• Journal of the Society of Disaster Information
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• v.12 no.1
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• pp.69-73
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• 2016

In this study, the applicability and validity of collocation method to nonlinear vibration issues in comparison to other solutions are confirmed, and the applicability of collocation method to nonlinear dynamic response issues in comparison to the response curve with F.E.M results is examined. Also, it is also examined how the influence of axial inertia varies according to the size of slenderness ratio.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.3
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• pp.519-527
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• 1987

Simple procedures have been formulated to compute approximate natural frequency of nonlinear systems by the use of variational principle. These procedures are applicable to motion of large amplitudes, even to systems which are not linearizable. The results obtained by these procedures have been found to have good agreements with computer solutions and exact solutions for systems having piece-wise linear springs and polynomial springs.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2002.12a
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• pp.203-206
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• 2002

동적 시스템의 동정은 시스템의 관측된 데이터를 가지고 동적 모델의 수학적 모델을 찾는 문제를 다루는 것이다. 기존의 고전적인 방법으로는 차분 방정식(ARX 또는 ARMAX) 또는 상태 공간 표현에 관한 계수들을 추정하기 위해서 회귀 기법 등을 사용하였다. 그러나 이러한 고전적인 방법들은 파라미터가 비선형이고, 실세계 문제에서 모델링 오차나 측정 잡음을 수반하게 되면 탐색의 어려움을 가지게 된다. 따라서 이러한 문제점을 극복하고자 퍼지 이론이나 신경망 이론 둥이 이용되었으나 본 논문에서는 비선형 동적 시스템의 파라미터 동정에 최근 복잡한 최적화 문제를 해결하는 도구로 점점 관심을 받고 있는 유전 알고리즘을 동정 알고리즘으로 제안하고, 비선형 동적 시스템의 파라미터 동정에 유전 알고리즘을 응용한 몇 가지 예를 제시하고자 한다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.7
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• pp.620-628
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• 2016

The homotopy algorithm provides a robust method for determining optimal control, in some cases the global minimum solution, as a continuation parameter is varied gradually to regulate the contributions of the nonlinear terms. In this paper, the Successive Backward Sweep (SBS) method, which is insensitive to initial guess, augmented with a homotopy algorithm is suggested. This approach is effective for highly nonlinear problems such as low-thrust trajectory optimization. Often, these highly nonlinear problems have multiple local minima. In this case, the SBS-homotopy method enables one to steadily seek a global minimum.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.3
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• pp.237-244
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• 2016

This paper presents a nonlinear Moving Least Squares(MLS) difference method for material nonlinearity problem. The MLS difference method, which employs strong formulation involving the fast derivative approximation, discretizes governing partial differential equation based on a node model. However, the conventional MLS difference method cannot explicitly handle constitutive equation since it solves solid mechanics problems by using the Navier's equation that unifies unknowns into one variable, displacement. In this study, a double derivative approximation is devised to treat the constitutive equation of inelastic material in the framework of strong formulation; in fact, it manipulates the first order derivative approximation two times. The equilibrium equation described by the divergence of stress tensor is directly discretized and is linearized by the Newton method; as a result, an iterative procedure is developed to find convergent solution. Stresses and internal variables are calculated and updated by the return mapping algorithm. Effectiveness and stability of the iterative procedure is improved by using algorithmic tangent modulus. The consistency of the double derivative approximation was shown by the reproducing property test. Also, accuracy and stability of the procedure were verified by analyzing inelastic beam under incremental tensile loading.

• Journal of the Korean Institute of Intelligent Systems
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• v.27 no.1
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• pp.15-21
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• 2017

In this paper, the decentralized fuzzy observer design technique is presented for discrete-time nonlinear interconnected systems, which are assumed to be with unknown interconnections. To design the decentralized fuzzy observer, the design problem is considered and the performance function is defined to solve the design problem. Based on the performance function, the sufficient condition is derived for the observer design, and its condition is formulated into linear matrix inequalities. Finally, by the simulation result, the validity of the proposed observer design technique is shown.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2000.11a
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• pp.429-434
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• 2000

본 연구에서는 등분포하중을 받는 laminated 박판의 거동해석을 제시하였다. 접착한 두 박판의 비선형 지배방정식을 Von Karman 식을 이용하여 유도하고 박판의 거동을 차분법을 이용하여 수치해석 한다. Interlayer에서의 전단변형을 고려하여 지배방정식에 포함시켜 하중 증분법(load incremental method)으로 기하학 비선형 해석을 수행한다. 하중 증분법에 따른 반복법을 도입하여 비선형 방정식을 해석했다. 해석방법의 타당성을 입증하기 위하여 해석결과들을 기존의 문헌의 결과와 비교, 검토함으로써 본 논문에서 제시한 이론 및 해석방법의 타당성을 입증한다. 차분법의 하중 증분법 알고리즘을 개발하여 예제문제에 대한 수치해석 결과들을 논하였다.(중략)

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.486-491
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• 1999

본 논문에서는 웨이브렛 신경회로망을 사용하여 알려지지 않은 비선형 시스템을 안정하게 적응 제어하는 문제를 다룬다. 비선형 시스템의 정확한 제어는 함수를 근사화하는 데 사용된 함수 근사화기의 정확성과 효율성에 의존한다. 이에 비선형 시스템 제어에 기준 함수의 선택이 자유롭고 함수 근사화 능력이 뛰어난 웨이브렛 신경회로망을 사용한다. 초기 웨이브렛 신경회로망 제어기 설정은 웨이브렛 신경회로망 변수인 신축과 이동 값을 제어기 입력의 시-주파수 특성을 분석해서 구하고, 연결강도는 Lyapunov 안정성 이론에 기초한 적응 법칙을 사용하여 조절한다. 이를 비선형 시스템인 역 진자 시스템에 적용한다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1996.05a
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• pp.85-93
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• 1996

비선형 해석의 중요성이 증가하고 있는 혼합형 고체 추진제의 비선형거동중 재료비선형에 대한 거시적/미시적 현상을 설명하고, 그 주요한 원인으로서 Mullin 효과와 결합제/충전미립자 사이의 접착분리(Dewetting)를 주로 고찰하였다. 이를 응용한 지금까지의 비선형 구성방정식의 개발동향을 검토하여 비교하였으며 최근에 제시되고 있는 손상변수를 분석하였다. 여러 변형률 크기에 대한 응력이완 모듈러스 실험을 통하여 변형률 크기가 손상변수로서 적합하지 않음을 보였으며, 변형률 크기에 따라 모듈러스의 저하가 크기 때문에 비선형 점탄성 해석이 중요한 문제임을 제시하였다.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.1
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• pp.65-72
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• 1993

A numerical method for nonlinear free-surface-wave problem is developed in this paper. The final goal of this study is to simulate the towing tank experiment of a ship model and to partially replace the experiment by the numerical model. The exact problem in the scope of potential flow theory is formulated by a variational principle based on the classical Hamilton's principle. A localized finite element method is used in the present numerical computations which made use of the following two notable steps. The first step is an efficient treatment of the numerical radiation condition by using the intermediate nonlinear-to-linear transition buffer subdomain between the fully nonlinear and linear subdomains. The second is the use of a modal analysis in the final stage of the solution procedures, which enables us to reduce the computation time drastically. With these improvements the present method can treat a much larger computational domain than that was possible previously. A pressure patch on the free surface was chosen as an example. From the present computed results we could investigate the effect of nonlinearity on the down-stream wave pattern more clearly than others, because much larger computational domain was treated. We found, specifically, the widening of the Kelvin angle and the increase of the wave numbers and the magnitude of wave profiles.