I am a professor emeritus of Seoul National University, where I taught and did research on marine hydrodynamics over 30 years. Now I am a member of National Academy of Sciences, Korea.
For a long cylinder floating on the sea surface, incident sea waves with a narrow frequency band ... more For a long cylinder floating on the sea surface, incident sea waves with a narrow frequency band excite body oscillations of short and long periods. Depending on the stiffness of the mooring system, the body displacement of the long-period motion can be comparable with, or even greater than that of the short-period oscillations. By combining the asymptotic methods of multiple scales and inner and outer expansions, we describe an essentially analytical theory for slow sway of both small and large amplitudes. Besides showing results for various quasi-steady and transient incident waves for a rectangular cylinder, we examine the effect of the gap between the keel of the body and the sea bottom. It is found in particular that a small gap can enhance moderate resonance by blocking the flow due to long waves and increase the apparent mass of the cylinder. Real-fluid effects are not included.
Journal of the Society of Naval Architects of Korea
Nonlinear free surface flow phenomena have teen studied by several kinds of numerical methods, of... more Nonlinear free surface flow phenomena have teen studied by several kinds of numerical methods, of which boundary element method has been known as most promising one. There, however, remain many difficulties to be solved in the numerical procedures by boundary element analysis. In this paper, an efficient calculation of elemental integrals and iterative solution algorithm for the resulting system of equations were thoroughly investigated in order to enhance the procedure of the boundary element analysis. Advantages of the herein developed boundary element analysis code are demonstrated in terms of accuracy and convergence for typical boundary-value problems with free surface.
Journal of the Society of Naval Architects of Korea
This study is constructed to investigate the sloshing effect on the motions of a two-dimensional ... more This study is constructed to investigate the sloshing effect on the motions of a two-dimensional rectangular cylinder experimentally and numerically. The modes of motion under consideration are sway and roll, and also experimental cases are divided by two categories; 1-DoF roll motion and 2-DoF motion (Coupling sway and roll). It is found that the sway response is considerably affected by the motion of the fluid, particularly near the sloshing natural frequency, while the roll response changes comparatively small. The dominant mode of motion is analyzed for 2-DoF experiments as well. The measured data for 1-DoF motions is compared with numerical results obtained by the Multi-modal approach. The numerical schemes vary in detail with the number of dominant sloshing modes; i.e. there is a single dominant mode for the Single-dominant method, while the Model 2 method assumes that the first two modes are superior. For the roll motion, numerical results obtained by the two different method...
This paper discusses the problems related to constructing a receding horizon filter for underwate... more This paper discusses the problems related to constructing a receding horizon filter for underwater inertial navigation systems which are subject to external disturbances. Noises are assumed to be bounded, additive, and contained in both state and measurement equations. An estimator is designed according to the sliding-window strategy to minimize the receding horizon estimation cost function. The derived filter is applied to a velocity-aided inertial navigation system. Simulations show that the derived filter is more accurate than the standard Kalman filter (KF) for underwater navigation systems subject to temporary unknown disturbances.
Proceedings of the 2004 International Symposium on Underwater Technology (IEEE Cat. No.04EX869), 2004
... X+X. Y'+ Y" Z'+Z. M'+Mm K'+K, N'+N, U + qsin )tanO+r cos)tanO q... more ... X+X. Y'+ Y" Z'+Z. M'+Mm K'+K, N'+N, U + qsin )tanO+r cos)tanO q cos) - rsin ) (qsin ) + r cos ))sec@ 0 where ), Band yare the roll, pitch, and yaw angles, respectively. M is the inertia mahix, and the additional state 6 denotes the IS linear damping coefficients. ...
This paper describes the estimation of hydrodynamic coefficients and the control algorithm based ... more This paper describes the estimation of hydrodynamic coefficients and the control algorithm based on a nonlinear mathematical modeling for a test bed autonomous underwater vehicle (AUV) named by SNUUV I (Seoul National University Underwater Vehicle I).
Ahstract- This paper describes the mathematical modeling, control algorithm, system design, hardw... more Ahstract- This paper describes the mathematical modeling, control algorithm, system design, hardware implementation and experimental test of a Manta-type Unmanned Underwater Vehicle (MUUV). The vehicle has one thruster for longitudinal propulsion, one rudder for heading angle control and two elevators for depth control. It is equipped with a pressure sensor for measuring water depth and Doppler Velocity Log for measuring position and angle. The vehicle is controlled by an on-board PC, which runs with the Windows XP operating system. The dynamic model of 6DOF is derived including hydrodynamic forces and moments acting on the vehicle, while the hydrodynamic coefficients related to the forces and moments are obtained from experiments or estimated numerically. We also utilized the values obtained from PMM (Planar Motion Mechanism) tests found in the previous publications for numerical simulations. Various controllers such as PID, Sliding mode, Fuzzy and Hen controllers are designed for ...
This study proposes a drag reduction device that uses three ribbons attached 120 degree apart to ... more This study proposes a drag reduction device that uses three ribbons attached 120 degree apart to vertical pipes. Experiments were conducted in a circulating water channel to investigate the effects of the ribbon length and the direction of the flow on various current velocities. Drag on a vertical cylinder was measured by a resistance dynamometer. Flow visualizations were conducted using laser sheet beams. Laser Doppler Velocimetry (LDV) was used to measure the velocity field in the wake. This experiment demonstrates that attached ribbons can be used to reduce the drag force on vertical pipes for various directions of incoming flows. The ribbon-type device is very simple and easy to fabricate for field applications. The results are promising for the application to offshore structures.
This paper discusses the problems related to constructing a receding horizon H∞ filter for underw... more This paper discusses the problems related to constructing a receding horizon H∞ filter for underwater inertial navigation systems which are subject to external disturbances. Noises are assumed to be bounded, additive and contained in both state and measurement equations. The estimator is designed based on the sliding-window strategy in order to minimize the receding horizon estimation cost function. The derived filter is applied to a velocity-aided inertial navigation system. It is clearly demonstrated in simulations that the derived filter is more accurate than an H∞ a priori filter for underwater navigation systems subject to temporary unknown disturbances.
This paper describes concurrent mapping and localization (CML) algorithm suitable for localizing ... more This paper describes concurrent mapping and localization (CML) algorithm suitable for localizing the SNUUV I, a small test autonomous underwater vehicle (AUV) developed by Seoul National University. Increasing use of AUV has led to the development of nontraditional navigation method such as CML. CML is intended to provide relative position by extracting information from the environment that AUV passes through.
In this paper an adaptive receding horizon Kalman filter is newly derived for underwater navigati... more In this paper an adaptive receding horizon Kalman filter is newly derived for underwater navigation systems, which are subject to statistically unknown noises contained in both system and measurement equations. The adaptive receding horizon Kalman filter gets feedback on the method. The filter is applied to a navigation system based on a LBL (long baseline) system. Experiment and simulation show that the derived filter estimates covariance of the system and measurement properly.
Hydrodynamic coefficients strongly affect the dynamic performance of an AUV. Thus it is important... more Hydrodynamic coefficients strongly affect the dynamic performance of an AUV. Thus it is important to have the true values of these coefficients in order to accurately simulate the AUV's dynamic performance. Although these coefficients are obtained experimentally such as through the PMM test, the measured values are not completely reliable because of experimental difficulties and errors involved. Another approach is
Depth and heading control of an AUV are considered for the predetermined depth and heading angle.... more Depth and heading control of an AUV are considered for the predetermined depth and heading angle. The proposed control algorithm is based on a sliding mode control using estimated hydrodynamic coefficients. The hydrodynamic coefficients are estimated with the help of conventional nonlinear observer techniques such as sliding mode observer and extended Kalman filter. By using the estimated coefficients, a sliding mode controller is constructed for the combined diving and steering maneuver. The simulation results of the proposed control system are compared with those of control system with true coefficients. It is demonstrated that the proposed control system makes the system stable and maintains the desired depth and heading angle with sufficient accuracy
For a long cylinder floating on the sea surface, incident sea waves with a narrow frequency band ... more For a long cylinder floating on the sea surface, incident sea waves with a narrow frequency band excite body oscillations of short and long periods. Depending on the stiffness of the mooring system, the body displacement of the long-period motion can be comparable with, or even greater than that of the short-period oscillations. By combining the asymptotic methods of multiple scales and inner and outer expansions, we describe an essentially analytical theory for slow sway of both small and large amplitudes. Besides showing results for various quasi-steady and transient incident waves for a rectangular cylinder, we examine the effect of the gap between the keel of the body and the sea bottom. It is found in particular that a small gap can enhance moderate resonance by blocking the flow due to long waves and increase the apparent mass of the cylinder. Real-fluid effects are not included.
Journal of the Society of Naval Architects of Korea
Nonlinear free surface flow phenomena have teen studied by several kinds of numerical methods, of... more Nonlinear free surface flow phenomena have teen studied by several kinds of numerical methods, of which boundary element method has been known as most promising one. There, however, remain many difficulties to be solved in the numerical procedures by boundary element analysis. In this paper, an efficient calculation of elemental integrals and iterative solution algorithm for the resulting system of equations were thoroughly investigated in order to enhance the procedure of the boundary element analysis. Advantages of the herein developed boundary element analysis code are demonstrated in terms of accuracy and convergence for typical boundary-value problems with free surface.
Journal of the Society of Naval Architects of Korea
This study is constructed to investigate the sloshing effect on the motions of a two-dimensional ... more This study is constructed to investigate the sloshing effect on the motions of a two-dimensional rectangular cylinder experimentally and numerically. The modes of motion under consideration are sway and roll, and also experimental cases are divided by two categories; 1-DoF roll motion and 2-DoF motion (Coupling sway and roll). It is found that the sway response is considerably affected by the motion of the fluid, particularly near the sloshing natural frequency, while the roll response changes comparatively small. The dominant mode of motion is analyzed for 2-DoF experiments as well. The measured data for 1-DoF motions is compared with numerical results obtained by the Multi-modal approach. The numerical schemes vary in detail with the number of dominant sloshing modes; i.e. there is a single dominant mode for the Single-dominant method, while the Model 2 method assumes that the first two modes are superior. For the roll motion, numerical results obtained by the two different method...
This paper discusses the problems related to constructing a receding horizon filter for underwate... more This paper discusses the problems related to constructing a receding horizon filter for underwater inertial navigation systems which are subject to external disturbances. Noises are assumed to be bounded, additive, and contained in both state and measurement equations. An estimator is designed according to the sliding-window strategy to minimize the receding horizon estimation cost function. The derived filter is applied to a velocity-aided inertial navigation system. Simulations show that the derived filter is more accurate than the standard Kalman filter (KF) for underwater navigation systems subject to temporary unknown disturbances.
Proceedings of the 2004 International Symposium on Underwater Technology (IEEE Cat. No.04EX869), 2004
... X+X. Y'+ Y" Z'+Z. M'+Mm K'+K, N'+N, U + qsin )tanO+r cos)tanO q... more ... X+X. Y'+ Y" Z'+Z. M'+Mm K'+K, N'+N, U + qsin )tanO+r cos)tanO q cos) - rsin ) (qsin ) + r cos ))sec@ 0 where ), Band yare the roll, pitch, and yaw angles, respectively. M is the inertia mahix, and the additional state 6 denotes the IS linear damping coefficients. ...
This paper describes the estimation of hydrodynamic coefficients and the control algorithm based ... more This paper describes the estimation of hydrodynamic coefficients and the control algorithm based on a nonlinear mathematical modeling for a test bed autonomous underwater vehicle (AUV) named by SNUUV I (Seoul National University Underwater Vehicle I).
Ahstract- This paper describes the mathematical modeling, control algorithm, system design, hardw... more Ahstract- This paper describes the mathematical modeling, control algorithm, system design, hardware implementation and experimental test of a Manta-type Unmanned Underwater Vehicle (MUUV). The vehicle has one thruster for longitudinal propulsion, one rudder for heading angle control and two elevators for depth control. It is equipped with a pressure sensor for measuring water depth and Doppler Velocity Log for measuring position and angle. The vehicle is controlled by an on-board PC, which runs with the Windows XP operating system. The dynamic model of 6DOF is derived including hydrodynamic forces and moments acting on the vehicle, while the hydrodynamic coefficients related to the forces and moments are obtained from experiments or estimated numerically. We also utilized the values obtained from PMM (Planar Motion Mechanism) tests found in the previous publications for numerical simulations. Various controllers such as PID, Sliding mode, Fuzzy and Hen controllers are designed for ...
This study proposes a drag reduction device that uses three ribbons attached 120 degree apart to ... more This study proposes a drag reduction device that uses three ribbons attached 120 degree apart to vertical pipes. Experiments were conducted in a circulating water channel to investigate the effects of the ribbon length and the direction of the flow on various current velocities. Drag on a vertical cylinder was measured by a resistance dynamometer. Flow visualizations were conducted using laser sheet beams. Laser Doppler Velocimetry (LDV) was used to measure the velocity field in the wake. This experiment demonstrates that attached ribbons can be used to reduce the drag force on vertical pipes for various directions of incoming flows. The ribbon-type device is very simple and easy to fabricate for field applications. The results are promising for the application to offshore structures.
This paper discusses the problems related to constructing a receding horizon H∞ filter for underw... more This paper discusses the problems related to constructing a receding horizon H∞ filter for underwater inertial navigation systems which are subject to external disturbances. Noises are assumed to be bounded, additive and contained in both state and measurement equations. The estimator is designed based on the sliding-window strategy in order to minimize the receding horizon estimation cost function. The derived filter is applied to a velocity-aided inertial navigation system. It is clearly demonstrated in simulations that the derived filter is more accurate than an H∞ a priori filter for underwater navigation systems subject to temporary unknown disturbances.
This paper describes concurrent mapping and localization (CML) algorithm suitable for localizing ... more This paper describes concurrent mapping and localization (CML) algorithm suitable for localizing the SNUUV I, a small test autonomous underwater vehicle (AUV) developed by Seoul National University. Increasing use of AUV has led to the development of nontraditional navigation method such as CML. CML is intended to provide relative position by extracting information from the environment that AUV passes through.
In this paper an adaptive receding horizon Kalman filter is newly derived for underwater navigati... more In this paper an adaptive receding horizon Kalman filter is newly derived for underwater navigation systems, which are subject to statistically unknown noises contained in both system and measurement equations. The adaptive receding horizon Kalman filter gets feedback on the method. The filter is applied to a navigation system based on a LBL (long baseline) system. Experiment and simulation show that the derived filter estimates covariance of the system and measurement properly.
Hydrodynamic coefficients strongly affect the dynamic performance of an AUV. Thus it is important... more Hydrodynamic coefficients strongly affect the dynamic performance of an AUV. Thus it is important to have the true values of these coefficients in order to accurately simulate the AUV's dynamic performance. Although these coefficients are obtained experimentally such as through the PMM test, the measured values are not completely reliable because of experimental difficulties and errors involved. Another approach is
Depth and heading control of an AUV are considered for the predetermined depth and heading angle.... more Depth and heading control of an AUV are considered for the predetermined depth and heading angle. The proposed control algorithm is based on a sliding mode control using estimated hydrodynamic coefficients. The hydrodynamic coefficients are estimated with the help of conventional nonlinear observer techniques such as sliding mode observer and extended Kalman filter. By using the estimated coefficients, a sliding mode controller is constructed for the combined diving and steering maneuver. The simulation results of the proposed control system are compared with those of control system with true coefficients. It is demonstrated that the proposed control system makes the system stable and maintains the desired depth and heading angle with sufficient accuracy
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