• 수산해양기술연구
• /
• 제22권1호
• /
• pp.11-18
• /
• 1986

Schooling behavier to a fishing gear and estimation of the volume of fish school in set net have ~ been studied by making use of such techniques as visual observations, underwater cameras, under- water televison. However, all of these observation techniques are subject to restrictions caused by illumination, underwater visibility, underwater transparent and sea conditions. For the above mentioned reasoa, one of the most effective method by this time become generally known a method using fish finder. In this paper, in order to control the fishing ground of set net effectively and to develope the telemetric fish finder, the experiments for the target strength, underwater shape of fishing gear, schooling behavier and volume of fish school with fish finder were performed at Galgott fishing ground of set net located Keouje Island, 15th-24th July and 18th-20th October in 1985. The results of these experiment showed that a method using fish finder in fishing grOlllld of set net is available for estimating distribution and school size, fish behavier in relation to a fishing gear and underwater shape of fishing gears.

• 한국측량학회지
• /
• 제23권4호
• /
• pp.401-408
• /
• 2005

현재 많은 구조물들이 수중에 건설되고 있으나. 수중환경은 지상과 비교하여 다른 매질로 이루어져 있기 때문에 수중구조물의 측정이 어려운 실정이다. 일반적으로 수중 구조물의 측정 방법은 줄자나, 깊이 게이지, 음향 위치시스템 등을 사용한다. 그러나, 줄자는 수중에서 정확한 장력을 가하기가 어렵기 때문에 정확한 거리를 측정하기 어렵고, 깊이 게이지는 설치에 장시간이 걸리는 단점이 있으며, 음향위치시스템은 제한된 공간에서 밖에 작업을 할 수 없고, 가격이 고가이다. 따라서, 본 연구에서는 첫째, 물-유리-공기와 같은 다중매질에서 광선의 경로를 이해하며 둘째, 현장에서 카메라 검정을 실시하여 내부표정요소를 비교하였다. 셋째, 큐브를 이용한 정확도 실험을 통해 사진측량을 수중대상물에 적용할 수 있는지의 여부를 알아보고, 마지막으로 교각모형과 하상의 수중대상물에 대해 수중사진측량을 수행하였다. 실험결과 수중 구조물과 수중지형에 수중사진측량을 적용하는 것이 가능하다는 결론을 얻었다.

• 한국항해항만학회지
• /
• 제37권3호
• /
• pp.269-273
• /
• 2013

수중음향 채널은 일반적으로 다중경로 전달과 분산 등으로 인해 통신하기에 어려운 매질 가운데 하나로 인식된다. MIMO (Multiple-input multiple-output) 기술은 대역이 제한된 수중음향 채널에서 데이터 전송율을 증가시키기 위해 최근 활발히 연구되고 있다. 이 경우 전송 다이버시티 기술을 적용할 수 있는데 대표적인 것이 Alamouti 구조이다. 이 논문에서는 실험을 통하여 전송 다이버시티 기술의 성능을 고찰하였다. 실험에는 2개의 송신기와 2개의 수신기가 사용되었으며, 실내의 음향수조에서 수행되었다. 실험 결과 5~8%의 오차율을 확인하였는데 이는 같은 전송율을 기준으로 SISO(Single-input single-output) 채널에서의 오차율 14.8% 보다 향상된 결과를 나타내었다.

• 한국해양공학회지
• /
• 제31권1호
• /
• pp.8-13
• /
• 2017

Cavitation is used in various fields. This study examined the drag reduction of an underwater vehicle using cavitation. In this study, the natural partial cavitation analysis results were verified using CFD code with the Navier-Stokes equation based on a mixture model. The momentum and continuity equations in the mixture phase were separately solved in the liquid and vapor phases. The solver employs an implicit preconditioning algorithm in curvilinear coordinates. The results of a computational analysis showed good agreement with the experiment. A computational analysis was also performed on the supercavity. The study investigated the cavity characteristics and drag of an underwater vehicle and studied the speed required to achieve a supercavity. Finally, a 1DOF analysis was carried out to investigate the thrust system for a supercavity. As a result, one of the methods for determining a suitable thrust system for a supercavitating underwater vehicle was presented.

• Ocean Systems Engineering
• /
• 제2권2호
• /
• pp.137-145
• /
• 2012

Recent developments in underwater image recognition methods have received large attention by the ocean engineering researchers. In this paper, an improved bi-dimensional empirical mode decomposition (BEMD) approach is employed to decompose the given underwater image into intrinsic mode functions (IMFs) and residual. We developed a joint algorithm based on BEMD and Canny operator to extract multi-pixel edge features at multiple scales in IMFs sub-images. So the multiple pixel edge extraction is an advantage of our approach; the other contribution of this method is the realization of the bi-dimensional sifting process, which is realized utilizing regional-based operators to detect local extreme points and constructing radial basis function for curve surface interpolation. The performance of the multi-pixel edge extraction algorithm for processing underwater image is demonstrated in the contrast experiment with both the proposed method and the phase congruency edge detection.

• 한국정보통신학회:학술대회논문집
• /
• 한국해양정보통신학회 2007년도 추계종합학술대회
• /
• pp.165-169
• /
• 2007

Due to the complexity of underwater acoustic channel, signal estimation in underwater acoustic communication field is considerably affected from time-varying multipath fading channels. On this reason, the original signals should have many long training signals to estimate the channel and the purposed signals, and the bit rate of signals having information may have small rate. In order to avoid this loss of efficiency in underwater communication, this paper employed a blind channel identification method which don't use training signals. Simulations have predicted performance of the employed method in multipath environment and an aquatic plant experiment has verified the simulation results.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2000년도 하계학술대회 논문집 C
• /
• pp.1658-1660
• /
• 2000

Simple signs were usually exchanged as the means of underwater communications. As people recently, need more informations for underwater activities, necessities of underwater communication systems exchanging hunman voice are increased. The purpose of this paper is understanding the ordinary characteristics of underwater communication and investigating the necessary conditions for a good underwater communication system by making a basic communication module. The experiment is achieved by applying AM (Amplitude Modulation) which is mainly used for the underwater communication systems and using common ultrasonic transducers. Ultrasonic transducers usually have narrow bandwidth for transducing electrical energy to mechanical energy. For improvement of sound reconstruction, transducers need more bandwidth which covers voice's frequency range, and goof linearity characteristics in this frequency range. As underwater transmissions have many factors to distort signals. Amplitude Modulation is not a proper way for underwater communications. Using digital signal by sampling human voice should be a good way for this systems, because digital communication simplify transmitting signals.

• International Journal of Ocean System Engineering
• /
• 제1권2호
• /
• pp.68-75
• /
• 2011

This paper addresses an underwater landmark for updating UUV positioning information. A method is proposed in which the landmark's cubic shape and edge are recognized. The reliability, installation load, and management of landmark design were taken into consideration in order to assess practical applications of the landmark. Landmark recognition was based on topological features. The straight line recognition confirmed the landmark's location and enabled an UUV to accurately estimated its underwater position with respect to the landmark. An efficient recognition method is proposed, which provides real-time processing with limited UUV computing power. An underwater experiment was conducted in order to evaluate the proposed method's reliability and accuracy.

• 한국통신학회:학술대회논문집
• /
• 한국통신학회 1984년도 춘계학술발표회논문집
• /
• pp.33-36
• /
• 1984

An underwater communication technic using AM modulated ultrasonicwave was studied. The experiment were performed in the ahechoic water tank with 60KHz carrier wave and the frequency response of the system by demodulated signals were measured varing the degree of modulation and distance between transmitter and receiver. The bandwidth of transmitted signals was limited by the acoustic characteristics. As the result, it was found out that this kind of system is applicable to the underwater speech communication.

• 대한조선학회논문집
• /
• 제61권1호
• /
• pp.1-7
• /
• 2024

Underwater sound speed is an important analysis parameter on an estimation of the underwater radiated noise (URN) emitted from vessels. This paper aims to present an underwater sound speed measurement procedure using a cross-correlation of time-domain acoustic signals and validate the procedure through an experiment in a reverberant water tank. For the purpose, time-domain acoustic signals transmitted by a Gaussian pulse excitation from an acoustic projector have been measured at 20 hydrophone positions in the reverberant water tank. Then, the sound speed in water has been calculated by a linear regression using 190 cross-correlation cases of distances and time lags between the received signals and the result has been compared with those estimated by the existing empirical formulae. From the result, it is regarded that the presented experimental procedure to measure an underwater sound speed is reliably applicable if the time resolution is sufficiently high in the measurement.