• Journal of Ocean Engineering and Technology
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• v.7 no.2
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• pp.141-149
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• 1993

삼 자유도를 가진 부유물체의 동적 응답을 이론적으로 연구하였다. 평면내 방향 운동모우드에 대한 지배방정식을 선형화한 후, 그들의 조화해를 평명밖 방향 운동모우드의 방정식과 연성시켰다. 그렇게 해서 주어지는 방정식은 시간에 따라 변화하는 계수를 가진 형태로서, 평면밖 방향의 운동만을 보일 것으로 예측되는 부유물체가 평면밖 방향의 운동을 보일 수도 있음을 밝혔다. 동역학적 불안정성과 그 결과로 나타나는 평면밖 방향의 대진폭 운동을 보이고 있다. 본 결과는 주기적으로 동요하는 부유물체가 서로 연성된 운동을 하는 현상으로도 해석할 수 있다.

• Journal of Astronomy and Space Sciences
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• v.26 no.3
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• pp.317-328
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• 2009

Relative dynamic models of satellites which describe the relative motion between two satellites is fundamental for research on the formation flying. The accuracy of various linearized or nonlinear models of relative motion is analyzed and compared. A 'Modeling Error Index (MEI)' is defined for evaluating the accuracy of models. The accuracy of the relative dynamic models in various orbit circumstance are obtained by calculating the modeling error with various eccentricities of the chief orbit and distances between the chief and the deputy. It is found that the modeling errors of the relative dynamic models have different values according to the eccentricity, J2 perturbation, and the distance between satellites. Since the evaluated accuracy of various models in this paper means the error of dynamic models of the formation flying, the results of this paper are very useful for choosing the appropriate relative model of the formation flying mission.

• Journal of Korea Society of Industrial Information Systems
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• v.10 no.4
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• pp.54-64
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• 2005

The study investigated genetic algorithms for the optimal control model of maximum height vertical jumping. The model includes forward dynamic simulations by the neural excitation-control variables. Convergence of genetic algorithms is very slow. In this paper the micro genetic algorithm(micro-GA) was used to reduce the computation time. Then a near optimal solution from micro-GA was an initial solution for VF02, which is one of well-developed and proven nonlinear programming algorithms. This approach provided the successful optimal solution for maximum-height jumping without a reasonable initial guess.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.4
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• pp.335-341
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• 2010

To improve the performance of inner loop based on PD controller for a unmanned helicopter, neural networks are applied. The performance of PD controller designed on the response characteristics of error dynamics decreases because of uncertain nonlinearities of the system. The nonlinearities are decoupled to modified dynamic inversion model(MDIM) and are compensated by the neural networks. For the training of the neural networks, online weight adaptation laws which are derived from Lyapunov's direct method are used to guarantee the stability of the controller. The results of the improved performance of PD controller by neural networks are illustrated in the simulation of unmanned helicopter with nonlinearities,

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.2
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• pp.77-86
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• 1999

In the previous $paper^{(1),(2)}$, a geometrically non-linear finite element formulation of spatial cables subjected to self-weights and support motions was presented using multiple noded cable elements and how to determine the initial equililbrium state of cables was addressed. In this paper, in order to perform dynamic non-linear analysis of ocean cables subjected to support motions and earthquakes, a numerical method to calculate Morison forces and incorporate effects of earthquake motions is presented based on the Newmark method. Challenging example problems are presented in order to investigate dynamic non-linear behaviors of ocean cables subjected to support motions and earthquake loadings.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.430-435
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• 2005

조화가진력이 작용하는 고정경계를 가진 완전원판의 비선형 진동에 대한 응답특성을 연구하였다. 원판의 비대칭모드의 고유진동수 근처에 가진주파수가 작용하는 주공진에서의 응답은 정상파(standing wave)뿐만 아니라 진행파(traveling wave)가 존재한다고 알려져 있다. 주공진 근처의 정상상태 응답곡선에서 최대한 5개의 안정한 응답이 존재하는 것으로 밝혀졌으며, 이들은 1개의 정상파와 4개의 진행파로 나타난다. 이 진행파중 2개는 Hope분기에 의해 안정성을 잃은 후 주기배가운동을 거쳐 혼돈운동에 이르게 된다. Lyaponov 지수를 사용하여 혼돈운동을 정량적으로 평가하였으며, 주평면의 개념을 이용하여 이 혼돈운동의 흡인영역이 Fractal임을 확인하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.5
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• pp.28-33
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• 2005

Nonlinear aeroelastic characteristics of a two dimensional typical section model with bilinear plunge spring are investigated. Doublet-point method(DPM) is used for the calculation of supersonic unsteady aerodynamic forces which are approximated by using the minimum-state approximation. For nonlinear flutter analysis structural nonlinearity is represented by an asymmetric bilinear spring and is linearized by using the describing function method. The linear and nonlinear flutter analyses indicate that the flutter characteristics are significantly dependent on the frequency ratio. From the nonlinear flutter analysis, various types of limit cycle oscillations are observed in a wide range of air speeds below or above the linear flutter boundary. The nonlinear flutter characteristics and the nonlinear aeroelastic responses are investigated.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.4
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• pp.317-325
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• 2016

In this study, nonlinear earthquake responses of a soil-structure interaction(SSI) system which is subjected to a three-directional ground motion are examined. The structure and the near-field region of soil, where the geometry is irregular, the material properties are heterogeneous, and nonlinear dynamic responses are expected, are modeled by nonlinear finite elements. On the other hand, the infinite far-field region of soil, which has a regular geometry and homogeneous material properties and dynamic responses is assumed linearly elastic, is represented by three-dimensional perfectly matched discrete layers which can radiate elastic waves into infinity efficiently. Nonlinear earthquake responses of the system subjected to a three-directional ground motion are calculated with the numerical model. It is observed that the dynamic responses of a SSI system to a three-directional motion have a predominant direction according to the characteristics of the ground motion. The responses must be evaluated using precise analysis methods which can consider nonlinear behaviors of the system accurately. The the method employed in this study can be applied easily to boundary nonlinear problems as well as material nonlinear problems.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.966-967
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• 2008

2kW급 선형 압축기용 액츄에이터로 직선 왕복 운동을 동작하게 하기 위하여 2상 영구자석형 횡자속 선형 전동기(Permanent Magnet Transverse Flux Linear Machine; PM-TFLM)와 스프링을 조합하여 선형 공진 시스템을 구성하였다. 선형전동기의 이동자를 공진점부근에서 왕복 운동을 하기 위해서 빠른 왕복 운전과 적절한 운전 알고리즘이 필요하게 된다. 먼저 2상으로 이루어진 PM-TFLM의 순시 토오크 제어를 위하여 벡터 제어 알고리즘을 설계하여 구현하고 피스톤, 스피링 및 부하에 따라 운전제어를 수행하는 방법에 대하여 연구를 하였다. 종래의 3상 교류 전동기의 순시 토오크 제어에 적용하는 벡터제어 알고리즘을 2상 PM-TFLM에 적용하여 그 타당성을 보이고 빠른 왕복운전을 안정적으로 수행함을 실험을 통하여 입증하였다.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.3
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• pp.53-58
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• 1992

The memory effect in maneuvering motion is very small and usually neglected. But, considering the maneuvering motion in waves, we need to calculate the memory effect strictly. Meanwhile. it is popular to treat the wave exciting forces as the steady sinusoidal forces and simply add to the right-hand side of the equation of the motion. This paper treats the memory effect in maneuvering motion when we take the wave exciting forces as the simple external forces and discuss the validity of such treatments.