JOURNAL OF COMPUTATIONAL METHODS IN ENGINEERING (ESTEGHLAL)
Year:2018 | Volume:37 | Issue:1 |Papers Count:9

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.

In this paper, a high-order finite element discretization and its newly developed fictitious domain approach, the 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.

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.

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.

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.

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.

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.

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 dynamicdirectional 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.