wise distribution of inter-story drifts and maximum rotation of beams for the regular plane moment resisting frames used in this work.

Iran plateauis on the tape of ALP-Himalayan and is located in one of the the most active earthquake prone in the world. As earthquake has made many human calamity, sofar.Undoubtedly urban development without cinsidering this phenomenon will lead to human(bodily)and financial damages. Incomplete and sometimes false estimations from maximum acceleration earthquake on design during its useful life is of the most important damages factors on designs.Nishapur is situated in the east of Iran and it is very important because of over population, historical and cultural segnificance and situating near three active fault.so, it looks necessary that for more precise estimation of used earthquake parameters on structure design. so it proceed to data collection and refining such fault specification and earthquake catalogand survey the situation seismic study area and by using of lowering relation,is done the confired and also possible analysis of, aximum accceleration in an area with 200km radius. Analysis the possible risk on risk level 1identic to interpret the instruction seismic upgrading on existing buildings is for 475return peroid in 50 years the useful life of the structure[1] and finally it drawed the maximum estimated acceleration maps shape for two types(Vs375m/s hard).

In this paper, for the first time functionality using FRP material as case of buckling restrained brace to prevent buckling, has been studied by stress tests on various samples in vitro. The experiments was performed on different samples bracing with GFRP case and bracing without GFRP case with a fixed length of 800mm and the results were interesting. In the testing sample bracing without casing, the maximum axial compressive load bearing by bracing was recorded 52.45 kN, while it was lower submitted to tensile steel core, namely 198 kN And overall buckling was developed. But in the testing sample bracing with GFRP case was surrounded around of fort axis in total free length core, the axial compressive load bearing by core was recorded 200 kN while it was most of submitted to tensile steel core and It was found that this innovation has contributed conditions buckling restrained brace, while there is no buckling in the bracing view. Also check the load-displacement curve showed that the energy absorption capacity of the sample bracing with GFRP case was surrounded around of fort axis in total free length core was Compared to other samples has increased substantially.

In this paper the frequency domain Modeling of a multiconductor line illuminated by a nearby lightning stroke is described, considering also variations of the line parameters along its length (nonuniform line case).
Modeling of the illuminated line is based on Taylor’s formulation, while the incident electromagnetic field is described following Master and Uman’s expressions. The numerical Laplase transform algorithm is used for the frequency time transformation is required. Comparison whit an experimental result previously published is provided for an initial validation of the method. As a second application example, a test case is used to analyze the effect of the point of impact on the magnitude and waveshape of the transient overvoltages obtained. The effect of line nonuniformities is also discussed.

In this study, a collaboration model is proposed to determine the optimal order quantity and the corporate social responsibility (CSR) investment in a two-stage pharmaceutical supply chain. The supplier, which is socially concerned, invests to improve CSR by implementing the medication take-back program. Furthermore, considering a newsvendor setting, the retailer has to determine its order quantity before each season. Firstly, the member's performance in both centralized and decentralized decision making is investigated and the optimal solutions are derived, then a collaboration model is proposed to determine the optimal order quantity and MTBP investment to maximize the whole SC profit while ensuring both members participate in the scheme