مجله مهندسی مکانیک
سال پنجاهم شماره 1 (پیاپی 90، بهار 1399)

Increase of strength and development of aerial structures has long been of interest to researchers. In this study, to investigate the T-joint T6-6061 aluminum alloy using friction stir welding process, laboratory samples were made, and also the software simulations were performed to find out the appropriate amounts of tools dynamic effects. Fluent commercial software has been used to better understand heat generation and distribution in the welding process. For this purpose, the T6-6061 aluminum joint with different linear and rotational tools speeds was studied. Depending on the selected parameters in the process, the strongest connection was produced in the 1600 rpm rotational speed and 68 mm/min linear velocity. The failure place of all tensile samples was located on the aluminum T appendage. Tunnel void was the major defect in the joints which disappeared with increasing heat input and simultaneous cooling rate to the joint. The maximum strength produced in these experiments is 188 MPa which is close to the strength of the aluminum base metal.

In the last two decades, many researchers have focused on the problem of automation of vehicles, and many research has been devoted to solving the challenges posed by this area. One of the important aspects in this area is the problem of localizing the vehicle and mapping the environment simultaneously in an unknown environment, which is briefly referred to as SLAM. So far, many methods have been proposed to solve this problem, but few of these researches have been implemented on the platform of collaborative robots. In this paper, SLAM problem is extended to multi robot platform by employing extended kalman filter. Due to lack of knowledge about the measurement noise covariance, the elements of this matrix adapted according to the actual data received from the sensor by employing particle swarm optimization technique. Then, to solve this problem in the dynamic environment, probability hypothesis density filter is used to track the dynamic objects in the field of view of sensors. Finally, the performance of the algorithm is evaluated in a MATLAB environment.

The purpose of this article is to investigate the effect of composite patch on stress intensity factor (SIF) for internal and external semi-elliptical crack located in spherical pressure vessel. The composite patch is wrapped only around the crack. The three dimensional analysis is done by Finite Element Method (FEM). ANSYS Parametric Design Language (APDL) codes are developed to facilitate modeling of semi-elliptical crack in spherical pressure vessel. By using these codes the effect of some parameters such as crack geometry (crack depth/thickness of vessel and crack depth/ half-length of crack), the ratio of composite thickness to metal thickness, the ratio of composite patch width to half-length of crack and composite material on stress intensity factor values are investigated and discussed in detail. The results show that composite patch has significant reduction in stress intensity factor at crack tip. Also it can be concluded that composite patch is more effective for deeper and slender crack. In addition composite patch is more effective to decrease stress intensity factor of external crack in comparison to internal crack.

In Polymer Electrolyte Membrane Fuel Cell (PEMFC), heat and water are generated as a side-production. The accumulated water leads to a decrease in PEMFCs efficiency; therefore, water has to be removed and flooding has to be prevented. In this study, by an experimental model and implementation of transparent Gas-Diffusion Layer (GDL), water transport in PEMFC is visualized and the fingering mechanisms in GDL are studied. The effect of added Micro Porous Layer (MPL) on water flooding in GDL has been also examined. Results show the characteristics of the two-phase regime in GDL are similar to the capillary fingering. Moreover; the fingers inside the GDL are generated by the capillary forces. In addition, it is observed that lateral flow on the Catalyst Layer (CL) leads to an increase in water flooding in GDL in which PEMFC efficiency is decreased.

The energy absorbers are the mechanical structures that are used for transformation some or whole kinetic energy resulted from collision to other kinds of energy. Efficiency improvement of these absorbers has been always the goal of researchers, and so the various methods have been used to this field. In this paper, firstly, the effect of cutting-edges on initial crushing load, mean crushing load, absorbed energy and the mode of crashworthiness of thin-walled cylindrical aluminum tubes is investigated. Then the effects of geometrical dimensions of the tube-like thickness, diameter, semi-apical angle, the geometry and dimensions of the edge and the angle of applied load on the crashworthiness behavior of thin-walled structure are examined. The results show that creation of symmetrical cuttings on the edge, decrease the initial crushing load. These cuttings decrease mean crushing load and absorbed energy too. These declines in mean crushing load and absorbed energy are negligible in compared to initial crushing load. This phenomenon makes this system useful for cases in which initial shock is significant. The results also show that initial crushing load for the 2 squares cutting-edges and for the 4 cutting-edges were reduced about 18.7 % and 34 %, respectively, compared to the initial crushing load of the thin-walled cylindrical tube-like without cutting-edges.

In this paper, optimal integral sliding mode controller with fractional derivative for ¼ active suspension vehicle in order to achievement of safe control and passenger comfort in presence of uncertainty has been designed. Since, hydraulic actuator has nonlinear behavior, controller should be designed robustly. Therefore, sliding mode control as a robust controller is used. In the proposed method, sliding mode controller with fractional integral sliding surface is defined. In order to optimal design, fractional integral sliding surface parameters using particle swarm optimization (PSO) is optimized. Finally accuracy and performance of proposed method is validated by using active and passive method. Simulation results are shown performance of the proposed method in presence of road uncertainty.

In the production of metal matrix composites when the size of the additive particles is reduced from micrometer to nanometer, all of the conventional producing methods are inefficient. Composites produced by these methods only improve the mechanical properties and in many cases result in weakness of other properties of the produced composite. In this study, AA6061 / SiC layered nanocomposite and also homogeneous nano-composite were produced with FSP process. Since the focus was on improving the impact resistance and reducing the fracture failure at high strength. Three-point bending, Charpy shock and hardness tests were performed on the specimens. Also, the cross-sectional fracture of the specimens were performed by electron microscopy (FE-SEM). The results showed that the flexural properties, traction absorption and FG composite layer breakage were improved compared to homogeneous HNC composites, which made the composite produced at the same high strength not too brittle, and this would widen the range of application of the composite. The results also showed that improvement of hardness, bending and impact properties are 15, 68, 16 respectively.

In this paper, the evaluation of infrared thermography has been done to detect subsurface defects of polymer composite pipes made by filament winding method. In this method, in order to stimulate the test specimen, the heat flux is applied over the surface of the specimen and the thermal response is processed to detect defects. Experimental investigation was applied by hot air, optical pulse, and modulated stimulation on specimens were made with common controlled defects in composite materials. Interpretation of the results were utilized in the calculation of defects’ size and location, it was observed that in specimen with 4 mm thickness dry fiber defect with a minimum size of 3040 mm, delamination and inclusion defects with a minimum size of 25*25 mm clearly is detected and is measured. The evaluation of thermal stimulation techniques shows in the examined samples, according to the type of cylindrical structure and ability of applying thermal fluid to its internal side, the method of hot air stimulation by the blower is a reliable method and provides trusted results.

In this research, response surface methodology (RSM) was used to rank the parameters of GTN damage criterion in the order of significance in the study of metallic sheets formability, so as to select a limited number of the most significant parameters to have the GTN criterion calibrated. A total of 7 GTN parameters were selected for this purpose. Then, considering a suitable range for each parameter, a total of 143 experiments were designed using RSM. In these experiments, the minimum limit strain obtained from the forming limit diagram (FLD0) of AISI 304 steel sheet was taken as response. In order to calculate the FLD0, M-K model was simulated using Abaqus finite element (FE) software. In these simulations, GTN criterion was used to predict fracture in the defect zone of the M-K model. Upon performing analysis of variance (ANOVA) on the data obtained using the FE simulations, the GTN criterion parameters were ranked in the order of significance. Furthermore, using the calibrated values of the GTN parameters, forming limit diagram of AISI 304 sheet was obtained completely at an acceptable accuracy.

In advanced composites , intelligent materials such as memory alloys have been used to improve the mechanical properties of various applications. In this study, the superellasticization property of the shape memory alloys has been used to improve the tensile strength of polymer - reinforced fiber composites. The effects of volumetric percent and thickness of memory alloy wire on the composite reinforced with unidirectional carbon fibers under tensile loading are investigated. For this purpose, composite specimens reinforced with unidirectional carbon fibers were constructed by placement of one, three, and five wires of memory alloy with thicknesses of 0.2 , 0.3 and 0.4 mm. The results showed that when the samples are stretched, a significant proportion of the tensile load is transferred to the wire, and due to the high strain tolerance in the shape memory alloys, the strength of this composite compared with the composite sample is increase about 7 times.

Recently, some researchers proposed a new algorithm for the bidirectional evolutionary structural optimization (BESO) in which adding and removing of elements is controlled by a signal parameter of removal ratio of volume (or weight). Nevertheless, their BESO improvement suffers from some restrictions like premature stopping of the iterative process due to the closeness of the adding and removing coefficients. In this study, the BESO method is modified such that eliminates the previous restrictions and increase its efficiency significantly. Several examples are presented for structural optimization of a plate in two states of elastic and elastoplastic with stiffness and stress criteria. From the three examples, one can conclude that the modified BESO algorithm is more robust than the ESO and BESO algorithm previously proposed. It is also concluded the maximum stress and the performance index are improved in comparison with the case when the signal parameter is the same. Overall, the proposed modification prevent the premature termination of the optimization process when the optimization process is based on the hard kill method with both adding and removing the elements.

Although clearance in mechanisms facilitates manufacturing and assembly, it will lead to undesirable results such as an increase in vibration and a decrease in accuracy. Joint clearance is considered as the main cause of errors in the position and the direction of the links. This research has investigated the possibility of using encoder signals to estimate the extent of clearance in the joints of a slide crank servomechanism. The output signal of the encoder was studied in three modes of zero, low and high clearances. It was done on the point of the part that serves as a link for servomechanism. The output signals of encoder were tested, analyzed and compared with those in joints with/without clearances. It was found that the signals had a sinusoidal waveform in the joint with ideal clearance but it has a distorted waveform in the joint which has high clearance. The results show that the distortion available in encoder signals may be used as a criterion to estimate and monitor clearance condition in slide crank mechanisms

In this paper, an experimental analysis of exergy and energy for a three-stage compression refrigeration cycle that located in unit 147 of south pars gas company has been investigated. In the cycle, vapor of propane cools with the propane refrigerant. Experimental results that recorded from different points of the cycle are collected for all days in a year. After recording of temperature, pressure mass flow of refrigerant, and thermodynamic calculation of the cycle specification, the variation of temperature, pressure and flow rates of different cycles, exergy efficiency, operating coefficient, exergy of equipment destruction, consumption and heat input into the cycle, and the results as a medium diagram Monthly in a year. According to the results, the highest and lowest values of efficiency observed in months of July and April, respectively. Also, the highest and lowest average values of exergy was obtained for a series of expansion valves and suction drum sets for one year.

In this study, a hybrid system including of a solid oxide fuel cell cycle, a domestic hot water heat exchanger and a single-stage water-ammonia absorption chiller are simulated for the simultaneous generation of power, cooling and hot water. , and it is examined from the perspective of energy, exergy and exergy-economic. After evaluating the results in the base input mode, the effect of changing the fuel cell flow density and fuel consumption coefficient on the system performance is investigated. The basic shows that overall work is 4,418 kW, the total irreversibility is 1,650 kW and the overall exergy efficiency is 378/0. Also, the air heat exchanger, water heat exchanger and fuel cell are introduced as components that should be considered more than other components from the exergy-economic point of view, since they are almost the largest amount of cost pertaining to these components

Aortic stenosis is caused by narrowing of the orifice of the aortic valve. Stenosis is described by calcium deposition on the leaflets. With the growth of stenosis, hemodynamics, mechanical performances and blood flow through the valve are changed. This study proposes the comparison of two new fluid-structure interaction of healthy and stenotic aortic valve finite element code ADINA during a complete cardiac cycle. Due to the hardening of calcified aortic valve, the orifice area decreased from 2.4 cm2 for the healthy AV to 1.4 cm2 for the stenosis case. The axial velocity and mean pressure gradient increased in mid systole. In addition, strain concentration and higher stress values were observed on the leaflets in stenotic valve than healthy case. Pressure distribution and velocity results were in good agreement with echocardiography data in published literatures. Although improvements are still needed, our computed data were well simulated closing and opening of the healthy and the calcified aortic valves.

Nanometric machining process is an advanced method for fabrication of components with sub-micron tolerances and nanometric roughness. In spite of traditional machining systems, machining of the brittle materials, such as silicon, could be achieved by this technique. Due to the nanometric nature of this method, the behavior of material removal would be different with the bulk workpieces. Consequently, workpiece dimension also affect the final quality of the machined components. In this study, the effect of workpiece width and dimension on machining quality has been investigated by molecular dynamics technique. Machining parameters and molecular dynamics analysis condition were assumed invariant. The results revealed that shrinking the workpiece dimension consumedly would result in an initial shock. This issue leads to segmented chips and reducing surface finish. Besides, the results indicated that by tool advancement, workpiece temperature would increase; however, this is much faster in workpieces smaller than 21nm. In addition, it was clarified that increasing in the workpiece dimensions, reduces resultant force and its fluctuations.

In the present research, the fluid flow around a rectangular flow-disturbing rib in a rectangular microchannel has been numerically studied. The aim of this study is investigating the effect of key design parameters including the height and the length of rib and the Reynolds number on the hydrodynamic characteristics of fluid flow. Also, the forced convective heat transfer of the nanofluid flow in the aforementioned microchannel has been numerically studied. The aim of this study is investigating the effect of volumetric fraction of nanoparticles and the rib on the heat transfer. The steady, two-dimensional, and incompressible governing equations in laminar and turbulent regimes have been solved by the finite volume method in a smooth unstructured grid with appropriate number of cells clustered in the regions with intense gradients of flow parameters. The validation of simulations has been conducted by comparing the results with the available experimental data in the literature. This comparison shows a good agreement between them. The results of present work with great and validated details can be applied in the design of microsystems.

In this paper, the stress intensity factor for circumferential crack in an isotopic cylinder has been determined. The thickwalled cylinder is subjected to a one-dimensional axisymmetric thermal shock on the outer surface according to the classic thermoelasticity (CTE), Green-Lindsay (G-L) and Green-Naghdi (G-N) theories. The considered unified form of governing equations involves CTE, G-L and G-N theories. The effects of temperature-strain coupling and the inertia term in governing equations are considered. The circumferential crack stress intensity factor determinates using weight function method. Considering relaxation times in generalized theories governing equations result in predicting higher temperature and stress values in comparison with CTE. Also, generalized theories stress intensity factor is higher than CTE significantly. Moreover, the maximum stress intensity factor in generalized theories occurs for a crack that the peak of stress wave reaches to its tip. Because of neglecting energy dissipation in G-N type II governing equations, its maximum of stress and stress intensity factor is higher than G-L theory.

In this paper, an analytical analysis for thermal and mass transfer effects of a non-homogeneous catalytic mixture into a microchannel is investigated with considering flow regime effects. The importance of the present work is to find out the selective Knudsen number and investigating the possessions of mass and heat jump coefficients on the present problem. The governing equations include energy, molar fraction and catalytic conversion equations, and the effects of flow regime is introduced into the problem through boundary conditions. The obtained results are compared in three different values of the Knudsen number with experimental data. The maximum errors rather than experimental data for Knudsen number equal to 0.1 is 7.54 percent but for Knudsen numbers of 0.01 and 0.001, the errors is increased to 35.4 percent. Therefore, the selective Knudsen number for catalytic micro-channel is equal to 0.1. The greatest increase in fuel conversion with increasing Knudsen number is occurred in the low Reynolds number with a value of 35.2%. Furthermore, the increasing rates of fuel conversion and surface mole fraction with increase of Knudsen number are nearly equal, which this issue is due to entrance of fluid from continuous to slip regime.

Metallic bellows have many applications in various industries such as oil and gas industries. In recent decades, various processes such as mechanical and hydroforming methods for production of bellows have been proposed. Hydroforming process is one of the best methods for manufacturing of metallic bellows with expected characteristics. In this paper, hydroforming process of metallic bellows for AISI 304 stainless steel has been investigated experimentally and numerically. For this purpose, effects of some process parameters such as internal pressure, die stroke, radius of die corner, friction coefficient, thickness and length of tube on metallic bellows formability has been studied. The results show that with an increase in the internal pressure and also die stroke length, the height of convolution is increased and the thickness of outer diameter of bellows is decreased. In addition, the other numerical investigations show that by reducing in the friction coefficient and also initial thickness and length of tube, convolution height is increased and the thickness of a point positioned on convolution crown is decreased. It should be noted that a good agreement between the results of experimental work and numerical simulations were obtained that show a good precision in the performed numerical simulations.

While several articles have reported aneurysm occurrence in the coronary arteries, this kind of aneurysm has not been sufficiently studied in the literature, and most of the related studies have focused on the investigation on aneurysm in the abdominal aorta. Considering the potential risk of rupture in the coronary artery aneurysm due to mechanical stresses and its severe complications, the effect of the geometrical parameters of the aneurysm such as its radius, length and symmetry on the stress distribution on the aneurysm wall has been investigated in this paper. For this purpose, a fluid-structure interaction analysis has been performed in the framework of the finite element method to determine the von Mises stress on the aneurysm wall induced by pulsating blood flow. The accuracy of the developed model is evaluated by comparing its results with available data in the literature for a benchmark problem. It has been observed that the aneurysm radius has a more significant effect on the wall stress than its length. Furthermore, increasing the aneurysm radius or reducing its length will increase the maximum wall stress. Asymmetric aneurysm is subjected to higher stresses compared to the symmetric one.

Laser welding is a significant method for welding all kinds of alloys. High speed welding, low distortion and easy automation are the advantages of this method. In this study, pulsed Nd:YAG laser butt joint welding was performed on 304 and 316 Austenitic stainless Steels workpieces. All the parameters were designed by Full Factorial Method which the center point was repeated for 10 times. Henceforth, the effect of power, pulse duration, laser velocity and chemical composition on width and depth of welding area, ultimate tensile strength, elongation and Ferrite Number were studied. The welding process was performed in 1.2 and 1.8 KW as power, 3 and 4.4 ms as pulse duration and 0.2 and 0.8 mm/s as velocity of welding. Thus, the upper level of input parameters were selected as the optimal case. This was done by surveying all the samples to achieve maximum UTS, size of the weld and Ferrite Number. In these conditions, output error for width of weld, depth of weld, U.T.S, elongation and Ferrite Number was 2, 5, 1.6, 25 and 2%.

In this paper, the inviscid and viscous ultrasonic flow field of a steam turbine blade with Denton method is investigated. The novelty of this paper is, improving Denton's finite volume method by adding the turbulence viscous term on 2-D modeling. This is an area that better understanding can lead to improved design. The unsteady Navier - Stokes equations govern the overall behavior of compressible viscous flow and treated by the time marching scheme. For simulation in FORTRAN is used the finite volume method for discrete and Baldwin - Lomax model for the effects of turbulence in viscous flow. Independency of the number of grid points are obtained. Pressure distribution has been validated with experimental data and on the shock zone show good correlation and reduction of numerical errors with experimental data.

In this paper, the bending analysis of a thin circular sector plate (with inner and outer radius) made of homogeneous material with various boundary conditions including simply support and clamped edges under the act of uniformly and non-uniformly loadings resting on a nonlinear Winkler foundations (elastic) is studied. To do this, for bending analysis of sector thin plate subjected to uniform and nonuniform loading a combination of the Extended Kantorovich Method (EKM) along with weighted residual method was employed to solve the fourth-order governinig bending partial differential equation (PDE) of the plate in the polar coordinates of r and θ. The obtained results for bending deflection of the plate are compared with those from finite element method (FEM) and also with the literature in special cases. Also, the effect of changes in different parameters including geometry of the plate, linear and nonlinear stiffnesses of Winkler foundation, types of various boundary conditions and uniform and nonuniform loading in the bending response of the plate is investigated.

The collector is one of the ways to achieve clean thermal energy, and the most important of these systems can be pointed out to the compound parabolic concentrator (CPC). This paper focuses on measuring the amount of heat transfer in a CPC containing two water pipes as well as a water-based nano-fluid. In this research, a 3D model using Fluent software (Finite volume Method) was used to simulate and solve the governing equations (continuity, momentum and energy) in a collector with 500 and 55 mm for length and diameter, respectively.Based on the numerical results, for a collector with diameter of 55 mm, the use of 6 mm water pipes will achieve the highest heat transfer rate around 1.974 C for 8% volume fraction. The results indicate that the vortices formed around the cold water pipe are larger than vortices around the hot water pipe in all nano volume fractions (0, 2, 4, 6, 8 and 10%) for a pipe with diameter of 6 mm and this is because of the high temperature gradient between the walls and the cold pipe.

In this study, the liquid-solid fluidized bed was simulated using a combination of Lattice Boltzmann and smoothed profile method and then by changing the geometrical parameters contains of, particles diameter, width of the bed, initial bed height and the placement of the particles in non-uniform particles bed, their effects on porosity are studied. The hydrodynamic model of the flow is based on the LBM and SPM is adopted to enforce the no-slip boundary condition at the liquid-solid interface. The kinematics and trajectory of the discrete particles are evaluated by Newton's law of motion. Comparison of numerical and empirical results for porosity at different velosities showed acceptable accuracy. Also, Simulations indicate that an increase in width of the bed and particles diameter increased porosity and an increase in initial bed height decreased the porosity of the bed. Finally, the effect of placement of particles in none uniform fluidized bed showed the highest porosity accurse where particles with a small diameter stay on particles with a large diameter, also where the particles are mixed together the lowest porosity was accrued.

There are several ways to increase the aerodynamic efficiency ratio of the wing. One of the most important ones is the use of winglet at the tip of a finite wing. In the present study, four split blended winglets with different upper winglet height mounted on RQ170 Micro-Aerial Vehicle half model and its effects on the drag reduction in zero angles of attack compared with wing without winglet in low Reynolds number. Also, the effect of split blended winglet in different Reynolds number and angles of attack were investigated experimentally. The tests were carried out in a wind tunnel with a low speed and turbulence. The Reynolds number based on the Mean Aerodynamic Chord is changed from 22000 to 46500, and the angle of attack is adjusted from 0◦ to 20◦. The results are representing the drag reduction in all Reynolds number and angles of attack due to using split blended winglet. It was found that with increasing Reynolds number at zero angles of attack, the drag coefficient decreases. Also, the installation of the split blended winglet with the 3cm height of upper winglet has more reduction in total drag coefficient.

In this research, buckling of composite plates made of curvilinear fiber with considering gap and overlap effects was studied. Two paths for curvilinear fiber were considered, namely, the linear variation of fiber angle and constant curvature path. An in-house computer program in Python language was written for locating the gaps and overlaps and modeling stages. Then the analysis was performed by ABAQUS finite element software. Two aspect ratios of length to width of the composite plate were considered. Results show that for plate with the length greater than the width, more improvement in buckling load was obtained by using curvilinear fibers. Also the results show that, without considering gap and overlap effects, the linear variation of fiber orientation and the constant curvature path caused more than sixty and fifty percent increase in the buckling load in comparison with maximum buckling load of the composites made of the straight fibers, respectively. For both paths, by considering gap and overlap effects, buckling load can increase more than thirty and ninety percent, respectively.

The performance of refrigeration cycle depends not only on their configuration, but also on thermodynamic properties of working pair. Typical absorption systems use refrigerant/absorbent combinations of lithium bromide-water and water-ammonia. Because of difficulties in using these combinations, researchers proposed Ionic Liquids as novel alternative absorbent of refrigerant which can be used in absorption refrigeration cycles. In this study, the performance of the absorption refrigeration system with two different ionic liquids, thermodynamically and economically investigated and compared with the water-lithium bromide system. Multiobjective optimization using genetic algorithm is carried out for optimization of cycle. The thermodynamic properties of mixtures as the working fluid pair are predicted using Non-Random Two Liquids model. The coefficient of performance, exergetic efficiency and product cost flow rate are the parameters which were selected as objective functions. The optimal values of objective functions and design parameters were found and compared to the initial values. Among the combinations include ionic liquids, the highest coefficient of performance and exergetic efficiency and minimum product cost flow rate are obtained for the water-1-ethyl-3methylimidazolium trifluoroacetate combination.

In this paper, performance of a solar air heater has been investigated by using of transverse ribs. For this aim, the governing equations for fluid flow including mass, momentum and energy conservation laws have been solved by Fluent software. With respect to having turbulent flow in solar air heaters and noticeable portion of radiation in heat transfer, turbulence and radiation have been considered either and for finding best models for turbulence and radiation, results have been compared with previous experimental studies for solar air heater without ribs. Then effects of parameters such as existence of ribs, changing effective heat flux, geometry and arrangement of the ribs in different mass flow rates, have been studied by using of obtained best models. The results confirmed enhancement of thermal performance by using of transverse ribs and illustrated that wedge shaped ribs have the best thermal performance among the investigated geometries. In addition, optimum arrangement of the ribs is different for various Reynolds numbers. So that in low Reynolds numbers optimum gap between two adjacent ribs is more than it in high Reynolds numbers.