• The Journal of the Acoustical Society of Korea
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• v.38 no.2
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• pp.161-167
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• 2019

In this paper, the performance verification of an around-view sonar and an excavation depth measuring sonar applicable to track-based ROVs (Remotely Operated underwater Vehicles) for heavy duty work is studied. For the performance verification, an experiment is carried out in a water tank and at sea by attaching the around-view sonar and the excavation depth measuring sonar for a heavy work ROV. In the case of the around-view sonar, image sonars are mounted on ROV in four directions (front, back, left and right) and in the case of the excavation depth measuring sonar, the same kind of MBES (Multi Beam Echo Sounder) is mounted on the front of the ROV. The result of an operation test of the ROV equipped with these sonars shows that the sonar systems are rarely affected by high turbidity due to sedimentation during the operation. In the case of the around-view sonar, it is possible to see rock formation, gravel and sandbank 30 m ahead of the ROV. It is confirmed that the excavation depth can be measured after the ROV has performed the excavation. This experiment demonstrates that the ROV can improve the efficiency of the work by utilizing the around-view sonar and the excavation depth measuring sonar.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.235-235
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• 2003

• The Journal of the Korea institute of electronic communication sciences
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• v.8 no.1
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• pp.27-40
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• 2013

This study is about development of technology system for an advanced deep-sea unmanned underwater robot of S. Korea analysed by the application of scenario planning. It was developed a 6000m class next-generation deep-sea unmanned underwater vehicle(or robot, UUV) system, soonly ROV 'Hemire' and Depressor 'Henuvy' in 2006 at S. Korea and motion control, adaptive control algolithm, a work-space manipulator control algolithm, especially the underwater inertial-acoustic navigation system robust to initial errors and sensor failures. But there are remained matters on position tracking of the USBL, inertial-acoustic navigation system, attitude sensor, designed sonar sensors. So this study suggest the new idea for settle the matters and then this idea help the development of the underwater inertial-acoustic navigation system robust to initial errors and sensor failures, such as acoustic signal drop-out, by modifying the error covariance of the failed sonar signal when drop-out occurs. As a result, the future policy for deep-sea unmanned underwater robot of S. Korea is to further spur the development of new technology and more improvement of the technology level for deep-sea unmanned underwater robot system with indicator and imaginary wall as external device.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.2
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• pp.159-168
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• 2019

This study was designed to investigate the physiological response of humans to alcohol during underwater activity and to complete related risk analysis. After comparing human responses to alcohol during underwater activity, we analyzed physiological changes and risk level using a new risk analysis method developed in this study, 'Risk Assessment and Analysis (RAA)'. RAA is a modified method based on an internal control frame work. It has 3 steps, the first of which is to analyze risk correlation. The second step is to quantify risk and build a risk database. The last step is to analyze the diagramed risk map. Using RAA, the risk levels of alcohol use underwater were calculated and diagramed. The diagramed risk map was then used to analyze the difference between risk levels underwater before and after alcohol use. As a result, it was found that risk level underwater increased after alcohol use. This study shows alcohol use increases the ratio of high risk groups during underwater activity. It also indicates that risk levels can be quantified according to the likelihood and impairment scale, which can potentially help in identifying high risk groups for intensive management underwater.

• Journal of Preventive Medicine and Public Health
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• v.17 no.1
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• pp.211-215
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• 1984

Forty one male workers employed in an underwater construction field were surveyed in the viewpoints of epidemiological analysis of decompression sickness (caisson's disease). Nineteen out of the entire forty one workers have been, or had been suffering from decompression sickness (as 46.3% of incidence rate) after decompression. The results obtained were as follows: 1. There was a significant relation between duration of work and incidence of disease. 2. Type II (severe type) comprised majority of cases (16 cases, 84.2%) despite any significant correlations were not present between severity types and recompression times. 3. Most frequently cited symptoms were lower limb pain (89.5%), upper limb pain (79.0%), pruritus (68.4%) and so on, however, 10% of patients complained of neurological symptoms. 4. There were not any significant correlations between disease incidence and worker's age or relative body weight.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1116-1120
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• 2004

In the nuclear power plant, there are several cylindrical vessels such as reactor vessel, pressuriser and so on. The vessels are usually constructed by welding large rolled plates, forged sections or nozzle pipes together. In order to assure the integrity of the vessel, these welds should be periodically inspected using sensors such as ultrasonic transducer or visual cameras. This inspection is usually conducted under water to minimize exposure to the radioactively contaminated vessel walls. The inspections have been performed by using a conventional inspection machine with a big structural sturdy column, however, it is so huge and heavy that maintenance and handling of the machine are extremely difficult. It requires much effort to transport the system to the site and also requires continuous use of the utility's polar crane to move the manipulator into the building and then onto the vessel. Setup beside the vessel requires a large volume of work preparation area and several shifts to complete. In order to resolve these problems, we have developed an underwater mobile robot guided by the laser pointer, and performed a series of experiments both in the mockup and in the real reactor vessel. This paper introduces our robotic inspection system and the laser guidance of the mobile robot as well as the results of the functional test.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.4
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• pp.382-389
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• 2017

We are developing a prototype underwater glider for subsea payload delivery. The idea is to use a glider to deliver payloads for subsea installations. In this type of application, the hydrodynamic forces and dynamic stability of the glider is of particular importance, as it has implications on the glider's endurance and operation. In this work, the effect of two different wing forms, rectangular and tapered, on the hydrodynamic characteristics and dynamic stability of the glider were investigated, to determine the optimal wing form. To determine the hydrodynamic characteristics, tow tank resistance tests were carried out using a model fitted alternately with a rectangular wing and tapered wing. Steady-state CFD analysis was conducted using the hydrodynamic coefficients obtained from the tests, to obtain the lift, drag and hydrodynamic derivatives at different angular velocities. The results show that the rectangular wing provides larger lift forces but with a reduced stability envelope. Conversely, the tapered wing exhibits lower lift force but improved dynamic stability.

• Journal of Advanced Research in Ocean Engineering
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• v.3 no.3
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• pp.136-148
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• 2017

The paper presents dual arm ROV manipulation using deep reinforcement learning. The purpose of this underwater manipulator is to investigate and excavate natural resources in ocean, finding lost aircraft blackboxes and for performing other extremely dangerous tasks without endangering humans. This research work emphasizes on a self-learning approach using Deep Reinforcement Learning (DRL). DRL technique allows ROV to learn the policy of performing manipulation task directly, from raw image data. Our proposed architecture maps the visual inputs (images) to control actions (output) and get reward after each action, which allows an agent to learn manipulation skill through trial and error method. We have trained our network in simulation. The raw images and rewards are directly provided by our simple Lua simulator. Our simulator achieve accuracy by considering underwater dynamic environmental conditions. Major goal of this research is to provide a smart self-learning way to achieve manipulation in highly dynamic underwater environment. The results showed that a dual robotic arm trained for a 3DOF movement successfully achieved target reaching task in a 2D space by considering real environmental factor.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.708-713
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• 2004

This research develops a sensorless hydraulic servo system of Parallel-Typed robot for harbour construction. Purpose of the robot is to mechanize the construction, which is accomplished through a joystick's operating by a stoneworker (or diver). The robot is attached on the end of an excavator as its attachment or transported by a crane to reach the desired place. The embedded compact controller is installed on the robot body and controlled by wireless telecommunication. For underwater work, it is necessary to waterproof the robot and its sensors. Especially, a sensor waterproof is a main drawback for the underwater robot. This leads us to develop a hydraulic robot position controller using an observer which gives the position information without any position sensor. We design a neural network to identify the displacement change according to the command voltage to servo valve. To verify the sensorless controller, this paper presents the performance of the sensorless control for which the position is given by the observer comparing with that of the sensor control for which the position is measured by LVDT sensors.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.2
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• pp.128-133
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• 2008

This paper describes underwater discharge phenomena and breakdown characteristics in case that the standard lightning impulse voltage is injected to the needle and spherical electrodes installed in the hemisphere water tank. The objective of this work is to understand the basic features related to transient ground impedance against lightning surges. The discharge luminous images were observed and the dependence of breakdown voltage on the polarity of applied voltage and water resistivity were investigated. As a consequence, streamer corona is initiated at the tip of needle and spherical electrodes and is propagated toward grounded tank with stepwise extension. The breakdown voltage characteristics measured as a function of water resistivity showed V-shaped curves. Breakdown voltage and time curve of needle electrode is higher than that of spherical electrode.