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text
article
2013
per
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Modares Mechanical Engineering
Tarbiat Modares University
1027-5940
13
v.
2
no.
2013
0
0
http://mme.modares.ac.ir/article_1575_05fc4e8d8c25a93bcf53baac90a56382.pdf
A comparative study of turbulence models performance in predicting the frequency of naturally-excited oscillating jet flows
محسن
جهانمیری
دانشگاه صنعتی شیراز
author
Amir
Omidvar
دانشگاه صنعتی شیراز
author
مسعود
خراتی کوپایی
دانشگاه صنعتی شیراز
author
text
article
2013
per
This paper presents a comparative study of turbulence models performance in prediction the oscillating characteristics of naturally excited jet flows. The unsteady averaged Navier-Stoks equations for turbulent incompressible flow and five variant turbulence closures are used in this study. A large family of turbulence models exists in the literature which is far too extensive to be reviewed here. The models are ranged from simple algebraic expressions for the eddy viscosity to more elaborated formulations which introduce a separate transport equation for each component of the Reynolds stresses. The software, FLUENT 6.3.26, was employed for solving the governing equations. Computational results compared with reported experimental data. The standard k-ε and SST k-ω models clearly showed better results than the others. The accuracy of standard k-ε model decreases with decreasing the nozzle inlet velocity and it failed to predict the minimum excitation velocity (minimum excitation kinetic energy) in the self excited fluidic nozzle.
Modares Mechanical Engineering
Tarbiat Modares University
1027-5940
13
v.
2
no.
2013
1
11
http://mme.modares.ac.ir/article_1573_a8ac6fdc097f0d250592d2cdf046ed6f.pdf
Improve the accuracy of fracture toughness equation coefficients resulting from irregular surface cracks generated by Vickers test of B4C-C composites
Mehdi
Tajdari
استاد دانشگاه آزاد اسلامی واحد علوم و تحقیقات اراک- گروه مکانیک
author
HamidReza
Baharvandi
دانشیار دانشگاه صنعتی مالک اشتر- گروه مواد
author
AliReza
Moradkhani
کارشناس ارشد مهندسی مکانیک- ساخت و تولید- دانشگاه آزاد اسلامی واحد علوم و تحقیقات تهران- گروه مکانیک
author
text
article
2013
per
Abstract - Vickers test method and many equations presented by researchers are used for determining the fracture toughness of brittle materials.These equations are generally based on the relationship between the crack lengths around the indentation zone of Vickers test and the fracture toughness in the specimen. There is only one equation including a semi-empirical coefficient based on the indentation surface and the fracture toughness of the specimen. In this paper, improvement the accuracy of semi-empirical coefficient in this equation is studied for determining the fracture toughness of specimens without additives and containing 5 wt% phenolic resin experimentally. Increasing the accuracy of semi- empirical coefficient leads the increasing the extent of application and accuracy of the results of fracture toughness obtained from the equation. The accuracy of fracture toughness equation coefficients semi- empirical coefficient from 0.003693 to 0.003655 arrived. This equation has minimal cost of experiments for determining fracture toughness of different brittle materials.
Modares Mechanical Engineering
Tarbiat Modares University
1027-5940
13
v.
2
no.
2013
12
21
http://mme.modares.ac.ir/article_1574_ba9a77ae79a369d17acaa8344c8bc8e1.pdf
Numerical simulation of a Stirling-type double inlet pulse tube refrigerator
مسعود
عربلو
دانشگاه تربیت مدرس
author
علی
جعفریان دهکردی
دانشگاه تربیت مدرس
author
text
article
2013
per
In this paper a CFD code has been developed to investigate effects of the double inlet on the performance of a Stirling type pulse tube refrigerator. In this respect, set of governing equations have been written in a general form such that all porous and non-porous sections of the system can be modeled. In order to discretize the governing equations, a second order method has been used for time, a second order upwind method for mass, enthalpy flow and temperature in the surfaces of the control volumes and the central differential scheme has been employed for pressure and heat conduction terms. Results show that application of double inlet optimizes the phase shift between velocity and pressure and suitably decreases the fluid temperature along the pulse tube, causing to increase COP of the system. Furthermore, it is observed that a minimum temperature of 56.5 K and COP of 0.0352 @ 80 K is attainable using optimum double inlet; whereas, for a simple refrigerator a minimum temperature of 71.3 K and maximum COP of 0.0227 @ 80 K are concluded.
Modares Mechanical Engineering
Tarbiat Modares University
1027-5940
13
v.
2
no.
2013
22
32
http://mme.modares.ac.ir/article_1572_502025a8ec2da25e13078ea92968da8c.pdf
Thermal buckling analysis of FGM sector plates using differential quadrature method
mehrdad
jabbarzadeh
مدیر گروه مکانیک دانشگاه آزاد اسلامی واحد مشهد
author
محمد کاظم
باغدار دلگشا
دانشجوی کارشناسی ارشد دانشگاه آزاد اسلامی واحد مشهد
author
text
article
2013
per
Abstract - In this article , thermal buckling analysis of functionally graded annular sector plate is studied. The mechanical and thermal properties of the functionally graded sector plate are assumed to be graded in the thickness direction . The equilibrium and stability equations are derived based on the first order shear deformation plate theory (FSDT) in conjunction with nonlinear von-karman assumptions. Differential quadrature method is used to discretize the equilibrium and stability equations. In this method a non-uniform mesh point distribution (Chebyshev-Gauss-Lobatto) is used for provide accuracy of solutions and convergence rate . By using this method, there is no restriction on implementation of boundary conditions and various boundary conditions can be implemented along any edges . Finally, The results compared with other researches and the effects of plate thickness, sector angle, annularity, power law index and various boundary conditions on the critical buckling temperature are discussed in details .
Modares Mechanical Engineering
Tarbiat Modares University
1027-5940
13
v.
2
no.
2013
33
45
http://mme.modares.ac.ir/article_1571_79b17e4430753278feedcc9bb06a0ae0.pdf
Study on the effects of bias magnetic field and mechanical pre-stress on sensitivity and linear measurement range of Terfenol-D force sensor
سهیل
طالبیان
دانشگاه تربیت مدرس
author
یوسف
حجت
دانشگاه تربیت مدرس گروه ساخت و تولید،
author
مجتبی
قدسی
دانشگاه تربیت مدرس
author
شاهد
میرزامحمدی
دانشگاه تربیت مدرس
author
محمدرضا
شیخ الاسلامی
دانشگاه تربیت مدرس
author
text
article
2013
per
Terfenol-D, known as a giant magnetostrictive material, is used in many sensors such as force sensor. In these sensors, external force is measured due to variation of magnetic flux density passing through Terfenol-D. To improve the performance, Terfenol-D is exposed to bias magnetic field and mechanical pre-stress. In this paper, Effects of bias magnetic field and mechanical pre-stress on sensitivity and linear measurement range of a force sensor are studied and optimum values of them are recognized. Initially based on magnetomechanical coupling equations, theoretical model of sensor that includes effective parameters on sensitivity and linear measurement range is developed. Then using experimental set-up, magnetomechanical properties of Terfenol-D are investigated and values of essential parameters for theoretical model are extracted. Finally, employing theoretical model and experimental results, the response of sensor under dynamic external forces is simulated and effects of bias magnetic field and mechanical pre-stress on sensitivity and linear measurement range of the sensor are studied. Based on the obtained results, to increase sensitivity and linear measurement range of sensor, values of bias magnetic field and mechanical pre-stress should be relatively determined considering the amplitude of external force.
Modares Mechanical Engineering
Tarbiat Modares University
1027-5940
13
v.
2
no.
2013
46
55
http://mme.modares.ac.ir/article_1570_ecef8c4c6cb0ea2e06d849b4ae3e456b.pdf
Thermodynamic Analysis of a Tri-generation Cycle with HCCI Engine as Prime Mover
Niloufar
Sarabchi
فارع التحصل دانشگاه تبریز- دانشکده مکانیک
author
سید محمد
سیدمحمودی
دانشیار/ دانشگاه تبریز- دانشکده مکانیک
author
Rahim
Khoshbakhti Saray
دانشیار دانشگاه صنعتی سهند- دانشکده مکانیک
author
text
article
2013
per
A tri-generation cycle consisting of a homogeneous charge compression ignition (HCCI) engine and an ammonia-water absorption cogeneration cycle are proposed and analyzed. The energy of engine exhaust gases are utilized to run absorption cogeneration cycle. Also the energy of cooling water can be used in residential applications. A single zone model with capability to consider chemical kinetic talculations is developed for the HCCI engine. The results show that increasing the pump pressure ratio of the cogeneration cycle causes a decrease in the refrigeration output and an increase in first law efficiency. At a particular value of this pressure ratio the second law efficiency is maximized. It is shown that the contribution of engine in the total exergy destruction in the tri-generation system is much higher than those of the other components. With an ammonia concentration of 0.4 in the solution leaving the absorber and with an ambient temperature of 25oC, the maximum exergy efficiency occurs when the pump pressure ratio is 9.486. At this condition, the fuel energy saving ratio and CO2 emission reduction are 27.97% and 4.8%, respectively. It is also shown that the second law efficiency of the tri-generation system is 5.4% higher than the second law efficiency of the HCCI engine.
Modares Mechanical Engineering
Tarbiat Modares University
1027-5940
13
v.
2
no.
2013
56
69
http://mme.modares.ac.ir/article_1569_9b11d7c5ca8068471544bc75cccbf095.pdf
Mechanical Properties, Thermal Behavior and Water Absorption of PP/Wood Fiber/CaCO3 Nanocomposites
ن
ا
دانش آموخته کارشناسی ارشد مهندسی ساخت و تولید
author
ی
رز
تبریز
author
Karim
Shelesh-Nezhad
Assistant Professor-University of Tabriz
author
text
article
2013
per
Nanocomposites based on polypropylene/wood fiber (PP/WF 70/30) compound containing 2.5 to 10 phc of nano-CaCO3 and 5 phc of maleated polypropylene (MAPP) as compatibilizer were prepared by melt compounding followed by injection molding. The mechanical properties, thermal behavior as well as water absorption were characterized and the morphology was studied using scanning electron microscopy. The presence of nano-CaCO3 declined the amount of water absorption as high as 60 wt%. The incorporation of nano-CaCO3 into PP/WF compounds led to the 12% increment of flexural modulus, 22.5% rise in impact strength, and 9% increase in elongation at break. The results of DSC experiments indicated that the addition of nano-CaCO3 can elevate the crystallization temperature and reduce the degree of crystallinity of PP in PP/WF/CaCO3 nanocomposites. The maximum values of crystallinity, flexural modulus and flexural strength were achieved at 5 phc loading of nano-CaCO3, and the maximum crystallization temperature and impact strength were attained by adding 7.5 phc of nano-CaCO3. The reduction of tensile strength, as high as 8.8%, in PP/WF/CaCO3 nanocomposites was attributed to the decrease of PP crystallinity, as well as the presence of nano-CaCO3 at the PP/WF interface.
Modares Mechanical Engineering
Tarbiat Modares University
1027-5940
13
v.
2
no.
2013
70
78
http://mme.modares.ac.ir/article_1568_e0c7fb2d2091638ecd0c025ed01ae1ee.pdf
Improving the accuracy of laser scanning using dithering technique and simultaneous laser and camera calibration
خلیل
خلیلی
عضو هیأت علمی گروه مهندسی مکانیک/ دانشگاه بیرجند
author
سیامک
خطیبی
عضو هیأت علمی گروه مهندسی کامپیوتر/ دانشگاه BTH، سوئد
author
سید محمد
امام
دانشجوی دکتری دانشگاه بیرجند
author
text
article
2013
per
Ttriangulation technique is one of the most commonly techniques used in three dimensional measurements. The depth reconstruction accuracy is a direct impact of the quantization process, and so it is related to the pixel size of the sensor. By decreasing the pixel size, the accuracy can be improved however it will affect the quality of the image as it reduces the SNR. Dithering technique may be used to reduce the errors during quantization. The current study introduces a novel technique in which a relative fine movement between object and sensor is generated during picture capture. The calibration of laser and camera is another important factor affecting the accuracy of the scanner. In this study, the laser is calibrated in high precision with the camera simultaneously without any extra mechanical device. The paper firstly describes the theory of the noise introduction technique followed by modeling and simulation of the process. The results obtained from simulation show great improvement in measurement accuracy. To evaluate the result in a real world, a control rig was designed and built following which experiment were performed. The results showed considerable improvement in measurement accuracy. The result of both simulation and experiments are reported.
Modares Mechanical Engineering
Tarbiat Modares University
1027-5940
13
v.
2
no.
2013
79
92
http://mme.modares.ac.ir/article_1567_4efe513b93534fd9a39d0e3f1a13e24a.pdf
Mechanical properties of hydrogen functionalized graphene: A molecular dynamics study
Arefesadat
Hadizadeh Kheirkhah
گروه فیزیک دانشگاه تربیت مدرس
author
Esmaeel
Saievar Iranizad
بخش فیزیک دانشگاه تربیت مدرس
author
text
article
2013
per
Molecular dynamics simulations have been performed to study the mechanical properties of hydrogen functionalized graphene. We find out that Young’s modulus and tensile strength of pristine graphene are in good agreement with experimental results. It is shown that hydrogen functionalization can considerably modify the mechanical properties of graphene. It is also found that the patterned orrandom hydrogen coverage have different effects on the mechanical properties of graphene. Using molecular dynamics simulation, we study the mechanical properties of hydrogen functionalized graphene under tension and shear deformations at constant room temperature. Young’s modulus and shear modulus, tensile and shear strengths and tensile and shear fracture strains are mechanical parameters that are calculated in order to investigate the mechanical properties of hydrogen functionalized graphene. Results show that in some cases, hydrogen coverage pattern is important independent of its coverage percentage. The underlying mechanisms were explained considering the difference between sp^2 and sp^3 hybridization.
Modares Mechanical Engineering
Tarbiat Modares University
1027-5940
13
v.
2
no.
2013
93
99
http://mme.modares.ac.ir/article_1566_056ffa8aa0fd6fa2de64efe526e010e5.pdf
Experimental Study of the Effect of Nanoclay on Fatigue Life of Air Spring
محمد
باقری
دانشگاه تربیت مدرس
author
سیامک
اسماعیل زاده خادم
author
text
article
2013
per
The objective of this work was to investigate the effect of nanocaly on fatigue life of air spring. The studies on the air spring fatigue life have shown that the inner layer of the rubber composite bellows of the air spring plays the most important role on its fatigue life. So, as a new idea to improve the life of the air spring, in this research, NR/BR and 0, 3, 5, 7 % of nanoclay were separately melt-blended. X-ray diffraction was employed to characterize the nanocomposite morphology. Then, the curing time of the unvulcanized compound was defined by rheometer test and the final nanocomposites compounds were provided according to their curing characteristics. After that, tensile, heat built-up, tear and fatigue tests were performed on the standard test specimens. It was shown that by increasing the nanoclay percentage, the elasticity modulus, tear strength and heat built-up were increased whereas tensile strength and elongation at break point were decreased. The results also showed that by the addition of 3 % and 5 % of nanocaly to NR/BR, its fatigue life was increased about 33 % and 57 %, respectively, whereas the fatigue life of the compound containing 7 % nanoclay was decreased about 14 %.
Modares Mechanical Engineering
Tarbiat Modares University
1027-5940
13
v.
2
no.
2013
100
108
http://mme.modares.ac.ir/article_1565_f7c7df7aa71e83b6350b73daf37bde54.pdf
Desing combined cooling, heating and power system for residential buildings in Tehran climate
حسن
قاسم زاده
دانشگاه تربیت مدرس
author
مهدی
معرفت
دانشگاه تربیت مدرس
author
عزیز
عظیمی
دانشگاه شهید چمران اهواز
author
text
article
2013
per
In the combined cooling, heating and power system, electricity is produced by prime mover. Recovered heat from the prime mover supplies heating and cooling demands. In this research, primary energy saving and carbon dioxide emission reduction are employed to evaluate the performances of cchp system compared with conventional system for residential buildings in Tehran. The combined cooling, heatig and power system follows Maximum electrical or thermal demand and Maximum rectangle electrical or thermal demand management. The results indicate that cchp system for residential five, eleven-storey buildings, in maximum rectangle electrical demand, maximum rectangle thermal and maximum electrical demand modes is the best strategy, if cooling demand is produced by absorption chiller and electric chiller. In the best strategy, primary energy saving and carbon dioxide emission reduction are 13% and 12%, respectively. If cooling demand is produced only by absorption chiller, primary energy saving and carbon dioxide emission reduction are decreased. In this case, maximum electrical and thermal demands are the worst strategies. In the worst case, energy consumption and carbon dioxide emission in cchp are increased 39% and 56% compared to the conventional system, respectively. Payback period in these strategies are calculated 5.5 and 7 years for 11 and 5 tories.
Modares Mechanical Engineering
Tarbiat Modares University
1027-5940
13
v.
2
no.
2013
109
122
http://mme.modares.ac.ir/article_1564_7ff7dbd042543cabb9cbe7579a368a0c.pdf
Investigation of Microstructure and Anisotropy of Mechanical Properties of the ARB-Processed Commercial Purity Aluminium with Interpassing Heat Treatment
Mojtaba
dehghan
دانشگاه سمنان
author
فتح اله
قدس
دانشگاه سمنان
author
مهدی
گردویی
استادیار/ دانشگاه شاهرود
author
text
article
2013
per
Investigation of Microstructure andAnisotropy of MechanicalProperties of the ARB-Processed Commercial Purity Aluminium with Interpassing Heat Treatment Abstract Accumulative roll bonding (ARB) is a severe plastic deformation (SPD) process that may be defined as multistep rolling process in order to create high strength metals with ultra-fine grained (UFG) in nanometer level. In this study,ARB process with interpassing heat treatment was carried out on the commercial pure Aluminium sheet up to 13 cycles.The variation of microstructure during the cycles of ARB process to access to grains with nanometer dimensions was investigated. In addition, micro-Vickers hardness measurement was carried out throughout thickness of the ARB processed sheets. Eventually, the changes of strength and elongation and also anisotropy of mechanical properties of the sheets during the cycles of process was studied by uni-axial tensile test in 3 directions (roll direction (RD), transverse direction (TD) and direction of 45o toward RD). Keywords: ARB Process, Nanostructure, Micro-Vickers Hardness, Mechanical Properties, Anisotropy.
Modares Mechanical Engineering
Tarbiat Modares University
1027-5940
13
v.
2
no.
2013
123
132
http://mme.modares.ac.ir/article_1563_6ffabd41a96b7c04d1c39128c998ec37.pdf
َWater-Alumina natural convection heat transfer in an inclined L shape cavity
Samaneh
Karimi
دانشگاه شهرکرد
author
behzad
ghasemi
هیات علمی دانشگاه شهرکرد
author
text
article
2013
per
Water-Alumina natural convection heat transfer in an inclined L shape cavity ABSTRACT A numerical investigation of water-alumina natural convection laminar flow in an inclined L shape cavity is performed. Two wall of the cavity are hot with the temperature of Th, two walls are cold with the temperature of Tc , and two other walls are thermally adiabatic. The two dimensional continuity, momentums and energy equations are solved numerically with a finite volume approach using the well known SIMPLE algorithm. The influence of pertinent parameters such as Rayleigh number, Ra, solid volume fraction, , inclination angle, , and cavity aspect ratio, A, on the fluid flow, fluid temperature and cavity heat transfer characteristics is studied. The results indicate that nanofluid with higher nanoparticles has better performance. The results also show that the inclination angle has a significant effect on the heat transfer performance at high Rayleigh numbers. Keywords: Natural convection, nanofluid, L shape cavity, Rayleigh number.
Modares Mechanical Engineering
Tarbiat Modares University
1027-5940
13
v.
2
no.
2013
133
144
http://mme.modares.ac.ir/article_1562_3c2672600ec1f951419dd5de4107012e.pdf
Effects of configuration of stack outlets and cooling towers on flow field and plume dispersion
علی اصغر
ُصدیقی
دانشگاه صنعتی خواجه نصیرالدین طوسی
author
مجید
بازارگان
author
text
article
2013
per
In this paper, pollutants flows coming out of stacks or cooling towers with different outlet shapes have been numerically studied. The effects of exhaust outlet on plume rise, and the pollutant dissipation are investigated. To simulate the flow turbulence, realizable k – ε model is employed for the case of a stack flow with more than one exhaust outlet on the influence of wind condition. The plume rise and dissipation of pollutant are depending on the direction of the wind and the shape of exhaust outlet. Depending on wind direction and shape of exhaust outlet, higher or lower levels of plume rise can be obtained with various kind of pollutant dissipation. These changes are due to the influence of high pressure upstream and low-pressure downstream flow fields of outlet from stacks on the counter vertex rotating pair. The maximum concentration and dissipation of pollutant for various wind directions and output configurations are examined.
Modares Mechanical Engineering
Tarbiat Modares University
1027-5940
13
v.
2
no.
2013
145
152
http://mme.modares.ac.ir/article_1561_95569390244526ca0e3f6bc2b3fc3e8c.pdf