Modares Mechanical Engineering
Year:2015 | Volume:15 | Issue:8|Papers Count:51

In the present work, the elastodynamic field of the scattering of an anti-plane high frequency elastic shear wave due to an embedded nano cylindrical cavity in an infinite elastic medium is obtained by considering the effects of couple-stresses. In the theories accounting the effects of couple-stresses in their formulations, a new characteristic length of material is introduced into the formulations which enable them to capture size effect at micro and nano scale. Also, contrary to classical continuum theory which has difficulties in describing dispersion of wave at high frequencies, observed dispersive wave in experiments can be explained in the framework of these theories. In this work, the analytical expressions of elastodynamic fields around the cavity are obtained by considering equation of motion, dispersion relation and appropriate boundary conditions in the framework of two theories considering couple-stresses. Also, the dynamic stress concentration factor around the cavity within these theories is obtained, and, as a limiting case, the results of two cases of dynamic stress concentration factor in classical theory as well as static stress concentration factor in couple stress theories are recovered. In the framework of these theories, by several examples, the effects of frequency of incident wave and the ratio of couple stress characteristic length to the size of the cross section of the cavity on the displacement field, stress field and dynamic stress concentration factor around the cavity are studied, and the results are compared with the corresponding classical solutions.

In this research the designed mechanism for chasing and repousse of sheet metal is studied. This mechanism is similar to incremental sheet metal forming. In this kind of sheet metal forming, sheet surrounding is fixed and forming tool pastes the desired pattern on sheet metal incrementally. The major differences between designed mechanism and traditional incremental forming are as follows: control on the punch energy and sequence, and fixing the sheet by using protectant material behind it instead of clamping sheet sides. In this mechanism, the solenoid is used as a hammer. The plunger moves to the center of the coil while energized. Striking energy could be controlled by controlling the excitement voltage and punching sequence could be adjusted by manipulating the excitement algorithm. In this paper, the utilized solenoid is simulated. The mechanical and magnetic relations are merged for this. Flexible mesh is used to make it possible for the plunger to have movement. An experimental setup is executed to measure force on the plunger during stroke, this is used for validation. Plunger head is one important parameter affecting strike energy, thus an appropriate plunger head angle is investigated. Plunger mass is changeable, so this parameter is considered and drilled plunger is simulated. Finally, the effect of coil cover on strike energy and power is studied.

Sandwich structures have low weight and high stiffness. Sandwich panels with open and prismatic cores are kind of these structures that have special properties. These panels are named based on the number of corrugations of the core. In this paper weight optimization of these panels is carried out by Gravitational Search Algorithm based on yielding and buckling constraints. This algorithm is heuristic algorithm that is based upon the Newtonian gravity force and the laws of motion. For optimization of the weight, core and surface thickness and panel height are assumed as design variables. The results show that for specific panel, the design variables and the weight of panel are increased by increasing the load. Also the core and surface thickness are decreased and the weight and panel height are increased by increasing core corrugate number at specific loading. Also, the panels with one and two corrugates in the core, have the minimum weight and highest structural efficiency. By comparing the results with some previous studies, it is shown that the Gravitational Search Algorithm is useful tool in achieving lower weight in these panels and has good convergence rate.

In present study, the wake flow field of a submarine model was investigated experimentally in a wind tunnel. These experiments were conducted in four different locations X/L= 0.85, 1, 1.25 and 1.5 downstream of the model at Reynolds number of 3.85×105 by a five hole probe. The effect of various factors such as the variation of Reynolds number, the installation of the trip strip on the model nose surface, the mounting of the appendages on the submarine bare hull model and the nose shape effect on the wake structure were investigated in this study. The results showed that the installation of the trip strip on the nose surface did not have recognizable effects. By Increasing the Reynolds number, the amount of the dropping velocity in the wake field decreased due to the decreasing of the separation region on the after-body section. Presentation of the appendages on the model surface lead to the increasing of the wake area. The effect of the nose shape on the wake of the submarine model is the main innovation in the present work. Investigations showed that the velocity in the central part of the wake for non-axisymmetric nose shape (TANGO) decreased in comparison with the axisymmetric nose shape (SUBOFF and STANDARD).

Cold tube rolling process is one of the current seamless tube manufacturing methods. One of the serious problems of this process is micro-cracks in final product. Numerical modeling is a method to predict and reduce these micro-cracks. In the current paper, damage in cold three-roller pilger process is simulated by finite element method. In these simulations to predict damage evolution three different damage models, including Lemaitre model, modified Lemaitre model and cumulative damage model are used. In conjunction with these models isotropic and combined hardening rules are also considered. Forming benchmarks are simulated to validate provided codes for the mentioned models. Then the process is simulated and good agreement is observed between current results and previous numerical and experimental results. The results show that three models correctly predict damage distribution but predicted damage by Lemaitre model is more than modified Lemaitre model due to ignoring crack closure in compressive loads. It is also concluded that using combined hardening rule predicts damage growth less than using isotropic hardening. All of the models suggest that crack initiation takes place in the outer surface of the tube.

Frame structures have several applications in industries. They are used to carry all types of loadings. Usually catastrophic failure in these structures initiates from small cracks. Catastrophic failure can be prevented by detecting the cracks early and replacing or repairing the cracked members. The change in dynamics and vibration characteristics is one of the consequences of cracks in structures. In this work, detection of surface cracks in frame structures with regards to the change in natural frequencies of the system is studied. The finite element has been used to compute the natural frequencies of cracked structures. Then, according to the difference in natural frequencies of intact and cracked structures the locations and depths of cracks have been determined by the solution of an inverse problem. For the inverse problem the ant colony optimization algorithm has been employed. It is shown that, while the changes in natural frequencies are good means for crack detection in a separate beam, it is not sufficient for crack detection in a frame structure. It seems that, other characteristics of the system such as changes in natural modes must be considered.

In this study, experimental study of profile geometry effect on Polycrystal Diamond Compact (PDC) drill bits performance and durability was conducted. In an extensive field study, three samples of bits were chosen among NIOC bits collection. PDC bit profile consists of apex, cone, nose, shoulder and gage, all of which are effective on stability, penetration rate, aggressiveness and durability. Verification of the effect of PDC bit profile geometry needs to first determine the exact geometry. Complicated geometry of these PDC bits was obtained by 3D-scan and cloud of points. Then cutters arrangement of the profile was produced. In experimental study, field test of these bits was conducted in the same condition (WOB, ROP, fluid velocity and drilling mud weight) in Ahwaz oil rig in Asmari formation. Drilling length and penetration rate was measured and the bits dull grading based on IADC standards was determined. Results of the bits test showed the effect of profile geometry on PDC bits performance and durability. Optimization of profile geometry of PDC bits causes an increase in penetration rate, stability and durability.

An experimental procedure is used to determine the transient response of an elastomeric isolator under the impact loading conditions and a numerical procedure is developed to evaluate the corresponding acceleration transmission ratio and shock response spectrum. In the experimental analysis the elastomeric isolator is connected to a resonance beam subjected to the shock loading of a pendulum striker and the shock level is measured using acceleration sensors mounted along three orthogonal directions in the basement and free end of isolator. The shock response spectrum diagram and the level of wave attenuation are determined based on the measured acceleration levels for a wide frequency range. Finite element model based on mode superposition approach is developed to analyze the impact response of elastomeric isolator using the mode shapes with frequency in the range of impact excitation spectrum. Due to the importance of longitudinal response of isolators, the numerical model is employed to evaluate the longitudinal output acceleration time history of isolator. The number of elements, time step for motion equation integration and the number of mode shapes are studied and the optimized corresponding values are selected based on the convergence of the numerical results. The calculated results for wave attenuation level and shock response spectrum diagrams correlate well with the experimental measurements under two different impact loading conditions and the present model can be used to evaluate the performance of isolators depending on the level of impact loads, transmission acceleration and displacement ratios in the output of elastomeric isolators.

Identification and classification of signals which are heard by underwater microphones (hydrophones) can be used extensively in harbor traffic management, especially in economical harbors. However, automatic identification and classification of acoustic signals which are received by passive sonar system is a challenging problem, because of variation in temporal and frequency characteristics of signals (even they are received from a same source). In this paper, a novel method for classification of acoustic signals is presented, based on DWT as preprocessing, a diverse range of feature extraction methods (principal component analysis and its variations (6 methods) and discriminant analysis and its variations (3 methods)), and 4 ensemble learning methods with 3 classifiers (multilayer perceptron (MLP), probabilistic neural network (PNN) and support vector machine (SVM)). Performing a diverse range of performance tests, the performances of different methods are assessed and the best ones are chosen for the proposed method. The proposed method is used to extract features and classify acoustic signals of 8 ships. Using the proposed method, some real signals and their noisy version are classified. The accuracy of the proposed method in classification of test signals with Gaussian white noise with -5, -10 and -15 signal-to-noise ratio is obtained as 99.83%, 97.06% and 83.56%, respectively.

Despite the fact that fiber reinforced plastic composites have excellent mechanical properties, various failure mechanisms can still occur in these materials. Delamination is the most common failure mode in laminated composites that can occur under quasi-static and fatigue loading conditions. The present study is concerned with the investigation of mechanical and Acoustic Emission (AE) behavior of delamination in glass/epoxy composites under mode I quasi-static and fatigue loading conditions. First, the unidirectional and woven specimens were subjected to mode I quasi-static loading. The behavior of the delamination in the specimens was investigated and interlinear fracture toughness of the specimens was calculated. Then, according to the information obtained from quasi-static loading, similar specimens were subjected to the fatigue loading. The mechanical and AE behavior of the delamination under fatigue loading was investigated. A linear relationship was established between cumulative AE energy and fatigue crack growth and fatigue crack growth curve was predicted using the AE method. Then, energy release rate variations curve and fatigue crack growth rate diagram were predicted using AE method. The predicted results by AE have good compatibility with the visually based data that is recommended by the standard. The results indicate that, the AE method has good applicability for health monitoring of composite structures subjected to quasi-static and fatigue loading conditions.

In this paper the mixed convection and entropy generation in square cavity filled with Al2O3-water Nano fluid with the presence of constant axial magnetic field, is analyzed. The upper and bottom walls are adiabatic. Discretization of the governing equations were achieved through finite volume method and solved with SIMPLE algorithm. In this research the effects of the Rayleigh number (103-106), Hartmann number (0-100) and also inclination angle (0-90o) are investigated. When the cavity is rotated, it is observed that the mean Nusselt number and total entropy generation increase when the Rayleigh number increases in cavity. In square cavity, regardless of the Ha number, by increasing of the inclination angel, the mean Nusselt number and entropy generation rate, increase until inclination angel 30o, then decreases. Also when the magnetic field is rotated, it is observed that the mean Nusselt number decrease when the Hartmann number increases. The mean Nusselt number when the cavity rotates with specific inclination angel is less than state that the cavity rotates with specific magnetic field. For finding optimum condition of heat transfer, Artificial Neural networks (ANN) were used. The results from optimization show that as the Rayleigh number increases, the optimum angel decreases. Whatever the Rayleigh number more increases, the decrement in optimum angel more intenses. Also in low the Rayleigh number, as the Hartmann number increases, the optimum angel decreases firstly then increases. In high Rayleigh number, as the Hartmann number increases, the optimum angel increases too.

Phenomenon of dispersion and deposition of nano- and micro-particles in turbulent flows have been focused on in the past decades. In this paper, particle dispersion and deposition in gasparticle two-phase turbulent flow inside two-dimensional channel with rectangular artificial roughness is studied using an Eulerian-Lagrangian method. The RSM turbulence model with enhanced wall treatment was used to simulate the anisotropic turbulent gas phase flow. The gas phase flow predictions were validated by comparing the results with available experimental data for fully developed asymmetric turbulent channel flow. In discrete phase, Lagrangian approach was applied for particle tracking. The Lagrangian equation of particle motion includes drag, gravity, Saffman lift, and Brownian forces. The particle phase simulation results were validated by comparing the present work with available equations and valid data for gas particles turbulent flow inside two-dimensional smooth channel. The gas phase simulation results show that by increasing the artificial roughness height, recirculation region that is created in the space between two ribs, becomes larger. The particle phase results show that the rate of deposition in the channel with artificial roughness is function of gravity force and flow pattern in the mentioned space. The rate of deposition for small particle is affected significantly by gas flow pattern in the space between two ribs. However, for large particles the gravity force is more dominant.

Inconel 625 is nickel-based super alloy that is widely used in power plants industry, aerospace systems, and mineral industries due to its properties such as high tensile strength, high corrosion resistance and excellent fabric ability. Resistance spot welding (RSW) is one of the important joining processes for assembling super alloy sheets, due to its accuracy and high production rates. In the present research, the influences of electrode tip diameter and other RSW parameters on distribution of temperature and nugget formation are investigated by the finite element method for Inconel 625 superalloy. The process is simulated with 2D axisymmetric coupled electro thermal and uncoupled mechanical finite element model by ABAQUS software. The diameter of computed weld nuggets is compared with experimental results and good agreement is observed. So, FE model developed in this paper provides prediction of quality and shape of the weld nuggets and temperature distributions with variation of each process parameter suitably. The results show that increasing electrode tip diameter decreases weld nugget diameter in constant welding current, but in general, the electrode tip diameter cannot be selected less than distinct value.

Cold roll-forming is process by which metal sheet will obtain its required section form by being passed through series of rotating rollers. The pre-notched sections have frequent usage in different industries. The problem with these products is the deformation of the holes after completion of the forming process. Also, there are problems like edge waves, buckling, bending, distortion of the holes, etc. In order to analyze and predict the important parameters in deforming the ellipsoidal holes during the cold roll-forming of U-channel section, three-dimensional model with finite element has been taken into account. The effective parameters of forming the Uchannel section with pre-notches such as the minor and major hole diameter, hole spacing, the distance of holes from the flange edge, thickness and the material were intended. Furthermore, by usage of response surface methodology, the set of tests were designed. Afterward, set of out-put parameters such as: edge buckling, the wave of the holes, the change of the hole spacing size, the change of the distance of the holes from the flange edge, and the change of the hole size were considered. The output parameters were measured and the chart of experiment design was completed. Then, by applying ANOVA, the accuracy of the statistical results was obtained. Also, by comparison of the results with experimental study, the accuracy of the simulated models was analyzed. Finally, the effect of the significant parameters has been extracted both in statistical form and mathematical functions.

The importance of pollutant control and shortage of fossil fuel reservoirs have caused the development of injector systems and researches on optimum fuel consumption of internal combustion engines. The main purpose of this work is to study the effect of fuel injection start angle on engine performance features such as indicated power, exhaust emissions (CO and HC), ignition delay and fast burn length in single cylinder port injection SI engine using gasoline and natural gas individually as fuel. Injection period, ignition timing, engine speed and throttle plate position were fixed and start angle of injection (SOI) was varied. The obtained results show that higher indicated power and lower CO emission are achieved when SOI is adjusted so that the injecting fuel and flowing air are entering simultaneously into the cylinder; however, higher unburned HC emission is resulted at the condition. Heat release rate analysis was used to evaluate ignition delay and fast burn length. The results show that the lowest ignition delay happens when the SOI is adjusted so that the part of injected fuel at the late intake stroke is higher; and the fast burn length is decreased as both injecting fuel and flowing air are entering into the cylinder during the injection period.

A New approach of retrofit design methodology in cogeneration heat and power systems based on constructal theory is presented in this paper. A cogeneration system may consist of different turbines, steam levels and steam generators. The steam demand of each level is determined and should be supplied. The purpose of this paper is to retrofit the existing total site heat and power cogeneration system utilizing the concepts of constructal theory. Developing constructal theory to total site cogeneration systems may lead to dividing the total site into different constructs. In this paper the total site cogeneration system will be divided into three constructs: turbines, turbine array between each two levels and steam generators array. Using constructal theory simplifies the total site complex system to simpler system that can be solved easily by simple search and sort method. The best configuration of the total site would have the minimum operating cost. Using constructal theory would simplify the optimization procedure of cogeneration systems in addition to reach better conceptual design, especially in more sophisticated systems. The methodology is applied to sophisticated total site heat and power cogeneration system as case study from literature. The constructal retrofit results in 14.1% and 14.3% reduction in operating cost and fuel consumption respectively.

In order to utilize robots for industrial tasks, designing suitable path is necessary. Executing the path in the presence of obstacles makes the path planning task difficult one. In addition, path planning is time consuming task and needs expertise to define certain path for each industrial job. In this paper, by use of Jerk-minimum method, B-Spline curves, via-point, and obstacle avoidance algorithm are used to automatically generate suitable and safe path for simulated 7 degrees of freedom industrial manipulator. A user determines via-points for robot trajectory using Kinect sensor then employing combination of Jerk-minimum method and B-Spline curves, path is generated. This path is checked by an obstacle avoidance algorithm, and final path is generated. The obstacle avoidance algorithm uses the inverse kinematic equation of the robot to modify the robot trajectory. One advantage of the proposed method is it facilitates trajectory planning for the user and creates smooth trajectory for the robotic arm.

Taguchi method has been used since 1980 as an effective way to optimize the design process engineering tests. In this paper, optimal conditions of the mixed convection and entropy generation in square cavity filled with Cu-water nanofluid is analyzed using Taguchi method. For this purpose an L16 (43) orthogonal Taguchi array is used. Discretization of the governing equations was achieved through finite volume method and solved with SIMPLE algorithm. The effect of Richardson number (0.1-100), the volume fraction of copper nanoparticles (0-10%) and the wavelength of the wavy surface (0-1) as effective parameters for analysis in four levels are considered. This analysis was performed for fixed Grashof number 1.4. The results show that the mean Nusselt number decreases by increase of the Richardson number, the volume fraction of nanoparticles and the wavelength of the wavy surface. It is found that the Flat plate (for wavy surface with the wavelength 0) and the volume fraction 0% in the Richardson number 0.1 is optimal design for heat transfer while the geometry with f=5%, Ri=100 and l=0.25 is optimal design for entropy generation. Finally for maximum heat transfer and minimum entropy generation the geometry with f=0%, Ri=1 and l=0.25 can be considered as an optimal design.

Effects of secondary sonic jet injection in divergent part of supersonic nozzle on flow field structure and thrust vector control performance has been numerically analyzed. Three dimensional multi-blocks extended numerical code has been used to model the complexity of turbulence flow by k-w SST model. Structured computational domain has been applied and the initial results of simulation were validated by the previous experimental result. Different injection power is generated by varying the injection surface and pressure ratio with respect to throat pressure. Injection power increment causes changes in performance and sometimes lowers it. In the current research, aside from description of complete complex flow features, allowable power range to increase system performance has been presented. In this range, increasing the injection mass flow rate decreases the amplification factor, but increases the deflection angle and axial thrust augmentation as the most important performance parameters. Out of estimated range for allowable mass power injection performance parameters behave differently, which demonstrates drastic drop in performance.

Development and application of high-speed underwater vehicle is the motivation for many researchers to consider super-captivating flows. Frictional drag decreases and vehicle’s velocity increases due to cavity generation. The objective of the present research is to find the coefficients of relation to estimate cavity length around submersible vehicle equipped with wedge-shaped cavitator-which has important practical applications. For this purpose, the super cavitation phenomena has been simulated numerically around three bodies with different geometry. In the first stage, to validate the results of numerical simulation of present work well established experimental result of cylindrical body with hemispheric cap is used for comparison. This comparison is used for parameters effecting numerical method, turbulence flow model and mass transfer model. As this comparison is confirmed, the simulation is continued in the second stage for super cavitation phenomena initiation around wedged-shaped cavitator with three angles of 15 and 30 and 45 degrees. Inthe third stage, the super cavitation flow is analyzed around submersible body equipped with wedged-shaped cavitator. The cavity length and related coefficients are obtained for three cases using different cavitation numbers. The developed equation is similar for all cases with different coefficients. The averaged Navier-Stokes equations are solved in transient case using finite volume method.

Regarding the progress in technology and increase in the capabilities of the robots, one of the main challenges in the field of robotics is the problem of real-time and collision-free path planning of robots. This paper focuses on the problem of path planning of 3-DOF decoupled parallel robot called Tripteron in the presence of obstacles. The proposed algorithm is synergy-based algorithm of convex optimization, disjunctive programming and model predictive control. This algorithm has many advantages compared to previous methods reported in the literature including not getting stuck in the local optimums and finding the global optimum and high computational speeds. Finally, the algorithm will be implemented on model of the real robot. It should be mentioned that this algorithm has been implemented using Gurobi optimization package with C++ programming language in Qt Creator environment and the simulation of the parallel mechanism is performed by the CAD2MAT package for MATLAB. Obtained results reveal that the maximum computational time at each step is less than one second which, for this particular application, could be regarded as real-time algorithm.

In this paper, an optimal active controller is designed to prevent the shimmy vibrations in aircraft nose landing gear. The controller is designed according to the linearized system while the input is implemented on the real non-linear plant. Shimmy vibration is the lateral and torsional vibrations in the wheel that is self-excited and causes instability in high speed performances. This phenomenon is highly impressive since this malfunction over long period of time can damage the landing gear of the aircraft, its fuselage and can even harm the passengers. Thus, control and suppression of this vibration is extremely important. In this paper, using the nonlinear dynamics of the nose landing gear system, the equivalent linearized system is extracted and then its related linearized state space is derived. Stability, controllability and observability of the system are investigated based on the linearized model of the system and damping the shimmy vibrations is performed with the least amount of consumed energy using Linear Quadratic Regulator (LQR). To estimate the states of the system which are not measurable using ordinary sensors, an observer is designed and implemented using separation principal. To verify the performance of the proposed controller, vibration response of the open loop system is compared with the closed loop response of the designed optimal controller. Considerable improvement can be seen in the performance of the closed loop system since not only are the vibrations effectively damped but also the consumption of energy is minimized. Finally, digital control system is extended in order to implement the proposed controller on the discretized model of the system and the effect of sampling rate on the accuracy of the system is studied.

Trajectory tracking is one of the main control problems in the context of Wheeled Mobile Robots (WMRs). On the other hand, control of under actuated systems possesses particular complexity and importance; so it has been the focus of many researchers in recent years. In this paper, these two important control subjects have been discussed for Tractor-Trailer Wheeled Mobile Robot (TTWMR), which includes differential drive wheeled mobile robot towing passive spherical wheeled trailer. The use of spherical wheels instead of standard wheels in trailer makes the robot highly under actuated and nonlinear. Spherical wheels have been used for the trailer to increase robots’ maneuverability. In fact, standard wheels create nonholonomic constraints by means of pure rolling and nonslip conditions, and reduce robot maneuverability. In this paper, after introducing the robot, kinematics and kinetics models have been obtained for the system. Then, based on physical intuition new controller has been developed for the robot, named Lyapaunov-PID control algorithm. Then, singularity avoidance of the proposed algorithm has been analyzed and the stability of the algorithm has been discussed. Simulation results reveal the suitable performance of the proposed algorithm. Finally, experimental implementation results have been presented which verify the simulation results.

In the current study, the streamline simulation technique is used for definition of new objective function to optimize the production rates during water injection process. The streamline simulation technique, in comparison with common numerical methods for simulation of multi-phase flow in porous media, is much faster with less computational memory requirement. This method represents the key parameter of “Time of Flight” which helps to consider complex heterogeneity of porous media in an easier way. In order to optimize oil production rates from reservoir, function based on averaged time of flight has been introduced in which minimization of this function can be used to have uniform fronts of water for flooding of oil. For this target, two optimization techniques, the Artificial Bee Colony (ABC) and the Sequential Quadratic Programming (SQP) method are employed to optimize the objective function and their results are compared. Advantages and disadvantages of these two methods are investigated and based on their advantages, new hybrid approach is proposed which utilizes the benefits of both techniques to converge to the optimum solution. In the hybrid approach the SQP algorithm is initialized with the ABC method. In order to validate the mathematical model, 2D homogeneous model is used for optimization. Next 2D heterogeneous model and 3D complex reservoir model are investigated. In all the mentioned problems, it is observed that the hybrid approach, in comparision with the two other methods, can approximate the optimum point with approximately 15% higher speed.

In this paper, the heat transfer enhancement by the nanoparticles in the film condensation of Nano fluid over cooled plate is studied numerically. Shooting method and modified-Euler scheme are employed to solve the condensation boundary layer equations. The effect of changes in the plate angle, Nano fluid type, volume fraction of nanoparticles and Jacob number, on the velocity and temperature profiles and Nusselt number are investigated. Resulting graphs are compared and validated with the available theoretical results for the base fluid and Nano fluid. The results show that the presence of nanoparticles in the liquid film of condensation increases the heat transfer from it. As the plate distances from the vertical position, the temperature change across the boundary layer is close to linear and thus, the heat transfer descends. Also, it can be seen that the average Nusselt number is almost constant up to the angle of 20o, and then reduces in gradual manner, so that for instance, for water-TiO2 Nano fluid, by increasing the angle up to 60o, the temperature gradient is reduced by about 20 percent. Furthermore, it is seen that the relationship between the ratio of Nano fluid to pure water Nusselt number and the nanoparticles volume fraction is linear, while the slope of the line for water-Cu and water-Ag is higher than other studied Nano fluids, i.e., these two Nano fluids are more effective in heat transfer enhancement. The obtained results also confirm the fact that the Nusselt theory is only applicable in low Jacob numbers.

Today, the demand for joining dissimilar metals of aluminium and steel to reduce the vehicle weight in the automotive, aerospace and shipbuilding industries has witnessed rapid growth. In the present study, 5083 aluminum alloy was joined to galvanized steel and plain carbon steel with 4043 and 4047 filler metals by using the welding-brazing hybrid method. The brittle intermetallic compound (IMCs) layer formed in the interface of steel-weld seam was found to have significant influence on the joint strength. The results also indicated that increasing heat input enhanced the thickness of IMCs layer. The thickness of IMCs layers, as measured from microstructural images, was in range of 2-6 mm. Further, the results obtained from microstructural observation showed that with equal weld heat input, the thickness of IMCs layer for the joint produced with 4047 filler metal was approximately half of that obtained for the joint produced with 4043 filler metal. The highest mechanical resistance (of about 170 MPa) was obtained for aluminum to galvanized steel joint with 4047 filler metal. Moreover, in this joint, the failures occurred in the welded seam and for aluminum to plain carbon steel joint, it was in the interface of steel-weld seam. The results obtained by Energy dispersive x-ray spectrometry analysis of IMCs layer for aluminum to galvanized steel joint showed the presence of the FeAl3 intermetallic compound. This was confirmed by x-ray diffraction analysis of the fracture plane.

The present paper investigates turbulent flow of film cooling on model turbine blade leading edge using two scale-resolving attitude of turbulent flow modeling. In the first attitude the detached eddy simulation (DES) approach based on Spalart-Allmaras and in the second attitude the large eddy simulation (LES) approach will be used. Results show that the DES approach due to its hybrid nature and applying RANS models in near walls, predicts the Fluctuations of span wise direction in coolant pipe lower. As result, the coolant flow imports to the main flow with lower turbulence. Also DES approach predicts less turbulent kinetic energy lateral distribution and further turbulent heat flux in near walls. So, in DES approach the adiabatic effectiveness on turbine blade leading edge predicted lower than LES approach and experimental data. In addition, results show that mixture of coolant jet and mainstream hot gas in DES approach is estimated lower than LES approach. In total, it can be deducted that although DES approach provides acceptable results in far wall region, but in near wall region it has problems in correct prediction of turbulence Specifications. In addition, the main advantage of DES approach in comparison with LES approach is 40% reduction of computational cost that can explain using this approach.

One of the major subsystems of each airplane is landing gear system which must be capable of tolerating extreme forces applied to the airplane during landing. Using conservative techniques to find landing loads result in overestimation and unnecessary extra structural weight. New commercial softwares can simulate real landing conditions with acceptable accuracy if detailed mechanical data about landing gear system subparts are provided. Although these softwares work well but due to lack of detailed information about the subparts at the conceptual design phase, complexity and time consuming of modeling, expensive license price, etc. they do not seem to be the best choice for design purpose. In this study, in order to calculate landing loads more precisely than the estimating conservative methods, flight dynamic differential equations of an airplane during landing phase are derived and through numeric and state space techniques are solved for different initial conditions including, three point landing, two point landing and one wheel landing. Each landing gear of the airplane is modeled as two-degree of freedom mass-spring damper set. Time history of the airplane center of gravity, pitch and roll angle, vertical landing loads of each landing gear and their spin-up loads for different landing types (different initial conditions) are obtained to show capabilities of this new, fast and accurate landing simulation code, generated.

In this paper, modeling and design of trajectory tracking control system for novel multi-rotor UAV (Unmanned Aerial Vehicle) is developed. The UAV is similar to quadrotor with an extra no feedback propeller which is added to center of vehicle. The additional rotor improves the ability of lifting heavier payloads, and anti-crosswind capability for quadrotor. For validation, the dynamic model is obtained via both Newton Euler and Lagrange approaches. The dynamical model is under actuated, nonlinear, and has strongly coupled terms. Therefore, an appropriate control system is necessary to achieve desired performance. The proposed nonlinear controller of this paper is an input-output feedback linearization companioned with an optimal LQR controller for the linearized system. The controller involves high-order derivative terms and turns out to be quite sensitive to un-modeled dynamics. Therefore, precise model of UAV is derived by considering actuator’s dynamics. To compensate the actuator’s dynamic and moreover, to avoid complexity in the controller, second control loop is utilized. The obtained simulation results confirm that the proposed control system has promising performance in terms of stabilization and position tracking even in presence of external disturbances.

In this paper method has been developed to obtain an optimum material distribution for cylindrical shell with Functionally Graded (FG) material and additional piezoelectric outer layer. The objective of the optimization is to satisfy full stress loading criterion. For this purpose, firstly, solution method has been outlined in which the governing equations are developed by combining First order Shear Deformation Theory (FSDT) and Maxwell equations, with the use of Hamilton principle. Dynamic analysis is major concern in this solution method because of the significant dynamic displacements, strains and stresses due to the effect of moving load. Hence, the time dependent transient responses of the structure and stress distribution have been obtained. In the next stage, methodology has been introduced to obtain the optimum material distribution. In this method, instead of using pre-assumed material distribution functions which impose limitations to the manufacturing of the shell and also to the optimization solution, control points with Hermite functions are used. The thickness of the shell and volume fraction of the FG material at these points have been regarded as optimization variables. The optimization method is based on the genetic algorithm and to reduce the solution time, calculations are carried out using parallel processing in four cores. The results show that the developed method is capable of analyzing the FG structures and provides optimum solution. The major advantage of this method is its flexibility in providing volume fraction distribution of the material.

Due to the importance of acoustic response control of submerged vibrating structures, in this study, the optimization of acoustic power radiation from square stiffened plate under harmonic loading was investigated. Since one face of the plate is in contact with water, fully coupled analysis was used. The effect of fluid in the analysis was considered via added mass matrix. The added mass matrix was obtained based on both Rayleigh integral and the boundary element approaches. The obtained added mass matrix was then added to the mass matrix of the structure calculated from the finite element discretization of plate. Several variables such as acoustic pressure at specific points and also radiated power were calculated. Results show good agreement between obtained results from the Rayleigh integral and the boundary element. To reduce the radiation power, dynamic absorbers in the form of lumped mass and mass-springs in specific locations on the plate surface were considered. Because optimization procedure requires several evaluations of cost function in the design variable space, model reduction can save great amount of computational effort. Therefore, the truncated modal matrix was employed and its effectiveness and precision on the obtained results were studied. Finally, Genetic Algorithm (GA) was used for minimizing the appropriate goal function in three case studies: concentrated mass on cross-points, dynamic absorbers on cross-points and combination of two former cases. All the studied cases resulted in significant reduction in the goal function index.

The panel flutter is concentrated with aerospace researchers because of fatigue failure on structures. The usage of the numerical simulation is in good company with analytical method. The 2D cylindrical panel flutter is simulated with Navier Stokes equations for fluid flow with finite volume theory. Also, simulation is prepared with piston theory for analytical solution of irrotational fluid. Comparison of full numerical finite volume and assumed mode method in post flutter domain is produced. Non-linear shell with the effect of in-plane load, thermal load and aerodynamic load with 3rd order piston theory is modeled to solve with assumed mode method. The effect of camber in flutter and post flutter is investigated with both methods. Pressure distribution is defined numerically and analytically for viscid and inviscid flow. The effect of expansion waves decreased the pressure of the second half of shell in analytical method compared to numerical. The principle of Hamilton is used and virtual work, virtual potential energy and virtual kinetic energy are developed. The 4th order Runge-Kutta method is used to solve nonlinear ODEs numerically. The most important output depends on similar result for flat plate and different result on curved plate with numerical and analytical solution.

There are many researches on the vibration behavior of the multi-phase flow in the pipes. However, there is no general statistical study on the dynamic response of such systems. Therefore in this paper, at first, the nonlinear equation governing the transverse vibration of the pipe is derived using the Hamilton's principle. The nonlinearity in the system is induced by considering large deflections. The interaction between the pipe and the multi-phase fluid flow and the resultant uncertainty is modeled by random excitation which is produced by using normal distribution function. After extraction of the governing equation and discretizing it by the Galerkin method, the equations are solved numerically. The statistical parameters of the response have been extracted by Monte-Carlo simulation. With studying on the deflection of one point on the pipe and also considering corresponding upper and lower limit band (confidence interval), extended results of uncertainties effects have been obtained. The results show that with increasing the velocity of the fluid, the uncertainty of the response is increasing. Also, by considering nonlinear model, the probabilities of failure are increased.

Using the soft fingers increases stability and dexterity in object grasping and manipulation. This is because of the enlarged contact interface between soft fingers and object. Although slippage phenomenon has crucial role in robust grasping and stable manipulation, in most of the previous researches in the field of finger manipulation, it is assumed that the slippage between finger and object does not occur. In this paper, slippage dynamic modeling in object grasping and manipulation using soft fingers is studied. Because of the enlarged contact interface between soft fingers and object, frictional moment along with tangential frictional force and normal force is applied on the contact interface. Therefore, novel method for dynamic modeling of planar slippage using the concept of Friction Limit Surface is presented. In this method, equality and inequality relations of different states of planar contact are rewritten in the form of single second-order differential equation with variable coefficients. These coefficients are determined based on the slippage conditions. This kind of dynamic modeling of contact forces can be used for designing the controllers to prevent the undesired slippage. The method is used in study of slippage analysis of three-link soft finger manipulating rigid object on horizontal surface. In order to increase the accuracy of dynamic modeling of soft finger, dynamics of soft tip is integrated with the dynamic of finger linkage. Dynamic behavior of this system is shown in the numerical simulations.

In this paper, by expanding Muskhelishvili’s stress functions and with use of Schwarz’s alternating method, the stress distribution in plate with two quasi-rectangular cut outs has been studied. Muskhelishvili presented the mentioned stress functions for studying the stress distribution in an isotropic plate with circular or an elliptical cut out. In order to expand the Muskhelishvili’s analytical solution for deriving the stress functions related to quasi-rectangular cut outs, conformal mapping function has been used. This conformal mapping transformed the area external to the quasi-rectangular cut out into the area outside the unit circle. Considering Schwarz’s alternating method, for calculating the stress distribution around two cut outs, complex series with unknown coefficients have been used. In this study, the effect of different parameters such as the location of the cut outs relative to each other, bluntness and aspect ratio of cut out sides on stress concentration factor can be investigated. The finite element method has been used to verify the accuracy of semi-analytical results. Comparison of two methods demonstrates the precision of obtained semi-analytical solution and indicates that it can be used for computing stress distribution in plates with two rectangular cut outs. Analysis of the proposed solution shows that the mentioned parameters have significant effect on stress distribution and stress concentration factor decreases noticeably with selection of appropriate values of these parameters.

In the present paper, the shape and position of internal cooling passages within an axial turbine blade have been optimized to achieve uniform temperature distribution with the minimum cooling air flow while the maximum temperature is below the allowable value. Four cooling passages are made within the blade. The cross section shape of each passage is parameterized using new method based on an 8-order Bezier curve. This curve, which is represented in terms of Bezier control points, has much flexibility and can produce large variety of shapes. The shape of the blade surface profile remains unchanged during the optimization process. The numerical simulation has been carried out using conjugate heat transfer method to predict the temperature distribution in both solid and fluid regions and semi-empirical relation is employed to evaluate the heat transfer coefficient for internal cooling passages. The multi-objective optimization is performed for NASA C3X blade through the Fluent/Gambit packages coupled with differential evolution (DE) optimization algorithm. The cooling passages shape generated during the optimization process shows that the present method of shape parameterization produces fairly smooth and realistic geometries. The optimization outcomes are given as Pareto front.

The analysis of notched composite parts in structure due to the existence of high stress concentration and undetermined behavior is an exigent issue. In this research, the progressive damage analysis has been applied to predict the failure of notched woven glass-epoxy composite laminates under tensile loading. Stress analysis and investigation of the effect of the hole size on it have been performed by the analytical and numerical methods. Developing UMAT in the ABAQUS finite element package has made the utilization of the 3D progressive damage analysis feasible. Max. Stress, Yamada-Sun and Tsai-Wu failure criterions have been implemented to predict the damage initiation due to the absence of significant failure criteria for woven composites. Instantaneous and recursive property degradation methods have been used to simulate the damage propagation. The tensile characteristic distance has been computed without any experiments. The comparison of stress and failure analysis with experimental results shows good agreement. Finally, using tensile characteristic length obtained by progressive damage method, the possibility of safety factor determination in the composite joints for optimum design has been provided.

In this research an inverse design algorithm, called ball-spine algorithm (BSA) is developed on 90-degree bend duct between the radial and axial diffuser of centrifugal compressor with viscous swirling inflow to bend duct. The shape modification process integrates inverse design algorithm and quasi-3D analysis code. For this purpose, Ansys CFX software is used as flow solver and inverse design algorithm is written as code inside it. Shape modification is accomplished for viscous and inviscid flow to check the effect of viscosity on convergence rate. Also, the effect of swirl velocity in shape modification process is investigated by considering increased pressure as the target parameter. The algorithm reliability for swirling flow is verified by choosing different initial geometries. Finally, aerodynamic design of the bend duct with BSA is accomplished to reduce losses in 90-degree bend. Shape modification process is carried out by improving the current wall pressure distribution and applying it to the inverse design algorithm. Results show that convergence rate and stability of BSA are favorable for designing ducts with swirling viscous flow. So the pressure recovery coefficient of the 90-degree bend duct is increased 4%.

In this paper, the spacecraft formation flying using virtual structure algorithm is studied. In spacecraft formation flying, several small spacecraft have been used instead of employing single one to achieve the same goal. In virtual structure method, the position and orientation of each spacecraft is measured with respect to position and attitude of virtual node in every moment. Two robust control methods are proposed to control formation. At first, the robust m synthesis control method is used to attenuate the influence of the sensor noises, environment disturbances and parametric uncertainties but it is done with heavy computations. The second method is in the standard form of optimization problem. It is composed of state feedback controller and Lyapanov stability theory. The Linear Matrix Inequality (LMI) controller computations are very efficient and the controller is robust against parametric uncertainties and most of the disturbances. The implementation of control methods on virtual node guarantees robust stability and performance. Concerning actuator constraints, simulation example is provided to show the effectiveness of the proposed control schemes to track the desired attitude and position trajectories despite system uncertainties.

In the present study, in order to investigate the effect of impact angle and sand jet pressure on the erosion rate and residual stress in sand molding operation, the experiments are performed using gray cast iron (GCI), pearlitic ductile iron (PDI) and austempered ductile iron (ADI) as workpiece materials. To fulfill this objective, experimental tests are conducted in full factorial design with workpiece material, impact angle and jet pressure as input and erosive wear rate and residual stress as output parameters. According to the results, variation of impact angle of erosive particles intensively affects the erosion rate of materials in way which, among the experiments that are carried out in lower impact angles (15 to 30o), ADI cast iron shows the maximum erosive strength; however, as the impact angle shifts to higher values (75 to 90o), PDI cast iron becomes more resistant against erosion. It can also be noted from the SEM images that in sand shooting process, the presence of flake graphite in gray cast iron causes more formed and grown cracks which significantly intensifies its erosion rate relative to ADI and PDI cast irons. Additionally, comparative analysis of results revealed that formation of surface micro cracks in gray cast iron material causes less induced compression residual stresses relative to ADI cast iron whose great stiffness leads to higher magnitudes of compression residual stress in sand molding operation. In addition, it is observed that regardless of employed material, increase of erosive particles shooting pressure increases erosion rate of the workpiece.

Nowadays the forming limit curves are very useful in formation of metal sheets and the effect of yield criteria is one of the most important parameters in prediction of the limit strain, especially in anisotropic aluminum sheets. In this paper, first the effects of advanced BBC2008, Soare 2008, Plunkett 2008 and Yld2011 yield criteria on limit strain calculation and then on forming limit stress diagram will be investigated. Plastic instability model is studied based on Marciniak-Kuczynski model and the non-linear equations are solved by using Newton-Rophson method. These functions are used to evaluate the limit forming predictability of AA2090-T3 aluminum sheet based on the Swift hardening law and are compared with the forming limit curves predicted by Hill’s 1948 classic yield criterion. It was observed that the classic yield functions are not appropriate for anisotropic aluminum sheets forming estimation. Numerical results obtained from the forming limit diagram for AA5754 with Plunkett2008 yield function and Swift hardening law, although confirm the experimental results at close range to plane strain case, CPB06ex2 yield criterion predicts the behavior of anisotropic aluminum sheets. The limit strain prediction for AA3104-H19 using Yld2011 yield criterion and Voce hardening law show better conformity with experimental results.

Considering the determinant role of glazing systems in energy consumption, it is imperative to survey the thermal performance of double coated glazing systems in accordance with the harsh climatic conditions and available local and foreign products' situation. In this paper, the radiative properties of local coated and non-coated glazing units are measured by the spectrophotometer and emissometer apparatus. These thermal and solar properties were not available in any datasheet. In the second step, through the accurate calculation method of EnergyPlus software, the amount of energy loss due to the radiative properties of glazing units was simulated in two extreme climates (very hot and humid climate and cold climate). By choosing the simulation method instead of real measurements in this step, it became possible to evaluate the effect of different parameters (such as climate, orientation and glazing specification) on the annual energy loss through the glazing units by eliminating other factors like energy transfer through opaque surfaces and ventilation. The simulation results indicate that using double glazing unit with low-E coating on the third surface (from the exterior) of the double glazing, significantly reduces energy consumption of the glass unit (up to 97 percent) for all orientations in the cold climate. In hot climates like Bandar Abbas, using reflective coatings (with dark blue color) in double glazing units is the best possible alternative since it lessens the energy transfer through the glass unit (up to 70 percent) compared to the clear double glazed ones.

In this research, novel severe plastic deformation (SPD) method entitled cyclic flaring and sinking (CFS) is presented for producing the ultrafine-grained (UFG) thin-walled cylindrical tubes. Finite element (FE) results showed that CFS process has good strain homogeneity and requires low load. CFS process includes two different flaring and sinking half-cycles. At flaring half cycle, the flaring punch with two stepped regions is pressed into the tube. Shear and normal tensile strains are applied as result of the existence of shear zones and increase in the tube diameter. In the second half cycle, the tube is then pressed to sinking die that applies the same shear strains and normal compression strain so that the initial diameter of the tube is achieved and high plastic strain is applied. This process can be run periodically on the tube to exert more strain and consequently finer grain size and ultimately achieve better mechanical properties. The results indicated that the yield and ultimate strengths of the CFS processed Al (1050) tube were significantly increased to 165 MPa, and 173 MPa, respectively from the initial values of 50 MPa, and 115 MPa. The elongation to failure was decreased to about 14% after three cycles from the initial value of 42%. In addition, the hardness increases to ~38 Hv after ten cycles of CFS from ~23 Hv.

a theoretical nonlinear droplet deformation model with an accurate estimation of aerodynamic force, which is appropriate for Lagrangian droplet tracking schemes, is presented and validated. The modeling is based on keeping track only of the fundamental oscillation mode. This conventional approach has been used in many deformation-based breakup models including Taylor Analogy Breakup, Droplet Deformation and Breakup, and Nonlinear Taylor Analogy Breakup. However, these models have some shortcomings such as the use of several calibration coefficients, two-dimensional analysis, and rough approximation of aerodynamic forces in large deformations. This paper is intended to amend these defects. The formulation is based on mechanical energy equation. The pressure distribution profile around the deformed droplet is approximated using piecewise sinusoidal function which depends on Reynolds number and droplet deformation. The final kinetic equation is numerically solved using fourth-order Runge-Kutta method and the results are compared with those of other models, experiments, and Volume of Fluid simulation. Numerical results show that the present model predicts slightly greater deformations in comparison with other models for the unsteady case, which is more consistent with the experimental data. Considering the steady case, the results of present model stand between that of Taylor Analogy Breakup and Nonlinear Taylor Analogy Breakup model, and provide satisfactory predictions. The stream lines obtained from simulation match those calculated analytically, suggesting the appropriateness of the assumptions used in the modeling. Overall, the present model is found to be appropriate for the estimation of droplet deformation.

In this study, novel robust impedance control for lower-limb rehabilitation robotic system using voltage control strategy is used. Most existing control approaches are based on control torque strategy, which requires knowledge of robot dynamics as well as dynamics of patients. This obliges the controller to overcome complex problems such as uncertainty and nonlinearity involved in the dynamics of the system, robot and patients. Conversely, the voltage-based control approaches are free from the system dynamics. In addition, it considers the actuator dynamics. The performance of voltage-based approaches is demonstrated by experimental result in robotic applications. Compared with torque control scheme, it is simpler, less computational and more efficient. Nevertheless, uncertainty of actuator dynamics results in challenges for the voltage control strategy applications. The present paper presents novel robust impedance control based on the voltage control strategy. To overcome uncertainties, the adaptive fuzzy estimator is designed based on the voltage-based strategy. The proposed control is verified by stability analysis. To illustrate the effectiveness of the control approach, 1-DOF lower-limb rehabilitation robot is designed. Both torque-based impedance control and the voltage-based impedance control are compared through therapeutic exercise. It is shown that the voltage-based impedance control performs better than the traditional torque-based impedance control. Simulation and experimental results both show that the proposed voltage-based robust impedance control is superior to voltage-based impedance control in presence of uncertainties.

Aeolian vibration of conductors could cause extensive damages to the electric power transmission networks. The use of Stock Bridge dampers is very common method to control the transmission line vibration amplitude. Due to the complexity of the cable-wind interaction, the Energy Balance Method (EBM) is extensively used for calculating the steady state amplitude of the system. In the present study EBM incorporating the traveling wave method are developed for calculating the steady state amplitude of the cable with arbitrary number of dampers. The wave propagation was produced by superposition of two travelling waves. The proposed method is subsequently employed to study the effect of the number, location and impedance of dampers on dissipated energy and damper performance as well. The results show that damper installation at optimum location is more effective than the damper number increase, in which case does not necessarily lead to the dissipated energy increase. Furthermore, in this study simple equation relating ISWR (Inverse Standing Wave Ratio) to Absorption Coefficient is introduced. The importance of this equation is due to the fact that only ISWR can be readily measured, but not the absorption coefficient itself, which is based upon the measurement of the travelling wave amplitudes. Finally, investigation on damper dynamic characteristics effects on absorption coefficient reveals that the real parts of damper impedance having complete absorption is independent of vibration frequency; and if the magnitude of damper impedance is lower than that of the cable for all the frequency range, complete absorption will never occur.