Energy Science and Technology
Rasool Esmaelnajad; Navid Farrokhi
Abstract
Increasing the power and improving the performance of diesel engines is always considered by diesel engine manufacturers. Changing the geometry of the injector outlet orifice has a major impact on fuel-air mixing and combustion. In the current study, the geometry of the injector orifice is changed from ...
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Increasing the power and improving the performance of diesel engines is always considered by diesel engine manufacturers. Changing the geometry of the injector outlet orifice has a major impact on fuel-air mixing and combustion. In the current study, the geometry of the injector orifice is changed from circular to annular cross-section, and the effect of different injection pressures on diesel engine performance is investigated. All numerical simulations are performed by using AVL Fire code. The results show that the annular injector improves combustion and engine performance by forming better fuel distribution. Fuel injection pressure affects the performance of the annular injector in terms of droplet distribution and breakup. At low injection pressures, due to the long injection duration, most of the fuel energy release occurs after the top dead center (TDC). Therefore, the engine performance is improved, and the combustion chamber temperature and pressure are limited. However, at high injection pressures, less combustion occurs after the TDC. By changing the injector geometry to the injector with an annular cross-section orifice, the maximum reduction in SFC value is for case P5 and injection durations 10 degrees, which is decreased by 21.4%. The maximum power increase was 15% for a 2.5% fuel increase at an injection pressure of 100MPa. While NO pollutant increased slightly by changing the type of injector at different injection pressures, the soot produced at the beginning of the combustion process was well oxidized before the end of the work phase, and its amount reached less than 2e-6.
Welding
Saman Khalilpourazary; Reza Abdi Behnagh; Ramezanali Mahdavinejad; Nasib Payam
Abstract
This study focused on the optimization of Al—Mg to CuZn34 friction stir lap welding (FSLW) process for optimal combination of rotational and traverse speeds in order to yield favorable fracture load using Grey relational analysis (GRA). First, the degree of freedom was calculated for the system. ...
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This study focused on the optimization of Al—Mg to CuZn34 friction stir lap welding (FSLW) process for optimal combination of rotational and traverse speeds in order to yield favorable fracture load using Grey relational analysis (GRA). First, the degree of freedom was calculated for the system. Then, the experiments based on the target values and number of considered levels, corresponding orthogonal array, Grey relational coefficient and Grey relational grade were performed. In the next step, Grey relational graph of each level was sketched. The performed graph and analysis of Grey results proved the impact of rotational speed and traverse speed on fracture load of resultant joints. Finally, the optimum amount of each parameter for better strength of the welds was obtained. This study showed feasibility of the application of Grey relational analysis for achieving dissimilar friction stir lap welds with the highest quality.
Dynamic Response
Chandan Kumar; Vikas Rastogi Rastogi
Abstract
This work deals with effects of asymmetric stiffness on the dynamic behaviour of the rotor system. The analysis is presented through an extended Lagrangian Hamiltonian mechanics on the asymmetric rotor system, where symmetries are broken in terms of the rotor stiffness. The complete dynamics of asymmetries ...
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This work deals with effects of asymmetric stiffness on the dynamic behaviour of the rotor system. The analysis is presented through an extended Lagrangian Hamiltonian mechanics on the asymmetric rotor system, where symmetries are broken in terms of the rotor stiffness. The complete dynamics of asymmetries of rotor system is investigated with a case study. In this work, a mathematical model is developed considering symmetry breaking of a finite rotor due to stiffness. The natural frequency and amplitude of the rotor are obtained analytically through extended Lagrangian formulation. The asymmetries in rotor are also modeled through bond graph modeling technique for the computational analysis. The simulation result shows a considerable agreement with the analytical results. The limiting dynamics of rotor is shown and analyzed through simulation.
Manufacturing Processes
S. Khalilpourazary; P. M. Kashtiban; N. Payam
Abstract
Nowadays, in order to reach minimum production cost in machining operations, various optimization methods have been proposed. Since turning operation has different parameters affecting the workpiece quality, it was selected as a complicated manufacturing method in this paper. To reach sufficient quality, ...
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Nowadays, in order to reach minimum production cost in machining operations, various optimization methods have been proposed. Since turning operation has different parameters affecting the workpiece quality, it was selected as a complicated manufacturing method in this paper. To reach sufficient quality, all influencing parameters such as cutting speed, federate, depth of cut and tool rake angle were selected as input parameters. Furthermore, both surface roughness and tool life were considered as the objectives. Also, ST37 steel and M1 high speed steel (HSS) were selected as workpiece material and tool, respectively. Subsequently, grey relational analysis was performed to elicit optimal values for the mentioned input data. To achieve this goal, first, degree of freedom was calculated for the system and the same experiments were performed based on the target values and number of considered levels, leading to calculating grey relational generating, grey relational coefficient and grey relational grade. As the next step, the grey relational graph was sketched for each level. Finally, optimum values of the parameters were obtained for better surface roughness and tool life. It was shown that the presented method in the turning operation of ST37 led to high surface quality and tool life.
Meshless Numerical Methods
M. Y. Hashemi
Abstract
In this paper, the laminar incompressible flow equations are solved by an upwind least-squares meshless method. Due to the difficulties in generating quality meshes, particularly in complex geometries, a meshless method is increasingly used as a new numerical tool. The meshless methods only use clouds ...
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In this paper, the laminar incompressible flow equations are solved by an upwind least-squares meshless method. Due to the difficulties in generating quality meshes, particularly in complex geometries, a meshless method is increasingly used as a new numerical tool. The meshless methods only use clouds of nodes to influence the domain of every node. Thus, they do not require the nodes to be connected to form a mesh and decrease the difficulty of meshing, particularly around complex geometries. In the literature, it has been shown that the generation of points in a domain by the advancing front technique is an order of magnitude faster than the unstructured mesh for a 3D configuration. The Navier–Stokes solver is based on the artificial compressibility approach and the numerical methodology is based on the higher-order characteristic-based (CB) discretization. The main objective of this research is to use the CB scheme in order to prevent instabilities. Using this inherent upwind technique for estimating convection variables at the mid-point, no artificial viscosity is required at high Reynolds number. The Taylor least-squares method was used for the calculation of spatial derivatives with normalized Gaussian weight functions. An explicit four-stage Runge-Kutta scheme with modified coefficients was used for the discretized equations. To accelerate convergence, local time stepping was used in any explicit iteration for steady state test cases and the residual smoothing techniques were used to converge acceleration. The capabilities of the developed 2D incompressible Navier-Stokes code with the proposed meshless method were demonstrated by flow computations in a lid-driven cavity at four Reynolds numbers. The obtained results using the new proposed scheme indicated a good agreement with the standard benchmark solutions in the literature. It was found that using the third order accuracy for the proposed method could be more efficient than its second order accuracy discretization in terms of computational time.
Composite Materials
Y. Bayat; H. Ekhteraei Toussi
Abstract
In many cases, a torsional shaft may be a thick-walled radially inhomogeneous cylindrical object. The hollow shafts made of functionally graded materials (FGMs) are such kind of compositions which were studied in this paper. Cylindrical FG shafts are composed of ceramic and metallic parts with power ...
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In many cases, a torsional shaft may be a thick-walled radially inhomogeneous cylindrical object. The hollow shafts made of functionally graded materials (FGMs) are such kind of compositions which were studied in this paper. Cylindrical FG shafts are composed of ceramic and metallic parts with power function distribution across the radial direction. The ceramic phase is isotropic elastic and the metallic phase was elastic-plastic. In this paper, the volume fraction-based elastic–plastic mixture rule of renowned Tamura–Tomota–Ozawa (TTO) was used to model the behavior of the composite material. The elasto-plastic torsion problem was modeled and solved analytically. The results were compared with the simulations of ABAQUS and the accuracy of the solutions was evaluated. Depending on the thickness and level of inhomogeneity, different modes of yielding were obtained. The results showed that plastic zone could occur at the inner or outer surfaces or simultaneously at both surfaces; even it may start in-between the thickness. Moreover, the influence of material inhomogeneity and thickness of shaft upon the plastic zone development were studied and discussed.
Fluid Mechanics
Rahim Shamsoddini
Abstract
Liquid sloshing is a common phenomenon in the transporting of liquid tanks. Liquid waves lead to fluctuating forces on the tank wall. If these fluctuations are not predicted or controlled, they can lead to large forces and momentum. Baffles can control liquid sloshing fluctuations. One numerical method, ...
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Liquid sloshing is a common phenomenon in the transporting of liquid tanks. Liquid waves lead to fluctuating forces on the tank wall. If these fluctuations are not predicted or controlled, they can lead to large forces and momentum. Baffles can control liquid sloshing fluctuations. One numerical method, widely used to model the liquid sloshing phenomena is Smoothed Particle Hydrodynamics (SPH). Because of its Lagrangian nature, SPH is suitable for simulating free surface flow. In the present study, a relatively accurate Incompressible SPH (ISPH) method improved by kernel gradient correction tensors, particle shifting algorithms, turbulence viscosity calculations, and free surface particle detectors is applied for the free surface flow modeling. In comparison to the other SPH Simulations and experimental data, these results show that the present algorithm is effective for simulating free surface problems. The present algorithm has been applied to simulate liquid sloshing phenomena, while the aim of this study is the investigation of vertical and horizontal baffle effects on the control and damping of liquid sloshing. Results show that for vertical baffles, baffle size has a major role in sloshing fluctuation damping. For horizontal baffles, also including size, the baffle base position has a significant role in liquid sloshing fluctuation damping. When horizontal baffle is near the free surface, sloshing fluctuation-damping increases.
Computational Fluid Dynamics (CFD)
Alireza Alinezhad; Ataallah Soltani Goharrizi; Ataallah Kamyabi
Abstract
In this paper, heat transfer and fluid flow around a solid cylinder wrapped with a porous layer in the channel were studied numerically by computational fluid dynamics. The homogeneous concentric and eccentric porous medium around a rigid and solid cylinder is supposed at local thermal equilibrium. The ...
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In this paper, heat transfer and fluid flow around a solid cylinder wrapped with a porous layer in the channel were studied numerically by computational fluid dynamics. The homogeneous concentric and eccentric porous medium around a rigid and solid cylinder is supposed at local thermal equilibrium. The transport phenomena within the porous layer and volume-averaged equations were employed; however, the conservation laws of mass, momentum and energy were applied in the channel. The main purpose of this study is to analyze and compare the heat flux of concentric and eccentric porous layer in the Reynolds number range of 1 to 40 and Darcy numbers of 10-2 to 10-6. It is found that with the decline of Darcy number, the vortex length is increased behind the solid cylinder surface. In addition, the heat flux rate of the cylinder is raised with the increase of Reynolds number. Finally, the results showed that the average Nusselt numbers in different Darcy and Reynolds numbers are higher in the eccentric porous layer than in the concentric porous layer. For example, our findings show that in , and , the average Nusselt number in the eccentric porous layer is higher than the concentric porous layer.
Biomechanics
Mehdi Jahangiri; Mohsen Saghafian; Mahmood Reza Sadeghi
Abstract
A numerical study of hemodynamic parameters of pulsatile blood flow is presented in a stenotic artery with A numerical study of hemodynamic parameters of pulsatile blood flow is presented in a stenotic artery with non-Newtonian models using ADINA. Blood flow was considered laminar, and the arterial wall ...
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A numerical study of hemodynamic parameters of pulsatile blood flow is presented in a stenotic artery with A numerical study of hemodynamic parameters of pulsatile blood flow is presented in a stenotic artery with non-Newtonian models using ADINA. Blood flow was considered laminar, and the arterial wall was considered rigid. Studied stenosis severities were 30, 50, and 70% of the cross-sectional area of the artery. Six non-Newtonian models were used to model the non-Newtonian behavior of blood, and their results were compared with the Newtonian model. The results showed that in Power-law and Walburn-Schneck models, unlike other models, shear stress values before and after the stenosis were smaller than Newtonian models. Also, in maximum flow rate, the Carreua, generalized Power-law, Casson, and Carreua-Yasuda models showed a reduction in global importance factor of non-Newtonian behavior, and subsequently, the results approached Newtonian model. In minimum flow rate, the global importance factor of Newtonian behavior increased, which highlighted the importance of Newtonian model. In minimum flow rate, Carreua-Yasuda model was more sensitive to the non-Newtonian behavior of blood compared to Carreua, Casson, and Power-law models. Also, in that time period, Walburn-Schneck was less sensitive to the non-Newtonian behavior of blood. On the other hand, this model did not show sensitivity when the flow rate was at its peak. Power-law model overestimated the global importance factor values. Therefore, Power-law model was not suitable, because it showed extreme sensitivity to dimension. Walburn-Schneck model was not suitable too because it lacked sensitivity.
Micro and Nano Systems
Aylar Khooshehmehri; Abdollah Eslami Majd; Elham Arabsheybani
Abstract
The hemispherical resonator gyro (HRG) is a type of precision inertial sensor that has the advantages of direct angle measurement and unlimited dynamic range. The overall accuracy of the HRG is due to the quality of its resonator shell, and improving the performance of resonators requires a proper understanding ...
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The hemispherical resonator gyro (HRG) is a type of precision inertial sensor that has the advantages of direct angle measurement and unlimited dynamic range. The overall accuracy of the HRG is due to the quality of its resonator shell, and improving the performance of resonators requires a proper understanding of the processes of energy damping in each resonance cycle, which has a significant impact on sensor performance. In this paper, in order to investigate the losses in the hemisphere shell resonator, first, the equations governing the shell are studied, and three-dimensional modeling is performed in COMSOL software. By performing mechanical simulations, the resonance modes and the natural frequency of the shell are investigated, and finally, the second and third resonance modes are selected as the optimal operating mode of the gyroscope. Also, by performing thermal simulations, the dominant energy damping processes, such as thermo-elastic damping and anchor loss were analyzed and simulated, and the effect of shell material on damping was investigated. Then the quality factor of the resonator was evaluated based on its geometry and material. In this way, according to the scope of work of the gyroscope, this process can be used to design the specifications of the shell to achieve a resonator with the desired quality factor.
Composite Materials
Hamed Khosravi; Reza Eslami-Farsani
Abstract
This work reports the high-velocity impact response of multiscale anisogrid composite (AGC) panels. The aim of the present study is to evaluate the influence of surface-modified multi-walled carbon nanotubes (S-MWCNTs) at different S-MWCNTs contents (0-0.5 wt.% at an interval of 0.1 wt.%) on the high-velocity ...
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This work reports the high-velocity impact response of multiscale anisogrid composite (AGC) panels. The aim of the present study is to evaluate the influence of surface-modified multi-walled carbon nanotubes (S-MWCNTs) at different S-MWCNTs contents (0-0.5 wt.% at an interval of 0.1 wt.%) on the high-velocity impact responses of E-glass/epoxy AGC. Surface modification of MWCNTs is confirmed by Fourier-transform infrared (FTIR) and thermogravimetric (TGA) analyses. AGC panels were fabricated via a manual filament winding technique. E-glass fiber roving and E-glass woven fabric are employed as reinforcing agents in ribs and skin, respectively. The impact test is done on the composite panels by a cylindrical projectile with a conical nose. The results showe that the highest enhancement in the impact characteristics is attributed to the panel containing 0.4 wt.% S-MWCNTs. Based on the analysis of fracture surfaces, enhanced interfacial fiber/matrix bonding is observed for the S-MWCNTs loaded specimen. Furthermore, the incorporation of MWCNTs leads to the reduced damaged area and enhanced tolerance of damage.
Computational Fluid Dynamics (CFD)
Kandassamy K; B. Prabu
Abstract
Heat dissipation in electronic circuits is important to maintain their reliability and functionality. In this work, microchannel based bio-inspired flow field models are proposed and numerically analyzed. The proposed flow fields have single to four inlet-outlet pairs. COMSOL is used to do the numerical ...
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Heat dissipation in electronic circuits is important to maintain their reliability and functionality. In this work, microchannel based bio-inspired flow field models are proposed and numerically analyzed. The proposed flow fields have single to four inlet-outlet pairs. COMSOL is used to do the numerical analysis. Conjugate heat transfer analysis is done on the quarter sectional models, utilizing bi-axial symmetry of the flow fields to reduce computational cost. Constant heat flux is applied to the base of the proposed heat sinks. The results show that the thermal and hydraulic resistances of the proposed models are lower than traditional micro-channel arrayed heat sinks. The four inlet-outlet pairs model shows a thermal resistance of 0.121 to 0.158 C/W at constant Re inlet condition, achieved with a pumping power of 0.102-0.126W. Two and four inlet-outlet pair models with aspect ratio 8.6 have a thermal resistance of 0.069 and 0.067 C/W, for pumping powers 2.078 and 4.365 W respectively. The pressure drop of the proposed models is lower than the conventional microchannel arrays.
Robotics
M. Mohammadi; R. Dehghani; A. R. Ahmadi
Abstract
In this paper, a quadrotor with two manipulators constrained on a straight path is modeled and a robust adaptive controller is proposed for it. Adding two manipulators to quadrotor increases its capabilities and applications in industry. Here, these two manipulators are used to place the robot on a constraint ...
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In this paper, a quadrotor with two manipulators constrained on a straight path is modeled and a robust adaptive controller is proposed for it. Adding two manipulators to quadrotor increases its capabilities and applications in industry. Here, these two manipulators are used to place the robot on a constraint path so that the quadrotor can perform monitoring operations more accurately, since the under-actuated quadrotor becomes over-actuated by these constrained manipulators and one can use this feature to accurately control the position of the robot. Reduced form of motion equations is derived for the constrained quadrotor and based on this a robust adaptive controller is proposed. The nonlinear terms in the dynamic model are approximated by basic functions with constant weights; and adaptive laws are designed by projection operator. Stability analysis is performed based on the Lyapunov theory. Evaluation of the presented controller is done by some numerical simulations. The simulation results showed that the robot tracks the reference path with bounded error in spite of dynamic uncertainties and wind force; and satisfies the considered constraints.
Fatigue
J. Amirian; H. Safari; M. Shirani; M. Moradi; S. Shabani
Abstract
Generally, fatigue failure in an element happens at the notch on a surface where the stress level rises because of the stress concentration effect. The present paper investigates the effect of a notch on the fatigue life of the HSLA100 (high strength low alloy) steel which is widely applicable in ...
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Generally, fatigue failure in an element happens at the notch on a surface where the stress level rises because of the stress concentration effect. The present paper investigates the effect of a notch on the fatigue life of the HSLA100 (high strength low alloy) steel which is widely applicable in the marine industry. Tensile test was conducted on specimens and mechanical properties were obtained. Rotating bending and axial fatigue tests were performed at room temperature on smooth and notched specimens and S-N curves were obtained. Using the obtained S-N curve for smooth specimens, the fatigue strength factor for the notched specimens were predicted by Weibull's weakest-link, Peterson, Neuber, stress gradient and critical distance methods and compared with experimental results. It was found that the critical distance and also Weibull’s weakest-link methods have the best agreement with experimental results.
Plates and Shells
Reza Sharifian; Vagharshak Belubekyan
Abstract
This paper is concerned with an investigation into the localized instability of a thin elastic orthotropic semi-infinite plate. In this study, a semi-infinite plate, simply supported on two edges and under different boundary conditions of clamped, hinged, sliding contact and free on the other edge, is ...
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This paper is concerned with an investigation into the localized instability of a thin elastic orthotropic semi-infinite plate. In this study, a semi-infinite plate, simply supported on two edges and under different boundary conditions of clamped, hinged, sliding contact and free on the other edge, is studied. A mathematical model is used and a general solution is presented. The conditions under which localized solutions exist are investigated.
Composite Materials
S. Mohammadi*; F. Abdi
Abstract
In the presented work, sulfur concrete and rubber were used for producing functionally graded materials (FGM). The physical and mechanical properties of sulfur concrete and rubber were changed continuously across the thickness. On one side, there was just rubber and, on the other, there was pure sulfur; ...
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In the presented work, sulfur concrete and rubber were used for producing functionally graded materials (FGM). The physical and mechanical properties of sulfur concrete and rubber were changed continuously across the thickness. On one side, there was just rubber and, on the other, there was pure sulfur; the properties of each substance were moved to reach another. This kind of material was constructed by applying mechanical pressure on all layers together and heating in a casting die. Thus, it is essential to consider the quantity of sulfur and rubber at each layer and the rule obeyed by physical and mechanical properties. In the drop test, it was found that the elastic impact coefficient changed from sulfur concrete around 50% to rubber around near zero. It seems that, by changing some parameters like combination percentage or layers' thickness, it is possible to optimize the FGM.
Vibration
Rouhollah Hosseini; Mohsen Hamedi
Abstract
The concept of “energy harvesting” is to design smart systems to capture the ambient energy and to convert it to usable electrical power for supplying small electronics devices and sensors. The goal is to develop autonomous and self-powered devices that do not need any replacement of traditional ...
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The concept of “energy harvesting” is to design smart systems to capture the ambient energy and to convert it to usable electrical power for supplying small electronics devices and sensors. The goal is to develop autonomous and self-powered devices that do not need any replacement of traditional electrochemical batteries. Now piezoelectric cantilever structures are being used to harvest vibration energy for self-powered devices. However, the geometry of a piezoelectric cantilever beam will greatly affect its vibration energy harvesting ability. This paper deduces a remarkably precise analytical formula for calculating the fundamental resonant frequency of bimorph V-shaped cantilevers using Rayleigh method. This analytical formula, which is convenient for mechanical energy harvester design based on Piezoelectric effect, is then validated by ABAQUS simulation. This formula raises a new perspective that, among all the bimorph V-shaped cantilevers and in comparison with rectangular one, the simplest tapered cantilever beam can lead to maximum resonant frequency and highest sensitivity. The derived formula can be commonly used as a relatively precise rule of thumb in such systems.
Welding
Satish Chinchanikar; Vaibhav S. Gaikwad
Abstract
Researchers have worked on many facets of joining of similar/dissimilar aluminum alloys using different joining techniques and came up with their own recommendations. Friction Stir Welding (FSW) is widely preferred for joining aluminum alloys being an economical alternative to produce high-quality welds. ...
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Researchers have worked on many facets of joining of similar/dissimilar aluminum alloys using different joining techniques and came up with their own recommendations. Friction Stir Welding (FSW) is widely preferred for joining aluminum alloys being an economical alternative to produce high-quality welds. However, obtaining high strength welded joints without the detrimental and visible effects still needs attention considering the effect of hybrid FSW techniques, tool material and geometry, process parameters (tool rotation, welding speed, and plunge depth), and post welding treatments. This study presents the state of the art with the authors’ own inferences on the evaluation of FSW performances in terms of joint tensile strength, fatigue strength, corrosion resistance, residual stresses, microstructure, and microhardness. This study also presents attempts made by the researchers on modeling and parametric optimization of FSW to finding scope for application of advanced optimization techniques and development of predictive models for mechanical properties of welded joints. This study emphasizes more studies required on the comparative evaluation of FSW performance with the application of ultrasonic frequency combinedly or individually on advancing and retreating sides of plates.
Forming
Gh. Payganeh; J. Shahbazi Karami; K. Malekzadeh Fard
Abstract
In this paper, single, bi-layered and three-layered tube hydroforming processes were numerically simulated using the finite element method. It was found that the final bulges heights resulted from the models were in good agreement with the experimental results. Three types of modeling were kept with ...
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In this paper, single, bi-layered and three-layered tube hydroforming processes were numerically simulated using the finite element method. It was found that the final bulges heights resulted from the models were in good agreement with the experimental results. Three types of modeling were kept with the same geometry, tube material and process parameters to be compared between the obtained hydroformed products (branch height, thickness reduction and wrinkling) using different loading path types. The results were also discussed.
Vibration
M. M. Soleymani; M. A. Hajabasi; S. Elahi Mahani
Abstract
In this paper, a rectangular sandwich plate with a constrained layer and an electrorheological (ER) fluid core is investigated. The rectangular plate is covered an ER fluid core and a constraining layer to improve the stability of the system. The two outer layers of the sandwich structure are elastic. ...
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In this paper, a rectangular sandwich plate with a constrained layer and an electrorheological (ER) fluid core is investigated. The rectangular plate is covered an ER fluid core and a constraining layer to improve the stability of the system. The two outer layers of the sandwich structure are elastic. The viscoelastic materials express the middle layer behavior under electric field and small strain. Rheological property of an ER material, such as viscosity, plasticity, and elasticity, may be changed when applying an electric field. The ER core is found to have a significant effect on the stability of the sandwich plate. In this paper, based on the displacement field of each layer, the kinetic energy and strain energy are separately obtained for each layer. Transverse displacement of the second layer changes linearly between the transverse displacement of the first and third layers. The loss energy of the second layer consisting of the ER fluid is also calculated and, with the replacement of total kinetic energy, total strain energy, and energy dissipation in the Lagrange's equation, the structural motion equation is obtained. Natural frequencies and loss factor for the electric fields as well as the ratio of different thicknesses calculated are by Navier analytical method. As the applied electric field increases, the natural frequency of the sandwich plate increases and the modal loss factor decreases. With increasing the thickness of the ER layer, the natural frequencies of the sandwich plate are decreased. Thickness of the constrained layer also affects the stability of the sandwich plate.
Forming
Mohammad Honarpisheh; Ahmad Gheysarian
Abstract
Single point incremental sheet metal forming is a sheet metal forming process that forms products without the complex dies and tools with low cost. In this study, the incremental sheet metal forming process has been experimentally investigated on the explosively-welded Al/Cu bimetal sheets. Also, the ...
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Single point incremental sheet metal forming is a sheet metal forming process that forms products without the complex dies and tools with low cost. In this study, the incremental sheet metal forming process has been experimentally investigated on the explosively-welded Al/Cu bimetal sheets. Also, the effects of process parameters, such as arrangement of layer`s bimetal, tool diameter and tool path were investigated on the forming force, thickness distribution, formability and roughness. At first, the bimetals were produced by explosive welding process. Then, two tool diameters, step and spiral tool paths and layer arrangement were chosen as input parameters. The results showed that the forming force increases with increasing the tool diameter and using aluminum as a top layer (contact with tool). Also, using spiral tool path increases the average forming force and decreases the maximum thickness changing. The formability increases with increasing the tool diameter and using the copper as top layer with spiral tool path.
Fluid Mechanics
S. F. Ahmed
Abstract
Energy equation for turbulent flow in a rotating system was derived in terms of second order correlation tensors, where the correlation tensors were functions of space coordinates, distance between two points and time. To reveal the relationship of turbulent energy between two points, one point was taken ...
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Energy equation for turbulent flow in a rotating system was derived in terms of second order correlation tensors, where the correlation tensors were functions of space coordinates, distance between two points and time. To reveal the relationship of turbulent energy between two points, one point was taken as origin of the coordinate system. Due to rotation, the Coriolis force played an important role in the rotating system of turbulent flow. The correlation between pressure fluctuations and velocity fluctuations at the two points of flow field was applied to the turbulent energy equation, in which the Coriolis force and centrifugal force acted on the fluid.
Computational Fluid Dynamics (CFD)
Muhim Chutia
Abstract
The aim of this paper is to investigate the effect of the variable thermal conductivity and the inclined uniform magnetic field on the plane Poiseuille flow of viscous incompressible electrically conducting fluid between two porous plates Joule heating in the presence of a constant pressure gradient ...
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The aim of this paper is to investigate the effect of the variable thermal conductivity and the inclined uniform magnetic field on the plane Poiseuille flow of viscous incompressible electrically conducting fluid between two porous plates Joule heating in the presence of a constant pressure gradient through non-uniform plate temperature. It is assumed that the fluid injection occurs at lower plate and fluid suction occurs at upper plate. The governing equations of momentum and energy are transformed into coupled and nonlinear ordinary differential equations using similarity transformation and then solved numerically using finite difference technique. Numerical values for the velocity and temperature have been iterated by Gauss Seidal iteration method in Matlab programming to a suitable number so that the convergent solutions of velocity and temperature are considered to be achieved. Numerical results for the dimensionless velocity and the temperature profiles for different governing parameters such as the Hartmann Number (M) angle of inclination of magnetic field (α), suction Reynolds number (Re) Prandtl Number (Pr), Eckert number (Ec) and variable thermal conductivity (ԑ) have been discussed in detail and presented through graphs.
Energy Systems
Mohammed Ridha Jawad Al-Tameemi; Samir Gh. Yahya; Saadoon Abdul Hafedh; Itimad D. J. Azzawi
Abstract
A thermodynamic evaluation is conducted on a combined heat and power system integrating a gas turbine (GT), a heat exchanger (HX1), and an organic Rankine cycle (ORC). Traditionally, ORC bottoming GT cycle is limited to mechanical power production. The novelty of this study is to recover wasted heat ...
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A thermodynamic evaluation is conducted on a combined heat and power system integrating a gas turbine (GT), a heat exchanger (HX1), and an organic Rankine cycle (ORC). Traditionally, ORC bottoming GT cycle is limited to mechanical power production. The novelty of this study is to recover wasted heat from the GT cycle in multistage, which is used for the simultaneous production of mechanical power and hot water supply. In the first stage, the HX1 recovers heat from the GT cycle compressed air to heat the water stream. In the second stage, the ORC cycle recovers thermal energy from the GT turbine exhaust stream to produce extra mechanical power with the remaining latent heat used to heat the water. Two models are proposed for comparison using ASPEN Plus software linked with the RAFPROP database. The modelled GT, in this study, is adopted from an actual machine. The steady-state results show that the combined system achieves 51.55% thermal efficiency compared with a standalone GT efficiency, which is only 21%. The thermal efficiency is divided into 24% mechanical power and 27.55% thermal load. The output hot water temperature is 65 oC. The outcomes of increasing the GT pressure ratio (12-25) are higher combined cycle net power output by up to 16% with a 9.5% reduction in the thermal energy rejected to the environment. Also, the GT efficiency increases from 20% to 22.5%; however, the final water temperature declines from 67 oC to 60 oC, which is still appropriate for various heating applications.
Energy Science and Technology
J. Pirkandi; A. Amiralaei; M. Omian
Abstract
In this research, a combined cooling, heating and power system (CCHP) has been analyzed from the perspective of entropy and exergy. The primary driver and the cooling system for this combined system consist of a micro gas turbine and a hot water lithium bromide single-effect absorption chiller, respectively. ...
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In this research, a combined cooling, heating and power system (CCHP) has been analyzed from the perspective of entropy and exergy. The primary driver and the cooling system for this combined system consist of a micro gas turbine and a hot water lithium bromide single-effect absorption chiller, respectively. The effects of compressor pressure ratio, micro turbine inlet gas temperature and chiller cooling capacity on important system efficiencies and other operational parameters (e.g., electrical efficiency, thermal efficiency, combined heating and power cogeneration efficiency, and combined cooling, heating and power cogeneration efficiency) have been investigated. The findings indicate that the system has its highest electrical efficiency at a compressor pressure ratio of 5. Also at this pressure ratio, the cogeneration efficiency (combined heating, cooling and power) and the exergy efficiency are about 48% and 24%, respectively. Moreover, the increase of the turbine inlet gas temperature has had a positive effect on the investigated parameters. The results show that the increase of cooling capacity reduces the cogeneration efficiencies, but has no effect on the exergy efficiency. Also, by considering specific values for the studied parameters, the amounts of generated entropy and destroyed exergy in various parts of the system have been calculated. The results indicate that the highest amounts of entropy and exergy have been generated and destroyed in the combustion chamber. Parts of the results indicate a system state in which the overall efficiency (combined heating, cooling and power cogeneration efficiency) of the system has increased 13% relative to the system’s initial state.
