• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.19-19
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• 2020

한강 하구는 매우 다이나믹한 공간이다. 서해의 조석변화가 한강과 임진강에 영향을 미치는 동시에 한강과 임진강의 영향이 조석에도 영향을 미친다. 한강과 임진강의 유량은 서로에게도 영향을 미친다. 결과적으로 한강, 임진강, 조석이 서로 밀접하게 영향을 미치는 곳이 한강 하구이다. 그러나 지금까지 군사적인 문제로 인해 한강 하구에 대한 조사나 분석은 많이 이루어질 수 없었다. 그로인해 하구의 수리적인 영향이 정확하게 분석되지 못하였다. 본 연구에서는 한강 하구의 흐름 모의 결과를 바탕으로 조석변화의 특성을 분석하였다. 또한 신곡수중보 주위의 흐름 조사 결과를 바탕으로 하구에서 발생하는 조석 변화의 영향도 분석하였다. 한강 본류의 경우 평상시 조석이 영향을 미치는 범위는 잠실수중보 직하류까지이다. 한강 본류에 계획홍수량이 흐르는 경우 한강대교 지점에는 조석의 영향이 나타나지 않으며, 약 10,000cms 이상의 홍수량에서는 조석영향이 거의 나타나지 않는 것으로 분석되었다. 임진강의 경우에도 계획 홍수량이 흐를 경우 조석이 영향을 미치는 범위는 하구부 일정 구간에 한정된다. 한강 하구부에서 홍수시 조석의 영향으로 인해 홍수위가 상승될 수 있는 경우는 제한적이라고 할 수 있다. 임진강의 유량은 한강의 조석변화에도 영향을 미친다. 임진강에 평상시 유량이 흐르는 경우와 홍수량이 흐르는 경우에 나타나는 한강의 조석영향 범위 및 크기는 다르다. 반대로 한강의 유량은 임진강의 흐름에도 영향을 미치게 된다. 이와 같은 상호간의 영향은 매우 밀접하게 발생하게 된다. 한강 하구부에 설치되어 있는 신곡수중보는 조석의 변화에 큰 영향을 미치고 있다. 조석으로 인해 발생하는 수위의 변화가 수중보로 인해 줄어들게 되어 이 지점을 기준으로 수위차가 발생하게 된다. 만조시에는 수중보를 월류하는 흐름이 발생하는데 상류방향의 유속이 빠르게 나타난다. 수심방향의 유속변화도 크게 나타나는데 상류 및 하류 방향의 유속이 시간과 장소에 따라 매우 다양하고 복잡하게 나타나게 된다. 한강 하구부의 수리현상은 매우 복잡하지만 지금까지 조사되거나 분석되지 못한 것이 사실이다. 하구부의 지속가능한 관리를 위해서는 의사결정을 할 수 있는 기초자료와 분석 결과가 매우 중요하다. 본 연구의 결과는 한강 하구 조사와 분석을 위해 활용될 수 있으리라 기대된다.

• Journal of the Korea Society for Simulation
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• v.32 no.4
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• pp.1-10
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• 2023

This study examines the response when the shock by underwater explosion is transmitted to a vertical launch air-vehicle mounted on a ship using modeling and simulation, and is about a plan to increase method shock resistance to protect the air vehicle. In order to obtain an accurate mathematical model, a dynamic characteristic test was performed on similar equipment, and through this, the mathematical model could be supplemented. And, using the supplemented mathematical model, the air vehicle simulated the shock response by the underwater explosion specified in the BV043 standard. As a result of the first simulation, it was confirmed that air vehicle could not withstand shock, and air vehicle protection method using a ring spring type shock absorber was studied. In addition to the basic shape of abosber, it was confirmed that the ring spring absober can be used to increase the impact resistance of a shipborn vertical launch vehicle by performing simulations for each case by changing deseign varables.

• The Journal of the Acoustical Society of Korea
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• v.36 no.6
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• pp.419-424
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• 2017

TDoA (Time Difference-of Arrival) or DoA (Direction-of-Arrival) can be used for source localization. However, the localizing performance is dependent on relative position between source and receivers, receivers' geometric structure, sound speed, and so on. In this paper we propose a source localization method with enhanced performance that combines multiple information. The proposed method uses the time TDoA, DoA and sound speed as variables. LM (Levenberg-Marquardt) method which is one of nonlinear optimizations is applied. The performances of the proposed method was evaluated by simulation. As result of simulation, the proposed method has the lower average localizing error performance than the previous method.

• The Journal of the Acoustical Society of Korea
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• v.34 no.2
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• pp.117-129
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• 2015

A parametric array is a nonlinear phenomenon that generates a narrow beam of low-frequency sound using the nonlinearity of the medium. The low-frequency sound so generated has a low sound pressure compared with that of sound generated directly. Consequently, a transducer that can generate a primary wave with high directivity and level is required. This study designed, fabricated, and evaluated a multi-resonance transducer as a parametric array source. The designs of the unit transducers and array transducer were based on an analysis model. The design process was repeated to fabricate the optimum transducer. The fabricated transducer array can generate a 189 dB, 190 dB primary wave level at 6.3 m and a 134 dB difference frequency wave using the parametric array phenomenon. The difference frequency wave has a frequency of 15 kHz and high directivity with an $8^{\circ}$ half power beam width in a $12{\times}18{\times}10m$ water tank.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.7
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• pp.927-935
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• 2019

Screw-failure accidents in small ships frequently occur in coastal waters. In particular, vessels' propulsion systems are frequently coiled due to objects such as fish-nets and ropes that float on the sea. The failure of the ship's propulsion system can cause primary accidents such as ship operation delays and drifting due to loss of power; furthermore, the possibility of secondary accidents such as those involving operators in the underwater removal of rope stuck in a propeller. Ships that do not have the proper tools to solve these problems must be either lifted onto land to be repaired or divers must dive directly under the ship to solve the problem. Accordingly, some small vessels have been equipped with rope-cutter devices on the propeller shaft to prevent ship propeller system accidents in recent years; however, they are not being applied efficiently due to the cost and time of installation. To solve these problems, this study develops an underwater rope-cutter device and controller for the removal of propeller and shaft foreign material in small vessels. This device has simple structures that use the principle of a saw. Meteor gears and crank pins were used for the straight-line rotation of saw blades of the underwater rope-cutters to allow for long strokes. Furthermore, the underwater rope-cutting machines can be operated by being connected to the ship battery. The user, a non-professional, can ensure convenience and stability by applying reverse current prevention and a speed control circuit so that it can be used more conveniently and safely.

• Journal of the Institute of Convergence Signal Processing
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• v.23 no.4
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• pp.228-233
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• 2022

This study is an experimental study on how to use phase change materials(PCM) to generate electrical energy for long-term operation of underwater unmanned vehicles. The electrical energy generation method is a volume change and a pressure change that occur as a phase change material changes to a solid or liquid state according to temperature, and the change in pressure creates a flow of fluid to create electrical energy. Polyethylene glycol was used as a phase change material considering the temperature of the ocean. In addition, an electrical energy generating device that converts volume change into pressure at low temperature (1℃~2℃) in solid state and high temperature (21℃~25℃) in liquid state was fabricated. As a result of the experiment, the pressure change according to the phase change rapidly changed between 1 hour and 2 hours, and maintained a pressure of about 24MPa after 4 hours. Through this, it was confirmed that it can be used as a power source for underwater unmanned vehicles using phase change materials and temperature differences. In addition, it was found that a more improved design should be made in order to apply the phase change material to an underwater unmanned vehicle.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.10
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• pp.125-132
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• 2019

Because the water exposed to shock waves caused by an underwater explosion cannot withstand the appreciable tension induced by the change in both pressure and velocity, the surrounding water is cavitated. This cavitating water changes the transferring circumstance of the shock loading. Three phenomena contribute to hull-plate damage; initial shock loading and its interaction with the hull plate, local cavitation, and local cavitation closure then shock reloading. Because the main concern of this paper is local cavitation due to a near-field underwater explosion, the water surface and the waves reflected from the sea bottom were not considered. A set of governing equations for the structure and the fluid were derived. A simple one-dimensional infinite plate problem was considered to verify this uncoupled solution approach compared with the analytic solution, which is well known in this area of interest. The uncoupled solution approach herein would be useful for obtaining a relatively high level of accuracy despite its simplicity and high computational efficiency compared to the conventional coupled method. This paper will help improve the understanding of fluid-structure interaction phenomena and provide a schematic explanation of the practical problem.

• The tire
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• s.109
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• pp.40-44
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• 1983

당협회에서는 금년도에도 교통부, 치안본부, 한국도로공사의 후원으로 4차에 걸쳐 고속도로의 휴게소에서 무료 타이어 점검 및 서비스를 실시하였다. 금년도의 점검결과도 예년과 마찬가지로 타이어 정비불량률이 무려 45%에 달하고 있으며, 차종별로는 승용차가 53%로 가장 불량한 것으로 나타났으나, 이는 주로 공기압부적 차량이고, 실제로 타이어 정비상태가 가장 불량한 것은 트럭으로서 52%였다. 정비불량항목으로는 과마모가 제일 많아 전체 타이어 정비불량건수중 43%를 차지하였으며 트럭에 가장 많았다. 특히 관광버스에는 재생 타이어 취부률이 35%나 되었고 또한 트럭에는 눈올 때에만 사용토록 되어 있는 스노 타이어를 봄, 여름, 가을까지 계속 사용하고 있는 차량이 13%나 되어 발열에 의한 트레드 세페레이션 (Tread SEparation) 사고의 위험성이 많았다.

• Nuclear industry
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• v.16 no.2 s.156
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• pp.47-55
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• 1996

원자력발전소 2차 계통수중의 용존산소는 증기발생기 뿐만 아니라 터빈 급수가열기와 응축기 등 주요설비 부식의 직접적인 원인으로서, 원자력발전의 경제성 저하 및 원전설비의 안전성에 심각한 문제를 야기시키고 있다. 한국정수공업(주)는 최근 $\ulcorner$촉매수지식 용존산소 제거설비$\lrcorner$를 한국원자력연구소의 기술지원 아래 연구$\cdot$개발하여 고리원자력 1호기에 설치$\cdot$운용중에 있다. 그 개발경위와 활용전망 등을 알아본다.

• 제어로봇시스템학회:학술대회논문집
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• 1987.10b
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• pp.198-202
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• 1987

The regulator problem can be considered as some impulsive disturbance rejection one. In this point of view, the rate of decay is one of important factors for regulation and depends on how negative the real parts of the eigenvalues of closed-loop system. The algorithm that the closed-loop system has eigenvalues lying within a vertical. strip is useful for rapid disturbance rejection. This paper presents a design method for a linear quadratic regulator of two-time scale system with eigenvalues in a vertical strip by use of time-scale separation property.