مجله مهندسی مکانیک
سال چهل و هفتم شماره 4 (پیاپی 81، زمستان 1396)

In this paper, experimental of residual stress and distortion generated when welding a and numerical studies were carried out to investigate the welding effects on the buckling behavior of aluminum cylindrical shells under external hydrostatic pressure. The cylindrical shell that is made of AL 5083 was tested under hydrostatic pressure before and after it was welded. Also, the numerical study was done by finite element software code "ABAQUS". Moreover, numerical simulation based on finite element modeling was used to study the influence of welding sequences on the distribution cylindrical shell. The simulation consisted of sequentially coupled thermal and structural analyses. sequences on the d numerical results were adopted.

In this paper a composite plate with cross-ply lamination subjected to bending moment is analyzed and the 3D stress state in the plate is investigated. The interlaminar stresses in composite plates may lead to delamination of composite plies near the edges. An appropriate displacement field is employed for the cross-ply plate in which the global and local response of the plate to the loading is separated. The layerwise theory (LWT) is employed for formulation of the problem. The governing equations of the plate include several coupled differential equations which are related to the global and local equilibrium equations of the plate. The governing equations are solved and the displacement field in the plate is obtained. In order to increase the accuracy, 3 approch is used for calculation of the interlaminar stresses in the plate. A finite element solution is used to verify the results of the LWT and it is seen that the prediction of LWT is in good agreement by the finite element analysis. In the numerical results, the interlaminar stress state in the cross-ply composite platewhich is subjected to bending load is studied.

In this study, changing of inlet air swirl intensity of standard Harwell combustion chamber on dynamic flow, temperature, radiation heat flux and NO pollutant has been assessed. Due to the effect of swirling on dynamic behavior, a new equation has been utilized based on tangential and axial velocity component in order to achieve the swirl number. Furthermore, chemical reactions computation has been done using Eddy Dissipation model and flow computation and radiation heat flux were performed using standard k-ɛ and P1 models. The results show that increasing swirl number from 0.0 to 0.6 with amplification of internal recirculation zone of furnace will cause the combustion products into this area and mix air and fuel and accordingly, increase the combustion efficiency by eliminating the high temperature points as a main cause of NO generation. Moreover, increasing the swirl number in radial order and increasing the heat exchange area regardless of the maximum flame temperature reduction, will increase the flux radiation efficiency by 31.3% and reduce the NO pollutant by 58.6%.

In the present study, a three-dimensional and transient model of a proton exchange membrane (PEM) fuel cell with pin-type flow field is investigated. The governing equations, including the mass, momentum, species, charge and energy conservation equation along with electrochemical reactions, are numerically solved to investigate the transient behavior of the fuel cell. The results associated with the current density, chemical species and velocity distributions, along with the streamline pattern clarify the basic concept of the transport phenomena in the PEM fuel cells. The numerical results show that using the pin-type flow field, increase the oxygen transfer rate into the catalyst layer which results to an increase in the current density average value. As the transient time of the fuel cell is about few seconds, its start-up process is very quick. During this transient time, the operating parameters of the fuel cell such as current density, mole fraction of the reactants and pressure of the fuel cell reach to their steady state condition.

Resistance spot welding(RSW) is one of the most popular welding methods in joining sheet metals of cars, and etc. In RSW process, a high electric current is passed throw two sheets via electrodes, which results in the generation of a melting zone between the sheets, called nugget. The main purpose of this study is experimental investigation on static and fatigue strength of aluminum alloy 6061-T6 with 2 mm thickness. To achieve this goal, many samples were prepared and welded by different RSW’s parameters. The mechanical strength of welded samples was examined under tensile-shear test. The results show that, by increasing the nugget size, the static strength is improved. In addition, however at first, the fatigue strength is increased by improving the nugget size; it’s decreased significantly after a certain nugget diameter. The micro-structural study indicates the formation of cracks in the HAZ after the certain nugget diameter. However, these liquation cracks have no effect on the static strength of spot welded samples; they cause dramatically changes in the fatigue strength of samples.

In this study, the characteristics of flow wake around an elliptic cylinder have been investigated experimentally. To this end, a cylinder with elliptic cross section with an axis ratio of AR=2 of Aluminum at Reynolds numbers of 15000 and 30000 has been tested in the wind tunnel. Using existing methods the characteristics of a flow wake and drag coefficients of the model in the different cases have been investigated. To measure the mean velocity and turbulence intensity, the hot-wire anemometry has been used. Free-stream turbulence intensity of wind tunnel is 0.15 percent which in this sense, it has high accuracy. The experiments indicates that the increase in Reynolds number causes significant changes in the mean velocity profile. The results show that by increasing the Reynolds number, the turbulence intensity in the wake increases. The results show that by increasing the Reynolds number at a constant axis ratio, the width of wake becomes narrow, and the Strouhal number of wake associated with the Karman vortex increases. It is found that by increasing the Reynolds number, the parameters of drag coefficient and velocity defect reduce.

In this paper, multi objective optimization of volume fraction of step-formed functionally graded plate under biaxial loading is studied for increasing critical buckling load and decreasing structure weight. In step-formed functionally graded plates, material properties aren’t changed as continuous function in thickness direction; rather are changed as step by step at consecutive layers. The purposes of optimization problem are maximization of elastic critical buckling load and minimization of total weight of plate. The weighted sum method is employed for this purpose, considering the design variable as volume fraction that is various in adjacent layers. First order shear deformation theory is used for formulating the buckling analysis of functionally graded plate. Fuzzy combination of genetic algorithm and particle swarm optimization methods is applied for optimizing the volume fraction in different layers. Numerical results for step-formed functionally graded plate are compared with fully functionally graded plate that follows from simple power law with optimal power factor. Finally, effect of weighting factors, boundary conditions, number of layers, aspect ratio, load ratio, and width-to-thickness ratio are considered. It will be showed that applying design of step-formed functionally graded plate is better than continuous fully functionally graded plate.

The purpose of this paper is the thermodynamic performance analysis of a solar turbine cycle in three different weather conditions. The design parameters and decision variables in this system are compressor pressure ratio, temperature inlet turbine and the intensity of the sun's radiation. The results show that by increasing the intensity of the solar radiation, the electrical efficiency of the system increases and the maximum electrical efficiency occurs at a lower pressure ratio. Investigations show that by increasing the working pressure and the temperature inlet turbine, in spite of increasing the efficiency and net power of production, it will increase the lost exergy and destroyed which increases the rate of irreversibility. Therefore, from the thermodynamic point of view, the system should work as little as possible at lower working pressures. The results show that the highest rate of exergy destruction in the combustion chamber and the lowest in the solar receiver has occurred. It was found that by increasing the intensity of the sun's radiation, the amount of carbon dioxide production in combustion products decreases.

Systems having degrees of freedom more than the number of control inputs, are called under-actuated systems. Due to small size of actuators, their cost and energy utilization are decreased and they can be implemented in a more simple way. Inverted pendulum system which is an unstable, nonlinear, non-minimum phase and uncertain system, is one of the most applicable and fundamental cases of under-actuated systems. In this paper, an inverted pendulum is modelled as a two degrees of freedom model. Then, a linear multivariable feedback controller is designed to stabilize the experimental set-up. The experimental inverted pendulum is constituted of two links; while one actuator is installed on the first link joint. According to the simulation results, a DC servo motor with specifications of 12 v and 1.2 W nominal power, is selected as the actuator. Experimental results show that the designed controller can appropriately control and stabilize the experimental system around its unstable up-equilibrium point up to6o.

Nowadays, using new materials with acceptable properties and also reducing costs and harmful environmental effects has turned into an essential issue. So far, biocomposites have mostly been used for nonstructural applications. In this study, nanopowders were added to biocomposite to achieve better properties. In this regard, 4 different parameters including fiber loading, type of nanopowder and its weight percentage and also weight percentage of NaOH in alkali treatment, each factor in 2 levels, were considered in Taguchi design of experiment and 8 specimens were manufactured and tested based on ASTM D3039 standard test method to determine tensile properties. Analysis of variance (ANOVA) and Taguchi method were also conducted to determine the significance of each parameter on test results. Based on results, weight of fiber, kind of nanopowder, weight of nanopowder and weight percent of NaOH in alkali treatment are ranked 1st to 4th respectively and there is a complete agreement between the results obtained from S/N ratio analysis and ANOVA results corresponding to order of parameter significance.

In the present study, laminar flow and heat transfer of non-Newtonian fluid, including the solution carboxymethyl cellulose (CMC) at a concentration of 0.5 wt% is investigated numerically. Nano particles including the volume fraction of 1 and 1. 5 percent copper oxide nanofluid with a diameter nanoparticles are equivalent 100nm. Also in this research, the effects of coefficient of non-dimensional slip velocity is also considered in the cases of β*= 0-0.1. the Laminar flow and heat transfer of non-Newtonian nanofluid in a horizontal two-dimensional microtube with the length equals L=200mm and hydraulic diameter equals Dh = 3 mm is numerically simulated. A fixed heat flux equals of q"=1000W/m2 is applied on the walls of the horizontal microtube. The range of Reynolds numbers in this study between 100 ≤ Re ≤ 2000. In this study, the effect of slip velocity coefficient, the volume fraction of copper oxide nanoparticles and Reynolds number on the parameters of fluid flow and heat transfer of non-Newtonian nanofluids are considered. The results, in the form of figures, the Nusselt numbaer, coefficient of friction, velocity and non-dimensional temperature are depicted. Results of the study show that the increase in the volume fraction of solid nanoparticles and the coefficient of slip velocity increases the heat transfer coefficient. As well as the increase of the slip velocity coefficient has a big effect on reducing the coefficient of friction on the walls of the horizontalmicro tube.

Renal artery stenosis is a major cause of death and permanent harm to the body. The rigidness of the wall of the arteries is the main cause of atherosclerosis and renal artery stenosis. Therefore, the purpose of this study was to evaluate the effect of vessel wall thickening and renal artery stenosis on the entrance of blood flow through the arterioles of the kidney by using physical modeling, second goal of this study was to evaluate the effect of renal artery stenosis on the characteristics of the flow in the downstream and also to identify areas prone to congestion in the presence of renal artery stenosis. Actual geometry and boundary conditions was used for modeling. In this study, Newtonian and non-Newtonian models was assumed for the viscosity of blood and the results were compared to each other. The effect of mild (30%), moderate (50%) and severe (70%) occlusions was studied on the flow parameters. The areas which were prone to congestion were identified in occluded and non-occluded geometries and the results were compared. The results show that not much difference between Newtonian and non-Newtonian models for blood viscosity is noticed in the present geometry and blood can be considered as a Newtonian fluid. Investigation showed that the congestion-prone areas are located before and also in the first branch of bifurcation because in these areas the shear stress is maximum. The congestions haven’t influenced areas which were prone to occlusion, but the more percentage of stenosis the more there is possibility for occlusion.

In this article, requirement to extend star tracker performance to daytime including mission catalog and image based robust identification algorithm is considered. According to infrared point source catalogs such as 2 Micron All Sky Survey (2MASS), millions of stars are available in certain wavebands of short and near infrared. Mission catalog is filtered and uniformed version of 4000 highest quality infrared point sources2MASS. Most of 2MASS stars will be present in the star tracker field of view as spikes but not available in database. Therefore it is necessary to avoid their influence on recognition. In this algorithm, information extracted from a single pixel, whether it contains the star centroid or not is utilized. Euclidean distance transform (EDT) of every star with respect to its nearest star centroid is evaluated using Voronoi diagram of image with reduced dimension and stored in database. After processing the image, the map from each guide star is compared to database and in case the matching criterion is not satisfied, the star is eliminated in two greater loops until a similar pattern is recognizable. The algorithm shows considerable performance in the presence of spikes in the field of view.

In this study, effects of press pressure parameter on the polarization resistance of silver electrodes of zinc - silver oxide batteries in the KOH solution were investigated. For this purpose, initially four Ag electrodes (positive plate) with composition of 95 wt% silver oxide, 4.9 wt% carbon powder and 0.1 wt% resin by powder metallurgy method and with press pressure of 40, 60, 80 and 100 bar was prepared. Then, four silver electrodes were sintered at temperature 500°C for 13 minutes. Potentiodynamic polarization and electrochemical impedance spectroscopy methods were used in the 1.4% KOH solution to evaluate the polarization resistance of Ag electrodes. Scanning electron microscopy was used to examine the microstructures of electrodes and point analysis was accomplished by EDX method. Electrochemical tests results showed that with increasing press pressure, polarization resistance of silver oxide electrodes increased in the KOH solution. SEM images were showed that with increasing press pressure, the amount and size of apparent pores reduced in the electrodes. Also, point analysis results has implies on reduction of oxygen in electrodes with the reduction press pressure.

In this paper, free surface flows over a wedge with gradually and rapidly varied depths in a rectangular open channel are studied by comparing the simulation results and experimental data. The volume of fluid (VOF) method is used to model the two phase flow. The results of the standard k-ε, RNG k-ε, Realizable k-ε, k-ω, and SST k-ω models were compared experimental results. The results show that the standard k-ε model gives better results in comparison with experimental data. The results of the simulations are very close to the experimental data at the gradually varied portion of the flow. However, at rapidly varied section of the flow, the turbulence models fail to predict good results. Performance of this model in different volumetric flow rate is also investigated in detail.

The main goal of this paper is to determine the maximum Dynamic Load Carrying Capacity (DLCC) of redundant robotic manipulators. Here, a methodology based on the Pontryagin’s minimum principle has been employed to determine the maximum DLCC of the redundant robotic manipulators in point to point motion. In fact, the optimality conditions are achieved according to the principle of the calculus of variations. To determine the maximum DLCC of the mentioned robotic arm, the saturation limit of each motor and also the joint-limit avoidance of each joint are considered. Thus, by using the Hamiltonian function and the Pontryagin’s minimum principle, two sets of differential equations as well as an algebraic equation are developed. The boundary conditions of the system are determined in such a way that by solving these equations, the maximum DLCC and also the inverse kinematic of the system are obtained, numerically. Finally, to show the efficiency of the presented method, the maximum DLCC of a robotic arm corresponding to the humanoid hand with 4 degrees of freedom is evaluated. It is shown the obtained maximum DLCC of this humanoid-like robotic arm, is in the range of the load value that reported by the Ministry of Health and the National education.

Friction Stir Welding is a solid-state process, which means that the objects are joined without reaching melting point. Which has demonstrated very high suitability for the joining of dissimilar aluminium alloys. The aim of this investigation was to study residual stress and micro hardness distribution in different zones of dissimilar friction stir welding of AA6061-T6 and AA7075-T6 and compare it with the tungsten inert gas (TIG) welding of AA6061-T6 by using increment hole drilling technique. Also The evolution of the residual stresses in the thickness direction was investigated, it was found that the maximum residual stresses are below the yield strength of the material in the shoulder region and showed that the longitudinal residual stresses in the joint were much larger than the transverse residual stresses. Vickers micro hardness measurements were performed in the transverse cross section of the samples, the results showed that Hardness peak values were observed in SZ region adjacent to the advancing side whereas low hardness regions were measured across the weld corresponding to the HAZ of both alloys and at the SZ adjacent to the retreating side.

In this study, the effects on energy optimization in cold and mountainous atrium examined. Three atrium in the shape of a cube, flat and domed have been simulated. Designed with the length and width dimensions (30 m × 30 m) and a height of 7 meters in the center of each of the models in order to form a flat atrium dimension (14/30 × 13/80) square and cube size meters and height (3/50) meter radius dome shape (7) meters in height (7 meters) were studied. Simulations of these models in three modes of ventilation (0, 30, 70) percent during the coldest week of the year, from the date (30 January - 6 February) that the outside temperature (-0.69 to 10.64 °C) below zero and also during the hottest week of the year to date (22 July - 28 August) that the outside temperature (25.78 to 30.70 °C) is investigated. Numerical simulation results show that the optimal shapes of the dome-shaped atrium with natural ventilation are 30%. A field sample (experimental) atrium as a validation were studied. Compare the numerical and experimental results show that the numerical simulation accuracy is very good with experimental.

The aim of this research was to evaluate physical, mechanical and morphological properties and also thermal behavior of nanocomposites made from wood flour (WF), polypropylene (PP) and graphene. Here, maleic anhydride grafted polypropylene (MAPP) was added as a coupling agent to increase the interaction between the components. The nanocomposites with different graphene concentrations (0, 0.5 1, 1.5,2 wt. %) were mixed by melt compounding in an internal mixer and then the composites manufactured by compression molding method. Water absorption, thickness swelling, morphological, tensile properties and crystallinity behavior of the prepared nanocomposites were evaluated. The results showed that the tensile strength and modulus of the nanocomposites was increased by 33.4% and 7.9 % respectively with increasing of graphene contents to 1 wt.% compared to the control sample (without graphene). Addition of graphene contents to 0.5 wt % increased the impact strength by 5.7% compared to the control sample. Also water absorption and thickness swelling of the nanocomposites decreased with increasing with amount of graphene to 1wt%. The smooth fracture surfaces and good interaction between the components of the nanocomposites with incorporation of graphene in low concentrations were shown by scanning electron microscopy (SEM) micrographs. Thermal analysis using differential scanning calorimetry (DSC) showed that addition of WF and graphene to neat PP increased crystallinity and crystallization temperature compared with neat PP.

Cellular solids are extremely used in aerospace industries and civil infrastructures due to their low weight/strength index that leads to decrease in total weight and fuel consumption. Determination of mechanical properties of these structures is absolutely essential for structural design fulfillment. In this paper the calculation of in-plane elasticity properties of elliptical cell honeycomb composite structure is investigated. In this regard at the beginning, by using free body diagram of the smallest repeating unit of cell, the forces and moments applied on unit cell are obtained; and then by using strain energy theory and Castigliano's theory, the in-plane elastic constants are obtained. For validation of theory results, by using the ABAQUS finite element program, the elliptical honeycomb is simulated and by using normal and shear loading conditions and obtaining stresses and strains, the elastic constants are calculated and compared with theory amounts. The results show that the relation of the macroscopic Young's modulus and the macroscopic shear modulus are directly proportional to the thickness of the cell wall and inversely proportional to the small diameter of the ellipse.

In this paper, the energy and exergy of single effect absorption and combined ejector-absorption refrigeration cycles are carried out analytically. Having analyzed the cycles and presented the governing equations with their expansion in EES software, we analyze the energy and exergy (from the viewpoint of the first and second law of thermodynamics) of both single effect absorption and combined ejector-absorption refrigeration cycles (while the ejector is located between the condenser and the generator) and calculate the value of output variables. Furthermore, the effects of evaporator and generator temperature on irreversibility, coefficient of performance, exergy loss and exergy efficiency of the aforementioned cycles have been investigated. We observe that, under identical conditions (i.e. equal temperature of evaporator and condenser), the efficiency of the combined ejector-absorption refrigeration cycle relative to the single effect absorption refrigeration cycle can be increased by more than 30%, but there is not a significant difference in the exergy efficiency of the two cycles.

This article deals with intelligence in fuzzy control of manipulators with fixed base and the last flexible arm. The tip is moving on a path which is pre-specified. It is assumed that the dynamics of the system is unknown and variable. In control based on fuzzy logic, membership functions remain unchanged in the beginning of selected path to the end. This research deals with modifying membership functions during movement in order to improve system response by using neural network. Dynamic recurrent neural network is used to accelerate updating membership functions. Parametric equations of updating network weights are obtained based on reduction of joint angle errors, rate of joint angle errors and bending deformation. To verify the effectiveness of the proposed method, simulation for manipulator is made with three arms. System responses are compared in both the fuzzy controller and the proposed controller with each other. In order to prove the robustness of the control system, an example will be presented. The obtained results and surveys show the effectiveness of the proposed method.

In this paper, at fist two-degree-of-freedom quarter-vehicle model and four-degree-of-freedom half-vehicle model of two vehicles with passive suspension systems and linear characteristics are developed. Then responses of these models to a road unevenness which is modeled as an impulse function with 100 mm amplitude, are investigated. For analyzing the dynamic behavior of vehicle, State Space Method in Matlab/Workspace, Matlab/Simulink and Finite Element Method were developed. For validation, the results are compared to previous works with the same data. The simulation results of these two models are compared with results of a fullvehicle model in another article. Finally, the effect of the suspension parameters on the maximum displacement and acceleration of body is investigated. Obtained diagrams show that while crossing a vehicle over an impulse and 100 mm amplitude road unevenness, softer springs always improve ride quality and Stronger dampers, reduce ride quality but make requirement of having more space between body and tires.

Fossil energy such as oil, gas and coal, generally not fully recoverable and retrieve. Large amounts of wealth remains in situ, which in addition to the basic features and their geological which are out of our reach, in bulk at harvest time performance such as speed of operation and the way it goes. In this study, a numerical scheme for simulation of two phase water and oil in an oil reservoir is developed. Constant flow rate of water injected through injection well located in the center of the reservoir and oil produced through production wells in the corners of the reservoir. The water and oil saturation and pressure distribution within the reservoir simulated during a certain time period and the general results are examined and compared with CMG software outlet which a good agreement is achieved. The effect of a barrier in the reservoir is also examined. The results illustrate that as much as possible with an accurate diagnosis must be considered a suitable place to injection wells that are drilled so far of the oil barrier.

Conjugate heat transfer in a pulse tube is simulated numerically. Navier-Stokes equations are used for flow simulation and coupled fluid and solid energy equations are used for solving temperature domain in the tube. In the present paper, wall thickness, solid to fluid conductivity ratio, Womersley number, pulsating amplitude, Reynolds and Prandtl numbers have been considered to conduct a parametric study. By increasing wall thickness ratio from δ/Ri=0.13 to δ/Ri=1.0, Nusselt number increases almost %14. Results showed that pulsating flow Nusselt number is less than that of steady unidirectional flow for non-dimensional pulsating amplitude of less than one; however, it is higher than steady unidirectional Nusselt number for non-dimensional pulsating amplitude of more than one. The ratio of friction coefficient of pulsating to steady unidirectional flow is higher than one and it rises rapidly with increasing the pulsating amplitude. Nusselt number is reduced by increasing Womersley number for pulsating non-dimensional amplitude of less than one; however there is an optimum for pulsating amplitude of more than one which is 20 for pulsating amplitudes of 1.4, 2.4 and 3.

Breakwater or submerged obstacle is one of the methods used for protection of the coast. Breakwaters cause dissipation of wave energy by generation of turbulence flow and vortices. In this study, by insert a rectangular obstacle against a solitary wave, the generation and evolution of vortices have been investigated by using Particle Image Velocimetry (PIV) technique. The PIV results show due to flow separation, two vortices are formed around the front and back edges of the obstacle when the solitary wave approaches the obstacle. The closer the wave approaches the obstacle, the larger the vortices are. When the formed vortex over the front edge of the obstacle approaches its end, these two vortices are merged together and form a larger vortex. In the following, the reduction of wave height before and after the obstacle is measured through a wave gage altimeter sensor. The results show the existence of obstacle decreases up to 3% of wave height in comparison to that without obstacle. Finally, by integrating pressure and momentum flux from the PIV results around the obstacle, the drag force applied to the obstacle is obtained.

In this article, the leakage of the refrigerant in a two stage liquefaction system with multi component refrigerant is studied. Leakage is occurred due to various factors, including the existence of cavity in high pressure area and affects the performance of the process. Due to the absence of a specific method to handle leakage of refrigerant an innovative method is performed and validated by comparing experimental data. The results show the leakage at high-pressure points, causes a little reduction of specific work, but the product (liquefied natural gas) is significantly reduced. Additionally, it is shown that leakage increases the risk of temperature interference in heat exchangers, which should cause malfunctions in system operation.

The use of sedimentation tanks is one of the main steps in the water treatment process. Increase of the tank efficiency, due to change in input water characteristics or population increase is justifiable and has always been considered. In this project, the effect of middle baffle position as an effective factor in the tank geometry and change of flow rate in the velocity profile of tank have been studied experimentally. Measurements have been carried out in channel available in the fluid research laboratory. Rectangular tanks are studied in two cases of with and without middle baffle in operational different conditions. Dimension of rectangular tanks is 12 m×0.2 m×0.3 m. Baffle height is 7.5 cm and its effect on the velocity profile in distances of 1.2 m and 4 m from inlet of the tank in both full and half rate have been studied. Results show that the velocity distribution of baffled tank, especially in the second half of tank, compared to without baffle one, is more uniform. In the second half, Jet flow disappears, short circuiting is reduced and the efficiency of the middle baffle in high rate flow conditions will be reduced. Keywords:

It is convenient method to use a drag-reducing polymer to reduce entropy generation in annular two-phase flow. The drag-reducing polymer is a high molecular weight poly-alpha-olefin. In present paper for the first time, the explicit equation has been presented for the prediction the entropy generation in annular flow with drag-reducing polymer. The equation is function of the pipe diameter and superficial velocities. Entropy generation versus drag-reduction and holdup in different pipe's diameter (0.0127, 0.0254 and 0.0953 ) and in different superficial velocities are presented. The results are shown that entropy generation decreases with increasing , and pipe diameter but entropy generation increases with increasing gas and liquid superficial velocities. Therefore by adding drag-reducing polymer and correct determination of pipe diameter and superficial velocities using the presented explicit equation in this research, could be reduced the losses and increased in the production in related industries.

In this paper temperature distribution of oil in cylindrical tank with heater and mixer was studied by numerical simulation. All three heat transfer mechanisms in the outer surfaces were considered. Mesh was generated around the tank and after applying boundary conditions the temperature distribution was simulated by finite volume method. The effect of mixer on temperature distribution was investigated. As it is expected, when mixer was working the temperature distribution was uniform. Without mixer, there was a laminar flow from heated region to colder region and to the roof of tank and temperature distribution wasn’t uniform. In general, temperature was increased with elevation but in near of the roof the temperature is decreased since heat loss from roof.

A numerical analysis has been performed to investigate the laminar natural convection heat characteristics in a wavy cavity filled with CuO/water nanofluid The left and right walls are insulated and the wavy bottom and top walls are maintained at a constant temperature while the uniform magnetic field is considered. In performing the analysis, the governing equations are given in terms of the stream function-vorticity formulation. In order to solve Non-dimensionalized equations, discretizing with second-order accurate central difference method and was performed using the successive under relaxation with appropriate boundary conditions is considered. To validate the numerical model, various comparisons with previously published studies have been conducted and results are in a good agreement. The main objective is to survey the effects of the Rayleigh number, Hartmann number, and nanoparticles volume fraction on the fluid flow and heat transfer characteristics. Results are illustrated in contours of stream function, constant temperature, and Nusselt number. For all values of Rayleigh number, the presence of nanoparticles leads to significant enhancement in heat transfer.

In the solar greenhouses, natural ventilation is used to repel the unnecessary heat by opening the windows. This regular action is led to enter diverse of pest and insects to the greenhouse and consequence production damages. In the presented work, a novel case of solar greenhouses is simulated and represented. This design uses a special cover on the roof that reflects NIR and avoids greenhouse warming too much, in the hot seasons. With no more heat, the ventilation needs get less and the pests damages will be prevented. In this work, NIR reflected by the cover placed on the circular roof of the greenhouse is focused in the collector equipped in the focal line of the roof. The collector contains water and PCM that makes it possible to store huge amount of energy in a limited space. Considering energy received in a typical summer day, the optimum quantities for minimum collector radius versus maximum PCM volume is computed. Numerical investigation on this design is performed in three different geometries and results are reported as temperature contours and stream functions. In addition, energy stored in every three cases is calculated and compared with greenhouse heating load. The results shows that annual greenhouse heating load can be provided by energy stored in this system and prevents the bothersome insects at the same time.

Today, brittle and quasi brittle materials are widely used in the various structures such as aerospace structures, because of very low deformability as well as high strength and stiffness compared with their weight. There is a greater need for analysis of the brittle structures, with increasing application of these materials in the industries. In this paper first, the extended finite element method (XFEM)is applied to investigate the nucleation and crack growth mechanism of the brittle materials. Then, damage models based on cohesive zone models(CZM)are considered to predict initiation and crack growth. In the following, a number of benchmark problems are simulated; damaged and critical zones in them are predicted, using the ABAQUS commercial finite elements software. Finally, the numerical simulations results are compared with the experimental and theoretical results and validated. Comparison of the numerical and experimental results revealethat the stress-based damage criteria are more accurate than the strain-based damage criteria. Hence, it is concluded that in comparison with the stress-based damage criteria, using the stress-based damage criteria is more reliable in fracture prediction of brittle materials.

In the paper an auto-pilot with layered control architecture has been designed for an autonomous quad-rotor and an optimized proportional-derivative controller has simulated on the quad-rotor. In the auto-pilot with layered control architecture, quad-rotor will be controlled with a multi agent system which has at least 4 agents to control the system instead of just having a single controller. Each agent has placed in an independent layer with its own CPU, memory and processing equipment that perform individually. Nonlinear controllers such as back stepping and sliding mode are presented. In the layered learning process, a new optimization method for neural networks is presented in the paper which is named Growing Particle Swarm Optimization. In one of the layers some classic controllers such as back stepping and sliding mode is used to train the neural controller in the other layer. Optimization results show that the neural network controller can successfully learn the controlling task using Growing Particle Swarm Optimization.

The present study focuses on the flow around a horizontal axis wind turbine. Large Eddy Simulation has been employed in order to study the flow at different rotational speeds. Anisotropic residual stress tensor is driven by The Smagorinsky model. Three simulations were performed at different tip speed ratio of 3, 6 and 10. The acquired results are in good agreement with presented experimental data in literatures. It is also revealed that development of the wake is decreased when downstream velocity is increased along the horizontal line at different downstream distance of wind turbine. In addition, velocity defect behind the wind turbine is increased when tip speed ratio increases but the recovery of wake is happened faster. At rotational speed equals 6, minimum velocity is 54% of the initial velocity and maximum efficiency is 67% at the lateral section of wind tunnel where the tip of blade is located, while they are 26% and 68% respectively when rotational speed is 10. Turbulence intensity is increased by increasing Tip Speed Ratio while separated vortices from the blade are disappeared later. The effect of separated vortices from the blades of wind turbine are not seen when rotational speed is 3, while they are revealed at rotational speed of 6 and 10. As a result, it can be concluded that the effect of separated vortices are augmented when rotational speed is increased.

Vibrational behavior of nanotubes is investigated in different papers based on different theories which our investigation shows that there is big difference in their results. So, in this paper, vibrational behavior of nanotubes is analyzed using Euler, Timoshenko beam theories and Sanders first order shear deformation shell theory. In order to considering effect of scale, nonlocal elasticity theory is combined with these three geometrical theories who are exactly solved for six combinations of classical boundary conditions. Results are compared with references and molecular dynamics results and validity and accuracy of presented methods are approved. It is approved that nonlocal Sanders first order shear deformation theory has the best accuracy and needs the lower scale parameter to predict natural frequencies.

Planetary gear boxes are widely used in power transmission systems with high torque to weight ratio, high speed reduction in low space and access to deceleration in several stages. The main objective of this research is an overview on the dynamics and vibrations of the planetary gear systems. This research provides a comprehensive study of relevant resources published in various journals for researchers who wish to work on the dynamics of planetary gear systems. For this reason, these topics have been expressed in several sub-sections that cover all the dynamics and vibrations of planetary gear systems. In the end, a summary of the issues discussed and suggestions for further research in this field are expressed.