• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.397-400
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• 2004

소음원 또는 방사음장을 가시화하기 위하여 소음원을 둘러싸는 한 면에서의 음압측정을 통해 임의의 3차원 공간상의 음향 물리량을 예측하는 음향 홀로그래피 방법이 사용되고 있으며 이때 반사파가 존재하지 않는 기본 가정을 만족해야 한다. 반사파가 존재하는 경우에는 반사파를 보정하거나 또는 반사파의 음장이 미치는 영향이 무시할 만큼 작다고 가정하여 음장 예측이 가능하게 된다. 최근 해양연구원에서는 음향 홀로그래피 방법을 이용하여 수중음장을 가시화하는 시스템을 개발하였으며 시스템 검증을 위해 무향수조 내 단순음원을 이용하여 음장예측을 수행하였다. 무향수조 표면에는 흡음처리가 되지 않아 표면 반사파가 존재하나 해석 결과 반사파의 영향이 작은 경우에는 반사파를 무시하고 음장해석의 수행이 가능함을 확인하였다.

• The Journal of the Acoustical Society of Korea
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• v.20 no.1
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• pp.68-76
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• 2001

Sonar is the system that detects objects and finds their location in water by using the echo ranging technique. In order to have excellent performance in variable environment, acoustic characteristics of this system must be analyzed accurately. In this paper, based on the finite element analysis, modeling and analysis of acoustic characteristics of underwater acoustic sensors are preformed. Couplings between piezoelectric and elastic materials, and fluid and structure systems associated with the modeling of piezoelectric underwater acoustic sensors are formulated. In the finite element modeling of unbounded acoustic fluid, IWEE (Infinite Eave Envelop Element) is adopted to take into account the infinite domain. When an incidence wave excites the surface of Tonpilz underwater acoustic sensor, the scattered wave on the sensor is founded by satisfying the radiation condition at the artificial boundary approximately. Based on this scattering analysis, the electrical response of the underwater acoustic sensor under incidence, so called RVS (Receiving Voltage Signal) is founded accurately. This will devote to design Sonar systems accurately.

• Proceedings of the Korea Information Processing Society Conference
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• 2015.10a
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• pp.351-354
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• 2015

지구 전체 표면적의 약 70%인 바다는 석유를 포함한 각종 수산자원이 풍부하지만 인간은 바다로 접근하기 위해 파도, 태풍 등의 날씨에 절대적인 영향을 받기 때문에 쉽게 접근하기 어렵다. 이 경우 해양 관련 정보를 얻고 분석 및 활용하기 위해 IoT (Internet of Things)의 기반 기술인 센서네트워크를 사용할 수 있다. 하지만 바다에 센서네트워크를 적용하기 위해서는 파도, 태풍을 포함한 염분 등을 충분히 고려해야 한다. 게다가 수중 통신을 사용할 경우 수중에서는 전파를 사용할 수 없기 때문에 음파와 같이 수중에서 통신이 가능한 방법을 선택해야 한다. 따라서 본 논문에서는 해양센서네트워크 기술의 현장 적용을 위한 고려사항에 대해 논의하고, 실제 가두리 양식장에 설치 운용한 사례를 소개한다.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.3
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• pp.37-44
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• 2000

An experimental study has been carried out at circulating water channel to investigate the viscous flow around breaking waves generated by a submerged hydrofoil(NACA0012). Detailed flow measurements were made at several critical points including an incipient wave-breaking point and a fully-developed wave breaker. Particle Image Velocimetry(PIV) was employed to visualize the flow field very close to the breaker as well as at the near- and far-wake of the breaker. Generation, development and decay of the wave breaker have been investigated. It is found that PIV technique could be well applied to the complex flow field, including the vortical structures near the free surface as well as the wake of the hydrofoil.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.141-141
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• 2017

국제해사기구(International Maritime Organization)는 선박 평형수로 인하여 발생하는 환경문제를 방지하기 위하여 지난 2004년 선박 평형수 관리 협약을 제정하였고, 2016년 핀란드의 비준함에 따라 2017년 9월 8일부터 발효될 예정이다. 이 협약에 대응하기 위하여 선박 평형수 처리기술이 개발되어 승인이 되었다. 이중 수중방전을 이용한 기술은 화학약품의 첨가 등이 없어 경제적이고 내부에서 발생하는 OH라디컬, 자외선, 충격파, 전기장, 오존 등에 다양한 요소들에 의하여 수처리가 가능하고, 중화를 위한 첨가제 등이 필요없어 친환경적이다. 본 연구에서는 부산 항만 근처연안에서 채취한 바닷물을 대상으로 수중방전을 이용한 방법을 연구하였다. 실험방법은 그림1과 같이 Point to Point 방식의 전극을 꾸몄고, 용액은 1L이며, 전압은 8kV, 30kHZ로 가해주었다. 광학분석장비(OES)를 이용하여 수중방전시 발생되는 빛 분석을 하였다. 실험결과 OES분석 결과 살균작용하는 OH 라디컬이 발생하는 것을 확인할 수 있었다. 또한 실험 도중 시료를 채취하여 $35^{\circ}C$ 48시간동안 배양하였다. 배양 결과 시간이 경과함에 따라 미생물의 개체가 그림 2와 같이줄어두는 것을 확인할 수 있었다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.1
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• pp.9-16
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• 2014

In recent years, the structural shock response to UNDEX (UNDerwater EXplosion) has been studied as much, or more, through numerical simulations than through testing for several reasons. Very high costs and sensitive environmental concerns have kept destructive underwater explosion testing to a minimum. Increase of simulation capabilities and sophisticated simulation tools has made numerical simulations more efficient analysis methods as well as more reliable testing aids. In this study, the main issue is the fluid-structure interaction. Here, appropriate relations between the acoustic pressure on the fluid surface and displacements on the structure surface are formed internally. The analysis was carried out using ABAQUS/Explicit and the results have been visualized in ABAQUS CAE. The shock loading history, acoustic pressure, stress of stand-off point, the velocity and strain energy time histories were presented.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.4
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• pp.382-390
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• 2009

The submerged body near the free surface is disturbed by the 1st and 2nd order wave forces, which results in unstable movements when no control is applied. In this paper, the vertical motions of the submerged body are analyzed, and the time-variant nonlinear system for the vertical motions of the submerged body is transformed to the time-invariant linear system in state space. Next, depth controller of the submerged body is designed by using LQR control, one of the modern optimal control technique. Numerical simulation shows that effective depth controls can be achieved by LQR control.

• Journal of Korean Port Research
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• v.12 no.1
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• pp.87-93
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• 1998

For the calculation of the free-surface elevation, a new finite difference scheme is studied where the third derivative term for the wave elevation is artificially added in the Eulerian expression of the free-surface boundary condition. The paper presents a comparative analysis with simulations performed by the classical MAC method. More schematic computations are carried out by changing the submergence-depth and angle-of-attack. The present study shows that this new method is very efficient for the simulation of free-surface elevation around the trailing edge.

• The Journal of the Acoustical Society of Korea
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• v.6 no.2
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• pp.48-53
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• 1987

The depth dependent sound fields have been calculated for a single frequency source to reveal the fluctuating sound energy at both near the surface and the bottom of the water layer. Those fluctuation are mainly due to the mode function behavior along the depth where the sound-speed gradient acts like trapping lower mode sound energy in those medium.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.2
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• pp.215-222
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• 2015

To improve the ocean waves of the ship maneuvering simulator, we study and summarize the visualization elements of the ocean waves and the overall direction of their implementation in detail. We categorize the visualization elements of the ocean waves into five groups, including wave surface, wave breaking, interaction, lighting effects, and underwater. We also analyze the design and implementation issues of the visualization of the ocean waves for ship maneuvering simulator with respect to realistic and real-time ocean visualization, ship dynamics, and application purposes. Through the analysis, we have found that the realistic visualization of ocean waves plays an important role in the generation of immersiveness, more accurate ship motion, and the various and controllable simulation scenarios for the ship maneuvering simulator. Additionally, we have confirmed that there are many visualization elements, methods, and limitations to be considered for the visualization of the ocean waves for ship maneuvering simulator, and we have concluded that the systematic design is required before implementation.