• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1996년도 추계학술대회
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• pp.70-73
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• 1996

Many researchers had considered biological systems as linear systems. In many cases of biological systems, the phenomena that show the regular and periodic dynamics are considered the normal state. However, some clinical experiments reported, in some cases, the periodic signals represented the abnormal state. We assume that signals from human body system are generated from deterministic, intrinsic mechanisms and can be represented a simple equation that show nonlinear dynamics dependent on control parameters. The objective of our study is to model a nonlinear dynamics correctly from the nonlinear time series using the genetic programming method; to find a simple equation of nonlinear dynamics using collected time series and its nonlinear characteristics. We applied genetic programming to model RR interval of ECG that shows chaotic phenomena. We used 4 statistic measures and 2 fractal measures to estimate fitness of each chromosome, and could obtain good solutions of which chaotic features are similar.

• 디자인학연구
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• 제15권4호
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• pp.379-390
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• 2002

새로운 패러다임으로의 전이를 의미하는 과학혁명은 필연적으로 지적 영역의 변화를 동반한다. 더욱이 과학과 예술의 관계는 서로를 가능케 하는 상생의 관계라 할 수 있다. 최근 비선형 과학에 대한 놀라운 관심과 함께 예술에의 신속한 적용은 양자의 긴밀한 상호작용을 다시 한 번 가늠케 한다. 과학과 예술에 있어서 중요한 것은 새로운 창조의 과정과 방법을 제시하는 일일 것이다. 이를 위하여 때로는 역발상을 시도하고, 또한 일상을 탈피하여 예측할 수 없었던 것들을 추적하는 모험과 탐구정신이 절실하다. 이와 같은 관점에서 본 연구는 비선형 패러다임의 기저가 되는 카오스 이론과 함께, 물리학과 수학에서 다루어지는 관련 이론들을 준거로 하여 비선형적 공간조형을 재검토하였다. 연구 과정에서 비선형은 일련의 계(a system)에 대하여 부분이 아닌 전체로 보아야 할 것에 대한 강력한 제안이며, 또한 새로운 질서요 창조의 원리임을 확인할 수 있었다. 이울러 본 연구는 비선형적 공간 조형에 있어서 형태적 차용에 급급한 디자인 행위를 지양하도록 하는데에 암묵적 의도가 있었다. 따라서 비선형 동력학 현상의 원리와 프로세스를 이해, 적용함으로써 비선형이 지닌 창조적 속성이 공간에 총체적으로 발휘되기를 기대해 본다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.662-667
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• 2005

Nonlinear dynamics of active piezolaminated plates are investigated with respect to the thermopiezoelastic behaviors. For largely deformed structures with small strain, the incremental total Lagrangian formulation is presented based on the virtual work principles. A multi field layer wise finite shell element is proposed for assuring high accuracy and non-linearity of displacement, electric and thermal fields. For dynamic consideration of thermopiezoelastic snap through phenomena, the implicit Newmark's scheme with the Newton-Raphson iteration is implemented for the transient response of various piezolaminated models with symmetric or eccentric active layers. The bifurcate thermal buckling of symmetric structural models is first investigated and the characteristics of piezoelectric active responses are studied for finding snap through piezoelectric potentials and the load path tracking map. The thermoelastic stable and unstable postbuckling, thermopiezoelastic snap through phenomena with several attractors are proved using the nonlinear time responses for various initial conditions and damping loss factors. Present results show that thermopiezoelastic snap through phenomena can result in the difficulty of buckling and postbuckling control of intelligent structures.

• Structural Engineering and Mechanics
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• 제9권4호
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• pp.397-416
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• 2000

The present study deals with the nonlinear dynamics and stability of autonomous dissipative either imperfect potential (limit point) systems or perfect (bifurcational) non-potential ones. Through a fully nonlinear dynamic analysis, performed on two simple 2-DOF models corresponding to the classes of systems mentioned above, and with the aid of basic definitions of the theory of nonlinear dynamical systems, new important phenomena are revealed. For the first class of systems a third possibility of postbuckling dynamic response is offered, associated with a point attractor on the prebuckling primary path, while for the second one the new findings are chaos-like (most likely chaotic) motions, consecutive regions of point and periodic attractors, series of global bifurcations and point attractor response of always existing complementary equilibrium configurations, regardless of the value of the nonconservativeness parameter.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.240-243
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• 2003

Combustion instability phenomena have been observed in various different combustion systems. For each specific combustion system, pressure fluctuations measured during high frequency combustion instability presented many different characteristics. High frequency instability occurring in a lean premixed gas turbine combustor mar be dominantly affected by a nonlinear relation between pressure oscillations and heat release rate fluctuations, and gas dynamics plays a crucial role in determining an amplitude of a limit cycle for a liquid rocket thrust chamber. Combustion instability phenomena manifest their inherent nonlinear characteristics. One is a limit cycle and the other bifurcation described by nonlinear time series analysis.

• 한국소음진동공학회논문집
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• 제12권11호
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• pp.873-881
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• 2002

The fluid induced vibration (FIV) phenomena of an equivalent airfoil system of MAV have been investigated in low Reynolds number flow region. Unsteady flows with viscosity are computed using two-dimensional incompressible Navier-Stokes equations. The present fluid/structure interaction analysis is based on one of the most accurate computational approach with computational fluid dynamics (CFD) and computational structural dynamics (CSD) techniques. The highly nonlinear fluid/structure interaction phenomena due to severe flow separations have been analyzed for the low Reynolds region that has a dominancy of flow viscosity. The effects of Reynolds number and initial angle of attack on the fluid/structure coupled vibration instability are shown and the qualitative trend of FIV phenomenon is investigated.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제15권4호
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• pp.283-288
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• 2015

In this paper, we propose a dynamic mathematical model of love involving various external forces, in order to analyze the chaotic phenomena in a love model based on Romeo and Juliet. In addition, we investigate the nonlinear phenomena in a love model with external forces using time series and phase portraits. In order to describe nonlinear phenomena precisely using time series and phase portraits, we vary the type of external force, using models such as a sine wave, chopping wave, and square wave. We also apply various different parameters in the Romeo and Juliet model to acquire chaotic dynamics.

• Kyungpook Mathematical Journal
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• 제52권4호
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• pp.459-472
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• 2012

A piecewise smooth system is characterized by non-differentiability on a curve in the phase space. In this paper, we discuss particular bifurcation phenomena in the dynamics of a piecewise smooth system. We consider a two-dimensional piecewise smooth system which is composed of a linear map and a nonlinear map, and analyze the stability of the system to determine the existence of dangerous border-collision bifurcation. We finally present some numerical examples of the bifurcation phenomena in the system.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제1권1호
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• pp.104-112
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• 2001

Simply, Nonlinear dynamics theory means the complicated and noise-like phenomena originated form nonlinearity involved in deterministic dynamical system. An almost all the natural signals have nonlinear property. However, there exist few analysis software tool or package for a research and development of applications. We develop nonlinear time series analysis simulator is to provide a common and useful tool for this purpose and to promote research and development of nonlinear dynamics theory. This simulator is consists of the following four modules such as generation module, preprocessing module, analysis module and ICA module. In this paper, we applied to Electroencephalograph (EEG), as it turned out, our simulator is able to analyze nonlinear time series. Besides, we could get the useful results using the various parameters. These results are used to diagnostic the brain diseases.

• 한국전자통신학회논문지
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• 제7권5호
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• pp.1073-1078
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• 2012

본 논문에서는 MEMS에서 비선형적인 특성을 확인하기 위하여 Duffing 방정식을 가지는 MEMS 시스템을 제안하고 여기에 다른 종류의 비선형 항을 삽입하였을 때의 비선형 현상을 분석하였다. 검증 방법으로 파라미터 변화에 의한 카오스 운동이 있음을 시계열 데이터, 위상 공간, 전력 스펙트럼을 통하여 확인하였다.