Showing 657 results for Type of Study: Research
F. Moradpouri,
Volume 38, Issue 2 (2-2020)
Abstract
Wave-field extrapolation based on solving the wave equation is an important step in seismic modeling and needs a high level of accuracy. It has been implemented through a various numerical methods such as finite difference method as the most popular and conventional one. Moreover, the main drawbacks of the finite difference method are the low level of accuracy and the numerical dispersion for large time intervals (∆t). On the other hand, the symplectic integrators due to their structure can cope with this problem and act more accurately in comparison to the finite difference method. They reduce the computation cost and do not face numerical dispersion when time interval is increased. Therefore, the aim of the current paper is to present a symplectic integrator for wave-field extrapolation using the Euler method. Then, the extrapolation is implemented for rather large time intervals using a simple geological model. The extrapolation employed for both symplectic Euler and finite difference methods showed a better quality image for the proposed method. Finally the accuracy was compared to the finite difference method
M. Jamei, H. R. Ghafouri,
Volume 38, Issue 2 (2-2020)
Abstract
In this study, we present a numerical solution for the two-phase incompressible flow in the porous media under isothermal condition using a hybrid of the linear lower-order nonconforming finite element and the interior penalty discontinuous Galerkin (DG) method. This hybridization is developed for the first time in the two-phase modeling and considered as the main novelty of this research.The pressure equation and convection dominant saturation equation are discretized using the nonconforming Crouziex-Raviart finite element (CR FEM) and the weighed interior penalty discontinuous Galerkin (SWIP) method, respectively. Utilizing the nonconforming finite element method for solving the flow equation made the pressure and velocity values be consistent with respect to the degrees of freedom arrangement at the midpoint of the neighboring element edges. The boundary condition governing the simulation is the Robin type at entrance boundaries, and the time marching discretization for the governing equations is the sequential solution scheme. An H (div) projection using Raviart-Thomas element is implemented to improve the results’ resolution and preserve the continuity of the normal component of the velocity field. At the end of each time step, the non-physical oscillation is omitted using a slope limiter, namely, modified Chavent-Jaffre limiter, in each element. Also, in this study, the developed algorithm is verified using some benchmark problems and the test cases are considered to demonstrate the efficiency of the developed model in capturing the shock front at the interface of fluid phases and discontinuities.
H. Mohammadiun, M. Mohammadiun, M. H. Dibaee Bonab, M. Darabi, S. R. Hejazi, V. Janipour Bidsardareh,
Volume 39, Issue 1 (8-2020)
Abstract
: In this research, dimensionless temperature and entropy generation for the steady state flow in the stagnation point of incompressible nanofluid impinging on an infinite cylinder have been investigated. The impinging free stream is steady with a constant strain rate k. Similarity solution of the Navier-Stokes equations and energy equation is derived in this problem. A reduction of these equations is obtained using appropriate transformations introduced in this research. The general self similar solution is obtained when the heat flux on the cylinder wall is constant. All solutions brought above are presented for Reynolds numbers Re=ka^2/2vf that range from 0.1 to 1000 and the selected values of particle fractions, where a is the radius of the cylinder and υf is the kinematic viscosity of the base fluid. Results show that for Reynolds numbers examined, as the particle fraction increases, the depth of diffusion of the fluid velocity field in axial direction decreases, whereas Nusselt number is raised. Also, the maximum value of entropy generation has been calculated.
M. Rezaee, M. M. Ettefagh, R. Fathi ,
Volume 39, Issue 1 (8-2020)
Abstract
Although the traditional automatic ball balancer (ABB) has numerous advantages, it has two major deficiencies, i.e., it has a limited balance stable region and it increases the vibration amplitude of the rotor at transient state. These deficiencies limit the applicability of ABBs. In this regard, a new type of ABB called “the Ball-spring autobalancer” has been proposed to resolve the mentioned deficiencies of the traditional ABBs. In order to investigate the capability of the Ball-spring AB in balancing rotors, it is necessary to study its dynamics accurately. The dynamics of a rotor with linear bearing equipped with a Ball-spring AB has been studied previously; however, in real situations, the bearings have nonlinear characteristics. Here, the dynamics of a rotor with nonlinear bearings equipped with a Ball-spring AB is investigated by the multiple scales method for the first time. The results show that the nonlinearity at the rotor bearings does not impair the advantages of the Ball-spring AB.
N. Cheraghi, M. Miri, M. Rashki,
Volume 39, Issue 1 (8-2020)
Abstract
This paper presents a probabilistic assessment on the free vibration analysis of functionally graded material plates, including layers with magneto-electro-elastic properties, using the 3D solution and surrogate models. The plate is located on an elastic foundation and the intra-layer slipping effect is also considered in the analysis by employing the generalized intra-layer spring model. Due to the high computational cost of the 3D solution in calculating the free vibration frequency of the plate, surrogate models are used. The meta models including kriging method, radial fundamental function method and polynomial response surface method are used to construct the surrogate model. For surrogate models training, the results of the three-dimensional solving method are used. The elastic foundation hardness, the intra-layer slipping effect, the material properties index, and the layer densities are considered as the variables with uncertainty. The three-dimensional solution method is validated through a comparison with other available reference. The results obtained through the surrogate models have been compared to those of the 3D solution formulation, showing a good agreement. The effects of some parameters including the elastic foundation hardness, the intra-layer slipping effect, the density of each layer, and the material properties index on the fundamental frequency of functionally graded material plates are investigated. By using three-dimensional solution method and Kriging Surrogate Model, it is shown that the shear and transverse components of elastic foundation hardness and the density of each layer have the greatest effect on the fundamental frequency of the functionally graded material plates.
S. A. Ahmadi, M. H. Pashaei, R. A. Jafari-Talookolaeilokoolaei,
Volume 39, Issue 1 (8-2020)
Abstract
In this paper, three-dimensional displacement response of a cylindrical sandwich panel with compressible core under the action of dynamic pulse loading is addressed using the extended high order sandwich panel theory. Also, local dynamic pulse buckling of facesheets is studied by considering the Budiansky-Roth buckling criterion. It is assumed that the sandwich panels consist of orthotropic face sheets and an isotropic viscoelastic foam core layer. The effects of various parameters including the panel span, core and facing thickness, pulse duration and maximum pressure on the non-linear dynamic response and buckling strength of the sandwich cylindrical panel are studied. The results obtained from the present method are compared with finite element solutions using the commercial software ANSYS and those reported in the literature, showing a good agreement. It is revealed that applied core non-linear theory could be satisfactory for the dynamic pulse response of sandwich viscoelastic panels. It is also shown that the pulse buckling strength of panel increases with a decrease of the panel radius or an increase of the panel thickness.
S.m. Naghavi, G.a. Sheikhzadeh,
Volume 39, Issue 1 (8-2020)
Abstract
Lattice Boltzmann method is one of computational fluid dynamic subdivisions. Despite complicated mathematics involved in its background, end simple relations dominate on it; so in comparison to the conventional computational fluid dynamic methods, simpler computer programs are needed. Due to its characteristics for parallel programming, this method is considered efficient for the simulation of complex geometry flows, in which a large amount of computational memories is needed. Because of the curved boundaries in the complex geometries, detecting the proper curved boundary condition is unavoidable for the lattice Boltzmann method. For this purpose, more works have been done, and different curved boundary conditions have been proposed. At the present work, first, some curved boundary conditions have been reviewed; then a simplified curved boundary condition is proposed. A computer program based on the lattice Boltzmann method, in FORTRAN language, has been prepared; in this program, the boundary condition along with some others applied on it is proposed. To verify the accuracy and correctness of the proposed boundary condition, 2D cavity flow has been simulated and compared to the available numerical results. Adaptation of the achieved results with those of previous researchers verifies the prepared program correctness. Also, two fluid flows have been simulated, a flow around a stationary cylinder in a 2D channel and one between two stationary and moving cylinders. The results of simulations with the proposed boundary condition, along with the previous boundary conditions, have been compared to the available results. Comparisons demonstrate that solutions with proper accuracy could be obtained by the proposed boundary condition.
N. Fattahi, M. Reisi-Nafchi, G. Moslehi,
Volume 39, Issue 1 (8-2020)
Abstract
Scheduling in production environments is used as a competitive tool to improve efficiency and respond to customer requests. In this paper, a scheduling problem is investigated in a three-stage flexible flowshop environment with the consideration of blocking and batch processing. This problem has been inspired by the charging and packaging line of a large battery manufacturer. In this environment, the first and third stages involve a single processor machine, and the second one consists of m identical parallel batch processing machines. The objective is to minimize the total weighted tardiness of the received orders.Given the lack of consideration of this problem in the literature, first, a mathematical programming model is presented for the problem. Also, due to the NP-hardness of the problem, a variable neighborhood search algorithm and a memetic algorithm are developed to solve it. The computational results show that the variable neighborhood search algorithm can solve instances up to 1200 orders and 15 machines with an average deviation of about 1.9%, relative to the best solution of the two algorithms, and the memetic algorithm can solve instances up to 1200 orders and 15 machines with an average deviation of about 7.8%, as compared e to the best solution of the two algorithms. In general, computational results show the better performance of the variable neighborhood search algorithm in comparison to the memetic algorithm.
F. Shabani, M. Saghafian, D. Saeidi, F. F. Momennasab ,
Volume 39, Issue 2 (2-2021)
Abstract
Particulate separation has many applications in medicine, biology and industry. In this research, the separation of polystyrene particles with a diameter of 10, 20 and 30 μm in the fluid flow of a microchannel is investigated. The microchannel consists of a spiral region and a straight region under the influence of acoustic waves. In the spiral region, the particles under hydrodynamic effects undergo the initial separation; then the particles enter the straight region of the microchannel, and the final separation of the particles is done by the force generated and exerted through the acoustic waves. The effects of acoustic frequency and the number of spiral region loops on separation are investigated. The results show that for measured dimensions and parameters, at 1 MHz acoustic wave, when the number of loops is 2 for the spiral region, the particles at the end of the path are in a suitable position for separation. In addition, the results show that the separation of particles with this hybrid system is better than that done by the simple methods, and the separation rate can be as high as 100%
Z. Z. Ahangari Sisi, M. Mirzaei, S. Rafatnia, B. Alizadeh,
Volume 39, Issue 2 (2-2021)
Abstract
Active vehicle suspension system is designed to increase the ride comfort and road holding of vehicles. Due to limitations in the external force produced by actuator, the design problem encounters the constraint on the control input. In this paper, a novel nonlinear controller with the input constraint is designed for the active suspension system. In the proposed method, at first, a constrained multi-objective optimization problem is defined. In this problem, a performance index is defined as a weighted combination of the predicted responses of the nonlinear suspension system and control input. Then, this problem is solved by the modified firefly optimization algorithm to find the constrained optimal control input. To evaluate the performance of the proposed method, the results of the unconstrained and constrained controllers are provided and discussed for various road excitations. The results show a remarkable increase in the ride comfort with the limited force, while other suspension outputs including the suspension travel and tire deflection being in the acceptable ranges. In addition, these controllers are compared with Sliding Mode Control (SMC) and Nonlinear Model Predictive Control (NMPC) in the presence of model uncertainty.
M. Abouei Ardakan, S. Talkhabi,
Volume 39, Issue 2 (2-2021)
Abstract
One of the common approaches for improving the reliability of a specific system is to use parallel redundant components in subsystems. This approach, which is known as the redundancy allocation problem (RAP), includes the simultaneous selection of the component type and its level for each subsystem in order to maximize the system reliability.Traditionally, there are two redundancy strategies, namely active and standby, for the redundant components. Recently, a new powerful strategy called mixed strategy has been developed. It has been proved that the mixed strategy has a better performance when compared to both previous strategies. The main issue in utilizing the mixed strategy is its complicated formulation and sophisticated calculations, leading to a time-consuming procedure for solving the problems. Hence, in this paper, a new formulation based on the recursive approach is introduced to ease the calculation of the mixed strategy. In the new formulation, the complex double integral calculations are removed and the calculation times is reduced. The proposed recursive formulation provides a general statement for the mixed strategy formula which is not changed by altering the number of components in each subsystem. This flexibility and stability in the formula can be very important, especially for large scale cases. In order to evaluate the new approach and to compare its performances with the previous formulation, a benchmark problem with 14 subsystems is considered and the results of the two formulation are compared with each other.
Z. Barouei, M. Jabbarzadeh,
Volume 39, Issue 2 (2-2021)
Abstract
In this paper, the nonlinear bending analysis for annular circular nano plates is conducted based on the modified coupled stress and three-dimensional elasticity theories. For this purpose, the equilibrium equations, considering nonlinear strain terms, are calculated using the least energy potential method and solved by the numerical semi-analytical polynomial method. According to the previous works, there have been no studies calculating all boundary conditions numerically based on three-dimensional elasticity. Typically, the research done on three-dimensional elasticity is either finite element or only for a simply-supported boundary condition. In this research, for the first time, the nonlinear analysis of bending is calculated with the help of three-dimensional elasticity for a variety of boundary conditions. Also, with the help of the modified couple stress theory, the results on the nano-scale scale have been studied. In the following, while validating the results, we investigate the changes in the scale parameter for the types of boundary conditions, the effect of changing the parameter of scale in different thicknesses, and the impact of the parameter of scale on the linear and nonlinear results.
R. Keshavarzi, Sh. Hatami, Sh. Hashemi,
Volume 39, Issue 2 (2-2021)
Abstract
Plates made of laminated composite materials with variable stiffness can have wide applications in various branches of engineering due to such advantages as high strength /stiffness to weight ratio. In these composites, curved fibers are used to reinforce each lamina instead of the straight fibers. In this paper, the application of finite strip method for the buckling analysis of moderately thick composite plates with variable stiffness is investigated. For buckling analysis, a semi-analytical finite strip method based on the first-order shear deformation theory is employed. In this method, all displacements are presumed by the appropriate harmonic shape functions in the longitudinal direction and polynomial interpolation functions in the transverse direction. The minimum potential energy method has been used to develop the stability formulations. This analysis examines the effect of using curved fibers instead of straight fibers on the laminate composites. The critical loads obtained from this analysis are compared with those of other researchers and the efficiency and accuracy of the developed finite strip method are confirmed. Comparison of the analysis results of these plates shows that changing the slope of the fibers can lead to a significant change in the buckling response. Also, increasing the number of the terms of shape functions in the longitudinal direction has a significant effect on the convergence to the desired results.
S. Esmizadeh, H. Haftbaradaran, F. Mossaiby,
Volume 39, Issue 2 (2-2021)
Abstract
Experiments have frequently shown that phase separation in lithium-ion battery electrodes could lead to the formation of mechanical defects, hence causing capacity fading. The purpose of the present work has been to examine stress intensity factors for pre-existing surface cracks in spherical electrode particles during electrochemical deintercalation cycling using both analytical and numerical methods. To this end, we make use of a phase field model to examine the time-dependent evolution of the concentration and stress profiles in a phase separating spherical electrode particles. By using a geometrical approximation scheme proposed in the literature, stress intensity factors at the deepest point of the pre-existing surface cracks of semi-elliptical geometry are calculated with the aid of the well-established weight function method of fracture mechanics. By taking advantage of a sharp-interphase core-shell model, an analytical solution for the maximum stress intensity factors arising at the deepest point of the surface cracks during a complete deintercalation half-cycle is also developed. Numerical results for evolution of the concentration profile and the distribution of the hoop stresses in the particle are presented; further, the stress intensity factors found numerically based on the phase field model are compared with those predicted by the analytical core-shell model. The results of the numerical model suggest that the maximum stress intensity factor could significantly vary with changes in the surface flux, increasing potentially by a factor of two within the range of parameters considered here, when the concentration difference between the two phases is decreased.
O. Bateniparvar, N. Noormohammadi, A. M. Salehi,
Volume 39, Issue 2 (2-2021)
Abstract
In this paper, Equilibrated Singular Basis Functions (EqSBFs) are implemented in the framework of the Finite Element Method (FEM), which can approximately satisfy the harmonic PDE in homogeneous and heterogeneous media. EqSBFs are able to automatically reproduce the terms consistent with the singularity order in the vicinity of the singular point. The newly made bases are used as the complimentary enriching part along with the polynomial bases of the FEM to construct a new set of shape functions in the elements adjacent to the singular point. It will be shown that the use of the combined bases leads to the quality improvement of the solution function as well as its derivatives, especially in the vicinity of the singularity.
M. Hashemian, M. Jabbarzadeh,
Volume 40, Issue 1 (9-2021)
Abstract
In this paper, nonlinear bending analysis of functionally graded rectangular and sectorial micro/nano plates is investigated using the modified couple stress theory. For this purpose, a higher-order shear deformation theory and von Kármán geometrically nonlinear theory are employed. The equilibrium equations and the boundary conditions for rectangular and annular sector plates are derived from the principle of minimum total potential energy and solved using the Semi-Analytical Polynomial Method (SAPM). One of the advantages of the implemented shear deformation theory is removing the defects of higher order shear deformation theory, and obtaining the response of the first and the third-order shear deformation theories at the same time. Afterwards, beside investigating the benefits of this theory compared with other ones, the results are verified with those by other researches. At the end, the effects of length scale parameter, boundary conditions, power law index, and geometrical dimensions are investigated
S. Moomivand, H. Davari-Ardakani, H. Mosadegh, M. Abouei Ardakan,
Volume 40, Issue 1 (9-2021)
Abstract
In this paper, a multi-mode resource constrained project selection and scheduling problem is investigated considering the reinvestment strategy in a flexible time horizon. Among a set of available projects, a number of projects are selected and scheduled regarding the constraints on renewable resources and precedence relations. The benefits of project portfolio selection and scheduling are compared in both fixed and flexible time horizons. For this purpose, upper and lower tolerance limits are considered for the predetermined time horizon. If the schedule exceeds the time horizon, a penalty cost will be charged. The objective is to determine the optimal time horizon. A mixed-integer linear programming model is proposed for this problem, and solved by GAMS software/CPLEX solver and also a combination of a proposed heuristic algorithm, Genetic Algorithm, and a local search method. Numerical results show that the proposed approach has an acceptable performance in terms of the quality of the solution and the running time. Also, dealing with the problem in a flexible time horizon is more profitable compared to a fixed time horizon.
P. Rastegar Rajeouni, A. R. Rahmati,
Volume 40, Issue 1 (9-2021)
Abstract
In order to simulate multiphase flow in the presence of dielectric current using the Lattice Boltzmann Method (LBM), three distribution functions are used, two of which for using the He-Chen-Zhang phase field model and one for solving the potential field. Initially, the ability of the code to apply surface tension was tested using the Laplace law and the drop release test. The results show that the present numerical program is capable of modeling well the regulated surface tension force. Then, the Rayleigh–Taylor instability simulation is used to evaluate the code's ability in applying volume forces. The results by the developed numerical program are in good agreement with the numerical results in the references. In this study, for the first time, the effect of electric field on a droplet immersed in another fluid and the presence of droplet in a porous medium is investigated by LBM. For this purpose, first the droplet motion due to the potential difference in the porous and non-porous media is investigated. After modeling the droplet motion due to the potential difference, two electric fields areapplied to the droplet to reverse the droplet deformation. Through various tests, it is shown that at a given potential difference, the droplet breaks down after much deformation and is divided into smaller droplets. The decomposition of droplets in a pre-mixed emulsion is a common technique in the production of monodisperse droplets. The presence of monodisperse droplets in an emulsion improves the physical properties of polymer science experts.
B. Movahedian Attar, M. Sadeghi,
Volume 40, Issue 1 (9-2021)
Abstract
Accurate determination of the response of structures under dynamic loads such as earthquake loads plays an important role in the safe and economical design of structures. The purpose of this paper is to utilize a novel solution method based on the use of exponential basis functions for dynamic analysis of Bernoulli beam subjected to different types of base excitations. This method was firstly introduced for solving scalar wave propagation problems, named as stepwise time-weighted residual method. The proposed method considers the solution as a series of exponential basis functions with unknown constant coefficients; and the problem is solved in time without the need for spatial discretization of the beam and by using an appropriate recursive relation to correct the coefficients of the exponential bases. In order to apply the earthquake excitation, first by using the central finite difference relation, the earthquake acceleration history is converted to displacement history. Moreover, the displacement history is applied to the beam as a time-varying boundary condition. In this study, the capabilities of the proposed method in solving several sample problems of vibration of single and multi-span beams under various stimuli such as earthquake acceleration variations are compared with the results of other existing methods.
M. Azizpooryan, N. Noormohammadi,
Volume 40, Issue 1 (9-2021)
Abstract
In this paper, static analysis of in-plane heterogeneous laminated composite plates is numerically studied. The Mindlin’s theory which considers linear transverse shear deformation has been implemented. The governing partial differential equation is satisfied by a weighted residual integration. Chebyshev polynomials of the first kind are used as basis functions and exponential functions make up the weight functions of the integration. The emerging integrals may be composed of some pre-evaluated 1D normalized ones, which effectively paces up the solution progress. To verify the method, several examples of homogeneous as well as heterogeneous plates with various lamination schemes and boundary conditions have been solved. Results are compared with those from the literature or by commercial codes, which reveal excellent accuracy of the proposed method.
