Showing 657 results for Type of Study: Research
Y. Mollapour, E. Poursaeidi, H. Shayani-Jam, O. Pedram,
Volume 40, Issue 1 (9-2021)
Abstract
Corrosive factors along with mechanical loads on the gas turbine compressor blades, cause phenomena such as pitting corrosion, stress corrosion cracking and corrosion fatigue. Due to erosion of particles in the presence of a corrosive environment, pitting happens on the blade surfaces, which is a source of subsequent cracks. Therefore, it is necessary to get knowledge of its mechanism in order to prevent the phenomena as much as possible. The main purpose of this paper is to investigate the growth of pitting corrosion in CUSTOM 450 stainless steel and to obtain strain values in the growing pits at the maximum bending region. In this regard, a two-point bending specimen was made and subjected to a potentio-static test under the potential of 350 mVSCE in the 3.5 wt% sodium chloride solution. Then the propagated pits were numerically examined. By the digital image correlation method, the local strain was calculated in the pits and a relation was presented to obtain the maximum strain time. Therefore, growth direction of pitting corrosion could be estimated by having maximum strain region. Finally, by simulating the pitting corrosion process of a stress-free sample under the potential of 350 mVSCE in 3.5 wt% sodium chloride solution in COMSOL Multiphysics software, variations in the concentration of ions, electric potential, and corrosion current density were shown in the existing pit. The potential was decreased by moving in-depth and the maximum current density was found at the depth of 18 μm. Thus, without the need of advanced laboratory facilities for surface scanning and analysis, useful information from surface corrosion conditions could be obtained
H. Asadigorji, A. Karami Mohammadi,
Volume 40, Issue 1 (9-2021)
Abstract
Complex nonlinear behaviors such as chaotic motion have devastating effects on dynamic systems. In this study, nonlinear behavior of simply supported rectangular viscoelastic plates was examined during supersonic aerodynamics and compared with the nonlinear elastic plate. Classical plate theory was used to obtain the plate equations, and Von- Kármán strain-displacement relations were used to consider the nonlinear geometric effects. The Kelvin Voigt model was also used to describe the viscoelastic properties and the “first-order piston theory" was used for supersonic aerodynamic flow. The equations of motion of the rectangular plate were extracted using the Lagrangian method and then, discretized by the Rayleigh-Ritz method. Solution of the equations was performed using fourth order Runge Kutta method. To investigate the dynamic behavior of the plates, the eigenvalues of the system, time history curves, phase portraits, Poincaré maps, and bifurcation diagrams were studied and analyzed. The results show that in some aspect ratios, the threshold for the occurrence of the flutter in the viscoelastic plate will be lower than that in the elastic plate. On the other hand, when the control parameter increases, complex nonlinear behavior such as chaos in the elastic plate goes simpler in the viscoelastic plate, such as periodic motion.
A. R. Rahmati , E. Kashai,
Volume 40, Issue 2 (1-2022)
Abstract
A two-phase lattice Boltzmann model considering the interaction forces of nanofluid has been developed in this paper. It is applied to investigate the flow and natural convection heat transfer of Al2O3–H2O nanofluid in an enclosure containing internal heat generation. To understand the heat transfer enhancement mechanism of the nanofluid flow from the particle level, the lattice Boltzmann method is used because of its mesoscopic feature and numerical advantages. By using a two-component lattice Boltzmann model, the heat transfer enhancement of the nanofluid is analyzed through incorporating the different forces acting on the nanoparticles and the base fluid . The effects of interaction forces, nanoparticle volume fractions (0.0-0.05), and internal and external Rayleigh numbers (103-106) on the nanoparticle distributions and heat transfer characteristics are investigated. The average Nusselt number increases with the increase of nanoparticle volume fraction and Rayleigh number. We also compared and analyzed adding internal heat generation on the nanoparticles and the base fluid separately, and it was found that by considering heat generation on the base fluid, it mostly affects the temperature field, and by considering that on nanoparticles, it mostly affects the stream field.
F. Hosseinlou,
Volume 40, Issue 2 (1-2022)
Abstract
Today many complex models, typically finite element models, have been employed in the analysis of jacket offshore structures. However, these comprehensive models are not readily adopted in engineering practice, especially during the preliminary design stage. As the dynamic analysis of jacket platforms is very complicated, it will be very advantageous to make a simplified computational method to assess dynamic performance of such structures. In this work a refined simplified model has been utilized to calculate dynamic responses of jacket platforms. In this regard, the model simplification based on the vibration modal data and Timoshenko’s beam equation has been employed to overcome the uncertainty problem in modeling. According to the curve fitting method on the set of frequency response functions to derive modal parameters, the concept of power spectrum density has been also used to confirm the proposed computational model.In this regard, first the behavior of the physical model in the frequency domainhas been presented and compared with the spectral results obtained from the simplified model based on Timoshenko beam. Because the modal test of the physical model was performed under the force of white noise, the dynamic responses of the simplified model were also extracted under the force of white noise using MATLAB software. In this paper, an applied mathematical model has been produced, and it has been demonstrated that the refined simplified model can reflect the real structural features.
F. F. Heidargheitaghi, M. H. M. H. Ghadiri Rad, M. Kazemi,
Volume 40, Issue 2 (1-2022)
Abstract
Continuously varying cross-section members have found wide applications in engineering for cost and resistance optimization. Since steel structures generally have more slender members compared to concrete structures, buckling analysis of steel members is of more importance. Determining the critical load of functionally varying cross-section columns using the analytical solution is a time-consuming process. In this paper, buckling analysis of non-prismatic steel columns is conducted using the meshless local Petrov-Galerkin (MLPG) method. In meshless methods, the scattered nodes are used rather than the elements to model the problem domain and its boundaries. The change of the inertia moment within the length of a column is characterized by introducing a power function with variable taper ratio and exponent. The radial basis function is used to discretize the differential equation governing the buckling. The penalty method is used for the imposition of the boundary conditions. Numerical examples of the critical buckling load for prismatic and non-prismatic columns using the proposed method are compared with the analytical solution, and the effectiveness of the MLPG method for buckling analysis of non-prismatic columns is validated. Also, buckling analysis of muscle column members subjected to non-uniform axial load is carried out to show the efficiency of the proposed method. The effect of several parameters such as non-uniformity of the load and variation of the cross-section on the buckling load of the column is discussed in details.
M. Nemati, M. Sefid, M. S. Barghi Jahromi, R. Jahangiri,
Volume 40, Issue 2 (1-2022)
Abstract
In the present work, the effect of magnetic field, changes in the angle of inclination of the cavity and the shape of nanoparticles on the flow field and heat transfer of water-alumina with uniform heat generation/absorption is investigated by Lattice Boltzmann method (LBM). The curved wall and the diagonal walls of the cavity are at a constant temperature of hot and cold, respectively. Nanoparticle volume fraction of 0, 0.02 and 0.04, Hartmann number of 0, 15, 30, 45 and 60, heat generation/absorption coefficient of -5, 0 and +5 and inclination angle of 45, 135 and 225 degrees are studied. The high accuracy of the results compared to previous studies confirmed the correctness of the code written in Fortran language. The results shows that in all cases, increasing the Hartmann number leads to a decrease in the maximum value of the streamlines and the average Nusselt number, with the lowest effect at 225 degrees. Also increasing the strength of the magnetic field leads to an average decrease of 28, 23 and 7% of the average Nusselt number for angles of 45, 135 and 225 degrees, respectively. Increasing the heat generation/absorption coefficient is a determining factor in the effectiveness of the magnetic field and adding nanoparticles, and increasing it reduces the amount of heat transfer. On average, heat generation reduces the average Nusselt number by 71, 98, and 145 percent for the angles of 45, 135, and 225 degrees, respectively. In general, the lowest value of the average Nusselt number is related to the angle of 225 degrees, but the effect of adding nanoparticles in increasing the average Nusselt number is the highest at this angle. Generally, an increase in the percentage of nanoparticles leads to an average increase of 12% in the average Nusselt number. The effect of nanoparticle shape is more apparent with increasing their volume fraction. The highest amount of heat transfer is related to the cylindrical nanoparticles, in which the average Nusselt number is on average about 6% higher than the spherical state.
P. Gilavand, H. R. Heidari,
Volume 40, Issue 2 (1-2022)
Abstract
In this paper, the effect of water- iron oxide (Fe3O4) nanofluid on a channel heat transfer in the presence of perpendicular to the flow variable magnetic field with creating axial obstacles using a mixed single-phasee model is investigated numerically. The effects of magnetic field are added to governing equations of ferrofluid by writing codes and the problem geometry is generated and networked in Gambit 2.4 software. The network used is constructed in a three-dimensional and the governing non-linear differential equations are solved according to the finite volume method by using the Fluent software. Also, the effect of parameters such as obstacles in the flow path, dimensionless number of magnetic field intensity and Reynolds dimensionless number on heat transfer have been studied. The results show that creating obstacles in the flow path causes turbulence in the fluid flow, which increases the overall heat transfer. Also, the application of a magnetic field on the magnetic nanofluid causes the penetration of the cool boundary layer in the central parts of the channel and with increasing the intensity of the magnetic field, the penetration of this layer increases. As a result, the amount of Nusselt number and heat transfer has increased, and this improvement in heat transfer and Nusselt number increases with increasing Reynolds number.
A. Panjebashi Naghsh, K. K. Esmaeili. Torkanpouri ,
Volume 40, Issue 2 (1-2022)
Abstract
One of the new methods for powering low power electronic devices is the use of mechanical energies due to vibrations. In this method, the piezoelectric material is employed for converting the mechanical energy of vibration into the electrical energy. The advantage of this method is needlessness of using the battery charging system. In this paper, the functionally graded (FG) cantilever with the piezoelectric layer is considered as energy harvester system. The mathematical model of the system is constructed and the governing equation for electromechanical coupling is presented. Then the effects of the system parameters on the generated power is studied. Finally, by considering uncertainties in energy harvester parameters, the effect of uncertainties on the produced energy is investigated by Monte-Carlo simulation method for the first time. The results show that although the amount of generated power in the first natural frequency is higher than the other frequencies, but around the first natural frequency, the effect of uncertainties is increased and thus, the reliability of the energy harvester will be decreased.
N. Mashhadi Mohammad Reza , H. Omranpour,
Volume 41, Issue 1 (9-2022)
Abstract
One of the most important issues in engineering is to find the optimal global points of the functions used. It is not easy to find such a point in some functions due to the reasons such as large number of dimensions or inability to derive them from the function. Also in engineering modeling, we do not have the relationships of many functions, but we can input and output them as a black box. Therefore, the meta-heuristic algorithms are presented.
In this paper, a meta-heuristic algorithm based on the behavior of vortices in fluid physics is presented. Technically, the algorithm is made up of vortices. Each vortex contains some particles. The particles move by the presented rotation matrix. This movement causes the local search. Also by selecting another vortex through the selection algorithm, each vortex attempts to escape the local optima and reach the global optima. The algorithm will explore and exploit the given function using its operators. Another innovation of this paper is the introduction of two new evaluation criteria for optimization algorithms. These two criteria show the behavior and convergence of algorithms along the way to reach the global optimal point or fall into the local optima. The proposed algorithm has been implemented, evaluated and compared with the numerical optimization state of the art algorithms. It was observed that the proposed method was able to achieve better results than most of the other methods in the major of twenty-four standard functions in different dimensions. (All codes available at http://web.nit.ac.ir/ h.omranpour/.).
R. Zardashti, S. A. Saadatdar Arani , S. M. Hosseini,
Volume 41, Issue 1 (9-2022)
Abstract
In this paper, a robust optimization method is developed to solve the Satellite Launch Vehicle (SLV) trajectory design problem in the presence of uncertainties using a powerful Particle Swarm Optimization (PSO) algorithm. Given the uncertainties such as uncertainties in the actual values of aerodynamic coefficients, engine thrust, and mass in the ascent phase of a SLV, it is important to achieve an optimal trajectory that is robust to these uncertainties; because it improves the flight performance, reduces the workload of the guidance-control system, and increases the reliability of the satellite. For this purpose, first the optimization problem is considered by using the criterion of minimizing the flight time of the SLV as a cost function, and three-dimensional equations of motion as constraints governing the problem. Then, by adding the mean parameters and the standard deviation of uncertainties in the cost function, a robust optimizer model is developed and the algorithm is used to numerically optimize the model. Monte Carlo's perspective has also been used to analyze the results of uncertainties and their continuous feedback to the optimization model. Finally, the optimal trajectory is obtained that is robust to the uncertainties. The resulting simulation results show the accuracy of this claim.
S. Torfeh, Ramin Kouhikamali,
Volume 41, Issue 1 (9-2022)
Abstract
Accurate modeling of fluidization and heat transfer phenomena in gas-solid fluidized beds is not solely dependent on the particular selected numerical model and involved algorithms. In fact, choosing the right model for each specific operating condition, the correct implementation of each model, and the right choice of parameters and boundary conditions, determine the accuracy of the results in the evaluation of the performance of fluidized beds. In this research, in order to accurately simulate heat transfer in fluidized beds, important and effective parameters on two-fluid Eulerian model that incorporate the kinetic theory of granular flow were investigated. For this purpose, effects of particle-particle and particle-wall restitution coefficient, specularity coefficient, granular temperature and effective thermal conductivity coefficients determination methods on the numerical solution were evaluated. These investigations were first carried out on heat transfer from hot air to solid particles in an adiabatic fluidized bed, and then on a fluidized bed with constant temperature walls for bubbling and turbulent regimes. Results showed that specularity coefficient and effective thermal conductivity are important parameters in heat transfer process from wall to bed. In this case, the zero value of the specularity coefficient causes the air temperature to increase by about 7 degrees in the bubbling regime and about 5 degrees in the turbulent regime, and its unit value gives the same results with the no-slip condition. In addition, considering the solid and gas material thermal conductivities causes the outlet air temperature to be about 26 degrees higher than the temperature that is obtained by considering the effective thermal conductivity coefficients with standard approach. The partial differential and algebraic form of the conservation equation for the particles kinetic energy show identical results in dense fluidized beds, although considering a constant granular temperature can cause computational errors.
H. Salehipour,
Volume 41, Issue 1 (9-2022)
Abstract
In this paper, static buckling of homogeneous beams coated by a functionally graded porous layer with different boundary conditions is investigated based on the Timoshenko beam theory. The principle of virtual work has been used to obtain the governing equations. Two different methods, namely analyticalsolution and numerical solution are used to solve the governing equations and extract the buckling force. The governing equations are coupled as a series of ordinary differential equations. In the analytical solution, these equations are first uncoupled using a series of mathematical operations, and are then solved. The obtained solution has a series of parameters and unknown constants. Using the boundary conditions at the boundaries of the beam, a homogeneous system of equations is extracted, from which the axial buckling force is obtained. In the numerical solution, the generalized differential quadrature method is used to solve the static equations. Finally, the numerical results are presented and the effects of various parameters such as thickness to beam length ratio, porous layer thickness, porosity parameter, etc. on the buckling of the beam are investigated. Comparison of the results obtained from the two analytical and numerical solution methods confirms the accuracy and validity of both methods.
M. Mohieddin Ghomshei, Sh. Namazi,
Volume 41, Issue 1 (9-2022)
Abstract
In this article, mechanical buckling analysis of tapered beams having constant width and variable thickness, made of two-dimensional functionally graded materials is studied. The beam is assumed to be made of metal and ceramic, where their volume fractions vary in both longitudinal and thickness directions based on the power law. The beam is generally subjected to combined concentrated and distributed axial loads. The set of governing equations are derived using the Principle of Minimum total Potential Energy (PMPE), and are solved numerically using Differential Quadrature Method (DQM) for clamped-free boundary conditions. Convergence and accuracy of the presented solution are confirmed for both cases of concentrated and distributed axial loads. The effects of different parameters on the critical buckling load of the beam for both load cases are studied including geometrical parameters, gradation indices in longitudinal and thickness directions, and variation of thickness. Also buckling analysis of the beam under a combination of concentrated load and distributed axial loads of linear, quadratic and exponential types are investigated. Numerical results show that the highest values of the critical buckling load belong to the linear distributed load, and the lowest value is owned by exponential load.
F. Jafarzadeh, S. Mehrabian,
Volume 41, Issue 1 (9-2022)
Abstract
In this study, a cold atmospheric He plasma jet is investigated. The jet is of dielectric barrier discharge type, consisting of a dielectric tube with two metal ring electrodes. The continuity, momentum and energy conservation equations as well as the Poisson equation for obtaining the potential and the electric field, accompanied with the ideal gas laws, are used for the simulation. The results show that the electron and ion densities, potential and space charge field, internal energy, temperature and velocity of the electrons increase with time. Moreover, the increment of the plasma length and its forward propagation along the jet axis with time is also observed. Therefore, it is expected that the values of the mentioned quantities increase with time, which results in the increment of the plasma jet length.
M. Keyhanpour, M. Ghasemi,
Volume 41, Issue 1 (9-2022)
Abstract
According to the declining trend of fossil fuel resources and the need to use renewable energies, appropriate research should be conducted for technical and functional studies in this regard. Therefore, in this research, a tubular PEM fuel cell as a suitable energy source with three-dimensional geometry has been numerically simulated and investigated. For a comprehensive study, the equations of continuity, momentum, energy, stress-strain, and fluid-solid-heat interaction at steady state are defined, coupled together, and then solved by a finite element numerical code. Assuming the cell voltage changes from 0.95 to 0.4 volts, the passage of compressible fuel and air through the channels and porous media of the electrode and catalyst, and also about 6 degrees increase in the average cell temperature, causes approximately 35 nm displacement in different parts. These displacements, due to fluid-solid-heat interactions, cause thermal and mechanical stresses. The maximum stress is about 3500 kN/m2 in the electrolyte due to its displacement limit (average displacement 12.8 nm). Then the relation of voltage variation with current density, stress, fuel flow rate, displacement and fuel cell temperature was shown. Also the results showed that the assumption of fluid-solid-heat interaction reduces the fuel cell power density by about 3%. Finally, the effect of different parameters such as fuel and air channel radius, electronic and ionic conductivity were investigated. For example, at a voltage of 0.4 volt, 20 percent reduction in the radius of air or fuel channels, or 100 percent increase in the electron or ionic conductivity, increases the electrical current density by about 2.17, 0.05, 3.69, and 40 percent, respectively.
M. Ghomeshi Bozorg,
Volume 41, Issue 1 (9-2022)
Abstract
In this paper, dynamic instability due to parametric and external resonances of moderately thick functionally graded rectangular plates, under successive moving masses, is examined. Plate mass per unit volume and Young’s modulus are assumed to vary continuously through the thickness of the plate and obey a power-law distribution of the volume fraction of the constituent. The considered rectangular plates have two opposite simply supported edges while all possible combinations of free, simply supported and clamped boundary conditions are applied to the other two edges. The governing coupled partial differential equations of the plate are derived based on the first-order shear deformation theory with consideration of the rotational inertial effects and the transverse shear stresses. All inertial components of the moving masses are considered in the dynamic formulation. Using the Galerkin procedure, the partial differential equations are transformed into a set of ordinary differential equations with time-dependent coefficients. The Homotopy Analysis Method (HAM) is implemented as a semi-analytical method to obtain stable and unstable zones and external resonance curves in a parameters space. The effects of the index of volume fraction, thickness to length ratio, and different combinations of the boundary conditions on the dynamic stability of the system are also investigated. The results indicate that decreasing the index of volume fraction, increasing thickness to length ratio, and higher degree of edge constraints (respectively from free to simply-supported to clamped) applied to the other two edges of the plate shift up the instability region and resonance curves in the parameters plane and, from a physical point of view, the system becomes more stable. In addition to using numerical simulations of the plate midpoint displacement, Floquet theory is also employed to validate the HAM results. Finally, the results of this study, in a particular case, are compared and validated with the results of other works.
P. Sheikhbahaei, F. Mossaiby,
Volume 41, Issue 1 (9-2022)
Abstract
Peridynamics is a nonlocal version of the continuum mechanics, in which partial differential equations are replaced by integro-differential ones. Due to not using spatial derivatives of the field variables, it can be applied to problems with discontinuities. In the primary studies, peridynamics has been used to simulate crack propagation in brittle materials. With proving the capabilities of peridynamics, the idea of using this theory to simulate crack propagation in quasi-brittle materials and plastic behavior has been proposed. To this end, formulations and models based on peridynamics have been developed. Meanwhile, the high computational cost of peridynamic methods is the main disadvantage of this theory. With the development of peridynamic methods and introduction of hybrid methods based on peridynamics and local theories, the computational cost of peridynamic methods has been reduced to a large extent. This paper introduces peridynamics and the models based on it. To this end, we first review peridynamics, its formulations, and the methods based on it. Then we discuss the modeling of quasi-brittle materials, simulation of plastic behavior and employing the differential operators in this theory.
