• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.8
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• pp.340-348
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• 2003

In this paper, we propose a novel formulation to solve a time-domain combined field integral equation (CFIE) for analyzing the transient electromagnetic scattering response from closed conducting bodies. Instead of the conventional marching-on in time (MOT) technique, tile solution method in this paper is based on the moment method that involves separate spatial and temporal testing procedures. Triangular patch vector functions are used for spatial expansion and testing functions for three-dimensional arbitrarily shaped closed structures. The time-domain unknown coefficient is approximated as a basis function set that is derived from tile Laguerre functions with exponentially decaying functions. These basis functions are also used as the temporal testing. Numerical results computed by the proposed method arc stable without late-time oscillations and agree well with the frequency-domain CFIE solutions.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.10
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• pp.1096-1103
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• 2003

In this paper, we analyze the transient electromagnetic response from three-dimensional(3-D) dielectric bodies using a time-domain PMCHW(Poggio, Miller, Chang, Harrington, Wu) formulation. The solution method in this paper is based on the Galerkin's method that involves separate spatial and temporal testing procedures. Triangular patch basis functions are used for spatial expansion and testing functions for arbitrarily shaped 3-D dielectric structures. The time-domain unknown coefficients of the equivalent currents are approximated by a set of orthonormal basis functions that are derived from the Laguerre polynomials. These basis functions are also used as the temporal testing. Numerical results involving equivalent currents and far fields computed by the proposed method are presented.

• Computational Structural Engineering
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• v.6 no.2
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• pp.103-114
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• 1993

An advanced time-domain finite element formulation is presented for the displacement and stress analysis of isotropic, linear viscoelastic problems of a hereditary-type constitutive law. The semidiscrete finite element method with linear time-stepping scheme and an elastic-viscoelastic correspondence principle are used in the theoretical development. An efficient treatment of hereditary integral is introduced to improve the numerical accuracy, to reduce the computation time, and to avoid the use of large memory storage. Two-dimensional numerical examples of plane strain and plane stress are solved under the assumption on the material property of being elastic in dilatation and like three-element Voigt model in distorsion, and compared with the analytical solutions and the past numerical results to show the versatility and efficiency of the proposed method.

• Journal for History of Mathematics
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• v.18 no.2
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• pp.31-42
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• 2005

Renaissance is revival of the ancient Greek and Roman cultures. So, in Renaissance period, the artists began to study Euclidean geometry and then their mind was a spirit of experience and observation. These spirits is namely modernism. In other words, Renaissance was a dawn of modern times. In this paper, we notice modern spirits and ones social backgrounds. Differential and integral calculus was created by these modern spirits. And in art field, 'painter of light', 'artist of moment' appeared. Because in the 17th and 18th centuries, the intelligentsia researched for motions, speeds and lights.

• Journal of Ocean Engineering and Technology
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• v.4 no.1
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• pp.62-70
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• 1990

Cauchy의 적분공식을 복소속도(complex velocity)에 적용하여 포텐시얼 유동을 해석하는 복소경계요소법이 개발되었다. 이 결과로 얻어지는 적분방정식은 경계면에서의 접선속도(tangential velocity)와 법선속도(normal velocity)의 함수로 주어진다. 자유수면에서의 접선속도의 시간변화(evolution of tangential velocity)를 수식화하기 위하여 새로운 비선형 동역학적 자유수면경계조건(nonlinear dynamic free surface boundary condition)을 유도하였다. 복소포텐시얼 대신 복소속도를 이용하는 이 방법은 유장내의 특이점(field singularity)을 용이하게 고려할 수 있으며, 수치미분없이 직접 경계면에서의 유속을 해로서 구하게 된다. 그러나 자유수면이 존재하는 문제의 경우에는, 자유수면에서의 동역학적 경계조건을 만족 시키기 위한 계산과정에 접선 벡타의 변화량을 추정하는 것이 포함되게 되어, 계산과정이 다소 복잡하게 된다.

• Journal of the korean Society of Automotive Engineers
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• v.13 no.5
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• pp.73-80
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• 1991

Air/fuel ratio control system for gasoline engines has been analyzed to determine the control gain of the system. In this analysis the engine is modelled to be a simple time delaying element and the ramp-and-jump method is used to control air/fuel ratio. The result shows that it is necessary to measure the air flow rate accurately to enhance the control performance. And also it is shown that the control gain must be determined in some bounded region to meet the fast dynamic response and high catalyst conversion efficiency together.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.41 no.6
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• pp.11-16
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• 2004

The integral term of PID controller have the advantage of reduced steady state error and the disadvantage of accumulated errors. We proposed a method that maintains its advantage and improvs the disadvantage in transient response. The proposed PID control method with modified integral parameter accumulates errors in increment section and ignores errors in decrement section. Therefore, the proposed PID control method decreases overshoot, and makes settling time faster than conventional PID control method.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.248-248
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• 2022

Hwang(2015)은 불연속 지형을 지나는 천수 흐름의 수치 해석에서 불연속 전면에 의한 추력(thrust)에 주목하여 그 영향을 흐름률(flux) 계산에 반영하는 새로운 기법을 제시하였다. 이 기법 덕분에 수심 적분 모형으로도 계단이나 보와 같이 직립한 하천 구조물의 불연속면을 경사로 완화하지 않고 직접 모의할 수 있다. 직립 측면 위어 실험에 Hwang(2015)의 기법이 적용됨으로써 연직면을 경사면으로 완화하여야 하는 기존의 수심 적분 모형에 비해 계산 격자 개수가 53%로 줄었다(Hwang, 2019). Hwang(2019)은 기존 모형과 비교를 통해, 정확도를 어느 정도 유지하면서도, 소요된 계산 시간이 20%에 불과하다고 주장하였다. 여기에서는 보다 다양한 직립 광정 위어 실험에 적용하여 수심 적분 모형에 의한 월류량을 검토하고자 한다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.2
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• pp.247-258
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• 2004

The composite shell element is developed for the solution of undamped forced vibration problem of composite curved panels. The finite element used in the current study is an 4-node enhanced assumed shell element with six degrees of freedom per node. The composite shell element is free of both shear and membrane locking phenomenon by using the enhanced assumed strain(EAS) method. A modification to the first-order shear deformation shell theory is proposed, which results in parabolic thorough-thickness distribution of the transverse shear strains and stresses. It eliminates the need for shear correction factors in the first order theory. Newmark's direct integration technique is used for carrying out the integration of the equation motion, to obtain the repones history. Parametric studies of curved composite panels are carried out for forced vibration analysis by geometrical shapes and by laminated composite; such as fiber orientation, stacking sequence.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.39 no.1
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• pp.27-32
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• 2003

Under the assumption of potential flow, free-surface flow around a hydrofoil is calculated by the high-order spectra1!boundary-integral method, This method is one of the most efficient numerical methods by which the nonlinear interactions between hydrofoil and free-surface can be simulated in time-domain. In this method. the wave potential which represents the nonlinear evolution of free-surface is solved by the high-order spectral method and the body potential which provides the effects of hydrofoil and shed vortex is solved by the boundary-integral method. The calculated free-surface profiles which are generated by a uniformly translating hydrofoil are compared with other experimental results. And they show relatively good agreements each other. As another example, free-surface flow generated by a heaving and translating hydrofoil is calculated and discussed.