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포텐셜함수 기반 초공동 수중운동체 플레이닝 회피 제어 연구
김선홍(Seonhong Kim),김낙완(Nakwan Kim),김민재(Minjae Kim),김종혁(Jonghoek Kim),이건철(Kurnchul Lee) 한국해양공학회 2018 韓國海洋工學會誌 Vol.32 No.3
In this paper, we focus on planing avoidance control for a supercavitating underwater vehicle based on the potential function method. The planing margin can be calculated using the relative position between the cavity center and vehicle center at the end of the vehicle. The planing margin was transformed into a limit variable such as the pitch angle and yaw angle limit. To prevent the vehicle attitude from exceeding the limit variable, a potential function based planing envelope protection method was proposed. The planing envelope protection system overrides commands from the tracking controller, and the vehicle attitude converges to a desired angle, in which the potential function is minimized. Numerical simulations were performed to analyze the physical feasibility and performance of the proposed method. The results showed that the proposed methods eliminated the planing, allowing the vehicle to follow tracking commands.
김도명(Do-Myung Kim),김덕렬(Deok-Ryeol Kim),김낙완(Nakwan Kim),석진영(Jinyoung Suk),김희섭(HeeSeob Kim),김규선(Gyu-Sun Kim),현영목(Young-Mok Hyun) 한국항공우주학회 2008 韓國航空宇宙學會誌 Vol.36 No.5
본 논문에서는 관측위성의 영상성능을 예측하고 해석하기 위하여 영상 성능의 주요 인자인 전체 시스템의 MTF를 산출하기 위한 시스템 MTF 구조도를 제안하였다. MTF 구조도의 각 요소에 해당하는 기본 모델은 우주 환경에서 광-구조, 열 변형, 자세 및 동역학 특성과 MTF간의 수학적인 관계식으로 표현된다. MTF 기본 모델은 중앙차폐가 있는 광학계의 회절한계, 수차, 비촛점, LOS 지터, 선형운동, 검출기 Integration MTF 등으로 구성된다. 가상의 지구관측위성모델에 대해 영상성능 예측모델링 기법을 적용하여 적절한 결과를 얻을 수 있음을 보였다. 각 기본 모델을 바탕으로 관측위성의 전체 영상성능을 해석하고 개념설계 단계에서 영상성능에 영향을 주는 주요한 설계 매개변수를 도출할 수 있다. A modulation transfer function(MTF) tree is established to estimate the overall MTF of an observation satellite and to analyze the image performance. Basic MTF models relevant to each MTF tree component are represented as mathematical relationship between optics-structural dynamics, thermal deformation, attitude and dynamic characteristics of a satellite and the effects due to the space environment. The Basic MTF models consist of diffraction limited MTF with central obscuration, aberration, defocus, line-of-sight(LOS) jitter, linear motion, detector integration, and so forth. Performance estimation is demonstrated for a virtual earth-observation satellite in order to validate the constructed modeling method. The proposed models enable the system engineers to calculate the overall system MTF and to determine the crucial design parameters that affect the image performance in the conceptual design phase of an observation satellite.
Integrated dynamics modeling for supercavitating vehicle systems
Kim, Seonhong,Kim, Nakwan The Society of Naval Architects of Korea 2015 International Journal of Naval Architecture and Oc Vol.7 No.2
We have performed integrated dynamics modeling for a supercavitating vehicle. A 6-DOF equation of motion was constructed by defining the forces and moments acting on the supercavitating body surface that contacted water. The wetted area was obtained by calculating the cavity size and axis. Cavity dynamics were determined to obtain the cavity profile for calculating the wetted area. Subsequently, the forces and moments acting on each wetted part-the cavitator, fins, and vehicle body-were obtained by physical modeling. The planing force-the interaction force between the vehicle transom and cavity wall-was calculated using the apparent mass of the immersed vehicle transom. We integrated each model and constructed an equation of motion for the supercavitating system. We performed numerical simulations using the integrated dynamics model to analyze the characteristics of the supercavitating system and validate the modeling completeness. Our research enables the design of high-quality controllers and optimal supercavitating systems.
Kim, Dae Hyuk,Kim, Nakwan The Society of Naval Architects of Korea 2014 International Journal of Naval Architecture and Oc Vol.6 No.1
An auto weather-vaning system for a Dynamic Positioning (DP) vessel is proposed. When a DP vessel is operating, its position keeping is hindered by ocean environmental disturbances which include the ocean current, wave and wind. Generally, most ocean vessels have a longitudinal length that is larger than the transverse width. The largest load acts on the DP vessel by ocean disturbances, when the disturbances are incoming in the transverse direction. Weather-vaning is the concept of making the heading angle of the DP vessel head toward (or sway from) the disturbance direction. This enables the DP vessel to not only perform marine operations stably and safely, but also to maintain its position with minimum control forces (surge & sway components). To implement auto weather-vaning, a nonlinear controller and a disturbance observer are used. The disturbance observer transforms a real plant to the nominal model without disturbance to enhance the control performance. And the nonlinear controller deals with the kinematic nonlinearity. The auto weather-vaning system is completed by adding a weather-vaning algorithm to disturbance based controller. Numerical simulations of a semi-submersible type vessel were performed for the validation. The results show that the proposed method enables a DP vessel to maintain its position with minimum control force.
Control Strategy for a Ventilated Supercavitating Vehicle in Initial Phase
Kim, Seonhong,Kim, Nakwan International Society of Offshore and Polar Engine 2016 International journal of offshore and polar engine Vol.26 No.2
<P>Supercavitation reduces the resistance of an underwater vehicle by enveloping it in a bubble. When the velocity of the vehicle is low and the depth is significant, natural supercavitation is inhibited. Consequently, an artificial cavity to which gas is supplied, called a ventilated cavity, is used to maintain the supercavitating condition. This study models ventilated supercavity according to the cavity closure type and the design depth and proposes a ventilation control strategy that swiftly changes the closure type from the toroidal vortex regime to the twin vortex regime in the initial phase of flight. Numerical simulations verify the efficacy of the proposed strategy.</P>
김낙완(Nakwan Kim),유창선(Chang Sun Yoo),강영신(Young Shin Kang) 한국항공우주학회 2008 韓國航空宇宙學會誌 Vol.36 No.6
적응제어신호를 저역필터에 통과시켜 점근적 추종과 과도구간 성능을 동시에 보장하는 £₁ 적응제어 기법과 비선형 시스템을 선형 시불변 형태로 변환하는 피드백 선형화 기법을 결합하여 £₁ 적응제어 기법의 적용가능 범위를 확대하였다. Barbalat의 보조정리를 이용하여 추종오차가 0으로 수렴함을 증명하고 과도구간의 추종오차도 원하는 크기로 감소시킬 수 있음을 보였다. This paper presents an approach to combine £₁ adaptive controller with feedback linearization, which extends the applicability of the £₁ adaptive controller to a wider class of systems. The £₁ adaptive controller guarantees the asymptotic tracking convergence and the transient performance of the tracking error. The feedback linearization transforms a nonlinear plant into a linear time invariant form. The asymptotic tracking convergence is shown by the use of Lyapunov stability analysis and Barbalat’s lemma.
Integrated dynamics modeling for supercavitating vehicle systems
Seonhong Kim,Nakwan Kim 대한조선학회 2015 International Journal of Naval Architecture and Oc Vol.7 No.2
We have performed integrated dynamics modeling for a supercavitating vehicle. A 6-DOF equation of motion was constructed by defining the forces and moments acting on the supercavitating body surface that contacted water. The wetted area was obtained by calculating the cavity size and axis. Cavity dynamics were determined to obtain the cavity profile for calculating the wetted area. Subsequently, the forces and moments acting on each wetted part-the cavitator, fins, and vehicle body-were obtained by physical modeling. The planing force-the interaction force between the vehicle transom and cavity wall-was calculated using the apparent mass of the immersed vehicle transom. We integrated each model and constructed an equation of motion for the supercavitating system. We performed numerical simulations using the integrated dynamics model to analyze the characteristics of the supercavitating system and validate the modeling completeness. Our research enables the design of high-quality controllers and optimal supercavitating systems.
신경회로망 기존제어기의 접합기법을 이용한 유도무기 제어
김낙완(Nakwan Kim) 한국항공우주학회 2007 韓國航空宇宙學會誌 Vol.35 No.3
불확실성과 비선형성은 비선형시스템의 제어기 설계에 중요하게 고려할 요소이다. 본 논문에서는 기존 제어기와 신경회로망을 접합하여 불확실성과 비선형성에 대처하는 기법을 소개한다. 이 기법은 기존의 제어기를 사용하기 때문에 신경회로망을 사용하기 위해 역변환 제어기와 같은 새로운 형태의 제어기를 설계할 필요가 없다. 이 기법은 유도무기의 수직 가속도 제어에 적용하여 그 효용성을 제시하였다. The effect of uncertainty and nonlinearity is an important aspect in a control design of a highly nonlinear plant. This paper presents an approach to address uncertainty and nonlinearity by augmenting an existing controller with a neural network based adaptive element. The approach has advantage in the sense that augmentation of neural network does not require to design a new controller architecture like an inversion controller. The approach is illustrated in an application of normal acceleration control for guided munitions.