Modares Mechanical Engineering
Year:2016 | Volume:16 | Issue:9|Papers Count:54

In this paper, sound transmission loss through double-walled orthotropic cylindrical shells based on three-dimensional elasticity theory is investigated. Hence, the purpose of this paper is to analyze the effect of the acoustic wave incidence under two different angles on sound transmission loss through the shell. The present model is a double-walled orthotropic cylindrical shell immersed in a fluid with an infinite length, whereas the acoustic plane incident waves impinge upon the shell with two different angels of q and d. The state space method is used to investigate the laminate approximated model along with transfer matrix approach for modeling both walls of cylindrical shell. In order to consider the two different angles of q and d, the corresponding wave equations have been modified according to the wave numbers. Comparing the results obtained from the present study with those of other researchers shows an excellent agreement between the results. Moreover, the effects of different parameters on sound transmission loss through the shell have been evaluated. The results show an enhancement of sound transmission loss in double-walled cylindrical shells rather than single-walled cylindrical shells, particularly in high frequency range. Also, the results indicate the dependency of sound transmission loss on both the q and d angles. In other words, the variation in two incident angles may cause significant variations in sound transmission loss.

In this paper, the modeling and simulation of manipulation of carbon nanoparticles have been investigated. The geometry plays a significant role in the dynamic behavior of nanoparticles manipulation and the evaluation of different geometric shapes of nanoparticles in this process is very important. To examine the geometrical effects, the manipulation of four different kinds of nano-carbon allotropes with the same mass has been studied. Furthermore, the manipulation of carbon nanotubes with different diameters has been simulated. For this purpose, the molecular dynamics method was used to improve our knowledge and understanding about the nanomanipulation processes and dynamics. It is found that the acting force on the tip decreases as the nanoparticle shape varies from sphere to cylinder in the manipulation of carbon allotropes with the same mass, further the manipulation is facilitated. In this state, the curvature radius of nanoparticle increases and the potential energy between nanoparticle and substrate reduces. In the manipulation of nanotubes, the results of nanotubes manipulation showed that increasing the diameter of the nanotube caused the force on the probe to increase. The indentation depth was extracted for each nanotube during the manipulation process. The results indicated that by increasing the diameter of the nanotube, the indentation depth increases. According to the application of carbon-based structures and nanotubes as the drug carriers in medicine, the results of this study can be used to improve the experimental projects and reduce the time and cost of them.

This paper presents a completely practical control approach for quadrotor drone. Quadrotor is modeled using Euler-Newton equations. For stabilization and control of quadrotor a classic PID controller has been designed and implemented on the plant and a fuzzy controller is used to adjust the controller parameters. Considering that quadrotor is a nonlinear system, using classic controllers for the plant is not effective enough. Therefore, using fuzzy system which is a nonlinear controller is effective for the nonlinear plant. According to the desired set point, fuzzy system adjusts the controller gain values to improve the performance of quadrotor which leads to better results than classical PID controller. To study the performance of fuzzy PID controller on attitude control of the system, a quadrotor is installed onto the designed stand. The system consists of accelerometer and gyroscope sensors and a microcontroller which is used to design fuzzy PID attitude controller for the quadrotor. Regarding to the considerable noises of the experimental data, Kalman filter is used to reduce them. Finally, using the Kalman filter leads to better estimation of the quadrotor angle position and the fuzzy PID controller performs the desired motions successfully.

In this study, the use of Ultrasonic Peening Technology (UPT) on the mill rollers graphite steel (GSH48) for enhancement of some of the surface mechanical properties was surveyed. One of the new technologies for severe plastic deformation is ultrasonic peening technology in which vibratory tool strikes the workpiece surface with continual reciprocating motions, resulting in severe plastic deformation on surface. This method improves mechanical properties like hardness, surface roughness, fatigue life and tension strength. With simulation and manufacturing of peening vibratory tool, preparation of process was accomplished including setting up the ultrasonic vibratory tool on lathe machine. The investigation of hardness tests, surface roughness, and fatigue and tension strength on the pieces was performed in different conditions, before and after the process of ultrasonic peening with one, two and three passes. The results showed increase of hardness up to 36% in depth of 0.2 mm. Also, the surface roughness was reduced from Ra=1.376 mm to Ra=0.545 mm. The most improvement in surface roughness and fatigue life was observed on the pieces with three passes of ultrasonic peening.

Recently, H-Infinity adaptive fuzzy controller (HAFC) and its potential application in improving vehicle stability has received increasing attention. This paper studied this application by developing a nonlinear model for the vehicle suspension mounting point displacement (SMD) and the variable geometry suspension system (VGS). The VGS model was developed by deriving the kinematic equations from the vehicle double wishbone suspension system for the vehicle handling model with eight degrees of freedom (8DOF). The limited area of the SMD necessitates the use of a proper controller, so in this paper the suitability of a proportional-integral-derivative controller (PID), an adaptive fuzzy controller (AFC), and HAFC was investigated for this purpose. The stability status and adaptation laws were assessed by Lyapunov synthesis and the result showed that integral of square error (ISE) achievable by HAFC for two standard maneuvers is lower than PID and AFC. The result also showed that SMD of HAFC is lower than AFC and extremely PID. The use of HAFC also resulted in the best vehicle stability, soft response and robustness.

This paper deals with studying and developing a proper constitutive model for liver tissue. For this purpose, deformation of liver in uniaxial compression, for two different strain rates, is analytically and numerically studied based on both hyperelastic and hyperviscoelastic constitutive models. Both of the models are based on a polynomial-form energy function. The stress-strain curves, for uniaxial compression obtained from these models have been fitted to the existing experimental data to determine the model coefficients. Moreover, the models are examined in uniaxial tension and pure shear loadings.ABAQUS commercial software, in which both of the models are available, has been used for numerical simulations. Thesn, to evaluate the computational analyses, analytical and numerical results have been compared with each other and also with the existing experimental data. The results show that the presented analytical solution and FE simulation are very close together and also both are accurate enough compared with the experimental data, and an acceptable stability is observed. Furthermore, the effect of friction coefficient between the sample and the compressing plate in uniaxial compression test has been investigated. FE simulation results show that the stress will increase with increasing friction coefficient. This implies that friction coefficient must be carefully selected to accurately describe the tissue’s response. Compared with previously published researches on other tissues, the constitutive models adopted here to predict liver behavior are mathematically more complex due to non-zero material constants. Analytical solution of these constitutive models is, in fact, the main challenge and innovation of this paper.

Interference fitting is widely used in the industry for connecting shafts and bushes. These types of joints are widely used as support of bearing machine parts. Rrepeated disassembling of shaft and bush interference fit, performed to repair and maintenance of machine parts, may cause serious damage to surface of joint parts depending on the roughness and surface quality of the contact surface of joint parts. Bushes are usually expendable parts, but the shaft parts are long integrated and complex parts which support other components of a machine. So providing a way to repair the shaft surface can be considered crucial and leads to restoration of damaged shaft and reduced costs. In this study, the effect of interference surface roughness on strength, friction coefficient of the contact surface and surface damage of interference fit joints during the disassembling procedure have been investigated. Finite element and experimental analysis were performed to estimate friction coefficient in contact surface of joint parts. Also, magnified pictures of contact surfaces were applied to evaluate the extent of damage in contact surface after disassembling of joints parts. Hard chromium plating was proposed to repair the shaft surface and the effect of hard chromium plating on strength of shaft and bush joints was measured experimentally. The results confirm successful use of hard chrome plating in repairing the shaft surface so that the strength of restored shaft joints was equal and in some instances even more than the initial joints.

In this study, falling ferrofluid droplet behavior in nonmagnetic viscous fluid under the uniform magnetic field in two-phase flow is studied numerically. To this approach, a hybrid lattice-Boltzmann based Shan-Chen model and finite-volume method is used. The lattice-Boltzmann equation with the magnetic force term is solved to update the flow field while the magnetic induction equation is solved using the finite volume method to calculate the magnetic field. To validate the flow field solution, two tests have been considered: the free bubble rising and Laplace law. In order to validate the magnetic field, permeable circle and deformation of static drop under magnetic field is simulated. The comparison of results between present study and previous researches shows that there is a good agreement between the results. The effects of the magnetic Bond number, susceptibility and magnetic field direction on deformation of the falling droplet are investigated. The results show that increase in the magnetic Bond number or susceptibility leads to a larger deformation of the droplet. Also, in horizontal magnetic field, the falling process takes longer time compared to the vertical magnetic field.

Wind turbines are highly complex structures for numerical flow simulation. Today, developments and increasing use of wind energy in the world has created a demand for progressively more accurate and efficient models for wind applications. Wind turbine wakes have significant effects on decreasing the produced power and blades fatigue loads, thus, the study on wake turbulence has great importance in wind turbine simulations. Actuator line model (ALM) is one of the most accurate models for characterization of the flow field and the turbulent wakes created by the turbines. AL model does not require boundary layer resolution and is therefore significantly more efficient than the fully-resolved computations. This model can accurately simulate the wakes of wind turbines operating in a flow field without any need to create or import the CAD turbine models and just by using turbine parameters. In this paper, AL method is implemented in openFOAM solver and a new method is used to spread forces on actuator lines. In order to validate the results, MEXICO rotor was modeled and large eddy simulation’s turbulence model is used to investigate the flow field around wind turbine. Simulation has been done for two different conditions including design conditions and stalled conditions. Results obtained for predicted wakes and performance parameters were compared to experimental data and it was observed that the ALM results agree well with measured data. Stall condition’s results were in better agreement with experimental data so that the thrust had 8.5% difference while torque and power showed difference of 2.8 and 2.4% respectively.

In ventilated cavitating flow structure, two parameters are very important, Fr number and gas entrainment coefficient.The objective of this paper is to investigate the ventilated cavitating flow structure by numerical methods and verify with experimental results. The numerical simulation is performed by ANSYS-FLUENT and homogenous mixture model with a free slip velocity and DES turbulence model, and the gravity effect is considered. The results show when the gas entrainment coefficient Qv is constant, two typical mechanisms of the gas leakage exist at different Fr numbers, namely toroidal vortex mode and two hollow tube vortex mode. With the increasing of Fr, the cavity would transfer from the two hollow tube vortices to the toroidal vortices. Moreover, when the Fr number keeps constant, the enlargement of the cavity causes the gravitational effect to be more significant for the case of larger value of Qv. The result also showed that the cavity length increase has a defined value and it does not increase even with more gas flow injection. With the increasing of gas entrainment coefficient, the drag coefficient decrease. DES turbulence model is a combination of two models, SST k- w and LES model and is suitable for simulating of two hollow tube vortices mode.

Metallic alloys exhibit rheological behavior similar to non-Newtonian fluids in the semi-solid temperature range. This behavior can be described using rheological models. In this study, the viscosity of semi-solid 7075 aluminum alloy was measured by using the results of load-displacement signals obtained from two different experiments: parallel plate compression and backward extrusion. The obtained data were used to determine the parameters of the Cross model in a wide range of shear rates.The effects of temperature (solid fraction) and shear rate were studied on the viscosity of the alloy. The results showed that with increasing temperature and decreasing the solid fraction the resistance to flow decreases, resulting in a reduced amount of applied forces. This reduction in applied forces results in reducing the viscosity. It was observed that the behavior of semi-solid alloy is shear thinning in which the viscosity decreases with increasing shear rate. Also, the calculated viscosity values of the four parameters Cross model were in good agreement with the obtained experimental results in a wide range of shear rates. The simulation results showed good agreement of the presented model for predicting the rheological properties and flow behavior of the semi-solid alloy in a wide range of shear rates.

Oil pipeline leakages, if not properly treated, can result in huge losses. The first step in tackling these leakages is to diagnose their location. This paper employs a data-driven Fault Detection and Isolation (FDI) system, not only to detect the occurrence and location of a leakage fault, but also to estimate its severity (size) with extreme accuracy. In the present study, the Golkhari-Binak pipeline, located in southern Iran, is modeled in the OLGA software. The data used to train the data-driven FDI system is acquired by this model. Different leakage scenarios are applied to the pipeline model; then, the corresponding inlet pressure and outlet flow rates are recorded as the training data. The time-domain data are transformed into the wavelet domain; then, the statistical features of the data are extracted from both the wavelet and the time domains. Each of these features is then fed into a Multi-Layer Perceptron Neural Network (MLPNN) which functions as the FDI system. The results show that the system with the wavelet-based statistical features outperforms that of the time-domain based features. The proposed FDI system is also able to diagnose the leakage location and severity with a low False Alarm Rate (FAR) and a high Correct Classification Rate (CCR).

In this paper, the behavior of curved sandwich beam with a soft flexible core, under low-velocity impact, loaded with environmental thermal effects by pursuing the use of the high order shear deformation theory of sandwich structures is investigated. The sandwich beam is comprised of composite sheets and foam core. The boundary condition is simply supported by probability of circumferential deflection. Two degrees of freedom for mass- spring model was used for modeling the impact phenomena. In the presented formulation, the first order of shearing deformation theory is used for sheets, the core displacement field is considered unknown and then by using elasticity theory and compatible condition in the core, sheets common face and the relation of stress-strain core deflection are determined. In order to derive the governing equations of beam structure, the Hamilton principle was used. For validation, the results obtained from this research are compared with the results of other researchers and also the numerical result of ABAQUS software. The comparison of results show good agreement. The effects of various parameters like impact velocity and mass, environmental temperature, core and sheets thickness and materials on core and sheets deflection and core stress and impact force were studied. The obtained results showed that increasing environmental temperature has a slight effect on impact force, but a more considerable effect on beam dynamic response. It is also shown that with increasing the hardness of beam, the energy absorption is reduced.

In this paper, a control method based on fuzzy systems is presented to drive and keep state of a sample quantum system into a pre-defined region. The considered quantum system is a third-order quantum system and the model of the system is bilinear model. In addition, measurements of the system in the defined region are obtained at each time by considering the effects of such measurements in the internal state of the system. The effect of unwanted inputs and structural uncertainties are also considered as bounded uncertainties in the system’s Hamiltonian. In this paper, it is assumed that the initial state of the system is determined and internal state system is available as the feedback signal at each instant of time. In the proposed control approach, an acceptable region is firstly defined around the desired final state. Then, an adaptive neuro-fuzzy inference system improved using imperialist competitive algorithm is used for driving the system’s state toward the desired final state within this region. In addition, a fuzzy supervisor is utilized to adjust a control parameter for preserving the state of the quantum systeminside the defined region. Simulation results, obtained by applying the proposed method to a sample third-order quantum system in presence of bounded uncertainties show the applicability and effectiveness of the method for controlling the quantum systems.

In recent years, coinciding with the expansion of biofuel production, attempts have also been made to optimize production processes. In this study, Response Surface Methodology (RSM) was used to investigate the transesterification reaction of rapeseed oil for biodiesel production. Three main factors, in order to convert triglycerides into fatty acid methyl esters (FAME), were applied according to a central composite design. These factors were catalyst concentration (NaOH), reaction temperature and time. The yield of methyl ester as the first response was determined using NMR method. The second response was the commercial cost of production. The results showed that the best conditions for producing biodiesel in constant molar ratio of 1: 6 oil: methanol were the temperature of 59.45oC, NaOH concentration of 0.31 %wt/wt and reaction time of 60 min. At these optimum conditions, the yield of methyl ester and cost of production for one liter biodiesel are 78.65% and 70.58 ¢, respectively.Also, some chemical and physical properties of biodiesel were compared with petro-diesel fuel.According to the results, biodiesel fuel is a suitable substitute for petro-diesel fuel.

In this paper, free convection heat transfer of Al2O3/water nanofluid within an enclosed cavity is studied by adopting the lattice Boltzmann Model. The left and right side walls of the cavity have a complexwavy surface and the left wall is heated by a sinusoidal temperature distribution higher than the right cold wall. The top and the bottom horizontal walls are smooth and insulated against heat and mass. In this study, the variation of density is slight thus hydrodynamics and thermalfields equation are coupled using the Boussinesq approximation. The density and energy distribution are both solved by D2Q9 model. The influence of pertinent parameters such as solid volume fraction of nanoparticles, Rayleigh numbers, complex-wavy-wall geometry parameters, phase deviation and amplitude of the sinusoidal temperature function onflow and heat transfer fields are investigated. Results show for Rayleigh numbers in the range of Ra=103 -105, with increasing volume fraction of nanoparticles, Nusselt number increases. In addition, it is shown that for a fixed Rayleigh number, the heat transfer performance depends on tuning the wavy-surface geometry parameters. The greatest effects of nanoparticles are observed for different values of the phase deviation with increase in Rayleigh number. This study can, provide useful insight for enhancing the convection heat transfer performance within enclosed cavities with complex-wavy-wall surfaces and sinusoidal temperature distribution.

In this paper, the dynamic behavior of atomic force microscope (AFM) based on non-classical strain gradient theory was analyzed. For this aim atomic force microscope micro-beam with attached tip has been modeled as a lumped mass. Micro-beam, stimulated via a piezoelectric element attached to the end of clamped and non-linear partial differential equation of the system has been extracted based on Euler-Bernoulli theory and converted into ordinary differential equation by using Galerkin and separation method. The classic continuum theory, because not taking size effect into consideration, has little accuracy in predicting the mechanical behavior of Nano devices. In this study, the stability region of micro-beam is determined analytically and validated by comparison with numerical results. Difference between presented analysis in dynamic behavior of micro-beam by classic and non-classic theories has been shown with a variety of diagrams. It is clear that considering the size effect changes the dynamical behavior of the problem completely and it is possible, and while classical theory predicts stable behavior for microscope the size effect is caused bi-stability. The results in this paper are very useful for the design and analysis of atomic force microscope.

Melting of Cyclohexane-Cu nano-material in a porous square cavity is studied numerically in this paper.The initial temperature of the cavity is Ti that is equal to melting temperature of nano-PCM (phase change material), Tm, The horizontal walls are adiabatic. Suddenly the left wall's temperature changes to Th>Tm. The effective parameters in this case are Ra,  j and ε which appear in the nondimensionalized equations. Nondimensionalized governing equations are obtained based on the Darcy model; a control volume approach is used for solving these equations. The effect of the variation of mentioned parameters (50 ≤ Ra ≤ 500, 0 ≤ j ≤ 0.05 and 0.1 ≤ e ≤ 0.6) is investigated on the heat transfer rate, fluid flow, isotherms and melting time of nano-PCM. The results show that changing any of the parameters will affect the increase or decrease of heat transfer rate and melting process time.For example variation of e has considerable effect on melt fraction in cavity with time. The results show that melting of PCM is prolonged when nano-particles are added. The results show that, increasing the Ra number, enhanced the power of natural convection heat transfer and the rate of nano-PCM melting in the cavity and therefor deforms the melting line.

Rotating cylindrical shells are applied in different industrial applications, such as gas turbine engines, electric motors, rotary kilns and rotor systems. So, it is of great interest to conduct some researches to improve the understanding of vibrational characteristics of rotating cylindrical shells. Grid stiffened laminated composite cylindrical shells are used as components of aerospace, marine industries and civil engineering structures. In this research free vibration of rotating grid stiffened composite cylindrical shell with various boundary conditions using the Fourier series expansion method is presented. Smeared method is employed to superimpose the stiffness contribution of the stiffeners with those of shell in order to obtain the equivalent stiffness parameters of the whole structure. The stiffeners are considered as a beam and support shear loads and bending moments in addition to the axial loads. Strain displacement relations from Sanders's shell theory are employed in the analysis. Using the Fourier series expansion and Stokes’ transformation, frequency determinant of laminated cylindrical shells is derived.The effects of shell geometrical parameters and changes in the cross stiffeners angle and axial loading on the natural frequencies are investigated. Results given are novel and can be used as a benchmark for further studies.

This paper investigates vibration analysis of a clamped-clamped beam attached to a nonlinear energy sink (with nonlinear stiffness and damping) under an external harmonic force. The beam is modeled using the Euler-Bernouli beam theory. Different locations for nonlinear energy sink are chosen and the effects of various parameters on behavior of the system are considered. Required conditions for occurrence of the Saddle-node bifurcations and the Hopf bifurcations in the system are studied. In vibration analysis, the frequency response diagram of the system is very important because it shows the best regions for attenuation of vibration and is a good criterion for designing nonlinear energy sinks; hence Complexification-Averaging method is used to find the amplitude of oscillation in terms of excitation load simply. For validation and comparison, numerical simulation (Runge-Kuta method) is used. The results demonstrate that by approaching the position of nonlinear energy sink to the beam supports, probability of occurrence of the Hopf and the saddle-node bifurcations decreases and increases, respectively; detached response curve will be formed in smaller range of external amplitude force.Moreover, by increasing external amplitude force, the steady state amplitude of the system increases smoothly.

Jig and fixture design for workpieces with freeform geometry has more complexity in comparison with the polyhedral parts. The locating and clamping system design construct the basis of the jig and fixture design activities. In this study, a theoretical analysis is suggested for automatic design of clamping points for freeform workpieces. The clamping design is performed in three main stages, in which the clamping application points are determined through the first two principles and are verified through the last stage. The mentioned principles consist of: (1) the minimum quantity of clamps, (2) the maximum clamping force components on the locating directions and (3) the workpiece static stability under the external wrenches. After mathematical modeling, the suggested analysis was implemented into the already designed CAFD framework by the authors. Three machining models were chosen as case studies to evaluate the capabilities of the implemented system in robust design of clamping layout. The minimum quantity of clamps (single clamp for two case studies and double clamp for the third one) was designed by the developed method that verified the robustness and reliability of the suggested and implemented clamping system design model. The automatic design of clamping scheme for workpieces (regardless of the geometry) besides its capability in integration with the other modules of fixture design activities provides the opportunity for the system to be used in industrial applications.

Due to the polar functional groups of PVC thermoplastic and its good adhesiveness to the metals, production and roll forming of PVC/ aluminuim/ glass fiber FMLs were investigated in this research.First, flexural strength and bonding quality between PVC matrix and aluminuim layer in the FMLs were studied by doing three point bending tests according to ASTM D790 standard. In the following, FMLs with dimension of 12×80 cm and two layups including [0.90, 0.90, Al] s and [45/-45, 45/-45, Al] s were produced using film stacking and hot pressing procedure. The FMLs were rollformed into 30, 45 and 60º channel section profiles at 160oC using a single stand roll forming process and geometrical defects including profile bowing, edge wrinkling, spring back and also aluminuim/composite layers delamination of the resulted profiles were evaluated. The FMLs also were roll formed into 86º channel section profiles using a multi stand roll forming process and the effects of multi stand roll forming on the defects stacking were evaluated. Finally, it was concluded that more than 45º bend angle increase in a roll forming stand results in composite/ aluminum delamination. Also, placement of the reinforcing fibers in the longitudinal direction of the profiles reduces the profile bowing and edge wrinkling defects significantly.

Hexapod walking robots can be employed for both walking and manipulation purposes. When manipulating, they have 6 degrees of freedom for top platform, high rigidity, high load capacity, high speed, and accuracy. On the other hand, it is well known that they have limited workspace when they are fixed in place for manipulation. Designing a hexapod robot resulting in a maximized workspace can greatly affect the efficiency of the robot when manipulating. Since radially symmetric hexapod walking robots can be modeled as three 2-RPR planar parallel mechanisms, we have used the methods and calculations that are used in this kind of mechanism for designing a radially symmetric hexapod walking robot. In this paper, after a thorough review on existing methods for calculating and improving 2-RPR planar parallel mechanism workspace, an algorithm is presented that results in a maximized reachable workspace. The merit of the method is that there is no need to calculate the workspace volume when maximizing it. Also, following this algorithm is necessary for design of the maximized workspace robot. In other words, the output of the presented optimization algorithm is a set of robot kinematic parameters, which guarantees the maximized volume of the robot’s reachable workspace.

In this paper, in order to build T shaped tube by hydroforming method, the drop hammer system is used which leads to the hydrodynamic load. To form the first piece as the die configuration, the hydraulic internal pressure and axial feeding is required, and in the study of this process a source of energy should be used in two ways. According to mentioned load path, the die is designed to get the impact of free fall weight by pistons on the die, which produces the hydraulic pressure. By putting the punches on both sides of the tube, axial feeding takes place by receiving the hydraulic pressure of Intermediate fluid, and the internal pressure transmits the fluid from the middle hole of the punches. It is worth noting that copper and aluminum tubes have been analyzed in experimental tests. To check the numerical analysis of final pieces and improve the quality of shaping, the finite element software ABAQUS is used. The simulation model of forming T shaped tube has been evaluated dynamically by considering the effect of strain rate and mechanical properties of tube material. The results of tests show that to have favorable deformation, all the input parameters such as the kinetic energy, fluid column, sealing, lubrication, gender and the thickness of tube should be proportional to each other. Also, in this study, the height of the bulge has been analyzed due to the thickness distribution, axial displacement and surface embrace.

In this paper the methodology of reliability analysis in aerial structures has been developed. This methodology has been carried out on a special specimen. The selected specimen is a cylinder strut of the landing gear system of a training airplane. This specimen is one of the most important parts of the landing gear system. Because of its special shape, no analytical solution exists for calculating the stress in it. Therefore, by means of the surface response method and Box-Behnken tables, a deterministic equation for calculating the stresses in critical points of the specimen has been produced. So, in order to obtain the reliability of this part via probabilistic method, Monte Carlo simulation has been used. The applied loads have been modeled with one pressure, one bending moment and one concentrated force.These loads have been assumed to be independent random variables. Also, the probability distribution function of the pressure and the bending moment have been assumed to be normal and the probability distribution function of the concentrated force has been assumed to be lognormal. The dimensions of the specimen are deterministic and the mechanical properties of the material are a normal distribution with standard deviation equal to 10 percent of its mean value. The results showed that the minimum reliability of this specimen is 99.9997 percent. So, the design of the cylinder strut is safe for aerial applications from the point of reliability.

In this research the possibility of mass reduction in a two-module cubic microsatellite with skin – frame structure is studied. Natural frequencies and effective mass distribution change by replacing isogrid structure with sandwich panel (honeycomb). Modal effective mass is a dynamic characteristic of structure and depends on natural frequencies, mode shapes, general masses and eigenvectors. Modal effective mass is a quantity that shows the importance of a mode when satellite is under acceleration loads through the baseplate. High modal effective mass shows high reaction loads on baseplate in corresponding frequency. Also, acting dynamic loads are affected by distribution of modes in frequency range. The sum of effects of different modes creates significant reaction loads. Hence, study of frequency and effective mass changes by converting the structure design from isogrid to sandwich structure is necessary. In this paper, the first two isogrid and sandwich structures with equal masses are compared. Then mass of sandwich structure is decreased in such a way that natural frequencies of light sandwich structure approach natural frequencies of isogrid structure. In equal masses case, natural frequencies of sandwich structure are twice the natural frequencies of isogrid structure but effective mass distribution of isogrid structure is better along the launch direction. By changing the isogrid structure design to sandwich panel structure and optimization of the new structure characteristics a noticeable reduction in mass and improvement in modal behavior could be obtained.

Metals and polymers are frequent materials for engineering purposes. Technological advances have called for new materials with high stiffness and low production cost, especially in automotive industry.Up until now, the most common approach has been to employ high strength metals like steel in manufacturing different parts and subsequently coating them with regard to their application, in order to reach maximum performance. One of the novel composites is metal-polymer hybrid which is produced by injection molding a layer of polymer on a laser cladded metal to form a laminated composite. The superiority of this method lies in the diversity of pattern and powder materials and feed rate in cladding that can be optimized for a particular loading in different applications. Evaluating parameters are holding pressure, mold temperature, cladding pattern, and polymer thickness. Simple Tension and threepoint bending tests showed that the maximum strength of joint adhesion was achieved at 50℃ mold temperature, lower holding pressure (70MPa), higher thickness (3mm), and parallel pattern. Moreover, better flexural modulus was reached at 50oC mold temperature, lower holding pressure (70MPa), lower thickness (2mm), and parallel pattern.

In this research, a three dimensional analytical method is presented for predicting the dynamic properties of polymer nanocomposites. In the present method elastic-viscoelastic correspondence principle is applied on the simplified method of cell, and loss modulus, storage modulus, loss factor and Hysteresis loop are obtained using energy method as well as force balance method. The considered nanocomposite possesses Polypropylene as a matrix reinforced by vapor grown carbon fibers. The representative volume element consists of three isotropic phases including fiber, interphase and matrix with linear viscoelastic behavior based on Zener model. Furthermore, the nanocomposite constituents dynamic properties are extracted in frequency domain by employing Fourier transform method and Schapery model. First, to ensure validation of the model, the results are compared with experimental results. Parametric studies such as the effects of number of subcells, fibers volume fraction (FVF) and aspect ratio, matrix/fiber link strength factor and interphase loss factor on the nanocomposite dynamic properties are investigated.. Obtained results reveal that the presented method has acceptable speed and accuracy. Moreover, fiber aspect ratio and FVF increasing leads to decreasing the nanocomposite hysteresis loop area, subsequently its damping capacity reduces. Interphase also contains considerable effects on the nanocomposite dynamic properties, so its modeling is of great importance.

In this paper, thermo-elastic analysis of functionally graded nanocomposite hollow cylinders reinforced by single walled carbon nanotube (SWCNT) subjected to a thermal load was carried out by a mesh-free method. It is assumed that the functionally graded nanocomposite hollow cylinder reinforced by carbon nanotube with finite length is simply supported. A One uniform and three kinds of functionally graded (FG) distributions of carbon nanotubes in the radial direction of cylinder are considered. Nanocomposite mechanical properties are estimated by micro mechanical generalized rule mixture model. Applying the virtual work principle, the governing equations are obtained and are discretized by the mesh-free method. In the mesh-free analysis, moving least squares (MLSs) shape functions are used for approximation of displacement field. The transformation method was used for the imposition of essential boundary conditions. Using finite difference method, temperature distribution was obtained by solving the thermal equation. To validate, the results of this analysis were compared with previous published works and a good agreement was seen between them. Then the effects of various parameters, such as the kind of distribution and the volume fractions of carbon nanotubes and the different geometrical parameter on the components of stress are studied.

In this paper, inverse design to determine unknown heat source distribution in a radiant enclosure using an optimization method is investigated to produce desired emissive power and heat flux profiles on a diffuse-nongray design surface of a two-dimensional radiant enclosure. The medium of enclosure is emitting-absorbing, and the design surface emissivity is assumed to be varied with respect to wavelength. Regarding diffuse-nongray design surface, the variation of emissivity with respect to the wavelength is approximated by considering a set of nongray bands with constant emissivity and then the radiative transfer equation is solved by the discrete ordinates method for each band. The total heat flux on each surface element of the design surface is approximated by a summation over the contribution of nongray bands. The conjugate gradient method is used to minimize an objective function, expressed by the sum of square residuals between estimated and desired heat fluxes over the design surface. The sensitivity problem is approximated by differentiation of the radiative transfer equation with respect to the unknown variables. The performance of the present method is evaluated by comparing the results with those obtained by considering a diffuse-gray design surface. The results show that the heat source distribution is well recovered over the heat flux specified design surface in an appropriate range of accuracy.

Nowadays, thin-walled tube bending (D/t ³20, D-tube diameter and t-tube thickness) in the critical bend ratio (R/D£2, R bend radius) is a widely used manufacturing process in the aerospace industry, automotive, and other industries. During tube bending, considerable cross-sectional distortion and thickness variation occurs. The thickness increases at the intrados and reduces at the extrados. Also, in some cases, when the bend die radius is small, wrinkling occurs at the intrados. In industry, the mandrel is used to eliminate wrinkling and reduce cross-sectional distortion, the choice of the mandrel depends on tube material, bending angle, radius tube and bending radius. However, in the case of a close bend die radius, using the mandrel is avoided. Because in addition to the cost of the process, with the mandrel the thinning of the wall increases at the extrados and this is undesirable in the manufacturing operation.So, in the present study, with regard to development of tube hydroforming, internal fluid pressure is used instead of the mandrel. Therefore, the purpose of the feasibility study, observation and analysis of the formation of tube bending process, the tube rotary draw bending process with two of the mandrels and the internal fluid pressure is simulated by software ABAQUS.

Skeletal muscle simulation remains a controversial topic as a result of its complex anatomical structure and mechanical characteristics such as nonlinear material properties and loading conditions. Most of the current models in the literature for describing the constitutive equations of skeletal muscles are based on Hill's one-dimensional, three element model. In this paper, a 3D constitutive model which is based on the hyper elastic behavior of skeletal muscle and energy function has been presented. By using the derivatives of such energy function for defining the Second Piola and Cauchy stresses, the model could describe the inactive behavior of skeleton muscles. The applied constitutive equations are an efficient generalization of Hamphury's model for the inactive behavior of skeletal muscle. In this paper by using a 3D model, different modes of deformations of skeletal muscle such as simple tension, biaxial and shear tests have been investigated and material properties constants for each mode of deformation has been optimized by Genetic Algorithm. Finally the results of the model simulations of each mode are compared with those obtained from experimental tests. Also, the model results are compared with the ones from two well- known hyper elastic Ogden and Mooney-Rivilin models in order to show the priority of the new developed 3D model.

The main objective of utilizing nozzles is to convert the chemical energy to kinetic energy producing thrust. A wide variety of parameters makes a significant impact on nozzle performance; one parameter that produces dramatic effect is back pressure or ambient pressure. Basically, a nozzle designed for a specific back pressure does not work properly when the engine is ascending. Consequently, designing of nozzles requires knowledge of full effect of back pressure on engine performance. In this study, numerical simulation of three solid propellant nozzles has been conducted in several flight conditions.In other words, simulation have been done in some ambient pressures which represent specific flight altitudes. Numerical modeling has been conducted aiding commercial code FLUENT. k-e RNG turbulence model has been used for calculating turbulence interactions with the flow. Mass flow rate, chemical species, and chamber temperature have been used as the inlet boundary conditions based on engine specifications. Numerical results show a reasonable accuracy in comparison with experimental measurements. Estimating nozzle thrust level as a function of altitude increment is the primary goal of this study. Furthermore, with the aid of this relation and a MATLAB code for computing average specific impulse, optimum expansion ratio can be achieved based on a specified mission.

The main objective of this research is to employ Imperialist Competitive Algorithm (ICA) to determine the optimum condition for an FG cylindrical shell with outer piezoelectric layer. Design parameter in this problem is volume fraction of the material. The shell is subjected to outer radial moving load and internal pressurized fluid. To formulate the problem, First Order Shear Deformation theory and Maxwell’s equation have been combined to develop governing equations and by solving these equations using analytical-numerical methods, the dynamic deformation has been obtained. Then, by adopting displacement-strain and stress-strain relationships, distribution of the dynamic stresses within the shell has been calculated. Due to the moving of the external load, the use of dynamic analysis is necessary so that the dynamic and transient response is significant compared with the static one. To validate the dynamic analysis the results are compared with those provided in the literature based on other solution methods or experimental measurements. Finally, a computer code has been developed to link the dynamic solution method with the optimization algorithm based on ICA to obtain the optimum values of the design parameters. The major advantage of this method is the use of control points along the thickness to define volume fraction rather than using predefined functions which usually impose unnecessary restrictions. The volume fraction between these control points is obtained by Hermite interpolation method. The results show the efficiency of the method and its major strength which is the flexibility and higher convergence rate to determine the optimum configuration.

Manufacturing in as short a time as possible, with highest quality and at minimal cost, is one of the key factors in industry. As a result, researchers are seeking new methods and technologies to meet such requirements. Liquid impact forming is one such method which has received wide currency especially in automotive and aerospace industries. In this method, which is considered one of the tubular hydroforming processes, forming is achieved by using liquid pressure. In this paper, liquid impact forming process was investigated experimentally and numerically for a thin-walled aluminium tube. In experimental part, a die was designed and manufactured to transform the cross section of the aluminium tube into a polygon which at the end of the process changes the cylindrical shape of the tube to a profile almost similar to a trapezoid. Results showed that a die in the form of matrix molding is not suitable for this type of geometry in such a process, while using another die which consisted of three parts resulted in a satisfactory forming. Simulation of this process was further implemented using finite element method and results relating to Von Mises stress distribution, displacement, strain energy, internal energy, thickness variation and the force required to implement the process were obtained.Displacement distribution in different regions indicated that no wrinkling occurred in the sample.Comparison between simulation and experimental results indicated that they were in good agreement.

In this paper design, fabrication and control of a robotic fish with flexible tail was presented. First, the short introduction of the robotic fish and its common control algorithms were reviewed. In the next step, the proposed mechanism of the robotic fish and its design procedure of the mechanical and electrical subsystems were explained. Mimic of the proposed robot was inspired from the Rainbow trout. The mechanical structure of the robotic fish consists of a body and a flexible tail. Oscillatory actuation of the tail was carried out utilizing a servomotor which was manipulated by pulse width modulation signal. The electrical subsystem of the proposed robot containing the electrical boards, electronic circuits, and a microcontroller are installed on the Aluminum platform which is located in a sealed case. The flexible tail is attached to the end-side of the sealed case, and the actuating force is transferred to the tail utilizing pulley and cable mechanism. Since the dynamics of the system under investigation is nonlinear, a fuzzy logic controller is proposed to control the movement of the robot for goal seeking purpose. The closed loop simulation of the system was carried using MATLAB software.In addition, experimental investigation of the robotic fish was performed in the laboratory.

Thin-walled structures are frequently used as energy absorbers in automotive, railway and aviation industries. This paper deals with the collapse and energy absorption behavior of thin-walled structures under dynamic axial loading Numerical modeling was performed using finite element code LS-DYNA.In order to validate the results of finite element analyses, a square tube was collapsed using universal test machine. This tube was then simulated in LS-DYNA, and the results were compared with those of experiments. There was good agreement between the numerical and experimental results. The tubes with different cross-sections namely square, hexagonal and octagonal shapes reinforced with inside ribs as well as with different scales (ratio of sectional side length of the inner tube to that of outer tube) 0, 0.25, 0.5, 0.75 and 1 were simulated in LS-DYNA. To determine the suitable cross-section in terms of crashworthiness, multi-criteria decision making method known as Technique of Order Preference by Similarity to Ideal Solution (TOPSIS) was employed. The results demonstrated that the double walled tube with octagonal cross-section possessing the scale between 0.25 and 0.5 had the best crashworthiness behavior. To find the optimum values of scale and wall-thickness, response surface method (RSM) and D-optimal criterion using design of experiments (DOE) were utilized Moreover, the effect of number of inside ribs (4 and 8) on the capability of absorbing energy was also investigated.The results showed that the octagonal tube with 4 inside ribs was able to absorb more collision energy.

In this work the effect of carbon nanotube length on the nanofluidic energy absorption system is investigated by using molecular dynamic simulation. For this purpose, four armchair rigid carbon nanotubes (8, 8), (10, 10), (12, 12) and (14, 14), and six lengths (5, 6, 7, 8, 9 and 10) for each one are studied. Results of simulations show that the surface of carbon nanotube is frictionless at all lengths and diameters, causing water molecules to be defiltrated from carbon nanotubes after applying the loadingunloading cycle on the system. Contact angle, which represents hydrophobic intensity of carbon nanotube, is decreased on average 4 % and 2 % by increasing length and diameter of carbon nanotube, respectively; therefore, infiltration pressure of water molecules through carbon nanotube is decreased an average of 30 % and 15 %, respectively. Moreover, the mass and size of carbon nanotube increase by increasing length and diameter of carbon nanotube, leading to the reduction of energy absorption density and efficiency. Also, density of water molecules in carbon nanotube unlike the bulk of liquid phase is non uniform and decreases at the first and second shells. In addition, it increases along the distance between these shells by increasing length of carbon nanotube.

Inconel alloys are a family of nickel-based superalloys that consist of a wide range of compositions and properties. Inconel 718 is one of the superalloys used in the aerospace industry due to its good mechanical properties; such as high corrosion and creep resistance at high temperatures. Despite these advantages, Inconel 718 is among the most difficult materials to be machined. In this paper, a finite element model for orthogonal machining of Inconel 718 was developed in order to investigate the effective parameters on the force, temperature and chip morphology. The plastic behavior of material was simulated with Johnson-cook material model, and constant shear friction factor (m) is used to model the friction between chip and tool interface. Then, the simulation results were compared with experimental values and good agreement was found between them. After validating the simulation results, the effect of coefficient friction, cutting speed and rake angle, on cutting edge temperature, force on the tool and chip morphology was achieved by using design of experiments (DOE) method.According to the results, feed rate (30% contribution) and friction coefficient (19% contribution) have the greatest impact on the force on the tool. Rake angle (31% contribution), cutting speed (21% contribution) and feed rate (20% contribution) are the most effective parameters on the cutting edge temperature. The friction coefficient and feed rate (both with 25% contribution) have the greatest impact on the chip geometry.

The appearance quality of automotive bodies is among the features which are, in recent years, significantly taken into consideration by designers throughout the world. Automotive bodies are, to a great extent, constructed from flexible sheet metal components and would deform and distort easily by even a slight assembly force. Therefore, errors due to manufacture and assembly processes of automotive bodies lead to major deviation from the ideal product and ultimately affect the appearance quality and cosmetic features of the vehicle. The effect of these errors, which commonly arise by dimensional, geometric or assembly tolerance of the components, can be examined by tolerance analysis. As one of the key quality characteristics in vehicle design, this paper evaluates the appearance quality of automotive bodies as a function of assembly derived errors. In the proposed methodology, by means of the nonlinear finite element analysis and by presenting the surface interrogation techniques, acomprehensive approach of quality appearance evaluation of vehicles is developed. The approach is validated by a vehicle example and the results show good agreement with practical data obtained from the production line.

Dynamics analysis of the rotational axially moving pipe conveying fluid under simply supported condition was investigated in this research. The pipe was assumed as Euler Bernoulli beam. The gyroscopic force and mass eccentricity were considered in the research. Equations of motion were derived using Hamilton’s principle, resulting in two partial differential equations for the transverse motions. The non-dimensional equations were discretized via Galerkin’s method and were solved using Rung Kutta method (order 15s). The frequency response curve obtained in terms of non-dimensional rotational speed. The bifurcation diagrams obtained in the case that the non-dimensional fluid speed, non-dimensional axial speed and non-dimensional rotational speed respectively varied and the dynamic behavior was numerically investigated based on the Poincare' portrait. Numerical simulations indicated that the system response increases by increasing non-dimensional axial speed of the pipe, nondimensional fluid speed and non-dimensional rotational speed of the pipe and then decreases after passing critical area. The system is unstable at critical point associated with non-dimensional axial speed. Poincare portrait indicates periodic motion in transverse vibrations of the pipe at some points of control parameters. Phase portrait and FFT (Fast Fourier Transform) diagrams were used for validation of the results.

In this paper, online manual guidance of industrial robots using impedance control with singularity avoidance is studied. In this method, operator enters the robot workspace, physically holds the endeffector equipped with force sensor and manually guides the robot. In doing so, the operator generates the desired trajectory for applications like welding or painting. Robot singular configuration is possible during the process which makes it unsafe due to unexpected high velocity robot joints and the physical human-robot interaction. Therefore, real-time identification of singularity position and orientation must be evaluated during trajectory generation. The use of manipulability ellipsoid is suggested as a simple method for the singularity identification. By combining the manipulability ellipsoid and impedance control, a simple and new approach is proposed to warn operator before reaching singularity. Based on the proposed approach, effect of opposite force is exerted on the human hand in the predefined distance to singularity. Real-time implementation is the main advantage of the proposed approach because it keeps robot away from reaching singularity. Real-time experiments are performed using a SCARA robot. In the first experiment, the operator stops the trajectory generation process when an opposite force is produced. In the second experiment, the operator insists on entering the singular points.Experimental results show the effectiveness of the proposed approach in dealing with singularity problem during the trajectory generation by an operator for industrial robots.

Inimitable properties of graphene sheets enable a variety of applications such as axially moving nanodevices. Axial velocity affects dynamical response of systems. In this study linear vibration of an axially moving two-layer graphene nonoribbon with interlayer shear effect is proposed using nonlocal elasticity theory. Based on this theory, stress at a point is a function of strain at all other points of the body. Euler-Bernoulli theory is used to model the system due to nanoribbon thickness and length. It is assumed that the layers have the same transverse displacement and curvature and there is no transverse separation between layers surfaces. A shear modulus is imported in the potential energy expression in order to consider the interlayer shear effect due to weak Van der Waals forces. Governing equations are obtained using Hamilton’s principle and are solved by Galerkin approach. Results for clamped-free boundary conditions are presented and compared to other available studies. Results for pinned-pinned boundary conditions are presented and it is observed that increasing axial velocity causes divergence and flutter instabilities in the system. Effects of different shear modulus and nonlocal parameter on critical speeds are also proposed.

In this paper, designing an optimal linear controller for non-holonomic wheeled mobile robots based on Linear Quadratic Gaussian (LQG) controller is considered. Parameters of the governing kinematics equation of motion are derived based on system identification techniques by using real experimental data. The autoregressive moving average-exogenous input (ARMAX) models are taken into account.The least square (LS) algorithm is utilized to estimate the parameters of the model. Thereafter, optimal model order and the performance of the model are determined using several statistical analyses. Also, the recursive LS (RLS) with forgetting factor is employed to demonstrate the convergence of the model parameters. Verification of the discrete linear model implies the possibility of using the linear controllers. Therefore, the optimal LQG controller for wheeled mobile robots is designed to track the reference trajectory. The Kalman observer is used to estimate un-measurable states of the robot.Furthermore, the optimal linear control together with system identification techniques yields a simpler controller than nonlinear controllers. Designed controller and verified model are simulated using the MATLAB-Simulink software. Results show the effectiveness of the controller in tracking the desired reference trajectory.

An algebraic method based on unknown input observer for fault estimation in linear time invariant system with unknown input is implementable if matching condition is satisfied. Matching condition limits practical application of these methods. In this article, a method is proposed for fault estimation which need not satisfy matching condition. Unlike classical methods, the provided method does not require auxiliary output for fault estimation. In the first step, the unknown input is divided in two parts: the matched and the unmatched unknown inputs. Assuming that there exist a dynamic model for the unmatched part, new augmented system is constructed. The augmented system is revealed as a new system with matched unknown input. Then, the effect of matched unknown input is perfectly removed from observer estimation using the traditional unknown input decoupling strategy. In the next step, the full order observer is designed for the augmented system. A fast adaptive law is employed for the fault estimation. Lyapunov stability condition of state and fault estimation are derived by linear matrix inequality (LMI) criteria. The effectiveness of the proposed method is shown via numerical simulation on a flexible joint example.

In this study, after fabricating a solar parabolic water heater, an efficient model is suggested to predict the efficiency of the solar water heater system (SWHS). Artificial neural networks (ANN) can create logical relations among the input parameters and target (s). The Efficiency is trained as a function of the input parameters, when conditions are desirable to measure the data, a network-trained function can be used to predict the efficiency of the solar system. The used data for the neural network analysis were measured by using experiments on a parabolic trough collector during four days in June. Variables such as solar radiation, ambient temperature and the output fluid temperature of the collector were considered as input parameters and the efficiency of the solar parabolic water heater was used as the output neural network. Different ANN models are presented based on the various input parameters and neurons. The ANN6 model with a 4-10-1 structure, with a root mean square error (RMSE) of 0.0061 and regression coefficient for train data (Rtrainl) of 0.99995, is the most accurate among the presented models. By increasing the input parameters, the RMSE decreases and accuracy of the models increases. When experimental tests are not impossible in similar conditions, the presented model can help researchers predict the efficiency of studied SWHS by saving time and cost.

of fluid-solid interaction has been studied as an introduction to simulate a wide range of engineering problems such as fluidized beds, sediment transportation and catalyst inks in fuel cells. An efficient method for performing such simulations is a combination of Lattice Boltzmann method (LBM) and Smoothed Profile method (SPM). In addition, the operations in the SPM are local; it can be easily programmed for parallel processing. In this approach, the flow is computed on fixed Eulerian grids which are also used for the particles. Owing to the use of the same grids for simulation of fluid flow and particles, this method is highly efficient for the purpose of parallel processing by means of GPU. In this study, a combination of Lattice Boltzmann method (LBM) and Smoothed Profile method has been implemented in parallel processing on GPU. For validationpurpose, the fluid flow within a channel was investigated. Results suggest that computational time can be reduced up to 80 times by means of GPU. Then, drag force exerted on a sphere in fluid flow and the sedimentation of one sphere in a quiescent fluid were studied. Results show that performance of GPU can be increased up to 6.5 million fluid nods per second by using this method.