مجله مهندسی مکانیک
سال چهل و هفتم شماره 1 (پیاپی 78، بهار 1396)

In this article, fatigue, oxidation and creep damages in the A356.0 aluminum alloy (including an aluminum-silicon-magnesium alloy, which has been used in diesel internal combustion engines) have been investigated under isothermal and un-isothermal cyclic loadings. In order to calculate different damages, Sehitoglu’s model was utilized, in which the total damage in materials under hightemperature cyclic loadings include the fatigue damage, the oxidation damage and the creep damage. Material constants in this model for the mentioned alloy were calculated by experimental data from isothermal fatigue tests (or low-cycle fatigue tests at constant room temperature and at 250°C) and non-isothermal fatigue tests (or out-of-phase thermo-mechanical fatigue tests) were performed on test specimens. Obtained results showed that the main damage under out-of-phase thermo-mechanical fatigue loadings was the oxidation and under high-temperature low-cycle fatigue loadings was the creep phenomenon. In addition, the model used for the A356.0 aluminum alloy had generally a proper accuracy and in lower strains (higher lifetimes), the error was increased. The standard error for Sehitoglu’s model under thermo-mechanical and low-cycle fatigue tests was 0.006 and 0.005%, respectively and the relative error for the total damage was 21 and 10%, respectively.

In this work, mechanical and thermal properties of ternary nanocomposites based on the polypropylene/short glass fiber/graphene nanoplatelets have been studied. The different groups of composites were produced using an internal mixer machine including 10, 20, 30 Wt.% of glass fiber and 0, 1, 2 Wt.% of exfoliated graphene nanoplatelets (xGnP). Then, standard specimens of tensile and impact tests were obtained by pressing. To investigate mechanical properties, we used uniaxial tensile test and charpy impact test. Also the melting, crystallinity temperatures and degree of crystallinity DSC test was performed. As well as morphology of samples was that applied by SEM. SEM images showed, that graphene presence has been improved fiber-matrix adhesion. The results showed that samples with much glass fiber have higher modulus and impact strength. Using graphene in samples with 10% and 20% glass fiber increase modulus. The use of 1% nano-graphene enhances tensile and impact strength and elongation, whereas presence of 2% graphene reduce strength and elongation. The DSC results showed that addition of xGnP to reinforced polypropylene with 10% glass fiber increases the crystallization temperature. Moreover presence of 1% graphene reduces the degree of crystallinity.

To simulate the plasma flow in a magnetoplasmadynamic thruster, with mass flow rate of 4g/s and total discharge current of 16 kA, the magnetohydrodynamic equations accompanied by an anode sheath model have been solved. In this model, the flow through anode sheath region has been considered as a collisionless and unmagnetized plasma. Under this circumstance, by determining the densities of electrons and ions, and by discretizing the Poisson’s equation, potential drops along the anode surface have been obtained. The numerical simulation has properly revealed the phenomena such as dense internal flow, three jets and hot spot near the cathode. Also, the acceleration mechanism of exhaust plume has been justified based on the concept of virtual nozzle and cathode jet phenomenon. The values of maximum temperature and thrust have been predicted in good agreement with the other numerical and experimental data, with the errors less than 3.5%. Moreover, electrical characteristics of plasma in vicinity of anode such as the inverse dependence of anode fall with current density have been modeled in good accordance with the measured data.

In this research, the hybridization effect of Semic arbon fibers (SCFs) with glass fibers on tensile pr operties and burning rate of composites as compared to glass fibers reinforced e poxy matrix composite was investigated. In this reg ard, four plies composites with different arranging of SCFs and glass fibers w ere fabricated by hand lay-up method. The hybridiza tion of SCFs with glass fibers was caused reducing tensile strength and ela stic modulus of these composites as compared to gla ss fibers reinforced composite. But the failure strain of these composit es was improved. Also, the obtained results showed that both failure strain and tensile strength have important role on energy abso rption in composites that the effectiveness of thes e factors proportionate SCFs and glass fibers ratio. The results of rate and the cross section of burning showed that with increasi ng SCFs to glass fibers ratio, the flame retardancy of composite increases.

In an attempt to achieve efficient operation with respect to design and combined thermal and electrochemical perspective, a computational model of tubular SOFC is presented. The FLUENT software was used for the development of the model. The particular model, after validation against experimental observations for selected benchmark cases, was demonstrated to be a basic model for further research in this area. For validation of obtained result, i.e. COMSOL Multiphysics, was used which is based on Finite Element Method (FEM). The results showed that the difference of them is less than of 6% for power density and less than 7% for output voltage and so both software are acceptable.

Considering tip clearance in compressor blades results in the flow instabilities and leads to weakend aerothermo-dynamical and fluid-dynamical performances. In the present paper, effects of blade tip clearance size on a centrifugal compressor performance especially at near stall condition have been investigated. The current study is carried out on Iran University of Science and Technology centrifugal compressor test rig. The method of investigation is on the basis of computational fluid dynamics technique. In this paper, the Fluent solver package has been used for simulations. The Reynolds-Averaged Navier-Stokes (RANS) equations in three-dimensional and viscous form have been solved by a segregated implicit second-order scheme. The grid consists of 2,550,000 cells with structured hexahedral meshes. To validate the numerical simulation results, overall performance curves and static pressure distribution on the impeller casing were compared with each other in numerical and experimental conditions. The results showed good agreement of numerical results and experimental data. After validating numerical solutions, 5 blade tip clearance size conditions have been investigated numerically. Final results showed that increasing tip clearance size from 1.3 up to 3.7 percent of blade chord lowers the loading factor and efficiency 3.7% and 4.7% respectively.

In this study, a solar assisted heat pump dryer with in direct model of evaporator- collector has been evaluated. The effective output parameters of the cycle are the coefficient of performance and the specific moisture extraction rate. In addition, the influence of different factors including condenser temperature, relative humidity of ambient air, slope angle of collector and temperature of evaporator on these parameters have been studied. For calculation of absorbed heat radiation in collector, the existing average temperature and the average daily radiation on a horizontal surface has been used. In direct expansion cycles, the absorbed heat by the collector in the evaporator case, vaporizes liquid refrigerant phase in the saturated gas phase. In this system, evaporator element is collector case, as well as the coils of evaporator. An element of collector can be used for two the first one is the absorbing heat and increasing temperature and the second the ability to be used as evaporator. In this study, a flat collector is used to absorb heat. The purpose of this study is to investigate promoting thermodynamic operation coefficient of entire cycle and humidity separation rate. The results of this study is capable of being evaluated for average radiation rate of Birjand, Tehran and Shiraz. This study also can be used for different refrigerants. The results show that the coefficient of performance of R134a refrigerant is 24% and 20%higher than R410a and R407c respectively.

This study implements an inverse method for obtaining heat input during the friction welding process in terms of time, with specified sequences. Using limited experimental data leads to precise evaluation of heat generation during the process. Solution accuracy was improved by integration of analytical formulation, consideration of temperature-dependent thermophysical properties and slip definition in three-dimensional finite element model. Specifically, conjugate gradient method was used as inverse method to calculate the unknown parameters. Heat generation within sliding, sticking state was obtained using friction and slip dependence of time and deducted from exponential approximation of angular velocity of matrix. Favorable situation for friction stir welding is the case that workpiece does not experience the melting temperature. Online CO2 gas cooling flow was used to obligate the desired span of temperature. Numerical calculation of heat flux during friction stir welding of Al5052-O accompanied by cooling stage was considered and inverse method was integrated to evaluate governing parameters. Effect of cooling stage in temperature distribution of workpiece was simulated numerically. Calculated unknown parameters indicate good prediction of heat flux, which satisfy the measured temperature, and characteristic parameters of the process.

A new combined cogeneration cycle producing power and cooling is proposed and analyzed in detail. The cycle is a combination of hydrogen fed solid oxide fuel cell (SOFC) and an ammonia water generator- absorber- heat exchanger (GAX) absorption refrigeration system. Using the Engineering Equation Solver (EES), the solution to the electrochemical and thermodynamic equations simulates the cycle performance. The results show that for the same condition, the energy and exergy efficiencies of the proposed cycle is 68.2% and 5.88% higher than those of the stand-alone fuel cell, respectively. The net produced power and cooling as well as the input hydrogen mass flow rate increase with rising the current density, so that the energy efficiency increases and the exergy efficiency decreases. Optimization is also performed for the proposed cycle and it is observed that both the net produced power and exergy efficiency are maximized at some pressure ratio and fuel cell operating temperature. The results indicate that the air pre- heater contributes the most in the cycle irreversibility.

In the present paper, a nano-composite drive shaft of a heavy vehicle is modeled in ABAQUS. The main purposes in designing a drive shaft are increasing the critical speed, increasing the critical buckling torque, and decreasing its weight. In this article, the multi objective optimizing algorithm, NSGA II, is used to find the optimum design points. In the next step, the objective functions are computed in the design points, and then some mathematical equations for the objective functions are calculated using neural network GMDH. At last, the final front is extracted and the optimum points are indicated in some diagrams. A point is selected using Near to Ideal Point method (NIP) as well.

DBD plasma actuators are one of the effective devices for active flow control, which has received substantial attention during the last decade. In this paper, to find the optimum performance of plasma actuators, the effect of geometrical variables (including the gap between electrodes, dielectric thickness, and covered electrode width) and electrical variables (including voltage and frequency) on induced flow velocity and power consumption, is experimentally investigated. This is the first investigation in which design of experiment (DOE) approach is used to find the interaction among variables. The results show that each of the mentioned variables has a different effect on the start of uniform plasma discharge, induced flow velocity, power consumption, and the start of the filamentary plasma discharge regime. Furthermore, the results show that unlike the uniform discharge regime, in filamentary discharge regime increasing power consumption results in decreased induced flow velocity. The results of this investigation can be used to select the optimum actuator in which the ratio of induced flow velocity to power consumption is maximum, and to prevent from entering the filamentary discharge regime.

In this paper, the influences of the geometrical parameters of reactive muffler on acoustic attenuation performance and pressure drop have been investigated by using FEM. These effects consist of: to extend the inlet tube into the expansion chamber and increasing its length, adding holes to the extension and changing their number and position. The equations have been solved along with damped Newton method. The k-ε turbulent model was used for flow field analysis. The results show that the acoustic attenuation performance improves and the pressure drop decreases by extending the inlet tube and increasing its length. Moreover adding holes to extension, increasing their number and setting the holes near the end of expansion chamber increase the maximum attenuation frequency without considerable change of the pressure drop. So they can be used to improve the design of muffler at target frequency range.

The purpose of this research is the numerical study of the effect of a uniform electric field on the hydrodynamic and evaporation of a perfect dielectric drop. Converning equations are the incompressible flow equations including conservation of mass, momentum and energy. The level set method along with the ghost fluid method is used to model the interface. Numerical results show that electric stresses at the interface cause drop deformation and elongation in the direction of electric field. The amount of this deformation is increased by an increase in the ratio of electric force to surface tension force (electric capillary number). Droplet deformation is compared with the available analytical and numerical results and good agreement is observed. In the next step, electric field effect on the drop evaporation rate is considered. Electric field causes enhancement of drop evaporation. This enhancement is due to the drop deformation. Drop deformation increases evaporation by enhancement of contact surface between the drop and environmental fluid and also by creating large temperature gradients around the drop.

Nowadays, substitution of the heat exchangers equipped with continuous helical baffles is a new methodology to improve of the heat exchangers efficiencies. In this paper, heat and fluid flow fields through the heat exchangers equipped with segmental and continuous helical baffles are analyzed numerically using the computational fluid dynamics. Comparison of segmental and continuous helical baffles shows lower pressure drop and upper temperature differences for heat exchangers equipped with the later baffles. Also the effects of two major geometrical ratios: the shell to pipe diameters, D/d, and the baffle pitch to shell diameter, B/D, on the efficiency of the heat exchangers are studied. Numerical methodology of solution and governing equations is validated by iterative numerical analysis of a heat exchanger that had experimental data for comparison. Consistency between the numerical and experimental are occurred. The results show that for D/d near to 11.5, the variations of both parameters, temperature difference between output and input of the shell and the pressure drop with respect to D/d, changes from decreasing manner to increasing manner. Similar results also occurred near the ratio of the baffle pitch to shell diameter, B/D of about 2. Post processing of the results also shows the thermal performance index of the heat exchanger has its maximum value for D/d ratio greater than about 16 and the B/D ratio lower than one.

The main objective of this study is the feasibility of using Modified Park-Paulino-Roesler (M-PPR) cohesive zone model to simulate The damage in adhesive layer of the double cantilever beam specimen with metal adherents. Considering VIS method for capturing the crack initiation, fracture energy of Araldite® AV138 adhesive with bond-line thickness equal 0.2 mm has been identified based on the linear elastic fracture mechanics (i.e. classic beam theory (CBT), corrected beam method (CBM) and compliance based beam method (CBBM)) and J-integral method (Pradeep method). Following, the bi-linear traction-separation law is first utilized to numerically simulate damage in adhesive layer. The force-displacement curve results obtained through experiments would further be compared with the simulated model and thus bi-linear parameters for this specific adhesive thickness would be inversely obtained. The M-PPR cohesive parameters can be determined by satisfying the boundary conditions along with bi-linear extracted cohesive parameters. First, it is concluded that CBBM is the best method to obtain adhesive fracture toughness in mode I. Using the obtained cohesive parameters and calibration of both models, M-PPR cohesive model in addition to use in metal adhesive joints, presented comparative advantage relative to bi-linear model to simulate adhesive joints under peeling. Meanwhile, effects of the geometrical parameters such as the initial length of the crack and the thickness of substrates on the ultimate strength and stiffness of the adhesively bonded joint have been evaluated.

In this study, a combined solar-intermittent infrared drier powered by a photovoltaic system was built and the drier system parameters have been considered. In fact, by combining solar and infrared drying systems, the advantages of the two systems have been used to remove their defects. Therefore, drying kinetics, electrical energy consumption and temperature history of the potato slices with a thickness of 3, 5 and 7 mm at temperatures of 50, 60 and 70 ° C in the drier have been investigated. The results were compared with a similar test results in a natural flow solar drier. Studies show that in comparison to solar drying, at least 75% up to 83% reduction in the drying times was achieved. The highest and lowest specific moisture extracted rate of sliced potatoes will be 0.56 and 0.23 kg/kWh, respectively. Finally, with regard to the specific moisture extracted rate and drying duration, the potato drying at 50 ° C in the present drier is recommended.

In this paper, a similarity solution is presented to obtain the rate of heat transfer in nanofluid film condensation on a horizontal cylinder. Recent experimental observations show that the nanoparticles follow the base fluid vapor in evaporator and also attend in the condensate film in the condenser. Due to the significant effect of nanoparticles on heat transfer enhancement in the condensate film, this phenomenon is studied numerically in this paper. The effects of circumferential change, Jacob number, volume fraction of nanoparticles and different types of nanofluids on the velocity and temperature profiles, as well as Nusselt number are investigated. The results show that with Alumina and TiO2 nanoparticles in the base fluid, convective heat transfer coefficient in condensate film increases, while in the case of Cu and Ag nanoparticles, conductive heat transfer is dominant and in effect, Nusselt number decreases. It is found that far from upper stagnation point up to the angle 90o, the role of convective terms increases and right after, decreases up to lower stagnation point. Also convective heat transfer descends as the cylinder radius is reduced. According to the obtained results, one can say that only in low Jacob numbers, the Nusselt theory results in acceptable results.

In this paper a mathematical model is developed to able surgeon to predict the temperature of the process based on tool’s rotational speed, feed rate, tool diameter and effective interactions between parameters. The allowable range of parameters in bone drilling operation is introduced to obtain a quick and swift operation as desirable. Experiments were designed and modeled using response surface method and to ascertain operation condition, optimization was performed. Results show that within the range of the variables, with an increase in tool diameter and cutting speed the rate of temperature increment, boosts up. It is noted that the behavior of the feed rate is complex where in this paper is investigated precisely. Introduced response surface model is able to anticipate temperature behavior based on input parameters.

In this paper, by using the classical molecular dynamics and coarse grained molecular dynamics, the mechanism of automatic nanomanipulation with atomic force microscope nano-robot was modelled and it was shown that the rupture of tip is the most error source in the automatic nano-manipulation process, where is manipulation of particles on the substrate frequently. By this, to prevent from the non-favorable effects of deformation of tip on the result of nano-manipulation, a control plan was introduced. By definition of root mean squares as a criterion for measurement of the level of deformation, a simple feedback of it was used to control the system. After that the model proposed and validated in comparison with some experimental works, by using the coarsening the molecular dynamics, the system is converted into a relatively simple model and was suggested for implementation into the manipulation processes. By using this model, it was observed that although the aluminum tip leads to the worst result, by using the shape feedback, the positioning error has been reduced considerably. Positioning error without and with feedback was reported for a nickel tip as 37.77% and 17.77%, respectively. These values show the efficiency of the presented shape feedback approach.

In this research, the effect of plasma induced by electric field over the incompressible fluid in dielectric barrier discharge reactors has been simulated numerically. To simulate dielectric barrier discharge, plasma fluid method is used. Helium is used as the background gas. Five species and nine Reactions for this gas are applied to the model. For these simulations, conservation equations for each species and the Poisson equation for the electric field should be applied. Then, the calculated electro-hydrodynamic force is applied as the body force to the fluid flow equations. This simulation determined the various density species of Helium gas. The results showed that the chemical reactions taken in to account, give lower generation rate for positive charge species. Hence, charge density drops especially in the positive electrode relative to the negative one. Therefore, plasma produced near the negative electrode affects the fluid flow more than the positive one. However, considering charge density generated and arrangement of electrodes, the overall influence on the fluid flow will be little.

In this article, modeling and optimization of power consumption of two–stage compressed air system have been investigated. This system includes two centrifugal compressors and a shell and tube intercooler. For modeling of power consumption, actual compressors, isentropic efficiencies are calculated from experimental data. Also for modeling of outlet temperature of the intercooler and calculation of thermal effectiveness, the neural network algorithm was used. In these equations isentropic the efficiency of compressors is a function of inlet temperature and thermal effectiveness of the intercooler is a function of inlet air temperature, inlet water temperature of the intercooler and inlet volumetric flow rate of the system. For optimization of power consumption, the Lagrangian method is used. Power consumption and isentropic efficiency of the first and second stage compressors, thermal effectiveness of the intercooler and entropy generation of compressors are considered as the objective function and optimization conditions, respectively. In comparison to the experimental data, the modeling provided suitable accuracy. The optimization effectively reduced the power consumption of the system, especially in summer, in a way that the minimum and maximum reduction was 2.9% and 9.6%, respectively.

In this article, the transfer function of a servo hydraulic fatigue testing machine for composite material specimen is identified based on gray box technique. The system uncertainty is determined by means of the identified linear model. A Feedback and forward robust controller and an adaptive controller based on gain scheduling technique are designed to adjust the closed loop gain for minimizing the error between the amplitude of the reference signals and outputs. Using frequency response analysis of the closed loop system, the control system can compensate low frequency uncertainty up to 10 rad/sec. The experim ental results for block loading fatigue tests, confirms the robust performance of the proposed control system.

In this article, failure and damage in second mode of adhesive composite joint was investigated according to the bending in endnotch flexure specimen. To create an adhesive joint between two composite plates made of unidirectional glass fiber, Araldite 2011 resin was used which is widely capable in manufacturing turbine blades and aerospace industries. At the first, failure of second mode fracture of adhesive joint mechanisms has experimentally investigated. Then with considering this result with strain energy release rate on mode II of fracture in specimen for Araldite 2011, 776.22 J/m2 was calculated. In the following calculating critical strain energy release rate on mode II by using experimental results, XFEM method used for modeling crack growing in adhesive joint by using Abaqus software. At the end the amount of mode II fracture toughness for Araldite 2011 is calculated from numerical method which is 40.53MPa√m.

Propose of this paper are the determination of material and thickness of brush of potentiometer of XU7 engine and solving the defect of poor functioning. The contact force value of potentiometer is an important design parameter. Hence, the static analysis is performed at first for determination of the material and the thickness of the brush providing the desired force. Then an experimental method is used for verifying the results. Potentiometer functioning is investigated at dynamic mode using signal processing methods. Therefore, the output signal of some of the normal and defective potentiometers with different materials and under different working condition and cycles are recorded. A feature vector is defined for each signal. This feature vector has four elements that the first element is achieved using principle component analysis. The other elements are kurtosis, skewness and mean of the signal. Using these feature vectors and their classes, a classifier is developed for recognition of normal and defective components.

One of the principle design stages of the machine tools, especially based on parallel mechanisms is the deflection analysis of its structure under machining forces. In this paper a new four degrees of freedom parallel robot with three translational and one rotational degrees of freedom was investigated to find the best design configuration. At first the kinematics and force analysis of the mechanism as the base of design analysis considering the load distribution on its various components were implemented. Then, deflection of the different components of structure under external torque and forces on the moving platform was obtained. To confirm the force relations and static analysis of the mechanism, the structure of robot by the FEM in ANSYS environment was analyzed. At last, the results of theoretical relations calculated by the MATLAB were compared with the simulated results obtained by the FEM. It was found a good consequently, the agreement between these two of the proposed design method.

In this paper finite element simulation of hydroforming T shaped tube steel with elastic-plastic non-dependent temperature behavior by the aid of ABAQUS has been done and the effects of some parameters like fillet radius, internal pressure and friction coefficient on thickness distribution and residual stresses have been studeid. According to the results, these parameters have tangible effect. In extreme conditions, residual stresses are about to 90 percent of yield strength and thickness has been reduced to 40 percent. Afterall simulation results have been validated with experimental data and comparison showed good proximity.

In the present study, different biomechanical models in a sitting position have been investigated. The differences of these models are in terms of the number degrees of freedom, the complexity and the direction of the vibration analysis that consist the vertical, horizontal and lateral directions. In addition, mathematical models indurin finite element, lumped-parameter, multi-body and matrix models that are presented in literature, are reviewed. These models have been compared with the experimental data in terms of compliance and the best model is specified. In addition, the history of important laboratory works in from 2000 to 2015, which are vital for validation are collected and presented. In fact, compliance biomechanical models with experimental results, shows the good biomechanical model. Finally, 6-DoF biomechanical model of human body for a sitting posture without backrest is introduced, which is utilized for investigating vibrations in vertical direction. Model parameters using genetic algorithms is obtained by minimizing the errors. This model is validated with the experimental results which presented by Boileau et al.The results demonstrated that the presented model has better compliance with the experimental data in compare with the previous models.

In this paper, flutter of an aircraft wing with a control surface is considered. The wing is modeled as an elastic cantilever beam and the control surface is assumed to be a rigid beam with limited length which is connected to the aircraft wing by two torsional springs. Hamilton's principle is used to obtain the equations of motion and boundary conditions of the wing and the control surface. To precisely consider the spanwise location of the control surface in the system governing equations the Heaviside function is used. Also, Theodorsen unsteady model is used to simulate the aerodynamic lift and moment. The resulting partial differential equations are transformed into a set of ordinary differential equations through the assume mode method. Then eigenvalue analysis is employed to determine the system stability boundaries and effects of different design parameters on the system aeroelastic behavior are studied. Numerical results show that increasing the length of the control surface and its distance from the wing root decreases the flutter speed. Furthermore, increasing the torsional stiffness of springs connecting the wing to the control surface increases the flutter velocity.

In this research, the number of battery replacement during 10-years working time of e-motorcycle is concerned instead of the initial energy storage system price. The 10-years equivalent price of energy storage system is defined as initial price and the replaced battery prices during 10-years. The life model of battery is necessary for determination of the number of battery replacements during 10-years. The existence of UC in HESS improves the power specification, which increases acceleration performance and regenerative braking capacity. This moderates battery current and rises battery lifetime. In addition, the number of required battery replacements is decreased and the 10-years equivalent price of energy storage system will be reduced. The results show the optimum sized HESS has very good power specification. The 10-years equivalent price of HESS is about 3400 $ lower than conventional ESS price, while the initial price of HESS is about 840 $ higher.

The aim of this research is to investigate the effect of using disk oil skimmer in the water treatment units of refineries and to evaluate the performance and efficiency of these types of oil removers. Due to the lack of sufficient information on the design and construction of this equipment, an experimental prototype needed to be manufactured. Such a prototype has been constructed in Pars oil refinery to simulate and investigate the efficiency of oil disk skimmer. It was subjecte to different tests in order to study parameters such as disk material, oil temperature, optimum disk rotation and the distance of disk form rear barrier. The results indicate that aluminum disk with 12 rpm has higher efficiency and the more distance from rear barrier, the higher efficiency yields. Finally the use of disk oil skimmer is strongly recommended; although more research is needed for the design and fabrication of industrial-scale

In this work, a comparative study has been presented for the most common configurations of the CO2 supercritical single stage refrigeration cycle from energy, exergy, economic and environmental points of view. In order to find out the effects of degree of superheating, using an internal heat exchanger and using an expander instead of expansion valve on the performance of the supercritical CO2 refrigeration cycle, a thermo-economic analysis has been performed. The results show that the increasing of coefficient of performance of the cycle with dual expansion process is not considerable. Also, the use of an internal heat exchanger in a cycle by an expander is not beneficial. Moreover, using expander in basic cycle leads to an increase of 27.3 % in thermodynamic performance and a decrease of 16.1% in total cost rate. This cycle has the lowest penalty cost due to emission of CO2.

In this study, the effect of nano scales, van der Waals intermolecular force and steretching effect on the torsion-bending coupled pull-in instability parameters of torsional nano-mirror by using higher order strain gradient theory have been considered. In this model, the modified strain gradient theory, governing equations of system are derived then instability variables such as pull-in angle, pull-in displacement and pull-in voltage versus geometric and material characteristics are investigated and obtained results compared with experimental results. Results show that van der Waals force have much effects on nano-mirror performance. Furthermore, it is found that influence of van der Waals force on the changes of pull-in variables of nano-mirror depends on bending-torsion stiffness ratio and neglecting van der Waals attraction may lead to considerable error during simulations of pull-in instability. Therefore steretching effect similar to van der Waals force could highly affects pull-in parameters for small-gap torsional mirrors that increased pull-in parameters of system. Interestingly, the present model is able to predict experimental results well and more accurately than previous classic models and reduce the gap between experimental results with previous theories.

One of the essential subjects, affecting on submarine's performance is a comprehensive knowledge of its maneuverability and sensitivity to change hydrodynamic parameters. The hydrodynamic parameters are assessable by experiments which are directly related to geometric and environmental parameters. Since these coefficients are the result of the fluid-structure interaction, they have a degree of uncertainty and are not constants. The main objective of this paper is to evaluate the sensitivity of the hydrodynamic coefficient of a submarine to understand the its response to uncertainty of these coefficients. In this research, the dependence of hydrodynamic momemt to circular maneuverability diameter resulted by rudders was investigated. Furthermore, low sensitivity of drag coefficients against lift coefficients by control surfaces and submarine body were also considered. Increasing of lift coefficient related to maneuverability and decreasing the drag in slowness and stability of submarine are of the other outcomes.

The intermolecular potential model of the lattice Boltzmann method is used to simulate the droplet formation and breakup process of mixing of immiscible fluids. The aim of this research is to investigate non-Newtonian droplet formation in Newtonian continuous phase in a co-flowing micro-channel. The dimensionless numbers such as Capillary and velocity ratio are the most important dimensionless numbers in determination of fluid flow characteristics in the micro-channel. The influences of capillary number, nonNewtonian index and velocity ratio are studied on the droplet formation. The final droplet size, droplet generation frequency and detachment point of the droplet are completely analyzed. The results reveal that with increasing the non-Newtonian index, the required time for detachment of the droplet and the formation length is decreased. Increasing the Capillary number leads to a reduction in the detachment length. The size of droplet is also decreased due to the reducing velocity ratio and Capillary number. Moreover, the effect of non-Newtonian index on the distance between the droplets is checked.

The paper aims to develop a new algorithm to enhance the performance of the classic and traditional SINS/GPS navigation systems, particularly in attitude and heading angles estimation. A comprehensive algorithm is designed for utilization of AHRS navigation in the integrated inertial navigation system. State estimation method in the proposed algorithm contains two-step filter. The first filter is located out on the AHRS system and the orientation parameters are estimated. The outputs of this filter are fed into the SINS/GPS system. Then, the second filter is implemented and the position and velocity parameters are estimated. The performance of the proposed algorithm is assessed through vehicular test.

In this paper, ultrasonic lap welding process has been used for welding of standard specimens of polypropylene composites reinforced with glass fiber with 4 mm thickness. The tensile-shear strength and appearance properties of welds under was used different conditions of time, pressure and vibration amplitude and glass fiber content were investigated. To investigation the relationship between input variables and appearance properties of welds and weld strength, the response surface method to decrease the number of experiments and costs considering four factors at three levels. Based on experimental observations, effects of input parameters on appearance of welds were clearly evaluated. The results indicated that amplitude and pressure had the most and the least significant effect on the tensile-shear strength of these composites respectively. Best appearance condition of welds (which has least weld defects) was resulted at an amplitude of 33 µm, welding time of 0.4s, pressure of 1.5 bar and glass fiber content of 10%. Increase of welding pressure, time and glass fiber content in composites has negative effects on welds appearance status and causes weld defects increase.

In this paper thermo-mechanical analysis for a rotating thick cylinder made of FGM is carried out. For this purpose, governing differential equations of the temperature and displacement distribution for the FGM cylinder have been developed assuming plane strain and axial symmetry. Then, by considering an exponential function form for the material property distribution of the FGM along the cylinder thickness; and, using analytical solution method, the governing differential equations for temperature distribution have been solved. Based on the calculated temperature distribution and governing differential equations for displacement the mechanical behavior of the cylinder has been investigated. Finally, according to the stress distributions for different rotating speed and internal pressure, the safety factors have been obtained and the optimum material distribution is determined.

In this research, fluid flow around a pitching airfoil in dynamic stall is simulated by numerical method and the most important impact of parameters on the aerodynamic forces are investigated. In this simulation, the geometry is NACA0012 airfoil. turbulent flow and dynamic grid was used. The basic equations are discretized based on the a control volume method and solved by the PIMPLE algorithm with an open source code, OpenFOAM. Reynolds number was 105 and SST K-ω model is used for modeling of turbulent flow. First, the results were compared and validated with experimental data. Then the effect of Reynolds number, reduced frequency, amplitude and airfoil thickness on the aerodynamic coefficients and dynamic stall location are investigated. The mentioned parameters on maximum lift coefficient, drag coefficient, the ratio of the aerodynamic coefficients and the dynamic stall have asignificant impact. However, these parameters dont have a significant impact on the slope of the lift coefficient curve. Among the above-mentioned parameters, the most important parameter that affects the ratio of the maximum lift to drag is the airfoil thickness and the most important parameter that plays a role in delaying the dynamic stall is reduced frequency. Also, the location of separation point and maximum aerodynamic forces depend on the flow pattern around airfoil.

In this study the failure modes and loads for multi-pin joints of the unidirectional fiberglass epoxy composite laminates, using the finite element method and experimental tests have been analyzed. In addition, a pattern was introduced in which the pins were placed in the optimized positions by using artificial neural networks and genetic algorithm method. In the multi-pin joints, the variations of pitch to diameter ratio, width to diameter ratio and distance from the edge of the laminate to diameter ratio of pin have a significant impact on the connection failure. Due to the fact that there is not the exact solution for the failure of these kinds of laminates, for optimization in each case, the FE simulation was performed and for the optimization the results were fitted using the neural network method. The fitted model was used as input to the genetic algorithm. Considering the constraints of the problem and dimensional characteristics, the optimal pattern was presented when the failure occur later than the others. The difference between the experimental data and the finite element results was analyzed.