• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.430-435
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• 2001

This paper introduces a pressure correction method for microflow computation. Conventional CFD methods with no slip boundary condition fail to predict the rarefaction effect of the wall when simulating gas microflows in the slip-flow regime. Pressure correction method with an appropriate slip boundary condition is an efficient tool in analyzing microscale flows. The present unstructured SIMPLE algorithm adopts both the classical Maxwell boundary condition and Langmuir boundary condition proposed by Myong. The simulation results of microchannel flows show that the proposed method has an effective predictive capability for microscale flows.

• 대한공간정보학회지
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• 제19권4호
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• pp.55-63
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• 2011

어안렌즈는 사각이 넓어서 터널 내부 벽면의 영상을 취득하는 데 유용하다. 원통투영의 원리를 이용하여 어안렌즈터널 영상을 우리의 눈에 익숙한 일반 영상으로 변환시킬 수 있는데, 이 과정에서 여러 종류의 왜곡이 발생하게 된다. 본 논문은 투영영상의 터널 바닥면과 벽면 사이 경계선에서 발생하는 왜곡을 다루고 있다. 경계선 왜곡의 발생 원인을 분석하고 모형을 제작하여 보정량 계산식을 유도하였다. Visual C++로 제작한 소프트웨어를 이용하여 계산된 보정량을 투영영상에 적용한 결과 경계선이 보정된 영상을 얻을 수 있었다. 투영영상에 나타난 다른 왜곡에 대한 연구가 추가된다면 어안렌즈 영상을 통해 실제 터널 벽면과 유사한 영상을 얻을 수 있을 것으로 기대된다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.15-16
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• 2003

An implicit pressure correction method on unstructured Cartesian grid is developed for the incompressible Navier-Stokes equations. An immersed boundary method is also incorporated to treat the body geometry. Tests show that with an appropriate amount of dissipation, the method is second order accurate both in time and space. The driven cavity flows with and without immersed bodies are computed to demonstrate the capability of the present scheme.

• 대한조선학회지
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• 제11권2호
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• pp.1-6
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• 1974

The three-dimensional correction factor of the added mass of finite-length elliptic cylinders in vertical vibration in a free surface was calculated. This problem has already been dealt by T. Kumai[5] to contribute to analytical prediction of the three-dimensional correction factor for the added mass in vertical vibration of ships. In Kumai's work, the body boundary condition involved in the appropriate boundary value problem was approximately treated in the course of obtaining the solution. In this work, obtaining the solution derived from mathematically exact treatment of the body boundary condition, the author recalculated the three-dimensional correction factor for length-beam ratio $4{\sim}8$, beam-draught ratio $2.00{\sim}4.50$ and number of nodes from 2 to 7. And the numerical results were compared with both Kumai's results and the author's experimental data for two and three-noded vibrations of the cylinder of beam-draught ratio 2.40 The comparison of the numerical results shows that the author's are always higher than the Kumai's as expected. And the comparison of the numerical results with experimental data shows that the Kumai's numerical results have less deviation in case of two-noded vibration, and that, in case of three-noded vibration, the author's numerical results are in fairly good correspondence.

• 한국전산유체공학회지
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• 제7권2호
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• pp.8-16
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• 2002

A numerical study on the use of the momentum interpolation method for flows with a large body force is presented. The inherent problems of the momentum interpolation method are discussed first. The origins of problems of the momentum interpolation methods are the validity of linear assumptions employed for the evaluation of the cell-face velocities, the enforcement of mass conservation for the cell-centered velocities and the specification of pressure and pressure correction at the boundary. Numerical experiments are performed for a typical flow involving a large body force. The numerical results are compared with those by the staggered grid method. The fact that the momentum interpolation method may result in physically unrealistic solutions is demonstrated. Numerical experiments changing the numerical grid have shown that a simple way of removing the physically unrealistic solution is a proper grid refinement where there is a large pressure gradient. An effective way of specifying the pressure and pressure correction at the boundary by a local mass conservation near the boundary is proposed, and it is shown that this method can effectively remove the inherent problem of the specification of pressure and pressure correction at the boundary when one uses the momentum interpolation method.

• 한국항공우주학회지
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• 제34권12호
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• pp.67-74
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• 2006

아음속풍동 폐쇄형 시험부내의 비정상 벽면효과 보정 연구의 일환으로 시험부 벽면압력을 사용하는 비정상 흐름에 대한 blockage 보정 기법을 개발하였다. 시험부 벽면압력은 프리에 급수로 전개하고, 전개된 각 계수를 벽면압력측정 방법을 사용하여 전 주기에 대해 일괄적으로 보정하는 준 정상상태 보정 방법을 제시하였다. 본 연구에서 제시된 방법을 검증하기 위해 수치적으로 계산된 폐쇄형 시험부내의 원형실린더 및 강제 진동하는 익형의 비정상 흐름에 적용하였다. 그 결과 본 연구에서 제시된 방법은 자유흐름 상태와 일치되는 blockage 보정 결과를 보임을 확인하였다.

• East Asian mathematical journal
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• 제40권1호
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• pp.109-118
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• 2024

This paper proposes a numerical method based on domain decomposition to find approximate solutions for one-dimensional convection-diffusion equations with Neumann boundary conditions. First, the equations are transformed into convection-diffusion equations with Dirichlet conditions. Second, the author introduces the Prediction/Correction Domain Decomposition (PCDD) method and estimates errors for the interface prediction scheme, interior scheme, and correction scheme using known error estimations. Finally, the author compares the PCDD algorithm with the fully explicit scheme (FES) and the fully implicit scheme (FIS) using three examples. In comparison to FES and FIS, the proposed PCDD algorithm demonstrates good results.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2007년도 Proceedings of ISRS 2007
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• pp.270-273
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• 2007

In this paper, a SAR-despeck1ing approach of adaptive iteration based a Bayesian model using the lognormal distribution for image intensity and a Gibbs random field (GRF) for image texture is proposed for noise removal of the images that are corrupted by multiplicative speckle noise. When the image intensity is logarithmically transformed, the speckle noise is approximately Gaussian additive noise, and it tends to a normal probability much faster than the intensity distribution. The MRF is incorporated into digital image analysis by viewing pixel types as states of molecules in a lattice-like physical system. The iterative approach based on MRF is very effective for the inner areas of regions in the observed scene, but may result in yielding false reconstruction around the boundaries due to using wrong information of adjacent regions with different characteristics. The proposed method suggests an adaptive approach using variable parameters depending on the location of reconstructed area, that is, how near to the boundary. The proximity of boundary is estimated by the statistics based on edge value, standard deviation, entropy, and the 4th moment of intensity distribution.

• Journal of Mechanical Science and Technology
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• 제18권6호
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• pp.955-960
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• 2004

Some characteristics of the eigenvalue sensitivities have been found for beams in the paper. For cantilever beams and simply supported beams, the sensitivities of the eigenvalues to the stiffness correction factor of one element are equal and opposite to the sensitivities to the mass correction factor of the symmetrically positioned element. For beams with other boundary conditions, however, the relationship does not hold. The relationship has been proven analytically for simply supported beams.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1993년도 한국자동제어학술회의논문집(국내학술편); Seoul National University, Seoul; 20-22 Oct. 1993
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• pp.799-804
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• 1993

In this paper, the scheme of combining the orbit correction and attitude control of a 3-axis stabilized satellite is suggested. Being coupled and complimentary, it is preferable to achieve the required orbit correction and the desired attitude control simultaneously. A solution of the probes simultaneous control of orbit correction and attitude of a satellite, is obtained by solving the two point boundary value problem numerically. The first-order gradient algorithm is used to solve the numerical problem. The simulation results show that the East-West station keeping process with the combined system of an orbit correction and an attitude control is satisfactory.