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은희창,정헌수 한국소음진동공학회 1997 소음 진동 Vol.7 No.5
Using Generalized Inverse Method presented by Udwadia and Kalaba in 1992, we can obtain equations to exactly describe the motion of constrained systems. When the differential equations are numerically integrated by any numerical integration scheme, the numerical results are generally found to veer away from satisfying constraint equations. Thus, this paper deals with the numerical integration of the differential equations describing constrained systems. Based on Baumgarte method, we propose numerical methods for reducing the errors in the satisfaction of the constraints.
구속조건을 고려한 일반화된 해밀턴의 운동방정식 ( Generalized Hamiltonian considering constraints )
은희창,이영인,정헌수 대한건축학회 1998 大韓建築學會論文集 : 構造系 Vol.14 No.8
Lagrange 역학으로부터 해밀턴의 운동방정식이 유도된다. 그러나 주어진 시스템 이 임의의 구속조건이 부여될 경우에는 해밀턴에 의한 일반화된 운동방정식을 유도하기란 상당한 어려움이 있다. 특히 구속조건이 nonholonomic일 경우에는 그 방법이 매우 복잡하거나 어려운 점이 있다. 따라서 본 연구에서는 해밀턴 역 학을 근거로 구속된 시스템의 운동을 묘사하는 방법을 제시한다. 이 방법은 기존 의 다른 방법과는 달리 주어진 조건식을 시간에 관해 미분만을 취하여 이를 지 배방정식에 대입함으로써 보다 용이하고 간단히 접근할 수 있는 장점이 있으며, 예제를 통하여 그 결과의 타당성을 입증한다. 그러나 해밀턴의 역학은 가상일 법 에 그 근거를 두고 있는 바 명백한 시간의 함수를 갖는 구속조건은 좀처럼 적용 하기 어렵다. 또한 Chetaev 형태의 구속조건이외의 nonholonomic 구속조건일 경 우에는 모멘타의 정의를 수정해야 하는 등의 복잡한 문제점들이 있으므로 이에 대한 연구들은 향후에 고려되어야 할 것이다.
구속조건을 이용한 부정정 구조의 정적 해석에 관한 연구
은희창,서일교 濟州大學校 産業技術硏究所 2001 산업기술연구소논문집 Vol.12 No.1
This paper presents an explicit static-equilibrium equation of indeterminate structures to satisfy the compatibility conditions. The static analysis of indeterminate structures considers the equilibrium of forces as well as the compatibility conditions. The satisfaction of the compatibility conditions also requires the constraint forces. In this paper. the new equilibrium equation to consider the conditions is derived by minimizing the performance index. which is the function of the difference of the real displacements and the displacements of unconstrained structures without the conditions. Through a simple static analysis of indeterminate structure. it was observed that the weight matrix in the performance index takes the stiffness matrix. And Nature takes the constraint forces as the minimum values of all forces to satisfy the given geometric conditions. Also. several examples illustrated the validity of the proposed method.
On Shear Capacity of Reinforced Concrete Deep Beamswith Rectangular Web Openings
은희창,양근혁,이영호,정헌수 대한건축학회 2005 Architectural research Vol.7 No.2
Based on an experimental study, this study provides an equation to describe the shear strength of high-strength concrete deep beams with rectangular openings and without web reinforcements. Twenty-four concrete deep beams were tested with the variables of concrete strength, size of web opening, and shear span-to-depth ratio. The proposed equation is expressed as the sum of the shear strength provided by longitudinal bars and concrete. It is illustrated that the proposed equation predicts the load-carrying capacity of the deep beams more properly than the experimental equations proposed by other researchers.
Analytical Method for Constrained Mechanical and Structural Systems
은희창,박상렬,이은택,정헌수 대한기계학회 2004 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.18 No.10
The objective of this study is to present an accurate and simple method to describe the motion of constrained mechanical or structural systems. The proposed method is an elimination method to require less effort in computing Moore-Penrose inverse matrix than the generalized inverse method provided by Udwadia and Kalaba. Considering that the results by numerical integration of the derived second-order differential equation to describe constrained motion veer away the constrained trajectories, this study presents a numerical integration scheme to obtain more accurate results. Applications of holonomically or nonholonomically constrained systems illustrate the validity and effectiveness of the proposed method.
An Analytical Approach for Structural Synthesis of Substructures
은희창,박상렬,이은택 대한기계학회 2004 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.18 No.9
A structure is broken down into a number of substructures by means of the finite element method and the substructures are synthesized for the complete structure. The divided substructures take two types: fixed-free and free-free elements. The flexibility and stiffness matrices of the free-free elements are the Moore-Penrose inverse of each other. Thus, it is not easy to determine the equilibrium equations of the complete structure composed of two mixed types of substructures. This study provides the general form of equilibrium equation of the entire structure through the process of assembling the equilibrium equations of substructures with end conditions of mixed types. Applications demonstrate that the proposed method is effective in the structural analysis of geometrically complicated structures.
Structural and Mechanical Systems Subjected to Constraints
은희창,이은택,정헌수,박상렬 대한기계학회 2004 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.18 No.11
The characteristics of dynamic systems subjected to multiple linear constraints are determined by considering the constrained effects. Although there have been many researches to investigate the dynamic characteristics of constrained systems, most of them depend on numerical analysis like Lagrange multipliers method. In 1992, Udwadia and Kalaba presented an explicit form to describe the motion for constrained discrete systems. Starting from the method, this study determines the dynamic characteristics of the systems to have positive semidefinite mass matrix and the continuous systems. And this study presents a closed form to calculate frequency response matrix for constrained systems subjected to harmonic forces. The proposed methods that do not depend on any numerical schemes take more generalized forms than other research results.
Substructuring and Decoupling of Discrete Systems from Continuous System
은희창,구재오 대한건축학회 2012 Architectural research Vol.14 No.1
This study proposes analytical methods to establish the eigenfunction of continuous system due to substructuring and decoupling of discrete subsystems. The dynamic characteristics of updated continuous system are evaluated by the constraint effect of consistent deformation at the interfaces between two systems. Beginning with the dynamic equation for constrained discrete system, this work estimates the modal eigenmode function for the continuous system due to the addition or deletion of discrete systems. Numerical applications illustrate the validity and applicability of the proposed method.