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Publication Date: 2009
International Journal of Hydrogen Energy (03603199) 34(5)pp. 2396-2407
This paper presents exergy analysis of a hybrid solid oxide fuel cell and gas turbine (SOFC/GT) system in comparison with retrofitted system with steam injection. It is proposed to use hot gas turbine exhaust gases heat in a heat recovery steam generator to produce steam and inject it into gas turbine. Based on a steady-state model of the processes, exergy flow rates are calculated for all components and a detailed exergy analysis is performed. The components with the highest proportion of irreversibility in the hybrid systems are identified and compared. It is shown that steam injection decreases the wasted exergy from the system exhaust and boosts the exergetic efficiency by 12.11%. Also, 17.87% and 12.31% increase in exergy output and the thermal efficiency, respectively, is demonstrated. A parametric study is also performed for different values of compression pressure ratio, current density and pinch point temperature difference. © 2008 International Association for Hydrogen Energy.
Publication Date: 2010
International Journal Of Thermodynamics (13019724) 13(4)pp. 153-160
In this paper, an exergetic performance analysis of unglazed transpired collectors (UTC), as well as an exergetic optimization of a typical UTC is performed. A steady-state model is used to calculate heat transfers and pressure drop through the perforated plate and back wall. In order to maximize the exergy efficiency, the optimization procedure is carried out for some important parameters including plate hole diameter and hole pitch. A maximum efficieny of 2.28% is obtained. In spite of all the thermal performance advantages, the exergetic efficiency of the UTC is significantly lower than its energetic efficiency. Other parameters such as incident solar radiation, approach velocity, plate hole diameter and pitch are examined in the parametric study.
Publication Date: 2010
pp. 217-221
Elastomers, in particular rubbers, are used in a wide variety of products ranging from rubber hoses, isolation bearings, and shock absorbers to tires. Rubber has good properties and is thermal and electrical resistant. We used carbon nanotube in rubber and modeled this composite with ABAQUS software. Because of hyperelastic behavior of rubber we had to use a strain energy function for nanocomposites modeling. We tested a sample of rubber and gained uniaxial, biaxial and planar test data and then used this data to get a good strain energy function. Mooney-Rivlin form, Neo-Hookean form, Ogden form, Polynomial form, reduced polynomial form, Van der Waals form and etc, are some methods to get strain function energy. Modulus of elasticity and Poisson ratio and some other mechanical properties gained for a representative volume element (RVE) of composite in this work. We also considered rubber as an elastic material and gained mechanical properties of composite and then compared result for elastic and hyperelastic rubber matrix together.
Publication Date: 2010
Journal of Solid Mechanics (discontinued) (20087683) 2(1)pp. 43-49
An elastomer is a polymer with the property of viscoelasticity, generally having notably low Young's modulus and high yield strain compared with other materials. Elastomers, in particular rubbers, are used in a wide variety of products ranging from rubber hoses, isolation bearings, and shock absorbers to tires. Rubber has good properties and is thermal and electrical resistant. We used carbon nanotube in rubber and modeled this composite with ABAQUS software. Because of hyperelastic behavior of rubber we had to use a strain energy function for nanocomposites modeling. A sample of rubber was tested and gained uniaxial, biaxial and planar test data and then the data used to get a good strain energy function. Mooney-Rivlin form, Neo-Hookean form, Ogden form, Polynomial form, reduced polynomial form, Van der Waals form etc, are some methods to get strain function energy. Modulus of elasticity and Poisson ratio and some other mechanical properties gained for a representative volume element (RVE) of composite in this work. We also considered rubber as an elastic material and gained mechanical properties of composite and then compared result for elastic and hyperelastic rubber matrix together. © 2010 IAU, Arak Branch.
Publication Date: 2011
Micro and Nano Letters (17500443) 6(6)pp. 402-404
Nanostructured thin film copper fabricated by electron beam-physical vapour deposition (EB-PVD) method has unique properties, which make it different from the other deposits. In this study, nanostructured copper deposits were produced by EB-PVD as well as pulse plating techniques. Transmission electron microscopy was used for investigating the morphology of the deposited film. Surface roughness of deposits was measured by DEKTAK profilometer. Furthermore, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarisation methods were used to study the corrosive behaviour of the films. The surface morphology of corroded samples was obtained by scanning electron microscopy (SEM). Data obtained by polarisation, EIS and SEM suggested that corrosion resistance of EB-PVD deposit was higher than pulse plating deposit. This might be caused by its lower surface roughness and high purity owing to deposition in high vacuum. © 2011 The Institution of Engineering and Technology.
Publication Date: 2011
International Review of Mechanical Engineering (19708734) (1)
The SCalar Dissipation Scheme (SCDS-1) and MAtrix Dissipation Scheme (MADS-1) are two common artificial dissipation schemes that have been used for several years. Two new artificial dissipation schemes are introduced by using the QUICK scheme in this paper (SCDS-2, MADS-2). The capability of these four artificial dissipation schemes is compared for two different problems. First for the channel flow problem and then for the moving vortex problem. The results of two problems show that the accuracy of these new artificial dissipation schemes (SCDS-2, MADS-2) are almost equal to two other schemes (SCDS-1, MADS-1). The implementation of the boundary conditions is more convenient in the new schemes. Also the new artificial dissipation schemes don't need any sensor. © 2011 Praise Worthy Prize S.r.l. - All rights reserved.
Publication Date: 2011
Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering (20413025) (8)
The conventional vorticity confinement methods have a constant confinement parameter that should be determined for every problem by trial and error. In this article, vorticity confinement parameters are successfully developed for compressible flows. The first new confinement parameter is proportional to spectral radii of the flux Jacobian matrix. Therefore, the confinement parameter implicitly contains the grid size and the other local fluid properties. In order to gain confidence in the applicability of vorticity confinement, it would be ideal to completely eliminate such constant parameters. In the next part of this article, a suitable relation is introduced for the vorticity confinement parameter that does not need any constant coefficient. The scalar dissipation scheme (SCDS-1) and matrix dissipation scheme (MADS-1) are two common artificial dissipation schemes that have been used for several years. Two new artificial dissipation schemes are introduced by using the QUICK scheme in this article (SCDS-2, MADS-2). The capabilities of these four artificial dissipation schemes are compared for channel flow problem. Then, the new confinement parameters and artificial dissipation schemes are used for solving moving vortex in a uniform flow and supersonic shear layer problems. The methods have been shown to be very effective at treating shock waves and vortex dominant flows. © Authors 2011.
Publication Date: 2012
Journal Of Applied Fluid Mechanics (17353572) (3)
In this paper vorticity confinement parameters are successfully developed for compressible flows. The first new confinement parameter is proportional to spectral radii of the flux Jacobian matrix. Therefore, the confinement parameter implicitly contains the local conditions of the flow field. This new method is named as lambda vorticity confinement method. In order to gain confidence in the applicability of vorticity confinement, it would be ideal to completely eliminate constant coefficients from confinement parameters. Because these constant coefficients should be determined for every problem by trial and error and it takes a long time. In the next part of this paper, a suitable relation is introduced for the vorticity confinement parameter that doesn't need any constant coefficient. This new method is named as adaptive vorticity confinement method. Then the capability of these new methods is compared with the other vorticity confinement methods for solving shock-vortex interaction and three dimensional moving vortex problems.
Publication Date: 2012
Materials and Design (02641275) 34pp. 603-608
Elastomers, particularly rubbers, are viscoelastic polymers with low Young's modulus. In this research, carbon nanotubes were used in the rubber and a rubber-carbon nanotube composite was modeled by ABAQUS™ software. Due to hyperelastic behavior of the rubber, strain function energy was used for the modeling. A sample of rubber was tested and uniaxial, biaxial, as well as planar test data obtained in these tests were used to get an energy function. Polynomial and reduced polynomial form are two common methods to achieve strain energy function. In this paper, elasticity modulus and Poisson ratio were measured for a representative volume element (RVE) of composite. Rubber was also considered as an elastic material and its composite properties in this state compared by hyperelastic rubber matrix assumption. ABAQUS was used to create a three dimensional finite element model of a single long wavy nanotube with diameter of D which perfectly bonded to matrix material. Nanotube waviness was modeled by sinusoidal carbon nanotube shape. Results showed that mechanical properties of the rubber will extremely change by adding carbon nanotube. Furthermore, several volume fractions of carbon nanotube in rubber were modeled and it was shown that stiffness of nanocomposite increases by more volume fraction of carbon nanotubes. © 2011 Elsevier Ltd.
Publication Date: 2012
Micro and Nano Letters (17500443) 7(4)pp. 380-383
Corrosion resistance of nanocrystalline 316L stainless steel was compared with a coarse-grained (CG) one using potentiodynamic polarisation and electrochemical impedance spectroscopy methods and electron microscopy. The results showed that the corrosion resistance of nanocrystalline 316L stainless steel was higher than CG stainless steel. It was attributed to unstable passive layer on CG 316L stainless steel, which could be removed in a corrosive medium. The lower grain size facilitated fast diffusion of Cr and formation of passive layer. Nanocrystalline 316L stainless steel showed a relatively stable current density in anodic potentials, which was related to the higher corrosion resistance of nanocrystalline 316L stainless steel. © 2012 The Institution of Engineering and Technology.
Publication Date: 2013
Journal of Computational and Theoretical Nanoscience (15461955) 10(4)pp. 1033-1037
Two carbon nanotubes with different diameters can form a carbon nanotube junction, which can be applied to build some electromechanical devices such as semiconductors, nano-nuzzles, and nano-diffusers. In this research, two zigzag carbon nanotubes with chiral vector (5, 0) and (10, 0) were considered and their mechanical properties were obtained from the molecular mechanic approach. Then, Special algorithm was used to connect latter CNTs. To model this junction molecular mechanic approach was applied. In the next step, mechanical properties and natural frequencies of the connected carbon nanotubes were measured. In this research, it was found that there is a remarkable increase in Young modulus of carbon nanotube junction. Furthermore, natural frequencies of connected carbon nanotubes, plus primary carbon nanotubes were compared together. Moreover, considering the same boundary conditions with primary carbon nanotubes, it was revealed that connected carbon nanotubes have different vibration behaviors. Copyright © 2013 American Scientific Publishers All rights reserved.
Motahar, S. ,
Nikkam, N. ,
Alemrajabi, A.A. ,
Khodabandeh, R. ,
Toprak, M.S. ,
Muhammed, M. Publication Date: 2014
International Communications in Heat and Mass Transfer (07351933) 56pp. 114-120
In this research, mesoporous silica (MPSiO2) nanoparticles were dispersed in n-octadecane as an organic phase change material (PCM) in order to produce a novel composite for thermal storage. Stable PCMs containing 1wt.%, 3wt.% and 5wt.% MPSiO2 nanoparticles (PCM/MPSiO2) were fabricated by dispersing MPSiO2 in PCM. MPSiO2 particles were investigated by SEM and TEM techniques, which showed high order of porosity and spherical particles of ca. 300nm. The thermal conductivity in both solid and liquid phases was measured by transient plane source (TPS) technique in the temperature range of 5-55°C. A maximum thermal conductivity enhancement of 5% for 3wt.% MPSiO2 at 5°C, and 6% for 5wt.% MPSiO2 at 55°C was experimentally obtained. Moreover, it was observed that enhancement in thermal conductivity is non-monotonic in solid phase with increasing MPSiO2 particle loading. The viscosity results showed that for mass fractions of nanoparticles greater than 3% in liquid PCM, the behavior of liquid is non-Newtonian. Also, the viscosity of PCM containing MPSiO2 nanoparticles was measured to be increased up to 60% compared to the liquid PCM for 5wt.% MPSiO2 at 35°C. © 2014.
Motahar, S. ,
Nikkam, N. ,
Alemrajabi, A.A. ,
Khodabandeh, R. ,
Toprak, M.S. ,
Muhammed, M. Publication Date: 2014
International Communications in Heat and Mass Transfer (07351933) 59pp. 68-74
In the present study, titanium (IV) oxide (TiO2) nanoparticles were dispersed in n-octadecane to fabricate phase change material (PCM) with enhanced properties and behavior. Thermal conductivity (TC) and viscosity of n-octadecane/TiO2 dispersions were experimentally investigated using transient plane source (TPS) technique and rotating coaxial cylindrical viscometer, respectively. The results showed that the TC of n-octadecane/TiO2 dispersion depends on temperature and nanoparticle loading. A non-monotonic behavior of TC enhancement in both solid and liquid phases was observed. In solid phase, the maximum TC enhancement occurred at 3wt.% of nanoparticles. When the nanoparticle mass fraction was over 4% in liquid phase, the TC started to decrease. The rheological behavior of the n-octadecane/TiO2 samples indicated that dispersions with low nanoparticle mass fractions demonstrate Newtonian behavior, and for higher mass factions the shear-thinning behavior was observed. Shear stress vs. shear rate curves showed that the liquid phase of PCM behaves like a Bingham plastic fluid for mass fraction greater than 1%. As expected, the effective viscosity could be influenced by temperature. At the shear rate of 48.92s-1 for 3wt.% nanoparticles, the effective viscosity decreased by 26.8% while temperature increased from 35°C to 55°C. For the investigated n-octadecane/TiO2 dispersions, new thermophysical correlations are proposed for predicting TC and rheological properties. © 2014 Elsevier Ltd.
Publication Date: 2015
Applied Thermal Engineering (13594311)
In this paper, effects of turbine blade roughness and steam condensation on deviation angle and performance losses of the wet stages are investigated. The steam is assumed to obey non-equilibrium thermodynamic model, in which abrupt formation of liquid droplets produces condensation shocks. An AUSM-van Leer hybrid scheme is used to solve two-phase turbulent transonic steam flow around turbine rotor tip sections. The dominant solver of the computational domain is taken to be the AUSM scheme (1993) that in regions with large gradients smoothly switches to van Leer scheme (1979). This guarantees a robust hybrid scheme throughout the domain. It is observed that as a result of condensation, the aerothermodymics of the flow field changes. For example for a supersonic wet case with exit isentropic Mach number Me,is = 1.45, the deviation angle and total pressure loss coefficient change by 65% and 200%, respectively, when compared with dry case. It is also observed that losses due to surface roughness in subsonic regions are much larger than those in supersonic regions. Hence, as a practical guideline for maintenance sequences, cleaning of subsonic parts of steam turbines should be considered first. © 2015 Published by Elsevier Ltd.
Publication Date: 2016
Journal of Solid Mechanics (discontinued) (20087683) 8(4)pp. 781-787
This work is conducted to obtain mechanical properties of microtubule. For this aim, interaction energy in alpha-beta, beta-alpha, alpha-alpha, and beta-beta dimers was calculated using the molecular dynamic simulation. Force-distance diagrams for these dimers were obtained using the relation between potential energy and force. Afterwards, instead of each tubulin, one sphere with 55 KDa weight connecting to another tubulin with a nonlinear connection such as nonlinear spring could be considered. The mechanical model of microtubule was used to calculate Young's modulus based on finite element method. Obtained Young's modulus has good agreement with previous works. Also, natural frequency of microtubules was calculated based on finite element method. © 2016 IAU, Arak Branch. All rights reserved.
Publication Date: 2016
Journal of Mechanical Science and Technology (1738494X) (3)
In this paper, the AUSM-van Leer hybrid scheme is extended to solve the governing equations of two-phase transonic flow in a steam turbine stage. The dominant solver of the computational domain is the non-diffusive AUSM scheme (1993), while a smooth transition from AUSM in regions with large gradients to the diffusive scheme by van Leer (1979) guarantees a robust hybrid scheme throughout the domain. The steam is assumed to obey non-equilibrium thermodynamic model. The effects of condensation on different specifications of the flow field are studied at subsonic/supersonic flow regimes. It is observed that as a result of condensation, the aerothermodymics of the flow field changes. For example in supersonic wet case (Pb = 14.55 kPa), pressure loss coefficient of rotor and total entropy generation are, respectively, 77% and 29% more than those in dry conditions. Also the value of rotor deviation angle reaches 6.27° in wet case and Pb = 14.55 kPa. © 2016, The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.
Publication Date: 2016
Applied Thermal Engineering (13594311) 102pp. 1462-1472
Piston bowl geometries are crucial to the combustion and emission characteristics of reactivity controlled compression ignition (RCCI) engines. The present numerical study explores the effects of piston bowl geometry on natural gas/diesel RCCI performance and emissions at medium engine load. Three different piston bowl geometries including stock, bathtub and cylindrical with constant compression ratio 16.1:1 are selected using double injection strategy and influences of engine speed, piston bowl depth and chamfered ring-land are investigated. It is found that the bowl profile does not affect combustion of RCCI engine at low engine speeds, but it has much considerable effect at higher engine speeds. The results obtained also show that bathtub design yields the best performance and emissions at higher speeds. It is also reported that both piston bowl depth and chamfered ring-land can also affect engine-out emissions specially UHC and CO emissions. © 2016 Elsevier Ltd. All rights reserved.
Publication Date: 2016
Heat and Mass Transfer (09477411) 52(8)pp. 1621-1631
In the present study, carbon-based nanomaterials including multiwalled carbon nanotubes (MWCNTs) and vapor-grown carbon nanofibers (CNFs) were dispersed in n-octadecane as a phase change material (PCM) at various mass fractions of 0.5, 1, 2 and 5 wt% by the two-step method. The transient plane source technique was used to measure thermal conductivity of samples at various temperatures in solid (5–25 °C) and liquid (30–55 °C) phases. The experimental results showed that thermal conductivity of the composites increases with increasing the loading of the MWCNTs and CNFs. A maximum thermal conductivity enhancement of 36 % at 5 wt% MWCNTs and 5 °C as well as 50 % at 2 wt% and 55 °C were experimentally obtained for n-octadecane/MWCNTs samples. Dispersing CNFs into n-octadecane raised the thermal conductivity up to 18 % at 5 wt% and 10 °C and 21 % at 5 wt% and 55 °C. However, the average enhancement of 19 and 21 % for solid and liquid phases of MWCNTs composite as well as 33 and 46 % for solid and liquid phase of CNFs promised a better heat transfer characteristics of MWCNTs in n-octadecane. A comparison between results of the present work and available literature revealed a satisfactory enhancement of thermal conductivity. For the investigated n-octadecane/MWCNTs and n-octadecane/CNFs composites, a new correlation was proposed for predicting the thermal conductivity as a function of temperature and nanomaterials loading. © 2015, Springer-Verlag Berlin Heidelberg.
Publication Date: 2016
International Communications in Heat and Mass Transfer (07351933) 73pp. 1-6
In the present paper, the effect of using a heat pipe on the melting and solidification behavior of a phase change material (PCM) in a vertical cylindrical test cell was experimentally studied. The experiments were performed using a constant temperature thermal reservoir to provide constant temperatures above and below the melting point for heating and cooling. The melting and solidification experiments were run in test cells with and without heat pipes. The experimental results indicate that utilizing a heat pipe in PCM test cell dramatically enhance the melting and solidification rate. Heat pipe surface temperature was measured during experiments. It shows heat pipe isothermally transmits heat very well. By applying different reservoir working temperature, it is concluded that a 15 °C increase in reservoir temperature in melting experiment with heat pipe almost decreases the melting time by 53% and a 10 °C decrease in temperature in solidification reduce the solidification time by 49%. The growth of solid layer and solid-liquid interface in PCM during solidification was experimentally investigated. © 2016 Elsevier Ltd.
Publication Date: 2016
Journal Of Applied Fluid Mechanics (17353572) (2)
In the present paper, the hybrid AUSM-van Leer scheme is extended to solve the governing equations of twophase condensing flows. The method of moments with the classical homogeneous nucleation theory is used to model the non-equilibrium condensation phenomenon. Firstly, the hybrid method is validated using two test cases (i.e. Laval nozzle and rotor-tip cascade) and the results are compared with the MacCormack method. Then the hybrid method is used to solve two other problems (i.e. wavy channel and VKI stage). Based on the numerical results of the paper, the hybrid AUSM-van Leer scheme is an accurate method to simulate twophase transonic flows with nucleation. If the super cooling degree reaches to its maximum value, the nonequilibrium condensation begins and wetness fraction increases suddenly. Also across a shock the wetness fraction decreases due to evaporation of the droplets.
Publication Date: 2016
Scientia Iranica (10263098) (6)
Petroleum Refinery Wastewaters (PRW) contain water-soluble hydrocarbons which cannot be separated by physical methods. In recent years, there have been enormous approaches to treat PRW. The most outstanding methods involve biological, photocatalytic, electro-and photo-Fenton, etc. Using microbial fuel cell is a new method to treat PRW. In this paper, PRW treatment in MFC was studied using oxygen and permanganate as cathodic electron acceptors. Also, effects of temperature and external resistance on MFC performance and PRW treatment were investigated. Finally, an electrochemical model was fitted on empirical polarization curves to evaluate activation, ohmic, and mass transfer losses. Maximum power production was 0.03 W/m2 at 33°C using oxygen as cathodic electron acceptor. Also, COD removal eficiency was 49.27% during 44 h. To enhance power production of the MFC, potassium permanganate was used as cathodic electron acceptor. At the temperature of 33°C and 0.2 g/L of permanganate concentration, the maximum power density was 0.95 W/m2 and COD removal eficiency was 78% during 44 h. © 2016 Sharif University of Technology. All rights reserved.
Publication Date: 2017
Scientia Iranica (10263098) (2)
In the present paper, an in-house CFD code is developed using Roe scheme to simulate a condensing two-phase flow in blade to blade passage of a steam turbine. Effects of condensation on the flow field of steam turbine rotor tip section are investigated for different outlet pressures. Firstly, comparison is performed between results of wet and dry cases. Then, effects of outlet pressure variations on the flow field are studied. Finally, effects of condensation on different specifications of the flow field (total pressure loss coefficient, entropy generation, and deviation angle) are investigated. Also, the mechanism of flow deviation in the cascade flow field is described. Condensation has a great influence on the behavior of the flow field based on the numerical results of this paper. It changes the out-flow direction, and consequently the flow entering to the next blade deviates from its on-design condition; thus, additional losses are produced. For example, the value of deviation angle reaches 7:62° for wet case and exit Mach number Me = 1:45. Also, there are stagnation pressure loss and entropy generation due to non-equilibrium condensation that reduce the efficiency of the steam turbine. © 2017 Sharif University of Technology.
Publication Date: 2017
International Journal of Heat and Mass Transfer (00179310) 109pp. 134-146
This paper presents an experimental investigation on the melting process of n-octadecane as a phase change material (PCM) with dispersed titanium oxide (TiO2) nanoparticles. Experiments were performed in a rectangular enclosure heated at constant rates from one vertical side corresponding to Rayleigh numbers in the range 0.57 × 108–43.2 × 108and Stefan number in the range 5.7–23.8. The rheological behavior of liquid PCM/TiO2at the mass fractions of 2 and 4% tended to Bingham fluids, thus the melting experiment was conducted for Bingham numbers in the range 0–31.1. Heat transfer during melting was characterized by visualizing the solid-liquid interface as well as recording the temperature distribution in the enclosure. Experimental results showed that at the initial stage of melting, heat transferred by conduction, and at later times, natural convection dominated heat transfer. Dispersing TiO2nanoparticles led to increase in Bingham number and consequently the natural convection and melting rate deteriorated. Two correlations were proposed to predict the Nusselt number and melted volume fraction as a function of Fourier number, Rayleigh number, Stefan number, Bingham number and mass fraction of nanoparticles. © 2017 Elsevier Ltd
Publication Date: 2017
Energy Conversion and Management (01968904) 138pp. 162-170
The solidification process of n-octadecane as a phase change material (PCM) with dispersed titanium dioxide (TiO2) nanoparticles was experimentally studied. Experiments were performed in a rectangular enclosure cooled from one vertical side corresponding to the solid Stefan numbers in the range 0.17–0.239. The Rayleigh numbers at the initial of experiment were in the range 0.92–18.3 × 106. The rheological behavior of liquid PCM/TiO2samples at higher concentrations tended to Bingham fluids, thus the solidification experiments were conducted for Bingham numbers in the range 0–2.17. The solidification process was characterized by visualizing the progression of solid-liquid interface as well as recording the temperature distribution inside the enclosure. Experimental results showed that heat conduction was the dominant mode of heat transfer during the solidification. Dispersing TiO2nanoparticles led to enhance in thermal conductance and consequently the increase in solidified volume. An increase of 7%, 9% and 18% in solidified volume fraction was observed at the end of solidification for the mass fractions of 1 wt.%, 2 wt.% and 4 wt.%, respectively. A universal correlation was proposed to predict the solidified volume fraction as a function of Fourier number, Rayleigh number, solid Stefan number, Bingham number and mass fraction of nanoparticles with an error below 11%. © 2017 Elsevier Ltd
Ali, M. ,
Basti a., A. ,
Jamali a., A. Publication Date: 2017
Latin American Applied Research (03270793) 47(4)pp. 157-162
Selection of appropriate machining parameters which result in desired outcomes plays a key role in effective utilization of the electrochemical machining (ECM) process. In this paper, in order to correlate between ECM process parameters and cost functions, comprehensive mathematical models were first determined based on response surface methodology (RSM). Voltage, tool feed rate, electrolyte flow rate and concentration of NaNO3 solution were considered as the machining parameters while material removal rate (MRR) and surface roughness (Ra) were considered as cost functions. To do this, three scenarios of machining performances, Ra ≤ 0.9μm, 0.9μm ≤ Ra ≤ 1.8μm, and 1.8μm ≤ Ra ≤ 2.7μm, were considered for optimization search based on desirability functions. The goal is to find the optimum set of machining parameters in order to maximize the MRR while keeping Ra in specified ranges simultaneously. The results show that the errors between experimental and anticipated optimal values are less than 8.16% and hence confirm the effectiveness of the proposed approach. © 2003-2012 Latin American Applied Research Journal.
Publication Date: 2017
Neural Computing and Applications (09410643)
In the present study group method of data handling (GMDH) type of artificial neural networks are used to model deviation angle (θ), total pressure loss coefficient (ω), and performance loss coefficient (ξ) in wet steam turbines. These parameters are modeled with respect to four input variables, i.e., stagnation pressure (Pz), stagnation temperature (Tz), back pressure (Pb), and inflow angle (β). The required input and output data to train the neural networks has been taken from numerical simulations. An AUSM–Van Leer hybrid scheme is used to solve two-phase transonic steam flow numerically. Based on results of the paper, GMDH-type neural networks can successfully model and predict deviation angle, total pressure loss coefficient, and performance loss coefficient in wet steam turbines. Absolute fraction of variance (R2) and root-mean-squared error related to total pressure loss coefficient (ω) are equal to 0.992 and 0.002, respectively. Thus GMDH models have enough accuracy for turbomachinery applications. © 2016, The Natural Computing Applications Forum.
Ali, M. ,
Basti a., A. ,
Jamali a., A. Publication Date: 2017
Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering (20413009) 231(6)pp. 1114-1126
Electrochemical machining is a unique prevalent nonconventional manufacturing process used in different industries involving various process parameters, which greatly influence machining performance. Therefore, selection of proper and optimal parameters setting is a challenging issue. In this paper, differential evolution algorithm is applied to look for the optimum solution to this problem. Four parameters, i.e. voltage, tool feed rate, electrolyte flow rate, and electrolyte concentration; and two machining criteria, i.e. material removal rate and surface roughness (Ra) are considered as input variables and responses, respectively. The main purpose is to maximize material removal rate and minimize Ra to achieve better machining performance. In this way, comprehensive mathematical models have first been developed using response surface methodology through experimentation based on central composite design plan. Then, differential evolution algorithm has been utilized for optimizing the process parameters; both single- and multiobjective optimizations are considered, and optimal Pareto front is determined. Finally, optimization result of a trade-off design point in the Pareto front of Ra and material removal rate was also verified experimentally. This machined surface was examined with field-emission scanning electron microscope images. The results showed that the proposed approach is an effective and suitable strategy for optimization of the electrochemical machining process. © 2016, © IMechE 2016.
Publication Date: 2018
International Journal of Engineering, Transactions A: Basics (17281431) (1)
In the present paper, a supersonic wind-tunnel is designed to maintain a flow with Mach number of 3 in a 30cm×30cm test section. An in-house CFD code is developed using the Roe scheme to simulate flow-field and detect location of normal shock in the supersonic wind-tunnel. In the Roe scheme, flow conditions at inner and outer sides of cell faces are determined using an upwind biased algorithm. The in-house CFD code has been parallelized using OpenMp to reduce the computational time. Also, an appropriate equation is derived to predict the optimum number of cores for running the program with different grid sizes. In the design process of the wind-tunnel, firstly geometry of the nozzle is specified by the method of characteristics. The flow in the nozzle and test section is simulated in the next step. Then, design parameters of the diffuser (convergence and divergence angles, area of the throat, and ratio of the exit area to the throat area) are determined by a trial and error method. Finally, an appropriate geometry is selected for the diffuser which satisfies all necessary criteria. © 2018 Materials and Energy Research Center. All rights reserved.
Publication Date: 2018
Journal of Aerospace Technology and Management (21759146) 10
In this study, an efficient methodology is proposed for robust design optimization by using preference function and fuzzy logic concepts. In this method, the experience of experts is used as an important source of information during the design optimization process. The case study in this research is wing design optimization of Boeing 747. Optimization problem has two objective functions (wing weight and wing drag) so that they are transformed into new forms of objective functions based on fuzzy preference functions. Design constraints include transformation of fuel tank volume and lift coefficient into new constraints based on fuzzy preference function. The considered uncertainties are cruise velocity and altitude, which Monte Carlo simulation method is used for modeling them. The non-dominated sorting genetic algorithm is used as the optimization algorithm that can generate set of solutions as Pareto frontier. Ultimate distance concept is used for selecting the best solution among Pareto frontier. The results of the probabilistic analysis show that the obtained configuration is less sensitive to uncertainties. © 2018, Journal of Aerospace Technology and Management. All rights reserved.
Publication Date: 2018
Chinese Journal of Aeronautics (10009361) 31(12)pp. 2248-2259
This paper presents a Fuzzy Preference Function-based Robust Multidisciplinary Design Optimization (FPF-RMDO) methodology. This method is an effective approach to multidisciplinary systems, which can be used to designer experiences during the design optimization process by fuzzy preference functions. In this study, two optimizations are done for Predator MQ-1 Unmanned Aerial Vehicle (UAV): (A) deterministic optimization and (B) robust optimization. In both problems, minimization of takeoff weight and drag is considered as objective functions, which have been optimized using Non-dominated Sorting Genetic Algorithm (NSGA). In the robust design optimization, cruise altitude and velocity are considered as uncertainties that are modeled by the Monte Carlo Simulation (MCS) method. Aerodynamics, stability and control, mass properties, performance, and center of gravity are used for multidisciplinary analysis. Robust design optimization results show 46% and 42% robustness improvement for takeoff weight and cruise drag relative to optimal design respectively. © 2018 Chinese Society of Aeronautics and Astronautics
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University of Isfahan
Address: Isfahan, Azadi Square, University of Isfahan
