Journal of Computational & Applied Research in Mechanical Engineering (JCARME)Journal of Computational & Applied Research in Mechanical Engineering (JCARME)
http://jcarme.sru.ac.ir/
Sat, 22 Sep 2018 14:38:05 +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.Favorable Plug Shape of an Aerospike Nozzle in Design, Over and Under Expansion Conditions
http://jcarme.sru.ac.ir/article_775_181.html
The influence of the plug shape on the performance of an aerospike nozzle thrust force is studied in different back pressure conditions. To generate smooth plug contours, Cubic B-Spline technique is employed. In the current research, basis functions are obtained using Deboor’s relation. The flow field around the aerospike nozzle is investigated implementing various shapes and the best of the generated configurations is determined. The flow field is simulated using Navier-Stokes equations and k-ε turbulence model. A triangle unstructured grid is applied for discretization of the governing equations. The computational methodology utilizes steady state density-based formulation and a finite volume cell centered scheme is used to discretize the flow field equations. To accelerate the solution convergence, the flow field is divided into several zones and appropriate initial condition is assigned to each zone. Six different shapes of the plug are generated and the effect of the spike shape on the formation of the shock wave and expansion waves is investigated in each case. The thrust force is calculated for each case and the best configuration is determined in terms of the maximum thrust generation. Eventually, the temperature distribution is calculated along the nozzle for further investigations and it is concluded that the best configurations show a lower temperature rise compared to other designs.Fri, 31 Aug 2018 19:30:00 +0100A comparison between modal damping ratios identified by NExT-ERA and frequency domain impact test
http://jcarme.sru.ac.ir/article_767_181.html
In this research, the modal parameters of a beam in free-free condition are extracted by performing different experiments in laboratory. For this purpose, two different techniques are employed. The first methodology is considered as a time domain method in Operational Modal Analysis. While the other one is frequency domain impact hammer test which is categorized as an Experimental Modal Analysis method and can be regarded as the most common method in modal analysis. Checking the results obtained by the two methods, one can notice a distinct inconsistency in modal damping ratios extracted by each method. However, based on recent publications on the subject, it can be inferred that the time domain methods have better accuracy in identifying damping ratios of structures. In order to confirm the findings, the effect of excitation is examined for each method by altering the excitation tool. For the operational method, it is concluded that changing the excitation tool will not have a noticeable influence on the identified damping ratios, whilst for the Experimental Modal Analysis method changing the hammer tip leads to inconsistent results for damping ratios. This study exemplifies the deficiency of Experimental Modal Analysis methods in their dependency on excitation techniques.Fri, 31 Aug 2018 19:30:00 +0100Three-Dimensional Boundary Layer Flow and Heat Transfer of a Dusty Fluid Towards a Stretching ...
http://jcarme.sru.ac.ir/article_774_181.html
The steady three-dimensional boundary layer flow and heat transfer of a dusty fluid towards a stretching sheet with convective boundary conditions is investigated by using similarity solution approach. The free stream along z-direction impinges on the stretching sheet to produce a flow with different velocity components. The governing equations are reduced into ordinary differential equations by using appropriate similarity variables. Reduced nonlinear ordinary differential equations subjected to the associated boundary conditions are solved numerically by using Runge–Kutta fourth-fifth order method along with Shooting technique. The effects of the physical parameters like magnetic parameter, velocity ratio, fluid and thermal particle interaction parameter, Prandtl number, Eckert number and Biot number on flow and heat characteristics are examined, illustrated graphically, and discussed in detail. The results indicate that the fluid phase velocity is always greater than that of the particle phase and temperature profiles of fluid and dust phases increases with the increase of the Eckert number.Fri, 31 Aug 2018 19:30:00 +0100Analysis of deep drawing process to predict the forming severity considering inverse finite ...
http://jcarme.sru.ac.ir/article_769_181.html
An enhanced unfolding Inverse Finite Element Method (IFEM) has been used together with an extended strain-based forming limit diagram (EFLD) to develop a fast and reliable approach to predict the feasibility of the deep drawing process of a part and determining where the failure or defects can occur. In the developed unfolding IFEM, the meshed part is properly fold out on the flat sheet and treated as a 2D problem to reduce the computation time. The large deformation relations, nonlinear material behavior and friction conditions in the blank holder zone have also been considered to improve the accuracy and capability of the proposed IFEM. The extended strain-based forming limit diagram based on the Marciniak and Kuczynski (M-K) model has been computed and used to predict the onset of necking during sheet processing. The EFLD is built based on equivalent plastic strains and material flow direction at the end of forming. This new forming limit diagram is much less strain path dependent than the conventional forming limit diagram. Furthermore, the use and interpretation of this new diagram are easier than the stress-based forming limit diagram. Finally, two applied examples have been presented to demonstrate the capability of the proposed approach.Fri, 31 Aug 2018 19:30:00 +0100A Study on free convective heat and mass transfer flow through a highly porous medium with ...
http://jcarme.sru.ac.ir/article_771_0.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.Mon, 09 Apr 2018 19:30:00 +0100Torsional analysis of an orthotropic long cylinder weakened by multiple axisymmetric cracks
http://jcarme.sru.ac.ir/article_830_181.html
Abstract: The solution to problem of an orthotropic long cylinder subjected to torsional loading is first obtained by means of separation valuables. The cylinder is twisted by two lateral shear tractions and the ends of the cylinder surface of the cylinder are stress-free. First, the domain under consideration is weakened by an axisymmetric rotational Somigliana ring dislocation. The dislocation solution is employed to derive a set of Cauchy singular integral equations for the analysis of multiple axisymmetric planner cracks. The numerical solution to these integral equations is used to determine the stress intensity factors (SIFs) for the tips of the concentric planar cracks A preliminary comparison between results of this study and those available in the literature is performed to confirm the validity of the proposed technique. Several examples of multiple concentric planner cracks are solved and displayed graphically. Furthermore, Configuration of the cracks and the interaction between cracks is studied.Fri, 31 Aug 2018 19:30:00 +0100Effects of Different Turbulence Models in Simulation of Unsteady Tip Leakage Flow in Axial ...
http://jcarme.sru.ac.ir/article_773_181.html
Characteristics of rotor blade tip clearance flow in axial compressors can significantly affect their performance and stable operation. It may also increase blade vibrations and cause detrimental noises. Therefore, this paper is contributed to investigate tip leakage flow in a low speed isolated axial compressor rotor blades row. Simulations are carried out on near-stall condition, which is valuable of being studied in detail. In turbomachines, flows are non-isotropic and highly three-dimensional. The reason arises from the complicated structure of bounded walls, tip leakage flows, secondary flows, swirl effects, streamlines curvatures and pressure gradients along different directions. As a result, accurate studies on tip leakage flow would be accompanied by many challenges such as adopting suitable turbulence models. So, investigations are carried out numerically utilizing two well-known turbulence models of k-ε and k-ω-SST, separately. It is shown that the k-ε model yields poor results in comparison to the k-ω-SST model. To realize reasons for this discrepancy, turbulence parameters such as turbulent kinetic energy, dissipation and eddy viscosity terms at the tip clearance region were surveyed in detail. It is found out that estimation for eddy viscosity term is too high in the k-ε model due to excessive growth of turbulent kinetic energy, time scale, and lack of effective damping coefficient. This leads to dissipation of vortical structure of flow and wrong estimation of flow field at the rotor tip clearance region. Nevertheless, k-ω-SST turbulence model provides results consistent with reality.Fri, 31 Aug 2018 19:30:00 +0100Effect of Variable Thermal Conductivity and the Inclined Magnetic Field on MHD Plane Poiseuille ...
http://jcarme.sru.ac.ir/article_768_181.html
The aim of this paper is to investigate the effect of the variable thermal conductivity and the inclined uniform magnetic field on the plane Poiseuille flow of viscous incompressible electrically conducting fluid between two porous plates Joule heating in the presence of a constant pressure gradient through non-uniform plate temperature. It is assumed that the fluid injection occurs at lower plate and fluid suction occurs at upper plate. The governing equations of momentum and energy are transformed into coupled and nonlinear ordinary differential equations using similarity transformation and then solved numerically using finite difference technique. Numerical values for the velocity and temperature have been iterated by Gauss Seidal iteration method in Matlab programming to a suitable number so that the convergent solutions of velocity and temperature are considered to be achieved. Numerical results for the dimensionless velocity and the temperature profiles for different governing parameters such as the Hartmann Number (M) angle of inclination of magnetic field (α), suction Reynolds number (Re) Prandtl Number (Pr), Eckert number (Ec) and variable thermal conductivity (ԑ) have been discussed in detail and presented through graphs.Fri, 31 Aug 2018 19:30:00 +0100Evaluation of solar-chimney power plants with multiple-angle collectors
http://jcarme.sru.ac.ir/article_772_181.html
Solar chimney power plants are plants based on solar thermal power including three parts of collector, chimney and turbine, which is able to produce electrical energy. One of the effective parameters in increasing the power production is the collector angles versus horizon. In the present study, a numerical analysis of a solar chimney power plant for different angles of the collector (divergent, convergent and horizontal type collector) is proposed. The introduced numerical model uses mathematical models of heat transfer. In this regard, effect of various angles of the three considered collectors on temperature distribution and power production of the solar chimney is evaluated. Divergent type collectors produce more power than convergent and horizontal collectors, as they produce more velocity and mass flow rates. It will be shown that by increasing the angle of divergent-type collector (keeping the inlet height constant), the power production will be increased and the output temperature will be decreased, in a way that the angle variation of 0.8 to 1 will increase the divergent type collector output power by 11 % and will decrease the output temperature by 0.78%. In the other case, when the output height is kept constant and the collector angle changes, performance of the divergent type collector is better than the other two collectors. Power production in a constant mean height is shown to be 3 times and 1.5 times more than the convergent and horizontal collectors respectively.Fri, 31 Aug 2018 19:30:00 +0100Experimental study on thermal conductivity of polyurethane resin filled with modified nanoparticles
http://jcarme.sru.ac.ir/article_776_181.html
One of the ways to waste energy in buildings is wasting it from the walls. For this reason, insulating materials are used to prevent the loss of energy in buildings. Typically, common insulations are high thickness and thin coatings are used less. The purpose of this research is to introduce nanocomposite thin polymer coatings and its effect on thermal conductivity. For achieving this, chemically modified nano zirconium oxide and nano aluminum oxide in three different weight percentages (1, 3, and 5%) were used in polyurethane matrix for preparing nanocomposite coatings. To study thermal conductivity, the metallic plates are coated with prepared nanocomposites and the thermal conductivity of the samples was measured. The results show that by adding zirconium oxide and aluminum oxide nanoparticles in polyurethane matrix, the thermal conductivity of coatings in all three weight percentages compared to the coating without nanoparticles, decreased. The lowest thermal conductivity was found for 5% nano aluminum oxide composition, which, compared to the conductivity of the pure polyurethane resin, has decreased about 40% that leading to a decrease in the surface heat flux.Fri, 31 Aug 2018 19:30:00 +0100Presenting Three Design Methods for Axial Compressor Blade via Optimization
http://jcarme.sru.ac.ir/article_770_181.html
Improving the efficiency of compressors has been one of the most important goals of researchers over the years. In this paper, three different methods are presented for parameterization and blade optimization of axial flow compressor. All methods consist of flow analysis tool, optimization algorithms, and parametric geometry generation tool, that are different in each approach. Objective function is defined based on the aerodynamic performance of blade in the acceptable incidence angles range. A DCA blade is used as the initial guess for all methods. The performance of optimized blades and the initial blade are compared for evaluating the capability of various methods that a good agreement has been achieved. The results show that the value of performance improvement in each method depends on the number and type of the chosen parameters. All three methods have improved blade performance at the design incidence angle. However, only the first method shows significant performance improvement in off-design conditions.Fri, 31 Aug 2018 19:30:00 +0100Flow field, heat transfer and entropy generation of nanofluid in a microchannel using the ...
http://jcarme.sru.ac.ir/article_794_0.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<φ<0.04. The results show that by increasing the Knudsen number, the average Nusselt number and total entropy generation rate decrease. Moreover, with augmentation of the Reynolds number, the average Nusselt number and total entropy generation rate decrease. What’s more, by increasing the volume fraction of nanofluids, the temperature of the nanofluid reduces, and as a result, the temperature gradient as well as heat transfer increase.Sat, 16 Jun 2018 19:30:00 +0100Fuzzy Motion Control for Wheeled Mobile Robots in Real-Time
http://jcarme.sru.ac.ir/article_809_0.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.Sat, 04 Aug 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 +0100Three-dimensional characteristic approach for incompressible thermo-flows and influence of ...
http://jcarme.sru.ac.ir/article_822_0.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 benchmarkSat, 25 Aug 2018 19:30:00 +0100Turbulence Analysis of Shock Waves in Contractions with Rectangular Sections
http://jcarme.sru.ac.ir/article_823_0.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.Sat, 25 Aug 2018 19:30:00 +0100Experimental and Numerical Investigation of Bottom Outlet Hydraulic Model
http://jcarme.sru.ac.ir/article_827_0.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.Tue, 28 Aug 2018 19:30:00 +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 +0100