M. R. Rastan, A. Sohankar,
Volume 36, Issue 2 (3-2018)
Abstract
In the first part of the present study, a two dimensional half-corrugated channel flow is simulated at Reynolds number of 104, in no-slip condition (hydrophilic surfaces( using various low Reynolds turbulence models as well as standard k-ε model; and an appropriate turbulence model (k-ω 1998 model( is proposed. Then, in order to evaluate the proposed solution method in simulation of flow adjacent to hydrophobic surfaces, turbulent flow is simulated in simple channel and the results are compared with the literature. Finally, two dimensional half-corrugated channel flow at Reynolds number of 104 is simulated again in vicinity of hydrophobic surfaces for varoius slip lengths. The results show that this method is capable of drag reduction in such a way that an increase of 200 μm in slip length leads to a massive drag reduction up to 38%. In addition, to access a significant drag reduction in turbulent flows, the non-dimensionalized slip length should be larger than the minimum.
M. Ettefagh, H. Mirab , R. Fathi,
Volume 36, Issue 2 (3-2018)
Abstract
One of the new methods for powering low-power electronic devices employed in the sea, is using of mechanical energies of sea waves. In this method, piezoelectric material is employed to convert the mechanical energy of sea waves into electrical energy. The advantage of this method is based on not implementing the battery charging system. Although, many studies have been done about energy harvesting from sea waves, energy harvesting with considering random JONWSAP wave theory is not fully studied up to now. The random JONSWAP wave model is a more realistic approximation of sea waves in comparison of Airy wave model. Therefore, in this paper a vertical beam with the piezoelectric patches, which is fixed to the seabed, is considered as energy harvester system. The energy harvesting system is simulated by MATLAB software, and then the vibration response of the beam and consequently the generated power is obtained considering the JONWSAP wave theory. In addition, the reliability of the system and the effect of piezoelectric patches uncertainties on the generated power are studied by statistical method. Furthermore, the failure possibility of harvester based on violation criteria is investigated.
M. Salari, A. Akhtarpour,
Volume 36, Issue 2 (3-2018)
Abstract
The most important features and phenomena of the deformation behavior of rockfills are stress-dependent stiffness, hardening and dilative (or contractive) behaviors, as well as breakage, rotation and redistribution of particle size. An elasto-plastic constitutive model has been suggested by Vermeer and de Borst to simulate the shear behavior of soils, concretes and rocks. This research has tried to improve this model for numerical simulation of the shear behavior of rock fills. The improvement of the model has been performed through proposing new mobilized dilation and friction angles functions and new relationships for some parameters. For validation, a series of large-scale triaxial tests performed on the rockfill shell of Masjed-e-Soleyman dam have been simulated with the improved model. The results show that the improved Vermeer-De Borst model has a good accuracy to simulate the shear behavior of rockfills numerically.
M. Rabbani, M. H. Afrazeh, S. Amini, H. Farrokhi-Asl,
Volume 36, Issue 2 (3-2018)
Abstract
Integrating the concepts of maintenance and production planning strategies is one of the most recent and important issues for the reason of their effects on the final product price. This paper considers different situations for production lines, separately and independently, in ordinary time and overtime, assuming possibility of outsourcing. This paper aims to find an optimal maintenance strategy and to integrate maintenance strategy with production planning in batch production environment in order to reduce backorder sales and decrease the production and maintenance cost in the specified planning horizon. Therefore, a new mathematical formulation is proposed for this problem. The proposed mathematical model is solved with two metaheuristic algorithms, namely simulated annealing and harmony search algorithms, and the obtained results are compared with each other. Regarding numerical results, two applied algorithms show acceptable results and the performance of the algorithms are almost identical.
H. Zohali, B. Naderi, M. Mohammadi,
Volume 36, Issue 2 (3-2018)
Abstract
This paper addresses the lot sizing and scheduling problem for a number of products in flexible flow shop with identical parallel machines. The production stages are in series, while separated by finite intermediate buffers. The objective is to minimize the sum of setup and inventory holding costs per unit of time. The available mathematical model of this problem in the literature suffers from huge complexity in terms of size and computation. In this paper, a new mixed integer linear program is developed for delay with the huge dimentions of the problem. Also, a new meta heuristic algorithm is developed for the problem. The results of the numerical experiments represent a significant advantage of the proposed model and algorithm compared with the available models and algorithms in the literature.
A. Rahmani Firoozjaee, M. Sahebdel,
Volume 36, Issue 2 (3-2018)
Abstract
In this research, the element free Galerkin is implemented to simulate the bed-load sediment transport equations in two dimensions. In this method, which is a meshless method, the computational domain is discretized by a set of arbitrarily scattered nodes and there is no need to use meshes, elements or any other connectivity information in nodes. The hydrodynamical part of sediment transport equations is modeled using 2D shallow water equations; and the Exner equation describes the sediment continuity. Eventually, to appraise the ability of considered method, several benchmark examples are solved and then, the obtained results are compared with previously published works
M. Mohammadimehr, S. Alimirzaei,
Volume 36, Issue 2 (3-2018)
Abstract
In this research, the nonlinear buckling analysis of Functionally Graded (FG) nano-composite beam reinforced by various distributions of Boron Nitrid Nanotube (BNNT) is investigated under electro-thermodynamical loading with considering initial geometrical imperfection. The analysis is performed based on nonlocal elasticity theory and using the Finite Element Method (FEM). Various distributions of BNNT along the beam’s thickness are considered as uniform and decreasing-increasing functionally graded; and the extended mixture model is used to estimate the properties of nano-composite beam. The elastic medium around the smart nano-composite beam is modeled as elastic foundation. The governing equations of equilibrium are derived using energy method and nonlocal elasticity theory; and the critical buckling load is obtained for various boundary conditions such as simply-simply supported (S-S) and clamped-clamped (C-C) using the FEM. The results indicate that with an increase in the geometrical imperfection parameter, the stiffness of nano-composite beam increases and consequently the stability of the system increases. The effect of FG-X distribution type is more than uniform distributions. Also, the critical buckling load of nano-composite beam increases with an increase in the electric field and elastic foundation.
B. Sadeghian, M. Ataapour, A. Taherizadeh,
Volume 36, Issue 2 (3-2018)
Abstract
Friction stir welding is of the most applicable methods to join dissimilar metals. In this study, the thermal distribution during the joining of 304 stainless steel and 5083 aluminum alloy by friction stir welding method was simulated by the finite element method. Both, transient and stationary thermal solutions were used in the simulations and the two methods were compared correspondingly. To verify the model, two sheets of stainless steel and aluminum were prepared and the friction stir welding was applied. Additionally, by using thermocouples temperature, the history of points on the sheets was obtained during welding. Then, the simulation and the experimental results were compared to validate the model. Finally, an artificial neural network model was created and the effect of different input parameters on the maximum temperature under the tool was investigated.
F. Bazdidi Tehrani, S. I. Vasefi, A. M. Anvari,
Volume 36, Issue 2 (3-2018)
Abstract
In the present paper, turbulent convection of CuO-Water Nanofluid in a vertical channel is investigated numerically. In order to simulate the flow, the fluid is considered as a continuous phase while the discrete nanoparticles are dispersed through it. The dispersion of CuO nanoparticles in different flow conditions are studied in order to find the effective mechanisms of particles dispersion in the channel. The results show that in the fully developed turbulent convection flow, thermophoresis is more dominant than Brownian motion of nanoparticles and therefore the nanoparticles aggregation are more in the central areas of the channel. While in entrance region, where the boundary layer is not fully formed, the particles dispersion are more uniform. Also, an increase in the nanoparticles concentration will increase the turbulent velocity fluctuations in regions near the wall and this two-sided effect will cause improvement in turbulent flow thermal transmitance than the laminar flow.
M. Bashi Varshosaz, B. Naderi, M. Mohammadi,
Volume 37, Issue 1 (9-2018)
Abstract
The purpose of this research is to deal with the problem of two-stage assembly flow shop scheduling. A number of single-item products (identical) each formed of several different parts are ordered. Each part has m operations done at the first stage with m different machines. After manufacturing the parts, they are assembled into a final product with some non-identical machines. The purpose of the problem is to find the optimal sequence of the parts in the manufacturing stage, allocation and the optimal sequence of the products in the assembly stage. A mixed integer linear programming model and two metaheuristic algorithms, which are particle swarm with local search (MPSO) and simulated annealing (SA), are presented to solve this problem. Computational experiments are conducted to evaluate the performance of the proposed model and algorithms. The results show that the MPSO algorithm performs better than the SA one.
M. H. Bayati Chaleshtari, M. Jafari,
Volume 37, Issue 1 (9-2018)
Abstract
This paper aims at optimizing the finite isotropic plates with the hexagonal cutout subjected to plane loading using metaheuristic optimization algorithms. This research uses Differential Evolution Algorithm (DE) and Harmony Search Algorithm (HSA) from the evolutionary algorithm category, Big Bang- Big Crunch Algorithm (BB-BC) from the physics-based algorithm category, and Grey Wolf Optimizer Algorithm (GWO) and Particle Swarm Optimization (PSO) from the SI algorithm category; then the results of these algorithms are compared with each other. The results indicate that the grey wolf optimizer has the complete performance, short solution time and the ability to avoid local optimums. In the analysis of finite isotropic plate, the effective parameters on stress distribution around the hexagonal cutouts are cutout bluntness, cutout orientation, plate’s aspect ratio, cutout size, and type of loading. In this study, with the assumption of plane stress conditions, the analytical solution of Muskhelishvili’s complex variable method and conformal mapping is utilized. The plate is considered to be finite (the proportion ratio of the diameter of circle circumscribing to the longest plate side should be more than 0.2), isotropic, and linearly elastic. The finite element method has been used to check the accuracy of the results. Numerical results are in a good agreement with those of the present analytical solution. The results show that by selecting the aforementioned parameters properly, less amounts of stress could achieve around the cutout can lead to an increase in the load-bearing capacity of the structure.
H. Tanzadeh, H. Amoushahi,
Volume 37, Issue 1 (9-2018)
Abstract
A semi-analytical finite strip method was developed for the buckling analysis of laminated composite plates based on zigzag and third order shear deformation theories. The displacement functions of the plates were evaluated using a continuous harmonic function series in the longitudinal direction that satisfied the simply supported boundary conditions and a piecewise interpolation polynomial in the transverse direction. By considering the displacement-strain relations and strain-stress relations, the standard and geometric matrices were evaluated using the virtual work principle. The numerical results related to the buckling of single-layer and multi-layer plates were presented based on two different plate theories. The effects of different boundary conditions, length to thickness ratio, fiber orientation and modulus of elasticity were also investigated through numerical examples.
M. Bagheri, B. Keshtegar,
Volume 37, Issue 1 (9-2018)
Abstract
In this paper, a new method is proposed for fuzzy structural reliability analysis; it considers epistemic uncertainty arising from the statistical ambiguity of random variables. The proposed method, namely, fuzzy dynamic-directional stability transformation method, includes two iterative loops. An internal algorithm performs the reliability analysis using the dynamic-directional stability transformation method and an external algorithm performs the fuzzy analysis by applying the alpha-cut level optimization method based on the genetic algorithm. Implementation of the proposed method, which solves some nonlinear performance functions, indicates the efficiency and robustness of the dynamic-directional stability transformation method, as compared to other first order reliability methods.
S. Esmizade, H. Haftbaradaran, F. Mossaiby,
Volume 37, Issue 1 (9-2018)
Abstract
Experiments have frequently shown that phase separation in lithium-battery electrodes could lead to mechanical failure, poor cycling performance, and reduced capacity. Here, a phase-field model is utilized to investigate how phase separation affects the evolution of the concentration and stress profiles within the spherical/cylindrical electrode particles, during both insertion and extraction half-cycles. To this end, the governing equations are derived and then discretized using the central finite difference method. The resulting algebraic equations are solved numerically with the aid of the Newton-Raphson method to determine both the concentration and stress fields in the electrode particles. For further verification, the results are compared against predictions of an analytical core-shell model. The results suggest that, within the range of parameters considered here, phase separation could lead to a more than five-fold increase in the maximum tensile stress at the particles surface.
F. Shirmohammadi, M. M. Saadatpour,
Volume 37, Issue 1 (9-2018)
Abstract
In this article spectral modal method is developed for studying wave propagation in thin plates with constant or variable thickness. Theses plates are subjected to the impact forces and different boundary conditions. Spectral modal method can be considered as the combination of Dynamic Stiffness Method (DSM), Fourier Analysis Method (FAM) and Finite Stripe Method (FSM). Using modeling of continuous distribution of mass and an exact stiffness causes solutions in frequency domain. Unlike the most numerical methods, in this method refining meshes is no longer necessary in which the cost and computational time is decreased. In this paper the important parameters of the method and their effects on results are studied through different examples.
S. M. Zandi, A. Rafizadeh,
Volume 37, Issue 1 (9-2018)
Abstract
In this article, a meshless method based on exponential basis functions (EBFs) is presented to simulate the harmonic waves with moving free-surfaces generated by the piston-type wave maker. Accordingly, velocity potential is adopted in a Mixed Eulerian-Lagrangian (MEL) approach. Boundary conditions are met through a point-wise collocation approach. In order to update the geometry in the simulation time, the free surface points are only moved vertically. To reduce the reflection in the wave flume, a damping zone is added at the far end opposite to the wave maker, where the velocity is modified by adding an artificial damping term. The results indicated the ability of this numerical method in simulating free surface flow problems like non-linear waves with a good accuracy, as well as suitable performances and the least run time calculation.
F. Taheri-Behrooz, H. Khayyam Rayeni,
Volume 37, Issue 2 (3-2019)
Abstract
In this paper A progressive damage model based on multi-scale modeling has been developed to predict the initiation and propagation of damage in plain weave fabrics. For this purpose, microscopic damage in yarns and resin is calculated by an RVE (Representative Volume Element) FE simulation. By applying suitable boundary conditions of RVE, macro-scale average stresses were derived to extract the components of the equivalent stiffness matrix. Finally, by developing UMAT and USDFLD subroutines in the ABAQUS commercial software, the strength of the woven composite rings is predicted numerically. In order to confirm the numerical predictions, composite rings using the woven glass tapes of 5 cm width and epoxy resin are fabricated according to ASTM D2290 and tested. A good correlation between experimental and numerical results could confirm the accuracy of the finite element simulation.
M. Khashei, Sh. Torbat,
Volume 37, Issue 2 (3-2019)
Abstract
Financial crises in banking systems are due to inability to manage credit risks. Credit scoring is one of the risk management techniques that analyze the borrower's risk. In this paper, using the advantages of computational intelligence as well as soft computing methods, a new hybrid approach is proposed in order to improve credit risk management. In the proposed method, for modeling in uncertainty conditions, parameters of the neural network, including weights and errors, are considered in the form of fuzzy numbers. In this method, the underlying system is firstly modeled using neural networks and then, using fuzzy inferences, the optimal decision will be determined with the highest degree of superiority. Empirical results of using the proposed method indicate the efficiency and high accuracy of this method in analyzing credit rating problems.
S. M. Seyed Sharafy, S. Hatami,
Volume 37, Issue 2 (3-2019)
Abstract
Diagonal Strap bracing is one of the most applicable lateral bracing systems in light steel framing (LSF). In practice, one or more panels of Gypsum Wall Boards (GWBs) is used for the cladding of strap braced frames. Usually, the effect of these GWBs in modelling and design is neglected by designers, but this effect can affect the seismic performance of the system In this paper, firstly, a simple numerical method is developed to model the monotonic and cyclic behavior of cold-formed strap braced shear walls together with GWBs. Then, the effects of GWB on the lateral characteristics and seismic performance levels of shear walls are evaluated. It is found that neglecting GWB in the lateral design or modeling of LSF is not rational and GWB can increase the dissipation of earthquake energy, lateral strength and stiffness of the walls. Also, the shear wall composed of strap bracing and SWBs reaches a certain performance level in a less drift ratio in comparison to to only strap braced system
M. Jafari, M. Jamshidian, S. Ziaei-Rad,
Volume 37, Issue 2 (3-2019)
Abstract
The stored deformation energy in the dislocation structures in a polycrystalline metal can provide a sufficient driving force to move grain boundaries during annealing. In this paper, a thermodynamically-consistent three-dimensional, finite-strain and dislocation density-based crystal viscoplasticity constitutive theory has been developed to describe the distribution of stored energy and dislocation density in a polycrystalline metal. The developed constitutive equations have been numerically implemented into the Abaqus finite element package via writing a user material subroutine. The simulations have been performed using both the simple Taylor model and the full micromechanical finite element model. The theory and its numerical implementation are then verified using the available data in literature regarding the physical experiments of the single crystal aluminum. As an application of the developed constitutive model, the relationship between the stored energy and the strain induced grain boundary migration in aluminum polycrystals has been investigated by the Taylor model and also, the full finite element model. The obtained numerical results indicated that the Taylor model could not precisely simulate the distribution of the stored deformation energy within the polycrystalline microstructure; consequently, the strain induced grain boundary migration. This is due to the fact that the strain induced grain boundary migration in a plastically deformed polycrystalline microstructure is principally dependent on the spatial distribution of the stored deformation energy rather than the overall stored energy value.
