• Structural Engineering and Mechanics
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• v.52 no.6
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• pp.1099-1120
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• 2014

In this paper, reliability-based design optimization (RBDO) of structures is addressed. For this purpose, the global search and optimization capabilities of genetic algorithm (GA) are combined with the efficiency and reasonable accuracy of an advanced moment-based finite element reliability method. For performing RBDO, three variants of GA including a real-coded, a binary-coded and an improved binary-coded GA are developed. In these methods, GA performs (finite element) reliability analyses to evaluate reliability constraints. For truss structures which include finite element modeling, reliability constraints are evaluated using finite element reliability analysis. Response sensitivity required for finite element reliability analysis is obtained by direct differentiation method (DDM) rather than finite difference method (FDM). The proposed methods are examined within four standard test examples and real-world design problems. The results illustrate the superiority and efficiency of the improved binary-coded GA. Results also illustrate that DDM significantly reduces the computational cost and improves the efficiency of the optimization procedure.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.12 s.255
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• pp.1518-1525
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• 2006

Finite element analyses of structures made of the fiber reinforced composites require an adequate method to characterize the high anisotropic behavior induced by one or several layers of fiber cords with different spatial orientation embedded in a rubber matrix. This paper newly proposes a continuum based rebar element considering change of the orientation of the fiber during deformation of the composite. The mechanical behavior of the embedded fiber is modeled using two-node bar elements in order to consider the relative deformation and spatial orientation of the embedded fiber. For improvement of the analysis accuracy, the load-displacement curve of fiber is applied to the stiffness matrix of fiber. A finite element program is constructed based on the total Lagrangian formulation considering both geometric and material nonlinearity. Finite element analyses of the tensile test are carried out in order to evaluate the validity of the proposed method. Analysis results obtained with the proposed method provides realistic representation of the fiber reinforced rubber composite compared to results of other two models by the Halpin-Tsai equation and a rebar element in ABAQUS/Standard.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.1
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• pp.1-10
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• 2004

Adaptive finite element analysis, in which its solution error meets with the user defined allowable error, is recently used to improve the reliability of finite element analysis results. This adaptive analysis is composed of two procedures; one is the error estimation of an analysis result and the other is the reconstruction of finite elements. In the (p-method, an element size is controlled by relocating of nodal positions (r-method) and the order of an element shape function is determined by the hierarchical polynomial (p-method) corresponding to the clement solution error by the enhanced SPR. In order to show the effectiveness and the accuracy of the suggested rp-method, various numerical examples were analyzed and these analysis results were examined by comparing with those obtained by the existed methods.

• Journal of Mechanical Science and Technology
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• v.17 no.5
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• pp.679-690
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• 2003

As the rate of increase in areal density of the HDD has accelerated, dynamic characteristics of the HDD actuator need to be improved with respect to the performance of the tracking servo and shock transmission. Therefore, it is important to analyze the vibration characteristic of the HDD actuator that consists of the VCM part, E-block and pivot bearing. In this paper, vibration modes of the HDD actuator are investigated the using finite element and experimental modal analyses methods. To develop a detailed finite element model, finite element models of each components of the actuator assembly are constructed and tuned to the results of the EMA. The VCM coil is modeled as an equivalent finite element model that has an orthotropic material property using auto-model updating program. Auto-model updating program with improved sensitivity based iterative method is applied to build a detailed finite element model using the result of the EMA. A detailed finite element model of the HDD actuator is then constructed and analyzed.

• Structural Engineering and Mechanics
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• v.27 no.3
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• pp.311-331
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• 2007

The purpose of this paper is to study shear locking-free analysis of thick plates using Mindlin's theory and to determine the effects of the thickness/span ratio, the aspect ratio and the boundary conditions on the linear responses of thick plates subjected to uniformly distributed loads. Finite element formulation of the equations of the thick plate theory is derived by using higher order displacement shape functions. A computer program using finite element method is coded in C++ to analyze the plates clamped or simply supported along all four edges. In the analysis, 8- and 17-noded quadrilateral finite elements are used. Graphs and tables are presented that should help engineers in the design of thick plates. It is concluded that 17-noded finite element converges to exact results much faster than 8-noded finite element, and that it is better to use 17-noded finite element for shear-locking free analysis of plates. It is also concluded, in general, that the maximum displacement and bending moment increase with increasing aspect ratio, and that the results obtained in this study are better than the results given in the literature.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.6
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• pp.693-702
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• 2010

In this paper, FETI(Finite Element Tearing and Interconnecting) method is introduced in order to improve numerical efficiency of Staggered method. The porous media theory, the Staggered method and the FETI method are briefly introduced in this paper. In addition, we account for the MPI(Message Passing Interface) library for parallel analysis, and the proposed combined Staggered method with FETI method. Finally Lagrange multipliers and CG(Conjugate Gradient) algorithm to solve decomposed domain are proposed, and then the proposed method is verified to be numerically efficient by MPI library.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.859-865
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• 2007

This paper presents a method to analyze the unbalance response of a high speed polygon mirror scanner motor supported by sintered bearing and flexible supporting structures by using the finite element method and the mode superposition method. The appropriate finite element equations for polygon mirror are described by rotating annular sector element using Kirchhoff plate theory and von Karman non-linear strain, and its rigid body motion is also considered. The rotating components except for the polygon mirror are modeled by Timoshenko beam element including the gyroscopic effect. The flexible supporting structures are modeled by using a 4-node tetrahedron element and 4-node shell element with rotational degrees of freedom. Finite element equations of each component of the polygon mirror scanner motor and the flexible supporting structures are consistently derived by satisfying the geometric compatibility in the internal boundary between each component. The rigid link constraints are also imposed at the interface area between sleeve and sintered bearing to describe the physical motion at this interface. A global matrix equation obtained by assembling the finite element equations of each substructure is transformed to a state-space matrix-vector equation, and both damped natural frequencies and modal damping ratios are calculated by solving the associated eigenvalue problem by using the restarted Arnoldi iteration method. Unbalance responses in time and frequency domain are performed by superposing the eigenvalues and eigenvectors from the free vibration analysis. The validity of the proposed method is verified by comparing the simulated unbalance response with the experimental results. This research also shows that the flexibility of supporting structures plays an important role in determining the unbalance response of the polygon mirror scanner motor.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.2
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• pp.84-88
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• 2012

A numerical skill for effective treatment of inclined boundaries in a finite element method is introduced. A finite element method has been frequently used to simulate hydraulic phenomena in a coastal zone since it can be applied to irregular and complex geometry. In case elliptic partial equations are governing equations for a finite element model, however, there is a difficulty in treating boundary conditions properly for cases in which boundaries are vertically inclined. In this study, a method to treat such inclined boundaries using Bessel functions for a finite element method is introduced and compared with analytical solutions.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.1
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• pp.9-13
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• 2009

A simple outline for teaching adaptive scheme based finite element method for planar problems as a part of computer aided teaching of structural engineering curriculum is presented. Displacement based finite element formulation for planar problems and representative strain value based adaptive scheme for mesh generation are considered. As examples, a cantilever beam with a concentrated load treated as a planar problem and stretching of a plate with a circular hole are analyzed with displacement based finite element method with adaptive meshes. The examples and outlines show how adaptive based finite element method may become an essential part of computer aided teaching of structural engineering.

• Structural Engineering and Mechanics
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• v.86 no.3
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• pp.349-359
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• 2023

This paper presents a technique for determining the optimal number of elements in stochastic finite element analysis based on reliability analysis. Using the change-of-variable perturbation stochastic finite element approach, the probability density function of the dynamic responses of stochastic structures is explicitly determined. This method combines the perturbation stochastic finite element method with the change-of-variable technique into a united model. To further examine the relationships between the random fields, discretization of the random field parameters, such as the variance function and the scale of fluctuation, is also performed. Accordingly, the reliability index is calculated based on the explicit probability density function of responses with Gaussian or non-Gaussian random fields in any number of elements corresponding to the random field discretization. The numerical examples illustrate the effectiveness of the proposed method for a one-dimensional cantilever reinforced concrete column and a two-dimensional steel plate shear wall. The benefit of this method is that the probability density function of responses can be obtained explicitly without the use simulation techniques. Any type of random variable with any statistical distribution can be incorporated into the calculations, regardless of the restrictions imposed by the type of statistical distribution of random variables. Consequently, this method can be utilized as a suitable guideline for the efficient implementation of stochastic finite element analysis of structures, regardless of the statistical distribution of random variables.