Modares Mechanical Engineering
Year:2015 | Volume:15 | Issue:9|Papers Count:50

In recent years, measurement of residual stress by ultrasonic method has developed because of its nondestructive nature, portable equipment and being cheap and fast. In this research, the Capability of ultrasonic method by using longitudinal critically refracted or LCR wave in measurement of longitudinal welding residual stress has been scrutinized. For this purpose, two plates of aluminum alloy series 5000 were joined by TIG welding method. Measurement of longitudinal residual stress by ultrasonic method was done in closeness of surface via 5 MHz transducers based on acoustoelasticity theory. In order to create LCR wave and transmit it into specimen, an ultrasonic wedge was made based on Snell’s law. Also, a triaxial table was used to control the wedge movement and keep the pressure on it fixed. In order to calculate residual stress and increase in accuracy, acoustoelastic constant for each three welding zones, including weld metal, HAZ and base metal was obtained separately from uniaxle tension test. In order to validate ultrasonic method results, measured longitudinal residual stress by x-ray diffraction method in 5 points on the specimen surface was used. Finally, after comparing the results of the two used methods with each other, good agreement was seen which indicates the good ability of ultrasonic method in measurement of longitudinal residual stress.

Piezoelectric materials are used as sensor and actuator in order to control the vibrations of structures. Geometry and location of the piezoelectric sensors and actuators have a substantial effect on the consumed electric energy and performance of the control system, therefore, in this study by defining an appropriate cost function, an optimum length and location of the piezoelectric actuator was determined in order to achieve a desirable decrease on vibration amplitude of a cantilever beam by using appropriate control energy. The standard quadratic function of beam displacement and control energy was used as the cost function. Mathematical modeling was based on Euler Bernoulli beam theory and Hamilton's principle was used in order to achieve the equations of motion. In this approach, the control voltage of actuator layer appears in the boundary conditions of the problem, which turns it to a time varying boundary condition problem. By defining special displacement functions and homogenizing the boundary conditions, control voltage of the actuator appears as external excitement in the equations of motion. In the current study, optimum LQR and LQG controllers were investigated and Kalman filter theory was used in order to estimate the state variables. In numerical simulations, by investigating the performance of optimized limited or unlimited patches in comparison with complete one, the effective role of the objective function and optimization have been shown in decreasing applied control voltage.

This research discusses the effect of simultaneous usage of Propellant Utilization (PU) system and Flight Apparent Velocity Regulation (AVR) system. These systems were used for sending OBC commands to engine for adapting the engine working regime with flight conditions and fame to active control systems. Each of the PU and AVR systems has an effective role in access to final parameters such as mass and velocity at the end of active phase and simultaneous usage of these systems leads to increased range accuracy and payload mass. We study these effects on final parameters in this paper. Therefore, with dynamic simulation of liquid propellant engine during active phase in flight simulator, sending commands of these systems to change the engine working regime are provided. For a specific mission, results show that using the PU, range increased and presence of AVR is assisted to reach this range in front of disturbance during the flight. Another important result of this research is the payload mass increased for a specific mission with simultaneous usage of PU and AVR systems.

High-speed milling of titanium alloys is widely used in aerospace industries due to its high efficiency and good quality product. The paper empirically studies surface roughness, topography and microhardness variations in high speed milling of Ti6Al4V alloy. The experiments were conducted under minimum quantity lubrication environment. Carbide end mill tool with TiAlN coating and 6 millimeter diameter was used. Full factorial method was used to design experiments and analyze the effect of machining parameters including cutting speed and feed rate on surface roughness, topography and microhardness. The other cutting parameters, i.e. axial depth of cut and radial depth of cut were constant. The results showed that a high quality surface with roughness of 0.2 mm can be obtained by using high speed machining method. Also, microhardness variations versus cutting speed has two-fold nature. It indicates that firstly, by increasing cutting speed up to 375 m/min, microhardness increases and after that declines remarkably. In addition, by increasing feed rate, surface microhardness rises and the maximum microhardness was obtained at cutting speed of 375 m/min and feed rate of 0.08 mm/tooth, which showed 57% increase with regard to hardness of the base material. The images of surface topography showed that increasing of the cutting speed has a significant effect on reduction of surface tears and smears.

This paper concerns the effect of auxiliary fields and also the contour distance from the crack tips on accuracy of stress intensity factors of Functionally Graded Materials (FGMs), using the interaction integral method. In the first step, defining auxiliary fields of displacement, strain, and, stress appropriately, the interaction integral is derived which is independent from derivatives of properties of the materials. Actual and auxiliary fields of displacement, strain and stress are used to compute the interaction integral. Actual fields are obtained by isoperimetric finite element method, while auxiliary fields are constructed by use of the crack tip properties on the basis of Williams’ solution. These auxiliary fields are not appropriate, except near the crack tips. Therefore, different non-equilibrium and incompatibility formulations are used to consider the changes in non-homogeneous material. Considering the changes in FGMs as an exponential function, the results will then be obtained from these formulations and are compared with others recorded in the literature. Furthermore, considering different contours, the effect of contour distance from the crack tips on the stress intensity factors of FGMs is examined. The results confirm that the solutions using the incompatibility and constant constitutive tensor are more accurate. In contrast, the non-equilibrium method is not proper for contours which are placed far away from the crack tips and presents less accuracy.

In the present research, the high-order DG-ADER method is used to solve governing equations of two-phase drift flux model. The drift flux model is suitable for studying two-phase flows where the phases are strongly coupled. This model is composed of three differential equations including two continuity equations for two phases and a mixture momentum equation. The mixture model also uses an algebraic relation to link the velocity of the phases. The high-order DG-ADER numerical method, which is a new scheme to obtain high order accuracy of results, is used to solve the governing equations. The DG-ADER is a nonlinear method in which the reconstruction process is performed using WENO method and the time evolution part is achieved by discontinuous Galerkine approach. The results are compared with those reported by other researchers. Three problems including two two-phase shock tubes and a pure rarefaction test problem are solved using this method. The results show that DG-ADER method can solve the two phase flow problems with a very good accuracy even on a coarse grid. The drawback of this method is presenting numerical fluctuations with limited domain at the position of shock waves.

The existence of crack and notch is a significant and critical subject in the analysis and design of solids and structures. As most of the damage problems do not have closed-form solutions, numerical methods are current approaches for dealing with fracture mechanics problems. This study presents a novel application of the decoupled equations method (DEM) to model crack issues. Based on linear elastic fracture mechanics (LEFM), the J-integral is computed using the DEM. In this method, only the boundaries of problems are discretized using specific higher-order sub-parametric elements and higher-order Chebyshev mapping functions. Implementing the weighted residual method and using Clenshaw-Curtis numerical integration result in diagonal Euler’s differential equations. Consequently, when the local coordinate’s origin (LCO) is located at the crack tip, the geometry of crack problems is directly implemented without further processing. In order to present infinite stress at the crack tip, a new form of nodal force function is proposed. Validity and accuracy of this method is fully demonstrated through two benchmark problems. The numerical results agree very well with the results from existing experimental results and numerical methods available in literature.

In the present paper, the effect of combined cooling, heating and power generation systems(CCHP) in the reduction of pollutants emission has been investigated and a hotel with 80 rooms in Zahedan has been selected as case study, also gas engine (with part-load operation) as prime mover for designed CCHP system. In this work it is assumed that selling electricity to grid is possible. In the first phase, optimization for access to maximum reduction of pollutant emissions has been done. In the next phase, a multi-criteria function has been introduced and the optimization process, with Percentage of Relative Annual Benefit (PRAB) has been investigated and the results of these two phases have been compared. Results show CCHP systems have significant effect in reducing environmental pollutants emissions of CO, CO2 and NOx, as the percentage of reduced pollutants emission is positive in an extensive range of nominal power of gas engine. Also, results show that, for access to maximum reduction of pollutant emissions CO2, CO and NOx, Enom,max (RCO2)=1975KW, Enom,max (RCO)=2875kW and Enom,max (RCOx)=4975kw are needed. However, for annual benefit, as multi-critria objective function, a gas engine with nominal power Enom,max(PRAB)=2050kW is needed. In this case, in addition to the most annual benefit also have a good effect for reducing emission of pollutants. In the end, the effect of the number of prime mover as designing parameter assessed with increase from one into two and three numbers. Results show increasing prime mover causes Relative Annual Benefit and emission of pollutants to decrease.

In this study the delamination behavior of FMLs loaded under mode I and II conditions is investigated by using numerical modeling and acoustic emission (AE) data analysis. Test samples were made of prepreg (glass/epoxy composite) and aluminum 2024-T3 (chromic acid anodized). Detection of delamination initiation moment is required for calculation of interlaminar fracture toughness in mode I and II which is detected by using AE technic. Initiation and propagation of delamination is modeled by Abaqus software by using cohesive element. Load-displacement curve, progressive debonding and delamination face are the results taken from FEM and are compared with test results. Signal frequency processing is done for identifying delamination propagation and classification of fracture mechanism. Delamination mechanism is validated by Scanning electron microscope (SEM) images.

In this study, generated entropy of mixed convection of Al2O3–water nano fluids in a vertical channel with sinusoidal walls under a constant and uniform magnetic field was numerically investigated. The effects of various parameters such as volume fraction of nanoparticles, amplitude of sine wave, Reynolds, Grashof and Hartman numbers were studied. This study was carried out by assuming the laminar, steady state and incompressible flow. Also, the thermo physical properties of nanoparticles were assumed constant. The Boussinesq approximation was used to calculate the variations of the density caused by buoyancy force and the finite volume method and two phase mixture model were used to simulate the flow. The results showed that the entropy generation due to heat transfer and viscous effects increased by adding nanoparticles to the base fluid. Also, the results showed that the entropy generation due to heat transfer increases by increasing the Grashof number and decreasing the Reynolds number, while a reverse trend is observed for entropy generation due to viscous effects. By increasing the Hartman number, the entropy generation due to heat transfer increases at first and then decreases and entropy generation due to viscous effects reduces. For all studied intensities of magnetic fields, the entropy generation decreases using corrugated channels.

In this study out of plane active vibration control of a laminated composite rectangular plate with intermediate line support coupled with piezoelectric patches on both sides, upper and lower surface of the plate, is presented based on First order shear deformation plate theory (FSDT). Is this study, the piezoelectric patch is used as a sensor. In the relation of piezoelectric, electrical potential in the transverse direction is earned by satisfying electric boundary conditions (open circuit) and Maxwell's electricity equation. The Rayleigh-Ritz approach is used to obtain natural frequencies and vibration mode shapes of the plate. Forced vibration response is obtained by using by the modal expansion method. In this paper, the Linear Quadratic Regulator (LQR), Linear Quadratic Gaussian (LQG) and Fuzzy Logic Controller (FLC) are used to control and reduce the amplitude of the transverse deformation of a laminated composite rectangular plate which is excited by external force. In the numerical results, the effect of various inputs, e.g. positions of the external force, on the responses of the system are examined and discussed in detail. The proposed analytical method is validated with available data in the literature.

Computer modeling of human behavior is an interesting branch in motor control science and has attracted many researchers in the neuroscience and bioengineering fields. Having a good understanding of the role of Central Nervous System (CNS) and its strategies in planning and controlling of human movements will improve the bioengineering topics such as rehabilitation protocols and sport techniques. In present research a computer simulation of CNS's performance in designing the Sit-to-Stand transfer is developed. The mentioned simulation is based on decomposition hypothesis. Decomposition hypothesis states that the CNS decomposes a complicated movement to several simpler phases. According to this hypothesis, a modular and hierarchical movement planner (MHMP) which has recently been presented is modified to describe the function of CNS in planning the Sit-to-Stand different phases under combination of different environmental conditions. The performance of the modified MHMP is evaluated with experimental captured motion. The results show that the original MHMP has a good performance in planning the motion phases under single environmental condition but it fails under a combination of different conditions, while the modified MHMP shows good performance in such cases.

In this work effect of mass diffusion on the damping ratio in micro-beam resonators is investigated based on modified couple stress theory and the Euler-Bernoulli beam assumptions. The couple stress theory is a non-classical elasticity theory which is able to capture size effects in small-scale structures. The governing equation of a micro-beam deflection is obtained using Hamilton’s principle and also the governing equations of thermo-diffusive elastic damping are established using two dimensional non-Fourier heat conduction and non-Fickian mass diffusion models. Free vibration of the micro-beam resonators is analyzed using Galerkin reduced order model formulation for the first mode of vibration. A clamped-clamped micro-beam with isothermal boundary conditions at both ends is studied. The obtained results are compared with the results of a model in which the mass diffusion effect is ignored. Furthermore, the mass diffusion effects on the damping ratio are studied for the various micro-beam thicknesses, ambient temperature and length scales parameters. The results show that in the valid region, based on Euler-Bernoulli beam theory and before the critical thickness there is no difference between the results of mass diffusion and thermo-elastic damping and also the results indicate that by increasing the length scale parameter damping ratio decreases.

The purpose of the present research is to investigate effects of long multi-walled carbon nanotubes (MWCNTs) on mechanical properties of epoxy resin and unidirectional glass fiber reinforced laminated polymeric composites. Therefore, mechanical properties of polymer (pristine resin), 0.5 wt.% MWCNT/epoxy nano-composites, E-glass/epoxy laminated composites and 0.5 wt.% MWCNT/E-glass/epoxy laminated nano-composites were evaluated. The tensile, flexural and shear moduli and strengths of epoxy polymer and nano-composites reinforced with 0.5 wt.% MWCNTs were experimentally characterized. Next, the longitudinal and transverse tensile stiffness and strength, also in-plane shear and flexural moduli and the strength of glass fiber laminated composites and glass fiber laminated nano-composites reinforced with 0.5 wt.% MWCNTs were determined. Experimental results of tensile specimens of laminated Nano composites reveal that the presence of the long MWCNTs improves the bounding properties of fibers in adjacent plies and postpones the failure mechanisms like fiber fracture under tension or edge delamination under shear loading conditions. It can be concluded that the improvement of mechanical properties in laminated composites is more significant than those of the pure epoxy with addition of long multiwall carbon nanotubes. For instance, the longitudinal tensile strength and shear strength of laminated Nano composites increased by 34% and 26% in comparison with laminated composites, respectively.

Soft tissue’s cancers are related to major variations in the mechanical properties of the tissue. In recent years, a number of developing techniques have been introduced for early detection of soft tissue’s cancers. The major advantage of these methods over the common available techniques is that, while being noninvasive to the body, the accuracy of detection is noticeably increased. This article intends to analyze mechanical behavior of the breast tissue by considering a Mooney-Rivlin hyperelastic model. Coefficients of the model are defined by using a series of experimental mechanical datasets. For this purpose, a mechanical device is designed and fabricated based on a new non-invasive method named Artificial Tactile Sensing (ATS). The device is examined on 8 patients in the age range of 20 to 50 years referred to as “Jahad Daneshgahi Breast Diseases Clinic” while considering Helsinki agreement’s protocols. Due to wide anatomical variations of the breast tissue in individuals, 40 specified regions are examined on the tissues of all attended cases. Experimental stress versus strain datasets are collected for 40 test points. To achieve a reliable and optimized model, a genetic algorithm (GA) is used for calculating Mooney-Rivlin’s coefficients. Results confirmed that an accurate model can be afforded to estimate the soft tissue’s mechanical behavior with the least error. The model is suitable for disease diagnosis and follow-up procedure.

The applications of Ti-6Al-4V alloy, due to such features as high strength to weight ratio and excellent creep resistance, is increasing in various industries. However, because of the difficulty involved in chip removal of titanium alloys by traditional methods, special machining techniques have attracted more attention. In this study, wire electrical discharge machining process of Ti-6Al-4V alloy has been investigated. The distinct aspect of this research is the consideration of various cutting heights along with the effects of 8 process parameters on the two output characteristics, namely cutting rate and surface roughness. For this, a total of 108 experimental data have been collected and, based on signal-to-noise ratios, separate optimal parameters settings were obtained for maximum cutting rate and minimum surface roughness. The optimization results have been verified against the experimental data. According to analysis of variance, pulse on-time, with 77% contribution, is the most significant parameter affecting surface roughness. While pulse on-time and machining voltage, with combined contribution of 67%, are the most effective parameters for the cutting rate. In general, by decreasing pulse on-time and peak current and increasing pulse off-time and voltage, surface rohghness and cutting rate are decreased. Finally, using multi-objective optimization and based on the relative importance of process output characteristics, technology tables for the three investigated cutting heights are presented. The results indicates that, with respect to the surface roughness and cutting rate, optimal parameters levels and their rate of impacts are affected by the cutting height.

Hybrid layered manufacturing is one of the key methods among rapid manufacturing techniques in which a layer of molten metal is deposited on the substrate and desired geometry is completed by stacking the layers. Low cost, high rates of deposition and great applicability are some of the characteristics of hybrid layered manufacturing. Welding and face milling are the two steps of the process. In welding phase, metal is built up by weld lines to cover a given surface and in milling phase weld beads are truncated to achieve a flat and integrated layer. The focus in this article is to optimize two contradictory objectives, namely reduction in machining volume and increase in deposition rate. Thus, the first task is to formulate the bead model considering the metal build-up effect. Then, the situation needed for achieving quasi-flat layers in welding phase is studied and the unified model is extracted. Moreover, GA is used to find optimum values for the proposed model based on heat and process constraints. Finally the model is verified and conclusions are drawn. This article presents a new criterion by defining the heat constraint for the multi-objective function. Results show that for the 0.8 mm wire ER70S6, optimum values are 8.6 m/min for wire speed and 0.6 m/min for torch speed that yield a deposition rate of 4224 mm3/min without violating heat constraint.

In this paper 2D numerical model is used to study the effect of depth of airway surface liquid (ASL) on the mucociliary transport. An immersed boundary-lattice Boltzmann method is used to solve the momentum equation. In this study mucus is considered as the viscoelastic fluid and Oldroyd-B model is used as the constitutive equation of it. Immerse boundary method is used to study the propulsive effect of the cilia and also the effects of mucus- periciliary layer interface. Our results show that mean mucus velocity is maximized when the PCL depth is equal to the standard value of it, i.e. 6 mm. By increasing or decreasing the depth of PCL or increasing the depth of mucus layer, mean mucus velocity is reduced. Our study also shows that mucus viscosity ratio can play an important role on the muco-ciliary clearance. It means that by increasing the Newtonian part of mucus viscosity or by decreasing elastic contribution of the mucu, mean mucus velocity increases significantly. So reducing mucus velocity results from changing ASL depth can be completely modified by increasing the Newtonian part of mucus viscosity.

Variable pitch propeller (VPP) is used in advanced helicopters in order to achieve greater efficiency, better stability and attain higher altitudes. This study assesses the behavior of VPP propeller with coupled non-linear displacement in three degrees of freedom. Accordingly, the behavior of this type of propeller with changes of elastic axis distance, length, mass, speed, polar radius of gyration, stiffness in three degrees of freedom, and pitch have been investigated. In this paper, Gallerkin method is used to extract natural frequencies and the results compared with the results reported by other researchers. The results show convergence and accuracy of the used method. In this study, it was found that parameters of mass, length and rotational speed of the propeller have an effect on the natural frequencies, and all modes of vibration. However, other parameters except for the pitch angle effect on the odd or even number of frequency modes. It was also found that the pitch angle in the static mode does not influence on natural frequencies, but in the case of rotation of propeller, affects the natural frequency of vibration modes as sine or cosine form.

The present study investigates the manufacturing process of metallic bipolar plates made of SS316L with a thickness of 0.1 mm using rubber pad forming process. Two deformation types, convex or concave patterns, were used for producing channels in bipolar plates. The effect of concave and convex patterns on forming forces and slot filling will be created in the present study and then suitable condition for both patterns of deformation will be achieved. For carrying out the experimental examination, two dies, convex and concave pattern within equal dimensions were designed and manufactured. In order to accurately compare two die patterns, a rubber pad with hardness of Shore A 85 and thickness of 25 millimeters was used for forming of plates. A hydraulic press with capacity of 200 tons was used to produce force on die. The concluded results signify that in an equal magnitude of force, die with convex pattern shows more depth of filling than concave die. By increasing magnitude forming force up to maximum limit, depth of filling in concave die will be constant and further increases in magnitude of force will cause the rubber to be destroyed.

When two bodies slide on each other the asperities are engaged and friction is created. By superposing ultrasonic vibrations to one of the bodies, the friction force is reduced .This phenomenon is widely used in metal forming and metal cutting. In this research, experimental study of the effect of ultrasonic vibrations has been on sliding friction force in longitudinal direction. For this purpose, set-up was designed and fabricated. The main components of the setup, including generators, transducers, first engaged body and second engaged body. The Set-up was installed on the machine lathe for investigation of the effect of ultrasonic vibrations on sliding friction force in longitudinal direction. The experiments were performed for eight different performance conditions. Next, the effect of each parameter ultrasonic wave velocity, roughness and material of contact surfaces were studied on the reduction of the friction force due to addition of ultrasonic vibrations. The result show that range of reduction friction force due to addition of ultrasonic vibrations in longitudinal direction is between 40 to 100% for the different performance conditions ; also, friction force significantly reduced by increasing ultrasonic wave velocity so that friction force can be brought to zero by significant increase in ultrasonic wave velocity. The results also show that friction force has a greater reduction for the surface that has less roughness. Aluminum-aluminum surfaces can acheivereduction friction force from aluminum - steel surfaces.

In this paper, modeling and feedback linearization controller for trajectory tracking of a novel sixrotor UAV (Unmanned Aerial Vehicle) is developed. Because of the very simple structure and high maneuverability, quadrotors are one of the most preferred types of UAVs but the main problem in using them is their small payload. In the proposed novel model, two coaxial propellers are added to the center of vehicle to improve the ability of lifting heavier payloads, and to surpass anticrosswind capability of quadrotor, while the dynamic and steering principle is preserved. The dynamic model is obtained via Newton Euler approach. Model is under actuated, nonlinear, and has strongly coupled terms. Also, two types of nonlinear controllers are presented. The first is a conventional input-output feedback linearization controller which involves high-order derivative terms and turns out to be quite sensitive to sensor noise as well as modeling uncertainty. The second controller is a feedback linearization based on the hierarchical control strategy that yields easier controller. To compensate actuator’s dynamic and moreover, to avoid complexity of controller, a two-stage algorithm is utilized. The obtained simulation results confirm that the performance of hierarchical controller is more convenient in terms of position tracking and disturbance rejection than conventional controller.

Recently, many researchers have considered biomass utilization due to reduction of greenhouse gas effects and environmental impact. Achieving a system with the best performance for the application of this type of fuel with low calorific value has become a topic of interest to researchers. This study focuses on precise modeling of biomass gasification and designs a trigeneration system to produce cooling, heating and electricity using this clean source of energy. The capacity of system under study in the base case is 2.18 MW electrical power, 223.4 kW cooling and 1060 kW hot water. In the process modeling of biomass gasification a realistic model including tar content in syngas is developed. A parametric study of trigeneration system to find the objective function’s trend and to achieve the best performance parameter is carried out. Results show that two objective functions in the reasonable range conflict, which indicate the multi-objective optimization. In addition, results indicate that for the studied system in the reasonable range of decision variables, the exergy efficiency can improve between 10% and 20%. Furthermore, by drawing Pareto front curve, a suitable relation to estimate the trend of objective function is derived.

This paper focuses on nonlinear dynamic analysis of a solar-powered free piston hot-air engine. First, dynamic and thermodynamic equations governing the free piston hot-air engine are extracted. Accordingly, by coupling the obtained relationships, nonlinear behavior of the free piston hot-air engine is simulated. Then, motion and velocity of the pistons in steady state condition are discussed using numerical solution of the nonlinear equations and using the phase plane analysis. Next, the stroke of pistons, maximum and minimum volumes and pressure as well as the produced work and power are studied corresponding to the change of temperatures in the hot and cold chambers. Since the damping coefficient between power piston and the cylinder wall is variable due to the temperature changes and environmental conditions, its effect on the stroke of pistons, maximum and minimum volumes, pressure, produced work and power is investigated. The results obtained clearly indicate that there is an optimal power for a certain value of damping coefficient. Then, the stroke of the pistons, maximum and minimum volume and pressure as well as the produced work and power are studied according to the changes in engine parameters such as mass and stiffness of work and displacer pistons. The ranges of variations of engine parameters are selected so that the motions of displacer and power pistons fall into a limit cycle. Finally, sensitivity analysis of the produced power is carried out considering changes in engine parameters.

In this paper, dynamics and control of a Tendon-based continuum robot is investigated. The curvature is assumed constant in each section of continuum robot. Kinematic equation is established on the basis of the Euler-Bernoulli beam. The dynamic model of the continuum robot is derived using Lagrange method. In this paper, robot control is performed in two parts: first, Dynamic model is assumed to be known and position and velocity tracking control has been achieved using the feedback linearization method; but uncertainties in the dynamic model are constantly challenged the control of continuum robots. For unknown parametric quantities such as mass coefficients, one way is to simply substitute a fixed estimate for the unknown parametric quantities. In this case tracking error is not equal to zero but it is bounded. For many applications, we cannot assume that tracking error vector is not equal to zero. In such cases adaptive controller is used. In this paper the total mass of the primary backbone and secondary backbone are uncertain parameters, therefore, a new adaptive controller is presented to estimate those uncertainties. Tracking error is asymptotically stable by using adaptive controller. Simulation results show good performance in velocity and position tracking.

Simple structure and high maneuverability of quadrotors have made them one of the most preferable types of UAVs (Unmanned Aerial Vehicle). However, the main problem is their small payload capacity. In this paper, a novel five-rotor UAV is introduced. Dynamical model of UAV and two nonlinear controllers for trajectory tracking are developed. In the proposed UAV structure an extra propeller is added to the center of vehicle to improve the ability of lifting heavier payloads and open loop stability of quadrotor. The dynamic model is obtained via Newton Euler approach. The model is under actuated, nonlinear, unstable, and has strongly coupled terms. In order to have trajectory tracking two types of nonlinear controllers are designed for the UAV. First controller is designed based on input-output feedback linearization method. This controller involves high-order derivative terms and turns out to be quite sensitive to noises and modeling uncertainty. Second controller is a back-stepping controller based on the hierarchical control strategy that yields lower computational expense. Simulation results confirm acceptable performance of back stepping controller stability, position tracking, and robustness in presence of external disturbance.

In giant magnetostrictive transducer, Young modulus of the core considerably alters with changing its magnetic level. Young modulus change in Terfenol-D core has the highest value. This effect changes the resonance frequency and mode shapes of the transducer. This subject in Terfenol-D resonance transducer is studied in this paper. For this purpose, a resonance Terfenol-D transducer has been designed and fabricated. Node locations in the transducer are considered to add pre-load and bias mechanisms. Effect of Young modulus change on resonance frequency and mode shape were studied both analytically and by ANSYS FEM software. Range of resonance frequency change in the first mode is 1000 Hz and in the second mode is 100 HZ. Mode shapes changes are limited for both modes. In 40kA/m magnetic field bias, results from analytical and FEM simulation were verified with experimental results. Resonance frequency in this bias is 3100 Hz for the first mode and 8252 Hz for the second mode. Results have acceptable agreement with experimental results. Moreover, in this bias magnetic field, impedance responses between first and second modes are compared. Results show that selecting second mode is preferable for reducing disturbance of Young Modulus change on vibrational behavior.

Control of biped robots based on the concept of asymptotical stable periodic motions has become of interest of to researchers. Potential energy shaping, one of the most significant approaches in this regard, has been presented and well evaluated on planar 2D models ,thus far. In this paper, this concept is developed and investigated for general three-dimensional case, in the presence of non-holonomic constraints. First, the considered biped model is a 3D compass gait model with finite hip width and arc shaped feet whose stable passive walking has been shown in previous researches. In this approach, the passive periodic gaits which may be adopted for a particular ground slope can be reproduced on any arbitrary ground slope such as flat surface. In fact, thanks to the invariance property of kinetic energy as well as equivariance property of collision map with respect to slope changing action, this important goal is reached only by compensating the potential energy similar to that of passive walker. In other words, inducing a controlled symmetry to the system Lagrangian, we impose a virtual gravity in a new direction resembling the gravity direction of passive walker with respect to the ground. At the end, regarding practical challenges about the implementation of arc feet model, a compass gait model with flat feet and springs at the ankle joint has been proposed instead and the aforementioned control approach is applied again. Simulation results show the effectiveness of the presented approach for both models well.

In this study, using design of experiments, the effect of hybrid graphene Nano sheets and nano clay and compatibilizer maleic anhydride- grafted- polypropylene (PP-g-MA) on the impact strength polypropylene- based Nano composites were investigated. Design of experiments and analysis of experimental data with Minitab 16 software and response surface methodology were carried out. Producing Nano composites, based on the melt mixing was performed. Statistical models provided by response surface methodology show good agreement with experimental results and with respect to the values of R-sq and R-sq (adj) are suitable. Statistical analysis showed that by increasing the percentage of nanoparticles, impact strength decreases. Compounds morphology was performed by Scanning Electron Microscopy (SEM). Micrographs showed better dispersion of the particles at lower percentages. Thermal analysis using differential scanning calorimetry (DSC) showed that the presence of graphene has little effect on the melting temperature of the sample being tested, but Tc of Nano composites compared with pure PP increased about 4 percent. Also, the crystallinity was reduced by adding graphene. In the non-graphene Nano composites, the clay did not affect the melting temperature, but the crystallinity and crystallization temperature increased 10.73% and 2.23% respectively compared with pure PP, which showed nucleation effect of nano clay.

In this paper, one-dimensional numerical optimization of lead-acid battery with finite-volume method is performed using the governing equations of battery dynamics. For validation, the present results are compared with previous studies which show good agreement. The demand for batteries with high energy and power has increased due to their use in hybrid vehicles. The major shortcoming of lead-acid batteries in industry is low energy and high weight; therefore, a cell with higher energy and lower thickness is designed by using particle swarm optimization based on developed simulation code, which is less time consuming and much faster than experimental method. The results of optimization show that an optimal battery that has 85 percent higher energy can be made with the same cell length. The results also show that an optimum cell battery can be obtained with a 25 percent decrease in weight and 23 percent in dimensions while keeping the energy content constant.

Simulation and analysis of two phase flow that crosses over tube bundles is crucial in safety analysis and design of kettle reboilers and steam generators. The geometry complexity of the tube bundle flow field increases the difficulty of the conventional numerical analysis. One of the methods to reduce the numerical calculations cost is to use the porous media theory instead of the complete tube bundle modeling. Drag and tube bundle resistance force equations have been used in the porous media analysis. Based on available experimental results, two tube bundle arrangements have been considered. Due to existence of symmetric geometry and uniform energy source over the tube bundle, the two dimensional symmetric models have been used as well. It was observed that the predicted pressure drop in this research has acceptable adaptation with the experimental results. Meanwhile, by considering different outlet boundary conditions, calculated void fraction is compared to the experimental results and showed better accuracy than similar CFD research. It was observed that the enhancement of the tube bundle thermal power increases the void fraction in the heating area of the reboiler.

In recent years considerable attention has been given to the structural application of wood plastic composites (WPCs). Regarding the WPCs lower mechanical strengths, fiber reinforcements have been applied for strengthening the WPCs. Hybrid wood plastic composites (HWPCs) include two types of reinforcements of glass fibers and wood flours that are added to a polymeric matrix. WPC pallets, as an example, can exploit the mechanical strength of HWPCs. In previous work, wood plastic composite was reinforced by continuous glass fibers using a unique extrusion process. Embedding the continuous glass fibers in WPC matrix resulted in significant improvements in mechanical properties such as tensile and impact strengths. In this paper, a model has been proposed to predict the tensile strength and modulus of the WPCs reinforced with unidirectional glass fibers. The methodology applied in this research considers the WPC as matrix and the glass fibers as reinforcements. Since WPC matrix is brittle, the rule of mixtures corresponding to the brittle matrix composites was used to predict the tensile strength. Results indicated that the predicted tensile properties were in good agreement with experimental data. The obtained mean errors between the experimental and theoretical results for tensile strength and modulus were 9.5% and 8.6% respectively.

The objective of the present work is to investigate indentation in polymers and hyperelastic materials. Both experiments and numerical analysis have been carried out. Two different sports floorings were selected to test, monolayer rubber and two layer polyurethane (PU)/polyvinylchloride (PVC). To determine the value of hardness and indentation depth of indenter in the materials, experimental study was carried out according to quality standard test for sports flooring. The numerical analysis was also conducted by Abaqus software using simulation of experimental testing conditions, selection of the best hyperelastic model and comparison of the results to experimental test in order to ascertain the efficiency and accuracy of each simulation step. The accuracy of the results has been shown by comparision of experiments with numerical results. For the first sample, indentation depth was 0.575 mm (based on experimental result) and Yeoh’s model was employed to simulate with the error of 4.3%. The indentation depth and error (by selection of reduced polynomial form of order two models) were 0.425 mm and 0.94% for the second sample (PU/PVC), respectively. In addition, hardness was decreased from 78.1 to 75.3 when the thickness of rubber sports flooring was increased from 2.5 to 5 mm. In general, it can be concluded that the hardness values of polymers depend on their thickness, and on the other hand the indenter shape has an influence on indentation depth and force-displacement curves as well.

Vortex combustion chamber is a new generation of liquid propellant engines chamber where, with the help of different arrangement of injectors, an inner combustion chamber vortex flow is created. This vortex can considerably aid cooling and increase the amount of propellant components mixing in the combustion chamber, so it makes it possible to create a complete combustion in a low- capacity chamber. In this research, a vortex chamber has been designed and manufactured for carrying out cold tests with water as its working fluid in order to study impact of different parameters including pressure drop, injector quantity and input angle, chamber diameter and the thickness of the supporting step, on the performance of this type of chamber. The designed chamber has numerous capabilities such as ease of replacement, change in pressure drop and injectors’ input angle and studying thickness of different supporting steps to create vortex flow. Since practical investigation of all parameters is not cost-effective, cold test has been conducted for some samples and both simulation and validation have been done for it. The simulation results and chamber performance in the tests matched very well; therefore, as a result of simulation assurance, the processes and other parameters in the chamber could be studied. By doing these tests we can move toward design, manufacture and test of the main vortex combustion chamber.

In the present study, an active caster mechanism is introduced which will lead to improvement of the vehicle handling characteristics. In the presented survey, a 9-DOF nonlinear vehicle model which consists of steering system dynamic equations (which were derived by means of Kane dynamics method) and also the Magic Formula tyre model are being utilized for the simulation purposes. The relevant influences of the caster angle variations on the steady state response of the vehicle were investigated at the first step of the analyses. With respect to the results which were achieved by the mentioned approach, a fuzzy logic controller (FLC) was designed for controlling the caster angle. According to the yaw rate error (which will be defined as the difference between the actual and theoretically desired values), and the vehicle lateral acceleration, the mentioned controller alters the caster angle in order to attain a stable state of the vehicle. The desired dynamic motion of the vehicle is assumed to be in the form of the steady motion of the two-wheel model. Here, it is worth mentioning that the variations of the caster angle were limited in a conventional range. During some critical maneuvers, the performance of the caster angle controller was surveyed and the outcomes were compared with the uncontrolled vehicle. The results Show that the caster variation controller provides substantial capability to improve vehicle handling characteristics.

In this paper two automated and robust algorithms for generation of unstructured grids suitable for multiscale finite volume method in oil reservoirs are presented. The multiscale finite volume method is an efficient numerical method for flow simulation in porous media. The multiscale finite volume method has been extensively studied on structured grids. In this research multiscale finite volume method is extended to unstructured grids. Development of the MSFV method to unstructured grids provides advantages of flexibility and compatibility with geological structures. In this method calculations are carried out on three grids, fine grid, primal coarse grid and dual coarse grid. One of the main challenges to extend the multiscale finite volume method to unstructured grids is to generate primal and dual coarse grids. In this paper an algorithm for partitioning of unstructured grid and generating primal coarse grid is proposed. Also, a new algorithm for generating dual coarse grid is presented. Finally, the proposed algorithms for generating multiscale unstructured grids are employed for flow simulations in porous media. Numerical results show that the multiscale finite volume method with generated multiscale unstructured grids of this research can accurately predict the fine scale solution.

In this research, a numerical simulation of liquid jet ejecting from elliptical orifices into gaseous phase with different aspect ratios at Rayleigh regime is performed. The volume of fluid (VOF) method and large eddy simulation are used to simulate the liquid interface dynamics and the jet breakup utilizing the Open Foam software. In order to simulate the axis-switching phenomenon and jet breakup length, the dynamic mesh refinement is used for all the examined cases. The results, which are validated with recent experimental and numerical works, indicate that the jet breakup length increases by raising the Weber number from 20 to about 300. Also, it is shown that the jet breakup length decreases as the aspect ratio of orifices declines from 0.66 to 0.25. Finally, it is observed that for the orifices with lower aspect ratios, jet breaks into droplets with uniform sizes with almost no satellite droplets which always present in the circular jet breakup.

Due to high hardness, low density and heat resistance, ceramics are widely used in armor applications and industry, thus, in this study perforation process of projectile into ceramic targets is investigated analytically and numerically and a modified model is developed. In the analytical section, Woodward’s theory, one of the important theories in perforation process of projectile into ceramic targets, is investigated and some modifications are applied in Woodward’s model, hence the ballistic results of analytical method are improved and the modified model shows good agreement with the experimental results. However, in the analytical section, the modified model is based on Woodward’s model and modification of semi-angle of ceramic fracture cone, erosion, mushrooming and rigid form of projectile and also changes in yield strength of ceramic during perforation process, damage is considered. In the numerical section, a finite element model is created using Ls-Dyna software and perforation process of projectile into Ceramic-Aluminum target is simulated. The results of the analytical method and numerical simulation are compared to the results of the other investigators and results of modified model show improvement in prediction of ballistic results.

Due to the necessity of access opening, inspection paths, installation, entrance and exit doors, etc, creation of cutouts on the vessel structure is unavoidable. On the other hand, composite structures and structural analysis are complex and creating cutout and imperfect structure increases this complexity. The aim of this research is to determine the mechanical response of three cutout positions on composite pressure vessels under 30 bar external pressure, so that no buckling and fracture failure occurs. Also, the optimum composite vessel thickness for this condition and cutout effect has been determined in this study. The studied vessels are made from E-Glass fiber and Epoxy matrix. Finite element simulation was used to investigate the parameters effect. For this reason, commercial ABAQUS software and linear and non-linear analysis was carried out to examine the parameters. To evaluate the simulation results, two composite vessels were manufactured and fractured under external pressure. Moreover, the final vessel with three cutouts was tested under 30 bar external pressure. The concluded results show that the optimum thickness was 16 mm for vessel with three cutouts and creating the cutouts led to decreased buckling pressure. Also, with increasing cutout size the percentage of buckling pressure increased.

Anti-lock braking system (ABS) prevents the wheels from being locked in hard braking conditions and reduces the vehicle stopping distance to the minimum value by regulating the tire longitudinal slip at its optimum value. This paper presents a two-layer controller for ABS of trucks which is adaptable with different road conditions. In the upper layer, a fuzzy controller is designed to calculate the optimum longitudinal slip of each wheel for which the maximum braking force is achieved in different conditions. In the lower layer, a nonlinear controller is analytically designed based on the predictive method to track the optimum wheel slips calculated from the upper layer. In order to increase the robustness of the controller in the presence of system uncertainties, the integral feedback technique is also appended to the predictive method. All simulation studies are conducted using the professional software of Truck Sim to evaluate the performance of the controlled system in a real condition. The results show the effectiveness of the proposed control system in improving the braking performance of trucks in different road conditions.

A novel geometrically nonlinear high order sandwich panel theory for a sandwich beam under low velocity impact is presented in this paper. The equations are derived based on high order sandwich panel theory in which the Von-Karman strains are used. The model uses Timoshenko beam theory assumptions for behavior of the face sheets. The core is modeled as a two dimensional linear elastic continuum that possesses shear and vertical normal and also in-plane rigidities. Nonlinear equations for a simply supported sandwich beam are derived using Ritz method in conjunction with minimum potential energy principle. After obtaining nonlinear results based on this enhanced model, simplification was applied to derive the linear model in which kinematic relations for face sheets and core reduced based on small displacement theory assumptions. A parametric study is done to illustrate the effect of geometrical parameters on difference between results of linear and nonlinear models. Also, to verify the analytical predictions some low velocity impact tests were carried out on sandwich beams with Aluminum face sheets and Nomex cores. In all cases good agreement is achieved between the nonlinear analytical predictions and experimental results.

Notches are one of the most common discontinuities in engineering structures that are created for engineering design purposes. Dealing with V-notches in components made of brittle materials, because of the presence of high stress concentration near the notch tip, detected cracks in this region should be removed and repaired to avoid brittle fracture. The most usual repair method is to drill a circular hole at the V-notch tip. Clearly, this hole removes the crack and changes the initial notch geometry to a V-notch with end hole. Because of changing the initial notch feature, the load-carrying capacity of the new notch would be different from the initial one. Therefore, in order to assure the safety of the repaired structure, fracture assessment of the new notch is necessary. In the present research, first, a new test specimen, called Brazilian disk containing central V-notch with end hole made of PMMA is considered for conducting fracture tests at room temperature and the experimental fracture loads are recorded. Some new test results are provided concerning brittle fracture in V-notches with end holes under mixed mode I/II loading. Then, to predict the experimental fracture loads, the strain energy density criterion is utilized. From the obtained results, it is shown that the strain energy density criterion could successfully predict the static strength of notched Brazilian disk specimens for different notch angles and various notch radii.

In this study, the numerical investigation of transient natural convection with respect to the effects of two-way fluid-structure interaction is presented in a square enclosure containing a flexible baffle. The enclosure is filled with air of Prandtl number 0.71. Temperature is constant in both hot and cold vertical walls, while baffle and horizontal walls are adiabatic. Arbitrary Lagrangian-Eulerian (ALE) formulation is used to describe the fluid motion in the given model. Non-Dimensional equations of the fluid domain with relevant boundary conditions are discretized by the finite volume method (FVM), and PISO algorithm is used to solve the pressure-velocity coupling. Non-Dimensional equations of the baffle motion are solved by the finite element method (FEM) and also the Newton-Raphson iteration technique. Rayleigh number changes over the range of 103 to 106. Among the assessed situations, 25 percent and 35 percent of them respectively, indicate increment and reduction in the rate of heat transfer compared with the enclosure containing a rigid baffle. Maximum and minimum values of Num,ss variation are 4.5 and -15.4 percent, respectively. Compared with the rigid baffle, about 90 percent of the assessed cases indicate an increase in the time to reach the steady state situations, which is not considered favorable.

Creep behavior of butt-welded joints in pressurized steel pipes operating at high temperature is one of the major concerns in industry. The creep behavior of 1.25Cr0.5Mo weldment has been investigated in this paper. Three different layers: Base Metal (BM), Heat Affected Zone (HAZ) and Weld Metal (WM) have been considered and the creep behavior of each layer has been modeled using constitutive equations. Constitutive parameters have been determined using the results of uniaxial constant load creep tests. A numerical approach based on least square method has been used to calculate optimum values of the constitutive parameters. The results have been compared with those provided in the literature for different alloys and good agreement has been observed. Creep tests have been carried out at 30, 35, 40 and 50 MPa and temperature levels of 670, 700, 725, 750 and 800oC. Specimens have been machined out from Base and Weld Metal. Since machining specimens with appropriate size from HAZ is impossible, a method is proposed to obtain constitutive parameters for this layer. This method is validated by comparing the constitutive parameters that have been calculated for WM with those obtained using creep tests. Micrographical and microhardness tests show that there are significant differences in the microstructure of the layers. Consequently, the creep behavior of layers is different. The results show that steady state creep strain rate for WM is higher than the rates for BM and HAZ; also, at low stress levels, creep strain rate of HAZ is larger than BM.