Modares Mechanical Engineering
Year:2016 | Volume:15 | Issue:11|Papers Count:47

The electrohydraulic valves are commonly used in the engineering applications. These valves, as the medium elements, prepare the hydraulic systems for the electrical control applications. For the precise performance of these valves, disturbances in the valve elements dynamics will disturb the control process of the system. The electrohydraulic servo valves are greatly affected by the external acceleration, for instance in the aerospace applications. In a two stage flapper- nozzle electrohydraulic valve, the external acceleration changes the pressure of the fluid leaving the nozzles and affects the flapper and spool of the valve like a virtual force. Thus, when the applied current is zero, the acceleration diverts the spool of the valve from the equilibrium point, and unwanted performance in the valve occurs. In this study the pilot pressures of the spool are modeled in unsteady state condition. The effects of the acceleration on the flapper and the spool of the two stage electrohydraulic valve are investigated. At the end, the obtained model is verified by use of the experimental data.

In this paper, the effect of processing temperature on the elastic and viscoelastic properties including storage modulus, loss modulus and damping value of PVC/plain weave fiberglass composite laminates was investigated. For this, composite samples with [0.90]10 lay ups were produced in three different temperatures including 160oC, 200oC and 230oC using film stacking procedure. Firstly, the flexural strength and modulus of the samples were measured using three points bending test according to ASTM D790-07 standard. Then, viscoelastic properties of the samples were measured in the temperature range of 25oC up to 220oC using Dynamic Mechanical Thermal Analysis (DMTA) and the effect of temperature on the viscoelastic properties was studied. Also, the effect of fiber/ matrix impregnation quality on the thermal and dynamic properties of the samples was evaluated using optical microscope images. It was concluded that the temperature of 230oC is suitable to achieve high quality impregnation, according to both DMTA and three points bending test. Also, it was seen that increase of processing temperature up to 230oC increases the storage modulus; moreover, processing temperature does not affect the glass transition temperature of the samples.

The different kinds of sliding surfaces like clutches, and breaks are susceptible to a surface damage called thermo elastic instability. Instability refers to the unlimited growth turbulence of temperature and pressure, leading to very high local temperatures and wear on the hot spots. In this research, the effect of surface texture on the thermo elastic instability is investigated under mixed lubrication regime. For this purpose, a model consisting of a smooth surface with high thermal conductivity and a rough surface with low thermal conductivity is considered. Thus, a computer program is employed to numerically generate three different surface roughness patterns, i.e. transverse, longitudinal, and isotropic. Then the flow factors which are correction factors to the Reynolds equation for considering the surface roughness pattern are employed to study the effect of surface pattern on the thermo elastic instability. To conduct this study, an algorithm is developed to regenerate the thermo elastic instability results in the published literature and then is used to find the critical speed for three types of surface patterns beyond which thermo elastic instability leading to the formation of hot spots is likely to occur. Finally it is shown under similar operating conditions; the critical speed is highest for the longitudinal surface pattern.

In recent years, many studies have been done to fabricate super hydrophobic surfaces. These surfaces have slip condition which causes self-cleaning property and also drag reduction. The hierarchical micro/nanostructures which are coated with a low surface energy material are needed to fabricate high static contact angle super hydrophobic surfaces. In order to have thermal stability, chemical resistance and low surface energy Polytetrafluoroethylene (Teflon) is used in this research. To produce the super hydrophobic surface, an appropriate layer of Teflon is coated on the aluminum substrate and the micron sized aluminum particles are deposited on the Teflon layer by fluidizing method. Then to reduce surface energy, the second Teflon layer is sprayed on the top of the aluminum particles. At the end, using sprayed method the hydrophobic nanoparticles of silica are deposited on the surface as a final hydrophobic layer. The effect of Teflon thickness, size of micro-particles and addition of hydrophobic nano-particles are investigated. The scanning electron microscopy (SEM) images of the cured surfaces show that application of micro particles prevents the surface from being smooth after curing, creates appropriate micro-scale structures and also causes micro-scale cracks compared to smooth Teflon surfaces. The creation of these micro-structures leads to increasing static contact angle and decreasing dynamic angle of surfaces. By modifying the surface structures with aluminum micro-particles, Teflon layer coat and subsequent deposition of hydrophobic silica nano-particles, static contact angle of 165±3o and dynamic angle of less than 7 degrees are achieved.

Transporting an object using several mobile robots by formation control is an effective method in handling heavy and complicated objects either in known or unknown places. In this paper, to control the formation of three mobile robots and also to control interactive, a control algorithm has been designed based on semi-active suspension system of remote center compliance (RCC). The main objective of control structure of semi-active suspension system is to control the desired formation and appropriate transportation of the object at the same time and also separate the object and other robots from the effect of the errors occurred during creation of disturbance in a certain robot and prevent it from having effects on other robots. In order to terminate instability in impedance methods, multiple impedance control has been used in moving the object by cooperating robots. To follow the desired path and control of mobile robots formation, Leader follower method has been used. Simulation results indicate that the semi-active suspension control system, in order to minimize the vibrations caused by disturbance transferred to the set of robots, is optimum and more stable compared to passive suspension control system.

Modeling and simulation are useful tools to optimize and analyze the dynamic behavior of leadacid batteries. One of the main problems is that the governing equations of lead-acid batteries are highly coupled, which significantly increases the computational time of numerical methods in simulations. Using reduced order models (ROM) is one of the best ways to overcome this difficulty. In the present study, the one-dimensional electrochemical governing equations of leadacid battery are solved using model order reduction based on proper orthogonal decomposition (POD). To show the capability of this method, the governing equations including conservation of charge in solid and liquid phases and conservation of species are solved simultaneously for a leadacid cell during discharge, rest and charge process. The results of reduced order model including cell voltage, acid concentration and state of charge (SoC) are compared to the results of finite volume method (FVM). The obtained numerical results show that not only does the POD-based ROM of lead-acid battery significantly decrease the computational time (speed-up factor of 15), but also there is excellent agreement with the results of previous computational fluid dynamic (CFD) models.

Conventional Ritz and Galerkin methods based on local theory of elasticity employ polynomials as their approximating functions, however these methods are not convenient to use in three-dimensional nonlocal analysis. In the present study, to conquer this difficulty, a type of weighted residual approach with a set of trigonometric approximating functions was developed. By using appropriate trigonometric approximating functions it is possible to consider the effect of various edges boundary conditions on frequency behavior of nanoplate. Validation of present formulation is carried out by comparing numerical result with the published results. It is concluded that the effect of nonlocal parameter on natural frequencies is significant, especially in higher modes due to the lower wavelength of the mode. The research shows that in nonlocal elasticity there are distinct discrepancies between behaviors of two and three-dimensional results. In addition, the difference between the two- and three-dimensional results in local elasticity is not as noticeable as in nonlocal elasticity. Furthermore, the effects of length to thickness ratio, aspect ratio, nonlocal parameter and different boundary conditions on fundamental natural frequency of nanoplates were studied. This benchmark solution can be used to assess the accuracy of conventional two-dimensional theories.

The use of metal hydrides is one of the hydrogen storage methods. In this research, the process of hydrogen desorption from metal hydride storage with high diameter and constant flow rate was investigated using numerical simulation. a two-dimensional model with finite volume method is applied for simulation of hydrogen desorption. Simulation results were compared with available experimental data and good agreement was observed between them. In this study, a special design of metal hydride storage was investigated. This design allows the application of metal hydride beds with large diameter for a specific hydrogen outlet flow rate using aluminum fins. The simulation results verified the heat transfer enhancement effect of aluminum fins and showed the storage diameter can even be increased to 60 cm for outlet flow rate of 230 (Nlit/min). The comparison between the result of applying LaNi5 and C5 alloys revealed that the energy efficiency could be increased by using C5 alloys due to need of heating fluid with lower temperature. Moreover, the results showed that by increasing the outlet volumetric flow rate from 230 to 460 (Nlit/min), the storage diameter should be limited and therefore the smaller storage must be selected.

Shape sensitivity analysis of finite element models is useful for structural optimization and design modifications. Within numerical design optimization, semi-analytical method for sensitivity analysis is frequently applied to estimate the derivative of an objective function with respect to the design variables. Generally, numerical sensitivity analysis commonly suffers from severe error due to the perturbation size, and finding a method which is not sensitive to the perturbation size is a topic under study. Complex variable methods for sensitivity analysis have some potential advantages over other methods. For first order sensitivities using the complex variable method, the implementation is straightforward, only requiring a perturbation of the finite element mesh along the imaginary axis. This paper uses a complex variable and combines it with discrete sensitivity analysis, thus a new method is presented to obtain derivatives for linear structure. The advantages of this method are that it is quick, accurate and simple to implement. The methodologies are demonstrated using two dimensional finite element models of linear elasticity problems with known analytical solutions. Obtained sensitivity derivatives are compared to the exact solution and also finite difference solutions and it is shown that the proposed method is effective and can predict the stable and accurate sensitivity results.

In this paper, the elastic modulus of Nano cellulose/PLA Nano composites obtained by the two methods including Nano indentation and tensile tests were analyzed. Nano cellulose was extracted by Mechanical method from linter pulp fiber. Amount of usage of Nano cellulose was 3 and 5% wt, and master batch technique was used for improving nanoparticles distribution in polymer matrix. Then the mechanical properties of Nano composites with and without this technique were studied. Tensile test was performed in accordance with the standard method, and the atomic force microscope in peak force tapping mode was used for Nano indentation. Tensile test results showed that the use of master batch improves tensile modulus, tensile strength and strain at break. Also, by increasing Nano cellulose percentage from 3 to 5% in Nano composite with master batch, the tensile strength and strain at break increased. But this increase had no significant effect on tensile properties of Nano composite without master batch. A similar trend of strength test results was observed in Nano indentation results. Based on this result, use of master batch in Nano composite caused the increase in elastic modulus. The results of these two analyses were compared and tensile test showed lower modulus value than Nano indentation.

In this paper, the elastoplastic response of copper, steel and aluminum circular plates with clamped boundary conditions subjected to underwater explosion loading is investigated. Cavitation is a phenomenon that can be occurred forplatesin the process of underwater explosive forming. The total pressure of the explosion becomes zero at the cavitation time, so that the governing equations of motion time will be different before and after the cavitation. As a result, in terms of analysis and design, the cavitation time is significant in studying the behavior of a circular plate at underwater explosive loading. By applying the energy method and based on Hamilton principle and variation method the equations of motion of an underwater circular plate subjected to explosive loading are derived. Then, in order to obtain the forced response of the circular plate, the exact free vibration solution is derived to calculate the mode shapes. Then, the velocity and generated stress of plate during cavitation time are calculated and compared with the yield stress plates. Using this method, one can distinguish the occurance of cavitation with in the elastic or plastic regimes. By recognizing the time of cavitation in the range of elastic or plastic, the displacement and velocity field of plate are determined in duration of explosive loading. Results show that the cavitation time is on the order of microsecond. Depending on amount of charge mass and stand-off, the cavitation time may be occurred in elastic or plastic regime.

When a dynamic load passes a control volume of material as a shock wave, passing this wave through the control volume could cause different phases such as elastic and plastic. From the microscopic view, during phase change material flow would be taken in control volume which includes mass, heat, energy, and momentum transport. Phase change in material causes a material discontinuity in the control volume. During the phase change process, mass, heat, energy, momentum transport, etc will occur and the equations governing these phenomena are called transport equations. In this article, for the first time, the governing equations of elastoplastic behavior of beam under dynamic load are extracted using mass, energy and momentum transport equations. Using transport equations with non-physical variables in integral form will cause employing discontinuity conditions in governing equations and eliminate the discontinuity condition. These equations are also used in continuous modeling of beam elastoplastic behavior under dynamic loading and a continuous model is presented. Finite element method is used to solve the transport equation with non-physical variable. Finally, the time history of stress, strain and velocity wave propagation along beam are presented in elastic and elastoplastic phases.

In multi-pass groove welding, residual stress distribution, value and associated distortion are dependent on several factors, including the welding process-dependent parameters, mechanical properties of materials and fixtures. In present study, temperature distribution of three welding processes with different geometric designs are registered by the K type thermocouple. Each of the samples contains the same stainless steel plate A316 thickness that was welded based on welding procedure specification with gas tungsten arc welding method, with groove corner joints single bevel without gap and bevel face, single and double bevel with gap and bevel face. Created residual stress on a sample was initially measured by nondestructive ultrasonic transverse waves method. After cutting the vertical part (plate without groove), for hole drilling device installation purposes, the aforementioned stress was measured by the semi-destructive hole drilling method. While for two other geometrical designs only ultrasonic method has been used to prevent parts from being destroyed. All three aformentioned designs were modeled in Simufact. Welding finite element code (FE) and results were compared with experimental temperature and residual stress measurements. The comparison shows that experimental measurements and numerical values match with each other well, highlighting a reasonable validation of finite element models results. Current research results show that changing the geometry of the weld configuration has a significant effect on changes in the distribution and maximum value of transvers residual stress, but negligible influence on maximum longitudinal residual stress.

Performance increasing of robot-aided training in stroke elbow rehabilitation is the goal of this paper. Therapist holds on the arm of patient and guides the center of mass along a desired trajectory. In robotic rehabilitation, when the arm of patient is rotated within the desired boundaries, (s)he should ideally not feel the robot. The robot needs to actively compensate for the weight of the exoskeleton and reflected mass of the motors. A nonlinear torsion spring can be used and also a counter-torque as a function of arm angle is applied by the motor. Applying the springs affords more convenience, it allows smaller motors to be used, the size of required brakes can be reduced and inherent safety is introduced in rehabilitation robots. Furthermore, the robust controller design can be used to compensate the modeling errors and gravitational force. a novel elbow rehabilitation robot is designed based on the cable actuation. The strategy is not just ant gravitational forces because there should be joint-stiffness control. The uncertainty in the patients arm dynamic is effectively approximated. The motion of closed-loop control system in the presence of parametric uncertainties is investigated. The sliding mode controller with proportional-derivative controller is compared through computer simulation and improvement is observed.

This paper puts forward a novel numerical-experimental method for calculation of constants of advanced anisotropic yield criterion BBC2003. Calculation of the eight constants of this yield criterion demands experimental determination of eight mechanical properties of the material. These properties include: axial-yield stresses in 0, 45 and 90o with respect to the rolling direction, anisotropic parameters in the directions mentioned and plane strain yield stresses for 0o and 90o orientations. However, determination of the equi-biaxial yield stresses and anisotropic coefficients is relatively expensive. In the method presented in this paper, using a simple technique, the constants of the yield criterion are calculated based on plane strain yield stresses in 0o and 90o to the rolling direction. The system of equations involving the contestants of the yield function is solved numerically through defining an error function and minimizing it using steepest descent method. In two case studies, the constants of BBC2003 yield criterion for anisotropic sheets of aluminum alloys AA3105 and AA6061-O, were calculated using this method. Subsequently, the accuracy of perdiction of axial-yield stress and anisotropic coefficient in different directions as well as the coincidence of yield surface with experimental results for BBC2003 and Hill48 yield criteria have been investigated. The results show that the proposed method has good accuracy and stability in calculation of advanced yield criterion constants and consequently the mechanical properties of anisotropic sheets in different directions.

In this paper, a novel test rig for a quarter car suspension system of Samand with McPherson mechanism is fabricated and its elasto-damping elements are dynamically identified by a nonlinear model. The inputs of test rig are road roughness and its acceleration and the outputs are sprung mass acceleration, un-sprung mass acceleration, suspension deflection, and tire deflection which are recorded by sensors. The test rig of suspension system includes McPherson mechanism with nonlinear spring and damper. This system is categorized as a multi-input-multioutput (MIMO) identified system. The nonlinear least squares iterative method, as a gray-box identification method, is used for finding the elasto-damping coefficients of tire and suspension elements. In this method, a nonlinear mathematical model is considered for the system and its parameters are calculated using the test rig data. The Levenberg-Marquardt algorithm (LMA) is used to solve the non-linear least squares problem. The outputs of the identified nonlinear model are compared with the measured experimental data. As a result, the test rig outputs are followed by the outputs of the identified model with acceptable errors. The compared results indicate a good performance of the proposed model to estimate the behavior of the nonlinear suspension elements.

Today, laser 3D printers are one of the efficient devices for rapid prototyping process. There are a large number of studies about quality of samples in these printers. The laser sintering technique is the one of the popular methods for consolidation and shaping of semi-crystalline polymer powders. In this study, we considered the role of laser parameters including laser scanning pattern, laser scanning speed and power in tensile strength and stiffness as the important factors of the mechanical property of samples which are sintered by laser in single layer procedure. Experimental samples were sintered with low power CO2 laser on Polypropylene powder with 200 micrometer grain size. Tensile strength and stiffness had been measured according to ASTM D882 standard and results were reported. In this paper, main effects of factors and interactions were considered via the variance analysis under the imperative conditions that have been passed before. The regression equation was derived. A general full factorial method was employed as experimental design. The results show that the laser scanning pattern and laser power have the greatest effects on tensile strength and stiffness of produced samples. The maximum value of responses, 2.9 MPa for mechanical strength and 96 N/mm for stiffness demonstrate that the 2W power of laser with 1650 mm/min of scan speed can be the proper value to obtain an optimal response when the selected pattern is No2.

In flows with high Reynolds inside the U-shaped tubes, separation phenomenon occurs in the curvature of tubes causing pressure loss and in conditions associated with heat transfer undesirable increase surface temperature in that region is noted. Due to reduced heat transfer rate from surface to fluid temperature increase occurs in industrial applications in addition to reduced heat transfer which causes damage to surface pipes. In the present study, elimination of the separation zone through body force created by plasma actuators and because it reduces the maximum temperature occurred in this region and changes the Peclet number is simulation in this region. For this purpose, the plasma actuators5kV, 12kV and 19kV with square voltage function inside U-shaped tube in the three streams with Reynolds 3000,4500 and 6000 have been placed to influence actuators on separation control, and maximum temperature occurred at this point be investigated. Calculations using proposed model of Suzen with time-dependent numerical procedure has been done. And results during time performance of 0 to 50 have been reported. The result shows that maximum surface temperature that occurs in the region of separation in the presence of plasma actuator near this region has a significant reduction thatis due to the elimination and change separation region.

One of the most commonly occurring problems during machining is Machine tool chatter, which adversely affects surface finish, dimensional accuracy, tool life and machine life. Machine tool chatter can be modeled as a linear time invariant differential equation with time delay or delay differential equation. Infinite dimensional nature of delay differential equations is apparent in the study of time delay systems. The analytical stability methods are thus more difficult for these differential equations and approximate methods do not give accurate results. In this paper, a new method is developed to determine the exact stable region(s) in the parameter space of machine tool chatter. In this method, first, the bifurcation points are determined. Then, the Lambert function is used to decide on the stability characteristics of each particular region. The advantages of this method are simple implementation and applicability to high order linear time delay systems. From the resulting stability regions of this method, an optimal spindle speed can be chosen to suppress the chatter. The new approach is the most acceptable method in comparison to traditional graphical, computational and approximate methods due to excellent accuracy and other advantages.

As an effective forming method in aeronautical industries, peen forming is derived from shot peening process. Major application of this process is for producing large thin components with gentle curvature such as aircraft panels and wing skins. This process can be divided into two categories; peen forming without elastic pre-strain (conventional peen forming) and with elastic pre-strain (stress peen forming). In this research, numerical and experimental study of shot peening, peen forming and stress peen forming of aluminum alloy sheets were conducted. In order to perform experimental tests, steel shots with 0.4 and 0.6 mm diameter and aluminum alloys Al6061-T6 strips were used. For applying elastic pre-strain, fixtures with four pre-bending radii ¥, 500 mm, 375 mm and 250 mm were designed and manufactured. In numerical section, using the same parameters as applied in experiments, first by using a 3D model with random distribution of shots, shot peening process was simulated and induced and residual stresses in sheet, were obtained. Next, using this model and in a three-step procedure, peen forming and stress peen forming processes were simulated. The results showed that applying pre-strain has a considerable effecte on distribution of stress inside the sheet metal and thus on the final deformation of it. Along with increasing pre-bending moment (decreasing pre-bending radius), the resulting curvature in the sheet in the direction of the applied pre-bending, increases. According to the experimental and numerical results, in comparison with conventional peen forming, stress peen forming using 250 mm prebending radius increases the curvatures over 100%.

In this study, forced convective heat transfer characteristics of Al2O3/water Nano fluid flowing through a double pipe heat exchanger with plain twisted tape and cut twisted tape inserts are investigated experimentally to reveal the effect of cut twisted tape and Nano fluid concentration on heat transfer. Experiments are conducted in a turbulent flow regime with Re number ranging from 4000-34000 and in the particle volume concentration range of 0<j<0.1%. The results of thermal studies showed enhancement of convective heat transfer with Al2O3 Nano fluids compared with flow of water. Also, it was found that in higher Reynolds numbers the Nano fluid has better heat transfer capability. The effects of twisted tape with and without cuts on edges on heat transfer coefficient and rate were investigated. It was found that the twisted tape with cut edges could enhance heat transfer rate better than twisted tape without cut edges. The pressure drop was investigated for flow of Nano fluid and water. The results showed that there is a there is little difference between pressure drops in these cases. Friction factor and pressure drop in tube with plain twisted tape and cut twisted tape inserts are increased due to increasing flow resistance and contact surface between fluid and flow passage.

In-Situ Combustion (ISC) is one of the thermal heavy oil recovery methods in which the heat required to displace crude oil is generated by combustion of a small fraction of oil inside the porous reservoir. Therefore its practical use has been limited, despite the fact that in-situ combustion is potentially very advantageous over the other thermal methods. In the present work, aimed at acquiring a better understanding of ISC physics, the oil in place volume (expressing in terms of oil saturation) effects on performance of ISC is numerically investigated in 1D. In order to increase the model accuracy, a semi analytical model is used to account for heat loss to overburden and under burden. The numerical results show that in reservoirs with high initial oil saturation, the mobilized oil is deposited in the region near production well during the first days of ISC operation. Consequently, relative permeability of porous reservoir for gas phase considerably decreases. Moreover, combustion front propagation velocity reduces and the reservoir pressure significantly increases in the region upstream of the combustion front. As a result of the front velocity decrease, oil recovery rate decreases. Furthermore, if the pressure increase is not considered in designing the air injection system, the air injection rate will be decreased and can lead to front quenching. The results also show ignoring heat loss from the reservoir will lead to incorrect prediction of the mentioned process.

In this study, the self-starting of a Darrieus vertical axis wind turbine (VAWT) is enhanced using a J-shaped airfoil profile. The paper investigated the performance of VAWT with the J-shaped blades. Since the J-shaped blades utilize the lift and drag forces simultaneously, the turbine performance at low tip speed ratios (TSRs) is enhanced. Thus, it is expected that using these blades will improve the starting torque and output power. The main goal in this study is to find an optimum J-shaped profile acquiring the best performance of wind turbine. For this purpose, a 3kW J-shaped straight-bladed Darrieus type VAWT is investigated numerically using Open FOAM computational fluid dynamic package. It employs the finite volume method to solve the Navier-Stokes equations. The J-shaped profile is designed by means of eliminating a fraction of pressure side of Du 06-W-200 airfoil. The results indicate that the performance of turbine is optimized for J-shaped profile which eliminates the pressure side of airfoil from the maximum thickness toward the trailing edge. Moreover, by employing this J-shaped profile, the wind turbine performance is intensified TSRs and self-starting of turbine is improved.

In this study, the natural convection heat transfer is numerically examined in a square enclosure filled with a non-Newtonia power-law fluid. Two fixed temperature baffles are mounted on the left wall of the enclosure. The left wall of the enclosure and the baffles installed on it, are at a constant temperature of T_h and the right wall of the enclosure is at a constant temperature of T_c, while its horizontal walls are thermally insulated. The governing equations for the power-law fluid flow are solved with the numerical finite difference method based on the control volume formulation and SIMPLE algorithm. The study investigates the effects of relevant parameters such as the Rayleigh number ((10)Ù3£Ra£(10)Ù6), the power-law index (0.8£D£1.4), the baffles length (0£B£0.5) and the baffles distance from each other (0.1£D£0.8) on flow and temperature fields and the rate of heat transfer. The results show that an increase in Rayleigh number, particularly when n<1 improves the thermal performance of the enclosure. Furthermore, using non-Newtonian shear thinning fluids, especially at higher Rayleigh numbers, increases the rate of heat transfer. Results also show that, depending on the Rayleigh number and the power-law index, the length and position of the baffles have significant effects on the thermal performance of the enclosure.

In this study, effect of adding graphene and poly olefin elastomer (POE) in polypropylene matrix, in various mix times were studied. Method of fabricating samples was melt-blending samples with 0, 2, and 4 %wt of graphene, 0, 15, and 30 %wt of POE, and 8, 12, and 16 minute mixing times were used. For better analysis of mechanical properties, tensile and impact tests and DSC, SEM analyses were employed. Results of tensile tests indicated that addition of POE caused reduction of elastic modulus, reduction of tensile strength, good improvement of impact strength and poor improvement of elongation. While presence of graphene caused a good improvement of modulus with no meaningful effect on tensile strength, reduction of elongation and poor improvement of impact strength. DSC analysis of samples showed that graphene and POE has no visible effect on degree of crystallinity but graphen cause temperature of crystallinity increased. SEM observations showed that by increasing mixing time dispersion of grapheme improved. a reduction in the size of POE particles in blending of course agglomerations of grapheme in all samples showed that for the method of fabrication, surface area of graphene and percentage of graphene in samples was not unexpected.

Today, fast and accurate fault detection is one of the major concerns in industry. Although many advanced algorithms have been implemented in the past decade for this purpose, they were very complicated or did not provide the desired results. Hence, in this paper, we have proposed an emerging method for deep groove ball bearing fault diagnosis and classification. In the first step, the vibration test signals, related to the normal and faulty bearings have been used for both the drive-end and fan-end bearings of an electrical motor. After that, one dimensional Meyer wavelet transform has been employed for signal processing in the frequency domain. Hence, the unique coefficients for each kind of fault were extracted and directed to the adaptive neuro-fuzzy system for fault classification. The intelligent adaptive neuro-fuzzy system was adopted to enhance the fault classification performance due to its flexibility and ability in dealing with uncertainty and robustness to noise. This system classifies the input data to the faults in the race or the balls of each of the fan-end and the drive-end bearings with specific fault diameters. In the final part of this study, the new experimental signals were processed in order to verify the results of the proposed method. The results reveal that this method has more accuracy and better classification performance in comparison with other methods proposed in the literature.

A Forming Limit Diagram (FLD) is a graph which depicts the major strains versus values of the minor strains at the onset of localized necking. Experimental determination of a FLD is usually very time consuming and requires special equipment. Many analytical and numerical models have been developed to overcome these difficulties. The Gurson- Tvergaard- Needlemann (GTN) damage model is a micromechanical model for ductile fracture. This model describes the damage evolution in the microstructure with physical equations, so that crack initiation due to mechanical loading can be predicted. In this work, by using the GTN damage model a failure criterion based on void evolution was examined. The aim is to derive constitutive equations from Gurson’s plastic potential function in order to predict the plastic deformation and failure of sheet metals. These equations have been solved by analytical approach. The Forming Limit Diagrams of some alloys studied in the literature have been predicted using MATLAB software. The results of analytical approach have been compared with experimental and numerical results of some other researchers and showed good agreement. The effects of GTN model parameters including f0, fc, fN, ff, as well as anisotropy coefficient and strain hardening exponent on the FLD and the growth procedure of void volume fraction have been investigated analytically.

The aim of this paper is to investigate the Low-Density Lipoproteins (LDL) mass transfer in vessel walls using the Lattice Boltzmann Method (LBM). High Schmidt number of LDL leads to numerical instability of LBM. In order to solve this problem, LBM and finite volume method (FVM) are combined. In this hybrid method, the blood velocity field is solved by LBM using the single relaxation time, SRT, model and FVM has been used for LDL concentration equation. LBM is able to simulate flow and mass transfer for the Schmidt number, Sc, up to 3000 only if the time consuming multi relaxation time is used. However, the proposed hybrid method suggested in this article can be used to solve the problem for Sc as high as 107. Good agreement between our results obtained from the hybrid simulation and the available results in the literature and noticeable decrease in CPU time compared with when the LBM is used for both flow and mass transfer, indicates the ability of the hybrid method. Finally, the hybrid method is used to simulate the mass transfer of LDL particles and investigate the effective factors for increasing the surface concentration, such as the size of LDL particles, wall suction velocity, wall shear stress, Newtonian and non-Newtonian fluids behavior and change of concentration boundary layer with various Schmidt number.

It is of crucial importance to adjust the trim angle properly during the forward acceleration of a planning craft in cases such as sport competitions and military missions. In these applications, the goal of trim adjustment is to reach the final cruising speed as soon as possible. Present study tries to answer this question: How should the angles of the drive system and/or a control element be changed during acceleration phase in order for the craft to reach its final speed in the minimum possible time? This is an optimal control problem with the drive and control element angles as its control variables. To solve such problem, a 3-DOF dynamic model is developed based on the theoretical and empirical methods. Both propeller operation and the engine are taken into account for the propulsion system. Then, the solution algorithm of time-optimal control problem is explained according to an indirect method. Results for a planning mono-hull with two different weight distributions show a similarity in trend between the optimal solution for control variables and the hull instantaneous trim angle. As the second case study, the solution for an aerodynamically alleviated racing catamaran is presented.

In this paper, the effect of nonhomogeneous parameter in orthotropic Functionally Graded Material (FGM) in a cracked layer is investigated. It is assumed that the mechanical and thermal properties of material are dependent on x-coordinate (collinear with crack surfaces) in exponential form. The problem is solved for internal and edge crack in two ways, integral equations and generalized differential quadrature method. Thermal loading is such that temperature distribution in the layer is uniform. Because of variation in mechanical and thermal properties, stress distribution due to this loading is not uniform. In the solution of problem with integral equations method, first, thermo-elasticity problem with no cracks and then isothermal crack problem are separately solved. Afterward, with these solutions, the main problem will be solved. In order to solve isothermal crack problem, after conversion and simplifying the equations in orthotropic material, Navier’s equations will be solved with the Fourier. Numerical solution of the problem is the generalized differential quadrature element method that is being presented for verification of the results of the integral equations for a specific state in the diagram format. Also, the effect of temperature on intensity factor with various values of nonhomogeneous parameter is investigated.

In this paper, the important characteristics of solidification including supercoiling degree, solidification time, nucleation temperature, phase change temperature which effect on efficiency are experimentally studied. A purposely designed experimental device was used to investigate the solidification characteristics of titania Nano fluid (0.01%wt. 0.02% wt. and 0.04%wt.). The results clearly reveal that adding titania nanoparticles to Deionized water as a base fluid can reduce the time of solidification, phase change temperature and supercoiling degree. By adding 0.04% wt. titania nanoparticles, the solidification time, phase change temperature and supercoiling degree are reduced by 70%, 18%, 69% while nucleation temperature is enhanced by 29%. Thus, the time of solidification is more affected by adding nanoparticles than other solidification characteristics. Further, the experimental results show that Nano fluid heat flux is higher than that of base fluid. Also, a comparison of Fuzzy logic modeling and experimental results for liquid fraction is studied. The results reveal that the fuzzy logic modeling is a reliable and powerful technique for predicting the liquid transient fraction. From the results it is also concluded that extremely low concentration of titania has low average error.

The encounter between bubble pairs can occur in the bubble fows and may result in coalescence, which is one of the most important elementary physical processes occurring in liquid columns. Sufficient knowledge of the coalescence process of two bubbles can lead to a better description of the bubbly flow’s behavior. Effects of uniform magnetic fields on the interactions and coalescence of dielectric bubbles have not been studied up to now; therefore in this research, interactions and coalescence of two bubbles in a viscous stagnant liquid has been simulated numerically. Considered bubbles are spherical and fluids are stagnant, initially. Both liquid and gas phases are considered incompressible and dielectric where applied magnetic field is uniform. In the numerical simulation of the problem, the Finite Volume method was applied using the SIMPLE algorithm to discretize the governing equations while the finite difference method was used for discretizing of the magnetic field equation. For simulating the interface of two phases, the level set method has been incorporated. The results outlined in the present study agree well with the existing experimental and numerical results. Obtained results show that applied uniform magnetic field affects shape, dynamics and also interactions and coalescence of bubble pairs. Applied magnetic field enhances coalescence between in-line rising bubbles. Therefore, the external uniform magnetic field could be used for contactless control of the coalescence process between bubbles.

Today, due to ever-increasing demand for fast and precise movements and changes, along with small-scale actuations in many engineering fields, the use and efficiency of smart materials has increased in importance. Magnetic Shape Memory Alloy (MSMA) is one of the latest smart materials having both shape memory and magnetic properties. As a matter of fact, in normal room temperatures it has magnetic field-induced strains far more than any other smart materials such as magnetostrictive, piezoelectric or electrostrictive materials and its frequency response is greater than thermal shape memory alloy. However, on the downside, asymmetric hysteresis is a property that constrains its widespread applications. Prandtl-Ishlinskii model is one of the powerful phenomenological models for simulating asymmetric, non-linear hysteresis used to simulate smart material behavior. In the present study, MSMA hysteresis behavior simulation has been investigated through a new approach using generalized Prandtl-Ishlinskii model. After identifying the model parameters, the study compares the predicted output with the experimental results. To validate the model, using different data, model accuracy has been checked and prediction error has been shown. The experimental results have proved the capability of the model in predicting the hysteresis behavior. Thanks to invertible and simplistic potential of the generalized Prandtl-Ishlinskii model, the inverse of the model can be applied as a feed forward controller for compensating the hysteresis behavior. It should also be noted that all the experimental results have been yielded through using experimental set-up.

Electrohydraulic forming (EHF) is a high velocity forming process in which the electric energy stored in the capacitors is suddenly discharged between two electrodes submerged in a water filled chamber. During the discharge, the water between the electrodes vaporizes and creates a shock wave that is transferred to the blank using the water and forms it. One of the key parameters in electrohydraulic forming is the determination of the suitable position of the electrodes. In this research the effect of electrodes position in electrohydraulic free-forming is investigated using the finite element simulation. First, the experiments available in the literature are simulated using the software ABAQUS/ Explicit and compared with the experimental results, which show good agreement. Then by changing the position of the electrodes, the effect of their position on the formability and thickness distribution of the blank is investigated. The results indicate that formation of a component is only possible in limited positions of the electrodes and there is a position for the electrodes that not only improves the sheet thickness but also decreases the possibility of the failure.

Due to high strength and stiffness-to-weight ratio of composite cylindrical shells, they are increasingly being used in different industries. Applying different types of stiffeners is one of the ways to improve the buckling resistance of these structures. In this paper new analytical method based on smear method is developed to analyze the stiffened composite shells. The main difference of this method and previous methods is on technique of combination of shell’s and stiffeners’ stiffness parameters, and calculating the equivalent stiffness parameters. In the suggested method a three layered shell is designed in such a way that this shell and stiffeners have the same volume and stiffness. Putting these layers under the main layers of shell, the equivalent stiffness parameters could be calculated easily. Using the Ritz energy method the critical load of axial buckling of shell is calculated. The method is verified using finite element ABAQUS package. The results show that the proposed method has less difference from finite element’s results compare to previous methods. In addition, the effects of different parameters on buckling load and special buckling load of stiffened shell is investigated. The results show that in order to have efficient stiffened structure; there must be an adequate number of ribs and unit cells. It also shows that, although adding stiffening ribs increase the buckling load of the shell, the special buckling load does not increase necessarily. The optimum angle for helical ribs is 30 to 40 degrees respect to axis of the cylindrical shell.

Cracks in composite structures are the most common damages. For example, cracks in thickness direction (trans laminar fracture) would be due to inadvertent impact of the projectile with the aerospace structures. Most of studies, so far, aimed at studying the interlaminar crack propagation and emergence of the delamination phenomenon. In this paper, in an attempt to study the trans laminar crack propagation of composites, test specimens were prepared in the form of butterfly from a woven glass epoxy composite by hand layup and the autoclave process. Experimental fracture tests were performed in the first mode, mixed-mode and the pure second mode by changing the loading angle, using a specially developed fixture, based on Arcan. Load versus displacement curves were obtained. Using critical loads of the tests and the dimensionless stress intensity factors, obtained from the finite element analysis by ABAQUS software, trans laminar fracture toughness of the composite was determined. As the result, it can be seen that the opening mode trans laminar fracture toughness is larger than the shearing mode toughness. This means that trans laminar cracked specimen is tougher in tensile loading condition and weaker in shear. Finite element analysis was performed using effective elastic properties of the glass epoxy composite obtained from a homogenized woven composite model based on micromechanics. Finally, the effect of laminate thickness on the trans laminar fracture toughness behavior of the glass epoxy composite has been studied.

Considering uncertainties in the design process is one of the most important factors to achieve reasonable and reliable results. In this article, a collaborative structure, which is a multidisciplinary design optimization, is combined with a robust design approach to design an optimum and robust launch vehicle, while considering the effects of uncertainties. First, a liquid fuel vehicle is designed under two disciplines to send a 1200 kg mass to the 750 km orbit from the earth surface with 50.7o orbital inclination, using the collaborative structure. It should be said that the first discipline includes three subsystems that are engine design, geometry design and estimating the mass. Also, the second discipline includes three subsystems that are pitch program, aerodynamic calculations and trajectory simulation. Then, the optimum collaborative output is combined with the robust design in a multi-objective model to achieve the final vehicle configuration. The results show that the calculated mass of the first stage of the project using the collaborative robust design process is 3 tons heavier than the calculated mass using optimum collaborative design approach and the engines working time is increased. The overall size of the launch vehicle is increased too. The outputs of each subsystem have been evaluated and also, the overall results have been compared with another design process, i.e. MDF. This comparison shows the acceptable accuracy of the proposed approach.

In this paper, in order to reduce landing gear vibration two adaptive control systems are designed considering the landing and taxi phases. For this purpose, 6 degree of freedom equations of motion of the landing gear and the related transfer functions are extracted. a reduced order model of the overall transfer functions are given as a result of complicated dynamic model. a Lyapunov based model reference adaptive control is designed to absorb the vibration of front wheel of the landing gear at touchdown. In addition, a minimum variance adaptive controller is designed and implemented on the system to reject the band level disturbances during the taxi phase. The band disturbances are modeled as a colored Gaussian noise and the system parameters as well as noise characteristics are estimated using extended least square approach. Both control systems are investigated to assess the best performance. Numerical simulations of the system in Matlab/Simulink environment show the preferences and satisfactory performances of the proposed vibration control systems. These results are calculated against various inputs including model reference adaptive control and minimum variance approaches.

In this paper, behavior of functionally graded rubbers with large deformation has been modeled under different loading conditions. Rubbers have been assumed incompressible hyperelastic material. In the first section of this paper, behavior of isotropic FG rubber has been investigated in uniaxial extension, equibiaxial extension and pure shear. In the second section, behavior of isotropic FG rubber is investigated in mechanical and thermal loads, simultaneously. For this purpose, multiplicative decomposition of deformation gradient tensor has been used. At last, behavior of transversely isotropic FG rubber has been investigated in uniaxial extension, equibiaxial extension and pure shear. Material properties vary continuously in different specific direction in FG hyperelastic materials. For modeling nonlinear behavior of hyperelastic materials, strain energy functions are used. Strain energy functions are function of invariants of left Cauchy-Green stretch tensor. Modification in strain energy functions is required in order to for them to be used as FG rubbers. For this purpose, material constants of strain energy functions have been assumed to vary exponentially in the axial direction of bar. Moreover, stretches in different points of the bar are considered to be function of material properties variation in the length direction. Analytical solution has been compared with experimental data and good agreement has been found between them, therefore the proposed constitutive law has modeled material behavior with a proper approximation.

Under the critical thermal conditions, the human body cannot adapt itself to the environment using physiological thermoregulatory mechanisms. Under these conditions, using protective clothing is one of the effective ways to protect the human body against the thermal injuries. Therefore, in the present study, the effect of using Phase Change Materials (PCMs) on the performance of firefighters’ protective clothing has been numerically investigated under the critical scorching conditions. The main contribution of this study is the simultaneous modeling of PCM based protective clothing with physical and physiological mechanisms of the human body. For this purpose, multi-layer protective clothing with a PCM layer has been considered and its thermal performance has been investigated under scorching conditions for three different arrangements of the layers. The results show that the middle layer of protective clothing is the best position for implementing the PCM. Also, the best melting temperature for the mentioned PCM is about 40oC. Moreover, the results indicate that using the PCMs in protective clothing can increase the thermal tolerating time from 300 seconds (for non-PCM protective clothing) up to 900 seconds under the scorching conditions.

Modal analysis is one of the applicable methods used to identify the dynamic characteristics of structures. Inspection of structures to avoid resonance conditions can be achieved by extracting vibration modes using modal analysis. Since every point of the vibrating structure has its own characteristics such as the displacement, speed and acceleration, the measurement of these parameters in a specific time interval can be used to extract modal parameters. In this study, stereo vision as a noncontact measuring system is used to obtain the displacement of several points of the blade of a 2.5kW wind turbine with a length of 3m under the operational modal condition. At first, the camera calibration process is performed and then the three-dimensional data of the turbine blade are extracted from images recorded during the test. Consequently, modal parameters of the blade are calculated by analyzing the data. Finally, modal parameters obtained by three different methods including the stereo vision system, the finite element analysis and the testing accelerometer are compared. The results show that visually obtained data are sufficiently accurate to find the natural frequency of the first mode of the blade. The first natural frequency mode extracted by the stereo vision system shows a difference of 10.36% and 2.67% compared to those obtained by finite element method and the accelerometer, respectively.

In this paper, an explicit optimal line-of-sight guidance law for second-order binomial control systems is derived in closed-loop without acceleration limit. The problem geometry is assumed in one dimension and the final time and final position are fixed. The formulation is normalized in three forms to give more insight into the design and performance analysis of the guidance law. The computational burden of the guidance law is reasonable for today’s microprocessors; however curve fitting or look-up table may be used for the implementation of the second-order optimal guidance law. The performance of the second-order optimal guidance law is compared in normalized forms with zero-lag and first-order optimal guidance laws using third-, fourth-, and sixth-order binomial control systems with/without acceleration limit. Moreover, the effect of the final time, the equivalent time constant of the vehicle control system, the vehicle-to-target line-of-sight weighting factor in cost function, and acceleration limit are investigated. Normalized miss distance analysis shows that the miss distance of the secondorder guidance law is smaller than the two mentioned schemes for small total flight times, especially with large maneuvering capability.

Free vibration characteristics of rectangular composite plate with constrained layer damping and magneto-rheological fluid (MR) core are presented. Hamilton principal is used to obtain the equation of motion of the sandwich plate. Based on the Navier method, a closed-form solution is presented for free vibration analysis of MR sandwich plate under simply supported boundary conditions. The governing equation of motion is derived on the base of classical lamination theory for the faceplates. Only shear strain energy density of the core is considered. Using displacement continuity conditions at the interface of the layers and core, shear strain of the core is expressed in terms of displacement components of the base and constraint layers. The complex shear modulus of the MR material in the pre-yield region was described by complex modulus approach as a function of magnetic field intensity. The validity of the developed formulation is demonstrated by comparing the results in terms of natural frequencies with those in the available literature. The effects of magnetic field intensity, plate aspect ratio, and thickness of the MR core, base layer and constrained layer for three different stacking sequences of composite faceplates on the fundamental frequency and loss factor of the first mode are discussed. The results indicate significant effect of physical and geometrical parameters on the natural frequency and loss factor associated with the first mode.