Hangil Joe

Time-Delay Controller Design for Position Control of Autonomous Underwater Vehicle Under Disturbances

This paper presents an enhanced time-delay controller (TDC) for the position control of an autonomous underwater vehicle (AUV) under disturbances. A conventional TDC performs well when the involved data acquisition rate is fast. However, in AUV control applications that use a Doppler velocity log (DVL) navigation system, we cannot keep the data acquisition rate sufficiently fast because a DVL sensor generally supplies data at a slow acquisition rate, which degrades the performance of the TDC. To overcome this problem, we propose an integral sliding-mode controller to be supplemented to the conventional TDC to improve the control precision even if the DVL navigation system is in operation. The proposed controller is computationally simple and robust to unmodeled dynamics and disturbances. We performed computer simulations and experiments with the Cyclops AUV to demonstrate the validity of the proposed controller.

Integral sliding mode controller for precise manoeuvring of autonomous underwater vehicle in the presence of unknown environmental disturbances

We propose an integral sliding mode controller (ISMC) to stabilse an autonomous underwater vehicle (AUV) which is subject to modelling errors and often suffers from unknown environmental disturbances. The ISMC is effective in compensating for the uncertainties in the hydrodynamic and hydrostatic parameters of the vehicle and rejecting the unpredictable disturbance effects due to ocean waves, tides and currents. The ISMC is comprised of an equivalent controller and a switching controller to suppress the parameter uncertainties and external disturbances, and its closed-loop system is exponentially stable. Numerical simulations were performed to validate the proposed control approach, and experimental tests using Cyclops AUV were carried out to demonstrate its practical feasibility.

Development of mooring-less robotic buoy system using wave powered renewable energy

For long-term operation, a wave-energy harvesting robotic buoy system that holds position automatically without anchoring line is proposed. We made a prototypes which consists of the propulsion system and power generation system. We adopted the Wave glider platform to hold the buoy position without mooring, and developed a flip-type self-rectifying wave turbine system (WTS). We developed modeling equations to describe the proposed system and simulated them using numerical software, then tested their station-keeping ability and energy-harvesting power in wave tank. Developed prototype patrolled within a 3-m diameter area, and the WTS generated 10.1 W of power. The station-keeping area was smaller than that of the existing mooring buoy, which means that the robotic buoy system can obtain precise and accurate observation data in the ocean without additional costs for mooring systems, and its wave-harvested energy can provide sufficient electric power to maintain the whole system.

Development of passive acoustic landmark using imaging sonar for AUV's localization

We proposed and tested a passive acoustic landmark that can provide accurate navigation information for an autonomous underwater vehicle (AUV). The AUV used imaging sonar mounted on the vehicle to recognize shadows of the columntype landmark, and can measure vehicles own pose and relative position from the landmark which was set in a known position. The results of the proposed method had acceptable error (<;1 %) in the calculated position of the AUV. The proposed localization method will be useful to correct drift errors of inertial navigation systems for the AUV or to find the same position repeatedly.

Development of energy-harvesting unit and propulsion unit for a robotic buoy system

In this paper, we described about development of a robotic buoy for Internet of maritime thins (IoMT) technology. For IoMT, stand-alone data conllector is a key technology. The energy harvesting robotic buoy is proposed in the context. The proposed system is composed of three components: propulsion system, energy harvesting system, and buoyancy control system. The proposed system can hold its position within an uniform bound without mooring, and harvests wave energy. As a preliminary study, we developed hydrodynamic model for the whole system, and conducted simulation. Through the simulation, we implemented station keeping algorithm, and investigated optimal design parameters. To verify the simulation results we constructed prototype and carried out a series of experiments: station-keeping test, and power generation test. As a result, the whole system was proved that the propulsion system has sufficient manoeuvrability for station keeping within 3 m, and peak power generation was 8 W.

A new wave energy converter using flap-type blade and its power generation test

Wave energy is obvious source for renewable energy harvesting in oceans. A new WEC named wave turbine was proposed. The proposed system consists of a floating body and a submerged body. The floating body is same with that of a conventional buoy, and the submerged body is a power take off similar to a turbine which has flap-type blades in a round-frame rotor. To describe the proposed system, we developed numerical model. The performance of the proposed system was determined by several parameters: wave conditions, floating body geometry, blade shape, rotor hub design, and power storage system including generator and electrical load. Quantitative simulation was conducted to find optimal parameters including design of blade and rotor hub size. In addition, we constructed a prototype to conduct experiments. 4 types of blades were tested in power generation test, and the results was compared.

Multi-body point absorber system without a mooring

In this paper, we propose a multi-body point absorber system which can harvest ocean wave energy without needing a mooring. The proposed multi-body point absorber system consists of two elements: a multi-body point absorber that extracts the power from the wave, and a Wave Glider that keeps the whole system within a prescribed area. We describe the concept of proposed system. We analyze the heave dynamics of the multi-body point absorber and performed numerical simulations to validate its feasibility.

Red snow crab habitat monitoring using autonomous deep sea camera

An autonomous underwater camera is developed for monitoring the red snow crab habitat in deep sea. Most of the deep sea cameras are designed such that they can be used with special deep sea exploration instruments such as underwater vehicles. However, a developed camera can be attached to the fish traps for catching the red snow crab, and fishermen who are not underwater camera experts can handle this camera as well. Because the camera is an all-in-one type device that includes all electrical components for video recording such as the camera module, lights, and battery in a single cylindrical pressure housing, the camera can be used for periodical and frequent deep sea video recording along with fishing operations. Red snow crabs living on the seafloor, 1,000 m deep, are recorded using the camera, and the seasonal change in their activity is monitored.

On preprocessing methods for feature-based photo-mosaic underwater

In this paper, we studied some pre-process methods that make the feature matching faster, accurate and proper to be used in the photo mosaic process. Two properties and two image processing technique were considered: channel, size, contrast enhancement, and Gaussian smoothing. We investigated how they affect the feature quantity and matching result by controling related parameters. The smallest number of features were found in the red channel. As the image size decrease, the quantity of features and the computing time were decreased in the same manner in terms of ratio. Contrast enhancement methods made image features more distinct, but its amplification in the feature quantity was not that significant. The Gaussian smoothing increased the quantity of features in the way it has the maxima with an optimal sigma, blurring parameter. When the pre-processes are used in combination, the feature matching between pair images was improved 1.6 times more in quantity.

Iceberg worm: Biomimetic AUV for sea ice thickness survey using non-contact laser ultrasonic method

We propose a robot, named Iceberg worm, clinging to lower surface of ice shelf (or iceberg) for ice thickness measurement. The key technologies of the proposed robot are 1) Inverse buoyancy setting and adjustable buoyancy control system; 2) Biomimetic legs and crampons like insects feet; 3) Non-contact laser-ultrasonic ranging system; 4) Acoustic-taxis navigation like positive photo-taxis of bugs. A distinguishing characteristic of the proposed system is non-contact ice thickness measurement system by using laser-induced ultrasound, which improves measurement method on the cold and non-homogeneous rough surface of ice. In this paper, we presented technical issues to develop the proposed robot and imaginary methodologies.