• 한국수산과학회지
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• 제8권1호
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• pp.1-6
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• 1975

복잡하게 운동하고 있는 예망어구에서 발생하는 여러 가지 소음들을 분석 녹음하기 위해 수중 녹음장치를 제작하여 실제 소형 트로올망의 수중소음을 녹음 하였으며, 본 수중 녹음장치는 이동하고 있는 어구에서 발생하는 수중소음을 녹음하는데는 편리하고 효과적이었고 spectrum의 분석 결과는 다음과 같다. 1) 예일중인 트로올망의 수중소음이 주된 음원은 어구의 발줄과 해저와의 마찰에 의한 소음이라는 것을 알았다. 2) 이동중의 트로올망의 수중소음의 주파수 분포는 $DC\~5000\;Hz$이고 그중 우세한 주파수는 약 $500\~700Hz$ 였다. 3) 트로올망의 절대음압의 최대는 50m 수심에서는 약 22 dB이었다.

• 한국음향학회지
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• 제20권8호
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• pp.67-73
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• 2001

최근 수중음향에 대한 관심은 천해와 같은 복잡한 음파의 상호작용과 경계조건이 부정확한 해양환경으로 이동하고 있다. 천해 음향전파에 의해서 발생하는 어려움을 극복하기 위한 방법으로 음원의 광대역 스펙트럼에서 얻어지는 정보를 사용하여 견고성과 신뢰성을 증가시키는 광대역 정합장처리 기법이 사용된다. 본 논문에서는 협대역에서의 음장의 공간 일관성을 확장하여 다중 주파수를 사용한 주파수-공간 일관성 광대역 프로세서를 제안하였고, 이 프로세서를 실제 광대역 이동음원에 적용하여 음원위치추적을 수행하였다. 제안된 일관성 프로세서는 음원의 정위치 추정확률이 높았으며, 특히 정합장출력의 부엽준위에서 비일관성 프로세서와 비교해 일관성 프로세서가 상당히 낮은 준위를 나타내었다.

• 보존과학연구
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• 통권30호
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• pp.189-202
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• 2009

Ceramics from Taean shipwreck were studied to investigate the deterioration by soluble salts and desalination pattern according to each ceramic characterization. NaCl crystals were found as a crystal growth on the ceramic microstructure and deteriorated to push off the glaze layer of some Puncheong ware sample. As a result of monitoring the desalination pattern of ceramics for 74days, the earthenware sample with big pores and no glaze removed soluble salts so fast, but Puncheong ware and Whiteware samples removed lots of soluble salts slowly and continuously. Generally, it takes long time to remove soluble salts from porcelains, due to small pores and glaze, but the long-term desalination probably can cause the damage on the surface layer such like glaze. As some soluble salts still remains in the ceramic microstructures after desalination, it is very important to control and keep the relative humidity stable through the proper storage. There are various ceramic deterioration patterns by soluble salts. Therefore, it needs to select the desalination method of ceramics from shipwreck, considering the material characteristics and the production techniques.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2016년도 추계학술발표대회
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• pp.510-513
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• 2016

Detecting of the object in image processing is substantial but it depends on the object itself and the environment. An object can be detected either by its shape or color. Color is an essential for pattern recognition and computer vision. It is an attractive feature because of its simplicity and its robustness to scale changes and to detect the positions of the object. Generally, color of an object depends on its characteristics of the perceiving eye and brain. Physically, objects can be said to have color because of the light leaving their surfaces. Here, we conducted experiment in the aquarium fish tank. Different color of fish robots are mimic the natural swim of fish. Unfortunately, in the underwater medium, the colors are modified by attenuation and difficult to identify the color for moving objects. We consider the fish motion as a moving object and coordinates are found at every instinct of the aquarium to detect the position of the fish robot using OpenCV color detection. In this paper, we proposed to identify the position of the fish robot by their color and use the position data to control the fish robot gathering in one point in the fish tank through serial communication using RF module. It was verified by the performance test of detecting the position of the fish robot.

• 수산해양기술연구
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• 제19권2호
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• pp.93-98
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• 1983

When detecting underwater targets using echo sounder, the echo signals varies with the angular displacement of the transducer due to ship's motion. Then, the effect of the angular which effects the capability of the echo sounder must be investigated in relation to the detection of fish concentration, particularly, the abundance estimation of fish. In this pater, as the basic research to investigate the effect of the ship's motion when estimating the fish stocks by acoustic methods, the authors was theoritically considered the variations in the values of the two way directivity function of transducer in the direction of the targets which caused by the angular motion of transducer. Here, the effects of the movement of target and ship's running are neglected. At the same time, the data was applied to estimate the angular shift of the detectable area of echo sounder due to transducer displacement. From the results analyzed, we found that the angular shift of the detectable area due to ship's motion increases both as the roll angle increases and as the beamwidth becomes narrower, varies with the depth.

• 생태와환경
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• 제43권2호
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• pp.199-211
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• 2010

The objectives for this study were to evaluate spatial and temporal characteristics of water quality, based on long-term water quality monitoring data during 1993~2008. We found that physico-chemical and ecological conditions in the Daecheong Reservoir (DR) were modified by the construction of upper dam (i.e., Yongdam Reservoir). total phosphorus (TP), Secchi depth (SD), and chlorophyll-a (CHL) in the DR showed significant longitudinal decreases along the headwater-to-the downlake, indicating a large spatial variation, and this gradient was more intensified during the high-flow season (monsoon). Nutrient-rich water containing high nitrogen and phosphorus in the monsoon season (July~August) passed through the reservoir as a density current in the metalimnetic depth, and also high suspended solids increased in the metalimnetic depth, especially during the monsoon. According to the deviation analysis of Trophic State Index (TSI), >50% of TSI (CHL)-TSI (SD) and TSI (CHL)-TSI (TP) values were negatives, so that inorganic suspended solids (non-votatile solids) influenced the underwater light regime against phytoplankton growth. Also, ratios of CHL:TP after the dam construction evidently increased, compared to the values before the upper dam constructions, indicating a greater yield of phytoplankton in the unit phosphorus. Overall data showed that ecological and functional changes in Daecheong Reservoir occurred after the construction of upper dam (Yongdam Reservoir).

• Journal of Electrical Engineering and Technology
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• 제5권1호
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• pp.156-162
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• 2010

This paper describes electrical and optical characteristics of discharge developments in water under inhomogeneous fields caused by impulse voltages. Predischarge current and discharge light images were observed for different water resistivities and applied voltages between the hemispherical water tank and the needle electrode. The electrical parameters characterizing discharge developments are analyzed based on the discharge light images and voltage-current (V-I) curves, and electrical resistances derived by voltage and current waveforms. As a result, when the streamer corona is initiated at the tip of the needle electrode, the transient resistance suddenly drops and V-I curves form a 'loop'. The length of streamer propagation is increased with increasing peak value of the applied voltage, and the streamer corona extension is enlarged with increasing water resistivity. The electrical resistances before streamer corona initiation are rarely changed by different applied voltages. On the other hand, the electrical resistances after streamer corona initiation are found to be inversely proportional to the peak value of the applied voltage, and the decreasing rates for higher water resistivities are much higher than those for lower water resistivities. The time to streamer corona initiation and the time to the second current peak become shorter as the voltage increases. Finally, the calculated resistances after streamer corona initiation are almost the same trace of measured resistances, but they are smaller than the measured values.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2019년도 추계 학술논문 발표대회
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• pp.141-142
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• 2019

In this study, we conducted a comparative analysis of the effects of retention time and resuscitation method on the degree of resuscitation after reapplying mortar with much FA replacement. Results After applying NaOH to the top surface of 60 % FA-substituted mortar, the degree of resuscitation at $40^{\circ}C$ was high enough to increase the overall curing time, but there was no significant difference. However, with regard to the curing method, middle curing showed the greatest manifestation, followed by wrapping and underwater curing, but there was no significant difference. The resuscitation level on the 28th of the lumber was found to be revived to about 70~80 % at around 30 % without resuscitation.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.572-583
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• 2019

This paper aims to assess the applicability of the Runge Kutta Discontinuous Galerkin-Direct Ghost Fluid Method to the internal explosion inside a water-filled tube, which previously was studied by many researchers in separate works. Once the explosive charge located at the inner center of the water-filled tube explodes, the tube wall is subjected to an extremely high intensity fluid loading and deformed. The deformation causes a modification of the field of fluid flow in the region near the water-structure interface so that has substantial influence on the response of the structure. To connect the structure and the fluid, valid data exchanges along the interface are essential. Classical fluid structure interaction simulations usually employ a matched meshing scheme which discretizes the fluid and structure domains using a single mesh density. The computational cost of fluid structure interaction simulations is usually governed by the structure because the size of time step may be determined by the density of structure mesh. The finer mesh density, the better solution, but more expensive computational cost. To reduce such computational cost, a non-matched meshing scheme which allows for different mesh densities is employed. The coupled numerical approach of this paper has fewer difficulties in the implementation and computation, compared to gas dynamics based approach which requires complicated analytical manipulations. It can also be applied to wider compressible, inviscid fluid flow analyses often found in underwater explosion events.

• International Journal of Internet, Broadcasting and Communication
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• 제13권1호
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• pp.152-160
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• 2021

The purpose of this study was to investigate the difference in the number of repetitions and the change in electromyographic response during the maximum speed squat exercise according to the depth conditions and the maximum speed squat exercise according to the time of each depth. Ten men in their 20s were selected as subjects and the maximum speed squat was performed for one minute in three environmental conditions (ground, knee depth, waist depth). We found that the number of repetitions according to the depth of water showed a significant difference, and as a result of the post-mortem comparison, the number of repetitions was higher in the ground condition and the knee depth than in the waist depth. And the muscle activity of rectus abdominis, erector spinae, rectus femoris, biceps femoris was increased during ground squat exercise, activity of all muscle was decreased during knee depth squat exercise, and activity of rectus abdominis, erector spinae, biceps femoris, tibialis anterior, gastrocnemius was decreased during waist depth squat. In conclusion, muscle activity of lower extremities during squat exercise in underwater environment can be lowered as the depth of water is deep due to buoyancy, but muscle activity of trunk muscles can be increased rather due to the effect of viscosity and drag.