JOURNAL OF COMPUTATIONAL METHODS IN ENGINEERING (ESTEGHLAL)
Year:2013 | Volume:31 | Issue:2|Papers Count:11

Silos are structures used for storing different types of granular materials. Seismic behavior of reinforced concrete silos is very complex due to nonlinearity of reinforced concrete wall of silo and nonlinear behavior of granular material. In this paper, the effect of granular material-structure interaction is investigated for a reinforced concrete silo by using ABAQUS finite element package. A hypoplastic constitutive model is used for modeling the granular material. After modeling the granular material-structure interaction under seismic excitation, the results obtained are compared with those of models without granular material-structure interaction.

Hot–dip galvanizing process is simulated numerically. Over-thickness near the strip edge called edge over-coating in continuous hot-dip galvanizing process is a universal problem. Numerical results of using a cylindrical device installed at jet exit are presented to prevent over-thickness near the strip edges. This device prevents jets from colliding with each other in the region outside the strip and reduces flow oscillations. In addition to numerical investigation, cylindrical device is tested experimentally in Mobarakeh Steel Complex. Numerical and experimental results show that the installed device is very effective in reducing over-thickness near the strip edge, but cannot completely solve the problem.

In a strong earthquake, a standard reinforced concrete column may develop plastic deformations in regions often termed as plastic hinge regions. A plastic hinge is basically a damping device that dissipates energy through the plastic rotation of a rigid column connection, thus triggering the redistribution of bending moments. The formation of a plastic hinge in an RC column in the regions that experience inelastic actions depends on the characteristics of the earthquakes as well as the column details. In this paper, 462 inelastic time-history analyses have been performed to predict the nonlinear behavior of RC columns under the ground motions. The effects of axial load, height-to-depth ratio and amount of longitudinal reinforcement, as well as different characteristics of earthquakes are evaluated analytically by finite element methods and the results are compared with the corresponding experimental data. Analytical models for the columns analysed under high axial loads exhibit longer plastic hinges than those analysed under low axial loads. Based on the results, a simple expression is proposed to estimate plastic hinge length of RC columns subjected to earthquakes.

In this research, a simple and efficient algorithm is presented to accomplish nonlinear analysis for reinforced concrete (RC) beams using fiber method concepts. Nonlinear matrix analysis method based on the assessment of stresses with failure surface is utilized. In modeling the members, macro elements are used. Failure surfaces are established on different behaviors in compression and tension for concrete and elastic-perfect-plastic behavior for steel bars. To verify the accuracy of this algorithm, the experimental and ANSYS results are compared with those obtained by the proposed algorithm. Remarkable compatibility with diversity less than 6%, in the most critical situation, is gained between numerical predictions and experimental datas, demonstrating the reliability of the proposed algorithm.

Modeling free surface flow is a challenging problem in hydraulic research. The objective of this research is to compare those methods for simulation of flow around hydraulic structures. Accordingly, Incompressible SPH (ISPH) methods, with two different projection methods to enforce incompressibility, are utilized to model flow under a gate and then compared to each other from mathematical and numerical viewpoints. Moreover, the effect of pressure term approximation on conservation equation of mass and momentum with two different relations is investigated by error index. For verification of ISPH results, VOF method is applied to similar gate problem. Results show that two methods of enforcing incompressibility are numerically and mathematically equivalent if proper approximation terms are used in SPH method. Furthermore, VOF and ISPH results are in excellent agreement. Besides, two pressure terms obey similar chaotic error trend for inner and all particles (inner plus free surface).

In this numerical study, flow field, heat transfer and nanoparticles transport in Al2O3-water nanofluid natural convection in a square cavity are investigated. The governing equations are discretized using the control volume method.Transport mechanisms including Brownian diffusion and thermophoresis that cause heterogeneity are considered in nanoparticles transport model. It is shown that a better agreement with experimental results is achieved considering the transport model compared to the homogeneous model with equivalent properties. Transport mechanisms of nanoparticles affect buoyancy force and reduce heat transfer and cause formation of a small vortex near the top and bottom walls of the cavity.

In this paper, a technique for fabrication of nanocomposite Al6061-Al2O3 is presented. Next, the mechanical properties of the nanocomposite are obtained by experimental and simulation techniques. The volume of alumina is 0-3% in nanocomposite. Since the yield and hardness of nanocomposite are grain dependence, the Hall-Petch relation is used. Different unit cell methods are utilized to simulate the stress-strain diagram of the nanostructured aluminum and nanocomposite Al6061-Al2O3 in simple tension test. To do the modeling, a unit load is applied on the unit cell and the stress and strain in all nodes are homogenized to derive the stress-strain curve of the whole cell. A good degree of correlation is observed between experimental and predicted data. The results also indicate that the use of unit cell and embedded unit cell for modeling nanocomposites is both simple and powerful.

In this research, layup sequence of composite laminates was optimized by using the response surface method and Genetic Algorithms (GA) in order to increase their buckling capacity. In order to define the buckling function of composite cylinder by using response surface method, several finite element models were run, and by using least square method, two functions, namely, first and second order polynomial functions were obtained. A genetic algorithm was employed to optimize buckling capacity of the composite cylinder by changing layup sequence of the laminates. Finally, after optimization by GA, MATLAB software was employed to obtain buckling capacity of the optimum layup. In addition, in order to confirm the accuracy of the developed optimization method in this research, buckling capacity of a rectangular composite plate was obtained by the present method and was compared with the results of the other researchers.