• Structural Engineering and Mechanics
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• 제20권3호
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• pp.293-312
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• 2005

In this paper, free vibration of rotating beam with random properties is studied. The cross-sectional area, elasticity modulus, moment of inertia, shear modulus and density are modeled as random fields and the rotational speed as a random variable. To study uncertainty, stochastic finite element method based on second order perturbation method is applied. To discretize random fields, the three methods of midpoint, interpolation and local average are applied and compared. The effects of rotational speed, setting angle, random property variances, discretization scheme, number of elements, correlation of random fields, correlation function form and correlation length on "Coefficient of Variation" (C.O.V.) of first mode eigenvalue are investigated completely. To determine the significant random properties on the variation of first mode eigenvalue the sensitivity analysis is performed. The results are studied for both Timoshenko and Bernoulli-Euler rotating beam. It is shown that the C.O.V. of first mode eigenvalue of Timoshenko and Bernoulli-Euler rotating beams are approximately identical. Also, compared to uncorrelated random fields, the correlated case has larger C.O.V. value. Another important result is, where correlation length is small, the convergence rate is lower and more number of elements are necessary for convergence of final response.

• 공학논문집
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• 제3권1호
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• pp.159-169
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• 1998

이 논문에서는 수정곡면 카세그레인 안테나의 복사특성을 해석하였다. 부반사판의 복사특성은 GTD를 이용하여 계산되었고, 완전한 복사패턴은 반사파와 회절파의 합으로 표현되었다. 부반사판의 해석을 위해서 부반사판의 1,2차 미분값을 국지보간법을 이용하여 구했다. 주반사판의 복사특성 해석은 PO를 사용하여 유도된 표면전류밀도를 적분하므로써 수행되었다. Jacobi-Bessel 급수를 이용하여 적분식을 변형시켜서 계산 시간을 단축시켰다.

• 한국대기환경학회지
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• 제25권4호
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• pp.264-274
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• 2009

Concentration of Air Quality Models (CMAQ) has a deep connection with emissions and wind fields. In particular the wind field is highly affected by local topography and plays an important role in transport and dispersion of contaminants from the pollution sources. The purpose of this study is to examine the impact of interpolation on Air quality model. This study was designed to evaluate enhancement of MM5 and CMAQ predictions by using Four Dimensional Data Assimilation (FDDA), the SONDE data and the national meteorological station and the MODerate resolution Imaging Spectroradiometer (MODIS). The alternative meteorological fields predicted with and without MODIS data were used to simulate spatial and temporal variations of ozone in combined with CMAQ on June 2006. The result of this study indicated that data assimilation using MODIS data provided an attractive method for generating realistic meteorological fields and dispersion fields of ozone in the Korea peninsular, because MODIS data in 10 km domain are grid horizontally and vertically. In order to ensure the success of Air quality model, it is necessary to FDDA using MODIS data.

• 대한기계학회논문집A
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• 제27권8호
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• pp.1418-1425
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• 2003

In CAD systems, a surface to be machined is expressed by a series of curves, such as B-spline, Bezier and NURBS curves, which compose the surface and then in CAM systems the curves are divided into a large number of line or arc segments. These divided movement commands, however, cause many problems including their excessive size of NC data that makes almost impossible local adjustment or modification of the surface. To cope with those problems, the necessity of real-time curve or surface interpolators was embossed. This paper presents an efficient real-time tool-path generation method fur interpolation of NURBS surfaces in CNC machining. The proposed tool-path generation method is based on an improved iso-scallop strategy and can provide better precision than the existing methods. The proposed method is designed such that tool-path planning is easily managed in real-time. It proposed a new algorithm for regulation of a scallop height, which can efficiently generate tool-paths and can save machining time compared with the existing method. Through computer simulations, the performance of the proposed method is analyzed and compared with the existing method in terms of federate, total machining time and a degree of constraint on the scallop height.

• 한국BIM학회 논문집
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• 제7권4호
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• pp.31-38
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• 2017

Big Cyprus watershed, which is located in the Southwestern Florida and covers Everglades National Park that has high proportions of endangered species' habitats, plays an important role for the entire Florida ecosystem. Due to the rapid urbanization and high population growth, however, the watershed has been continuously polluted and the current regional watershed plan is not created to accommodate the speed of growth. The purpose of this study is to suggest proper protection policies and strategies for the Big Cyprus watershed by employing the Inverse Distance Weighted interpolation tool in Geographic Information System. The findings show that conservation priorities should be given in the North and South portion of the watershed area, which are proven to be the most important aisle for the habitats in the Big Cyprus. The study concludes with policy suggestions that local environmental planners should concentrate for adopting their new watershed plan in the near future.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2001년도 봄 학술발표논문집 Vol.28 No.1 (B)
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• pp.625-627
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• 2001

기존의 종이지도를 수치지도 처리과정으로 얻어진 등고선(contour line) 데이터는 원격탐사(Remote Sensing)와 지리정보시스템(GIS)의 응용분야에서 주로 사용되어지는 데이터이다. 이러한 등고선은 해당 지역의 DTM(Digital Terrain Model) 데이터 생성을 위해 보간(interpolation)하여 생성하는 데 연구가 집중되어 왔다. 본 논문에서는 DEM(Digital levation Model)으로부터 얻어진 등고선 데이터를 이용하여 사용자에게 3차원으로 가시화 해 줄 수 있는 기법을 소개한다. 등고선 추출을 위한 방법으로는 기존의 소개되어진 Marching Square 알고리즘을 적용하였고, 지역적인 최고점(local minimum)과 최소점(maximum)을 구하기 위해 등고선을 열린 등고선(open contour)과 닫힌 등고선(closed contour)으로 분류하게 된다. 지역적 최고, 최소점을 찾기 위한 탐색공간을 줄이기 위해 닫힌 등고선만을 닫힌 등고만을 대상으로 등고선 트리를 생성하였으며, 생성된 트리의 리프노드에 대해서 최고, 최소점에 대한 근사(approximation)를 수행하게 된다. 이렇게 구해진 근사된 장점들과 등고선 데이털 입력으로 하여 제한된 딜로니 삼각분할(Constrained Delaunay Triangulation)을 수행함으로써, 3차원 지형을 재구성할 수 있다. 실험에서 간단한 그리드 샘플데이터와 USGS로 획득한 데이터를 이용하여 속도 측정을 하였다. 결과적으로 저장공간 측면에서 적은 량의 데이터를 가지면서 등고선을 표현할 수 있는 3차원 지형을 랜더링할 수가 있음을 알 수 있다.

• Kyungpook Mathematical Journal
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• 제48권4호
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• pp.665-684
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• 2008

Runge-Kutta-Nystr$\"{o}$m (RKN) methods provide a popular way to solve the initial value problem (IVP) for a system of ordinary differential equations (ODEs). Users of software are typically asked to specify a tolerance ${\delta}$, that indicates in somewhat vague sense, the level of accuracy required. It is clearly important to understand the precise effect of changing ${\delta}$, and to derive the strongest possible results about the behaviour of the global error that will not have regular behaviour unless an appropriate stepsize selection formula and standard error control policy are used. Faced with this situation sufficient conditions on an algorithm that guarantee such behaviour for the global error to be asympotatically linear in ${\delta}$ as ${\delta}{\rightarrow}0$, that were first derived by Stetter. Here we extend the analysis to cover a certain class of ODEs with low-order derivative discontinuities, and the class of ODEs with constant delays. We show that standard error control techniques will be successful if discontinuities are handled correctly and delay terms are calculated with sufficient accurate interpolants. It is perhaps surprising that several delay ODE algorithms that have been proposed do not use sufficiently accurate interpolants to guarantee asymptotic proportionality. Our theoretical results are illustrated numerically.

• 한국측량학회지
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• 제18권3호
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• pp.295-303
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• 2000

본 연구는 GPS사용에 따른 많은 장점 때문에 보편화되어 가는 DGPS기술에 의한 조위측위의 효율성과 정도의 향상을 위한 것으로, 연구결과 여러 형태의 수학적인 회귀공식에 의하여 최적화공식의 선택 및 회귀처리가 가능하였다. 또한 종래에는 단계적인 방법에 의하여 GPS시간과 조위시간을 일치시켰으나 실시간적으로 평면과 표고(2D+1D) 좌표변환하여 해양바닥면의 높이를 Cm정확도로 계산하게 되었다. 이러한 시각동기화로 실시간 DGPS 수심측량은 지역적인 조류와 조위의 변화에 대처할 수 있다.

• 한국유체기계학회 논문집
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• 제15권5호
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• pp.48-53
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• 2012

This paper presents a systematic procedure for three-dimensional noise analysis of an axial-flow fan by using computational aero-acoustics based on Ffowcs Williams-Hawkings equation. Flow-fields of a basic fan model are simulated by solving three-dimensional, unsteady, Reynolds-averaged Navier-Stokes equations using the commercial code ANSYS CFX 11.0. Starting with steady flow results, unsteady flow analysis is performed to extract the fluctuating pressures in the time domain at specified local points on the blade surface of the axial flow fan. The perturbed density wave by rotating blades reaches at the observer position, which is simulated by an in-house noise prediction software based on Ffowcs Williams-Hawkings equation. The detailed far-field noise signatures from the axial-flow fan are analyzed in terms of source types, field characteristics, and interpolation schemes.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2017년도 춘계학술대회
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• pp.793-796
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• 2017

영상신호는 신호를 처리하는 과정에서 다양한 잡음에 의해 훼손되어지며, 이러한 신호를 복원하기 위한 많은 연구가 이루어지고 있다. 영상에 첨가되는 잡음에는 salt and pepper 잡음, AWGN(additive white Gaussian noise) 및 두 잡음이 혼합된 복합잡음이 대표적이다. 따라서 본 논문에서는 복합잡음 환경에서 훼손된 영상을 복원하기 위해, 잡음 판단을 통해 국부 마스크의 중심화소가 salt and pepper 잡음인 경우, 2차원 스플라인 보간법 및 메디안 필터로 처리하고, AWGN인 경우, 화소변화에 따른 가중치 필터로 처리하는 알고리즘을 제안하였다.