Hossein Shokouhmand; Hafez Bahrami
Abstract
In this study an analytical model for open loop pulsating heat pipes (PHPs) is presented. The model predicts the effect of different parameters such as evaporator temperature, length of evaporator, filling ratio, number of turn and tube diameter on PHP's performance.
The governing equations in two phase ...
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In this study an analytical model for open loop pulsating heat pipes (PHPs) is presented. The model predicts the effect of different parameters such as evaporator temperature, length of evaporator, filling ratio, number of turn and tube diameter on PHP's performance.
The governing equations in two phase flow including mass, momentum and energy equations are solved for both one dimensional liquid slugs and lumped vapor plugs numerically. The model includes the thin film layer concept which contributes to heat transfer in evaporator and condenser section. A proper model is also investigated to describe the steady oscillatory behavior of device. The results show that this model predicts well the oscillatory behavior of the phenomena. The obtained results are in good agreement with available data and can be properly used for predicting the trend of effective parameters on PHP's performance. It is found that sensible heat transfer has extremely more important role in increasing total heat transfer of PHP . The thermal resistance decreases due to increasing of the latent heat transfer. It can be seen that increasing of the evaporator temperature, while the temperature of the condenser is constant,will increase the total evacuated heat by PHP in specific filling ratio limits. The results show that the PHP's performance increases when the tube diameter increases. In this case, by using a specific non-dimensionalized model, a unique curve for arbitrary number of turn and FR can be obtained. Also it is found that PHP's performance reaches its maximum at filling ratio around 0.6 for different tube diameters.
Farzad Ebrahimi; Mohammad Hassan Naei
Abstract
Stress-intensity factors (SIFs) are the most important parameters in fracture mechanics analysis of structures. These parameters are evaluated for a stationary crack in functionally graded plates of arbitrary geometry using a novel Galerkin based mesh-free method. The method involves an element-free ...
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Stress-intensity factors (SIFs) are the most important parameters in fracture mechanics analysis of structures. These parameters are evaluated for a stationary crack in functionally graded plates of arbitrary geometry using a novel Galerkin based mesh-free method. The method involves an element-free Galerkin method (EFGM), where the material properties are smooth functions of spatial coordinates and two newly developed interaction integrals for mixed-mode fracture analysis. Numerical examples for mode-I fracture problems are presented to evaluate the accuracy of SIFs calculated by the proposed EFGM. Comparisons have been made between the SIFs predicted by EFGM and available reference solutions in the literature, generated either analytically or by FEM using various other fracture integrals or analyses. A good agreement is obtained between the results of the proposed meshless method and the reference solutions.
Hossein Shahi; Aghil Yousefikoma; Ali Reza Mehrabian
Abstract
A solution to the problem of identification and control of smart structures is presented in this paper. Smart structures with build-in sensors and actuators can actively and adaptively change their physical geometry and properties. As a particular example, a representative dynamic model of a typical ...
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A solution to the problem of identification and control of smart structures is presented in this paper. Smart structures with build-in sensors and actuators can actively and adaptively change their physical geometry and properties. As a particular example, a representative dynamic model of a typical fighter vertical tail, identified as the smart fin, is considered. Piezoelectric patches, which are mounted on the vertical tail, are employed as actuator in the model. The Frequency Response Function (FRF) of the smart fin is obtained from experiment. The corresponding transfer function is then derived using classic system identification (ID) techniques, using MATLAB® system identification toolbox, which is verified with the experimental data. The model obtained using system ID is then used to tune an optimal PID controller to reduce the vibration of the smart structure. To this end, several cost functions are defined and optimized by a genetic algorithm. Next, the obtained controllers are compared with each other and a suitable one is chosen as the system’s controller. Finally, It is shown in simulations that the designed controller is able to reduce the vibration of the smart fin very well.
Ali Asghar Atai; Masoud Shariat Panahi; Kave Ebrahimi
Abstract
Cables have always been under consideration as a structural element because of important features such as large strength to weight ratios and long spans. Their equilibrium analysis is an important issue in this regard. But this analysis involves highly nonlinear equations arising from large deformations ...
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Cables have always been under consideration as a structural element because of important features such as large strength to weight ratios and long spans. Their equilibrium analysis is an important issue in this regard. But this analysis involves highly nonlinear equations arising from large deformations and material nonlinearity. Different methods have been under use for numerical analysis of such structures. Using the principle of minimum total potential energy is one of the common methods of analyzing the equilibrium configuration of structures. In this method, which is considered an alternative to direct solution of nonlinear equations of equilibrium analytically or numerically by finite element for example, the total potential energy of the structure is minimized using optimization techniques and forces and deformations corresponding to the equilibrium configuration are computed. In cable structures, which under ideal assumption cannot withstand compressive forces, the potential energy functional has discontinuous derivative and thus the classic methods of optimization, which make use of the derivative of the objective function, cannot be used in this case. Usually, the energy consideration is used as the basis of obtaining the equilibrium equations of the structure but rarely is it used as a function the numerical minimization of which gives the equilibrium configuration. In this paper a new method of solving nonlinear equations of elastic equilibrium of cable structures is presented. In this method, first the potential energy functional of the cable structure with large deformations is established. Then, the Powell algorithm of optimization, which doesn't depend on the derivatives of the objective function, is applied and the equilibrium configuration as the minimizer of the functional is obtained. The proposed method has the ability to determine the force in each cable and displacements of the cable junctions (nodes) and the slack cables (cables with no tension) with great speed and accuracy compared to the classic methods. This work consists of a brief explanation of different analyzing methods of cable structures currently in the market. Then, the potential energy for a single cable is obtained and is generalized for a cable network. After that, the Powell's minimization technique is explained. In the examples section, a very simple structure for which the analytical result is available is considered as a validating example. Following that, several illustrative examples are considered. The results are in good agreement with previous published ones.
Gholam Hossein Liaghat; Saeed Zargar Azad
Abstract
Die less explosive forming of circular plates is one of the most useful methods in the industries especially chemical applications. Manufacturing of large vessel's head, multilayer rings and some parts of heat exchangers are the example of applying this method. Many theoretical and experimental researches ...
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Die less explosive forming of circular plates is one of the most useful methods in the industries especially chemical applications. Manufacturing of large vessel's head, multilayer rings and some parts of heat exchangers are the example of applying this method. Many theoretical and experimental researches about examining the explosive forming of simple and single layer plate have been done. The purpose of most studies was prediction of transversal displacement of plate and its profile of deformation with respect to the amount of impulsive load due to the explosion. On the other hand, no study has been done for analysis of behavior of bimetallic plate in the explosive forming process. However it can be easily shown that with some small change in plasto-dynamic equations of a simple plate, the behavior of a bimetallic plate in explosive forming process would be analyzed. The used methods in analysis of plasto-dynamic behavior of plates can be divided up to two categories. Some of them have used the equations of motion and wrote these equations for two or three phases of time. This routine is really complex especially in large deformation problems. In other hand, some researchers have applied energy methods for their analytical purposes. The major advantages of this routine is its simplicity. Because there is not necessary to consider the effect of plastic hinge motion for calculating desired parameters. In this paper, die less explosive forming of bimetallic circular plate is analyzed with “energy conservation law” very simply and comprehensively. It will be shown that with calculating full plastic moment and force of a bimetallic plate, the dynamic-plastic’s equations for the simple plates can be used and the displacement of plate's center and its deformed profile can be predicted. Also the presented model has some special capabilities. For example it considers the effects of bending moments and membrane forces simultaneously. Also it is possible to calculate the influence of rotatory inertia and high strain rate effect on the displacement of plate. Further with this analytical model the effect of various supporting condition and the different shape of profile of pressure can be studied. The accuracy and reliability of presented model will be verified with comparison of experimental results and analytical data. Also die less explosive forming process of bimetallic plate have been simulated with Ansys-Lsdyna software. Comparison of different results approves the capabilities of presented model in this article.
Caren Abrinia; Rahim Tahriri Masoule
Abstract
Many metal forming problems have been solved using the slip line field method but all of them have either been two-dimensional (plane strain or plain stress) or axisymmetric problems. In this paper a procedure has been proposed by which the slip line field solution to three dimensional problems of metal ...
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Many metal forming problems have been solved using the slip line field method but all of them have either been two-dimensional (plane strain or plain stress) or axisymmetric problems. In this paper a procedure has been proposed by which the slip line field solution to three dimensional problems of metal forming becomes possible. For this purpose the extrusion of shaped sections has been taken as a case study. For this problem the geometry of the deforming zone has been defined by streamlines and stream surfaces. Clearly for the three dimensional extrusion of shaped sections the stream surfaces are not plane surfaces, and on the other hand the slip line field formulation could only be applied to plane surfaces, therefore an approximation has been made to accommodate this difficulty. In fact the three dimensional surface has been approximated to a plane surface so that for each three dimensional stream surface there exists an approximate plane surface. Unlike the case for the axisymmetric problem where there was only one plane surface on which the formulation was defined and the revolved 360 degrees to complete the deforming zone here there are many plane stream surfaces that by summing them up together the deforming zone is defined. The slip line field formulation was then applied to each and every one of these surfaces and the extrusion pressure on each surface was calculated separately and by adding up all the components of the pressure on each surface the total extrusion pressure was obtained.
To account for the error evolved from the approximations made in the formulations, error functions were developed which showed how much error was developed due to the approximations. To verify the results comparison were made to the results obtained by upper bound and experimental methods. These comparisons showed very good agreements.
Mohammad Kazem Besharati Givi; Akbar Afaghi Khatibi; Mansour Akbari
Abstract
Evidence from the early and late industrializes shows that technology, as the commercial application of scientific knowledge, has been a major driver of industrial and economic development. International technology transfer is now being recognized as having played an important role in the development ...
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Evidence from the early and late industrializes shows that technology, as the commercial application of scientific knowledge, has been a major driver of industrial and economic development. International technology transfer is now being recognized as having played an important role in the development of the most successful late industrializes of the second half of the 20th Century. Our society stands to be significantly influenced by carbon nanotubes, shaped by nanotube applications in every aspect, just as silicon-based technology still shapes society today. Nanotubes can be formed in various structures using several different processing methods. In this paper, the synthesis methods used to produce nanotubes in industrial or laboratory scales are discussed and a comparison is made. A technical feasibility study is conducted by using the multi criteria decision-making model, namely Analytic Hierarchy Process (AHP). The article ends with a discussion of selecting the best method of Technology Transferring of Carbon Nanotubes to Iran.
Caren Abrinia; Seyyed Ali Reza Fazli Rad
Mehdi Ashjaee; Hossein Shokouhmand; Mehdi Amiri; Touraj Yousefi
Abstract
Laminar free convection heat transfer from vertical and inclined arrays of horizontal isothermal cylinders in air was investigated experimentally and numerically. Experiments were carried out using Mach-Zehnder interferometer and the FLUENT code was used for numerical study. Investigation was performed ...
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Laminar free convection heat transfer from vertical and inclined arrays of horizontal isothermal cylinders in air was investigated experimentally and numerically. Experiments were carried out using Mach-Zehnder interferometer and the FLUENT code was used for numerical study. Investigation was performed for vertical and horizontal cylinder spacing from 2 to 5 and 0 to 2 cylinder diameters respectively. The Rayleigh number based on the cylinder diameter varied between 103and 3×103.The effect of vertical and horizontal cylinder spacing and Rayleigh number on the local heat transfer from each individual cylinder was investigated. It was seen that the local heat transfer coefficient of each cylinder strongly depends on its position relative to the others. This variation of the local heat transfer coefficient was explained by the interaction of plume's temperature and velocity profiles.
Mohammad Ali Akhavan Behabadi; Hossein Shokouhmand; Masoud Jamali Ashtiani; Amir Mohammadpour
Abstract
The pressure drop of refrigerant R-134a flow boiling inside a horizontal tube has been investigated experimentally. The test set-up which was used in this investigation is a well instrumented vapor compression refrigeration system. These instruments are thermocouples, flow meter, pressure gauges and ...
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The pressure drop of refrigerant R-134a flow boiling inside a horizontal tube has been investigated experimentally. The test set-up which was used in this investigation is a well instrumented vapor compression refrigeration system. These instruments are thermocouples, flow meter, pressure gauges and the pressure drop measuring apparatus. This system consisted of three electrically heated evaporators called as pre-evaporator, test evaporator and after evaporator, respectively. The empirical pressure drop data for two phase flow boiling of R-134a inside a horizontal tube of 7.5mm internal diameter has been collected. The ranges of mass velocities and vapor qualities are 54-136 kg/m2s and 0.2-1, respectively. The collected data were compared with the predicted pressure drop values by seven different correlations. Finally, a new correlation was developed to predict the pressure drop of two phase flow inside evaporators.
Farzad Gheraghpour Samavati; Seyyed Ali Akbar Moosavian
Abstract
Parameter identification techniques are particularly attractive to determine the inertial parameters of robot manipulators and manipulated payloads. These parameters are particularly needed in implementation of a model-based controller for robot manipulators. In this paper, the inertial parameters of ...
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Parameter identification techniques are particularly attractive to determine the inertial parameters of robot manipulators and manipulated payloads. These parameters are particularly needed in implementation of a model-based controller for robot manipulators. In this paper, the inertial parameters of a manipulated rigid-body object have been estimated. The Newton-Euler equations will be employed to relate the measured joint forces and torques via acceleration-dependent coefficients to the inertial parameters. These parameters will then be estimated on-line by least square method with 100 data points. The Multiple Impedance Control (MIC) is an advanced model-based algorithm which enforces designed impedance on both a manipulated object, and all cooperating manipulators. The MIC is implemented here on a system of two cooperating Puma560 manipulators. As simulation results show, the response of the MIC algorithm in the occurrence of an impact due to collision with an obstacle is smooth, even with noticeable estimation error in moments of inertia parameters; which emphasizes the robustness of MIC algorithm.
Ahmad Kahrobaian; Hamid Reza Malekmohammadi
Abstract
A new method of optimization on linear parabolic solar collectors using exergy analysis is presented. A comprehensive mathematical modeling of thermal and optical performance is simulated and geometrical and thermodynamic parameters were assumed as optimization variables. By applying a derived expression ...
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A new method of optimization on linear parabolic solar collectors using exergy analysis is presented. A comprehensive mathematical modeling of thermal and optical performance is simulated and geometrical and thermodynamic parameters were assumed as optimization variables. By applying a derived expression for exergy efficiency, exergy losses were generated and the optimum design and operating conditions, were investigated. The objective function (exergy efficiency) along with constraint equations constitutes a four-degree freedom optimization problem. Using Lagrange multipliers method, the optimization procedure was applied to a typical collector and the optimum design point was extracted. The optimum values of collector inlet temperature, oil mass flow rate, concentration ratio and glass envelope diameter are calculated simultaneously by numerical solution of a highly non-linear equations system. To study the effect of changes in optimization variables on the collected exergy, the sensitivity of optimization to changes in collector parameters and operating conditions is evaluated and variation of exergy fractions at this point are studied.
