• 한국항공우주학회지
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• 제34권8호
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• pp.1-7
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• 2006

본 연구에서는 3차원 비정렬 중첩격자계를 이용한 서로 겹쳐진 물체들 간의 상대운동 해석기법에 대한 연구를 수행하였다. 홀 컷팅 과정에서 격자요소를 구성하는 모든 격자점들이 다른 물체의 내부에 위치하는 물체 경계의 격자요소들을 계산에서 제외하였고, 일부분이 다른 물체의 내부에 위치하는 격자요소들은 계산영역에 포함하였다. 비정상 유동의 계산을 위해 계산에서 제외되는 비활성 격자요소들에 내삽과 외삽을 통해 적절한 유동값을 부여하여, 상대운동이 진행됨에 따라 다음 시간단계에서 새롭게 활성 격자로 분류될 때 이전 시간에서의 유동값으로 이용될 수 있도록 하였다. 해석기법을 이용하여 기존에는 해석이 불가능했던 3차원 날개의 내부에서 발사체가 사출되는 운동과 발사체의 동체에서 다수의 핀이 전개되는 운동을 해석하였다.

• 방송공학회논문지
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• 제4권1호
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• pp.76-85
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• 1999

프랙탈 부호화 방식에서의 블록 손실 효과는 DCT 기반 블록 부호화 방식에서와는 달리 손실 블록의 참조에 의한 에러 전파 효과 때문에 보다 심각한 화질 저하를 초래한다. 따라서 본 논문에서는 Jacquin 방법에 의해 프랙탈 부호화된 영상을 ATM 망과 같은 손실망을 통해 전송할 경우 발생할 수 있는 블록 손실을 복구하는 방법을 제안한다. Jacquin 의 프랙탈 부호화 체계는 중요도에 따라 머리부호와 본체 부호의 2계층 부호화 체계로 구성된다. 제안된 블록 손실 복구 알고리듬의 핵심 기법은 블록 특성이 손실 블록과 유사한 인접 치역 블록들의 축소 사상 파라미터들을 사용하여 손실 화소들을 추정하는 츠랙탈 외삽이며, 이는 복호화 과정에서 반복적으로 손실 블록들에 적용된다. 실험을 통하여, 제안된 복구 알고리듬이 주관적 화질 뿐만 아니라 PSNR 에서도 우수한 성능을 갖고 있음을 보인다.

• 대한토목학회논문집
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• 제29권6B호
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• pp.543-550
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• 2009

선형외삽법에 기초한 전형적인 단시간 강우예측모형은 호우를 발생하는 강우시스템의 발달과정을 모의하지 못하는 한계를 내포하고 있다. 본 연구에서는 이러한 한계를 극복하기 위하여 기상레이더로 획득할 수 있는 여러 시간대의 반사도 정보로부터 획득한 정보변화 과정과 다항 회귀식을 이용하여 x방향과 y방향의 전파속도의 성장과정과 레이더 반사도의 성장과정 모의에 기초한 단시간 강우예측 모형을 개발하였다. 검정통계량이 제시한 결과는 2-CAPPI를 이용한 기존의 단시간 강우예측모형보다 개선된 결과를 보여주었다. 그럼에도 불구하고 본 모형이 완전한 물리적 모형이 아니라 자료사이의 상관성과 다항 회귀식을 이용한 통계적인 방법에 기초하였으므로 강우의 성장과 소멸과정을 구현과 예측성 개선에도 한계가 있음을 보였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2003년도 봄 학술발표회 논문집
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• pp.288-295
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• 2003

An adaptive procedure in finite element analysis is presented by p-refinement of meshes in conjunction with a posteriori error estimator that is based on the recovery technique. In case of the recovery technique, the SPR(superconvergent patch recovery) approach has been modified for p-adaptive mesh refinement. The strategy of finding a nearly optimal distribution of polynomial degrees on a fixed finite element mesh is discussed such that a particular element has to be refined automatically to obtain an acceptable level of accuracy by increasing p-levels non-uniformly. To verify the proposed algorithm, the limit value approach is proposed which utilizes the exact strain energy computed from the extrapolation equation. A new pre-processor is developed for the p-version finite element program in which the vector graphic editor is used for the automatic generation of node connection and coordinate by halfedge solid data structure according to uniform or nonuniform p-distribution. The general 2-D algorithm is also developed to generate face modes and internal modes in accordance with different mesh types. The quality of the error estimator is investigated with the help of two mumerical examples. The results show that the sequences of p-distributions obtained by the proposed error indicator closely follow the optimal trajectory.

• 한국군사과학기술학회지
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• 제16권2호
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• pp.169-174
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• 2013

In counterfire warfare, it is important to detect and attack enemy targets faster than the enemy using sensing The grided environmental data is usually provided by the numerical simulation coupled with a data assimilation technique and various inter- or extrapolation algorithms, both of which are based on the observation spanning from simple equipments to satellites. In order to employ the gridded environmental data in the M&S system frequently cutting area and changing its resolution, interpolation algorithms such as linear, cubic spline, IDW, and Kriging methods are necessary to apply. These methods, however, require much time in the M&S system. This paper introduces a technic to reduce time to change the resolution of data. using the binary search method, which finds a point to interpolate quickly and interpolate data in the vicinity of. We also show the efficiency of proposed methods by way of measuring the respective elapsed times.

• 한국군사과학기술학회지
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• 제17권6호
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• pp.800-809
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• 2014

The gridded environmental data is usually provided by the numerical simulation coupled with a data assimilation technique and various inter- or extrapolation algorithms, both of which are based on the observation spanning from simple equipments to satellites. But it is difficult to represent the natural phenomenon such as sea mount, internal-wave, warm eddy in modeling or observation because of increase in the complexity of model. This paper introduces the algorithm artificially representing the natural phenomenon and the techniques applying it to the gridded volume data and smoothing for natural effects. Moreover, the inserted results are analyzed by use of graphical tool. The results can be used for the battle simulation or acoustic model.

• ETRI Journal
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• 제30권3호
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• pp.492-494
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• 2008

While the retrial phenomenon plays an important role in communication networks and should not be ignored, retrial systems do not present an exact analytic solution, so approximate techniques are required. To the best of our knowledge, all the existing techniques are based on computing the steady states probabilities. We propose another approach based on the relative state values which appear in the Howard equations. The results of the numerical evaluation carried out show that this solution outperforms previous approaches in terms of both accuracy and computation time.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1087-1090
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• 2003

In this study, experimental procedures were suggested to investigate the sloshing behavior of a liquid storage tank subjected to inevitably external vibrating conditions. For this purpose. liquid storage tank with rectangular cross section was made of an acrylic resin for the visualization of liquid fluctuation. A specially designed vibrator was used to provide a specified vibrating condition to the liquid storage tank. Extrapolation technique was applied to determine sloshing natural frequency by using various sloshing frequencies at each vibrating displacement and liquid contents at a fixed vibrating frequency. Sloshing mode was also determined from continuous images or liquid fluctuation captured from a video camera. In addition, change in the height of the liquid free surface was measured by using a floating target and a laser displacement sensor. It is found that the suggested method can be applicable to identify the sloshing behavior of liquid storage tank with rectangular cross section.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.664-667
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• 2009

We would like to show a measuring technique of azimuthal anchoring energy of the nematic liquid crystals. The electro-optical setup of liquid crystal cell, crossed polarizers and magnetic field was assumed. The planar or hybrid alignment cells were prepared. The director in the light entering substrate and the polarization of light was adjusted into parallel to the magnetic field. The director orientation of exit substrate and analyser maintained perpendicular to the magnetic field. As the magnetic field strength is increased, the director deviates from the easy axis and rotates to the field direction. We obtained an equation calculating the change of transmission with the field and measured experimentally the transmission. By comparing the calculating and experimental data, we obtained the azimuthal anchoring strength.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.666-670
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• 2008

The low-speed preconditioning technique is applied to solve the compressible Reynolds averaged Navier-Stokes equations for low-speed flows. The space discretization is based on Roe's flux-difference splitting with third-order-accurate MUSCL extrapolation. Time integration is performed employing a diagonal approximate factorization algorithm. The dual-time stepping has been incorporated to solve the unsteady flows. Full multigrid method is implemented to accelerate the convergence rate. To verify the algorithms several cases have been tested. Demonstrated the improvement on convergence and quality of the solution.