
text
article
2013
per

Modares Mechanical Engineering
Tarbiat Modares University
10275940
13
v.
8
no.
2013
0
0
http://mme.modares.ac.ir/article_1662_cfde572492e39c93fde2ac63b65d80b0.pdf
Vibration analysis of rotating tapered cantilever beams and using genetic algorithms to detect cracks in these beams
Saeid
Talebi
MSc Student, University of Isfahan
author
Alireza
Ariaei
Faculty of Engineering, University of Isfahan
author
text
article
2013
per
The current article presents an analytical approach, for determining the natural frequencies of a rotating cracked Euler–Bernoulli beam with a varying transverse crosssection, using the socalled differential transform method (DTM). First, the natural frequencies of the beam are obtained for different values of the crack position and depth. The results have been validated against those obtained from experimental modal test, Abaqus software and some other methods reported in the literature and a good agreement between the results is observed. Then, the inverse problem is investigated. For this reason, the position and depth of the crack of the rotating beam with a varying transverse crosssection are estimated using the genetic algorithm and then, the natural frequencies are obtained from the modal test. It is seen that the numerical results have a suitable agreement with the actual position and depth of the crack that indicates the effectiveness of this method in determining the parameters of the crack in the rotating beams.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
13
v.
8
no.
2013
1
13
http://mme.modares.ac.ir/article_1650_9d3569e6eeb4bfa6196880f74c597a24.pdf
Nonisothermal Transient Flow Analysis in Gas Pipelines Using a linearized Flux Splitting Numerical Scheme
مرتضی
بهبهانی نژاد
Shahid Chamran University of Ahvaz
author
Aziz
Azimi
دانشگاه شهید چمران اهواز
author
محسن
شعبانی
دانشگاه شهید چمران اهواز
author
text
article
2013
per
Numerical simulation of nonisothermal transient gas flow is performed using implicit StegerWarming finite difference method. Because of nonlinearity of the governing equations, they are linearized at each time step. The linearization either reduces computational effort or analyzes the flowfield more conveniently. In order to validate and evaluate the accuracy of current numerical method, Fanno and shock tube flows are investigated first. Then, transient flow in a gas pipeline that its inlet pressure changes with time is simulated. The results of present study show that StegerWarming finite difference scheme can well captured the sudden changes in the flowfield. Moreover, the present method is able to analyze transient gas flows as nearly accurate as the nonlinear one with less computational effort.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
13
v.
8
no.
2013
14
27
http://mme.modares.ac.ir/article_1651_377c8c580828d96861a17a1a4ed7662f.pdf
A new curved boundary treatment for the lattice Boltzmann method
Omid
Mohammadipoor
دانشجو دکترا
author
حمید
نیازمند
دانشیار گروه مکانیک/ دانشگاه فردوسی مشهد
author
Seyed Ali
Mirbozorgi
استادیار دانشگاه بیرجند
author
text
article
2013
per
Since the lattice Boltzmann method (LBM) originally carries out the simulations on the regular Cartesian lattices; curved boundaries are often approximated as a series of stair steps. The most commonly employed technique for resolving curved boundary problems is extrapolation of macroscopic properties at boundary nodes. Previous investigations have indicated that using more than one equation for extrapolation in boundary condition potentially causes abrupt changes in particle distributions. Therefore, a new curved boundary treatment is introduced to improve computational accuracy of the conventional stairshaped approximation used in lattice Boltzmann simulations by using a unified equation for extrapolation of macroscopic variables. This boundary condition is not limited to fluid flow and can be extended to other physical fields. The proposed treatment is tested against several well established problems. Numerical results show that the present treatment is of secondorder accuracy, and has wellbehaved stability characteristics.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
13
v.
8
no.
2013
28
41
http://mme.modares.ac.ir/article_1652_834c37be04dc6b37cc5584f852721df9.pdf
Modal Analysis of a Beam Mass System using Time Varying Modal Analysis Methods
Hadi
Pourshahsavari
malek ashtar university
author
Esmaeel
Ghorbani
محقق
author
Mehdi
Keshmiri
Associated Professor, Isfahan University of Technology
author
text
article
2013
per
This paper discusses an adaptation of modal analysis concepts to timevarying periodic systems. It will be shown that the pseudomodal parameters preserve certain properties of the conventional modal parameters defined for LTI systems. For this reason, after definition of pseudo modal parameters for time varying systems, a new modal analysis method will be introduced in time domain and it will be shown that these parameters could explain the nature of system. For periodic time varying systems, state transition matrices are formed by an ensemble set of responses which are obtained through multiple experiments on the system with the same time varying behavior. In next step the pseudo natural frequencies of a beam with moving mass using introduced method will be extracted. In final, it will be proved that for a linear time periodic system, the pseudo natural frequency treats periodic too.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
13
v.
8
no.
2013
42
56
http://mme.modares.ac.ir/article_1653_b431b0756bbd9b79c748972a571684e2.pdf
Investigation of cooling rate on continuous cooling transformation behavior of API X65 pipeline steel
مسعود
رخش خورشید
دانشگاه بیرجند، دانشکده مهندسی، گروه مکانیک
author
Sayyed
Hashemi
The University of Birjand
author
text
article
2013
per
The transformation behavior and microstructural characteristics of API X65 pipeline steel were investigated by dilatometry and microstructural observation. Microhardness measurements were used to verify the observed microstructures. The test steel is imported from abroad and is used extensively in Iran natural gas transmission projects. The continuous cooling transformation curves of the test steel were constructed. The results showed that with increasing the cooling rate from 0.5 to 40°C/s, the microstructure changes from polygonal ferrite, quasipolygonal ferritepearlite to acicular ferrite. The microstructure was dominated by acicular ferrite in cooling rates higher than 5°C/s. The results can be used to design the optimum thermomechanical control process (through the selection of proper cooling rate) in domestic manufacturing process of the test steel.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
13
v.
8
no.
2013
57
67
http://mme.modares.ac.ir/article_1654_fae4a121852b8fb5a1ee99caef06168e.pdf
Evaluation of temperatureindependent thermophysical properties assumption of water based alumina nanofluid in natural convection within the enclosures
مسعود
خراتی کوپایی
دانشگاه صنعتی شیراز
author
Amir
Omidvar
استادیار دانشگاه صنعتی شیراز
author
ایمان
جلوداری
دانشگاه صنعتی شیراز
author
text
article
2013
per
In this research, validity of temperatureindependent thermophysical properties assumption of waterAl203 nanofluid in natural convection problems within the enclosures is investigated. The numerical results are obtained utilizing an inhouse finite volume code based on the SIMPLE algorithm. In order to do the validation the numerical results and those of existing correlations are compared. In order to evaluate the thermal performance of the enclosure, the average Nusselt number on the hot side wall in both temperatureindependent and dependent cases is compared Results show that, in the all considered solid volume fractions, the difference in the Nusselt number in the case of temperatureindependent properties is less than 10 percent in comparison with the case in which the properties are temperaturedependent when temperature difference is less than 5 ○C. As the temperature increases, the difference between Nusselt number in both cases increases and the effect of increase in solid volume fraction is to increase this difference. Results also show that the difference between these two cases is dependent solely on temperature differences between the hot and cold walls regardless of the temperature they have.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
13
v.
8
no.
2013
68
78
http://mme.modares.ac.ir/article_1655_dd6251f7f7558d9458a38c6457287ed4.pdf
Dynamic Balancing of an UnderActuated Differential Two Wheeled Manipulator by a Reaction Wheel
SeyedReza
Larimi
Msc. Mechanical Engineering on K.N.Toosi University
author
سیدعلی اکبر
موسویان
استاد دانشگاه خواجه نصیرالدین طوسی
author
text
article
2013
per
AbstractIn this article, a new stabilizing mechanism for a two wheel robot is proposed. Such systems, due to inherent instability, require dynamic stabilization. The conventional method for stabilizing these robots is moving the base back and forth, to use its inertia effects. Therefore, such strategies drastically depend on the ground surface, besides the robot is not able to reconfigure its manipulator to do any desired task. These limitations reduce the capability of the robot to manipulate objects, and to perform accurate tasks. In order to omit these restrictions, in the developed mechanism, a reaction wheel is used. The proposed mechanism exploits the inertia moment of reaction wheel to stabilize motion of the robot. Therefore, since there is no interaction between the reaction wheel and the ground surface, by using this mechanism there would be no concern about the surface that the robot moves on that. Also, manipulator of the robot can track the given trajectories, without considering stability limitations. In order to show the performance of proposed mechanism, a verified dynamics model of the robot is used and the control algorithm with various initial conditions is simulated.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
13
v.
8
no.
2013
79
92
http://mme.modares.ac.ir/article_1656_ef50ba28dfb89dc03c9c604feb4cb4d2.pdf
Comparison of Heat Transfer in a Cavity between Vertical and Horizontal Porous Layers using LBM
Mohsen
Nazari
Assistant Prof. of Mechanical Eng.
Shahrood Univ. of Technology
author
محمد حسن
کیهانی
دانشگاه صنعتی شاهرود
author
آلاله
انارکی حاجی باقری
دانشگاه صنعتی شاهرود
author
text
article
2013
per
In this paper, natural convection heat transfer inside an enclosure which is partially filled with porous layer is reported using lattice Boltzmann method. Generalized equations in modeling flow in porous media have been employed which are coupled with the lattice Boltzmann formulation of the momentum and energy equations. The present study investigates the effect of position of porous layer on heat transfer rate for different dimensionless parameters, such as Rayleigh number, Darcy number and porosity of the porous layer. In addition, a modified Rayleigh number is presented as an effective parameter which affects the degree of penetration of the fluid into the porous layers. The obtained results showed that the heat transfer rate in the case of vertical layer is more than that of horizontal porous layers.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
13
v.
8
no.
2013
93
107
http://mme.modares.ac.ir/article_1657_85d0485dc1f57f2b85a17d0826c12cc0.pdf
Design and optimization of Al2024 Siemens generator fan blade forging process
Reza
Saeedi
کارشناس ارشد مهندسی مکانیک، دانشگاه تربیت مدرس، تهران
author
Mohamad Hosein
Sadeghi
هیات علمی دانشگاه تربیت مدرس
author
آناهیتا
رضایی
کارشناس ارشد R&D ، شرکت مپنا ژنراتور، گروه مپنا
author
text
article
2013
per
Blade forging is an intricate process due to complicated geometry, high dimensional accuracy, complicated material flow, varying and sometimes very thin thicknesses. As a powerful tool, numerical simulation is used in different steps of designing process. Mechanical properties (stressstrain curves) of the material and friction factor of contact surface are of the most important inputs of the simulation. Thus, cylinder and ring compression experiments were conducted to obtain these inputs for Al2024 used in forging of 202 MVA Siemens generator fan blade. Because of high costs of blade forging and suitability of cylinder sidepressing this experiments were used to evaluate the compression tests and simulations. Good accordance was observed between simulation and experiment. Final forging die cavity and then preforms needed to produce a sound part are modeled. Designed preforming steps include extrusion, bending and upsetting. Blade final forging step was simulated in different temperatures of die and workpiece and strain rates and the optimum condition was determined.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
13
v.
8
no.
2013
108
122
http://mme.modares.ac.ir/article_1658_bf4a2b5697e78bb6c140d4a5939b4ae2.pdf
Modeling of abrasive waterjet cutting of glass using artificial neural network and optimization of surface roughness using firefly algorithm
حسین
امیرآبادی
استادیار گروه مکانیک دانشگاه بیرجند
author
khalil
khalili
University of Birjand
author
Abolfazl
Foorginejad
University of Birjand
author
Jawad
Ashory
University of Birjand
author
text
article
2013
per
Abstract In this paper, it is shown how to use the recently developed Firefly Algorithm to optimize abrasive waterjet cutting as a nonlinear multiparameter process. Back propagation neural network were developed to predict surface roughness in abrasive waterjet cutting (AWJ) process. In the development of predictive models, machining parameters of traverse speed, waterjet pressure, standoff distance and abrasive flow rate were considered as model variables. Firefly Algorithm by using back propagation neural network optimizes glass surface roughness in abrasive waterjet cutting and proposes appropriate parameters for minimum surface roughness. Testing results demonstrate that the model is suitable for predicting the response parameters. However this algorithm has not be tested for practical problems, the results showed this algorithm applicable for processes with complex nature.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
13
v.
8
no.
2013
123
134
http://mme.modares.ac.ir/article_1659_08c994b71032fa0fbf8c13956ce4a949.pdf
Analysis of performance convergent nozzle ejector in the PEM system
ارسلان
مقصودی
دانشجو
author
Ebrahim
Afshari
استادیار گروه مکانیک دانشگاه اصفهان
author
حسین
احمدی کیا
دانشیار گروه مکانیک دانشگاه اصفهان
author
text
article
2013
per
In this study, convergent nozzle ejector in the PEM fuel cell system is analyzed. This method can reduce the parasitic power of the fuel cell, recycle the unconsumed hydrogen to the fuel cell to increase the fuel usage efﬁciency, utilize the pressure potential energy of hydrogen and regulate the anode humidity with the recycle gas. For this purpose, continuity, momentum, energy and state equations are solved by numerical methods and effects of pressure drop (through the channel towards the anode), operating pressure and temperature of the fuel cell and also nozzle diameter on the ejector performance was analyzed. With decreasing of pressure drop, even in primary lower pressure, increasing of performance pressure the performance of ejector will improved. The temperature increase has no effect on the performance of the ejector itself, but has enormous effect on the fuel cell. Increasing the diameter ratio of the constant diameter zone to the nozzle diameter leads to increasing of recirculation anode line of the fuel in higher pressure.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
13
v.
8
no.
2013
135
150
http://mme.modares.ac.ir/article_1660_e9e9a894718eb1700639bf316d4dfcec.pdf
Low velocity impact on Timoshenko nanobeam using a nonlocal elasticity theory
سجاد
صیفوری
دانشگاه تربیت مدرس
author
غلامحسین
لیاقت
دانشگاه تربیت مدرس استاد مکانیک
author
مجید
فولادی
استاد دانشگاه شهید باهنر
author
text
article
2013
per
In this article, analytical solutions of low velocity transverse impact on a nanobeam are presented using the nonlocal theory to bring out the effect of the nonlocal behavior on dynamic deflections. Impact of a projectile (mass) on simply supported and clamped nanobeams are investigated using nonlocal Timoshenko beam theory. In order to obtain an analytical result for this problem, an approximate method has been developed wherein the applied impulse is replaced by a suitable boundary condition and initial momentum of projectile and nanobeam. A number of numerical examples with analytical solutions for nonlocal nanobeam and classical beam (steel and aluminum) have been presented and discussed. When the value of the striker mass is increased, the frequencies are decreased and the maximum dynamic deflection at the center of the beam is increased for both of the simply supported and the clampedclamped nanobeams. The inclusion of the nonlocal effect increases the magnitudes of dynamic deflections and decreases frequencies. Furthermore, the mass and the velocity of the nanoparticle (striker) have significant effects on the dynamic behavior of nanobeam.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
13
v.
8
no.
2013
151
160
http://mme.modares.ac.ir/article_1661_33a938488c0a87fb24f863e388a036c6.pdf