• 한국해양공학회지
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• 제35권5호
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• pp.336-346
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• 2021

The prediction of wave conditions is crucial in the field of marine and ocean engineering. Hence, this study aims to predict the significant wave height through machine learning (ML), a soft computing method. The adopted metocean data, collected from 2012 to 2020, were obtained from the Korea Institute of Ocean Science and Technology. We adopted the feedforward neural network (FNN) and long-short term memory (LSTM) models to predict significant wave height. Input parameters for the input layer were selected by Pearson correlation coefficients. To obtain the optimized hyperparameter, we conducted a sensitivity study on the window size, node, layer, and activation function. Finally, the significant wave height was predicted using the FNN and LSTM models, by varying the three input parameters and three window sizes. Accordingly, FNN (W48) (i.e., FNN with window size 48) and LSTM (W48) (i.e., LSTM with window size 48) were superior outcomes. The most suitable model for predicting the significant wave height was FNN(W48) owing to its accuracy and calculation time. If the metocean data were further accumulated, the accuracy of the ML model would have improved, and it will be beneficial to predict added resistance by waves when conducting a sea trial test.

• 대한조선학회논문집
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• 제58권3호
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• pp.144-157
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• 2021

Brake Horse Power (BHP) reduction ratios by air injection to the underside of the hull surface in an actual ship are predicted using an unstructured finite-volume CFD solver and compared with the sea trial results. In addition, air lubrication system installed on the existing vessel is investigated to find a good solution for additional drag reduction. As a results, it is found that the thickness of the air layer should be minimized within a stable range while securing the area covered by the air layer as much as possible. Furthermore, the amount of frictional drag reduced by air injection is found to be independent of surface roughness and still effective on rough surface. Based on the results of this study, it is expected that systematic and reliable air lubrication system can be designed and evaluated using the proposed method.

• 한국해양공학회지
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• 제32권6호
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• pp.518-526
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• 2018

As a new technical approach, this paper introduces a method for improving an electrically propelled outboard motor in consideration of the driving system applied to an electric-propulsion boat with solar cell energy. The most efficient model for a drive shaft, propeller shaft, and bevel gear was suggested and examined with respect to the results of test operation in prototype mode. Furthermore, this research included a performance evaluation of the manufactured prototype to acquire the purposed quantity value and the development items. After manufacturing the desired prototype of an electrically propelled outboard motor, the maximum sail time, thrust force, noise, and weight were evaluated in a performance test. An additional test in relation to the maximum sail speed (knots) of the completed prototype was conducted using a sea trial evaluation to acquire the optimum quantity.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2022년도 추계학술대회
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• pp.338-340
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• 2022

미래 선박시장을 주도하게 될 자율운항선박의 기술개발은 국·내외를 막론하고 활발히 진행되고 있다. 자율운항선박 기술 개발의 고도화와 단계적인 실증을 위해서 체계적인 성능시험은 필수적이며, 이를 위하여 시험해역을 포함한 육·해상 성능시험 인프라가 울산시 고늘지구 인근에 구축되고 있다. 시험해역의 안전관리와 시험선박을 지원하기 위하여 자율운항선박 성능실증센터에는 통합관제시스템이 구축되며 자율운항선박 기술 및 연계 기술의 개발과 연구에 활용될 수 있도록 기본설계를 통하여 요구사항을 반영하여 장비를 구성하였다.

• 한국음향학회지
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• 제25권7호
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• pp.333-338
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• 2006

수중 방사소음 측정시 낮은 신호대 잡음비를 가지는 신호에 대해 유용한 신호를 얻기 위해서는 잡음제거가 이루어져야 한다. 본 논문은 잡음제거를 수행하기 위하여 Donoho 등에 의해 제안된 Translation-Invariant (TI) 웨이브렛 기반으로 다중 임계치 함수를 적용한 잡음제거 기법을 제안한다. 기존의 웨이브렛 잡음제거 기법은 특이점 부근에서 Pseudo-Gibbs 현상이 발생하는 문제점이 있다 TI 웨이브렛은 신호의 특성 위치를 변화시켜 Pseudo-Gibbs 현상을 제거한다. 그리고 배경잡음 및 외부잡음을 제거하기 위해 각 노드별 변형된 소프트 임계치를 적용한 다중 임계치 함수를 제안한다. 제안 기법의 타당성을 검토하기 위해 모의 시뮬레이션과 해상실험을 수행한 결과 신호대 잡음비가 23dB 및 18dB 이상 개선됨을 확인하였다.

• 수산해양기술연구
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• 제53권2호
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• pp.177-186
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• 2017

This study is intended to provide navigator with specific information necessary to assist in the avoidance of collision and in operation of ships to evaluate the maneuverability of research vessel Jera. Authors carried out full-scale sea trials for turning test, zig-zag test, and spiral test at actual sea-going condition, which were performed on starboard and port sides with 10-20 rudder angle at service speed of 10 knots. The turning circle was much different at both of the turning of port and starboard which was longer at the starboard than at the port. In the zig-zag test results, the port and starboard was $10^{\circ}$ the first and second overshoot angles were $6.0^{\circ}$, $5.8^{\circ}$ and $6.3^{\circ}$, $7.1^{\circ}$ respectively and the first overshoot angles were $16.4^{\circ}$, $17.6^{\circ}$ when using $20^{\circ}$. Her maneuverability index T and N can be easily determined by using an analogue computer with the data obtained from the zig-zag tests where K is a constant representing the turning ability and T is a constant representing her quick response. In the zig-zag tests under $10^{\circ}$ or $20^{\circ}$ at rudder angle, the value K is 0.149. 0.123 sec- and T is 11.853 and 6.193 sec and angular velocity is $0.937^{\circ}/sec$ and $1.636^{\circ}/sec$. In the spiral test, the loop width was unstable at $+0.51^{\circ}$ and $-1.19^{\circ}$ around the midship of rudder, but the tangent line at $0^{\circ}$ was close to vertical. From the sea trial results, we found that she did comply with the present criterion in the standards of maneuverability of IMO.

• 수산해양기술연구
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• 제54권2호
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• pp.107-115
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• 2018

In this study, we tested Japanese trolling lines in the Jeju fishery. This fishery simulates the natural marine environment with many seabed rocks, and has been redesigned and manufactured it to be suitable for the Jeju fishery. In order to ensure that the trolling lines were deployed at the inhabitation depth of hairtails, the conditions required for the fishing gear to reach the target depth were determined for use during the experiment. The experimental test fishing was conducted at the depth of 120 m water in front of Jeju Seongsanpo and in the offshore area of Jeju Hanlim. The fishing gear used in the test fishing is currently used in a variety of field operations in Japan. However, several problems were identified, such as twisting of the line during its deployment and excessive sinking of the main line. The fishing gear was, therefore, redesigned and manufactured to be more suitable for the Jeju fishery environment. For the fishing gear to accurately reach the target depth, depth loggers were installed at the starting point of the main line and at the 250 m and 340 m points of the line. Depth and time were recorded every 10 seconds. According to the daytime positioning of hairtails in the lower water column, the target depth of the fishing gear was set at 100-110 m, which was 10-20 m above the sea floor. At a speed of 1.9 knots and with a 9 kg sinker attached, the main fishing line was deployed and catch yields at depths of 100 m, 150 m and 180 m were recorded and analyzed. When the 180 m main line was fully deployed, the time for the hairtail trolling lines to arrive at the appropriate configuration had to be 5 minutes. At this time, the depth of the fishing gear was 16-23 m above the sea floor, in accordance with the depths at which the hairtails were during the day. In addition, in order to accurately place the fishing gear at the inhabitation water depth of hairtails, the experimental test fishing utilized the results of the depth testing that identified the conditions required for the fishing gear to reach the target depth, and the result was a catch of up to 97 kg a day.

• 한국수산과학회지
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• 제32권3호
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• pp.284-289
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• 1999

수온, 먹이 및 shelter가 참전복에 미치는 효과를 조사하기 위하여 먹이종류 (배합사료, 미역)$\times$shelter 형태 (4종류)$\times$사육수온-(자연수, 가온수)$\times$2반복으로 평균체중 142mg인 참전복을 대상으로 15주간 사육 실험하였다. 생존율은 먹이종류와 사육수온에 따라 차이를 보여 자연수의 미역 공급구들이 대체로 낮은 경향을 보였다 (P<0.05). 증체율은 동일 수온에서 shelter 종류에 관계없이 배합사료 공급구가 현저히 높았으며 (P<0.05), 동일 먹이 공급구내에서는 가온수가 자연수보다 높았는데 특히 배합사료 공급구에서 이러한 차이는 더 현저하였다 (P<0.05). 실험 종료시 가식부의 수분 함량은 먹이와 수온에 따라서는 차이를 보였으나 shelter 종류에 따라서는 차이가 없었다. 단백질 함량은 실험구간에 유의한 차이가 없었으며 (P>0.05), 지질 함량은 자연수에 배합사료 공급구가 미역 공급구보다 전반적으로 높은 경향을 보였다 (P<0.05). 본 실험의 결과로부터 저수온기에 적당히 수온을 상승시킴과 동시에 해조류보다 배합사료를 공급하는 것이 사용 shelter 형태에 관계없이 참전복의 성장을 개선시키고 생존율을 높일 수 있을 것으로 판단된다.

• 한국산학기술학회논문지
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• 제21권4호
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• pp.546-551
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• 2020

함정에는 격벽으로 구분되어 나누어지는 공간인 격실이 종류와 목적에 따라 수개 혹은 수십 개가 존재한다. 이러한 격실들은 화재 및 화재로 인한 연기의 전이방지, 침수 시 침수의 확산 방지 등 특정 격실에서 발생하는 특이 상황들이 타 격실로의 전이를 방지하여 생존성 향상에 목적을 두고 설계된다. 생존성 향상 목적 달성을 위하여 각 격실들은 기밀 또는 수밀을 유지하도록 건조하며, 각 격실의 기밀 또는 수밀 정도를 확인하기 위하여 함정 건조 단계에서 평가를 수행한다. 건조하고 있는 군함에 관한 평가는 해군 지침에 의거하여 함 건조업체 주관으로 해군 및 국방기술품질원이 입회하여 평가를 실시한다. 생존성과 직결되는 만큼 격실 기밀 평가의 중요성은 매우 높아 명확한 기준에 따라 수행되고 있으나, 1개 이상의 복수개 격실 기밀 평가 시 1개 압력센서로 압력을 측정하여 격실 압력을 실시간으로 확인하는 것과 각 격실별 미세한 압력 변동 사항 확인이 제한되는 것을 식별하였다. 따라서 본 연구에서는 현재 수상함정 중 군함에서 실시하고 있는 그룹 격실 기밀평가 방안에 대한 개선 방안 및 신뢰성 검증 방안에 대해 서술하였다.

• 한국수산과학회지
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• 제36권2호
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• pp.113-119
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• 2003

A feeding trial was carried out to Investigate the effect of lipid level and herb mixture in the diets on growth of juvenile parrot fish, Oplegnathus fasciatus. Two plicate groups of fish averaging 4.5 g were fed four experimental diets containing herb mixture (0 and 5 g/kg diet) at each of two lipid levels $(8\%\;and\;16\%)$ for 8 months from summer to spring (water temperature, $7.2-25.4^{\circ}C)$. Weight gain improved with increasing dietary lipid level or supplementation of herb mixture during the first 4 months feeding period. Weight gain of fish fed the diet containing $16\%$ lipid level was significantly higher (P<0.05) than that of fish fed the diet containing $8\%$ lipid level. Weight gain of fish fed the diet with herb mixture was significantly higher (P<0.05) than that of fish fed the diet without herb at the $16\%$ lipid level. Feed efficiency was influenced by dietary lipid level or herb mixture during the first 4 months. On the other hand, weight gain and feed efficiency were not affected by dietary lipid level and herb mixture after 4 months until end of feeing period. Survival of fish fed the diet containing $8\%$ lipid without supplementation of herb mixture was the lowest among the groups (P<0.05). Lipid contents of liver and viscera tended to increase with increasing dietary lipid level during the first 4 months feeding period, however muscle lipid content was not influenced by dietary lipid and herb. Total cholesterol of serum was influenced by dietary lipid level during the first 4 months feeding period. These results indicate that an increase of dietary lipid level from $8\%\;to\;16\%$ and supplementation of herb mixture can improve growth performance of juvenile parrot fish when water temperature is optimum for growth such as the summer season in Korea.