Materials and Energy Research CenterInternational Journal of Engineering1025-249511119980201Mathematical Model of Unsteady Groundwater Flow Through Aquifers and Calibration Via a Non-Linear Optimization Technique11471191ENM. KolahdoozanCivil Engineering, Amirkabir University of Technology0000-0002-6419-804XH. M. V. SamaniCivil Engineering, Shahid Chamran University of AhvazJournal Article19700101In this study, the general partial differential equation of unsteady groundwater flow through non-homogeneous and anisotropic aquifer was solved by the fully implicit finite difference method with control volume approach. The calibration of permeability and storage coefficients as model parameters was performed by a transformation technique and application of Powell's non-linear optimization method. The developed model has been found efficient in terms of convergence and accuracy. Capability of the model, has also been demonstrated by being applied to a real aquifer. https://www.ije.ir/article_71191_9751251363e02da18b0438b45f8bb2f3.pdfMaterials and Energy Research CenterInternational Journal of Engineering1025-249511119980201Characteristic of P-type AlAs/GaAs Bragg Mirrors Grown by MBE on (100) and (311)A Oriented Substrates152071192ENMohammad Moravvej FarshiElecterical Engineering, Tarbiat Modarres UniversityJournal Article19700101P-type GaAs/AlAs distributed Bragg mirrors have been grown using molecular beam epitaxy on (100) and (311)A GaAs substrates in a similar conditions. A comparison of I-V measurements shows that the resistance of the ungraded mirrors grown on the (311)A substrate is 35 times lower than those grown on the (100) substrate with similar structure. The effective barrier heights for both (311 )A and (100) barriers were extracted from their Arrhenius behaviour, obtained from their current temperature dependence. The calculated values for (311)A and (100) effective barrier heights are 141 meV and 341 meV, respectively. The room temperature values of the specific differential resistance for both devices around zero bias [i.e. Rc=(dV/dJ)Iv=0] were calculated. The approximated values for (311)A and (100) devices are 80 mW-cm2 and 2.8mW-cm2 respectively. https://www.ije.ir/article_71192_77a43f0f032877903a69103aaf1c3127.pdfMaterials and Energy Research CenterInternational Journal of Engineering1025-249511119980201Quenching Effect on the Pb-Substituted Bi-Based Bulk Ceramic Superconductors212871193ENM. AkhavanMagnet Research Lab., Department of Physics, Sharif University of TechnologyH. SalamatiPhysics, Isfahan University of TechnologyJournal Article19700101The effect of cooling process for the synthesis and the superconductivity properties of Pb-substituted Bi-based materials, has been investigated. The preparation condition for the formation of (2,2,2,3) phase has been examined. The influence of thermal condition of the synthesis and quenching on the critical temperature and the content of 110K phase was investigated. Results of the ac-susceptibility, resistivity measurements, XRD, and SEM are given. Analysis is made of the effect of processing on the properties of grain boundaries in these materials.https://www.ije.ir/article_71193_206eb69cb8022f3249b65bdc11b894e6.pdfMaterials and Energy Research CenterInternational Journal of Engineering1025-249511119980201Boundary Layers and Heat Transfer on a Rotating Rough Disk293671194ENA. HeydariMechanical Engineering, Sharif University of TechnologyJournal Article19700101The study of flow and heat transfer over rotating circular disks is of great practical importance in understanding the cooling of rotatory machinery such as turbines, electric motors and design and manufacturing of computer disk drives. This paper presents an analysis of the flow and heat transfer over a heated infinite permeable rough disk. Boundary-layer approximation reduces the elliptic Navier-Stokes equations to parabolic equations, where the Keller-Cebeci method of finite - difference solution is used to solve the resulting system of partial-differential equations. The surface roughness is assumed to influence the turbulent boundary layer by adding a roughness parameter height K, while a variable surface temperature induces heat transfer into the flow of fluid over the rotating disk. Blowing and suction is also considered as a means of varying the surface shear distribution. The resulting curve-fit equations to the numerically calculated results of the skin-friction coefficient for three regions of laminar, transition and turbulent flow are shown to be consistent to those obtained for flow over a flat plate or a circular cylinder. To study the influence of surface roughness, calculations for various surface roughness parameters are made and results are presented. Velocity and temperature profiles and the shear stress and heat flux at the surface of the rotating disk are presented for a range of the above parameters.https://www.ije.ir/article_71194_b97db795d579246cf2b0384a0d8051e8.pdfMaterials and Energy Research CenterInternational Journal of Engineering1025-249511119980201Development of a Mathematical Model for Prediction of Pollutants Emission in D. I. Diesel Engines374271195ENB. Omidi Kashani, University of BirjandV. PirouzpanahMechanical Engineering, University of TabrizJournal Article19700101Major pollutants emission from Direct-Injection (D.I) diesel engines are predicted by means of a mathematical model. In order to construct such a model, an integral Multi-Zone Combustion Model (MZCM) is formulated, which basically consists of jet mixing and combustion submodels. In MZCM, variation of injection pressure is considered. Also time period of ignition delay is predicted by considering the physical and chemical processes. The MZCM provides input data such as zonal temperature, pressure, and mixture strength to the emission model. In the emission model, the major pollutants in diesel engines, such as Nitrogen Oxides (NOx) and soot particles are evaluated. For calculation of NOx concentration, extended Zeldovich mechanism has been used. For prediction of soot particles concentration, the amount of net soot is calculated by considering the difference between the rates of soot formation and soot oxidation inside zones. Results show that, soot particles form in the fuel rich zones and its oxidation occurs in the oxygen-rich zones of the fuel jet. NOx concentration in the middle zones of the jet (near stoichiometric) is high, while in the tip and tail of the jet is low. For verification, the model is validated with the conditions of typical medium and high speed D. I. diesel engines. The comparison shows a good agreement between the experimental and predicted results.https://www.ije.ir/article_71195_0707f77960b9e9d449451c0220b5ed33.pdfMaterials and Energy Research CenterInternational Journal of Engineering1025-249511119980201Appropriate Loading Techniques in Finite Element Analysis of Underground Structures435271196ENJ. HematianMining Engineering, Shahrood University of TechnologyJournal Article19700101Stability of underground structures is assessed by comparing rock strength with induced stresses resulted from ground stresses. Rock mass surrounding the opening may fail either by fracture or excessive deformation caused. Accurate calculation of induced stresses is therefore fundamental in the stability analysis of an opening. Although numerical methods, particularly finite element method, are very promising methods in finding out induced stresses, special care must be taken at various stages of constructing and analysing such models. This paper describes the significance of loading technique; the way that ground stresses are applied to the finite element model in finite element analysis (FEA) of underground structures. The purpose of this research is to illustrate the results obtained from similar models which were constructed in different ways regarding the loading technique. Key factors for choosing an appropriate loading method whilst considering the in-situ condition of the structure are addressed. To carry out this investigation, the three-dimensional finite element program, NASTRAN, was used. The results of FE models were compared with those obtained from closed solution methods as well as field investigations conducted both during this research and reported by others. Based on the results of this study, appropriate loading techniques are developed and suggested for various conditions. The application of these techniques to the stability analysis of underground structures resulted in encouraging findings.https://www.ije.ir/article_71196_0707f77960b9e9d449451c0220b5ed33.pdfMaterials and Energy Research CenterInternational Journal of Engineering1025-249511119980201Rate of Pressure Rise in SI Engine Cylinder and its Relation to Knock (RESEARCH NOTE)535971197ENM. Karimifar, Shahid Bahonar University of KermanJournal Article19700101Tremendous efforts have been devoted to study the complex phenomenon "knock in spark ignition engines. There is an increasing interest in providing some tools to study knock in simulated data. In the previous studies, engine cylinder pressure oscillation has been used to investigate knock. Unless those methods involved highly complex non-detailed chemical relations, the previous studies were dependent on the information derived from oscillations of the engine pressure data. Therefore, in this paper, in order to develop a technique for predicting knock with least dependency on detailed operating information and independent of engine pressure oscillations, rate of pressure rise of individual cycles was measured. This was carried out by measuring the slope of the best straight line fitted to 5-degree steps of experimental engine pressure data in which knock intensity are specified. The experimental data were measured in a research variable compression ratio engine over a wide range of operating conditions using pure iso octane and a commercial fuel at 0.25 degree crank angle intervals. A conversion unit was designed to convert the CUC-DOS measured raw data to MS-DOS data. A new criterion, completely independent of the engine cylinder pressure oscillations, was established to predict the occurrence of knock. Independency of the proposed technique on end-gas temperature and burning rate calculations eliminate the complexity and errors of calculating these parameters in the prediction procedures.https://www.ije.ir/article_71197_1ef3c207c1980ce6b1dfaa03980b7a50.pdf