• 한국해양공학회지
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• 제28권2호
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• pp.119-125
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• 2014

A vertical planar motion mechanism(VPMM) test was used to increase the prediction accuracy for the maneuverability of an underwater glider model. To improve the accuracy of the linear hydrodynamic coefficients, the analysis techniques of a pure heave test and pure pitch test were developed and confirmed. In this study, the added mass and damping coefficient were measured using a VPMM test. The VPMM equipment provided pure heaving and pitching motions to the underwater glider model and acquired the forces and moments using load cells. As a result, the hydrodynamic coefficients of the underwater glider could be acquired after a Fourier analysis of the forces and moments. Finally, a motion control simulation was performed for the glider control system, and the results are presented.

• 한국해양공학회지
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• 제28권5호
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• pp.466-473
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• 2014

Underwater gliders do not have any external propulsion systems that can generate and control their motion. Generally, underwater gliders would obtain a propulsive force through the lift force generated on the body by a fluid. Underwater gliders should be equipped with mechanisms that can induce heave and pitch motions. In this study, an inner movable and rotatable mass mechanism was proposed to generate the pitch and roll motions of an underwater glider. In addition, a buoyancy control unit was presented to adjust the displacement of the underwater glider. The buoyancy control unit could generate the heave motion of the underwater glider. In order to analyze the underwater dynamic behavior of this system, nonlinear 6-DOF dynamic equations that included mathematical models of the inner movable mass and buoyancy control unit were derived. Only kinematic characteristics such as the location of the inner movable mass and the piston position of the buoyancy control unit were considered because the velocities of these systems are very slow. The effectiveness of the proposed dynamic modeling was verified through sawtooth and spiraling motion simulations.

• 한국해양학회지:바다
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• 제24권2호
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• pp.332-350
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• 2019

2017년 8월 7일부터 25일까지 수중글라이더를 활용하여 $37.9^{\circ}N$ 위도 라인를 따라 동경 $129.0^{\circ}E{\sim}131.3^{\circ}E$ 사이를 왕복하는 단면 관측을 수행하였다. 해당 경로는 국립수산과학원 정기선박 관측라인 중 106 라인을 따른 것으로 이 경로를 따라 약 18일간 운용하였으며 위치 유지 모드로 동작했던 시간을 제외하고 총 440 km를 비행하였고, 그동안 고해상도 수온 및 염분의 공간 단면을 관측하였다. 본 관측 해역은 약 0.8 m/s의 강한 유속을 갖는 동한난류가 북상하고 있는 상황이었음에도 불구하고, 해당 수중글라이더는 지정된 경로에서부터 RMS 거리 400 m 이내를 벗어나지 않고 정확하게 106 라인을 따라 비행하였다. 본 관측에서 얻어진 고해상도 물성 단면 구조를 국립수산과학원 정선 관측 자료와 비교함으로써 해양환경에 지대한 영향을 끼치는 전선역이나 소용돌이와 같은 현상을 관측하기 위해서 고해상도 관측이 얼마나 중요한지 확인할 수 있었다. 이러한 수중글라이더 관측을 통해 이제까지 발견하지 못했던 새로운 소용돌이를 발견할 수 있었다. 이 소용돌이는 수평폭이 10~13 km, 수직폭은 200 m 가량되는 렌즈 형태를 가지고 있으며 시계방향으로 회전하는 아중규모 중층성 소용돌이(submesoscale intrathermocline eddy)다. 수온약층 내 혹은 직하부에 존재하면서 아중규모의 렌즈형태의 구조를 갖는 이러한 중층성 소용돌이는 동해에서 처음 발견되었기 때문에 Korea intrathermocline eddy(Keddy)로 명명하였다. 이 Keddy는 다음과 같은 전형적인 중층성 소용돌이(intrathermocline eddy)의 특징을 가지고 있다. Keddy는 수온약층 하부인 수심 약 170 m, 즉 중층에서 유속최대값을 갖는 특징이 있고, 따라서 해표면에는 해당 지오포텐셜 구조가 드러나지 않는 2차 순압성 구조를 가지고 있다. 또한 중앙부의 성층화가 주변보다 약하고, 수평크기가 1차 순압성 로스비 변형반경과 유사하며, 로스비 수가 0.7로 1에 근접한다.

• 한국해양공학회지
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• 제28권6호
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• pp.560-565
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• 2014

In this study, the problem of trajectory optimization for underwater gliders considering depth constraints is discussed. Typically, underwater gliders are controlled to dive and climb in a saw-tooth pattern at constant gliding angles. This approach is effective and close to optimal for deep water applications. However, the optimal path deviates from the saw-tooth path in shallow water conditions. This study focuses on finding more efficient gliding paths that can minimize the traverse time in the horizontal plane when the water depth is limited. The trajectory optimization problem is formulated into a minimum time control problem with inequality path constraints and hydrodynamic drag effects. A numerical approach based on the pseudo-spectral method is adopted as a solution approach, and the simulation results are presented.

• 전기학회논문지
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• 제67권2호
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• pp.261-269
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• 2018

In this paper, we propose a Takagi-Sugeno (T-S) fuzzy-model-based design for the tracking control of a class of nonlinear underwater glider. By using the partial linearization and the sector nonlinearity, the underwater glider with six degrees of freedom (6 DOF) is modelled by the T-S fuzzy model. The concerned tracking control problem with $H_{\infty}$ performance is converted into the stabilization one for the error dynamics between the given nonlinear underwater glider and the reference time-varying input. Sufficient conditions are derived for the asymptotic stabilizability of the error dynamics in the format of matrix inequality. Simulation results demonstrate the effectiveness of the proposed design methodology.

• 전기학회논문지
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• 제65권12호
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• pp.2037-2045
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• 2016

This paper presents a fuzzy-model-based design approach to the buoyancy and moment controls of a class of nonlinear underwater glider. Through the linearization and the sector nonlinearity methodologies, the underwater glider dynamics is represented by a Takagi-Sugeno (T-S) fuzzy model. Sufficient conditions are derived to guarantee the asymptotic stability of the closed-loop system in the format of linear matrix inequality (LMI). Simulation results demonstrate the effectiveness of the proposed buoyancy and moment controllers for the underwater glider.

• 전기학회논문지
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• 제65권12호
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• pp.2023-2029
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• 2016

This paper addresses a robust controller design technique for a nonlinear underwater glider with disturbances. We consider the buoyancy and pitching moment as control inputs, which generate additional nonlinearity on the plant dynamics. To deal with the nonlinearity, we utilize the optimal linearization technique. The conditions for the optimal linearization and the controller design are formulated in terms of matrix inequalities. The effectiveness of the proposed method is demonstrated through a simulation.

• 대한임베디드공학회논문지
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• 제12권5호
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• pp.343-350
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• 2017

Underwater glider with a single buoyancy engine could generally obtain propulsive forces by moving the center of buoyancy and gravity. Futhermore, The hull and internal structure of underwater glider are designed according to the purpose of long-time operation, high speed and a wide variety of payloads (sensors, communications and etc.). In this paper, Ray-type underwater glider featuring flatfish is considered in view of hydrodynamics. The hull design is especially performed by the analysis of fluid resistance and dynamic performance. The resistance performance is analyzed using the Computational Fluid Dynamics (CFD). In addition, a simulation program is implemented in order to verify the validity of dynamics modeling and dynamic performances.

• 대한임베디드공학회논문지
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• 제12권2호
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• pp.105-112
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• 2017

To control the depth of an underwater glider, a control method by using Lyapunov's direct method is proposed. The underwater glider has a torpedo-shape hull, a movable mass in the hull, and an inflatable buoyancy bag in the hull, but doesn't have large wings that increase the lift force for the conventional underwater glider. The control laws to adjust the position of the movable mass and the mass of the inflatable buoyancy bag are derived. For a selected speed and an angle of attack, we simulated the operation of the underwater glider using Matlab/Simulink. The efficiency of the proposed controller is shown in the fact that the control effort is active during only a short period of time when the zigzag trajectory is changed from downward to upward or vice versa.

• 대한임베디드공학회논문지
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• 제12권5호
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• pp.311-318
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• 2017

A reduced order observer is developed for depth control of a hybrid underwater glider which combines the good aspects of a conventional autonomous underwater vehicle and a underwater glider. State variables include the center of gravity of the robot and the weight of the buoyancy bag, which can not be directly measured. By using the mathematical model and available information such as directional velocities, accelerations, and attitudes, we developed a Luenberger's reduced order observer to estimate the center of gravity and the buoyancy weight. By simulations using Matlab/Simulink, the efficiency of the proposed observer is shown, where a LQR controller using full state variables is adopted as a depth controller.