• Title/Summary/Keyword: Underwater shock wave

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Uncoupled Solution Approach for treating Fluid-Structure Interaction due to the Near-field Underwater Explosion (근거리 수중폭발에 따른 유체-구조 상호작용 취급을 위한 비연성 해석방법)

  • Park, Jin-Won
    • 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.

Study on the measurement of the cylinder lengths of an underwater robot for harbour construction using a pressure sensor (압력센서를 이용한 수중항만공사 로봇의 실린더 길이 측정에 관한 연구)

  • Kim, Chi-Hyo;Kim, Tae-Sung;Lee, Min-Ki
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • 2012.06a
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    • pp.9-10
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    • 2012
  • This paper presents an observer to measure the lengths of cylinders of an underwater robot for harbour construction using a pressure sensor. In harbour constructing, we place heavy armour stones weighing over 2~3 tons on the surface of the bank to protect it from storming wave. This work typically done by a diver is difficult and dangerous so that we have developed Stone Diver which is the underwater robot for harbour construction. The robot needs a position sensor to control the hydraulic cylinder. The position sensors mounted outside the cylinders cause poor durability in construction site where shock and dust usually occur. However, the pressure sensor mounted inside a waterproof box improves the durability. Based on the dynamic parameters and the pressures in the cylinder, the observer measures the cylinder's position. This paper presents the positional accuracy of the pressure based observer and the performance of the underwater robot to assemble the armour stones.

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Study on the estimation of the cylinder displacement of an underwater robot for harbor construction using a pressure sensor (압력센서를 이용한 수중항만공사 로봇의 실린더 변위 추정에 관한 연구)

  • Kim, Chi-Hyo;Kim, Tae-Sung;Lee, Min-Ki
    • Journal of Navigation and Port Research
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    • v.36 no.10
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    • pp.865-871
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    • 2012
  • This paper presents an observer to estimate the displacement of hydraulic cylinders of an underwater robot for harbour construction using a pressure sensor. In harbour constructing, we place heavy armour stones weighing over 2~3 tons on the surface of the bank to protect it from storming wave. This work typically done by a diver is difficult and dangerous so that we have developed Stone Diver which is the underwater robot for harbour construction. The robot needs a displacement sensors to control the position of hydraulic cylinders. The position sensors mounted outside the cylinders cause poor durability in construction site where shock and dust usually occur. However, the pressure sensor mounted inside a waterproof box improves the durability. Based on the dynamic parameters and the pressures in the cylinder, the observer estimates the cylinder's position. This paper presents the positional accuracy of the pressure based observer and the performance of the underwater robot to assemble the armour stones.

Tests on Ventilation Control of PRAIRIE for Improving Acoustic Stealth Performance (음향스텔스 성능 향상을 위한 PRAIRIE 공기 분사량 제어 실험)

  • Lee, Heechang;Moon, Youngsun;Kang, Seunghee
    • Journal of the Korea Institute of Military Science and Technology
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    • v.23 no.6
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    • pp.602-608
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    • 2020
  • PRAIRIE(Propeller Air Induced Emission) system is a kind of underwater radiated noise suppression systems to reduce the probability of the identification or classification of our warship's acoustic signature by an enemy ship. It is effective in case of strong cavitation events. This is because air bubbles emitted from the PRAIRIE system mitigate drastic collapses of the cavity bubbles that can generate an intense shock wave. However, when the PRAIRIE system is operated in a non or weak cavitation condition, it might increase the total level of underwater radiated noise and induce the acoustic signatures. Therefore, this paper presents the trial results on ventilation control of PRAIRIE to find a more efficient operation depend on the cavitation condition. Then, we show a variation of the amplitude modulation characteristics according to ventilation control.

A Study on Transmitter and Receiver Design of Proximity Magnetic Sensor for Enhancement of Target Detection Range (표적 탐지거리 향상을 위한 근접자기센서 송수신기 설계에 관한 연구)

  • Ju, Hye-Sun;Chung, Hyun-Ju;Yang, Chang-Seob;Jeon, Jae-Jin
    • Journal of the Korea Institute of Military Science and Technology
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    • v.14 no.6
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    • pp.1151-1158
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    • 2011
  • Proximity magnetic sensor is able to detect the object target accurately in close range and it has been widely used in the underwater guided weapon system because there is no countermeasures from the target. In order to increase the damage of target by shock wave due to explosion of the underwater guided weapon system, the maximum detection range of the proximity magnetic sensor needs to be increased. In this paper, we describe the techniques of the optimum transmitting and receiving coils design using the Finite Element Method for the output power enhancement of the transmitter and the sensitivity improvement of the receiver. Finally, the proposed design techniques of the transmitter and the receiver were verified using a experimental setup and a prototype.

A study on the flow characteristics of compressed-gas flow rate control valve (압축가스 유량 제어밸브의 유동특성 연구)

  • Kim J. B.;Park W. G.;Han M. C.;Jung C. H.;An J. Y.
    • 한국전산유체공학회:학술대회논문집
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    • 2004.10a
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    • pp.25-28
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    • 2004
  • The purpose of this paper is to present essential numerical data of FCV(Flow rate Control Valve) which is used in a projectile ejection system for a underwater vehicle. A commercial CFD code is applied to analyze the 3 dimensional viscous compressible flow field within the FCV as four cases of opening rate, 25, 50, 75, and $100\%$. The flow coefficient of each cases are mainly calculated. And other characteristics such as the location of shock wave and total temperature distribution are also determined.

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A Study on the Transmitter Design for Transmitting Output Power Enhancement of Active Magnetic Sensor (능동형 자기센서의 송신출력 향상을 위한 송신기 설계에 관한 연구)

  • Chung, Hyun-Ju;Yang, Chang-Seob;Jeon, Jae-Jin
    • Journal of the Korean Magnetics Society
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    • v.23 no.5
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    • pp.159-165
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    • 2013
  • A active magnetic sensor has been widely used in the underwater guided weapon system because it is able to detect a target accurately in close range, but the target doesn't have any good countermeasure to overcome the threat from the active magnetic sensor. Recently, in order to increase the damage area of target by shock wave with explosion of the underwater weapon system and to detect small target, the maximum target detection range of the active magnetic sensor needs to be increased. One method for improving maximum target detection range is to improve output power from transmitter through demagnetization factor minimization of a transmitting core. Thus, in this paper, we describe the study results on the transmitter core shape design to enhance output power of the active magnetic sensor.

Underwater Explosive Welding of Stainless Steel and Magnesium Alloy (수중 충격파를 이용한 스테인레스 스틸과 마그네슘합금의 폭발용접에 관한 연구)

  • Lee, Joon-Oh;Kim, Young-Kook;Cho, Sang-Ho
    • Tunnel and Underground Space
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    • v.22 no.3
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    • pp.221-225
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    • 2012
  • Magnesium is one of the light weight materials, which can improve fuel economy and reduce emissions in automotive industry. Recently, magnesium alloys have gained considerable attention due to good mechanical properties. In this work, we have performed an explosive welding using the magnesium alloys (AZ31) and stainless steel (SUS 304). As a result, SUS304/AZ31 were successfully combined each other; however, a resolidified interlayer was observed at the point of welded layer. To reduce the resolidified interlayer, we have changed the thickness (0.5 mm and 1 mm) of stainless steel, distance (45 mm and 60 mm) between explosive and the center of materials and initial angle ($20^{\circ}$ and $30^{\circ}$) of explosive. In the case of the thickness 0.5 mm and angle of $30^{\circ}$, the resolidfied interlayer was not observed due to the increase of distance from the explosive. To accurately estimate the resolidified interlayer, electron probe micro-analyzer (EPMA) method and hardness were used. For the EPMA analysis, mixed materials were confirmed at the resolidified interlayer, and the measurement exhibited the middle value compared with the AZ31 and SUS304.

Electric Spark System as Underwater Acoustic Source - I. Pressure pulses from low electric energy - (수중음원으로써의 전기방전시스템- I. 낮은 전기에너지로부터의 음압펄스 -)

  • Kim, Sung-Boo;Kim, Sang-Han
    • The Journal of the Acoustical Society of Korea
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    • v.15 no.4
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    • pp.32-35
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    • 1996
  • The pressure pulses generated from the underwater electric spark system ranged from 0.4 to 1.6kJ are measured with the variation of source depth and range. The characteristics of pressure pulses obtained through this experiment continue to show the same electric energy and depth dependence previously reported, but two particular phenomena are observed. First, it is observed that the peak pressure of the 1st bubble pulse induced from implosion is higher than that of the initial shock wave, which is particularily apparent to high electric energy more than 10kJ previous studies. Second, it has been reported that the energy ratio (potential energy of bubble/intrinsic energy of source) has some tendency to "droop" on the low electric energy as 0.02 for 5kJ and 0.01 for 1kJ but the results of the present experiment show that it continues to have the ratio of 0.01 near 1kJ again.

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Voltage waveform detection of discharge breaking process used pulsed-power technique (펄스파워 기술을 이용한 방전파쇄과정의 전압파형 검출)

  • Chung, Y.H.;Yoon, S.H.;Lee, Y.S.;Lee, D.H.;Kim, H.J.;Cho, J.S.
    • Proceedings of the KIEE Conference
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    • 1999.07e
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    • pp.2195-2197
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    • 1999
  • Electric breakdown in the liquid produces a spark channel. The energy input into the channel causes expansion of a vapor gas cavity. If the power of the discharge is high enough, this expansion is fast enough to produce a shock wave which propagates through the liquid to the subject of destruction. We focused our attention on the correlation between electric parameters and the characteristics of the flash caused by point to-point electrode discharge in the water. By varying firing voltage and gap length, we obtained the features of the flash : amplitude, pulse width, and so on. In this paper, We have known that there is a concrete interrelation between underwater firing voltage and photodiode output.

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