• Journal of Advanced Marine Engineering and Technology
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• 제38권2호
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• pp.208-216
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• 2014

In case of any coastal ocean near the mouth of huge rivers, low salinity water can be formed due to its large amount of freshwater discharge. For the acoustic analysis on the low salinity environment, some oceanographic data of the East China Sea and the Atlantic Ocean were collected through KODC (Korea Oceanographic Data Center) and NODC (National Oceanographic Data Center) online service. In this paper, the T-S gradient diagram is introduced to show a relation between the gradients of temperature and salinity in view of acoustic surface channel formation. Existence of haline channel, quantitative contribution of gradients of salinity and temperature, effectiveness of the channel formation can be known by the T-S gradient diagram. After applying the collected data into the diagram, tropical regions of the Atlantic Ocean show strong haline channel due to its nearly invariant temperature and drastic change of salinity with depth. The averaged transmission loss in the channel is about 5.7 ~ 7.5 dB less than that out of the channel by the results of acoustic propagation model (RAM: Range independent Acoustic Model). On the other hand, the East China Sea and temperate region of the Atlantic ocean have weaker haline channel with less difference of the averaged transmission loss between in and out of the channel as 3.2 ~ 6.0 dB. Although data samples used in this study have limitation to represent the general physical structures of the three ocean regions, the T-S gradient diagram is shown to be useful and acoustic field affected by low salinity environment is investigated in this study.

• Ocean and Polar Research
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• 제36권1호
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• pp.1-12
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• 2014

This study investigates spatial and temporal variations in the generation and propagation of internal tides around the Korea Strait using a three-dimensional high resolution model (Regional Ocean Modeling System; ROMS). The model results were verified through comparison with in-situ current measurements from an array of 12 acoustic Doppler current profilers (ADCPs) deployed in the Korea Strait. Fluxes and distributions of internal tidal energy were calculated using simulation results gathered in February and August. Our analyses reveal that energetic semidiurnal internal tides are generated in a region around the Korea Strait shelf break ($35.5^{\circ}N$, $130^{\circ}{\sim}130.5^{\circ}E$), where the strong cross-slope semidiurnal barotropic tidal currents interact with a sudden topographical change. The semidiurnal internal tidal energy generated in summer displays values about twice as large as values in winter. Propagation of semidiurnal internal tides also reveals seasonal variability. In February, most of the semidiurnal internal tides propagate only into the open basin of the East Sea due to weak stratification in the Korea Strait, which inhibits their southwestward propagation. In August, they propagate southwestward to $35.2^{\circ}N$ along the western channel of the Korea Strait because of strong stratification. In addition, semidiurnal internal tides generated in a region west of Tsushima Island are found to propagate to the coast of Busan. This can be explained by the intensified stratification due to the strong intrusion of bottom cold water in the western channel of the Korea Strait during summer.

• 한국시뮬레이션학회논문지
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• 제30권1호
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• pp.11-20
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• 2021

최근 수중 무인 체계가 대두됨에 따라 핵심 기반 기술인 장거리 수중통신기술 및 고속 수중채널모델링 기술이 많은 관심을 받고 있다. 본 논문에서는 고속 수중채널모델링을 수행하기 위한 고속 음파전달모델을 제안하여, 정량적인 성능 분석을 통해 제안 기술의 적용 가능성을 살펴보았다. 수층에서의 파동 전파를 모사하기 위하여 고차 유한 차분 기법을 사용하였으며, 범용 그래픽 프로세서를 이용한 영역 분할 기법을 적용하여 여러 개의 그래픽 프로세서 병렬 처리를 통해 연산 속도를 향상시켰다. 제안한 기법은 반무한 매질에서의 해석해와의 비교 및 파선법에 기반한 VirTEX 모델을 이용한 결과와의 비교를 통해 그 타당성을 검증하였다. 최종적으로 수치예제를 통해 고속 수중채널 모델링 기법의 정량적인 연산 성능을 분석하였다. 개발모델의 연산 성능 향상 정도를 정량적으로 분석한 결과 그래픽 프로세서 수가 증가함에 따라 연산 속도가 선형에 가깝게 빨라지는 것을 확인하였다. 연산 영역의 크기가 2배로 증가할 때와 주파수가 2배로 증가할 때 계산 시간은 각각 2배와 8배로 증가하였다. 본 논문을 통해 제안한 고속 수중채널모델 기술은 해양무인체계의 수중통신기술 개발을 위한 수중통신 채널모델 및 분석 툴로 탑재되어 국방력 강화에 기여할 수 있을 것으로 기대된다.

• 한국연소학회지
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• 제18권2호
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• pp.1-7
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• 2013

Flame stabilization characteristics of premixed flames in narrow annular coaxial tubes (NACT) were investigated experimentally. The NACT burner was proposed as a model of a cylindrical refractory burner, and it was made of quartz tubes. Flame stabilization conditions affected by the characteristic length of the burner was investigated with the variation of the equivalence ratio and the flow rates. Flame behaviors in narrow spaces could be directly observed. Conclusively, more wide flame stabilization conditions could be obtained at the case of the decreased channel scale. A flame instability, such as combustion noise was detected concerned with the flame oscillation observed at the surface of multi channel stage. Some flame propagation characteristics had complicated tendencies that may exist in practical porous-media combustors. Therefore, this NACT burner can be a basic configuration for the development of flame stabilization model in porous media combustor, and it will enhance our understanding about the behavior of flames in meso-scale combustion spaces.

• 한국해안해양공학회지
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• 제10권3호
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• pp.125-131
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• 1998

본 논문은 경계처리 및 계산과정에 있어서 좀더 개선된 파랑 예측이 보장되도록 기존의 정방형 좌표계에서 수립된 포물선형 및 쌍곡선형 파랑 모델을 경계고정좌표계에 적용하였다. 일정 수심의 만곡 수로를 따라 진행 및 반사하는 파랑에 대한 이론해와 비교하여 수치 모델 결과는 모두 만족할만하였다. 포물선형 모델의 반사 파랑 모의는 반사물에 접근한 입사파를 다시 외해 경계 쪽으로 역계산하여 수행된다.

• Ocean and Polar Research
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• 제43권4호
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• pp.205-217
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• 2021

A shallow channel between Jeju and Udo Islands, which is located in the northeastern Jeju Island, is influenced by storm- or typhoon-induced currents and surface waves as well as strong tidal currents. This study examines the typhoon-induced current and wave patterns in the channel, using Acoustic Doppler Current Meter (ADCP) measurements and an ocean-wave coupled modeling experiment. Three typhoons were chosen - Chaba (2016), Soulik (2018), and Lingling (2019) - to investigate the responses of currents and waves in their pathways. During the pre-typhoon periods, dominant northward flow and wave propagation were observed in the channel due to the southeasterly winds before the three typhoons. After the passage of Chaba, which passed over the eastern side of Jeju Island, the northward flow and wave propagation were totally reversed to the opposite direction, which was attributed to the strong northerly winds on the left side of the typhoon. In contrast, in the cases of Soulik and Lingling, which passed over the western side of Jeju Island, strong southerly winds on the right side of the typhoons continuously intensified the northward current and wave propagation in the channel. The model-simulated current and wave fields reasonably coincided with observational data, showing southward/northward flow and wave propagation in response to the right/left side of the typhoon pathways. Typhoon-induced downwind flows, and surface waves could enhance up to 2m/s and 3m due to the strong winds that lasted for more than 12 hours. This suggests that the flow and wave patterns in the Udo channel are highly sensitive to the pathway of typhoons and accompanying winds; thus, this may be a crucial factor with regard to the movement of seabed sediments and subsequent coastal erosion.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권12호
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• pp.4967-4986
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• 2015

Multi-hop relaying communications have great potentials in improving transmission performance by deploying relay nodes. The benefit is critically dependent on the accuracy of the channel state information (CSI) of all the transmitting links. However, the CSI has to be estimated. In this paper, we investigate the channel estimation problem in one-way multi-hop MIMO amplify-and-forward (AF) relay system, where both the two-hop and three-hop communication link exist. Traditional point-to-point MIMO channel estimation methods will result in error propagation in estimating relay links, and separately tackling the channel estimation issue of each link will lose the gain as part of channel matrices involved in multiple communication links. In order to exploit all the available gains, we develop a novel channel estimation model by structuring different communication links using the PARAFAC and PARATUCK2 tensor analysis. Furthermore, a two-stage fitting algorithm is derived to estimate all the channel matrices involved in the communication process. In particular, essential uniqueness is further discussed. Simulation results demonstrate the advantage and effectiveness of the proposed channel estimator.

• 한국전자파학회논문지
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• 제17권5호
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• pp.490-499
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• 2006

본 논문에서는 지상-항공기간 통신 시험을 통해 장거리 해상 통신 환경에서의 전파 손실을 측정하고 이를 구면 대지 반사 모델을 통한 예측값과 비교하였다. 전파 손실 측정을 위한 항공기 통신 시험은 서해상에서 실시되었으며, 비행 전 구간에 걸쳐 항공기에 장착된 수신기의 수신 신호 세기를 측정하였다. 이때 통신 시험이 수행된 비행 경로 중 반사파의 반사점 인근에 섬이 존재하여 이로 인한 반사파가 수신 신호 간섭을 줄 것으로 예상되었다. 따라서 섬에 의한 반사파까지 고려한 구면 대지 반사 모델에 반사 계수, 발산 계수 및 송수신기의 안테나 패턴을 적용하여 예측한 전파 경로 손실과 항공기 이용해 측정한 전파 손실을 비교하였다. 비교 결과, 섬에 의한 반사파를 고려한 구면 대지 반사 모델로 전파 손실을 정확하게 예측할 수 있음을 확인하였다.

• 물과 미래
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• 제29권5호
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• pp.173-184
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• 1996

본 연구에서는 2차원 천수방정식을 지배방정식으로 이용하여 유속 및 수위분포를 계산할 수 있는 수치모델을 개발하였다. 유한체적법에 의한 이산화과정에서, 3차의 Runge-Kutta 방법과 3차 정도의 upwind scheme을 도입하여 지배방정식의 비정상항과 이송항을 이산화하였다. 개발된 모형의 정확성을 검증하기 위하여 마찰 없는 직사각형 수평수로에 적용하였으며, 수치모형에 의해 얻어진 수심과 유속이 정확해야 잘 일치하였다. 또한, 본 모형을 대칭 및 비대칭 단면축소부를 갖는 직사각형 수로에 적용하여 흐름에 대한 유속분포와 홍수파의 전파가 수치모의 하였으며, 그 결과는 흐름특성을 잘 묘사하였다.

• ETRI Journal
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• 제25권6호
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• pp.535-537
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• 2003

We propose a rigorous 2D approximation technique for the 3D waveguide structures; it can minimize the well-known approximation errors of the commonly used effective index method. The main concept of the proposed technique is to compensate for the effective cladding index in the equivalent slab model of the original channel waveguide from the modal effective index calculated by the nonuniform 2D finite difference method. With simulations, we used the proposed technique to calculate the coupling characteristics of a directional coupler by the 2D beam propagation method, and the results were almost exactly the same as the results calculated by the 3D beam propagation method.