JOURNAL OF COMPUTATIONAL METHODS IN ENGINEERING (ESTEGHLAL)
Year:2014 | Volume:32 | Issue:2|Papers Count:10

The pressurization step of a PSA process has been simulated using the lattice-Boltzmann method. The entropic D3Q27 lattice model for the multi-component oxygen-nitrogen combination of air streaming through a packed bed is proposed and a new boundary condition of oxygen and nitrogen adsorption was applied on the granules surface. The Boltzmann method satisfies both the Navier-Stokes equations and the Stefan-Maxwell diffusion equations. In order to evaluate the adsorption rate, the LDF model with the Langmuier multi-component isotherm were used. To verify the correctness of the presented model, the adsorption rate of each component has been compared with those obtained using the Langmuier isotherm model for single and multi-component test cases. Results confirmed the accuracy of the proposed model.

In this paper, a numerical model for simulation of free surface fluid flows is presented. This method is a combination of smart genetic algorithm and free surface fluid flow tracking algorithm based on donor and acceptor elements. The specification of the new combinational method can be summarized in determining orientation vector and plane constant passing through free surface cells. The proposed algorithm can be easily used in non-uniform grids. This numerical model has been applied to simulate some of benchmark flow problems and also compared with the experimental data and other researchers' results. The comparisons indicated that the described numerical model is able to make accurate predictions, and is also simple to apply for many fluid flow problems.

In this article, an exact finite strip method is developed for free vibration of rectangular thin functionally graded plates subjected to in-plan forces. First, a reference surface, instead of mid-plane of the plate, is used to extract the equation of motion based on classical plate theory so that there is no coupling between in-plane and out-of-plane equations of functionally graded plates. Then, an exact finite strip method is developed for the uncoupled differential equation of motion by keeping two parallel edges of the plate as simply supported. In the method, the multi-span plate is divided into a small number of strips. The shape function of each strip is sinusoidal in the direction perpendicular to the simple edges; and in the other direction, the shape function is the analytical solution of the differential equation governing free vibration of the functionally graded plate. Thus, the elements of exact stiffness matrix for any finite strip are a function of natural frequencies, in-plane forces, and material and geometry properties of the plate. As the standard eigenvalue algorithms cannot solve the free vibration problem, an efficient algorithm is developed to extract the natural frequencies from determinant of the stiffness matrix.Comparison studies are performed to verify the validity of the present results. Also, some examples are presented in an attempt to illustrate the ability of the exact finite strip method to solve various problems with different parameters such as boundary conditions, internal supports, in-plane forces, aspect ratio, and power of volume fraction. As expected, the natural frequency increases when the stiffness of supports and in-plane forces increase. The exact vibration solutions obtained for such plates can serve as important benchmark solutions for checking the accuracy of numerical methods for the analysis of FG plates. But, the classical plate theory used in this study is valid for thin plates; thus in comparison to shear deformation plate theories, the accuracy of results decreases when the plate thickness increases.

Operational modal analysis can be used as a useful method for modal identification of rotating machinery. Response of a rotary machine contains several powerful harmonic components which make the OMA methods face several problems. In this paper, kurtosis index is used for detection of response harmonic components. Then, CFDD method is modified for removing the harmonic effects and extracting the modal parameters. Accuracy, applicability and computational efficiency of the proposed method are evaluated through computer simulation of a 4DOF system, an operational modal analysis experiment on a steel beam, and operational modal analysis of a large industrial fan in Mobarakeh Steel Complex.

This paper studies the vibration characteristics of a cracked rotating tapered cantilever Euler–Bernoulli beam with linearly varying transverse cross-section using Differential Transform Method (DTM). The effects of the crack location, crack size, rotating speed and hub radius in calculating the natural frequencies and mode shapes of cracked tapered beam by using this method are investigated. Numerical results for a beam with and without crack with variable cross-section are obtained and compared with other methods. It is seen that the accuracy of the differential transform method for the vibration analysis of the beams with variable cross-section is higher than other methods, especially for the case of high rotational speed.

In this paper, different amplification patterns of 2-D semi-sine shaped valleys and their surroundings subjected to vertically propagating incident out-of-plane SH waves are presented. The half-plane time-domain BEM approach proposed by the authors was used to obtain the results. Compared to the previous studies on boundary elements, avoiding a wide range of ground surface meshing and focusing the elements only on the valley surface were the obvious distinctions of the present study. In this regard, effects of key parameters such as shape ratio of the valley and wavelength of incident waves were considered. Evaluation of the results indicated significant influence of the mentioned parameters on the valley surface behavior. Also, the amplification potential of semi-sine shaped valley under vertically out-of-plane SH wave had a higher amplitude than in-plane SV wave. The obtained results can be used for seismic micro-zonation discussion in order to correct and complete the existing studies.

Several earthquake experiences in the world have displayed that the amount of damage of structures with similar characteristics for a certain earthquake is strongly influenced by site conditions called site effects. These effects can cause nonuniform stimulation to crucial structures which are made on these sites. In this research, a three-dimensional boundary element method, which is one of the most powerful numerical techniques for analyzing problems, was used. This method is important especially for the issues related to the wave propagation, and for the investigation of displacement spectrum in different parts of canyon under different parameters (angles and materials). The results of this paper indicated that the displacement spectrum for a canyon site depended on soil type and wave incident angle, and could have various values in different parts of the same site. Therefore, these effects must be considered in designing important structures such as dams.

In the pressent study, the effect of the solid-state phase transformation on the evolution of residual stresses in circumferentially butt-welded medium carbon steel pipes is survied using an effective algorithme. For this purpose a thermoelastic- plastic analysis coupled with metallurgical analysis using finite element method is implemented. Welding process is simulated in 2-D and 3-D using two subroutines: one for applying heat flux and the other to consider the effect of phase transformation due to austenite-martensite transformation. The simulation results show that austenite-martensite transformation has significant effects on magnitude and distribution of residual stresses, and in some cases, it changes its nature from tensile to compressive stresses.

Reinforced concrete (RC) beams strengthened in flexure with a bonded fiber-reinforced polymer (FRP) plate may fail by debonding mechanism, in which the FRP plate is detached from the beam surface in lower levels of ultimate strain of FRP. This paper presents a new method based on the smeard crack approach for finite element simulation of debonding process. For this purpose, first the problems involved in numerical simulation of debonding were investigated. Then, a technique based on cohesive elements implied in the software was used. To evaluate the proposed technique, 4 experimental RC beams strengthened with FRP plates were modeled. The results showed that the predicted ultimate loads and the whole behavior of the beams under the loads were in very good agreement with experimental data.

A novel method is presented for hydraulic analysis of water distribution networks. In this method, each non-linear term in energy equations is estimated with a linear counterpart. Thereby, the system of linear-nonlinear equations is converted into a system of linear-linear equations and resolved. The solution is an appropriate estimation for the next iteration stage where the nonlinear terms are linearized in a smaller interval near it. The successive iterations are continued to a desirable precision. Comparing the multistage linearization algorithm with the Newton-Raphson, secant and global gradient methods in several examples confirms its less computational operation and faster convergence time.