Yong-Kon Lim

Technical communique: Point-to-point navigation of underactuated ships

This paper considers point-to-point navigation of underactuated ships where only surge force and yaw moment are available. In general, a ships sway motion satisfies a passive-boundedness property which is expressed in terms of a Lyapunov function. Under this kind of consideration, a certain concise nonlinear scheme is proposed to guarantee the closed-loop system to be uniformly ultimately bounded (UUB). A numerical simulation study is also performed to illustrate the effectiveness of the proposed scheme.

Discrete-time quasi-sliding mode control of an autonomous underwater vehicle

This paper presents a discrete-time quasi-sliding mode controller for an autonomous underwater vehicle (AUV) in the presence of parameter uncertainties and a long sampling interval. The AUV, named VORAM, is used as a model for the verification of the proposed control algorithm. Simulations of depth control and contouring control are performed for a numerical model of the AUV with full nonlinear equations of motion to verify the effectiveness of the proposed control schemes when the vehicle has a long sampling interval. By using the discrete-time quasi-sliding mode control law, experiments on depth control of the AUV are performed in a towing tank. The controller makes the system stable in the presence of system uncertainties and even external disturbances without any observer nor any predictor producing high rate estimates of vehicle states. As the sampling interval becomes large, the effectiveness of the proposed control law is more prominent when compared with the conventional sliding mode controller.

Performance Analysis of Channel Compensation and Channel Coding Techniques based on Measured Maritime Wireless Channel in VHF-band Ship Ad-hoc Network

In this paper, the parameters of the RTT (Radio Transmission Techniques) for SANET (Ship Ad-hoc NETwork), which is considered for the next generation maritime communication systems, are set up. A channel model has been analyzed based on the practical measured maritime wireless channel in VHF (Very-High Frequency) for SANET system. Also, by considering the frame structure including preamble, guard time and pilots for both single and multi-carrier systems, the BER (Bit Error Rate) performances are evaluated and analyzed in the aspects of channel compensation and channel coding techniques. Based on the simulation results, optimal modulation & coding schemes are suggested for SANET. That is, in single-carrier system by using differential modulation schemes, channel compensation is not necessary. However, channel coding is helpful to achieve additional gain. On the other hand, when 16-QAM modulation is employed in multi-carrier system, the implementation of both channel compensation and channel coding techniques show huge performance gain for various of K values, which are related to different maritime environments, and the rolling effects of wave.

Design of radio transmission technologies for VHF band ship ad-hoc network

For the purpose of providing high data rate real-time services, radio transmission technologies for ship ad-hoc network are designed in this paper. Based on the Recommendation ITU-R 1842–1, physical layer parameters of SANET are contrived to meet the requirements of that specification. Furthermore, the multi-hop frame structure for SANET is proposed and the link-level system performances are evaluated based on the designed parameters. Under the measured maritime channel environment, simulation results show not only the BER comparisons, but also the optimal MCS level for single carrier SANET with the bandwidth of 25 kHz.

Review on Underwater Navigation System Based on Range Measurements from One Reference

This paper reviews the underwater navigation system based on range measurements from a known reference station and extends it to 3-dimensional coordinate. We formulate the state equation in polar coordinate and derive a condition to keep observability of the navigation system. An autonomous underwater vehicle cruising with constant speed can estimate its trajectory with range measurements and additional depth, heading and pitch sensors only. Simulation studies are performed to evaluate the underwater navigation of a maneuvering AUV with range measurements. Simulation results illustrate that the extended navigation system provides convergence of the states estimates even with initial position errors.

Modified linear terminal guidance for docking and a time-varying ocean current observer

Unidirectional docking of a torpedo-type underactuated AUV (Autonomous Underwater Vehicle) has been developed. In this paper, guidance scheme considering drift caused by ocean currents will be investigated. To compensate drift, we design an ocean current observer. The observer is based on kinematic equations of the AUV. We also suggest a guidance scheme based on linear terminal guidance using the observer. The LTG (Linear Terminal Guidance) is in the framework of optimal control but there is no compensation against external disturbances. The conventional linear terminal guidance is modified to be adapted to unidirectional docking compensating the effect of ocean currents. Simulation results are also included.

System design of an ROV with manipulators and adaptive control of it

A remotely operated vehicle (ROV) equipped with two manipulators and an underwater stereo camera is being developed in KRISO (Korea Research Institute of Ships and Ocean Engineering) for seabed working. This paper describes the preliminary design of the ROV. An underwater stereo camera has been developed to enhance the working efficiency of the ROV with the manipulator in seabed operation. This paper presents the operational principle and the structure of the underwater stereo camera. The stereo camera consists of two CCD cameras and horizontally moving base, and it is embedded in a small pressure canister for underwater application. This paper also evaluates the implementation of an adaptive controller to the tracking control of the ROV/manipulator system.

A model estimation and multi-variable control of an unmanned surface vehicle with two fixed thrusters

This paper presents a dynamic model estimation using system identification (SI) technique and a multivariable controller design for an unmanned surface vehicle (USV) with two fixed thrusters. The catamaran shaped USV has been developed for marine research and surveying exploration in costal area. To validate the automatic control performance of USV, which is designed by classical PID controller, we carried out experiments to keep the USVs position at a fixed point and to track predefined positions. As a result, we have found that it needs time-consuming efforts to tuning the weight between heading and speed controller since the yawing and surge motions are tightly coupled to the two thrusters. In order to solve the problem, it is necessary to introduce the multivariable controller design method. And a numerical dynamic model is required for the model based design. This paper addresses the estimation of a dynamic model of the USV based on the experimental results and the design of Linear-Quadratic (LQ) controller based on a multivariable control method. To verify the efficiency of the designed controller using the estimated dynamic model, numerical simulations were carried out.

Time-varying Underwater Acoustic Channel Modeling for Moving Platform

This paper is concerned with modeling the time-varying underwater acoustic channel especially when its time variability is induced by transmitter and/or receiver motion. The relative motion between transmitter and receiver creates a Doppler shift of the received signal and introduces a time-scale variation to the channel which is characterized by Doppler spread and channel coherence time. In order to simulate the physically probable time-varying channel, we suggest a channel model which is based on the ray theory. It exploits the eigen-ray information of ray tracing to determine the discrete signal transmission paths and adds them to random diffusive multipaths whose amplitude and phase are modeled by Rayleigh and uniform distribution, respectively. If the carrier frequency is quite large, it satisfies the uncorrelated scattering assumption and gives the scattering function which shows how the signal is distributed over range and frequency. We apply the suggested model to a case of an underwater platform moving in the shallow water and present its result.

Underwater docking approach of an under-actuated AUV in the presence of constant ocean current

Abstract Underwater docking of an AUV (Autonomous Underwater Vehicle) provides a means of data transmit and battery recharge to extend the endurance capability of the vehicle. In this paper, we consider a torpedo-shaped under-***actuated vehicle and a funnel-shaped unidirectional docking station. The problem is that the desired heading to approach to the docking station compensating the effect of ocean current is different from the desired heading to be aligned to the direction of the dock entrance. We propose final approaching and guidance scheme in the terminal phase of underwater docking considering the effect of ocean current. A conventional PID controller for path following and a bang-bang controller for the final alignment are adopted. Switching criterion between two controllers is proposed. Simulation was carried out to validate the proposed scheme and results are included.