18
2008-4889
Iran University of Science & Technology
132
Other Related Subject
Thermal behavior analysis of the functionally graded Timoshenko's beam
Rahimi
GH.
Davoodinik
AR.
1
8
2008
19
7
105
113
19
07
2010
The intention of this study is the analysis of thermal behavior of functionally graded beam (FGB). The distribution of material properties is imitated exponential function. For thermal loading the steady state of heat conduction with exponentially and hyperbolic variations through the thickness of FGB, is considered. With comparing of thermal behavior of both isotropic beam and FGB, it is appea red that the quality of temperature distribution plays very important part in thermal resultant distribution of stresses and strains for FGB. So that, for detecting the particular thermal behavior of FGB, the function of heat distribution must be same as function of material properties distribution. In addition, In the case of exponential distribution of heat with no mechanical loads, in spite of the fact that the bending is accrued, the neutral surface does not come into existence.
133
Other Related Subject
Effects of Helix Angle Variations on Stability of Low Immersion Milling
Moetakef Imani
B.
Nasrabadi
Kazemi
Sadeghi
Kazemi
1
8
2008
19
7
115
122
19
07
2010
The stability behavior of low immersion helical end milling processes is investigated in this paper. Low radial immersion milling operations involve interrupted cutting which induces chatter vibration under certain cutting conditions. Time Finite Element Analysis (TFEA) is suggested for an approximate solution for delayed differential equations encountered during interrupted milling. An improved TFEA is proposed which includes the effects of helix angle variations on cutting force, cutting time and specific cutting force coefficients. For this purpose, five different cases were distinguished for engagement limits of the cutting edges. It has been observed that an increase in the helix angle improves the stability limit of the process. This is related to the flip bifurcation lobes that start to separate from the main lobes and shape isolated unstable islands. By further increasing the helix angle, unstable islands will vanish .
134
Other Related Subject
Maintenance Improvement of Ball Bearings For Industrial Applications
Riahi
M.
Ansarifard
M.
1
8
2008
19
7
123
126
19
07
2010
21
07
2014
In this research, the life expectancy of ball bearings in industrial applications is estimated based on known parameters. The overall mathematical calculation of such behavior is based on the theory of Lundberg and Palmgren. The proposed life estimation equation however lacks certain points to make it qualified as universal. A firm conclusion therefore could not be obtained on the basis of this equation alone, particularly when different operating conditions are involved. One such example is the life of ball bearings while operating in clean lubricant environment, which is approximately up to 20 times longer than the calculated life based on the previously prescribed equations. On the other hand, active life under contaminated lubricants is nearly close to one-tenth of the calculated life originally thought to be correct .
135
Other Related Subject
Improvement of simple and regenerative gas turbine using simple and ejector-absorption refrigeration
Garooci Farshi
L.
Mosafa
A. H.
Mahmoudi
S. M. Seyed
1
8
2008
19
7
127
136
19
07
2010
The exhaust gases of gas turbine power plant carry a significant amount of thermal energy that is usually expelled to the atmosphere this causes a reduction in net work and efficiency of gas turbine. On the other hand, the generated power and efficiency of gas turbine plants depend largely on the temperature of the inlet air, So that they both increase as the inlet air temperature decreases. The mentioned two problems can be solved by installing an absorption refrigeration cycle (ARC) at gas turbine inlet, working with thermal energy of exhaust gases. In this research, effect of inlet air cooling on gas turbine performance is studied. The work shows that, the net work and the efficiency will increase by 6-10% and 1-5% respectively for every 10°C decrease of inlet temperature. Since, coefficient of performance (COP) of ARC is low, with high pressure ratios in simple gas turbine (SGT) and with low pressure ratios in regenerative gas turbine (RGT), thermal energy of exhaust gases can not supply all the needed thermal energy for refrigeration cycle. The results show that, when an ejector is included in refrigeration cycle, the need for external energy source required for refrigeration cycle is reduced .
136
Other Related Subject
Quantitative Non-diagonal Regulator Design for Uncertain Multivariable System with Hard Time-domain Constraints
Rafeeyan
M.
1
8
2008
19
7
137
142
19
07
2010
In this paper a non-diagonal regulator, based on the QFT method, is synthesized for an uncertain MIMO plant whose output and control signals are subjected to hard time-domain constraints. This procedure includes the design of a non-diagonal pre-controller based on a new simple approach, followed by the sequential design of a diagonal QFT controller. We present a new formulation for the latter stage, which shows the role of off-diagonal elements in the design procedure. A numerical example is given to illustrate the effectiveness of the proposed method .
137
Other Related Subject
Modal analysis of a turbo-pump shaft: An innovative suspending method to improve the results
Sadegh
M.H.
Jafari
S.
Nasseroleslami
B.
1
8
2008
19
7
143
149
19
07
2010
Modal parameter extraction of high speed shafts is of critical importance in mechanical design of turbo-pumps. Due to the complex geometry and peripheral components of turbo-pumps, difficulties can arise in determination of modal parameters. In this study, modal properties of a turbo-pump shaft, was studied by experimental modal analysis, and using different excitation techniques. An innovative suspending method is proposed to reduce noise-to-signal ratio, resulting from classic suspensions. Comparison of the experimental results obtained from the proposed suspension method and the traditional ones shows that the proposed approach was a promising method, when classic methods fall short of expectations in analysis of complex structures. To validate the experimental results, numerical solution was carried out using simplified geometric modeling combined with the Finite Element Method. The simplified modeling approach can be considered as a reliable theoretical method for numerical modal analysis of similar structures. Comparison of experimental and numerical results shows that there is a good conformity between the results of two approaches .
138
Other Related Subject
Heat Transfer in Semitransparent Medium Caused by Laser Pulse
Izadpanah
E .
Akhavan Taheri
A .
Hekmat
M . H
Talebi
S .
1
8
2008
19
7
151
159
19
07
2010
In this paper, the combination of conduction with radiation into a semitransparent medium which includes absorption, emission and scattering has been investigated. In order to Study the conduction in medium, the Non-Fourier heat conduction has been applied. In this model there is a time delay between heat flux and temperature gradient. Also, in contrast with Fourier heat conduction, the speed of heat propagation is finite. The radiation transfer equation has been solved via approximate method. Also to solve the energy conservation equation and Non-Fourier heat conduction simultaneously, flux-splitting method has been applied. The results show that the transient temperature responses are oscillatory for Non-Fourier heat conduction. Also the Non-Fourier effect can be important when the thermal relaxation time of heat conduction is large. In the initial times, the difference of transient temperature responses between the Fourier and the Non-Fourier heat conduction is large under this condition. For the laser-flash measurement of thermal diffusivity in semitransparent materials, omitting the Non-Fourier effect can result in significant errors. Keywords:
139
Other Related Subject
Design and Performance Tests of a Mobile Mechanical Manipulator
Habibnejad Korayem
M.
Nakhaei
A.
1
8
2008
19
7
161
172
19
07
2010
Mobile mechanical manipulators are one of the automation aspects which were revealed in last years of twentieth century. These machines assume the responsibility of human and gradually expand the domain of their activities in industry. This paper is a presentation of the Sweeper Robot designed in the Robotic Laboratory of Iran University of Science and Technology. The original design of this robot allowing to its gripper to constantly remain parallel to the ground is presented. The dynamic and kinematical models of the robot have been computed. A software was developed in MATLAB to validate the kinematical and dynamic models of the robot by comparison with the experimental results. Once the robot was built and its systematic odometric error estimated by experiment, a control scheme for linear motions was developed to deal with this error. The approach is based on the introduction of an initial rectifying offset motion before starting the linear motion. Eventually, classical line tracking and image processing algorithms were used to complete our robot and the efficiency of our design to achieve its mission in picking and placing different objects according to various algorithms.
140
Other Related Subject
Cement-Implant Interface Fracture Failure by Crack Initiation Due to Interface Cavity Stress Concentration
Haghpanahi
M.
Ghomashchi
H.
1
8
2008
19
7
173
186
19
07
2010
Nowadays total joint replacements are widely used in the world, so in average 800,000 joint surgeries are done yearly only in Europe and North America. However implant loosening is and remains as the major issue of all implant failures and therefore causes revision surgery procedures. Studies and experiments have identified poor fixation of implants most likely is the main cause of long term implant failure and in this case the cement-implant interface cavities are very effective due to resultant stress concentration . In this study the theory of this problem, continuum and mathematical equations for an inhomogeneous material by using Eshelby’s equivalent inclusion method with a spherical void as a special type of inhomogenities is addressed and a new yield criterion with respect to the void’s volume fraction is derived and changes in material elasticity tensor concerning Mori-Tanaka’s theorem also determined, then by using finite element method and remeshing technique a macro scale cement-implant interface cavity is modeled and concerning the loss of strength due to void existence and the interface stress concentration, the crack initiation and propagation phenomenon is numerically investigated with respect to different orthopedic cement material properties. The results show that crack propagates at the interface at constant stress and strain by elastoplastic material and it propagates in cement bulk by considering elastic material properties for cement that both could cause implant loosening even in very small void’s volume fractions in which there are no significant changes in cement yield stress and elasticity tensor according to analytical solution. But numerical simulation shows that when a homogenous cement structure is achieved via high vacuum mixing method, there is a uniform stress distribution in the cement structure and no stress concentration zone forms even at high stress levels and also there is no appropriate local site for crack initiation.
141
Other Related Subject
Modeling Of Heat Transfer And Solidification Of Droplet/Substrate In Microcasting SDM Process
Jafari
A.
Seyedein
S.H.
Haghpanahi
M.
1
8
2008
19
7
187
198
19
07
2010
21
07
2014
Microcasting Shape-Deposition-Manufacturing is an approach to Solid-Freeform-Fabrication (SFF) process which is a novel method for rapid automated manufacturing of near-net-shape multi-material parts with complex geometries. By this method, objects are made by sequentially depositing molten metal droplets on a substrate and shaping by a CNC tool, layer by layer. Important issues are concerned with remelting dept of substrate, cooling rate and stress build up. In the present study attempts were made to numerically model the heat transfer and phase change within the droplet/substrate, making a better understanding of process performance. Thus, making a brief literature review, a 2-D transient heat transfer Finite Element Analysis was carried out by the use of ANSYS multiphysics, in which solidification is handled using apparent capacity method. Verification was done by available experimental data in the open literature to ensure model predictions. The model was run under various process parameters and obtained results presented in the form of temperature fields, solidification profiles, cooling curves and remelting history curves. Solidification profile studies predict a columnar dendritic solidified structure in the vertical orientation which was in agreement with metallographic sections published earlier. Parametric studied were also carried out under different boundary conditions, initial temperature of the droplet and Substrate temperature. It was concluded that 1) the process is not sensitive to convection/radiation effects from the surface. 2) the main parameter that can control the maximum remelting dept is initial temperature of the droplet. the more drop temperature, the more remelting dept. This parameter also affects cooling rate during solidification. 3) Increasing substrate temperature showed a decreased cooling rate in solid, which can be used to reduce residual stresses, but it had a minor effect on the cooling rates during solidification .