• Structural Engineering and Mechanics
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• v.32 no.5
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• pp.667-683
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• 2009

FE model-based dynamic analysis has been widely used to predict the dynamic characteristics of civil structures. In a physical point of view, an FE model is unavoidably different from the actual structure as being formulated based on extremely idealized engineering drawings and design data. The conventional model updating methods such as direct method and sensitivity-based parameter estimation are not flexible for model updating of complex and large structures. Thus, it is needed to develop a model updating method applicable to complex structures without restriction. The main objective of this paper is to present the model updating method based on the hybrid genetic algorithm (HGA) by combining the genetic algorithm as global optimization method and modified Nelder-Mead's Simplex method as local optimization method. This FE model updating method using HGA does not need the derivation of derivative function related to parameters and without application of complicated inverse analysis methods. In order to allow its application on diversified and complex structures, a commercial FEA tool is adopted to exploit previously developed element library and analysis algorithms. Moreover, an output-level objective function making use of measurement and analytical results is also presented to update simultaneously the stiffness and mass of the analysis model. The numerical examples demonstrated that the proposed method based on HGA is effective for the updating of the FE model of bridge structures.

• Radiation Oncology Journal
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• v.5 no.2
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• pp.165-168
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• 1987

The generalized Bathe method, proposed by Webb and Fox, which is a method of calculation of dose correction factor for the purpose of heterogeneous tissue, is complex even for a few kind of tissues. The method was modified for the purpose of getting a simple method that divide the multilayer of heterogeneous tissues into some groups of adjacent-tissue pairs. This new method could reduce the number of exponential terms and the time for calculating the dose correction factors by manual and computer calculation.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.4
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• pp.7-12
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• 2005

This study predicts the modified eigenvectors and eigenvalues of the damped structure due to the change in the mass, damping and stiffness of structure by calculation of the sensitivity coefficient using the original dynamic characteristic. The method is applied to examples of the damped 3 degree of freedom system by modifing the mass, damping and stiffness. The predicted dynamic characteristics are in good agreement with these from the structural reanalysis using the modified mass, damping and stiffness.

• 제어로봇시스템학회:학술대회논문집
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• 1994.10a
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• pp.243-246
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• 1994

In this paper, a self-learning fuzzy controller is designed with a fuzzy approximation of an inverse model. The aim of an identification is to find an input command which is control of a system output. It is intuitional and easy to use a classical adaptive inverse modeling method for the identification, but it is difficult and complex to implement it. This problem can be solved with a fuzzy approximation of an inverse modeling. The fuzzy logic effectively represents the complex phenomena of the real world. Also fuzzy system could be represented by the neural network that is useful for a learning structure. The rule of a fuzzy inverse model is modified by the gradient descent method. The goal is to be obtained that makes the design of fuzzy controller less complex, and then this self-learning fuzz controller can be used for nonlinear dynamic system. We have applied this scheme to a nonlinear Ball and Beam system.

• Journal of computational fluids engineering
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• v.2 no.2
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• pp.97-103
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• 1997

A modified Delaunay triangulation technique is tested for complicated computational domain. While a simple geometry. both in topology and geometry, has been well discretized into triangular elements, a complex geometry having difficulty in triangulation had to be divided into small sub-domains of simpler shape. The present study presents a modified Delaunay triangulation method based on the data structure of geometric modeller. This approach greatly enhances the reliability of triangulation, especially in complicated computational domain. We have shown that efficiency of Delaunay triangulation can be much improved by using both the GUI (Graphic User Interface) and OOP (Object-Oriented Programming).

• Computers and Concrete
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• v.1 no.4
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• pp.371-388
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• 2004

Our objective is to model static multi-cracking processes in concrete. The explicit dynamic relaxation (DR) method, which gives the solutions of non-linear static problems on the basis of the steady-state conditions of a critically damped explicit transient solution, is chosen to deal with the high geometric and material non-linearities stemming from such a complex fracture problem. One of the common difficulties of the DR method is its slow convergence rate when non-monotonic spectral response is involved. A modified concept that is distinct from the standard DR method is introduced to tackle this problem. The methodology is validated against the stable three point bending test on notched concrete beams of different sizes. The simulations accurately predict the experimental load-displacement curves. The size effect is caught naturally as a result of the calculation. Micro-cracking and non-uniform crack propagation across the fracture surface also come out directly from the 3D simulations.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.176-180
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• 2006

When the vibration troubles occur on the ship structure during the sea trial, the rectification work is very restricted because of in-situ limitation. Usually, the finite element method is used to improve vibration characteristics of the structure, but it takes lots of time and effort in modeling the structure and adjusting the finite element model in order to consider appropriate boundary conditions of a complex ship structure. Therefore, experimental methods have been in general suggested to obtain proper countermeasures without time-consuming in modeling. In this paper, FRE(frequency response function) synthesis method is applied to estimate natural frequency of the modified ship structure, which is obtained from experimental and numerical methods.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.421-424
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• 2004

Model updating is a very active research field, in which significant efforts has been invested in recent years. Model updating methodologies are invariably successful when used on noise-free simulated data, but tend to be unpredictable when presented with real experimental data that are-unavoidably-corrupted with uncorrelated noise content. In this paper, Reanalysis using frequency response functions for correlating and updating dynamic systems is presented. A transformation matrix is obtained from the relationship between the complex and the normal frequency response functions of a structure. The transformation matrix is employed to calculate the modified damping matrix of the system. The modified mass and stiffness matrices are identified from the normal frequency response functions by using the least squares method. Full scale pseudo dynamic pier test is employed to illustrate the applicability of the proposed method. The result indicate that the damping matrix of correlated finite element model can be identified accurately by the proposed method. In addition, the robustness of the new approach uniformly distributed measurement noise is also addressed.

• Wind and Structures
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• v.8 no.2
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• pp.89-106
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• 2005

For estimating the vortex excited vibrations of overhead transmission lines, the Energy Balance Principle (EBP) is well established for spans damped near the ends. Although it involves radical simplifications, the method is known to give useful estimates of the maximum vibration levels. For very long spans, there often is the need for a large number of in-span fittings, such as in-span Stockbridge dampers, aircraft warning spheres etc. This adds complexity to the problem and makes the energy balance principle in its original form unsuitable. In this paper, a modified version of EBP is described taking into account in-span damping and in particular also aircraft warning spheres. In the first step the complex transcendental eigenvalue problem is solved for the conductor with in-span fittings. With the thus determined complex eigenvalues and eigenfunctions a modified energy balance principle is then used for scaling the amplitudes of vibrations at each resonance frequency. Bending strains are then estimated at the critical points of the conductor. The approach has been used by the authors for studying the influence of in-span Stockbridge dampers and aircraft warning spheres; and for optimizing their positions in the span. The modeling of the aircraft warning sphere is also described in some detail.

• International Journal of Precision Engineering and Manufacturing
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• v.1 no.1
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• pp.133-145
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• 2000

Plastic molding designers are frequently faced with optimizing multiple defects in injection molded parts. these defects are usually in conflict with each other, and thus a tradeoff needs to be made reach a final compromised solution. In this study, an automated injection molding design methodology has been developed to optimize multiple defects of injection molded parts. Two features of the proposed methodology are as follows: one is to apply the utility theory to transform the original multiple objective optimization problem into single objective optimization problem with utility as objective function, the other is an implementation of a direct search-based injection molding optimization procedure with automated consideration of process variation. The modified complex method is used as a general optimization tool in this research. The developed methodology was applied to an actual molding design and the results showed that the methodology was useful through the CAE simulation using a commercial injection molding software package. Applied to production, this study will be of immense value to industry in reducing the product development time and enhancing the product quality.