نشریه مهندسی مکانیک مدرس
سال شانزدهم شماره 3 (خرداد 1395)

Widespread use in the machining procedures in producing industrial pieces, optimization of this procedure is one of most subjects that attract researchers interest. Finite element analysis based techniques are available to simulate cutting processes. Success and reliability of numerical models are heavily dependent upon work material flow stress models in function of strain, strain rate and temperatures. One of the most accurate and most useful equations are presented, the fundamental equation Johnson-Cook is. The basic equations for modeling the behavior of each material, is needed to determine the equation coefficients.The model parameters are determined by fitting the data from both quasi-static compression tests at law strain rates and machining tests at high strain rates. After getting result from the equation, its accuracy being checked either in compression tests or in machining tests by simulation with Abaqus software and its results are compared with the results of machining tests. Studies show the correctness of the equation in determining the dynamic behavior of 5083 alloy is established. Therefore, this equation can be used for modeling the behavior of the selected alloy in other shaping processes, and can be used its results.

In this research, the use of the exact difference method forcing scheme in the pseudo-potential multiphase model is suggested for the simulation of a droplet impact on a thin liquid film at a density ratio of 1000, and the effect of inertia, surface tension, and gravity forces are considered by means of their corresponding non-dimensional numbers (i.e. the Reynolds, Weber, and Bond numbers). For this reason, the Palabos open source software is modified by implementing the exact difference method in it. The results of our simulations in different Reynolds and Weber numbers show that the Weber number has a slight influence on the crown layer radius, meanwhile, the Reynolds number has a direct effect on the crown radius. The crown height is increased with an increase in the Reynolds and Weber numbers. Furthermore, the comparison between the pseudopotential model simulations and the free-energy model shows that crown shape is related on the surface tension in addition to the non- dimensional numbers and with a noticeable increase in surface tension the crown tip becomes bigger. The influence of the gravity force is investigated through the Bond number. According to the results, the crown height is noticeably affected by the Bond number. When the Bond number decreases, the crown radius and height increase. Therefore, the proposed model with the capability of being used for multiphase problems with large density ratios while producing a low spurious current could be utilized for a vast variety of other multiphase problems as well.

Oil well perforators (OWP) are explosive devices that are used in drilling industries of oil and gas wells to access the reservoir and increase the wells efficiency. Oil well perforators performance is measured by the depth of penetration that can cause, for this reason depth as the main parameter must be examined. In this article, a complete report of numerical simulation and performance optimization of these devices, which are indeed small sizes shaped charges, is presented. To do this, the multi-material eulerian and the lagrangian methods are used for simulation of the jet formation and its penetration into underground rock processes, respectively. For solving the problem of large deformation elements in lagrangian method, erosion criterion elements were used. Because the results of jet formation and penetration Process heavily influenced by the density of the mesh, In this study mesh sensitivity were examined.. Described simulation, is validated by the use of reliable results of some references and then, a new charge geometry is suggested which resolves the inhomogeneities in the distribution velocity of the tail and increases the effective length of jet in the penetration process.

Registration of point clouds is a key process in creating a digital model in reverse engineering. Registration is complex and ill-conditioned problem and these impede to achieve fully automatic comprehensive algorithm.in this study a new method to improve automation level is proposed. In this method, at first surface features are extracted from point clouds and then these data use for detecting correspondence points between point clouds. Registration process accuracy depends on carefully selected corresponding point between point clouds. In present research surface curvature and local shape are used for finding correct correspondence points. For feature extraction, surface curvature for each point of point clouds is calculated by using umbrella curvature and also a new method for determining local shape is presented. For each point of point cloud a shape number is determined. Determination of shape number is done by neighbors’ coordinates of point of concern. In this method, the corrected corresponding points are points that have almost equal umbrella curvature and shape number. Rigidity helps algorithm to find pairwise points. Analyzing results shows that the proposed algorithm performs well and has appropriate abilities on fully automatic registration of point clouds.

In this paper, a new model called connective layer is developed for simulation of linear dynamical behavior of bolted lap joints and model updating in 3D models. Connective layer unifies neighboring zones on sides of common surfaces of substructures in joint region. The constitutive relation of connective elements is defined by decomposing it into its normal and shear components. Unknown and different elastic properties with respect to the neighboring solid elements are defined for connective layer and the unknown parameters of the model are identified by a finite element model updating technique using modal test data. The frequency response of the structure is measured by exciting the structure using an impact hammer. Using an optimization algorithm in ANSYS, the difference between the experimentally measured frequencies and the predictions of the parametric model is minimized as objective function. The connective element performance is demonstrated by application to an actual structure containing a single lap bolted joint coupling two identical aluminum alloy 7075-T651 beams and finally comparison of results to those of interface elements. The outcomes of presented model have good correlation with experimental results. The proposed method predicts the higher mode frequencies which don’t have participation in model updating process with minimum error in comparison to those of interface element. Due to simplicity, accurate and computationally efficient manner, this model can be incorporated into commercial finite element codes to simulate bolted joints in large and complex structures.

Electrolyte type, due to the nature of its constituent ions, affects the reaction rate, the uniformity of the electric field and formation of the external layer on the workpiece surface in the machining area during the electrochemical machining process, as well as it causes to create different dissolution behaviors of the workpiece. Therefore in this study the effect of sodium chloride, sodium nitrate, potassium chloride and hydrochloric acid electrolytes with different currents on the electrochemical machining characteristics of stainless steel 304, including material removal rate, side gap and surface roughness, has been investigated. The results showed that the formation of passive layer during the machining with sodium nitrate electrolyte reduces the material removal rate and side gap compared with sodium chloride and potassium chloride electrolytes. According to the experimental results the surface roughness in the sodium chloride and potassium chloride electrolytes is decreased by increasing the machining current, but increases in the sodium nitrate electrolyte. Also the material removal rate slight increase and side gap increase at sodium chloride, sodium nitrate and potassium chloride when combined with hydrochloric acid. On the other hand, the surface roughness reduces in the combined sodium chloride and potassium chloride electrolytes, but increases in the combined sodium nitrate electrolyte.

In this paper, breakup of liquid jet is simulated using smoothed particle hydrodynamics (SPH) which is a meshless Lagrangian numerical method. For this aim, flow governing equations are discretized based on SPH method. In this paper, SPHysics open source code has been utilized for numerical solutions. Therefore, the mentioned code has been developed by adding the surface tension effects. The proposed method is then validated using dam break with obstacle problem. Finally, simulation of two-dimensional liquid jet flow is carried out and its breakup behavior considering one-phase flow is investigated. Length of liquid breakup in Reyleigh regime is calculated for various flow conditions such as different Reynolds and Weber numbers and the results are validated by an experimental correlation. The whole numerical solutions are accomplished for both Wendland and cubic spline kernel functions and Wendland kernel function gave more accurate results. Effect of fluid viscosity is investigated in the breakup length of the fluid as well. The accomplished modeling presented that smoothed particle hydrodynamics (SPH) is an efficient method for simulation of liquid jet breakup phenomena.

In present paper, a numerical study is performed for analysis of effects of geometrical and operational parameters of viscous micropump with the approach to Entropy Generation Minimization by Lattice Boltzmann Method. In study of effect of change in the geometric parameter L and operational parameters ∆P*, it was found that in all ∆P*s, two range of L=1.2 - 1.6 and L=4.4 - 4.8 at EGM viewpoint and two range of L=1.1 - 1.6 and L=4.4 - 4.9 at the minimum power of rotors viewpoint are introduced as optimum ranges. Due to the full overlap of optimum ranges at the EGM viewpoint with the minimum power of rotors viewpoint, the same range mentioned in the EGM viewpoint is selected as the optimal range. Results of the effect of change in the geometric parameter L and operational parameters Re showed that in all Res, two range of L=1.1 - 1.5 and L=4.5 - 4.9 at the EGM viewpoint and two range of L=1.2 - 1.6 and L=4.4 - 4.8 at the minimum power of rotors viewpoint are introduced as optimum ranges. Therefore, the common range of these viewpoint namely L=1.2 - 1.5 and L=4.5 - 4.8 can be selected as the most optimal range. Regarding the effect of change in the geometric parameter ε and operational parameters Re and ∆P* is determined in all Res and ∆P*s, the range of ε = 0.1 – 0.5 is selected as optimum range in the EGM viewpoint and the minimum power of rotors viewpoint.

Static and dynamic stress intensity factors are important parameters in the fracture behavior of the cracked bodies. In the present study the displacement correlation technique (DCT) is presented to calculate static and dynamic stress intensity factors of functionally graded materials (FGMs). The displacement field is obtained using finite element method (FEM) and ABAQUS software. To consider the variation of material properties, a subroutine is prepared in the UMAT subroutine of the software. Eight-node singularity elements are used in the FEM. As ABAQUS software is not able to calculate stress intensity factors of FGMs, so a MATLAB code is developed to obtain these factors. By analyzing an example under dynamic load, dynamic fracture behavior of orthotropic FGMs and effect of non-homogeneity parameter are investigated for two cases of material properties variation directions which are perpendicular to each other. To verify presented method, a center crack in a plate of homogeneous and FGM materials are analyzed under static and dynamic loads, the results are compared with data of literatures. The results show that, if the material properties vary parallel to the crack direction, the mode I dynamic stress intensity factor at the crack tip located in the stiffer part increases with increasing of non-homogeneity parameter, while for variation in the normal direction to the crack, this factor first increases and then decreases.

In this paper, the effects of the addition of an active toe joint on a 2D humanoid robot with heel-off and toe-off motions are studied. To this end, the trajectories of joints and links are designed firstly. After gait planning, the dynamic model of the humanoid robot in different phases of motion is derived using Kane and Lagrange methods. Then, the veracity of the derived dynamic model is demonstrated by two different methods. The under-study model, is in accordance with the features of SURENA III, which is a humanoid robot designed and fabricated at the Center of Advanced Systems and Technologies (CAST) located in University of Tehran. Afterward, the optimization procedure is done by selection of two different goal functions; one of them minimizes the energy consumption and the other maximizes the stability of the robot. At last, the obtained results are presented. According to the results, there is an optimum value for heel-off and toe-off angles in each velocity which minimizes the consumption of energy. The results also show that, the heel-off angle does not have any significant effects on the stability of the robot while increasing the toe-off angle improves the stability of motion. Finally, the effects of mass and length of the toe joint is inspected. These inspections suggest that heavier toe joints cause an increase in both energy consumption and stability of the robot while increasing the length of the toe joint does not have any effects on both goal functions.

In this paper, the effects of temperature and nanoparticles volume fraction on the viscosity of non-Newtonian hybrid nanofluid, containing water and ethylene glycol as a base fluid and multi-walled carbon nanotubes (MWCNTs) and silica (SiO2) as additives, have been investigated experimentally. The measurements have been carried out in temperatures range of 27.5°C - 50°C by using a Brookfield DV-I PRIME digital Viscometer for different shear rates. The stable and homogeneous samples, with the solid volume fractions of 0.0625%, 0.25%, 0.5%, 0.75%, 1%, 1.5% and 2%, were prepared by dispersing the equal volumes of dry MWCNTs and SiO2 nanoparticles in a specified amount of the binary mixture of water/EG (50:50 %vol.). The measurement results at different shear rates showed that the base fluid possessed Newtonian behavior, while all nanofluid samples exhibit a pseudoplastic rheological behavior with a power law index of less than unity (n

In this study, the relative humidity of the gases in the PEM fuel cell was changed and its effect on electro-osmotic flow was investigated. ýBy changing the humidity on both sides of the fuel cell and using the water balance equations, the values of the electro-osmotic flow, ýelectro-osmotic coefficient and net drag in different humidity levels were found. Results showed that variations of the electro-osmotic ýflow changed linearly by anode and cathode humidity to the special humidity and after that not much variation was seen. In addition, the ýresults revealed that humidity change at anode had more desirable effect than the cathode. For example, at 70% anode humidity and 35% ýcathode humidity with the current of 5A, the value of electro-osmotic flow was obtained as 2.66639E-06 mol/cm2.s, while in the former ýý35% and the latter 70% with the same current, this value was recorded as 2.56418E-06 mol/cm2.s. In addition, results showed that theýþ þvariations of the electro-osmotic coefficient changed linearly by humidity. It was determined the current change of fuel cell has not so ýeffect on the curves of electro-osmotic coefficient. The electro-osmotic coefficients varied between 0.636001 and 1.632476, which were ýin a good agreement with the values obtained in other related papers. In addition, the variations of the net drag in respect of humidity were ýinvestigated, too. It was determined that the net drag changed linearly by the cathode humidity with positive slope, but its variations by ýthe anode humidity were linearly with negative slope.ý

A dc-dc buck converter is an electronic circuit with wide application in power electronics. This converter acts as a nonlinear system then, it is necessary to use a robust controller to control and regulate the output voltage under load changes, circuit elements and other disturbances. In this paper, a new fast terminal sliding mode control (FTSMC) using the property of the terminal attraction as a function of the inverse tangent for buck DC-DC converter is provided. The performance of this new controller is compared with FTSMC common type in terms of output voltage convergence time and input control function structure. The superior property of this controller is low singular effect on the control function. Also, the controller has fast rate of convergence in different situations for output voltage stability in order to use in power electronic device of mechanical motion control systems such as types of robots and electric vehicle are pretty good. Simulation results confirm the proper performance of the new proposed fast terminal sliding mode control method compared to traditional fast terminal sliding mode converter for buck converter.

Due to increasing the heat transfer surface area and high providing capillary pressure with high permeability, porous structures play a key role in improving the performance of two phase heat transfer devices such as heat pipes. New porous structures (bi-porous structures), have two distinct size distribution of pores of which the small pores provide the capillary pressure required for delivering liquid to the surface and large pores help vapor escape from the surface through increasing its permeability. The main goal is to gain a deeper understanding of the evaporator section of heat pipes and comparison between the performances of two sample biporous structures. Towards this goal first the Kovalev modeling technique is applied to determine the possibility of each phase’s existence in pores of different sizes throughout the computational domain. One dimensional heat transfer in a bi-porous wick is investigated. Inside the domain the conservation equations are solved for each phase and the results such as heat flux versus wall superheat are presented. Thermo-physical properties of the fluid and the matrix like the fluid properties, phase saturation and permeability and the conduction heat transfer coefficient are calculated from the geometry of the matrix and experimental relationships.

Pure mode II fracture toughness of polymethyl methacrylate and its components has been studied by essential work of fracture (EWF) approach via experimental and numerical methods. EWF fracture tests with double edge notched tension (DENT) were performed on the RT-PMMA specimens at room temperature. In this investigation, the mode II fracture of polymethyl methacrylate/graft-acrylonitrile butadiene styrene (PMMA/g-ABS) blends with different weight percentage of rubber (0, 10, 15, and 20) and the thickness of samples 0.8 and 4 millimeters was investigated. The results showed that the value for the specific essential work of fracture given by including lower ligament length may be more accurate, because the ligament is completely yielded. The results also showed that for the load-displacement curves have self-similarity in shapes for the specimens with different rubber content, specimen thicknesses, and ligament lengths and the specific work of fracture (wf) increases significantly with the increasing of rubber content. The non-essential work of fracture (βwp) increases with the increasing of rubber content and the highest value belong to 20% composition in which for both thickness. The highest value of the essential work and the non-essential work of fracture belong to 20% composition in 0.8 mm specimen thickness 98.67 kJ/m2 and 99 kJ/m2, respectively. By changing the thickness of the samples the amount of the essential work of fracture showed significant changes.

Using the renewable energy resources has attracted the attention of researchers and automobile companies, because of limited fossil fuel resources, low efficiency of internal combustion engines and their environmental pollutions. By using the fuel cell systems instead of internal combustion engines can be partially overcome these problems. In this regard, the present article examines a PEM fuel cell system for using in an urban vehicle. In the first part of this article, by using the real component of system, the fuel cell system components including stack, membrane humidity of air and hydrogen, air compressor, water pump and pump cooler stack has been modeled in MATLAB Simulink environment. The mentioned model can evaluate the power consumption of system and its peripheral component and also required water, hydrogen and air for system. At the base case and the current density of 0.7A / cm2, 14% of power productions of stack are consumed by auxiliaries units. At this current density, the overall and net system efficiencies are 48.15% and 34.3%. In the second part of this article, the system from the point of view of the first law of thermodynamics has been optimized with objective functions of maximum output power and maximum efficiency. The results indicate that first model search method is best method for optimization, second at the Optimization with the aim of maximum power, pure power and system efficiency are increased 11.9% and 4% respectively and the power consumption by auxiliary unit is reduced 42%.

Linear and angular displacement measuring encoders are the most important measuring tools in the industry. Linear encoders are widely used in various positioning applications, such as numerical controlled (NC) machine tools and factory automation, since they are essential for precision positioning systems. In this study, a capacitive-type linear encoder with un-tethered slider is designed. The main components are made of printed circuit films. Hence, the encoder can be set up in thin inter spaces or on curved surfaces. The encoder consists of a long receiver film and a short transmitter film, respectively containing four-phase and two-phase electrodes. The transmitter is used as a slider and the receiver as a stator. In order to designs an unconstrained slider; the encoder employs a unique approach. Electrical power is supplied to the transmitter film by electrostatic induction which removes electric wires from the slider. In this study the encoder was built using a new signal processing circuit and its performance was evaluated. The new signal processing circuit is more compact and facilitates using this encoder for trade purposes. The result of experimental evaluation shows that the encoder has ±20 micrometers error.

In this paper, the fracture trajectory in blunt V-notched specimens under mixed mode loading is investigated by using two numerical approaches: 1) the extended finite element method (XFEM), 2) the incremental method. The first approach is an extended form of the finite element method in which the fracture takes place and grows according to the cohesive zone model. The second one is also an increment approach which the fracture initiation angle for notched specimen is first determined according to the concept of the maximum tangential stress (MTS) criterion. Afterward, a small crack is added to the notched specimen along the fracture direction and then a new cracked specimen is generated. In the next step, the fracture initiation angle is calculated from MTS criterion and another small crack is again added to the cracked specimen. These steps are continued until the crack reaches to the back boundary. To evaluate these methods, the fracture paths of the rounded-tip V-notched Brazilian disk (RV-BD)specimens under mixed mode loading are predicted by both XFEM and incremental method. It is shown that the incremental method can provide estimates more accurate than XFEM for the fracture initiation angle of the notched samples. It is also demonstrated that both methods can predict the fracture trajectory in good agreements with the experimental results

In present study, heat transfer in double-tube heat exchanger filled with metal porous material has been investigated. In contrast to the most of previous studies, fluid flow is considered turbulent in heat exchanger which is in a good agreement with the practical performance of these exchangers in the industry. Fluid flow and heat transfer equations have been discretized on a collocated grid by the means of finite volume method with simple algorithm. Discretized equations are solved with a numerical program in FORTRAN language in order to study the effect of porous material parameters and Reynolds of fluid flow on the heat transfer in double-tube heat exchanger. According to the results and analysis of porosity in the range of 0.8 to 0.95 as well as pore diameter of 1 mm up to 6 mm and diverse types of porous material, it is observed that the decrease in porosity, the increase in pore diameter and use of copper porous material (with high heat conduction coefficient), increase heat transfer. In the best case, overall heat transfer coefficient enhances up to 7 times. Moreover, the results reveal that the heat transfer enhancement ratio have no distinct difference with changing Reynolds number of turbulent flow in the range of 10000 to 80000. Performance evaluation criteria, which investigate the effects of pump lost power and thermal power, depicts that with using porous material the value of the pump lost power is of major importance which can be decrease by increasing the porous pore diameter.

Due to the low formability of aluminum alloys at ambient temperature, forming of these alloys is performed at high temperature. Research has shown that the results of simple tensile test to predict the materials behavior at high temperatures are not sufficiently accurate to predict the formability of aluminum tubes at high temperature. The mechanical properties of the tube are very important at high temperatures. In this study the formability of 6063 aluminum alloy tubes are investigated by free bulging test at temperature range 430°C to 600°C. Then the mechanical properties including flow stress, strain rate sensitivity coefficient and strength constant are obtained using tube multi-bulge test at temperature range 530°C to 580°C. For this purpose, hot metal tube gas forming process is used and the effect of process parameters such as the effect of temperature, pressure and time on the expansion ratio and height of the bulge are studied. The results show that the maximum expansion ratio is 58% at 580°C. Bursting pressure decreases from 1.9MPa to 0.6MPa with temperature increasing from 430°C to 600°C. The bulge height increases with increasing forming time at constant pressure. Also with increasing temperature in the temperature range 530°C to 580°C the flow stress and strength constant decrease and strain rate sensitivity coefficient increases.

In this research, the influence of adding carbon nanotubes on the tensile and the mode I interlaminar fracture of glass-fiber-epoxy laminated composite has been experimentally studied. For this purpose, the hybrid glass-fiber-epoxy-nanotube laminated composites which have 18 fiber-glass plain-weave layers were manufactured by hand lay-up method. The epoxy resin system is made of Epon828 resin with Epikure F205 as the curing agent. The multi-walled carbon nanotube (MWCNTs) modified with hydroxide (-COOH) is also dispersed into the epoxy system as a reinforcement in a 0%, 0.1%, 0.5% and 1% ratio in weight with respect to the matrix. In addition, the tensile nano-resin and hybrid nano-composite specimen were produced. The results of the tensile test of nano-matrixes indicate that the maximum change in Young's modulus, ultimate strength and fracture toughness of the samples is in the 0.5% sample, with a 31.2%, 21.4% and 16.66% increase with respect to neat sample, respectively. Moreover, the results of the tensile test of hybrid nano-composites indicate that the maximum change in fracture toughness, ultimate strength and fracture strain and of the samples is in the 0.5% sample, with a 12.6%, 9.8% and 12.6% increase with respect to neat sample, respectively. The result of the mode I interlaminar fracture toughness test of hybrid nano-composites show that the maximum change in value of the force (in force-displacement diagram) and value of the energy (of crack propagation in mode I interlaminar fracture), is in 0.5% sample, with a 24.4% and 24.15% increase respect to neat sample, respectively.

Research on microstructure of main engineering materials revealed that some of these materials exhibit similar microstructure patterns at different length scales. Since these patterns are replicated at different length scales the whole microstructure can be viewed as a set of periodic substructures. Homogenization technique for periodic microstructures has found many applications in simulation of composite materials by considering the geometry of fibers distribution. In this study a homogenization technique for periodic microstructures is developed. In this generalization a multi-step homogenization is being used. In each step of homogenization the geometry which is coincident with the true microstructure is produced to maintain the properties of the mechanical properties of the related cell. By using the presented method effect of size and grading of each of reinforcing phases and the interaction between fibers is taken into account. The results of the presented theory are compared with the existing experimental data on the particle reinforced composites. Good agreement between the presented theory and experimental data is found.

The purpose of this paper is to introduce a design and fabrication procedure for a solid propellant gas generator. Based on this procedure a gas generator was designed to supply the required operating fluid of a controllable flying object’s gaseous actuator of control surface which results of that design is presented in this paper as well. Supplying required pressure during the mission and gas flow rate with expected chemical characteristics are requirements of the design. At first the amount of necessary parameters like flow rate and pressure were specified. Then the design calculations were done according to proposed approach. In order to evaluate the design process and achieved data, a full scale gas generator set was built. Since this study includes specifying a proper formula for solid propellant of gas generator, a lab scale motor was used to qualify the propellant’s characteristics experimentally. After doing tests and comparing the results with output data of gas generator design procedure, convenient consistency was observed. Besides by doing several tests it was found that PSAN as oxidizer, HTPB as binder and chromium oxide as catalyst is a proper composition for solid propellant of gas generator. Finally, covering basic requirements of a solid propellant gas generator such as uniform flow rate and less presence of solid phase and corrosive components in combustion products by means of designed gas generator is an approval to show the validity of presented design method.

Owing to direct contact with the machined surface, the flank surface can cause unfavorable effects on the surface integrity in high speed milling. Thus, in this study, the influences of flank wear width on the main characteristics of surface integrity like roughness, topography, microhardness and electrochemical corrosion resistance during high speed milling process is investigated. Milling tests were performed under constant cutting conditions with three repetitions and using 12 tools with flank wear widths on the AISI 4340 hardened steel. It was concluded that using the tool with flank wear width up to 0.4 mm increase roughness and microhardness, uniformly (95% for surface roughness and 6.3% for microhardness relative to new tool). However, using a tool with the flank wear of 0.6 mm increases these outputs up to 484% and 18.6%, respectively. Surface topography images also revealed that using the tool with the flank wear width of 0.6 mm can cause irregular forms of material flow on the surface. Using the tool with the flank wear of 0.4 mm or less had an insufficient effect on the in-depth microhardness distribution. In addition, electrochemical impedance spectroscopy of the milled surfaces showed that relative to new tool, using tools with 0.4 and 0.6 mm flank wear, reduce Rcorr up to 22% and 83%, respectively. It indicated lower electrochemical corrosion resistance of milled surfaces with 0.6 mm worn-out tools.

In this paper a mathematical model of pulsatile, unsteady and non-Newtonian blood flow through elastic tapered artery with overlapping stenosis is proposed. The blood flow has been assumed to be non-Linear, fully developed, laminar, axisymmetric, two-dimensional. The non-Newtonian model chosen is characterized by Sisko model for discribe the rheology of blood. The artery has been assumed to be elastic and time-dependent stenosis is considered. Due to the blood flow depends on the pumping action of the heart, the blood flow has been assumed pulsate. The stenosed artery change in to a rectangular and rigid artery, using a radial coordinate transformation on the continuity and the nonlinear momentum equations and boundary conditions. The discretization of the continuity and the non-linear momentum equations and boundary conditions are obtained by finite difference scheme. The radial and axial velocity profiles are obtained and the blood flow characteristics such a resistive impedances and volumetric flow rate and the severity of the stenosis are discussed. The volumetric flow rate is minimum in the case of converging tapered arteries and the resistive impedances is maximum in the case of converging tapered arteries by effect of tapering angle.

This study presents a numerical investigation for laminar mixed convection flow of radiating gases in an inclined lid-driven cavity. The fluid is treated as a gray, absorbing, emitting and scattering medium. The governing differential equations consisting the continuity, momentum and energy are solved numerically by the computational fluid dynamics (CFD) techniques to obtain the velocity and temperature fields. Discretized forms of these equations are obtained by the finite volume method and solved using the SIMPLE algorithm. Since the gas is considered as a radiating medium, besides convection and conduction, radiative heat transfer also takes place in the gas flow. For computation of the radiative term in the gas energy equation, the radiative transfer equation (RTE) is solved numerically by the discrete ordinate method (DOM). The effect of lid driven speed, on the thermohydrodynamic behavior of two-dimensional cavity is carried out. Results are shown as contours of isotherms, streamlines and distributions of convective and total Nusselt numbers along the bottom wall of cavity. It is revealed that increasing in Reynolds number causes almost uniform temperature distribution in cavity, especially for 30° and 60° inclination angles.

One way to control the position of the missile is controling thrust vector that is moves with help of thrust due to exit of gas. All thrust vector control (TVC) methods are independent of aerodynamic forces of atmosphere and until the engine has thrust, maintain their performance. Secondary injection systems are one of the four major TVC methods. In this study,at first identify the components and design entire conceptualdesigning of system and the preliminary design of manifold of a type of thrust vector control system using a liquid injection thrust vector control (LITVC)has been proceed. Then the layouts of components on some components such as injectors and reservoirs, as well as detailed design of the system are discussed. Then the numerical simulation of flow and the designing and studying the sprayers in LITVC systems will be discussed. Also numerical designing and simulation in two parts: injection system and the injector spray effects into the main flow are analyzed and the results are presented and validated. The achievement of this study can be used as a model for designing and analyzing of various kinds of TVC systems with lateral fluid method on a variety of missiles with different launchers.

Aortic Valve simulation remains a controversial topic, as a result of its complex anatomical structure and mechanical characteristics such as material properties and time-dependent loading conditions. This study aims to integrate physiologically important features into a realistic structural simulation of the aortic valve. A finite element model of the natural human aortic valve was developed considering Linear Elastic and Hyperelastic material properties for the leaflets and aortic tissues and starting from the unpressurized geometry. It has been observed that although similar stress-strain patterns generated on Aortic Valve for both material properties, the hyperelastic nature of valve tissue can distribute stress smoothly and lower strain during the cardiac cycle. The deformation of the aortic root can play a prominent role as its compliance extremely changed throughout cardiac cycle. Furthermore, dynamics of the leaflets can reduce stresses by affecting geometries. The highest values of stress occurred along the leaflet attachment line and near the commissure during diastole. The effects of high acceleration on the performance of valve, valve opening and closing characteristics, and equivalent Von Mises stress and strain distribution are also investigated.

Although it seems that two categories of robotic systems, the dynamic object manipulation and dynamic biped walking systems, are completely different to be dealt with at the first glance, we believe that there exists strong relationship between these two types of robotic systems. This paper studies the correlation of the dynamic biped walking and dynamic object manipulation in all areas (passive, underactuated and fully-actuated classes). In this regard, the virtual problem of "the amputee walking robot" is defined to describe the relationship between these two kinds of robotic systems. From this viewpoint, the problem of dynamic biped walking is a special case of dynamic manipulation of multibody objects in which the multibody object does have a structure similar to the structure of biped robots. In other words, we can say that the ground manipulates the biped robot which is considered as a multibody object. Then, the concept of correlation is investigated in three different classes of the problem: passive, underactuated, and fully-actuated systems. For each of three categories, appropriate examples are studied. It will be shown that the details of the walking problem could be extracted from the mother problem of dynamic manipulation of multibody objects in all its aspects.

Thermal Barrier Coatings are used as thermal protective of parts using under high temperature circumstance. These coatings usually include three layers respectively: ceramic top coat, grown oxide layer and bond coat. Due to manufacturing process and special structure of thermal barrier coatings, failure mechanisms of these coatings are affected by applied loads on coated part. In this paper failure of these coating under thermal fatigue was studied numerically and experimentally. A specimen of Inconel 617 which were coated by air plasma method and it was tested in a test setup with capability of applying four point bending load, under thermal fatigue experiment with the maximum temperature of 1170 oC in addition to constant bending load with the magnitude of 7500 Nmm. Thermal fatigue test was contined until coating spallation and temperature of specimen surfaces was measured during the test. Finite elements modeling was performed by ABAQUS to simulate the experiments thermal and mechanical loading conditions with using cohesive zone model to model top coat delamination and failure. Finally with a little change in the model, was attempted to adapt the bending magnitude of the specimen from model on experiment result to estimate interfacial cohesive properties for these coatings from finite elements results.

In this paper, the internal inversion process of metallic cylindrical shells under dynamic axial loading is investigated experimentally and numerically. Experimental tests are performed on the steel tubes in a gas gun and the required force for internal inversion is obtained using the measurement system of impact loadings. Also, numerical analysis is carried out by the finite element software ABAQUS and the accuracy of simulated models are validated with the experimental results. In this paper, all geometrical properties of the tubes and die are assumed to be constant and the effect of the projectile mass and velocity is investigated on the shortening and energy absorption of the tubes which are affected by axial impact in the internal inversion process. Therefore the projectile is shot directly to the specimen with different masses and velocities. It is observed that if the projectile mass remains constant, increasing in the impact velocity has almost no effect on the constant inversion load and just increase the tube displacement but if the impact velocity remains constant, increasing the amount of projectile mass causes increasing in the constant inversion load besides of increasing in tube displacement. Comparing the results of numerical simulations with the experimental results shows a good agreement between them.

Ultrasound test is a widely used non-destructive method for determining the mechanical and metallurgical properties of materials. In this method, ultrasonic wave velocity or attenuation coefficient is measured and measurement accuracy is very important. In this paper, variations of longitudinal wave velocity are studied in the presence of a thermal gradient both theoretically and numerically using a 2D model. A linear temperature distribution is assumed and the length of the work piece and the temperature of the hot side are considered as varying parameters. A new 2D theoretical model is developed for this problem. The test piece is made of st37 steel. To evaluate the proposed equation, we assume constant temperatures and the length of the work piece are varied in the range of 0.05-0.1 m. Then, we study the effect of the temperature of the hot side from 398 -998 K. By ANSYS software, a novel two-dimensional finite element model (FEM) is developed in axisymmetric state for this problem. The results of the theoretical model are compared with those obtained from the numerical model and a very good agreement is observed.

In this research, an intelligent method is introduced for remaining useful life prediction of an internal combustion engine timing belt based on its vibrational signals. For this goal, an accelerated durability test for timing belt was designed and performed based on high temperature and high pre tension. Then, the durability test was began and vibration signals of timing belt were captures using a vibrational displacement meter laser device. Three feature functions, namely, Energy, Standard deviation and kurtosis were extracted from vibration signals of timing belt in healthy and faulty conditions and timing belt failure threshold was determined. The Artificial Neural Network (ANN) was used for prediction and monitoring vibrational behavior of timing belt. Finally, the ANN method based on Energy, Standard deviation and kurtosis features of vibration signals was predicted timing belt remaining useful life with accuracy of 98%, 98% and 97%, respectively. The correlation factor (R2) of vibration time series prediction by ANN and based on Energy, Standard deviation and kurtosis features of vibration signals were determined as 0.87, 0.91 and 87, respectively. Also, Root Mean Square Error (RMSE) of ANN based on Energy, Standard deviation and kurtosis features of vibration signals were calculated as 3.6%, 5.4% and 5.6%, respectively.

One important problem investigated in reverse engineering (RE) field is finding the best surface to approximate point cloud data. Swept surface is a surface type that in addition to various applications in CAD/CAM software, satisfies the whole standards required for use in RE software. The most important problem in utilization of swept surfaces for RE purposes is the finding of the areas belonging to it out of point cloud data. Through an algorithm presented in this paper, a method has been introduced to find these areas automatically. Currently, this process is performed by user intervention. In this paper, using kinematic surface formulation and slippable motion concept, a general method to find swept surfaces with any arbitrary central curve and profile is introduced. To this end, point cloud data are processed regarding slippable motion criterion using iterative segmentation algorithm, then by presenting an effective algorithm and employing the concept of hierarchical classification and drawing the dual graph, swept-surface-related areas are found. The introduced method is implemented in several models with different conditions for validation. It is observed that the results have good agreement with real model condition, showing the efficiency of this method in finding the swept surface.

In this study, optimum design of composite sandwich structures will be surveyed and presented using hybrid algorithm. Since, most modern payload fairings are constructed of a composite sandwich laminate, in this research the architecture of the fairing structure has been analyzed on the basis of the composite sandwich shell with a flexible core. However, from the geometrical point of view, fairing composed of two conical and cylindrical parts. Therefore, in the first phase, buckling analysis of conical composite sandwich shell has been done by using high-order theories and the obtained equations reduce to the governing equations of cylindrical sandwich shell when the semi-cone angle is set equal to zero. In the second phase, the obtained structure was optimized using hybrid algorithm. Due to the variety and complexity of design variables in composite sandwich structures, designing process leads to difficulties and obstacles in design optimization problems. Since, the most important selected discipline for optimizing the mass specifications of launch vehicle is structure, therefore with relying on optimization of the structure, after completion of optimization process, finally considerable mass reduction i.e. 40 percent comparing to the utilized fairing in this study (Fairing of Safir), will be concluded due to simultaneous changing of material and optimization.

In this study evaporation of biodiesel droplet under different operating conditions is investigated. The model is a common droplet vaporization model for multicomponent fuels. In this model, gas phase quasi-steady equations are solved analytically and energy and species transport equation in liquid phase are solved numerically. The sub-models are modified to consider high pressure effects. Peng-Robinson equation of state is used for gas phase and phase equilibrium is determined using fugacity. Effects of pressure on the thermophysical and transport properties of gas phase are considered. Five biodiesel with different composition are studied. These biodiesel have different composition of methyl esters. Biodiesel composition has little effects on droplet lifetime and maximum difference is about 20%. It is observed that increasing ambient temperature leads to decrease in droplet lifetime and increases temperature gradient inside droplet. Ambient pressure has different effects on droplet vaporization behavior at different ambient temperature. At lower temperature environment, increasing of pressure increases the droplet lifetime while at higher temperatures droplet lifetime first increases and then decreases with pressure. Increasing initial velocity of droplet reduces the droplet lifetime. Results show that at high pressures, droplet temperature reach to values near to critical temperature and accuracy of quasi-steady approximation decreases. Radius of vapor influenced sphere increases with temperature and decreases with pressure.

Time optimal trajectory planning of closed chain mechanisms has not been done by indirect method yet. In this paper, this problem is considered for a four bar mechanism and its solution is presented on the base of the indirect solution of optimal control problem. To this end, the additional coordinates are omitted using the holonomic constraints, so the dynamic equation is obtained with respect to only one generalized coordinate. Then the necessary conditions for optimality are derived using Pontryagin's minimum principle by considering the constraint on the applied torque. The obtained equations lead to a two-point boundary value problem (BVP) that its solution is the optimum answer. Unlike the direct methods that result in approximate solution, indirect method leads to an exact solution. But the main challenge in indirect method is solving the BVP. Solving this problem is sensitive to the initial guess. This problem is much more severe for time optimal problem which has a high nonlinear answer in bang-bang form. To overcome this problem an algorithm is proposed to solve the time optimal problem with any desired accuracy, and the initial solution can simply be zero at the start of the algorithm. But in the time optimal trajectory the large jerk is occurred, due to control signals switching. In order to overcome this problem, another algorithm is presented to calculate the minimum time with bounded jerk. Finally, the simulation results show the performance of the proposed method in time optimal trajectory planning.

In this study, the method of molecular dynamics simulation is performed to investigate the shockwave propagation in a solid. The simulation cell contains 51840 atoms at 5 K interacting by means of a pairwise potential. The shockwave is generated using the motion of a piston with different velocities in the solid and the resulted shockwave velocity is in good agreement with the experimental data and the Hugoniot curve. The piston hited the sample from one side of the simulation box, at speeds ranging from 1.2 to 1.3 times the speed of sound in solid argon at the chosen density. Some thermodynamics properties such as density, temperature and pressure are measured during propagation of shockwave. It is found that those thermodynamics properties (density, temperature and pressure) are remarkably and significantly increase when the shockwave passed through the solid. We also show that creating initial strain in the solid up to 6.5% can enhance the pressure increment in the solid up to 9%. The results can be useful in enhancing of the shockwave power by giving a detailed microscopic description of the process.

In this article, the linear quadratic regulator method (LQR) for voltage control of a linear time-varying model of a robot is used to design an on line adaptive optimal stable controller to trace the robot arm path. Normally, off line solving of Riccati differential equations in backward with final conditions for linear time-varying system or converting the Riccati differential equation to algebraic one in linear time-invariant system is inevitable in LQR. However, in this paper, the differential Riccati equations are considered as the adaptation laws along with a voltage control strategy to be solved on line in forward method with initial conditions. Choosing a proper Lyapunov function guarantees the asymptotic stability of the tracking. Furthermore, parametric model uncertainties such as mass parameter variation and external disturbances which affect the dynamics of the model, are also taken into account. Simulation results show the energy used by dc motors of the voltage optimal control strategy is less than that of the torque control strategy and as well as the classical PID one. The superior performance of the voltage optimal control over torque control strategy is also shown in presence of disturbance.

In this paper a combined cooling heating and power system for using heat losses in PEM fuel cell has been proposed, present system can use for residential application. This system consists of PEM fuel cell, Heat storage tank, absorption chiller, hydrogen tank, air compressor and pump. Heat generated in fuel cell has been absorbed by a working fluid and a part of heat has been given to absorption chiller and another part has been given to heat storage tank. Modeling of this system has been done from four energy, exergy, FESR and CDER perspective. Fuel cell of this CCHP system generates 38.63 kW electrical power and 39.17 kW heat power. Energy efficiency of fuel cell singly is 37.21% but when heat storage tank and absorption chiller has been used for recovering waste heat, energy efficiency reaches to 68%. Maximum irreversibility loss occurs in fuel cell which is calculated 47.21 kW and absorption chiller irreversibility has been calculated 5.94 kW. From viewpoint of FESR and CDER in comparison with conventional systems, FESR and CDER are 34% and 25% respectively. Also analyzes had been showed that with increasing fuel cell operating pressure energy and exergy efficiency increased and by increasing high pressure of chiller COP decreased

This paper experimentally investigated the effects of electrical discharge machining processes parameters on fatigue resistance of 16MnCr5 alloy steel. 16MnCr5 alloy steels have good wear resistance. For this purpose, pulse current and pulse time have been considered as variables in the process. The selected EDM parameters were pulsed current (8, 16 and 32A) and pulse time (25, 100 and 400µs). Tests were conducted in full factorial mode and the R. R. Moore fatigue test machine was used to determine the fatigue life of components. The results show that by increasing the spark current and pulse duration 16MnCr5 alloy steel fatigue life is reduced. Respectively, the greatest resistance to fatigue achieved at current of 8A and pulse time of 25 microseconds and lowest resistance to fatigue achieved at pulse current of 32A and pulse time of 400 microseconds. Resistance to fatigue crack depends on cracks density on the surface of the workpiece and heat-affected zone, where the density of cracks increase resistance to fatigue will be reduced. Also in the specimens that have low resistance to fatigue, fatigue cracks are initiated from multiple points of the cross-section. It seems the reason for this phenomenon is the high surface roughness in the samples. EDM machining with high energy sparks can decrease the fatigue strength of 16MnCr5 by as much as factors of 3-5.