• Journal of the Society of Naval Architects of Korea
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• v.35 no.3
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• pp.14-25
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• 1998

This paper describes the numerical modelling for the steady and unsteady forces of 3-D wings flying near the free surface based on a potential based panel method. For the steady problem where a wing flies over the fixed float surface, steady lift and drag forces are calculated for wings with and without end-plates having different sections, angle of attacks, aspect patios and flying heights. These numerical results are compared with the wind tunnel test results. The unsteady problem is treated as a boundary value one where a wing flies over the described wavy surface. The unsteady lift force variations of a wing due to different wave lengths and heights are calculated at different flying heights.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.3
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• pp.173-178
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• 2019

To analyze the diffraction properties of optical signals by periodic blazed 2D diffraction gratings, Toeplitz dielectric tensor is first defined and formulated by 2D spatial Fourier expansions associated with asymmetric blazed grating profile. The characteristic modes in each layer is then based on eigenvalue problem, and the complete solution is found rigorously in terms of modal transmission-line theory (MTLT) to address the pertinent boundary-value problems. Toeplitz matrix of symmetric and sawtooth profiles is derived from that of asymmetric blazed grating profile, and the diffraction properties for each profile are numerically simulated. The numerical results reveal that the asymmetric and symmetric profiles behave as anti-reflection GMR filter while the sawtooth profile works better as anti-transmission one rather than anti-reflection filter.

• Journal of Environmental Science International
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• v.6 no.5
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• pp.541-550
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• 1997

A least-square regression analysis is applied for the estimation of velocity streamfunction field based on discretely sampled current meter data. The coefficients of a streamfuunction that is expanded in terms of trigonometric basis function are obtained by enforcing the horizontal non-divergence of two-dimensional flow field. This method avoids Interpolation and gives a root-mean-square (rms) residual of fit which Includes the divergent part and noisiness of oceanic data. The Implementation of the method Is done by employing a boundary-fitted, curvilinear orthogonal coordinate which facilitates the specification of boundary conditions. An application is successfully made to the Texas-Louisiana shelf using the 32 months current meter data (31 moorings) observed as a part of the Texas-Louisiana Shelf and Transport Processes Study (LATEX). The rms residual of the fitting is relatively small for the shelf, which indicates the field Is Ivell represented by the streamnfunction.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2012.07a
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• pp.124-126
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• 2012

3차원 동영상은 수많은 응용분야에서 차세대 멀티미디어 콘텐츠로 큰 주목을 받고 있지만 2차원에서 3차원 콘텐츠로의 과도기인 현 시점에서 3차원 콘텐츠의 부족현상은 관련 산업분야의 큰 문제점으로 떠오르고 있다. 2D-to-3D 변환 기술은 높은 비용 없이 기존의 방대한 2차원 콘텐츠를 3차원 콘텐츠로 재사용하는 것이 가능하기 때문에 3차원 콘텐츠의 부족 문제를 해결할 수 있는 기술로 큰 관심을 끌고 있다. 본 논문에서는 블록 단위 초점 정보의 보간을 통한 새로운 초점 기반 3차원 변환 기법을 제안한다. 기존의 화소 단위 초점 측정치를 그대로 깊이 정보로 이용하는 경우나 분할 영역 단위 초점 측정치를 깊이 정보로 활용하는 경우는 이웃 화소간 깊이정보의 불연속성이 발생할 수 있지만 제안방식은 블록 초점 측청치의 보간수행으로 인해 이웃 화소 사이에서 뿐만 아니라 블록경계 혹은 영역경계에서도 특별할 스무딩필터 처리 없이도 화소간 깊이정보의 불연속성이 발생하지 않게 된다. 실험결과를 통해 제안한 방식이 기존의 방식들 보다 더 자연스러운 깊이 정보 추출 성능을 보여준다는 것을 알 수 있다.

• Tunnel and Underground Space
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• v.15 no.2 s.55
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• pp.145-156
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• 2005

MODFLOW, 3-D finite difference code, is widely used to model groundwater flow and has been used to assess the effect of excavations on the groundwater system due to construction of subways and mountain tunnels. The results of numerical analysis depend on boundary conditions, initial conditions, conceptual models and hydrogeological properties. Therefore, its accuracy can only be enhanced using more realistic and field oriented input parameters. In this study, SA(simulated annealing) was used to integrate hydraulic conductivities from a few of injection tests with geophysical reference images. The realizations of hydraulic conductivity random field are obtained and then groundwater flows in each geostatistically equivalent media are analyzed with a numerical simulation. This approach can give probabilistic results of groundwater flow modeling considering the uncertainty of hydrogeological medium. In other words, this approach makes it possible to quantify the propagation of uncertainty of hydraulic conductivities into groundwater flow.

• Korean Journal of Remote Sensing
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• v.12 no.2
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• pp.155-168
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• 1996

Speckle noise has been a primary concern to many applications of synthetic aperture radar (SAR) imagery. In recent years, several satellites with radar imaging systems were launched and the use of SAR data are expected to be increased rapidly The objectives of this study are to provide introductory understanding on radar speckle filtering and to compare the effects of several filtering methods that are relatively unknown to user community. Two study sites were extracted from the RADARSAT SAR data obtained over the suburban areas near Seoul. The study sites include relatively homogeneous cover types, such as reservoir, parking lot, rice pad, and deciduous forest. Five filters (mean filter, median filter, sigma filter, local statistics filter, and autocorrelation filter) were applied to the SAR imagery and their effects were evaluated from the aspects of both image smoothing and edge preservation. In overall, the evaluation results indicate that the local statistics filter and autocorrelation filter, that are based on a speckle model, are more effective to suppress speckle within homogeneous cover type while maintaining the edge sharpness between cover types.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.9
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• pp.12-26
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• 2004

A new treatment of cell-interface flux in AUSM-type methods is introduced to reduce the numerical dissipation. Through analysis of TVD limiters, a criterion for the more accurate prediction of cell-interface state is found out and M-AUSMPW+ is developed by determining the transferred property newly and appropriately within the criterion. The superiority of M-AUSMPW+ is clearly revealed in multi-dimensional flow problems. It can eliminate numerical dissipation effectively in a non-flow aligned grid system. As a result, M-AUSMPW+ is shown to be much more accurate and effective than other previous schemes in multi-dimensional problems. Through a stationary contact discontinuity, a vortex flow, a shock wave/boundary layer interactions and viscous shock tube problems, it is verified that accuracy of M-AUSMPW+ is improved.

• Journal of Intelligence and Information Systems
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• v.14 no.2
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• pp.193-206
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• 2008

Medical diagnosis can be considered a classification task which classifies disease types from patient's condition data represented by a set of pre-defined attributes. This study proposes a hybrid genetic algorithm based classification method to develop classifiers for multidimensional pattern classification problems related with medical decision making. The classification problem can be solved by identifying separation boundaries which distinguish the various classes in the data pattern. The proposed method fits a finite number of regional agents to the data pattern by combining genetic algorithms and local adaptive operations. The local adaptive operations of an agent include expansion, avoidance and relocation, one of which is performed according to the agent's fitness value. The classifier system has been tested with well-known medical data sets from the UCI machine learning database, showing superior performance to other methods such as the nearest neighbor, decision tree, and neural networks.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.12 no.3
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• pp.116-129
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• 2000

The interaction of incident monochromatic waves with a tensioned, flexible, circular membrane submerged horizontally below free surface is investigated in the frame of three-dimensional linear hydro-elastic theory. The velocity potential is split into two parts i.e. the diffraction potential representing the scattering of incident waves by a rigid circular disk and the radiation potential describing motion induced waves by elastic responses of flexible membrane. The fluid domain is divided into three regions, and the diffraction and radiation potentials in each region are expressed by the Fourier Bessel series. The displacement of circular membrane is expanded with a set of natural functions, which satisfy the membrane equation of motion and boundary conditions. The unknown coefficients in each region are determined by applying the continuity of pressure and normal velocity at the matching boundaries. The results show that various types of wave focusing are possible by controlling the size, submergence depth, and tension of membrane.

• Tunnel and Underground Space
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• v.11 no.4
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• pp.362-367
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• 2001

The stiff top layer in a soil profile, which can happen in winter, may change the isolation effect of the wave barrier. The research scope of this paper is the investigation of the propagation of surface waves in layered soil with a stiff layer on its top, and the isolation effect of the solid stiff wave barrier. The investigations have been performed numerically by the Boundary-Element Method as a two-dimensional problem. A strip foundation vibrated harmonically in vertical direction was considered as the vibration source. Three soil profiles, a homogeneous half-space, two profiles with different thickness of stiff top layer, with two different types of wave barriers were investigated. The profiles with a stiff top layer show considerable reductions of the amplitude of the vibration in comparison to the homogeneous soil profile. The layered soil profiles with a stiff top layer do not show wave propagation velocities as high as they are expected from the material properties. Furthermore the vibration amplitudes in a frozen soil are much smaller with distance than in a non-frozen soil.