A. R. Rahmati, R. Hajzaman,
Volume 35, Issue 2 (2-2017)
Abstract
In this study, for the first time natural convection heat transfer of Al2O3-water nanofluid with constant and variable
properties is investigated within square shape porous media using the lattice Boltzmann method. The horizontal walls of the
cavity are insulated, and left and right vertical walls are hot and cold, respectively. The Study have been carried out for Rayleigh
numbers of 103, 104, 105, 106, Darcy numbers of 10-2, 10-4, porosity coefficients of 0.4, 0.6, 0.9 and solid volume fraction of 0, 0.01,
0.02 and 0.03. In order to consider the effect of porous media, Darcy-Forchheimer model is used. The results show that the presence of the porous media decreases the velocity of nanofluid and consequently decreases the strength of the flow. With decreasing Darcy number and porosity coefficient, natural convection heat transfer weakens and the mechanism of natural convection of nano-fluids tends to that of thermal conduction. With increasing Rayleigh number, the strength of flow in cavity and average Nusselt number increases. In all cases studied, increase in volume fraction improves heat transfer. In constant properties model, by increasing solid volume fraction, average Nusselt number increases more than that of variable properties model. The results show that Lattice Boltzmann method has the ability to simulate flow in porous media.
M. Rabbani, F. Taghiniam, H. Farrokhi-Asl , H. Rafiei ,
Volume 35, Issue 2 (2-2017)
Abstract
In this paper, the solution of a non-linear model of Cell Manufacturing (CM) in certain and dynamic conditions is
studied, considering intracellular and extracellular costs, cell constructing costs, the cost of restoration and the cost of equipment
transportation per distance travelled. Since the number of cells in each stage of production is important, by optimizing the
number of cells, additional costs can be minimized. Therefore, the main objective of this study is to investigate the optimal
number of cells located. Bio-geographical Based Optimization (BBO) algorithm is applied in the CM for the first time in the
literature and the obtained results from this algorithm are compared with the results of well-known genetic algorithm. The results
shows the good performance of genetic algorithm. Finally, the conclusion and future research are provided.
F. Bazdidi Tehrani, D. Badaghi, M. Kiamansori , M. Jadidi,
Volume 35, Issue 2 (2-2017)
Abstract
The purpose of the present study is to investigate and analyze numerically, the effective mechanisms on the flow field and pollutant dispersion around a simple and long street canyon by means of Large Eddy Simulation (LES) approach using various inflow turbulence generation methods. For this purpose, four methods i.e. vortex, mapping, synthetic and no-inlet perturbation methods are used as inflow turbulence generators in LES. Results suggest that all methods are capable of capturing the two important structures of canyon vortex and corner eddy, which have great influences on air ventilation inside the street canyon. The magnitudes of concentration on the leeward wall of the first building are approximately four times as much as those
of windward wall of the second building. Among the various inflow turbulence generation methods, the vortex method is the most precise method and no-inlet perturbation method is the least precise method.
H. Kalani, A. Akbarzadeh, S. Moghimi, N. Khoshraftar,
Volume 35, Issue 2 (2-2017)
Abstract
Many efforts have been done in recent years to decrease the required time for analysis of FKP (Forward Kinematics
Problem) of parallel robots.This paper starts with developing kinematics of a parallel robot and finishes with a suggested
algorithm to solve forward kinematics of robots. In this paper, by combining the artificial neural networks and a 3rd-order
numerical algorithm, an improved hybrid strategy is proposed in order to increase the accuracy and speed of forward kinematics
analysis of parallel manipulators. First, an approximate solution of the forward kinematics problem is produced by the neural
network. This approximate solution is then considered as the initial guess for the 3rd-order Newton-Raphson numerical
technique. By applying Stewart-Gough parallel manipulator, the efficiency of the proposed method is evaluated. It is shown that
replacing the Newton-Raphson algorithm by the 3rd-order one leads to a reduction of the iterations required to reach the desired
accuracy level and thus a reduction of the FKP analysis time. Finally, Stewart robot is used to simulate the movement of jaw.
This novel algorithm can be applied to any forward kinematics of serial or parallel robots.
M. H. Yas, M. Nejati, S. S. Jafari,
Volume 35, Issue 2 (2-2017)
Abstract
In this paper, free vibration of carbon nanotube-reinforced functionally graded circular plates with hole has been
investigated. Distribution of carbon nanotubes are continuous and the gradual and graded changes of materials through the
plate thickness are considered as volume fraction. Considering the linear and non-linear variation of circular plates through the
radial direction and also considering the proposed function for the thickness, the plate thickness can be convex or concave.
Moreover, the motion equations of plate were obtained based on the third-order shear deformation theory. These equations are
coupled differential equations which can convert Ordinary Differential Equations (ODE) using the Trigonometric series
expansion of displacement fields such that they satisfy the axial symmetry condition. Solving the converted ODE equations is too
difficult. For this reason, the differential quadrature method is employed to solve these equations. The obtained results are
compared with the results reported by other researchers and an excellent agreement is observed between them. Finally, the effects
of different geometric parameters as well as different volume fracture of nanotubes on natural frequency have been studied.
S. Mirzaei , J. Akbari,
Volume 35, Issue 2 (2-2017)
Abstract
For solving the dynamic equilibrium equation of structures, several second-order numerical methods have so far
been proposed. In these algorithms, conditional stability, period elongation, amplitude error, appearance of spurious frequencies
and dependency of the algorithms to the time steps are the crucial problems. Among the numerical methods, Newmark average
acceleration algorithm, regardless of existence of spurious frequencies, is very popular in the structural dynamics due to its
unconditionally stability status of the method. Recently, several first-order methods have been introduced for resolving the
accuracy and stability issues. However, in these methods stability, accuracy and error in inversion of the state matrix are known
as major issues. When the state matrix became singular or ill conditioned, numerical errors will occure in the computational
process. Many of the available first-order methods were to improve the stability and accuracy and also to remove the error of
inversion. Even though the introduced methods are conditionally stable, no investigation on errors, occuring during dynamic
loading, has been reported for them. The main purpose of this paper is to utilize a specific decomposition method based on
Singular Value Decomposition (SVD) for modifying PIM algorithm. Using the SVD inversion technique, the singularity problem
of the state matrix has been resolved. In this paper, the modified method is called PIMS. As well, by applying the developed
method for dynamic loading, the error of responses has been investigated. The results show that PIMS algorithm is stable and,
comparing with secoend order Newmark and other available first order methods, has more accuracy.
M. S. Eskandarjuy , A. Baghlani,
Volume 35, Issue 2 (2-2017)
Abstract
In this paper, wave propagation method was applied to detect damage of structures. Spectral Finite Element Method
(SFEM) was used to analyze wave propagation in structures. Two types of structures i.e. rod and Euler-Bernoulli beam were
modelled using spectral elements. The advantage of spectral finite element over conventional Finite Element Method (FEM), in
wave propagation problems, is its accuracy and lower computational time. Two examples of rod and Euler-Bernoulli beam with
embeded concentrated mass were presented to illustrate the superiority of SFEM to FEM. Finally, a cracked beam was modeled
and analyzed using spectral finite elements and the location of the crack was determined using time history response of beam
structure.
Aliakbar Taghipour, J. Parvizian, S. Heinze, A. Duester, E. Rank,
Volume 37, Issue 1 (9-2018)
Abstract
finite cell method, are employed to compute a series of benchmark problems in the finite strain von Mises or J2 theory of plasticity. The hierarchical (integrated Legendre) shape functions are used for the finite element approximation of incompressible plastic dominated deformations occurring in the finite strain plasticity of ductile metals. The computational examples include the necking under uniaxial tension with notched and un-notched samples and the compression of a perforated plate. These computations demonstrate that the high-order finite element methods can provide a locking-free behavior with a pure displacement-based formulation. They also provide high convergence rates and robustness against high mesh distortions. In addition, it is shown that the finite cell method, on the top of the aforementioned advantages, provides easy mesh generation capabilities for highly complex geometries. The computational results are verified in comparison with the results obtained using a standard low-order finite element method known as the F-bar method. The numerical investigations reveal that both methods are good candidates for the plasticity analysis of engineering materials and structures made up of ductile materials, particularly those involving complex geometries.
M. Rabbani, E. Asgaari, A. Ghavamifar, H. Farrokhi-Asl,
Volume 37, Issue 2 (3-2019)
Abstract
In the recent decades, raw materials and resources have been remarkable issues for researchers; in other words, they play an important role in manufacturing industries or service organizations. On the other hand, the population is increasing every day. An increase in the population means the increased demand for goods or services. Therefore, more resources are needed to deliver services or goods. For this reason, government agencies and environmental agencies have developed and enforced stringent laws against producers and service providers who have exceeded the permissible limits for the environment; in some cases, the use of resources has been even restricted. In the meantime, the supply chain has become one of the major issues that can greatly influence this issue. In this research, the supply chain of the closed loop has been modeled due to uncertainty, disturbances and cost of production. The purpose of this problem has been to minimize the cost of the system in question based on the location decisions, and flow rates between levels and sales. The Lagrangian liberation solution method is used to solve this NP-hard problem. In the end, a numerical example has been employed to test the model and the proposed solution method. The results show that the time of implementation of the large-scale problem with GAMS is higher than that of the proposed method.
A. Noghrehabadi, R. Mirzaei, M. Ghalambaz,
Volume 38, Issue 1 (8-2019)
Abstract
The behavior of many types of fluids can be simulated using differential equations. There are many approaches to solve differential equations, including analytical and numerical methods. However, solving an ill-posed high-order differential equation is still a major challenge. Generally, the governing differential equations of a viscoelastic nanofluid are ill-posed; hence, their solution is a challenging task. In addition, the presence of very tiny nanoparticles (lower than 100 nm) induces new heat and mass transfer mechanisms which can increase the complexity of the behavior of the viscoelastic nanofluids. Therefore, creating or developing new analytical or semi-analytical approaches to solve the governing equations of these types of nanofluids is highly demanded. In the present study, by using a new idea and utilizing an optimization approach, a new solution approach has been presented to solve the governing equations of viscoelastic nanofluids. By using the optimization method, a basic initial guess was changed toward an optimized solution satisfying all boundary conditions and the governing equations. The results indicate the robustness and accuracy of the presented method in dealing with the high-order ill-posed governing differential equations of viscoelastic nanofluids.
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.
