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Publication Date: 0
pp. 429-463
Most of the weight of the proton exchange membrane (PEM) fuel cell stack is in the bipolar plates. The main function of bipolar plates is uniform distribution of gas reactants as well as distribution of cooling fluid (water or air) inside the fuel cell. Therefore, the plate design and the characteristics of the gas and cooling channels inside them are essential to the operation of the PEM. Although reactive gas channels and cooling channels perform separately, there are many similarities between them. For example, gas channels should be designed so that distribution of reactive gases on the electrode surfaces is uniform. Also, cooling channels should be designed so that temperature distribution inside the fuel cell is uniform. Further, pressure drop of reactive gases inside the gas channels and the fluid inside the cooling channels must be minimal. In this chapter, initially the characteristics, functions and making materials of bipolar plates along with the to make channels inside of them are investigated. Afterwards, gas channels, cooling channels and effects of the shape and size of channels on the PEM fuel cell performance are studied. Finally, different configurations of gas and cooling channel with emphasizing on the new configurations of these channel are researched simultaneously. © 2022 Elsevier Inc. All rights reserved.
Publication Date: 0
2pp. 1343-1352
The ultra-fast charging capability, distinct properties, fine performance and high capacity of nickel cadmium (Ni-Cd) and nickel metal hydride (Ni-MH) batteries along with their limited weight and size are very attractive for use in many applications including cordless and portable devices, emergency and standby power, telecommunication equipments, photovoltaic systems, electric vehicle, satellite and space craft and power plant supporting equipments. However, the limitation on their temperature requires a detail thermal analysis of these batteries. Thermal behavior of batteries are effected by their boundary conditions, type and construction, and more importantly by their chemical reaction. The purpose of this study is to investigate the effect of temperature on thermal behavior of the Ni-Cd and Ni-MH batteries. The governing equation is the transient and non-linear differential energy equation subjected to non linear radiation boundary conditions and source term. To solve the transient and non-linear governing differential energy equation a control volume based finite difference code is utilized. In formulation of the governing differential energy equation, the Ni-Cd and Ni-MH properties (K, C, ρ) are not constant and the chemical characteristic of the Ni-Cd and Ni-MH batteries, source term, vary with location and time. Calculated thermal characteristic of each battery is then compared to experimental results. The result shows that Ni-MH battery is thermally more suitable for space application and satellite. Copyright © 2004 by ASME.
In this entry, photo-reactors for catalytic solar hydrogen production are introduced and explained. To be an economical environmentally benign and sustainable pathway, hydrogen should be produced from a renewable energy source, i.e., solar energy. Solar driven water splitting combines several attractive features for sustainable energy utilization. The conversion of solar energy to a type of storable energy has crucial importance. In the first part of the entry, background information is presented regarding different photo-reactor configurations for water dissociation with light energy to generate hydrogen. The photo-electrochemistry of water splitting is discussed, as well as photo-catalytic reaction mechanisms. The design and scale-up of photo-reactors for photo-catalytic water splitting are explained by classification of light-based hydrogen production systems. At the end, a new photo-catalytic energy conversion system is analyzed for continuous production of hydrogen at a pilot-plant scale. Two methods of photo-catalytic water splitting and solar methanol steam reforming are investigated as two potential solar-based methods of catalytic hydrogen production. The exergy efficiency, exergy destruction, environmental impact, and sustainability index are investigated for these systems. The light intensity is found to be one of the key parameters in design and optimization of the photo-reactors, in conjunction with light absorptivity of the catalyst. © Springer Science+Business Media New York 2013. All rights reserved.
In this paper, an exergy-economic model is developed to analyze the performance of a direct steam solar tower - steam turbine - organic Rankine cycle (ORC) power plant under different working conditions. The solar power plant is connected to a power grid, and it is integrated with a hydrogen storage system. The hydrogen storage system is composed of an electrolyser, fuel cell, steam turbine and organic Rankine cycle. When solar energy is not available, electrical power is generated by the fuel cell, steam turbine and ORC using the hydrogen produced by the electrolyzer. The analyses are made for the maximum solar irradiation that is available in the city of YAZD in Iran. The effects of the current density and operating temperature on the performance of the solid oxide electrolyzer cell (SOEC) and solid oxide fuel cell (SOFC) are investigated. The effect of solar irradiation on the energy and exergy efficiencies of the cycle is investigated. The results indicate that increase of the solar irradiation leads to an increase of the energy and exergy efficiencies of the cycle. The solar tower has the highest exergy destruction and capital investment cost. © 2022 Proceedings of WHEC 2022 - 23rd World Hydrogen Energy Conference: Bridging Continents by H2. All rights reserved.
Determination of forming limit in sheet metal forming processes is very important and can reduce the number of costly trials. Therefore numerous numerical and experimental analyses have been reported. In this paper, 3D model of hydro-forming process of T-shape tube was simulated by finite element method. An integral ductile damage model, coupled with von Mises plastic criterion, has been applied to predict where and when onset of ductile rupture occurs in the process. Model is based on damage evolution and accounts nonlinear strain paths. Results have been compared with experimental tests and empirical observations. Because of bending effects and nonlinear strain paths assumptions, the ductile damage model showed good agreement with experimental tests and empirical observations. The results were satisfactory and acceptable. Hence ductile damage model can be used as a reliable criterion in prediction of ductile fracture in sheet metal forming processes.
Afshari, E. ,
Asghari, S. ,
Jahantigh, N. ,
Shamsizadeh, P. Publication Date: 0
pp. 417-440
Work production systems cannot convert all input energy into useful work, and in these systems, always a part of the input energy is rejected to the environment in the form of heat. Therefore, the efficiency of work production systems is limited. In these systems, one of the limiting factors of the work production rate is the disposal of the produced heat during the process. The lack of proper heat dissipation increases the temperature of the system and its various parts of damages. Cooling system is an inseparable part of work production systems. The cooling system can be very simple (a natural circulation air-cooling system) or very complex (a nuclear facility cooling system). Simple cooling systems are usually used for low energy production rates (a few watts) and complex systems for high production rates (several hundred megawatts). The polymer electrolyte membrane (PEM) fuel cell is not excluded from this issue. In addition to the production of electric power, heat is produced in the PEM fuel cell, which is even slightly more than the production power. Therefore, one of the most important challenges that affects the use of this fuel cell is the issue of heat removal from the cell and heat management in it, which is done by a cooling system. © 2023 Elsevier Inc. All rights reserved.
Publication Date: 2004
1pp. 921-927
This paper deals with design and analysis of intermittent supersonic wind tunnels. System can be constructed by allowing air at atmospheric pressure to pass through a converging-diverging nozzle, a test section and a diffuser into a vacuum tank. The governing equations of compressible fluid flow have been solved numerically using flux vector splitting method to obtain running time under which it works at the design Mach number. The formulation has been tested on the theory of quasi one-dimensional compressible flow. The numerical results are in good agreement with the results of the theory.
Poursina, M. ,
Antonio c.a.c., ,
Castro c.f., ,
Parvizian j., ,
Sousa l.c., Publication Date: 2004
Engineering Computations (02644401) 21(6)pp. 631-650
A numerical method for shape optimisation in forging is presented. The god of the optimisation is to eliminate work-piece defects that may arise during the forging process. A two-dimensional finite element code has been developed for the simulation of the mechanical process. The material is incompressible and it follows the Norton-Hoff law. To deal with contact constraint the velocity projection algorithm is used. The optimisation process is conducted using a genetic algorithm supported by an elitist strategy. A new genetic operator called adaptive mutation has been developed to increase the efficiency of the search. The developed scheme is used to design optimal preform shapes for several axisymmetric examples. Continuous and discrete design variables are considered. The objective function of the optimisation problem is associated with the quality of the final product. Comparing the obtained optimal results with the literature validates the proposed optimisation method.
Publication Date: 2005
6pp. 291-298
Seat cushion is in the primary load path between the seat and the occupant, and the potential for injuries to an occupant in an accident highly depends on it. The seat cushion is able to dissipate the kinetic energy due to impact in a controlled manner. Wide varieties of energy absorbing materials are used in aircraft interiors for occupant safety and ergonomic purposes. Flexible polyurethane foams are one among those used in seat cushions. Although comfort and aesthetics play an important role in the seat cushion design, safety is among the top criteria. Studies on seat cushions have demonstrated that the seat cushions generally amplify the lumbar/pelvis transmitted load to the occupant, making the seat cushion design further complicated for crashworthy design. The certification of seat cushion requires that their performance be demonstrated by dynamic full scale sled testing. Due to the high costs involved in dynamic testing, a mathematical hybrid multi-body model is developed in this study to simulate the dynamic responses of a bare iron seat, the seat cushion and the occupant represented by crash test dummy. The model is utilized to predict the lumbar load sustained when subjected to the FAR Part 23 and 25 dynamic test conditions for transport and general aviation category aircraft. The model is also used to determine the relative displacement and velocity of occupant against the seat pan. The results from the dynamic model are validated with full-scale sled tests performed at the National Institute for Aviation Research (NIAR), and hence can be utilized as a design tool for the selection of proper seat cushions. Copyright © 2005 by ASME.
Alshaer b.j., ,
Nagarajan h., ,
Beheshti, H. ,
Lankarani, H.M. ,
Shivaswamy s., Publication Date: 2005
Journal of Mechanical Design (10500472) 127(3)pp. 493-498
Clearances exist in kinds of joints in multibody mechanical systems, which could drastically affect the dynamic behavior of the system. If the joint is dry with no lubricant, impact occurs, resulting in wear and tear of the joint. In practical engineering design of machine, joints are usually designed to operate with some lubricant. Lubricated journal bearings are designed so that even when the maximum load is applied, the joint surfaces do not come into contact with each other. In this paper, a general methodology for modeling lubricated long journal bearings in multibody mechanical systems is presented. This modeling utilizes a method of solving for the forces produced by the lubricant in a dynamically loaded long journal bearing. A perfect revolute joint in a multibody mechanical system imposes kinematic constraints, while a lubricated journal bearing joint imposes force constraints. As an application, the dynamic response of a slider-crank mechanism including a lubricated journal bearing joint between the connecting rod and the slider is considered and analyzed. The dynamic response is obtained by numerically solving the constraint equations and the forces produced by the lubricant simultaneously with the differential equations of motion and a set of initial conditions numerically. The results are compared with the previous studies performed on the same mechanism as well a dry clearance joint. It is shown that in a multibody mechanical system, the journal bearing lubricant introduces damping and stiffness to the system. The earlier studies predict that the order of magnitude of the reaction moment is twice that of a perfect revolute joint. The proposed model predicts that the reaction moment is within the same order of magnitude of the perfect joint simulation case. Copyright © 2005 by ASME.
Publication Date: 2006
International Journal of Crashworthiness (15738965) 11(1)pp. 27-35
The main subsystems of an aircraft involved in crashworthiness are the seat cushion, which is part of the seat structure, as well as the restraints, fuselage, and landing gear. A crashworthy structure is designed so that in the event of a crash, it will absorb impact energy in a controlled manner. All energy absorption materials such as honeycombs, polyurethane foams, polymer foams, metallic foams, etc. are being used in aircraft structures, to ensure a safe and survivable trip for passengers, and even in packaging applications for sensitive instruments, equipment, and computers. Polyurethane foams are being used for acoustic purposes, as padding in the finished interior panels of the aircraft, and seat cushions, but they are primarily used in seating applications. The fact that a direct interaction exists between the occupant's body and the seat cushion means that the seat cushion must be ergonomically comfortable in addition to providing safety for passengers. All seat cushions must pass Federal Aviation Administration regulations prior to installation. These regulations require a dynamic sled test of the entire seat system in order to certify it. This traditional testing is also required for replacing old, deteriorated cushions with new buildup cushions, which is time-consuming and costly. Much effort has been taken to obtain reliable modeling in terms of substituting dynamic full-scale sled testing with a cheaper and simpler method of certification. The Advanced General Aviation Transportation Experiments (AGATE) group has proposed a methodology using quasi-static testing instead of full-scale sled testing. In this study, AGATE methodology was validated with experimental results from full-scale sled testing and quasi-static testing. Rate sensitivity of foams was investigated and a criterion using stress-relaxation testing techniques is proposed. This paper addresses full-scale sled testing and quasi-static testing of aircraft seat cushions. This investigation recommends that full-scale sled testing used for seat cushion certification be replaced with quasi-static testing. © Woodhead Publishing Ltd.
Moslemi naeini h., ,
Liaghat, G. ,
Mahshid, R. ,
Sajedinejad a., ,
Vahedi k., ,
Ahmadimehr b., Publication Date: 2006
Journal of Materials Processing Technology (09240136) 177(1-3)pp. 179-182
Large diameter pipes that are made by the U-O bending process, before an expanding operation, should have sufficient material and the required profile. Therefore an analysis of condition in each forming operation is necessary in order to obtain an optimum condition under the low O-shape forming load. In this paper, a forming analysis algorithm for the pipe profile from U-formed blank to circular pipe is presented. In order to obtain the realistic behaviour in the deformation process, a theoretical analysis is made for the elastic, linear work-hardening material. In this analysis the U-shaped blank is divided into some elements and the deformation of each element is analysed by considering the history of deformation. The result obtained from forming of a blank profile has been presented and then compared to the present data reported by other researchers. Good agreements between them show the validity of the program developed. © 2006 Elsevier B.V. All rights reserved.
Publication Date: 2006
2025 29th International Computer Conference, Computer Society of Iran, CSICC 2025 pp. 74-80
RoboCupRescue Simulation System is a platform for designing and implementing various artificial intelligent issues. In rescue simulation environments, Firebrigades should select fire points in a collaborative manner such that the total achieved result is optimized. In this work, we are going to propose a new method for fire prediction and selection in Firebrigade agents. This method is based on Evolving Fuzzy Neural Networks to obtain a set of trained fuzzy rules as rule base of Firebrigades Fire Selection System to select targets autonomously.
Publication Date: 2006
Journal of Fluids and Structures (10958622) 22(4)pp. 529-540
An efficient algorithm for the design optimization of the compressible fluid flow problem through a flexible structure is presented. The methodology has three essential parts: first the behavior of compressible flow in a supersonic diffuser was studied numerically in quasi-one-dimensional form using a flux splitting method. Second, a fully coupled sequential iterative procedure was used to solve the steady state aeroelastic problem of a flexible wall diffuser. Finally, a robust Genetic Algorithm was implemented and used to calculate the optimum shape of the flexible wall diffuser for a prescribed pressure distribution. © 2006 Elsevier Ltd. All rights reserved.
Publication Date: 2006
Journal of Materials Processing Technology (09240136) 174(1-3)pp. 325-333
Since 1980s the problem of manufacturing defect-free parts has been tackled with simulation tools. In this paper, a numerical method for shape optimisation of pre-form dies in a two-stage hot forging is presented. The object of optimisation is to eliminate work-piece defects that may arise during the forging process. A two dimensional finite element code has been developed for the simulation of the mechanical process and prediction of the defects. The material is incompressible and it follows the Norton-Hoff law. To deal with contact constraint, the velocity-projection algorithm is used. The optimisation method is based on a genetic algorithm supported by an elitist strategy. The developed scheme is used to design optimal pre-form dies for two axi-symmetric examples. The objective function is associated with the quality of the final product. Comparing the obtained optimal results with other articles justifies the proposed optimisation method. © 2006 Elsevier B.V. All rights reserved.
Publication Date: 2007
AIP Conference Proceedings (0094243X) 908pp. 963-968
Radial forging is an open die forging process used for reducing the diameter of shafts, tubes, stepped shafts and axels, and creating internal profiles for tubes such as rifling of gun barrels. In this work, a comprehensive study of multi-pass hot radial forging of short hollow and solid products are presented using 2-D axisymmetric finite element simulation. The workpiece is modeled as an elastic-viscoplastic material. A mixture of Coulomb law and constant limit shear is used to model the die-workpiece and mandrel-workpiece contacts. Thermal effects are also taken in to account. Three-pass radial forging of solid cylinders and tube products are considered. Temperature, stress, strain and metal flow distribution are obtained in each pass through thermo-mechanical simulation. The numerical results are compared with available experimental data and are in good agreement with them. © 2007 American Institute of Physics.
Publication Date: 2007
Proceedings of the IASTED International Conference on Modelling and Simulation (10218181) pp. 149-154
Almost all of the researches on object grasping by manipulators and cooperating robots consider no slippage between end-effectors and object, however it can occur. This paper presents dynamics analysis and control synthesis of a manipulator moving an object on a horizontal surface using contact force of end-effector considering slipping condition. Equality and inequality equations of frictional contact conditions are replaced by a single second order differential equation with switching coefficients in order to facilitate the dynamical modeling. Using this modeling of friction, a set of reduced order form is obtained for equations of motion of the system and a new method is proposed to control end-effector slippage on the object.
Publication Date: 2007
AIP Conference Proceedings (0094243X) 907pp. 487-492
One of the main objectives of forging process design is to ensure adequate metal flow in the dies so that the desired finished part geometry can be obtained without any internal or external defects. This paper presents a preform design method which employs a new criterion based on shape complexity factor to determine the necessity of preform stages for axisymmetric forging parts. The presented criterion was tested on several examples using finite element method to verify the models. Comparison of the new shape complexity factor with the other ones shows that the new criterion is more accurate in estimating the number of preform stages. © 2007 American Institute of Physics.
Publication Date: 2007
International Journal of Mechanical Sciences (00207403) 49(5)pp. 622-634
Slab analysis of asymmetrical sheet rolling is presented by considering non-uniform normal and shear stress profiles across the section of product. An important phenomenon considered in this paper is the deflection of plate at entry to the deformation zone and the amount of which is predicted by using a genetic algorithm (GA). In the utilized GA, the elimination/replacement operator and a new operator called "the adaptive mutation" are developed in order to increase the efficiency of the search. Shear stresses are taken into account in applying the Von-Mises yield criterion, and it is shown that this improves the accuracy of the model. Rolling force and pressure distribution predicted by the present model are shown to be in good agreements with the experimental and theoretical results of other investigators. © 2006 Elsevier Ltd. All rights reserved.
Publication Date: 2007
Iranian Polymer Journal (10261265) (8)
Moulded grating is a lattice of connected beams that has wide applications in various industries. In the case of structural applications, deflection control is usually expected to be the limiting factor in design rather than strength control. Thus, this research is mainly focused on an analytical solution to predict the load-deflection behaviour of a moulded grating under concentrated and uniform loads. The general differential equation of an orthotopic plate is expanded by considering a moulded grating as several beams with bending and torsional rigidities. Afterward, the developed model is validated by a finite element modelling technique as well as by the experimental data provided by Strongwell Company. Results showed that the data obtained by the proposed analytical model and those of the finite element method and experimental are in good agreement. Thus, using a developed closed form solution method in this article, the deflection of a grid with any arbitrary dimensions and meshes can be calculated properly.
Publication Date: 2007
pp. 36-43
Occupant lumbar load under CFR Part 23 and 25 is being obtained by using different methodologies including hybrid dynamic modeling and MADYMO analysis. The output of these methods is validated with full scale sled tests results. A crashworthy structure is designed such that in the event of crash, it absorbs impact energy in a controlled manner. The main subsystems of an aircraft involved in crashworthiness are seat cushion, which is part of seat structure, restraints, fuselage and landing gear. Polyurethane foams are being used as acoustic purposes, as padding in the finished interior panels of the aircraft, and seat cushions. Their main application is mostly in seating purposes to provide comfort for occupant. All the seat cushions have to pass Federal Aviation Administration (FAA) Regulations before being installed on the seats. These regulations require a dynamic sled test of the entire seat system for certifying the seat cushions. This traditional dynamic testing is also required for replacing the deteriorated cushions with new buildup cushions which is time consuming and costly. This research provides methodologies based on simulation and modeling to eliminate, or at least, minimize the number of full scale dynamic sled tests defined by regulations for aircraft seats.
Barzi, Y.M. ,
Ghassemi m., M. ,
Hamedi m.h., ,
Afshari, E. Publication Date: 2007
ECS Transactions (19386737) 7(1 PART 2)pp. 1919-1928
The purpose of this paper is to present a control volume based numerical model for simulation of fuel/air flow, electrodes, and electrolyte components of a single tubular solid oxide fuel cell. The SOFC uses a mixture of H 2, CO, CO2, and H2O (vapor) components (pre-reformed methane gas) as fuel. The developed model determines the effect of fuel and air mass flux on local EMF, state variables (pressure, temperature and species concentration) and cell performance. In addition, the effect of fuel hydrogen concentration on output characteristics of fuel cell is investigated If we consider a pure hydrogen fuel, we will have maximum Nerenst potential and power generation. While the hydrogen goes through the channel and is being consumed, vapor is introduced into the flow and hydrogen concentration is reduced along the flow direction. Therefore, the local Nernst potential decreases. For mixed fuel, output parameters are function of fuel molar composition. In general, this model shows how output parameters of the SOFC can be controlled and adjusted by inlet fuel and air mass flow rate as well as hydrogen concentration of the fuel. Finally the numerical study is validated by experimental results such as polarization curve and power density. © The Electrochemical Society.
Publication Date: 2007
AIP Conference Proceedings (0094243X) 907pp. 951-956
Resin flow analysis in the injection cycle of an RTM process was investigated. Fiberglass and carbon fiber mats were used as reinforcements with EPON 826 epoxy resin. Numerical models were developed in ANSYS finite element software to simulate resin flow behavior into a mold of conical shape. Resin flow into the woven fiber mats is modeled as flow through porous media. The injection time for fiberglass/epoxy composite is found to be 4407 seconds. Required injection time for the carbon/epoxy composite is 27022 seconds. Higher injection time for carbon/epoxy part is due to lower permeability value of the carbon fibers compared to glass fiber mat. © 2007 American Institute of Physics.
Publication Date: 2007
AIP Conference Proceedings (0094243X) 908pp. 1597-1602
This research focuses on the determination of thermal conductivity of single-walled carbon nanotube (SWCNT) composite materials using Finite Element Methods (FEM). The effects of SWNT array distribution on effective thermal conductivity of composites are investigated. The composite is analyzed at a microscopic scale by considering two fiber distribution patters: 1- a moderately aligned nano-array distribution, and 2- a random SWCNT nano-array distribution. A thermal conduction problem is solved in the composite domain to obtain the effective thermal conductivity in each case. A composite lamina with 12 percent SWCNT fiber volume fraction is investigated. ANSYS finite element software is used to perform the analysis. The results of FEM models are compared to thermal conductivities obtained using the weight-average formulations. Weight average formulations under-estimate the value of composite thermal conductivity. The effective thermal conductivity values obtained using the FEM models turned out to be much higher than the weight averaged results. © 2007 American Institute of Physics.
Publication Date: 2007
Proceedings of the Institution of Mechanical Engineers, Part K: Journal of Multi-body Dynamics (14644193) 221(4)pp. 551-556
The current article presents an analytical approach, as well as a calculation method for determining the dynamic response of Timoshenko beams under uniform partially distributed moving masses, using the so-called discrete element technique (DET). It is shown that the proposed methodology offers a compact and computationally efficient way of conducting parametric studies to evaluate the dynamic response of the beam-like structures with arbitrary boundary conditions such as railway and road bridges. First, a formulation is presented in a matrix form for beams under partially distributed masses. The results have been validated against analytical formulations, finite difference, and finite element results. A number of parametric studies were conducted to assess the effects of the moving mass velocity and moving mass length on the beam deflection. A major aspect of the work is the study of successive travelling masses for which the transient effects are important. Both analytical and DET results showed that the critical speeds were affected for successive moving masses. Finally, the effects of rotary inertia were studied for a range of inertia values to quantify the error arising from using the Bernoulli-Euler formulation for beams with large inertias. © IMechE 2007.
Publication Date: 2008
8pp. 877-885
Considering slippage in the end-effectors of a set of two cooperating manipulators grasping an object, this paper presents a new dynamic modeling and control synthesis of grasping phenomenon. This dynamic modeling is based on a new formulation for frictional contact where equality and inequality equations in the standard Coulomb Friction model are converted all to a single second order differential equation with switching coefficients. Accuracy of the friction model is verified by comparing its results with those of SimMech. Then equations of motion are reduced to conventional form for nonconstrained system. Assuming the new reduced order system to be BIBO, internal stability of the whole system is analyzed. In the control synthesis of the system a multi phase controller is utilized to control the trajectory tracking of the object as well as slippage control of the end-effectors on the object surfaces. For the proposed controller, a proof is given for system stability and its performance and robustness are shown numerically. The results show superiority of the method and its desirable and excellent performance. Copyright © 2007 by ASME.
Publication Date: 2008
International Journal of Material Forming (19606206) 1(SUPPL. 1)pp. 371-374
Radial forging is an incremental forming process, where the total deformation is achieved by successive individual forming steps. Most researchers investigating radial forging processes have used axisymmetric models. In this research, multi-pass hot radial forging of short hollow and solid products are investigated using a 3-D finite element simulation. The workpiece is modeled as an elastic-viscoplastic material. Three-pass radial forging of solid cylinder and tube products are simulated. Temperature, stress, strain, and metal flow distributions are obtained in each pass through a 3D thermo-mechanical simulation. Finally, the results of 3D FEM models are compared with results obtained by axisymmetric FEM models from previous work and with available experimental data. © Springer/ESAFORM 2008.
Publication Date: 2008
2(PARTS A AND B)pp. 1047-1055
Considering slippage between finger tips and an object, adaptive control synthesis of grasping and manipulating an object by a multi-fingered system is addressed in this paper. Slippage can occur due to many reasons such as disturbances, uncertainties in parameters and dynamics. In this paper, using a novel representation of friction and slippage dynamics, a new approach is introduced to analyze the system dynamics. Then an adaptive controller with a simple update rule is proposed to ensure the bounded trajectory tracking and slippage control, and at the same time to compensate for parameter uncertainties including coefficients of friction. The performance of the proposed adaptive controller is shown analytically and studied numerically. © 2008 by ASME.
Publication Date: 2008
International Journal of Material Forming (19606206) 1(SUPPL. 1)pp. 17-20
In this paper both back-propagation artificial neural network (BPANN) and regression analysis are employed to predict the maximum downward deflection of the exit profile in roll-forming of symmetric channel section. To prepare a training set for BPANN, some finite element simulations were carried out. Sheet thickness, flange width, fold angle and friction coefficient were used as the input data and the maximum downward deflection as the specified output used in the training of neural network. As a result of the specified parameters, the program will be able to estimate the maximum downward deflection of the exit profile for any new given condition. Comparing FEA and BPANN results, an acceptable correlation was found. © Springer/ESAFORM 2008.
Publication Date: 2008
Advanced Robotics (01691864) 22(13-14)pp. 1559-1584
Grasping an object by a cooperating system such as multi-fingered hands and multi-manipulator robotic system has received much attention. Research has focused on analysis of force-closure grasps and the synthesis of optimal grasping, when there is no slipping condition. Although the control system is designed to keep the contact force in the friction cone and avoid the slipping condition, slippage can occur for many reasons. In this research, dynamics analysis and control synthesis of a manipulator moving an object on a horizontal surface using the contact force of an end-effector are performed considering the slipping condition. Equality and inequality equations of frictional contact conditions are replaced by a single second-order differential equation with switching coefficients in order to facilitate the dynamic modeling. Accuracy of this modeling is verified by comparing the results of the model with those of SimMech. Using this modeling of friction, a set of reduced order form is obtained for equations of motion of the system. A new method is proposed to control the object motion and the end-effector undesired slippage based on the reduced form. Finally, performance of the method is evaluated both numerically and experimentally. © 2008 VSP.
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University of Isfahan
Address: Isfahan, Azadi Square, University of Isfahan
