• Ocean Systems Engineering
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• 제2권2호
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• pp.83-97
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• 2012

In the present work, design procedure and computer simulation of an AUV are documented briefly. The design procedure containing the design of propulsion system and CFD simulation of hydrodynamics behavior of the hull leads to achieve an optimum mechanical performance of AUV system. After designing, a comprehensive one dimensional model including motor, propeller, and AUV hull behavior simulates the whole dynamics of AUV system. In this design, to select the optimum AUV hull, several noses and tails are examined by CFD tools and the brushless motor is selected based on the first order model of DC electrical motor. By calculating thrust and velocity in functional point, OpenProp as a tool to select the optimum propeller is applied and the characteristics of appropriate propeller are determined. Finally, a computer program is developed to simulate the interaction between different components of AUV. The simulation leads to determine the initial acceleration, final velocity, and angular velocity of electrical motor and propeller. Results show the final AUV performance point is in the maximum efficiency regions of DC electrical motor and propeller.

• 수산해양기술연구
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• 제55권4호
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• pp.294-302
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• 2019

As a series of fundamental researches on the development of an automatic identification monitoring system for fishing gear. Firstly, the study on the installation method of automated identification buoy for the coastal improvement net fishing net with many loss problems on the west coast was carried out. Secondly, the study was conducted find out how to install an automatic identification buoy for coastal gill net which has the highest loss rate among the fisheries. GPS for fishing was used six times in the coastal waters around Seogwipo city in Jeju Island to determine the developmental status and underwater behavior to conduct a field survey. Next, a questionnaire was administered in parallel on the type of loss and the quantity and location of fishing gear to be developed and the water transmitter. In the field experiment, the data collection was possible from a minimum of 13 hours, ten minutes to a maximum of 20 hours and ten minutes using GPS, identifying the development status and underwater behavior of the coastal gillnet fishing gear. The result of the survey showed that the loss of coastal net fishing gear was in the following order: net (27.3%), full fishing gear (24.2%), buoys, and anchors (18.2%). The causes were active algae (50.0%), fish catches (33.3%) and natural disasters (12.5%). To solve this problem, the installation method is to attach one and two electronic buoys to top of each end of the fishing gear, and one underwater transmitter at both ends of the float line connected to the anchor. By identifying and managing abnormal conditions such as damage or loss of fishing gear due to external factors such as potent algae and cutting of fishing gear, loss of fishing gear can be reduced. If the lost fishing gear is found, it will be efficiently collected.

• 대한조선학회논문집
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• 제43권2호
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• pp.177-185
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• 2006

Cavitation is the dominant noise source of the marine vehicle. Of the various types of cavitation , tip vortex cavitation is the first appearance type of marine propeller cavitation and it generates high frequency noise. In this study, tip vortex cavitation behavior and noise are numerically investigated. A numerical scheme using Eulerian flow field computation and Lagrangian particle trace approach is applied to simulate the tip vortex cavitation on the hydrofoil. Vortex flow field is simulated by combined Moore and Saffman's vortex core radius equation and Sculley vortex model. Tip vortex cavitation behavior is analyzed by coupled Rayleigh-Plesset equation and trajectory equation. The cavitation nuclei are distributed and released in the vortex flow result. Vortex cavitation trajectories and radius variations are computed according to nuclei initial size. Noise is analyzed using time dependent cavitation bubble position and radius data. This study may lay the foundation for future work on vortex cavitation study and it will provide a basis for proper underwater propeller noise control strategies.

• 화약ㆍ발파
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• 제37권3호
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• pp.13-24
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• 2019

본 논문은 명시적 유한요소 해석을 이용하여 군함이나 수상함 아래의 수중에서 어뢰가 폭발할 때의 파편들의 거동을 조사하기 위하여 작성되었다. 본 연구에서는 LS-DYNA에서 라그랑주-오일러 (ALE) 접근법이라 불리는 유체-구조물 상호작용(FSI) 기법을 적용하여 어뢰파편과 선체의 응답을 관찰하였다. 오일러 모델은 공기, 물, 폭약으로 구성되며, 라그랑주 모델은 파편과 선체로 이루어져 있다. 본 모델링의 핵심은 최악파편이 어뢰로부터 가까운 곳(4.5 m)에 위치한 선체에 파공을 일으킬 수 있는지 여부를 파악하는 데 있다. 시뮬레이션은 별도의 두 단계로 수행되었다. 첫 번째의 예비해석에서는 팽창하는 어뢰의 외피가 찢어지는 데 폭약에너지의 30%가 소모된다는 가정 하에 수중폭발 시의 파편속도에 대해 잘 알려져 있는 실험결과를 토대로 최악파편의 초기속도를 결정하였다. 두 번째의 총괄해석에서는 최악파편이 선체에 부딪치기 직전에 보일 것으로 예상되는 파편의 종단속도를 찾고자 하였다. 그 결과, 주어진 조건 하에서 최악파편의 초기속도는 매우 빠른 것으로 나타났다(400 및 1000 m/s). 하지만 충돌이 발생할 때의 파편과 선체 간의 속도차이는 불과 4 m/s 정도로 매우 작았다. 이 결과는 물에 의한 큰 항력의 영향도 있지만 선체에 부여한 비파괴 조건도 영향을 끼쳤을 것으로 보인다. 하지만 적어도 본 논문에서 가정한 해석조건 하에서는 최악파편의 느린 상대속도로 인하여 선체에 파공이 발생하기는 어려운 것으로 나타났다.

• 수산해양기술연구
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• 제46권1호
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• pp.20-31
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• 2010

In this research, the submersible fish cage was designed to avoid structural and biological damage during harsh sea conditions. The submersible cage system consists of netting, mooring ropes, a floating collar, floats, sinkers and anchors. Whole elements of the cage were modeled on the mass-spring model. The computer simulations were carried out to investigate the dynamic behavior of the cage and to calculate mooring line tension subjected to tidal currents and waves. As expected, the tension values in the mooring line of the submerged position are 36% less compared to that of the surface cage under the same loading conditions. As the wave was used in combination with the current velocity of 1m/s, the average tensile load for the submerged cage showed 85% of the value for the floating cage. The simulation results provide an improved understanding of the behaviors of the structure and valuable information on the optimized design of the cage system exposed to open ocean environmental factors.

• 수산해양기술연구
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• 제39권1호
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• pp.77-83
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• 2003

Autonomous mobile robots based on the Web have been already used in public places such as museums. There are many kinds of problems to be solved because of the limitation of Web and the dynamically changing environment. We present a methodology for intelligent mobile robot that demonstrates a certain degree of autonomy in navigation applications. In this paper, we focus on a mobile robot navigator equipped with neuro-fuzzy controller which perceives the environment, make decisions, and take actions. The neuro-fuzzy controller equipped with collision avoidance behavior and target trace behavior enables the mobile robot to navigate in dynamic environment from the start location to goal location. Most telerobotics system workable on the Web have used standard Internet techniques such as HTTP, CGI and Scripting languages. However, for mobile robot navigations, these tools have significant limitations. In our study, C# and ASP.NET are used for both the client and the server side programs because of their interactivity and quick responsibility. Two kinds of simulations are performed to verify our proposed method. Our approach is verified through computer simulations of collision avoidance and target trace.

• International Journal of Ocean System Engineering
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• 제3권1호
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• pp.16-21
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• 2013

This paper presents a design of fuzzy PD depth controller for the autonomous underwater vehicle entitled KAUV-1. The vehicle is shaped like a torpedo with light weight and small size and used for marine exploration and monitoring. The KAUV-1 has a unique ducted propeller located at aft end with yawing actuation acting as a rudder. For depth control, the KAUV-1 uses a mass shifter mechanism to change its center of gravity, consequently, can control pitch angle and depth of the vehicle. A design of classical PD depth controller for the KAUV-1 was presented and analyzed. However, it has inherent drawback of gains, which is their values are fixed. Meanwhile, in different operation modes, vehicle dynamics might have different effects on the behavior of the vehicle. In this reason, control gains need to be appropriately changed according to vehicle operating states for better performance. This paper presents a self-tuning gain for depth controller using the fuzzy logic method which is based on the classical PD controller. The self-tuning gains are outputs of fuzzy logic blocks. The performance of the self-tuning gain controller is simulated using Matlab/Simulink and is compared with that of the classical PD controller.

• 수산해양기술연구
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• 제47권3호
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• pp.234-240
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• 2011

In order to obtain the fundamental data about the behavior of sharks by underwater audible sound, this experiment was carried out to investigate the auditory characteristics of tiger shark Scyliorhinus torazame which was caught in the coast of Jeju Island by heart rate conditioning method using pure tones coupled with a delayed electric shock. The audible range of tiger shark extended from 80Hz to 300Hz with a peak sensitivity at 80Hz including less sensitivity at 300Hz. The mean auditory thresholds of tiger shark at the frequencies of 80Hz, 100Hz, 200Hz and 300Hz were 90dB, 103dB, 94dB and 115dB, respectively. The positive response of tiger shark was not evident after the sound projection of over 300Hz. At the results, the sensitive frequency range of tiger shark is narrower than that of fish that has swim bladder. In addition, it is assumed that the most sensitive frequency in auditory thresholds of Chondrichthyes is lower than that of Osteichthyes. Critical ratios of tiger shark measured in the presence of masking noise in the spectrum level range of about 60-70dB (0dB re $1{\mu}Pa/\sqrt{Hz}$) increased from minimum 27dB to maximum 39dB at test frequencies of 80-200Hz. The noise spectrum level at the start of masking was distributed at the range of about 65dB within 80-200Hz.

• 수산해양기술연구
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• 제48권4호
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• pp.479-486
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• 2012

In order to obtain the fundamental data about the behavior of conger by underwater audible sound, this experiment was carried out to investigate the hearing ability of Conger eel Conger myriaster which was in the coast of Jeju Island by heartbeat conditioning method using pure tones coupled with a delayed electric shock. The audible range of conger eel extended from 50Hz to 300Hz with a peak sensitivity at 80Hz including less sensitivity over 200Hz. The mean auditory thresholds of conger eel at the frequencies of 50Hz, 80Hz, 100Hz, 200Hz and 300Hz were 105dB, 92dB, 96dB, 128dB and 140dB, respectively. The positive response of conger eel was not evident after the sound projection of over 200Hz. At the results, the sensitive frequency range of conger eel is narrow in spite of swim bladder. Auditory masking was determined for Conger eel by using masking stimuli with the spectrum level range of about 60~70dB (0dB re $1{\mu}Pa/\sqrt{Hz}$). According to white noise level, the auditory thresholds increased as compared with thresholds in a quiet background noise including critical ratio at 68dB of white noise from minimum 26dB to maximum 30dB at test frequencies of 80Hz and 100Hz. The noise spectrum level at the start of masking was distributed at the range of about 68dB within 80~100Hz.

• 한국철도학회논문집
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• 제17권2호
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• pp.100-105
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• 2014

해중철도 부근에서 테러나 사고에 의해 수중폭발이 발생하였을 경우, 함체에 치명적인 손상을 가할 수 있으므로, 충분한 강도를 확보해야 한다. 본 연구에서는 설계 목적으로 해중철도 인근에서 수중폭발이 발생한 경우, 경험에 기초한 공식을 이용하여 충격압을 추정하고, 충격압에 의한 해중철도의 응답을 해석할 수 있는 간이 해석 방법을 제안하였다. 해중철도 함체를 탄성 지지된 보로 이상화하고, 초기 최대 충격압이 작용하는 보에 대해 정적 유한요소해석을 실시한 후, 동하중 계수와 조합함으로 최대 변위 및 굽힘 모멘트를 계산한다. 간이해석 결과는 상용 유한요소해석 소프트웨어를 이용한, 시간에 따른 과도응답해석 결과와 비교하여 양호한 일치를 보임을 확인하였다.