• Journal of Mechanical Science and Technology
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• 제16권10호
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• pp.1303-1313
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• 2002

Effects of the reduced frequency of upstream wake on downstream unsteady boundary layer flow were simulated by using a Wavier-Stokes code. The Wavier-Stokes code is based on an unstructured finite volume method and uses a low Reynolds number turbulence model to close the momentum equations. The geometry used in this paper is the MIT flapping foil experimental set-up and the reduced frequency of the upstream wake is varied in the range of 0.91 to 10.86 to study its effect on the unsteady boundary layer flow. Numerical solutions show that they can be divided into two categories. One is so called the low frequency solution, and behaves quite similar to a Stokes layer. Its characteristics is found to be quite similar to those due to either a temporal or spatial wave. The low frequency solutions are observed clearly when the reduced frequency is smaller than 3.26. The other one is the high frequency solution. It is observed for the reduced frequency larger than 7.24. It shows a sudden shift of the phase angle of the unsteady velocity around the edge of the boundary layer. The shift of phase angle is about 180 degree, and leads to separation of the boundary layer flow from corresponding outer flow. The high frequency solution shows the characteristics of a temporal wave whose wave length is half of the upstream frequency. This characteristics of the high frequency solution is found to be caused by the strong interaction between unsteady vortices. This strong interaction also leads to destroy of the upstream wake strips inside the viscous sublayer as well as the buffer layer.

• 환경영향평가
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• 제17권5호
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• pp.299-309
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• 2008

Cumulative effects can be defined as impacts on environment which results from incremental impacts of a proposed project, which covers other past, present, and reasonably foreseeable future actions. The necessity of Cumulative Effect Assessment is that, when there are several projects near the project area, environmental effects of individual project can be larger or smaller than those of individual project without having projects nearby because of synergy, ascending and descending effects. This study was intended to help Environmental Impact Assessment practitioners identify spatial and temporal boundaries during the scoping stage. To do this, literature review of domestic and foreign legislations, guidelines, textbooks and papers related to Environmental Impact Assessment and Cumulative Effect Assessment was accomplished. This study suggests that continuous research be needed in order to identify spatial boundaries for other assessment fields and to develop methodologies for cumulative effect assessment.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2009년도 IWAIT
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• pp.273-277
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• 2009

A compressed video stream is very sensitive to transmission errors that may severely degrade the reconstructed image. Therefore, error resilience is an essential problem in video communications. In this paper, we propose novel temporal error concealment techniques for recovering lost or erroneously received macroblock (MB). To reduce the computational complexity, the proposed method adaptively determines the search range for each lost MB to find best matched block in the previous frame. And the original corrupted MB split into for $8{\times}8$ sub-MBs, and estimates motion vector (MV) of each sub-MB using its boundary information. Then the estimated MVs are utilized to reconstruct the damaged MB. In simulation results, the proposed method shows better performance than conventional methods in both aspects of PSNR.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2015년도 학술발표회
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• pp.253-253
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• 2015

This research evaluated the effect of two main sources on the results of the ocean regional circulation model (ORCMs) during downscaling and nesting the results from the coarse data. The two sources should be the domain size, and temporal and spatial resolution different between driving and driven data. The Big-Brother Experiment is applied to examine the impact of them on the results of the ORCMs separately. Within resolution of 3km grid point ORCMs applying in the Big-Brother Experiment framework, it showed that the simulation results of the ORCMs depend on the domain size and specially the spatial and temporal resolution of lateral boundary conditions (LBCs). The domain size can be selected at 9.5 times larger than the interest area, and the spatial resolution between driving data and driven model can be up to 3 of ratio resolution and updating frequency of the LBCs can be up to every 6 hours per day.

• 한국통신학회논문지
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• 제22권6호
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• pp.1195-1209
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• 1997

This paper presents a new morphological spatio-temporal segmentation algorithm. The algorithm incorporates luminance and motion information simultaneously, and uses morphological tools such as morphological filtersand watershed algorithm. The procedure toward complete segmentation consists of three steps:joint marker extraction, boundary decision, and motion-based region fusion. First, the joint marker extraction identifies the presence of homogeneours regions in both motion and luminance, where a simple joint marker extraction technique is proposed. Second, the spatio-temporal boundaries are decided by the watershed algorithm. For this purposek, a new joint similarity measure is proposed. Finally, an elimination ofredundant regions is done using motion-based region function. By incorporating spatial and temporal information simultaneously, we can obtain visually meaningful segmentation results. Simulation results demonstratesthe efficiency of the proposed method.

• 대한원격탐사학회지
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• 제20권3호
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• pp.163-173
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• 2004

The objective of this study is to develop a method to generate micro-relief digital elevation model (DEM) data of the tidal mudflats using multi-temporal Landsat Thematic Mapper (TM) data. Field spectroscopy measurements showed that reflectance of the exposed mudflat, shallow turbid water, and normal coastal water varied by TM band wavelength. Two sets of DEM data of the inter-tidal mudflat area were generated by interpolating several waterlines extracted from multi-temporal TM data acquired at different sea levels. The waterline appearing in the near-infrared band was different from the one in the middle-infrared band. It was found that the waterline in TM band 4 image was the boundary between the shallow turbid water and normal coastal water and used as a second contour line having 50cm water depth in the study area. DEM data generated by using both TM bands 4 and 5 rendered more detailed topographic relief as compared to the one made by using TM band 5 alone.

• 대한전자공학회논문지SP
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• 제37권4호
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• pp.35-45
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• 2000

본 논문에서는 동영상에 효과적으로 적용 가능한 정점 기반 모양 정보 부호화 알고리즘을 제안한다. 제안한 방법은 영상 사이에 존재하는 시간적 중복성을 해결하기 위해 현재 영상의 외곽선으로부터 정점을 선택 할 뿐 아니라 이미 근사화 되어 부호화된 이전 영상으로부터도 정점을 선택하여 상대적으로 부호화하였으며 고정된 오차 한계 이내에서 비트 발생량이 최소가 되도록 정점을 선택한다. 이는 코드표현 방법이 정해져 있을 때 비율-왜곡 측면에서 최적이다. 쟁점 선택은 가중치를 갖는 방향그래프에서의 최단 경로 탐색으로 모델링되어 최적의 정점을 선택하도록 하였으며 실험 결과 기존의 모양 정보 부호화 방법보다 적은 비트율을 요구하였다. 제안한 방법은 실시간 부호화를 필요로 하지 않는 저장 매체를 위한 객체 기반 부호화 시스템 및 웹을 통한 동영상 전송에 이용될 수 있다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.392-397
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• 2001

A numerical study is performed to investigate the interaction between subsonic axial turbine blade boundary layer and periodically oncoming rotor induced wakes. An implicit scheme for solving the compressible Navier-Stokes equation is developed, which adopts a 4th-order compact difference for spatial discretiztion, a 2nd order Crank-Nicolson scheme for temporal discretization and the dynamic eddy viscosity model as the subgrid scale model. The efficiency and the accuracy of the proposed method are verified by applying to some benchmark problems such as laminar cylinder flow, laminar airfoil cascade flow and a transitional flat plate boundary layer flow. Computational results show good agreements with previous experimental and numerical results. Finally, flow through a stator cascade is simulated at $Re = 7.5{\times}10^5$ without free-stream turbulence intensity. The velocity fields and skin friction coefficients in the transitional region show similar trends with previous boundary layer natural transition.

• 음성과학
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• 제10권1호
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• pp.27-39
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• 2003

This study attempts to verify the reliability of automatically generated segment labels as compared to those obtained by conventional labelling by hand. First of all, an autolabeller is constructed using the standard HMM speech recognition technique. For evaluation, we compare the automatically generated labels with manually annotated labels for the same speech data. The comparison is performed by calculating the temporal difference between an autolabel boundary and its corresponding hand label boundary. When the mismatched duration between two labels falls within 10 msec, we consider the autolabel as correct. The results suggest that overall 78% of autolabels are correctly obtained. It is found that the boundary of obstruents is better aligned than that of sonorants and vowels. In case of stop sound classes, strong stops in manner-of-articulation wise and velar stops in place-of-articulation wise show better performance in boundary alignment. The result suggests that more phone-specific consideration is necessary to improve autosegmentation performance.

• 한국멀티미디어학회논문지
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• 제12권11호
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• pp.1563-1571
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• 2009

H.264/AVC의 시간적 오류 은닉을 위한 새로운 경계 정합 방법과 은닉된 영상의 화질 향상을 위한 후처리 방법을 제안한다. 시간적 오류 은닉은 참조 프레임에서 가장 유사한 블록으로 오류가 발생한 블록을 대체시키는 방법이다. 가장 유사한 블록을 찾기 위해 H.264/AVC에서는 오류가 발생한 블록의 바깥 경계의 화소값과 참조블록의 안쪽 경계의 화소값을 단순 비교한다. 그러나 기존의 방법은 좁은 범위의 화소값 만을 비교하므로 부정확한 블록으로 오류 블록을 대체할 확률이 높다. 본 논문에서는 더욱 정확한 블록으로 오류 블록을 대체하기 위하여 참조 블록의 안쪽 경계의 화소값과 바깥 경계의 화소값을 오류 블록의 바깥 경계의 화소값과 비교하고 후보 움직임 벡터의 최솟값과 최댓값을 기준으로 일정 검색 범위내의 추가적인 후보 움직임 벡터를 설정하는 보다 향상된 경계 정합 방법, 그리고 변형된 디블록킹 필터를 통해 오류 없이 복호된 블록과 오류가 은닉된 블록과의 경계를 부드럽게 하는 후처리 방법을 제안한다. 실험을 통하여 제안된 방법이 기존의 블록 정합방법보다 최대 약 0.9 dB의 화질 향상을 보여주는 것을 확인하였다.