• Journal of the Korea Institute of Military Science and Technology
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• v.6 no.2
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• pp.20-34
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• 2003

The good sea-keeping capability of the SWATH(Small Waterplane Area Twin Hull) ship has been attractive for research or surveillance vessels. Especially, for the naval ships accomplishing the underwater acoustic missions, it is necessary to access and minimize the underwater radiated noise level generated by the ships. Therefore, acoustic signature management and control are very important topics for these vessels. Underwater radiation pattern in the low frequency range is dominated by the tonals from the vibration of onboard machinery. In this work, the radiated noise level generated by the propulsion machine in the submerged hull is predicted using the transfer function technique and the hull transfer function for the submerged hull is determined by analyzing the longitudinal/circumferential stiffened infinitely long cylindrical shell and considering the empirical database of the previous vessels. It is confirmed that the transfer function technique can give useful information for identifying the noise source and estimating its contribution to the total radiatied noise level.

• Journal of Ocean Engineering and Technology
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• v.27 no.2
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• pp.114-120
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• 2013

A superhydrophobic surface means that the contact angle between the solid surface and a water droplet is more than $150^{\circ}$. Materials with a superhydrophobic surface have a self-cleaning function because of the Lotus effect, in which water is not absorbed by the material but rolls off of it. If such a Lotus effect can be applied to the surface of underwater vessels, submarines, torpedos, and so on, enhanced vessels can be made based on this lubricant effect reducing the friction coefficient for the liquid. Because polymer composites can be easily applied in various nanotechniques, they are more advantageous than conventional materials like iron in terms of a superhydrophobic surface. Furthermore, a superhydrophobic surface bring enhanced anticorrosion and ecotechnology because no paint is needed on underwater vessels.

• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.1
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• pp.42-48
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• 2019

Since the underwater telephone was sold in a short time, there are few repair equipments. And equipment is difficult to locate fault. Equipment with transducers must be inspected underwater, and a relative naval vessels is required to perform an operational check. So we developed a tester device to test the transmission card through the spectrum and transmission power, and to develop a device that can conduct operational tests on land. Therefore, the development of the tester reduces the incidence of naval vessels and contributes to the development of domestic underwater communication test equipment.

• International Journal of Ocean System Engineering
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• v.3 no.3
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• pp.136-141
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• 2013

The present research was aimed at comparing performance of metallic and polymer composite shells of a typical underwater vessel of length and inner diameter of 1650 mm and 350 mm respectively, based on the critical buckling pressure for operating depth of 1000 m using ANSYS. High strength steel, aluminium alloy, titanium alloy, glass / epoxy and carbon / epoxy materials were examined. The results indicated weight savings of 46 % in carbon/epoxy and 31 % in glass / epoxy when compared with high strength steel, based on the thickness of the shell for sustaining 10 MPa buckling pressure.

• Journal of Sensor Science and Technology
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• v.31 no.5
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• pp.330-336
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• 2022

This paper proposes a method to calibrate the electrode misplacement in underwater electric field sensor arrays (EFSAs) for accurate measurements of underwater electric field signatures. The electrode misplacement of an EFSA was estimated by measuring the electric field signatures generated by a known electric source and by comparing the measurements with the theoretical calculations under similar measurement conditions. When the EFSA measured the electric field signatures induced by an unknown electric source, the electric properties of the unknown electric source were approximated by considering the optimized estimation of the electrode misplacement of the EFSA. Finally, the measured electric field signatures were calibrated by calculating the theoretical electric field signatures to be measured with an ideally installed EFSA without electrode misplacement; the approximated electric properties of the unknown electric source were also taken into account. Simulations were conducted to test the proposed calibration method. The results showed that the electrode misplacement could be estimated. Further, the electric field measurements and the electric field-based localization of underwater vessels became more accurate after the application of the proposed calibration method. The proposed method will contribute to applications such as the detection and localization of underwater electric sources, which require accurate measurements of underwater electric field signatures.

• Journal of Ocean Engineering and Technology
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• v.20 no.3 s.70
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• pp.7-14
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• 2006

This paper discusses the structural design and analysis of a 6,000 meters depth-rated capable deep-sea unmanned underwater vehicle (UUV) system. The UUV system is currently under development by Maritime and Ocean Engineering Research Institute(MOERI), Korea Ocean Research and Development Institute (KORDI). The UUV system is composed of three vehicles - a Remotely Operated Vehicle (ROV), an Autonomous Underwater Vehicle (AUV) and a Launcher - which include underwater equipment. The dry weight of the system exceeds 3 tons hence it is necessary to carry out the optimal design of structural system to ensure the minimum weight and sufficient space within the frame for the convenient use of the embedded equipments. In this paper, therefore, the structural design and analysis of the ROV and launcher frame system were carried out, using the optimizing process. The cylindrical pressure vessels for the ROV were designed to resist the extreme pressure of 600 bars, based on the finite element analysis. The collapse pressure for the cylindrical pressure vessels was also checked through a theoretical analysis.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.109.5-109
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• 2002

Autonomous underwater vehicles (AUVs) are unmanned underwater vessels to investigate sea environments, oceanography and deep-sea resources autonomously. Docking systems are required to increase the capability of the AUVs to recharge the batteries and to transmit data in real time in underwater. This paper presents a visual servo control system for an AUV to dock into an underwater station with a camera. To make the visual servo control system , this paper derives an optical flow model of a camera mounted on an AUV, where a CCD camera is installed at the nose center of the AUV to monitor the docking condition. This paper combines the optical flow equation of the camera with the AUV's equation o...

• Journal of Ocean Engineering and Technology
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• v.17 no.1
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• pp.1-7
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• 2003

Autonomous underwater vehicles (AUVs) are unmanned, underwater vessels that are used to investigate sea environments in the study of oceanography. Docking systems are required to increase the capability of the AUVs, to recharge the batteries, and to transmit data in real time for specific underwater works, such as repented jobs at sea bed. This paper presents a visual :em control system used to dock an AUV into an underwater station. A camera mounted at the now center of the AUV is used to guide the AUV into dock. To create the visual servo control system, this paper derives an optical flow model of a camera, where the projected motions of the image plane are described with the rotational and translational velocities of the AUV. This paper combines the optical flow equation of the camera with the AUVs equation of motion, and deriver a state equation for the visual servo AUV. Further, this paper proposes a discrete-time MIMO controller, minimizing a cost function. The control inputs of the AUV are automatically generated with the projected target position on the CCD plane of the camera and with the AUVs motion. To demonstrate the effectiveness of the modeling and the control law of the visual servo AUV simulations on docking the AUV to a target station are performed with the 6-dof nonlinear equations of REMUS AUV and a CCD camera.

• 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.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.16 no.1
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• pp.30-36
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• 2020

In SMART, the flow mixing header assembly (FMHA) is used to mix the coolant flowing into the reactor core to maintain a uniform temperature. The FMHA is designed to have enough stiffness so the resonance with reactor internal structures does not occurs during the pipe break and the seismic accidents. Since the gap between the FMHA and the core support barrel assembly is very narrow compared with the diameter of FMHA, the hydrodynamic mass effect acting on the FMHA is not negligible. Therefore the hydrodynamic mass characteristics on the FMHA are investigated to consider the fluid and structure interaction effects. The result of modal analysis for the dry and underwater conditions, the natural frequency of primary vibration mode for the horizontal direction is reduced from 136.67 Hz to 43.76 Hz. Also the result of frequency response spectrum seismic analysis for the dry and underwater conditions, the maximum equivalent stress are increased from 13.89 MPa to 40.23 MPa. Therefore, reactor internal structures located in underwater condition shall consider carefully the hydrodynamic mass effects even though they have sufficient stiffness required for performing its functions under the dry condition.