نشریه مهندسی مکانیک مدرس
سال هفدهم شماره 1 (فروردین 1396)

In this paper, minimum-time low-thrust planar orbit transfer problem is solved by fuzzy optimal control. Trajectory dynamic restricting assumptions and using analytical averaging method, the governing equations of orbit transfer problem in its desired form with constant acceleration magnitude is achieved. Then, using Euler discretization method, the whole differential dynamic equations, performance function and transversality conditions are represented in a discrete form. Calling membership function concept of fuzzy environment, this algorithm transfers classical optimal control including performance index and trajectory transversality conditions associated with uncertanities to fuzzy environment. Thereafter, introducing slack variables all the inequalities change to equality conditions. Applying Bellman-Zadeh approach, optimal control problem turns to parameter optimization problem which then is solved by Lagrange multipliers technique. Finally, solving the set of nonlinear algebraic equations made by optimality necessary conditions simultaneously is achieved by nonlinear programming method. Numerical fuzzy optimal control results are validated with available analytical results which show the priorities of this method in orbit transfer trajectory optimization in presence of uncertainities. FOC approach is categorized into direct methods for solving optimal control problems, while it is far from their defects e.g. curse of dimensionality and burdensome computational load so that it applies fuzzy approach and expert knowledge to simply solve the problems.

This paper aims at optimizing the parameters involved in stress analysis of finite isotropic plates, in order to achieve the least amount of stress around a quadrilateral cutout located in a finite isotropic plate under in- plane loading using a novel Swarm Intelligence optimization technique called Ant lion optimizer. In analysis of finite isotropic plate, the effective parameters on stress distribution around quadrilateral cutouts are cutout bluntness, cutout orientation, plate’s aspect ratio, cutout size and type of loading. In this study, with the assumption of plane stress conditions, analytical solution of Muskhelishvili’s complex variable method and conformal mapping is utilized. The plate is considered to be finite (proportion of cutout side to the longest plate side should be more than 0.2), isotropic and linearly elastic. To calculate the stress function of a finite plate with a quadrilateral cutout, the stress functions in finite plate are determined by superposition of the stress function in infinite plate containing a quadrilateral cutout with stress function in finite plate without any cutout. Using least square boundary collocation method and applying appropriate boundary conditions, unknown coefficients of stress function are obtained. Moreover, the finite element method has been used to check the accuracy of results. The obtained results show that the mentioned parameters have a significant effect on stress distribution around a quadrilateral cutout and that the structure’s load- bearing capacity can be increased by proper selection of these parameters.

In the present work, the transient behavior of a single spool turbojet engine as a function of fuel flow rate is investigated, using fourth order nonlinear dynamic model based on the airplane longitudinal dynamics, compressor and turbine dynamics and dynamics of rotor. Taking into account the thermodynamic variables in all five components of the engine and representing desired parameters as function of time are contributions of the paper. Moreover, we use inter-component volume method in our study which results in more accurate simulations. In this method, by adding the pressure and temperature fluctuations, caused by saved mass, a more precise model is obtained. Taking advantage of this method and using the governing thermodynamic and Gas dynamic equations, the governing dynamic equations of engine are obtained. By solving the equations in MATLAB software, the influence of the fuel flow rate on the output variables is studied. It should be mentioned that fly considered horizontal and in specific height of 2500 (m) at all of the simulation period. Engine thrust is specifically considered as the desired modeling parameter. In addition, the variation in airplane velocity, as an important parameter in the internal fuel flow rate, is added to the simulations, resulting in more accuracy. Studying the dynamic behavior of the engine thrust is a pre-requisite to the design of appropriate controllers that is the next step of this research.

In this study, performance of a coplanar single chamber solid oxide fuel cell with oxygen-methane-nitrogen under steady state conditions is investigated. The cell geometry is considered two dimensional and the computational domain is consists of gas chamber, anode electrode, cathode electrode and electrolyte. Oxygen-methane-nitrogen mixture is fed to the cell with initial mass fraction of 0.07, 0.14 and 0.77 respectively. All physical properties are considered as temperature dependent. The fully coupled nonlinear governing equations including mass, momentum, species and charge conservation equations are formulated in commercial software and solved using finite elements method. To show the model accuracy, the current model results are compared with a similar numerical model. Finally, the cell performance analysis including velocity, temperature and concentration of all species is discussed. The results show that the maximum temperature is occurred at anode side. This is due to methane oxidation reaction which is extremely exothermic. This temperature growth is an advantage for the cell to be able to reduce its working temperature. Furthermore, it is shown that a large amount of hydrogen leaves the chamber without any use. This is the main reason of low performance occurred in this type of cell.

The aim of this study was to investigate the influence of stand-off distance and the explosive ratio parameters on metallurgical and mechanical properties of three-layers explosively bonded copper-aluminum-copper interface. To illustrate effects of these two parameters, samples welded with different stand-off distances and explosive ratios. Optical microscopy, scanning electron microscopy, microhardness and tensile-shear strength tests carried out on the samples. The results indicate a suitable joint with proper metallurgical and mechanical properties in copper-aluminum-copper plates. Microscopic images showed the semi unsymmetrical wavy interface with cracks and voids, also by increasing the explosive ratio, locally melted zones was increased at the interfaces. Elemental analysis confirmed the brittle intermetallic compounds at the interface that produce cracks in these areas. Also, the wavelength increased with increasing explosive ratio. Hardness increased near the interfaces due to the severe plastic deformation and increased with increasing the explosive ratio. Tensile-shear test results showed the decrease in bond strength caused by increasing the explosive ratio.

In current work for the first time, buckling analysis of bidirectional functionally graded (BFG) Euler beam having arbitrary thickness variation rested on Hetenyi elastic foundation is presented. Moreover, a new scheme based on calculus of variations and collocation method for converting the buckling problem to an algebraic system of equations is proposed. The mentioned scheme leads to obtain the buckling characteristic equation of beam and therefore the first buckling loads are obtained. Various conditions including variation of mechanical properties across the thickness and through the axis, arbitrary thickness variation, Hetenyi elastic foundation, special boundary conditions like the shear hinge and classical boundary conditions like the clamped, simply supported, clamped-simply supported and cantilever beams are considered to show the compatibility of proposed scheme with the various circumstances. The fast convergence and compatibility with the various circumstances are the advantages of the proposed technique. Due to lack of similar studies in the literature, the same exercises are conducted by using the Spectral Ritz method for pursuing the validity of the proposed scheme. The same basis is used for Spectral Ritz and proposed methods. There is an excellent agreement between the results of well-known Spectral Ritz method and the results of proposed scheme, which validates the outcomes of proposed technique.

In this paper, the extended Finite Element Method (XFEM) is implemented to compute the Stress Intensity Factors (SIFs) for rectangular media subjected to a hygrothermal loading. In governing hygrothermoelasticity equations, the cross coupled of temperature and moisture fields and temperature-dependent diffusion in some cases are considered. Furthermore, an interaction integral for hygrothermal loading is developed to compute the stress intensity factors. The non uniform mesh of isoparametric eight-nod rectangular element is used in XFEM to decrease the absolute error in SIFs computations. In order to numerical results validation, the SIF of mode I is obtained analytically. The coupled governing equations are firstly decoupled in terms of new variables and then solved by the separation of variable method. According to the results, the moisture concentration gradient has a significant effect on the SIFs so should be considered in the model. Up to reaching temperature to its steady state, the cross coupled of temperature and moisture synchronies their time variation which affects on the time variation of SIF. At early time of thermal shock, the SIF for shorter cracks is not necessarily lesser than the longer ones. Also, the mode I SIF for longer and inclined cracks is smaller. On the other hand, considering the moisture concentration as a temperature function increases the time required to reach the moisture steady state.

Nowadays one of the main challenges facing fluid dynamics simulations is the long duration of numerical calculations. Mathematical operations in numerical solution of differential equations using traditional hardware such as CPU, are done in a series of orderly calculations and therefore take a lot of time to complete. A new solution procedure for numerical calculations is presented using FPGA (Field Programmable Gate Arrays) hardware, which will enable parallel processing inside the hardware. The main goal of this research is to use FPGAs instead of CPUs for numerical solution of the Laplace equation and therefore to accelerate its solution. FPGA is an integrated circuit containing a number of logic blocks. The architecture of this hardware can be reprogrammed and configured after manufacturing. So, it's possible to design and implement complex circuits for various applications using an FPGA. In the present research, first, the ability of FPGAs in mathematical operations on floating point numbers is studied. Then, the Laplace problem is implemented and solved numerically on a specific FPGA hardware using different mesh size and numerical methods. The time duration and precision results of the calculations are compared to the results from a CPU. The calculation procedure on the FPGA is up to twenty times faster than a conventional CPU, with the same data precision. Several numerical and analytical solutions are used to validate the results.

Development of wave energy convertors (WEC) is one of the main challenges that naval architectures have encountered, recently. One of the most important approaches before construction of WECs is the evaluation of their conceptual models in computational fluid dynamics (CFD) software. Therefore, in the current article, an innovative model of wave energy convertor is presented and hydrodynamic performance of proposed model in Persian Gulf has been examined. For accurate simulation of dynamics of WEC, mesh morphing technique is utilized. Since the presented WEC is an innovative design and there is no experimental result for validation purpose, it is tried to verify the numerical setup using similar experimental problems which have the various characteristics of the considered problem. Then, several different geometries including flat and foil pedals, and big and small semi-spherical pedals as a part of WEC have been analyzed, numerically. Small semi-spherical pedal has been determined as the best possible geometry. Number of pedals has been another parameter which has been studied and eight pedals model has been recognized as optimum choice. Finally, optimum WEC has been simulated in nine different waves and the results have been presented.

In fire community, predicting large scale fire behavior is the main target of researches. Flame spread from one area to another is one of the most important fire behaviors which may lead to destruction of buildings, jungles and etc. Therefore, in recent years, flame spread of solid is attracting many attentions and many studies focused on these phenomena. Pyrolysis modeling is one of main aspects in flame spread simulations via computational fluid dynamics (CFD) method. A 1D pyrolysis model has been developed based on OpenFOAM, an open source toolbox in order to enhance FireFOAM solver potential to simulate flame spread on solid materials. The prediction of developed pyrolysis model has been compared with empirical data for surface temperature and mass loss rate of PMMA. Uncertainties in experimental measurements caused for input parameters not to be unique, thus, a particular set of model input parameters have to be determined to reach an acceptable agreement between pyrolysis model and experimental results. Using optimization method is very common in that matter. The non-linear nature of problem and input parameters being numerous would make optimization calculation expensive. In this article, the effects of input parameters (as PMMA properties) have been investigated to firstly, to observe the effects of material properties on pyrolysis process. In the other hand, the most influential properties are introduced in order to reduce computational costs in optimization process by optimizing only these properties.

Fuel consumption, emissions and output power are some of the very important factors for automotive engine design. Since the combustion efficiency depends on the quality of the air-fuel mixture and mixture quality depends on the fuel injection parameters, the investigation of spray features is an overall goal in direct injection engines. In this paper, simulation of GDI spray is carried out in a constant volume chamber contains nitrogen in four different injection pressure using the AVL Fire software. The results are validated against the Istituto Motori-CNR experimental data. The log-normal probability distribution as an initial droplet diameter and Huh-Gosman model as secondary breakup were used. Then the combustion of EF7 Engine with direct injection was studied and wall film thickness was compared at different injection pressures and injector angles. Also, the effects of wall temperature and single-stage and two-stage fuel injection with different ratios of injected fuel mass were evaluated on the wall film. Since the fuel can be injected into the combustion chamber in both intake and compression stroke according to engine operating conditions in gasoline direct injection engines, the simulation was done for open cycle engine.

Some solutions are presented to show the ability of the spectral line-based weighted sum of gray gases approach to solve the radiative transfer equation in absorbing-emitting non-gray media. The medium contains heat sources and is atradiative equilibrium state which occurs in high temperature systems. The non-gray gaseous medium is divided into a number of gray gases, and the radiative transfer equation is solved for each gray gas by the discrete ordinate method. The intensities are found by a summation over all gray gases, and the temperature field is updated by an iterative procedure. The updated coefficients obtained from high-temperature molecular spectroscopic database (2010thedition) are employed in the spectral line-based weighted sum of gray gases model. The method is verified through comparison with a benchmark problem for the case of a specified temperature distribution, and also for thecase of a variable temperature distribution (radiative equilibrium). Several examples are taken into account to show the ability and performance of proposed procedure for the radiative equilibrium calculations in media with heat sources and different boundary conditions (constant temperature and insulated walls).

This paper investigates mapping of stiffness, damping and mass matrices for joint and Cartesian space in robot impedance control. The stiffness mapping is studied more than others for serial and parallel robots by lots of researchers. But all the mapping methods are considered for small displacement or static problems. In fact there is no formulation for large displacement or dynamic problems. So in the presented paper, impedance mapping is studied by considering old methods against new one. The new proposed method is called Large Displacement Mapping Method. Two main methods are presented in researchers’ works and are studied beside the new proposed one in this paper. A test is designed and simulated by Simulink/MATLAB in order to analyze different methods clearly. Then the proposed test is applied on a SCARA robot practically. According to simulation and experimental results, only the proposed method can map the stiffness, damping and mass matrices in large displacement case. The results show, as robot is getting away from the initial position, more deviation is happened. Considering impedance control mapping results, two main differences are seen in stiffness and damping matrices while mass matrix mapping result is the same in all three methods.

In this paper, laser brazing of austenitic stainless steel (type 321) and martensitic stainless steel (type 410) was performed using 400W pulsed Nd:YAG laser with nickel-based filler metal (BNi-2). Laser brazing process was carried out at different gap distances. Microstructure and composition analysis of the filler metal and the brazed joints were examined by optical Microscopy (OM) and Scanning Electron Microscopy (SEM). Mechanical properties of the brazed joints were measured in the form of Micro hardness and tensile test. Results show that filler metal shows good wetting and spreading on 321 and 410 stainless steel in laser brazing process. Filler metal consists of nickel solid solution, nickel-rich boride and chromium-rich boride. The laser brazed joints are mainly comprised of the nickel solid solution, nickel-rich boride in the center of the joints and chromium-rich boride in near interface with substrates. The average micro hardness for filler metal was 550 HV compared to 500 HV for laser brazed joints. The tensile strength of laser brazed joints is varied from 200 to 500 MPa because of different gap distances.

In this paper, a thermodynamic based constitutive model used to model the behavior of magnetic shape memory alloy (MSMA) during applying strain in an energy harvester. In this type of energy harvester, applying strain changes the internal magnetization of MSMA and as a result changes the flux density around it. Using a coil the flux change can be converted to voltage. In order to study the effect of changing MSMA dimensions on the amount of harvested energy, the demagnetization factor for different dimensions derived from an analytic expression for ferromagnetic prisms and the results are validated by reference data. Increasing MSMA thickness results in increasing longitudinal demagnetization factor and decreasing transversal demagnetization factor. The constitutive model of MSMA is used in modeling an energy harvester using two different configurations; one a pickup coil turned around MSMA and second a system with ferromagnetic core to conduct magnetic flux and the pickup coil around core. Simulation of two models at different thicknesses shows that increasing thickness in system with coil around MSMA results in linear increase of voltage while this parameter in second configuration leads to a nonlinear increase of voltage. Furthermore, simulations show that increase of MSMA width, results in linear increase of output voltage in both configurations but with steepest rate for system with ferromagnetic core. Finally, increasing the length of MSMA specimen shows no changes in voltage for the system with coil around MSMA, while linear increase in voltage for the system with core is recorded.

This paper presents an experimental study on the effects of printing parameters on the tensile strength of the polymer-metal composites printed via Fused Deposition Modeling (FDM) technique .In the recent years, 3D printer systems have been widely employed in various industries. FDM is one of the most widely used 3D printer systems worldwide due to its simplicity and lower cost. Although extensive research works have been carried out in the area of 3D printing, less efforts have been reported in developing new materials and their use in FDM process. The materials utilized in this study consisted of Cu particles in ABS polymeric matrix with a constant 25 wt.% of metal powder. The filament production line was implemented to accustom with the manufacturing process. The printing variables were selected as nozzle (orifice) diameter, layer height, fill pattern and nozzle temperature that were examined in three levels. Taguchi method was employed to find the optimal FDM process parameters. The main effect, signal-to- noise ratio and analysis of variance were employed to analyze the process parameters in order to achieve optimum tensile strength of the composite material specimens. Finally, the specimens were produce at the optimized parameters to confirm the tests and method.

Circular micro-plates are used in microelectromechanical systems (MEMS) such as micro-pumps and ultrasonic transducers due to their special geometry. One of the most important problems with electrostatic micro-actuators is pull-in instability which prevents large displacements. Stabilization in beyond pull-in displacements can be attained using an appropriate controller. This paper presents a position control problem for an electrostatic micro-actuator consisting two circular clamped micro-plates to enhance the stroke and speed up the input commands. To consider the modeling error and geometric uncertainties, a fuzzy controller is applied. First, the equation of the plates vibration is derived using Lagrange equation with single mode assumption. Fuzzy rule-base is constructed according to static and dynamic simulations. Genetic algorithm is utilized for finding the optimum parameters of the controller to accelerate accomplishing the commands. Finally, the maximum voltage of the plates is fitted with a function using the optimization results for full range gap commands. The performance of the fuzzy controller along with this function is depicted applying step, multiple step and chirp commands. The obtained results show that the objective has been met well.

Unlike metals for which the fracture characterization methods have been standardized in the context of linear elastic and elastic plastic fracture mechanics theories, for polymeric materials the linear and especially nonlinear theories of viscoelastic fracture mechanics has not been completely developed due to complexities regarding the viscoelastic nature of these materials. For rubbers, even the rate independent theories based on nonlinear finite elasticity have not been widely used. In practice, most researchers make use of the same methods as applied for metals to rubbers. In this paper, the common methods of fracture characterization of rubbers based on J integral and the different challenges regarding them are reviewed. Specificly, the energy dissipation effects in regions far from the crack tip and the correction methods proposed to compensate for these effects are discussed. Performing fracture toughness tests on SENT specimens of a rubbery material based on polybutadiene, it is shown that the well-known multiple specimen method for determination of Jc has a strong sensitivity to experimental errors that exhibits itself as initial crack length dependence of Jc values and is just usefull when testing numerous specimens and removing the experimental errors. On the other hand, the locus method of dissipation correction, gives a single reliable Jc value using a fewer number of specimens and with a considerably lower sensitivity to the experimental errors. Also, using this method the specimen length dependence of Jc values reported in the literature is removed, and hence, it is possible to obtain a dimension independent Jc value.

In this paper dynamic model analysis, position control and locomotion generation of a 2-link robotic fish has been presented. For this purpose, the dynamic model of a 2-link robotic fish based on Lighthill hydrodynamic theory is employed. The effect of system inputs on robot linear velocity, radius curvature of path and hydrodynamic efficiency is investigated with a large amount of simulations. A position controller is designed to generate path by the point to point method. By defining target point and angle and distance errors, control design strategy is proposed to limit the angle error to the neighborhood of zero. It is shown that bounding angle error in a ten degree neighborhood of zero, makes the distance error tend to zero. Despite former methods in which, driving both angle and distance errors to zero simultaneously result in huge control effort, the proposed control strategy in addition to improve performance by spending less control effort, make the controller structure simpler and no need to velocity feedback. Finally by using the results of model analysis, it is shown that using minimum amplitude for the 2-link robot drives the average hydrodynamic efficiency of path close enough to its optimum value.

In this paper, the fluid- solid interaction in an electrostatic microbeam by using three- dimensional aerodynamic theory has been studied. Modified couple stress theory is used to model the elasticity depends on the size of the microbeam. The proposed model can be used as a mass micro- sensor. To analyze the dynamic behavior of the microbeam a DC voltage applied to the system and then by applying an AC voltage dynamic characteristics of the system around static deformed condition is analyzed. Because of non-linear nature of the governing equations to solve them reduced order model based on Galerkin is used. Results have shown that considering the couple stress and also increase the size of the length characteristic parameter reduces the size of the fluid pressure differential created between the two sides of the microbeam. However, according to the three- dimensional aerodynamic theory for fluid-solid interaction, change of the pressure difference created does not lead to creation difference in predicting the size of the added mass between the classical and modified couple stress theories. In another part of the results has been shown that the presence of added mass to what extent can makes changes in the frequency response curves drawn for the system. Also applied the couple stress theory and increase the size of the length characteristic parameter makes the system more rigid and consequently reduce the amplitude of the vibration and frequency response curves shift to the right.

Inlet distortion that may be occurred for various reasons at the entrance of a gas turbine, it is caused to disturbed in compressor performance conditions and also all engine components, so it is very important to investigate its controlling methods. The aim of this paper is numerical simulation of inlet distortion in an axial compressor rotor and active control of the instabilities by the air injection at the blade tip region. Flow simulation of inlet distortion is accomplished at compressor entry with five different geometries of circumferential blockage (amounts of circumferential blockage are: 5%, 10%, 15%, 20% and 25% of the compressor inlet duct). For active control of instabilities, 12 injectors have been mounted upstream of the rotor blade row that distributed in circumferential directions symmetrically. The injection mass flow rate does not exceed 2% of the compressor main flow rate at the design point. ANSYS CFX was used for simulation and the turbulence model of k-ω SST has been used through the calculations. The results show that increasing inlet distortion cause to decrease performance and rotor efficiency. Furthermore, for this rotor modeling condition, in 5% and 10% blockage, air injection can improve the rotor performance, but for more than 10% blockage, a strong wake region is formed after the distortion screen and air injection can cause negative effects on rotor performance. Because the strong instabilities can adversely affect the injectors flow and this method instead of modifying the flow field, make it more non uniform than before.

Different applications of thin-walled tube drawing process especially in case of manufacturing the medical apparatuses has caused that different aspects of this process have been investigated by many researchers. In this paper, considering the shear stress as well as the linear variation of normal stress in elements located in the deforming zone, an analytical solution based on the slab method is presented for tube drawing process with a fixed plug. The pressure on the die surface is assumed to be different from that one on the plug surface. Moreover, taking into account a thin-walled pipe, the plain strain condition is applied to the process. In order to verify the accuracy of analytical solution, the process is wholly simulated using ABAQUS/Explicit software. The results show that the drawing stress can be decreased through increasing the die angle or decreasing the plug angle. Moreover, the drawing stress decreases from inner surface of the wall toward the outer surface. In addition, the pressure on die-tube interface is more than that one on the plug-tube interface while the difference of these pressures be increased for greater die angle. The present closed form solution can be utilized as an efficient tool in the related industries to calculate the required tension stress in tube drawing process.

Conical shells are widely used in various engineering applications such as mechanical, civil and aerospace engineering. In the present paper, based on the first order shear deformation theory (FSDT) of shells, the nonlinear vibration behavior of truncated conical shells with different boundary conditions is investigated using a numerical approach. To this end, the governing equations of motion and corresponding boundary conditions are derived by the use of Hamilton's principle. After catching the dimensionless form of equations, the generalized differential quadrature (GDQ) method is employed to obtain a discretized set of nonlinear governing equations. Thereafter, a Galerkin-based scheme is applied to achieve a time-varying set of ordinary differential equations and a method called periodic grid discretization is used to discretize the equations on the time domain. The pseudo arc-length continuation method is finally applied to obtain the frequency-amplitude response of conical shells. Selected numerical results are presented to examine the effects of different parameters such as thickness-to-radius ratio, small-to-large edge radius ratio, semi-vertex angle of cone, circumferential wave number and boundary conditions. It is concluded that the changes of the vibrational mode shapes and circumferential wave number have significant effects on the nonlinear vibration characteristics and hardening effects.

In this article the vibration analysis of a viscoelastic cantilever beam with piezoelectric layers under aeroelastic force and base excitation is investigated. The beam viscoelastic material is assumed to obey the Kelvin-Voight model. Also the piezoelectric layers are located at the top and bottom beam surfaces with series connections. The aeroelastic force based on piston theory is considered to act as an external force on the beam and also the base excitation is assumed to be random. In this research the cantilever beam with two piezoelectric layers are considered as a mechanism to harvest the bending vibration energy. First, the Galerkin method is used to convert the governing partial differential equation into a set of ordinary differential equations. Then the resulted nonlinear ordinary differential equation coupled with electrical circuit equation of piezoelectric layer are solved numerically by Rung-Kutta method. Finally, by analyzing the response of the governing equations, the influence of the system parameters on the vibration behavior of beam and output voltage are discussed. Results show that the increase of fluid velocity increases vibrational energy system which leads to increase of both vibration amplitude and output voltage. In addition, it was shown that structural damping has a significant impact on the output voltage.

In this paper a controller has been presented based on the predictive control to drive and control the bipedal Nao robot. One of the challenges in the practical applying of these types of controllers is their high computational loading and the time-consuming control operations in each time step, in which it is suggested to use Laguerre Functions to reduce the computational loading of the predictive controller. In this study, at first using the conventional methods for the identification, and via the real data obtained from the Nao robot in Mechatronics research center of Qazvin Azad University, a proper model is proposed for walking the Nao robot which is considered as a two-dimensional motion in the plane. Then a controller will be designed to control the robot motion using the model based predictive controller. The purpose of this control approach in the first place is to stabilize the walking of the robot and then to guide and keep it on the desired trajectory, so that this trajectory tracking can be performed well as much as possible. Moreover, in order to evaluate the efficiency of the proposed controller, this controller has been compared with a proportional-integral-derivative controller and will be studied. The simulation results show the effectiveness of the proposed controller performance in the robot trajectory tracking, which finally comparing the obtained results from both of the control approaches, indicates the efficiency and different capabilities of the proposed method in this study.

In this paper, flexural behavior of composite sandwich beams under four point bending loading has been studied experimentally and numerically. The skins and the core of the sandwich composite beam have been made of woven glass/epoxy composites and polyvinylchloride foam with 70 kg/m3 density, respectively. The experiments were performed on the beams with different lengths and two different types of layup sequence for the skins as 0/90 and ±45. Failure was initiated in the beams due to indentation of the foam and extended to the face sheet failure under the loading roller. Numerical simulation of the sandwich beam has been performed using ABAQUS commercial software to verify experimental results. During the numerical simulations, the nonlinear material models were employed for shear stress-strain behavior modeling of the foam and the face sheets. In addition, due to the large deformation during bending test geometrical nonlinearity assumption was used in FE analysis. Failure initiation was predicted in the face sheets using modified Hashin criteria. Nonlinear stress analysis and failure predictions in the face sheets and the foam were conducted using USDFLD subroutine in ABAQUS software. Also crushable foam model was employed to simulate the plastic behavior of the foam core. The load-displacement curves and failure mechanisms predicted by the numerical simulations illustrated good correlation with the experimental data.

Bimetallic Copper clad aluminum according to standard ASTM B566 can be used in telecommunication networks and signal transmission. The quality of this product in terms of bonded layer’s, in reference standard is important. The interlayer pressure affected during the drawing process on the quality of bonded layer’s. Sample of Bimetallic wire in 9.5 mm diameters was produced by Copper clad with thickness of 0.45 mm. Bimetal wire formed by wire drawing process with 6.2% reduction in area. In this study the effect of tow parameters of wire drawing process: semi die angle and reduction of area on interlayer pressure using ANSYS 17 for simulation is examined. .By comparing the force-displacement curve in experimental and modeling works, simulation accuracy was good. During the investigation it was found always with reduce reduction of area, percent of the maximum interlayer pressure depend on semi die angle. So that by increases of reduction in area for 5 degrees semi die angle, interlayer pressure does not change. But, for 45 degrees semi die angle the worst effect of reduction in area changes in interlayer pressure is sudden. The pressure changes with increased the semi die angle, depends on the reduction of area. So that the maximum interlayer pressure in 6.2% reduction in area is decreased with increases of semi die angle between 5 to 45 degrees; But, the interlayer pressure in 20% reduction in area, increases with increasing the semi die angle.

Surface pressure fluctuations beneath turbulent boundary layer on a flat plate have complex physical behavior and due to its importance in acoustic noise generation, extensive studies have been devoted to predicting or measuring the surface pressure behavior. In the present study to investigate the surface pressure fluctuations under zero pressure gradient, a flat plate with a chord length of 580 mm has been used. All experiments were carried out in a subsonic wind tunnel and at three free-stream velocities: 10, 15 and 20 m/s. In order to measure unsteady pressure fluctuations, a condenser microphone is used as a pressure transducer. Moreover, various parameters of turbulent boundary layer are measured to provide the input variables of semi-empirical models. A single constant temperature hot-wire anemometer has been used for boundary layer measurement. Surface pressure spectra has been measured at various velocities and their collapse on a single curve by normalizing with different variables of turbulence boundary layer is studied. The results show that the best collapses in low and middle frequencies can be obtained by using mixed variables. However, in high frequency range the pressure spectra collapses when it is normalized by inner layer scales. Finally, after ensuring the accuracy of surface pressure spectra results, the efficiency of semi-empirical models for predicting turbulent boundary layer wall pressure spectra is evaluated. The results show the effectiveness of the Goody’s semi-empirical model for prediction of surface pressure spectra by using turbulent boundary layer parameters.

Transparency is an evaluation criterion for teleoperation systems based on force and position error. Generally, conventional control architectures do not lead to a high transparency to preserve the stability. A novel method is the model-mediated teleoperation approach which estimates the environment impedance on slave site and transmits it to master, where the force is calculated locally by creating a virtual environment. This procedure increases the transparency without degrading stability and with time delays in system. Correctly locating the virtual environment has a significant effect on improving the transparency of the system; however, the proposed methods for this aim either require simplifying environment model or adversely affect the transparency. In this paper a novel, yet very simple, algorithm is presented for determining the location of the virtual environment and collision time. The main feature of this algorithm is that firstly it is independent of environment model and thus is applicable to all environments, and secondly it increases the transparency of the system without using additional sensors. The proposed approach is implemented on a single-degree-of-freedom bilateral teleoperation system with time delay. For estimating environment impedance, novel accurate and robust methods are utilized. Impedance and sliding-mode controllers are used for controlling the master and slave, respectively, and the performance of the system is investigated in interaction with hard and soft environments. Simulation results indicate that the transparency of the system is suitably high in interaction with both environments; however, model jump occurs merely at the first moment of contact with the hard environment.

In this paper, dynamic stability of a simply supported beam excited by a sequence of moving masses is investigated by preserving nonlinear terms in the analysis. This type of loading is important in problems such as motion of vehicles on bridges, high-speed transportation on rails, machining processes, conveying pipelines and barrel dynamics, so its investigation is important from practical viewpoint. The intermittent loading across the beam results in a periodic time-varying equation system. The effects of convective mass acceleration beside large deformation beam theory are both taken into account in the derivation of governing equations which is performed through adopting Hamilton's principle for mass-varying systems. In order to deal with the coupling between longitudinal and transversal deflections, the inextensibility assumption is implicitly introduced into the Hamiltonian formulation and an appropriate interpretation is presented to maintain this approximation reasonable. The method of multiple scales is implemented to find the domains of stability and instability of the problem in a parameter space. The results of applying the method forecast a qualitative change in beam behavior due to nonlinear terms. Results of different numerical simulations show the validity of the analytical approach obtained by the applied perturbation method.

The aim of present article is investigation of evaporation of single- and multi-component fuels droplet and study the effect of unsteadiness term on it. Two approaches are used; a fully transient and quasi-steady approaches. The species, momentum, and energy equations for gas phase and species and energy equations for liquid phase are solve numerically by assuming variable properties with respect to temperature. The results obtained from the fully transient approach show an acceptable compliance with experimental data at atmospheric pressure in a wide range of fuel volatility and ambient temperature for the single- and multi-component fuels. Heptane, decane, and hexadecane are used in order to investigate the effects of fuel volatility on evaporation.The steadiness of processes in the gas phase has been checked by using two measures of unsteadiness related to the mass and heat diffusion of fuel vapor on the droplet surface. The deviations of the results of the quasi-steady approach from the fully transient have been justified by the unsteadiness measures. The results show that fuel and ambient temperature have significant effects on the unsteadiness. For heavier fuels and higher ambient temperature, the diviation of quasi- steady approach from fully transient increases. Also the diviation becomes higher when the differences between volatility of component increase. Therefore, it is concluded that the quasi-steady approach presents reasonable results for lighter fuels in the case of single component and whenever the volatilities of components are very close.

In this paper, a quantum intelligent robust controller via a combination of sliding mode control with boundary layer and quantum neural networks, for uncertain nonlinear systems in presence of external disturbances, is presented. Based on the adjustable time variant rejection regulator and rejection parameter, a time variant sliding surface as an adaptive chain of the first ordered low pass filters is defined. A three layers quantum neural network is designed to identify the uncertain nonlinear functions in system dynamics. In this method, the control gain and the break-frequency bandwidth are tuned adaptively. Also, the effects of uncertainties and the un-modeled frequencies are eliminated and chattering phenomenon doesn’t occur. Also, for facilitating analytical theory of the presented method and derivation of the adaptive laws a theorem is proved. Finally, the simulated examples show that the proposed method presents an intelligent adaptive robust tracking control such that the control amplitudes and the integral absolute error index of the tracking trajectory are much less than the other methods. Therefore, effective identification, eliminating the effects of system uncertainties, adjustable control gain and break-frequency bandwidth and more accurate tracking are some of the advantages of this method.

The purpose of this paper is to investigate the effect of viscoelastic ankle foot prosthesis on below-knee amputee gait cycle by using dynamic simulation of human walking. A two dimensional, seven segment model is developed to simulate normal and amputee entire gait cycle equipped with foot-ground contact model in order to simulate entire gait cycle in an integrated way. In the first step, optimization procedure was coupled with forward dynamic to simulate normal gait cycle. Next step was started by replacing ideal torque generator of ankle joint with passive elements that represents passive prosthetic ankle-foot, in order to simulate below-knee amputee gait cycle. The optimal coefficients of joints that were obtained from dynamic simulation of normal gait cycle were then used for amputee model’s intact joints. Three type of optimal passive ankle foot prosthesis were designed using forward dynamic optimization and the simulation results were employed to compare the performance of different prostheses. The results indicated that using viscoelastic ankle foot prosthesis decreases speed-normalized total work, cost function, dynamic effort and increases speed of the amputee model. Hence using viscoelastic ankle foot prosthesis can improve below-knee amputee walking pattern

Identification of spin maneuver flight characteristics focused in this paper. To analyses an airplane flying quality, identification of the dynamic modes and extracting their characteristics is essential for assessment of the airplane dynamic stability and response-to-control. The paper aims to present a new method for identification of some flight modes, including natural and nonstandard modes, and extraction of their characteristics the same as instantaneous frequency and instantaneous damping ratio, directly from measurements of flight parameters in the time domain in nonlinear flight regime. Firstly, a conceptual method based on the Empirical Mode Decomposition (EMD) algorithm is proposed. The key issue of the EMD algorithm is to represent the signal as the summation of the pattern and detail parts, besides separating them from each other. by utilize the Empirical Mode Decomposition (EMD) capabilities in real-time, a local-online algorithm is introduced which estimates the signal intrinsic mode functions Secondly, by applying Hilbert- Huang transformation to IMFs obtained by EMD algorithm the flight characteristics the same as instantaneous frequency and instantaneous damping ratio for flight mode has been estimated from spin measured flight data. The results indicate the appropriate performance of the identification method in nonlinear flight regime.

In the present study, the interaction between Turgo turbine and water flow was simulated using 2D immersed boundary method. For this purpose, the available computer code was validated by some reliable results of numerical fluid - structure interaction study. Due to the complexity of modeling whole turbine and its details, only the part of Turgo turbine involving three blades was simulated and the obtained results of study was generalized to whole turbine. In order to increase the efficiency of Turgo turbine and obtain the optimal design criteria, different parameters of its components including the concavity of turbine blade, turbine water head, water discharge and the number of blades were investigated. The optimal value of each parameter is obtained according to efficiency values of turbine. Finally, the optimal values of mentioned parameters were used to propose some optimal pattern for the design of Turgo turbine. Also, the results of the analysis showed that the immersed boundary method despite having simple formulation and algorithm can be utilized to provide a reliable numerical solution to simulate interaction between the parts of turbine and water flow.

Control systems under normal conditions can provide a desirable performance. But when faults occur in the system, maintaining the appropriate operating condition is a difficult and often necessary matter. In fact, lack of timely fault detection in sensitive systems will lead to damage significant amounts of resources and information. As a result, a growing tendency in the field of fault detection in both scientific and industrial communities has been created. However, if the system under consideration is nonlinear, fault detection cannot be possible with linear methods. In this case the main difficulty is in accurately modeling of process which effects on the accuracy of fault detection and troubleshooting. Fuzzy systems theory, is an effective tool to deal with the complicated and uncertain situations. This paper has considered the problem of fault detection based on the modeling for nonlinear systems using interval type-2 fuzzy system. Our proposed method for fault detection is to create a confidence bound using te estimation of upper and lower bounds for the system output which can be done using a type-2 fuzzy system. Here, a residual signal is produced which determines the presence or absence of fault in the system. In this method in case of deviating the output graph of the control system from the estimated upper and lower bounds, the occurrence of fault can be detected. Finally, in order to show the capabilities of proposed method, the method is applied on three-tank and electro-hydraulic nonlinear systems and the results are very satisfying.

In this paper, a novel model based on the indicial functions concept is presented to calculate the unsteady aerodynamic loads in the incompressible and subsonic compressible flow. Indicial functions represent the two-dimensional airfoil response to a unit step change in the angle of attack or the pitch rate about the reference axis. In contrast to the incompressible flow where the aerodynamic loads can be determined in terms of a single indicial function, four indicial aerodynamic functions are required to find them in the compressible one. If the indicial functions are known, the unsteady loads can then be obtained through the superposition of indicial responses using Duhamel’s integral for any arbitrary motion. For the purpose of combination the aerodynamic loads for the entire subsonic flow speed range, i.e. 0≤M≤0.8, a new, efficient and Mach dependent approximations of the indicial functions are presented by using the analytical as well as numerical data. Using four instead of seven Mach dependent coefficients in the common indicial functions, the required coefficient are decreased from 28 to 16 to fully describe the aerodynamic loads. Utilizing the indicial functions, then a novel and convenient form of unsteady aerodynamic loads and the corresponding state-space representation is presented; having a unified formulation in incompressible and subsonic compressible flight speed regimes. Based on the strip theory as well as the modified lift curve slope, the finite span effect of 3D wings is also included. The generated indicial functions is validated against available results, which shows a good agreement.

In this paper investigate the effects of friction stir pre-mechanical processing on damage evolution of 7075-T6 aluminum alloy by implementation of stress state dependent damage model which described in phenomenological way. For this purpose, specimens with special geometry were designed from sheet with friction stir pre-mechanical processing and without it of mentioned alloy. Each of these specimens demonstrate special stress state at fracture location in uniaxial tensile test. Material parameters determine for two different fracture initiation models, Xue and Hosford-Coulomb by using experimental result. By using each of these models, plastic strain to fracture surface obtained at stress state parameters for pre-mechanical friction stir condition and without it which can use to specify strain plastic to fracture for different stress state at different pre-mechanical friction stir and without it for this material. Also a phenomenological stress state dependent damage model and evolution of it investigated for this material at different pre-mechanical friction stir and without it by using these models. The experimental results show increase of plastic strain of material because of pre-mechanical friction stir and damage model show decrease of evolution of ductile damage because of this pre-mechanical processing. Also by comparing of damage result which obtained by using two different fracture initiation, Xue and Hosford-Coulomb conclude that using Xue model has better result than Hosford-Coulomb model and this model has more reliability to predict evolution of internal damage for this material and this model fracture surface has good compatibility with experimental results.

In this paper, design, fabrication and test of piezoelectric fiber composite transducer for Lamb wave inspection of fluid loaded plates has been investigated. First, dispersion and wave structure analysis has been performed in order to select proper mode and frequency for fluid loaded plate inspection. The S1 mode with zero out of plane displacement in free boundaries of a plate with predefined thickness has been extracted, afterward a piezoelectric fiber composite comb transducer has been designed and fabricated. Having manufactured the transducer, necessary tests has been done in order to prove that the transducer generated Lamb mode at selected mode and frequency is not affected by the fluid loading, in both pitch-catch and pulse-echo techniques. The tests has been done successfully and then crack detection in fluid loaded plate by means of fabricated transducers has been examined again in both pulse-echo and pitch-catch arrangements. It has been shown that in pitch-catch test, the presence of a predefined crack leads to decrease in S1 mode related peak in receiver. Moreover, in pulse-echo test, due to the interference of crack reflected wave signal with the transducer resonance response, continues wavelet transform, as one of time-frequency signal processing methods, has been employed successfully for crack detection. Consequently, the fabricated signal has necessary efficiency for damage detection in fluid loaded plates using lamb waves.

In this paper, a two-dimensional numerical approach is used to study the mass transfer in drying process of a moist object affected by electric field in a smooth channel. Finite volume method is used to solve governing equations of electric, flow, temperature, and the concentration fields in flow phase, as well as the temperature and the moisture fields in the moist object. The computational methodology includes the use of a structured, non-uniform quadrilateral grid, and the Standard K-ɛ model was adopted as the turbulence model. The initial temperature of moist object is equal to the air temperature. In this study, firstly, the computed results are compared with the experimental data and the results agree very well. Secondly, the effect of Reynolds number, applied voltage and the position of the emitting electrode on the drying rate of moist object is evaluated. The numerical results show that the drying rate of moist object with increment Reynolds number enhances without the electric field. Also, in presence of electric field, in constant Reynolds the influence of EHD phenomenon on the drying rate increases with increment of applied voltage. In addition, the results show that as the electrode position is established toward the leading edge of moist object, the maximum moisture evaporation reaches.

In this study, design and analysis of a robotic mechanism, able to traverse low diameter pipes for inspection, maintenance or doing special tasks, has been addressed. Using a mechanism able to move properly along pipes with different diameter while having appropriate adaptability when passing complex routes or bends is so important. So, in this study, considering a simple mechanism based on utilizing shape memory alloy actuator, a micro-robot is designed for inspection of narrow pipes or channels. The robot has a suitable flexibility in addition to an appropriate adaptability for passing complex routes. The robot kinematics and dynamics is analyzed and dynamic equations of the robot are extracted and solved. The robot functionality in the simulation is verified through Adams and Matlab software. Finally, using a suitable controller the amount of robot traction force in addition to normal force between robot wheels and the inner surface of pipe has been measured and controlled. The simulation results predict the appropriate functionality and success of the robot in the inspection of pipes with varying diameter in horizontal, vertical or any other inclination state.

One of the main problems in the classical methods for analyzing crack is a discontinuity in materials and specific conditions at the crack tip. Existing computational methods for the modeling of fracture in a continuous body are based on the partial differential equations of classical continuum mechanics. These methods suffer from the inherent limitation that the spatial derivatives required do not exist at crack tips or along crack surfaces. To overcome this problem, Peridynamic theory (PD), which has been introduced in recent years, could be used to improve the analysis of cracked structures. In the present paper the crack growth and propagation in an inclined crack in the plate is studied. The governing equation is developed and solved using Peridynamic theory and the results are validated using other investigations. Effects of various pre-crack angles and speeds of load application are studied. As it will be illustrated, the PD theory can reasonably model an inclined crack growth and predict the complex phenomenon of crack linear growth or crack branching at various conditions of applying loads. In addition, the results show that the amount of crack growth can be increased by increasing the rate of loading.

In this paper a push recovery controller for balancing humanoid robot under severe pushes for situation that contact surface is small is presented. Human response to progressively increasing disturbances can be categorized into three strategies: ankle strategy, hip strategy and stepping strategy. The reaction of human to external disturbances in the situations that contact surface is small or stepping is not possible is generating upper body angular momentum. In this way in this paper, a single model predictive controller scheme is employed to controlling the capture point by modulating zero moment point and centroidal moment pivot. The proposed algorithm is capable of recovering balance of humanoid robot under severe pushes without stepping in situation that contact surface is shrunked to a strip. The goal of the proposed controller is to control the capture point, employing the centroidal moment pivot when the capture point is out of the support polygon, and/or the zero moment point when the capture point is inside the support polygon. The merit of proposed algorithm is shown successfully in different simulation scenarios using characteristic of SURENA III humanoid robot.

In this research, microhardness variations of subsurface in hole making on a AISI4340 steel workpiece was studied experimentally. For this purpose, four hole making methods were used including; helical milling, profile milling, drilling with and without predrilling. The design of experiments utilized full factorial method in which two main cutting parameters including cutting speed (Vc) and feed rate (fz) were changed in three levels. Nine experiments were performed for each process and Hardness variations of substrate layer along the hole radial and axial distances were investigated (216 hardness measurements points). Results showed that the measured hardness in all of the experiments were higher than bulk material hardness, regardless of cutting conditions and the maximum hardness value was found in the upper levels of cutting parameters of traditional drilling method (729 Vickers). In addition, due to workpiece temperature and work hardening increasing with prolongation of the process time, the maximum hardness value was obtained on the exit surface of hole in all processes. Also, least microhardness variations was found when using traditional drilling with predrill which represents superiority of non-continues, multistage hole making processes and conventional drilling using predrill in creation of holes with more uniform properties.

In this work, a new friction spot welding process called “Threaded Hole Friction Spot Welding” was introduced to join aluminum and short-carbon-fiber-reinforced polypropylene composite sheets. The new process was based on the filling of the pre-threaded hole on the metallic sheet by the melted polymer. Mechanisms of bonding were investigated using macro/micro structural investigation of the joints. The effects of the tool rotational speed on the mechanical strength and fracture energy of the joints were also studied. The results showed that the hole is completely filled with the melted polymer. Formation of a reaction layer composed mostly of Al, C and O as well as mechanical locking between the threaded hole and the re-solidified polymer inside the hole was effective on the joint strength. Maximum shear-tensile strength of the joints reached to ~80 percent of the strength of the polymeric composite sheet. Moreover, strength and fracture energy of the joints increased with enhancement of the tool rotational speed. Variation of the joint strength was explored at the light of the fracture surface features as well as the hardness of the re-solidified polymer inside the hole.

In the present study, flow regimes of co-current, air-water two-phase flow in a vertical tube with 70 mm internal diameter were investigated. Simulation accomplished by open source software, OpenFOAM, and One Fluid model has been used to simulate two-phase flow, which in this model, the interface of two-phase flow has been followed by Volume of the Fluid model. Hitherto, most of the researchers conducted experimentally and the researchers in many of numerical studies just investigated the small tubes. The simulation had investigated according to boundary conditions of the vertical tube. Air and water superficial velocities in inlet and pressure in outlet were constant. Moreover, a no-slip condition in the internal tube walls has been considered. The main purpose of this study is to identify the flow regimes based on the superficial velocities of air and water in the inlet. Moreover, the diagrams of density distributions of phases were obtained, with respect to the behavior of each two-phase flow pattern which can be identified. Superficial velocity of air and water were in the range of 0.01-15 m/s and 0.1-1.5 m/s, respectively. By analysis of results, bubbly, slug, churn and annular regimes; furthermore, semi-annular and Cap-Bubbly sub-regimes were observed.

There has been much interest in recent years in improving material properties by grain refinements using severe plastic deformation (SPD). With applying severe plastic deformation to metals, the structure changes and nanostructure produce. In this study, ultra-fine grained pure titanium fabricate by combination of Equal channel angular pressing and Extrusion process in different passes (1, 2, 4 and 6 pass). ECAP and Extrusion processes were carried out at 400°C. Then, mechanical and microstructural properties of UFG pure titanium billets produced b combination process of ECAP and extrusion process were examined and the effect of passes on mechanical and microstructural properties was investigated. The results showed that mechanical properties were improved significantly. Ultimate strength increased up to 941MPa, in the best state, while for initial sample was 505MPa, in other word ultimate stress increased about 86.3%. With this combinational method, ultimate stress increased about 60.8% for 1 pass sample, 78.8% for 2 pass sample, 86.3% for 4 pass sample and 80.8% for 6 pass sample rather than initial state. In higher passes the rate of increase are reduced due to the grains size saturation. Hardness increased from 81.85 Hv to 216.65 Hv; In other words, hardness increased 164% from initial value. Further passes of the process only have a minor effect on increasing of billet hardness. Scanning Electron Microscope also revealed that brittle fracture were takeplaced in all sample with shallow dimples.

Nanoparticles are being used nowadays to improve the mechanical and structural specification of Fiber Reinforced polymers (FRPs) due to production of hybrid & Multi scale composites. Electrophoretic deposition has been utilized to deposit a smooth layer of carbon nanoparticles on the surface of woven glass fibers, and later in the fiber/matrix interface of composite structure. Initially, the experimental parameters in deposition of CNTs investigated. Suspension concentration, field strength and process duration effects has been studied on the quality and quantity of deposition mass. Then the best situation has been used to fabricate CNT reinforced glass fiber-epoxy composite to evaluate its short beam strength and also quasi static indentation performance subject to lateral shear loads. Results demonstrates the salient effect of grafted CNTs in the nanocomposites interface on their mechanical behavior. The interlaminar shear strength of prepared nanocomposites has been increased by 42% regarding control samples and 10% improvement achieved in their quasi static performance. It has been shown that there is a range of optimum values for field and concentration due to stability of process and also deposition mass. The stability of process will restrain the field and concentration in the process. In best practices the current density values encountered between 0.5 and 1 mA/Cm2. The effect of field strength was around 8.5 times, but the effect of concentration was around 5.5 times. The current density diagram was steady in stable processes and the first three minutes of each process known as the effective deposition time.