Journal of Computational & Applied Research in Mechanical Engineering (JCARME)Journal of Computational & Applied Research in Mechanical Engineering (JCARME)
http://jcarme.sru.ac.ir/
Tue, 19 Mar 2019 18:06:50 +0100FeedCreatorJournal of Computational & Applied Research in Mechanical Engineering (JCARME)
http://jcarme.sru.ac.ir/
Feed provided by Journal of Computational & Applied Research in Mechanical Engineering (JCARME). Click to visit.A Study on free convective heat and mass transfer flow through a highly porous medium with ...
http://jcarme.sru.ac.ir/article_771_181.html
The paper addresses the effects of Soret on unsteady free convection flow of a viscous incompressible fluid through a porous medium with high porosity bounded by a vertical infinite moving plate under the influence of thermal radiation, chemical reaction, and heat source. The fluid is considered to be gray, absorbing, and emitting but non-scattering medium, and Rosseland approximation is considered to describe the radiative heat flux in the energy equation. The dimensionless governing equations for this investigation are solved analytically by using perturbation technique. The effects of various governing parameters on the velocity distributions, temperature distributions, concentration distributions, local skin-friction coefficient, local Nusselt number and local Sherwood number are shown in figures and tables and analyzed in detail. It was noticed that the velocity distribution increased with increasing buoyancy parameters, temperature profiles decreased with increasing Prandtl number and concentration fields decreased with increasing the Schmidt number and chemical reaction parameter.Thu, 31 Jan 2019 20:30:00 +0100Numerical investigation on the effects of six control rods arranged in equilateral triangular ...
http://jcarme.sru.ac.ir/article_1035_0.html
The present work deals with heat transfer characteristics as well as fluid flow patterns in laminar flow regime for a circular cylinder with six control rods arranged in equilateral triangular geometries. The computations have been carried out by a finite volume approach using the overset grid method. The unsteady flow at Re= 200 and Pr= 0.7 and 7.0 was examined. The effect of the control rods on suppression of the fluid forces applied on a main cylinder has been investigated by numerical solution of the Navier-Stokes equations. Based on the results obtained, the arrangement employed in this study indicated the significant performance in reducing the oscillatory force coefficients of the primary cylinder. Except for some gap ratios, it is indicated that both drag and lift coefﬁcients are much lower than that for a single cylinder. Moreover, forced convection heat transfer was calculated using local and mean Nusselt numbers at the surface of the cylinders. The instantaneous streamlines, the vortices and isothermal contours were presented in order to analyze the temperature field and flow field around the cylinders.Sun, 24 Feb 2019 20:30:00 +0100Fuzzy motion control for wheeled mobile robots in real-time
http://jcarme.sru.ac.ir/article_809_181.html
Due to various advantages of Wheeled Mobile Robots (WMRs), many researchers have focused to solve their challenges. The automatic motion control of such robots is an attractive problem and is one of the issues which should carefully be examined. In the current paper, the trajectory tracking problem of WMRs which are actuated by two independent electrical motors is deliberated. To this end, and also, computer simulation of the system, first the system model is derived at the level of kinematics. The system model is nonholonomic. Then a simple non-mode-based controller based on fuzzy logic will be proposed. The control input resulted from fuzzy logic will then be corrected to fulfill the actuation saturation limits and non-slipping condition. To prove the efficiency of the suggested controller, its response, in terms of the required computational time burden and tracking error, will be compared with a previously suggested method. The obtained simulation results support the superiority of fuzzy based method over a previous study in terms of the considered measures.Thu, 31 Jan 2019 20:30:00 +0100Effects of the asymmetric behavior of the shape memory alloy on nonlinear dynamic responses of ...
http://jcarme.sru.ac.ir/article_1034_0.html
In the present article, dynamic behavior of sandwich plates with embedded SMA wires is evaluated for two cases: (i) stress-strain curve of the superelastic behavior of the SMA is symmetric and (ii) the mentioned curve is non-symmetric. A modified version of Brinson’s constitutive model is proposed and used in the present research. In this regard, in addition to the proposed advanced algorithm for determination of the martensite volume fraction, a Picard iterative solution algorithm is used in conjunction with Newmark’s numerical time integration method for solving the resulting finite element equations. In order to increase the accuracy of the results, variations of the martensite volume fraction and material properties of individual points of the structure are updated continuously. Therefore, the kinetic equations of the phase transformation of the SMA are coupled with the motion equations, to accurately model the nonlinear behavior of the sandwich plate. For analysis of the thick sandwich plate, a higher order global-local theory with novel 3D-equilibrium-based corrections has been utilized. One of the features of this theory is the capability of estimation of the nonlinear in-plane displacement components, and precise assessment of the transverse shear stresses through satisfying the continuity conditions of the shear stresses at the interfaces between layers. Another advantage of the proposed theory in comparison with the conventional approaches is the ability to simulate changes of the core thickness. This is especially important in cases where the core is relatively thick or soft.Sun, 24 Feb 2019 20:30:00 +0100Calculation of lateral velocity estimation and error discrimination for railway wheelset to ...
http://jcarme.sru.ac.ir/article_949_181.html
Lateral velocity has very backbone position in the railway vehicle wheelset dynamics as it usually becomes cause of derailment by sliding due to insufficient adhesion ratio. This impropriate balance is pretext owing to contamination and weather procures the disturbances. This perturbation makes hindrances in proper running of wheelset on track. To analyze the noise, Kalman filter is used based upon the railway dynamic modeling to estimate the actual signals to control the noise by measurement. Thus error percentage is also computed to detect the slippage by adhesion on applicable analysis of creep co-efficient. The motion and velocity of Lateral and yaw analysis for railway vehicle wheelset is of great importance for the slip and sliding point of view. As usually hit has been observed that fatal accidents, destruction of railway vehicle with railway tracks and damage of costly lives happen due to improper control on the lateral and yaw railway dynamic system with chaos management as well as technical point of view. Since controllable estimated lateral velocity assures minimum wheel slide.Thu, 31 Jan 2019 20:30:00 +0100GRASP ANALYSIS OF A FOUR-FINGERED ROBOTIC HAND BASED ON MATLAB SIMMECHANICS
http://jcarme.sru.ac.ir/article_1033_0.html
The structure of human hand is a complex design comprising of various bones, joints, tendons, and muscles functioning together in order to produce the desired motion. It becomes a challenging task to develop a robotic hand replicating the capabilities of the human hand. In this paper, the analysis of the four-fingered robotic hand is carried out where the tendon wires and a spring return mechanism is used for the flexion and extension motion of the fingers respectively. Stable grasping and fine manipulation of different objects are desired from any multi-finger robotic hand. In this regard, it becomes necessary to check the performance of the four-fingered robotic hand. Simulations are performed for the hand to grasp objects of different size and shapes and the hand model is controlled in MATLAB environment using the SimMechanics toolbox. Here the Kinematics and Dynamics study of the hand system is carried out by importing the Solidworks model into the SimMechanics. Simulation results demonstrate that the developed hand model is able to grasp objects of varying size and shapes securely.Sun, 24 Feb 2019 20:30:00 +0100Experimental and numerical investigation of bottom outlet hydraulic model
http://jcarme.sru.ac.ir/article_827_181.html
Using experimental models along with conducting numerical analysis have been widely used in performance recognition and optimization of hydraulic equipments. Numerical modeling has lower cost rather than experimental one; however practical tests are commonly used because of the hydraulic structure importance especially in dams. Meanwhile numerical methods could be used for future designs through validating numerical models. In this paper, volume of fluid method, VOF, has been employed to simulate the free surface flow at the dam bottom outlet form bell mouth section up to the downstream channel. Since the flow through the gates has high Reynolds number, the standard k-ε and also Reynolds Stress Model, RSM, turbulence models is used and the results compared. The discharge coefficient and the ventilated air velocity through the vents is computed numerically and compared with the experimental data. Comparison between the experimental data and numerical simulation results shows good compatibility, especially in RSM turbulence model rather than k-ε turbulence model. The results show that the maximum error percentage in simulation of the discharge coefficient and the ventilated air velocity is 9% and 3% respectively.Thu, 31 Jan 2019 20:30:00 +0100INFLUENCE OF INSERTION OF HOLES IN THE MIDDLE OF OBSTACLES ON THE FLOW AROUND A SURFACE-MOUNTED CUBE
http://jcarme.sru.ac.ir/article_1032_0.html
The aim of our study is to analyze the impact of insertion holes in the middle of obstacles on the flow around a surface-mounted cube, In order to do this; we studied four configurations of obstacles in a channel with a Reynods number based on obstacle height ReH = 40000. The hexahedral structured meshes were used to solve the fluid dynamics equations .The finite volume method are employed to solve the governing equations using the ANSYS CFX code and the turbulence model k-ω SST. The streamwise velocity profiles, the Time-averaged streamlines, the turbulence kinetic energy and the drag coefficient are presented. The results showed the appearance of a second vortex behind obstacles with hole from diameter D/H=0.2. The turbulence kinetic energy was greater on top of the obstacle, it was more intense for the obstacle without hole, this intensity decreased as the hole diameter increased. The drag coefficient was improved only for the case D/H=0.32Sun, 24 Feb 2019 20:30:00 +0100Fuzzy gain scheduling of PID controller for stiction compensation in pneumatic control valve
http://jcarme.sru.ac.ir/article_856_181.html
Inherent nonlinearities like, deadband, stiction and hysteresis in control valves degenerate plant performance. Valve stiction standouts as a more widely recognized reason for poor execution in control loops. Measurement of valve stiction is essential to maintain scheduling. For industrial scenarios, loss of execution due to nonlinearity in control valves is an imperative issue that should be tackled. Thus, an intelligent technique is required for automated execution, observation and enhancement. The paper shows the creative utilization of an intelligent controller for nonlinearity diagnosis in control valves. This is a Fuzzy Gain Scheduling (FGS) PID smart controller that tunes its gain parameters in real time to manage a control valve’s inherent nonlinearity. The viability of the FGS PID controller is experimentally verified in a laboratory scale plant. An execution comparison between FGS PID and classical PID controllers are undertaken for their set point following and disturbance rejection at different operating points. Experimental results show that the FGS PID controller outperforms the classical PID controller for all explored cases effectively managing stiction based oscillation in the controller output.Thu, 31 Jan 2019 20:30:00 +0100Design and manufacture a novel tool in the incremental sheet metal forming process and its ...
http://jcarme.sru.ac.ir/article_1031_0.html
One of the methods for making prototypes is incremental forming process. In this method, the forming tool, performs a pre-programmed movement by the CNC machine and runs the desired path. This modernization process is used in the automotive, aerospace, military, medical and other industries. One of the most influential parameters in this process is forming tool. This parameter is effective in forming forces, surface roughness, sheet formability and thickness distribution. In this study, the forming tool was investigated and rotating geometry tool was compared with a rigid tool. Also, the effects of step down, feed rate and spindle speed were investigated on the forming force, surface roughness and thickness distribution by comparing mentioned forming tools. The results indicate that the forming forces, sheet surface quality and thickness changes increase with increasing step down and feed rate. Using the rotary tools improves the forming forces, surface roughness and thickness distribution rather than the non-rotating tool.Sun, 24 Feb 2019 20:30:00 +0100Numerical investigation of vertical and horizontal baffle effects on liquid sloshing in a ...
http://jcarme.sru.ac.ir/article_992_181.html
Liquid sloshing is a common phenomenon in the transporting of liquid tanks. Liquid waves lead to fluctuating forces on the tank wall. If these fluctuations are not predicted or controlled, they can lead to large forces and momentum. Baffles can control liquid sloshing fluctuations. One numerical method, widely used to model the liquid sloshing phenomena is Smoothed Particle Hydrodynamics (SPH). Because of its Lagrangian nature, SPH is suitable for simulating free surface flow. In the present study, a relatively accurate Incompressible SPH (ISPH) method improved by kernel gradient correction tensors, particle shifting algorithms, turbulence viscosity calculations, and free surface particle detectors is applied for the free surface flow modeling. In comparison to the other SPH Simulations and experimental data, these results show that the present algorithm is effective for simulating free surface problems. The present algorithm has been applied to simulate liquid sloshing phenomena, while the aim of this study is the investigation of vertical and horizontal baffle effects on the control and damping of liquid sloshing. Results show that for vertical baffles, baffle size has a major role in sloshing fluctuation damping. For horizontal baffles, also including size, the baffle base position has a significant role in liquid sloshing fluctuation damping. When horizontal baffle is near the free surface, sloshing fluctuation-damping increases.Thu, 31 Jan 2019 20:30:00 +0100Combined Effect of Hall Current and Chemical Reaction on MHD Flow through Porous Medium with ...
http://jcarme.sru.ac.ir/article_1026_0.html
Unsteady flow with magneto-hydrodynamics and heat generation through porous medium past an impulsively started vertical plate with constant wall temperature and mass diffusion is considered here. The effect studied is a combination of Hall current and chemical reaction. The motivation behind this study is the applications of such kind of problems in industry. In many industrial applications electrically conducting fluid is subjected to magnetic field. The fluid is passed through porous medium. The flow may be on a plate. There may be substance on the plate which may cause chemical reaction. The solution of flow model studied here is obtained by using Laplace transform method. The respective profiles have been drawn for velocity. The numerical data have been obtained using latest software techniques available. The profiles have been analyzed and discussed. The values of Nusselt number, Sherwood number, and drag on plate have been tabulated for analysis. The findings have been summarized in conclusion section.Tue, 19 Feb 2019 20:30:00 +0100Experimental analysis of shock waves turbulence in contractions with rectangular sections
http://jcarme.sru.ac.ir/article_823_181.html
Formation of shock waves has an important role in supercritical flows studies. These waves are often occurring during passage of supercritical flow in the non-prismatic channels. In the present study, the effect of length of contraction wall of open-channel for two different geometries (1.5 m and 0.5 m) and fixed contraction ratio was investigated on hydraulic parameters of shock waves using experimental model (models 1 and 2). For achieving to this goal, values of height and instantaneous velocity were measured in various points of shock waves observed in contractions for four Froude Numbers. In general, non-uniform distribution of velocity and turbulence intensity profiles were completely clear. Comparing results of models 1 and 2, show that the height and velocity values of formed waves in the model 2 is so much more than the model 1. Also, motion of the shock waves was accompanied with longitude gradient decrease of turbulence kinetic energy. The results of the present research can be very useful for designer engineers.Thu, 31 Jan 2019 20:30:00 +0100Numerical modeling and comparison study of elliptical cracks effect on the pipes straight and ...
http://jcarme.sru.ac.ir/article_1025_0.html
The present work deals with the effect of an external circumferential elliptical crack located at thickness transition on a varied stepped diameter pipe . The purpose is the application of the extended finite element method (XFEM) for the calculation of SIF at the thickness transition region of pipe considering internal pressure and compare the effect of the crack between pipes straight and with thickness transition. To model a crack with precision , enrichment functions are used to enrich the displacement approximation, the level set functions are calculated from the crack mesh and definition of the strategy of integration has been performed. A comparative study is made on SIF of crack defect in straight pipe compared to one with thickness transition using XFEM for the crack and pipe geometrical parameters variations. The result shows that the XFEM is an effective and practical tool for elliptic crack modeling in a pipe with thickness transition because a crack is easily modeled through enrichment functions.The comparison of the SIF of a similar defect between pipes shows that a pressurized pipe with thickness transition is more sensitive to the used cracks.Tue, 19 Feb 2019 20:30:00 +0100Laminar mixing of high-viscous fluids by a cylindrical chaotic mixer
http://jcarme.sru.ac.ir/article_932_181.html
Laminar mixing of glycerin in a chaotic mixer is carried by means of the blob deformation method. The mixer was a cylindrical vessel with two rotational blades which move along two different circular paths with a stepwise motion protocol. The flow visualization was performed by marking of the free surface of the flow with a tracer. The effects of controlling parameters such as rotational speed of blades, blades length, and rotational speed amplitude on mixing efficiency and time were analyzed by measuring of the area covered by the tracer. The results revealed that increasing rotational speed intensifies stretching and folding phenomenon, and consequently better mixing can be obtained. Also, the better condition in flow kinematic was provided to blend as stepwise motion protocol with wider amplitude adopted. A reduction in mixing time could be observed as the blades with longer length were used. In addition, it was also found that the promotion of mixing by rotational speed is more effective than that of two other parameters. The quantitative data and qualitative observations proved the potential of proposed chaotic mixer in wide range of industrial processes including chemical reaction and food processing in which laminar mixing is required.Thu, 31 Jan 2019 20:30:00 +0100Parametric study on axial compressor performance in design condition
http://jcarme.sru.ac.ir/article_1024_0.html
In This paper, a parametric study of compressor performances was performed by streamline curvature method (SLC). Effects of three input parameters in design process, e.g., number of blades, distribution of blade thickness, and blade sweep angels, on the main objective parameters in aerodynamic design, e.g., velocity distribution, efficiency and pressure ratio, has been investigated in the parametric study. Initially, a certain two stage axial compressor has been designed by SLC. Validation of the results is confirmed by comparing the obtained results with the experimental ones. Regarding various values for aforementioned input parameters, the first stage of the axial compressor is redesigned and the output parameter is established. Therefore, the sensitivity of the design results to each of the aforementioned parameters is recognized. Results show that increasing the blades sweep angle causes to improve the flow behavior such as efficiency and pressure ratio in axial fan and reducing it have a completely contrary result. Also, reducing the rotors blades number leads to an increase in the pressure ratio and efficiency while its increase cause to a contrary result. , it is concluded that reduction in the blades number has the stronger effect on the performance parameters than its increment. The results also show that effect of the thickness in the hub is greater than the thickness of the tip and its increase leads to reduce both efficiency and pressure ratio.Tue, 19 Feb 2019 20:30:00 +0100Flow field, heat transfer and entropy generation of nanofluid in a microchannel using the ...
http://jcarme.sru.ac.ir/article_998_181.html
In this study, the finite volume method and the SIMPLER algorithm is employed to investigate forced convection and entropy generation of Cu-water nanofluid in a parallel plate microchannel. There are four obstacles through the microchannel, and the slip velocity and temperature jump boundary conditions are considered in the governing equations to increase the accuracy of modeling. The study is conducted for the Reynolds numbers in the range of 0.1<Re<10, Knudsen numbers ranging of 0<Kn<0.1, and volume fraction of nanoparticles ranging of 0<φThu, 31 Jan 2019 20:30:00 +0100Numerical investigation of upward air-water annular, slug and bubbly flow regimes
http://jcarme.sru.ac.ir/article_1023_0.html
In this paper, numerical investigation of upward two phase flow of air-water has been studied. Different conditions of flow regimes including annular, wispy annular, slug, churn and bubbly are simulated based on Hewitt and Roberts map, and a good agreement between the experimental data of the map and the numerical simulation has been observed. Accordingly, a proper CFD model in CFD software of Fluent with the required User Defined Function (UDF) has been obtained to simulate two phase flows of fluids with large density ratio in vertical tubes. The simulation is carried out with the volume of fluid (VOF) method and piecewise interface calculation (PLIC) algorithm for tracking the interface for the annular, wispy annular, churn and slug flow regimes and drift flux model for bubbly with proper selection of computational cell and time step sizes. Furthermore, water and air momentum fluxes have been changed and the changes to the flow patterns are studied.Tue, 19 Feb 2019 20:30:00 +0100Three-dimensional characteristic approach for incompressible thermo-flows and influence of ...
http://jcarme.sru.ac.ir/article_822_181.html
In this paper the characteristics of unsteady three-dimensional incompressible flows with heat transfer are obtained along with artificial compressibility of Chorin. At first, compatibility equations and pseudo characteristics for three-dimensional flows are derived from five governing equations (continuity equation, Momentum equations in three directions, and energy equation) and then results are simplified to two dimensional flows. Pseudo Mach hyper-cone (four dimensional cone) are found and its cross-section with physical axis is calculated numerically. Unlike compressible flow, this is not a sphere. It is found that the pseudo acoustic speed within the incompressible flow is function of artificial compressibility parameter and the directions. In two dimensional, Pseudo Mach cone is obtained by numerical solution of characteristic equations. Unlike compressible flow, the cross section of Mach cone with x-y plane is not circle. This shape is not oval, too. The influence of artificial compressibility parameter on convergence history and accuracy was surveyed by simulation of cavity flow as a benchmarkThu, 31 Jan 2019 20:30:00 +0100Numerical study of induction heating by micro / nano magnetic particles in hyperthermia
http://jcarme.sru.ac.ir/article_1022_0.html
Hyperthermia is one of the first applications of nanotechnology in medicine by using micro/nano magnetic particles that acts based on the heat of ferric oxide nanoparticles or quantum dots in an external alternating magnetic field. In this study, a two-dimensional model of body and tumor tissues imbedded was considered. Initially, the temperature distribution was obtained with respect to tumor properties and without the presence of an electromagnetic field. Then, the effect the electromagnetic field on the temperature distribution was studied. The results have been compared with other papers. These results indicated that the use of the electromagnetic field causes a significant rise in the tumor temperature; however, the risk of damage to the healthy tissues surrounding the cancerous tissue seems to be high. Then, the micro/nanoparticles were injected into the tumor tissue to focus energy on cancerous tissue and maximally transfer the heat onto this tissue. The temperature distribution in the state was compared with the case without the nanoparticles and other numerical works. The results demonstrated that with the injection of nanoparticles into the tumor, the maximum temperature location was transferred to the center of the tumor and also increases to 6°C. After determining the temperature distribution in the presence of nanoparticles, the effects of different variables of the problem were studied. According to the obtained results, the increase in the concentration and radius of nanoparticles have a positive effect on the temperature distribution in the tissue; on the other hand, the increase in the frequency and size of the electrodes have a negative effect. The relevant equations were solved numerically using the finite difference method.Tue, 19 Feb 2019 20:30:00 +0100Effectiveness of alumina nanofluid on slotting end milling performance of SKD 11 tool steel
http://jcarme.sru.ac.ir/article_1021_0.html
SKD 11 tool steels are among the most popular metals in mould industries for making different kinds of cold work molds and dies with high accuracy and long service life. They have a high percentage of carbon and chromium (12% chrome) with attractive properties of high wear resistance, good hardenability, high oxidation resistance, good corrosion resistance after quenching and polishing, small deformation after heat treatment. However, it is grouped under difficult-to-cut materials and makes it extremely difficult and expensive to machine using conventional machining processes. The demand for higher quality, lower manufacturing costs, particularly the environmental friendly characteristics has created the stimuli for manufacturers and researchers to find alternative solutions. An excellent media is formed in cutting zone by using MQL nanofluids in order to enhance the thermal conductivity and tribological characteristics, therefore improving the machining performance. The formation of lubricating film as well as the rolling action of nanoparticles in contact zones has gained much attention in the machining field. In this research work, the application of MQL Al2O3 nanofluids with vegetable oils and emulsion 5% is developed for slotting end milling of SKD 11 steel using normal HSS tool. The cutting forces, tool wear, tool life and surface roughness are investigated to evaluate the effectiveness of MQL nanofluid on cutting performance. The experimental results reveal that the cutting forces and cutting temperature decrease and the surface quality and tool life enhance. Furthermore, the improvement of the thermal conductivity of nanofluids is proven when compared to the pure fluids. Due to the rise of viscosity and thermal conductivity, the soybean oil-based nanofluid, which is almost inherently nontoxic, gives them superior lubricating and cooling properties suitable for MQL application compared to emulsion-based nanofluids. The novel environmental friendly technology definitely brings out many technological and economic benefits in machining practice.Mon, 18 Feb 2019 20:30:00 +0100Development Length of Laminar Magnetohydrodynamics Pipe Flows
http://jcarme.sru.ac.ir/article_1020_0.html
In this article, a laminar magnetohydrodynamics (MHD) developing flow of an incompressible electrically conducting fluid subjected to an external magnetic field is considered. The aim of the study is to propose a correlation for computing the development length of the laminar MHD developing flow in a pipe. A numerical approach is considered to solve the problem. In the first step, the numerical Finite Volume Method (FVM) is conducted to analyze the problem. Hereafter, the artificial neural network (ANN) is used to develop the datasets and in the last step, the curve fitting is applied to find a correlation for prediction of the development length as a function of the Reynolds and Hartmann numbers. In addition, the effect of the problem parameters on the development length are studied. It is found that the development length declines with the increase of the Hartmann number and grows with the rising of the Reynolds number.Mon, 18 Feb 2019 20:30:00 +0100Experimental study and application of computational fluid dynamics on the prediction of air ...
http://jcarme.sru.ac.ir/article_1015_0.html
The shape of the air flow in the interior is heavily influenced by the air distribution system and the way air enters and exits. By numerically simulating flow by computational fluid dynamics, one can determine the flow pattern and temperature distribution and, with the help of the results, provide an optimal design of the air conditioning system. In this study, a chamber was first constructed and the temperature distribution inside it was measured. There was a fan installed at the back of the chamber for drainage. At the chamber entrance, three inlet for entering the flow were considered. The air from the middle inlet was heated by a heater. To prevent heat loss, the body of the enclosure was insulated. Several temperature sensors were installed at certain positions of the chamber for temperature measurement. Using Fluent software, the model of a full-sized chamber was created. Meshing is a hybrid and was used as a boundary layer Mesh. The inlet and outlet temperature of the chamber and the air output rates as boundary conditions were used in the simulation. Numerical analysis for K-ε and K-ω turbulence models was performed and different wall conditions were investigated. The numerical simulation results were in good agreement with the measurement results. Using the K-ε turbulence model with a scalable wall function had a better accuracy than other models. Changes in velocity and temperature were presented in graphs and contours at different positions of the compartment.Mon, 18 Feb 2019 20:30:00 +0100The effect of injection parameters on dimensional accuracy of wax patterns for investment casting
http://jcarme.sru.ac.ir/article_1000_0.html
Thermal expansion and hot deformation are two phenomena that cause dimensional errors in investment casting. This error occur in dimensions between the die pattern and the wax pattern. Therefore, the wax's thermo-physical and thermo-mechanical properties, the metal die features, and the process parameters affect the dimensions of the wax pattern. Some important effective process parameters are the injection temperature, the injection temperature, the die temperature and the holding time. In this paper, the effect of injection parameters on dimensional accuracy of wax models created by a metallic die has been studied. The Taguchi formulation based on design of experiments has been applied in order to obtain the optimum condition to achieve the best dimensional accuracy. The studied specimen with “F” shape has 10 dimensions. The root mean square (RMS) of dimensional differences has been considered for accuracy analysis. The results has shown that if the injection temperature, the injection pressure and the holding time be considered as 80oC, 20 bar, and 2.5 minute, respectively, the best accuracy may be achieved.Mon, 04 Feb 2019 20:30:00 +0100Investigation of injection timing and different fuels on the diesel engine performance and emissions
http://jcarme.sru.ac.ir/article_999_0.html
Start of fuel injection and fuel type are two important factors affecting engine performance and exhaust emissions in internal combustion engines. In the present study, a one-dimensional computational fluid dynamics solution with GT-Power software was used to simulate a six-cylinder diesel engine to study the performance and exhaust emissions with different injection timing and alternative fuels. Starting the fuel injection from 10 °CA BTDC to the TDC with an interval between two units and from alternative fuel bases (diesel), including methanol, ethanol, diesel and ethanol compounds, biodiesel and decane. To validate the model, a comparison was made between simulation data and experimental data (including torque and power), which showed that the validation error was less than 6.12%, which indicates the software model validation. Also, the modeling results showed that decane fuel had a higher brake power and brake torque of more than 6.10 % while fuel injected at 10 °CA BTDC compared to the base fuel, and illustrated a reduction of 5.75 % in specific fuel consumption due to producing higher power. In addition, with the advanced of injection timing compared to baseline, the amount of CO and HC in biodiesel fuel reduced and it’s amount was 83.88% and 64.87% respectively, and the lowest NOX emission with the retardation of starting injection, to decane fuel was awarded. In general, the results showed that decane fuel could be a good alternative to diesel fuel in diesel engines when it started fuel injection at 10 °CA BTDC.Mon, 04 Feb 2019 20:30:00 +0100Cooling a hot obstacle in a rectangular enclosure by using a MHD nanofluid with variable properties
http://jcarme.sru.ac.ir/article_991_0.html
In this study, cooling of a hot obstacle in a rectangular cavity filled with water-CuO nanolfuid has been examined numerically. This cavity has an inlet and outlet and the cold nanofuid comes from the left side of the cavity and after cooling the hot obstacle, it goes out from the opposite site. All of the walls are insulated, and the SIMPLER algorithm has been employed for solving the governing equations. The effects of fluid inertia, magnetic field strength, volume fraction of nanoparticles, and the place of outlet on heat transfer rate has been scrutinized. According to the results, the average Nusselt number builds up as the outlet place goes down. In other words, when the outlet is located at the bottom of the cavity, the rate of the heat transfer is maximum. Moreover, by increasing the Reynolds number and volume fraction of nanoparticles, the average Nusselt number builds up as well.Tue, 22 Jan 2019 20:30:00 +0100Investigation of natural convection heat transfer of MHD hybrid nanofluid in a triangular enclosure
http://jcarme.sru.ac.ir/article_976_0.html
Natural convection heat transfer is studied numerically in a triangular enclosure. The enclosure is isosceles right triangle and its bottom wall is hot, the hypotenuse is cold and the other wall is adiabatic. Also, a vertical magnetic field is applied in the enclosure, and there is hybrid nanofluid inside the enclosure. This study is conducted for Rayleigh numbers of 103-105, the Hartmann numbers between 0-80, and the volume fraction of nanofluid is between 0-2 percent. Based on the obtained results, as the Hartmann number augments, the temperature of the center of the enclosure decreases due to weakening of the heat transfer flow by increasing the magnetic field forces. In addition, as the Hartmann number augments, the streamlines approach to the walls because the horizontal momentum forces decrease when the Hartmann number increases. Furthermore, by increasing the density of nanoparticles, the heat transfer rate increase, and as a result, heat transfer builds up. Finally, heat transfer improve when the hybrid-nanofluid is employed rather than ordinary nanofluid.Mon, 07 Jan 2019 20:30:00 +0100A Method for Detecting Bubbles in Two-phase Gas-Liquid Flow
http://jcarme.sru.ac.ir/article_963_0.html
Detecting bubble in two-phase flow has been a basic issue in two-phase flow systems. A new method for measuring the frequency of bubble formation is presented in this paper. For this purpose, an electronic device was designed and constructed which works based on a change in intensity of laser beam. For this purpose, continues light beam is embedded just above the needle, which is received by a phototransistor. When bubbles go through this light beam, make a deviation on that and change the intensity of light. So, the electrical resistance between two bases of phototransistor changes and this variation sensed by an electronic board. According to the number of interruption and duration time, the frequency of bubble formation can be calculated. Liquid and gas phases of present work are water and air respectively. Tests are performed in constant liquid height (60 mm above the needle), constant needle diameter (1.6 mm), and gas flow rates between 50 to 1200 ml/hr. Also, three other methods utilized for measuring bubble frequency: image processing (IP), numerical modeling, and theoretical model. Results show that with increasing flow rate of the gas phase frequency of formation increases approximately in a linear manner. Validation of methods with IP method shows that the new device has very good accuracy for measuring bubble formation frequency. So because of the simplicity of using and low cost, it can be a superseded method of image processing.Tue, 04 Dec 2018 20:30:00 +0100MHD THERMAL RADIATION AND CHEMICAL REACTION EFFECTS WITH PERISTALTIC TRANSPORT OF THE ...
http://jcarme.sru.ac.ir/article_952_0.html
In this paper, we analyze the thermal radiation and chemical reaction impacts on MHD peristaltic motion of the Eyring-Powell fluid through a porous medium in a channel with compliant walls under slip conditions for velocity, temperature, and concentration. Assumptions of a long wave length and low Reynolds number are considered. The modeled equations are computed by using the perturbation method. The resulting non-linear system is solved for the stream function, velocity, temperature, concentration, skin-friction coefficient, heat transfer coefficient and mass transfer coefficient. The flow quantities are examined for various parameters. Temperature depresses with an enhancee in the radiation parameter, while the opposite effect is observed for the concentration. The fluid concentration enhances and depresses with generative and destructive chemical reaction respectively. The trapped bolus whose size diminishes as the Powel-Eyring parameter increases while it enhances as another Powell fluid parameter increases. The trapped bolus whose size rises when Darcy number enhances.Fri, 30 Nov 2018 20:30:00 +0100Entropy Generation Analysis of Non-Newtonian Fluid in Rotational Flow
http://jcarme.sru.ac.ir/article_924_0.html
The entropy generation analysis of non-Newtonian fluid in rotational flow between two concentric cylinders is examined when the outer cylinder is fixed and the inner cylinder is revolved with a constant angular speed. The viscosity of non-Newtonian fluid is considered at the same time interdependent on temperature and shear rate. The Nahme law and Carreau equation are used to modeling dependence of viscosity on temperature and shear rate, respectively. The viscous dissipation term is adding elaboration to the formerly highly associate set of governing motion and energy equations. The perturbation method has been applied for the highly nonlinear governing equations of base flow and found an approximate solution for narrowed gap limit. The effect of characteristic parameter such as Brinkman number and Deborah number on the entropy generation analysis is investigated. The overall entropy generation number decays in the radial direction from rotating inner cylinder to stationary outer cylinder. The results show that overall rate of entropy generation enhances within flow domain as increasing in Brinkman number. It, however, declines with enhancing Deborah number. The reason for this is very clear, the pseudo plastic fluid between concentric cylinders is heated as Brinkman number increases due to frictional dissipation and it is cooled as Deborah number increases which is due to the elasticity behavior of the fluid. Therefore, to minimize entropy need to be controlled Brinkman number and Deborah number.Fri, 09 Nov 2018 20:30:00 +0100Computational evaluation of the homogeneity of composites processed by accumulative roll ...
http://jcarme.sru.ac.ir/article_923_0.html
A new computational method based on MATLAB was used to study the effect of different parameters on the homogeneity of composites produced by a severe plastic deformation (SPD) technique known as accumulative roll bonding (ARB). For higher number of passes, the degree of particle agglomeration and clustering decreased and an appreciable homogeneity was obtained in both longitudinal and transverse directions. Moreover, it was found that the rolling temperature does not have any tangible effect on the distribution of particles. Furthermore, it was shown that while faster homogeneity can be obtained in the transverse direction by cross accumulative roll bonding process, there is not any significant difference between homogeneity of particle distribution between this technique and other routes. In fact, after enough passes, the homogeneity level in all processing methods tends to a common value. Finally, the evolution of the mechanical properties of the composites sheets based on the work hardening, composite strengthening, grain refinement at high ARB cycles, and bonding between particles and the matrix was also briefly discussed.Fri, 09 Nov 2018 20:30:00 +0100High-velocity impact properties of multi-walled carbon nanotubes/E-glass fiber/epoxy anisogrid ...
http://jcarme.sru.ac.ir/article_922_0.html
This work reports on high-velocity impact response of multiscale anisogrid composite (AGC) panels. The aim of the present study was to evaluate the infleunce of surface-modified multi-walled carbon nanotubes (S-MWCNTs) at different S-MWCNTs contents (0-0.5 wt.% at an interval of 0.1 wt.%) on the high-velocity impact responses of E-glass/epoxy AGC. Surface modification of MWCNTs was confirmed by fourier-transform infrared (FTIR) and thermogravimetric (TGA) analyses. AGC panels were fabricated via a manual filament winding technique. E-glass fiber roving and E-glass woven fabric were employed as reinforcing agents in ribs and skin, respectively. The impact test was done on the composite panels by a cylindrical projectile with a conical nose. The obtained results showed that the highest enhancement in the impact characteristics was attributed to the panel containing 0.4 wt.% S-MWCNTs. Based on the analysis of fracture surfaces, enhanced interfacial fiber/matrix bonding was observed for the S-MWCNTs loaded specimen. Furthermore, the incorporation of MWCNTs led to reduced damaged area and enhanced tolerance of damage.Fri, 09 Nov 2018 20:30:00 +0100Experimental investigation on constant-speed diesel engine fuelled with biofuel mixtures under ...
http://jcarme.sru.ac.ir/article_921_0.html
The petroleum product has seen drastic demand in recent past. Bio fuels is the only solution to overcome this power crisis. In the view of sustainable energy development, bio diesel and its additives have become the best options for fossil fuel-based engines. In this work, a bio diesel mix was used to show the possibility utilization of different bio fuels. Experimental investigation was carried out on a direct-injection constant-speed (Rated speed- 1500 rpm) diesel engine at different injection pressures of 180, 220 and 260 bar with natural aspiration and supercharging modes. The blends of Bio diesel (used cooking oil, with a mix of algae) and diesel fuels are the selected fuel to investigate. At lower injection pressures, brake speciﬁc fuel consumption of the engine was low and further lowered with supercharging operation. With the reduction of injection pressures, brake thermal efﬁciency values are improved and the same was observed with supercharging. With the rise in injection pressures NOx emissions increased due to rise in temperature and unburnt hydrocarbon emissions were slightly increased. The algae bio diesel was used as an additive to increase the stability of bio diesel. The overall observation indicates that a moderate injection pressure of 220 bar is advisable.Fri, 09 Nov 2018 20:30:00 +0100Crashworthiness design of multi-cell tapered tubes using response surface methodology
http://jcarme.sru.ac.ir/article_908_0.html
In this article, crashworthiness performance and crushing behavior of tapered structures with four internal reinforcing plates under axial and oblique dynamic loadings have been investigated. These structures have a tapered form with five cross sections of square, hexagonal, octagonal, decagon and circular shape. In the first step, finite element simulations performed in LS-DYNA were validated by comparing with experimental data. The code generated in LS-DYNA was then used to investigate energy absorption behavior of the tapered structures. Response surface methodology and historical data design technique were employed to optimize the cross section perimeter (tapered angle) of the tapered structures by considering two conflicting crashworthiness criteria including EA (energy absorption) and PCF (peak crushing force). The optimization results showed that the optimal tapered angle enhanced by increasing the number of cross section sides (or number of corners). Then, the optimized tapered structures with different cross-sections were compared with each other using a ranking method called TOPSIS to introduce the most efficient energy absorber. The decagonal structure was finally found to be the best energy absorber.Sat, 03 Nov 2018 20:30:00 +0100Effect of blade profile on the performance characteristics of axial compressor in design condition
http://jcarme.sru.ac.ir/article_907_0.html
The choice of geometrical shape of the blades has a considerable effect on aerodynamic performance and flow characteristics in the axial compressor. In this paper, the effects of the blades shape on the aerodynamic design characteristics are investigated based on Streamline Curvature Method (SCM). Initially, the Streamline Curvature Method (SCM) is used for design of certain two-stage axial compressor. Comparing the current results with experimental ones indicate good agreement. The first stage of the axial compressor is selected with three different blade profiles. First case (case I) has the polynomial camber with naca thickness distribution series 6. Second case (case II) has the standard naca profile series 6 and third case (case III) has the modified standard naca profile series 4. Results reveal that using the standard airfoils in the stators leads to improved flow conditions such as loss coefficient and pressure ratio. Contrary, this profile selection may cause to increase in the stagger angle that is not favorable. Aerodynamic Design with a polynomial camber line in the rotor demonstrate a better aerodynamic behavior in loss coefficient, pressure ratio and diffusion factor. Whilst the use of such a camber line in the stator leads to the formation of less favorable aerodynamics conditions than the standard airfoil.Sat, 03 Nov 2018 20:30:00 +0100Magneto Prandtl nanofluid past a stretching surface with non-linear radiation and chemical reaction
http://jcarme.sru.ac.ir/article_906_0.html
In this article, we examined the behavior of chemical reaction effect on a magnetohydrodynamic Prandtl nanofluid flow due to stretchable sheet. Non-linear thermally radiative term is accounted in energy equation. Constructive transformation is adopted to formulate the ordinary coupled differential equations system. This system of equations is treated numerically through Runge Kutta Fehlberg-45 method based shooing method. The role of physical constraints on liquid velocity, temperature and concentration are discussed through numerical data and plots. Also the skin friction co-efficient, local Nusselt number and local Sherwood numbers is calculated to study the flow behavior at the wall, which is also presented in tabular form. A comparative analysis is presented with the previous published data in special case for the justification of present results. Output reveals that for larger values of elastic and Prandtl parameter enhanced the thickness of momentum layer and reduces the rates of both heat and mass transport. Also increment of slip parameter decelerated both temperature and concentration filed while nonlinear form thermal radiation rapidly increases the temperature.Sat, 03 Nov 2018 20:30:00 +0100Numerical analysis of heat transfer enhancement and flow structure of alternating oval tubes by ...
http://jcarme.sru.ac.ir/article_903_0.html
In this research, the convective heat transfer in turbulent water fluid flow in alternating oval tubes is studied using computational fluid dynamics. The purpose of this study is to analysis the heat transfer enhancement and secondary internal flows under the different alternate angles. Also, comparing the effect of two schemes for the domain discretization to use in the solution variables’ gradients on simulation results are investigated. The secondary flow causes to increase in the numbers of multi-longitudinal vortices (MLV) by changing the angle of pitches. These phenomena permit the cold fluid flow to stream in more paths from center to tube wall and better condition for mixing of fluids. Consequently, the heat transfer enhances by using the alternating oval tubes. However, forming the multi-longitudinal vortices cause an increase in pressure drop. Also, by raising the angle of pitches, the friction factor and the average of Nusselt number are amplified. It is also observed that the average heat transfer coefficient in the transition range is more than in the other areas. The mean Nussult numbers of this kind of tubes in the angles of 40°, 60°, 80°, and 90° improved 7.77%, 14.6%, 16.93%, and 24.42%, respectively in comparison with the round tube. The performance evaluation criteria (PEC) for all alternating oval tubes under the constant inlet velocity boundary condition indicated that the highest value (PEC=1.09) had been obtained at the lowest Reynolds number (Re=10,000) in the alternating oval tube 90°.Fri, 26 Oct 2018 20:30:00 +0100Experimental study and numerical simulation of three dimensional two phase impinging jet flow ...
http://jcarme.sru.ac.ir/article_902_0.html
Hydrodynamic of a turbulent impinging jet on a flat plate has been studied experimentally and numerically. Experiments were conducted for the Reynolds number range of 72000 to 102000 and a fixed jet-to-plate dimensionless distance of H/d=3.5. Based on the experimental setup, a multi-phase numerical model was simulated to predict flow properties of impinging jets using two turbulent models. Mesh-independency of the numerical model was studied to ensure the preciseness of results. Numerical and experimental forces on the target plate were compared to examine performance of turbulent models and wall functions. As a result, the force obtained by the Reynolds stress turbulent model alongside with non-equilibrium wall function was in good agreement with the experiment. The correlation equations were obtained for predicting the water thickness over the target plate and impingement force versus Reynolds number. It was also indicated that the maximum shear stress on the target plate was located at radial dimensionless distance of r/d=0.75.Fri, 26 Oct 2018 20:30:00 +0100Identification of rotor bearing parameters using vibration response data in a turbocharger rotor
http://jcarme.sru.ac.ir/article_901_0.html
Turbochargers are most widely used in automotive, marine and locomotive applications with diesel engines. To increase the engine performance nowadays, in aerospace applications also turbochargers are used. Mostly the turbocharger rotors are commonly supported over the fluid film bearings. With the operation, lubricant properties continuously alter leading to different load bearing capacities. This paper deals with the diagnostic approach for prediction of shaft unbalance and the bearing parameters using the measured frequency responses at the bearing locations. After validating the natural frequencies of the rotor finite element model with experimental analysis, the response histories of the rotor are recorded. The influence of the parameters such as bearing clearance, oil viscosity and casing stiffness on the unbalance response is studied. By considering three levels each for shaft unbalance and oil viscosity, the output data in terms of four statistical parameters of equivalent Hilbert envelopes in the frequency domain are measured. The data is inversely trained using Radial Basis Function (RBF) neural network model to predict the unbalance and oil viscosity indices from given output response characteristics. The outputs of the RBF model are validated thoroughly. This approach finds changes in the rotor bearing parameters from the measured responses in a dynamic manner. The results indicate that there is an appreciable effect of lubricant viscosity at two different temperatures compared to other parameters within the operating speed range. The identification methodology using the neural network is quite fast and reliableFri, 26 Oct 2018 20:30:00 +0100INCLINED LORENTZIAN FORCE EFFECT ON TANGENT HYPERBOLIC RADIATIVE SLIP FLOW IMBEDDED CARBON ...
http://jcarme.sru.ac.ir/article_900_0.html
The present paper focuses on numerical study for an inclined magneto-hydrodynamic effect on free convection flow of a tangent hyperbolic nanofluid embedded with Carbon nanotubes (CNTs) over a stretching surface taking velocity and thermal slip into account. Two types of nanoparticles are considered for the study; they are single and multi-walled nanotubes. The presentation of single-parameter group (Lie group) transformations reduces the independent variable number by one, and hence the partial differential governing equations with the supplementary atmospheres into an ordinary differential equation with the appropriate suitable conditions. The obtained ordinary differential equations are then numerically solved by employing fourth order Runge-Kutta technique along with shooting method. The effects of the various parameters governing the flow field are presented with the help of graphs. The investigation reveals that the non-Newtonian MWWCNTs Tangent hyperbolic nano-liquid reduces the friction near the stretching sheet contrasting SWCNTs. This combination can be used as a friction lessening agent/factor. Usage of CNTs shows an excellent performance in enhancing the thermal conductivity of the nanoliquid and single wall carbon nanotubes (SWCNTs) has higher thermal conductivity than multi wall carbon nanotubes (MWCNTs) even in the presence of radiative heat transfer and heat source. Comparison with existing results available in literature is made and had an excellent coincidence with our numerical method.Fri, 26 Oct 2018 20:30:00 +0100Automatic implementation of a new recovery coefficient for Reliable contour milling
http://jcarme.sru.ac.ir/article_889_0.html
In contour milling, to render the machining process more automated with significant productivity without remaining material after machining, we have developed a new recovery coefficient, inserted in the computation of contour parallel tool paths, in order to fix the radial depth of cut in the way to ensure an optimized overlap area between the passes in the corners, without residuals. Thus, this parameter, which has been earlier inserted by the user, is now being independent and is implemented automatically from the input data of the contour shape of the pocket. In order to prove the effectiveness of our approach, we also performed a detailed comparison with the classical methods found in the literature. From the results we can see clearly that our new method removes the residuals efficiently in an automatic way and minimizes the toolpath length respect to the other methods. Furthermore, this proposed approach can easily work on the actual machine tool.Sun, 21 Oct 2018 20:30:00 +0100Analytical Study of nano-bioconvective flow in a horizontal channel Using Adomian Decomposition ...
http://jcarme.sru.ac.ir/article_883_0.html
In this paper, the convective flow of a nano-fluid in a horizontal channel has been investigated. The Non-Linear model that characterizes the flow of the considered nano-fluid is the one proposed by Nield and Kuznetsov. The partial differential equations of the dynamics, the thermal, the concentration of the nanoparticles and diffusion (velocity, temperature, nanoparticle volume fraction and density of motile microorganisms) resulting from mathematical modeling are reduced to non-linear differential equations. The latter are solved numerically and analytically by the Runge-Kutta method of order 4 (RK4) based shooting method (Tir) and the Adomian decomposition method (ADM) respectively. In this work, special attention was paid to the effects of the physicals parameters (𝛿𝜃,δ_,s and Nt⁄Nb parameters) on the velocity distributions, temperature, nanoparticle volume fraction and the density of motile microorganisms. The comparison of ADM results with numerical based shooting method solution also shows the validity of the analytical the Adomian Decomposition Method (ADM).Sat, 20 Oct 2018 20:30:00 +0100An advection-diffusion multi-layer porous model for stent drug delivery in coronary arteries
http://jcarme.sru.ac.ir/article_874_0.html
Arterial drug concentration distribution determines local toxicity. The safety issues dealt with Drug-Eluting Stents (DESs) reveal the needs for investigation about the effective factors contributing to fluctuations in arterial drug uptake. The current study focused on the importance of hypertension as an important and controversial risk factor among researchers on the efficacy of Heparin-Eluting Stents (HES). For this purpose, the effect of blood pressure is systematically investigated in certain cardiac cycle modes. A comprehensive study is conducted on two classes, pulsatile (time-dependent), to have a more realistic simulation, and non-pulsatile (time-independent) blood flow, each one in four modes. The governing equations applied to drug release dynamics are obtained based on porous media theory. The equations are solved numerically using Finite Volume Method (FVM). Results reveal that there is a significant difference when the plasma flow considered and when it is neglected (regardless of time dependency). Moreover, the concentration level is more decreased in pulsatile blood flow rather than the non-pulsatile blood flow, although the penetration depth for pressure and concentration are nearly 20% and 5% of the wall thickness, respectively. In other words, the mass experienced by the arterial wall is lower in pulsatile blood flow in comparison to non-pulsatile blood flow. As a consequence, the risk of toxicity is declined as the blood pressure increases. Also, it can be seen that the polymer is diffusion-dominated so that no significant changes in the release characteristics are observed in the presence of the plasma filtration.Sat, 13 Oct 2018 20:30:00 +0100Application of Combined Mathematical modeling/Optimization Methods Coupled Pitch Controller in ...
http://jcarme.sru.ac.ir/article_832_0.html
A common method utilized in wind turbines is pitch angle control whereby via varying the angle of wind turbine blades around their own axis, power generated at high speeds of wind is held around maximum amount and is kept away from the severe mechanical stress on wind turbine. In current study, in order to control pitch angle, a control method based on using PI controller is suggested. Therefore, gains of the PI controller are regulated through combining the Firefly evolutionary algorithm and MLP neural network in such a way that the controller at its output sends a suitable controlling signal to the pitch actuator to set the pitch angle and so by varying the blades pitch angle suitably at high speeds of wind, the produced generator power remains around its nominal value. A wind turbine 5MW made by NREL (National Renewable Energy Laboratory) has been utilized based on FAST software code to simulate and analyze the results. The simulation results show that proposed method has a good performance.Tue, 11 Sep 2018 19:30:00 +0100Dynamic Stress Concentration in a Hybrid Composite Laminate Subjected to a Sudden Internal Break
http://jcarme.sru.ac.ir/article_821_0.html
In this work, transient dynamic stress concentration in a hybrid composite laminate subjected to a sudden internal crack is examined. It is assumed that all fibers lie in one direction and the applied load acts along direction of fibers. Two types arrangements are considered for the fiber; square and hexagonal arrangement. Using shear lag model, equilibrium equations are deduced and upon proper application of initial and boundary conditions, the complete field equations are obtained using finite difference method. The results of dynamic effect of fiber breakage on stress concentration are well examined in presence of a second type fiber. These results are compared to those of their static values in both models. The effect of surface cracks on stress concentration, as a result of fiber breakage, is also examined. The values of dynamic stress concentrations is deduced and compared to those of a lamina. Also, the peak stress concentration during transition time for fibers to reach static equilibrium is calculated and compared with those of static values.Sat, 25 Aug 2018 19:30:00 +0100