• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.4
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• pp.661-669
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• 1999

이 논문은 탄성지반위에 놓인 원호형 곡선보의 자유진동에 관한 연구이다. 회전관성 및 전단변형을 고려하여 두 개의 매개변수로 표현되는 탄성지반위에 놓인 원호형 곡선보의 자유진동을 지배하는 미분방정식을 유도하고, 이를 수치적분기법과 시행착오적 행렬값탐사법이 결합된 수치해석기법으로 해석하였다. 회전-회전, 회전-고정 및 고정-고정의 단부조건을 갖는 곡선보의 최저차모드 3개의 고유진동수를 산출하였다. 곡선보의 수평높이 지간길이비, Winkler 지반계수, 전단지반계수에 따른 고유진동수 변화를 분석하였으며, 회전관성 및 전단변형의 영향을 고찰하였다.

• Journal of the Korean Society of Marine Environment & Safety
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• v.17 no.3
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• pp.295-300
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• 2011

Ship are a box-shaped structure. It is used often fore and aft parts, bilge strake, deck with camber of ship structures. When this structure is compared with flat plate structure, it different to behaviour. Generally, if it subjected to axial compressive load, ultimate strength depend on the change of curvature. Also, In this paper, stiffened curved plate with 1/2+1+1/2 bay model subjected to compressive load carried out the elasto-plastic large deflection series analysis. and parameter effect considered slender ratio, web height/thickness as well as change of curvature and investigated collapse mode for analysis model.

• Journal of Broadcast Engineering
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• v.16 no.3
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• pp.510-519
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• 2011

Intra mode decision is a useful coding tool in Distributed Video Coding (DVC) for improving DVC coding efficiency for video sequences having fast motion. A major limitation associated with the existing intra mode decision methods, however, is that its efficiency highly depends on user-specified thresholds or modeling parameters. This paper proposes an entropy-based method to address this problem. The probabilities of intra and Wyner?Ziv (WZ) modes are determined firstly by examining correlation of pixels in spatial and temporal directions. Based on these probabilities, entropy of the intra and the WZ modes are computed. A comparison based on the entropy values decides a coding mode between intra coding and WZ coding without relying on any user-specified thresholds or modeling parameters. Experimental results show its superior rate-distortion performance of improvements of PSNR up to 2 dB against a conventional Wyner?Ziv coding without intra mode decision. Furthermore, since the proposed method does not require any thresholds or modeling parameters from users, it is very attractive for real life applications.

• Journal of the Korean Institute of Intelligent Systems
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• v.14 no.6
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• pp.752-758
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• 2004

In this paper, we proposed an adaptivefuzzy sliding control algorithm using gradient descent method to reduce chattering phenomenon which is viewed in variable control system. In design of FLC, fuzzy control rules are obtained from expert's experience and intuition and it is very difficult to obtain them. We proposed an adaptive algorithm which is updated by consequence part parameter of control rules in order to reduce chattering phenomenon and simultaneously to satistfy the sliding mode condition. The proposed algorithm has the characteristics which are viewed in conventional VSC, e.g. insensitivity to a class of disturbance, parameter variations and uncertainties in the sliding mode. To demonstrate its performance, the proposed control algorithm is applied to an inverted pendulum system. The results show that both alleviation of chattering and performance are achieved.

• Computational Structural Engineering
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• v.11 no.4
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• pp.287-294
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• 1998

입면의 형태가 임의의 층에서 큰 차이를 보이는 3차원 비정형 setback 구조물의 동적 거동 특성과 이들 구조물의 동적 거동에 미치는 바닥 슬래브의 면내 변형 효과를 분석하였다. 비정형 setback 구조물의 전반적인 동적 거동특성을 분석하기 위하여 베이스 부분의 평면적과 타워 부분의 평면적 비(R?), setback 발생위치(L?)등을 매개 변수로 사용하였다. 48개의 비정형 setback 구조물들에 대한 해석 수행 결과 setback 구조물은 정형 구조물에 비해 횡방향 1차 모드의 유효 모드 중량(effective modal weight)이 작게 나타나는 경향을 보이기 때문에 setback 구조물의 동적 거동을 파악하기 위해서는 등가 정적 해석법 대신에 동적 해석을 수행할 필요가 있음을 알 수 있었다. 바닥슬래브의 면내 변형은 보다 긴 구조물의 고유 진동 주기값을 가져오며 모드 순서 및 모드 형상에도 변화를 준다. 이러한 사실은 바닥슬래브의 면내 변형으로 인하여 횡방향 저항 요소들간의 전단력 분포와 층 변위가 영향을 받을 수 있다는 것을 의미한다. 이러한 현상은 횡방향 저항 요소들간의 강성 차가 심한 프레임-전단벽 시스템에서 두드러지게 나타난다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.6
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• pp.659-666
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• 2015

In this paper, various influence factors on the impact-echo test which is an effective method in characterizing defects such as such as the delamination in the concrete structures were studied. The side to thickness ratio(a/h), the relative position of impacting and sensing points over the delamination that have great effects on the flexural and impact-echo(thickness) modes were investigated and examined by the parametric finite element analysis. As a result, the flexural modes dominate in the case of a/h > 2 and the thickness mode was more evident when a/h < 2. With regard to the relative position of impact source and sensing point to the defect, the flexural modes dominate even when either the loading or sensing point was over the delamination defect. However, the thickness mode prevails when both the impacting and sensing points are over the solid region beyond the delamination area.

• Journal of the Korean Society for Advanced Composite Structures
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• v.1 no.2
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• pp.36-43
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• 2010

In this study, the buckling loads and mode shapes characteristic of circular and non-circular(elliptical) closed composite shells were analyzed. To analyses the buckling behaviors, we develop and report an improved generalized shell element called 4EAS-FS through a combination of enhanced assumed strain and the substitute shear strain fields. A flat shell element has been developed by combining membrane element with drilling degree-of-freedom and a plate bending element. The combined influences of length, thicknesses, cross-sectional parameters, and fiber-angle on the critical buckling loads and mode shapes of circular and non-circular(elliptical) closed shells are examined.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.12
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• pp.202-211
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• 1998

The present paper proposes a modal analysis procedure to obtain exact modal parameters (natural frequencies, damping ratios, eigenvectors) for general, non-uniform beam-like structures. The proposed method includes a derivation of the system dynamic matrix for a Timoshenko beam element. The proposed method provides not only exact modal parameters but also exact frequency response functions (FRFs) for general beam structures. A time domain analysis method is also proposed. Two examples are provided for validating and illustrating the proposed method. The first numerical example compares the proposed method with FEM. The second example deals with a non-uniform beam structure supported in joints with damping property. The numerical study proves that the proposed method is useful for the dynamic analysis of continuous systems consisting of beam-like structures.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1994.10a
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• pp.58-61
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• 1994

본 연구에서는 내부 외부 진동원(8-30Hz)에 따른 격자보 구조의 동적 응답을 효과적으로 제어하기 위해 격자보 구조의 동적 거동에 지배적인 영향을 미치는 철근비, 질량, 탄성계수 등 여러 인자들의 비교, 분석을 통해 동적 거동에 영향을 미치는 인자를 분석함으로써 격자보 구조의 설계시 인자의 변화에 따른 동적 거동 특성을 예측하여 이에 적절히 대응할 수 있도록 도모하였다. 이를 위해 국내에 건설된 반도체 공장의 격자보 구조 중에서 기본 해석 모델을 결정하고 이에 대해 실험적 모드 해석과 유한 요소 해석을 사용해서 기본 해석 모델의 모드 매개변수를 구하고, 기본 해석 모델에 사용되는 각 인자가 고유 진동수에 미치는 영향을 비교.분석하였다.

• Journal of KSNVE
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• v.9 no.5
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• pp.966-974
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• 1999

This paper introduces modeling and its modal analysis procedure for exact and closed form solution of in-plane vibrations of general Timoshenko frame structures using exact dynamic element method(EDEM). The derivation procedure of the exact system dynamic matrices for Timoshenko beam frames is described. A new modal analysis procedure is also proposed since the conventional modal analysis schemes are not adequate for the proposed, exact system dynamic matrix. The proposed method provides exact modal parameters as well as all kinds of closed form solutions for general frame structures. Two numerical examples are presented for validating and illustrating the proposed method. The numerical study proves that the proposed method is useful for dynamic analysis of frame structures.