• Journal of the Society of Naval Architects of Korea
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• v.41 no.1
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• pp.15-22
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• 2004

Twin-skeg type stern shapes are recently adopted for very large commercial ships. However it is difficult to apply a CFD system to a hull form having twin-skeg, since grid topology around a twin-skeg type stern is more complicated than that of a conventional single-screw ship, or of an open-shaft type twin-screw ship with center-skeg. In the present study a surface mesh generator and a multi-block field grid generation program have been developed for twin-skeg type stern. Furthermore, multi-block flow solvers are utilized for potential and viscous flow analysis around a twin-skeg type stern The present computational system is applied to a 15,000TEU container ship with twin-skeg to prove the applicability. Wave profiles and wake distribution are calculated using the developed flow analysis tools and the results are compared with towing tank measurements.

• Journal of computational fluids engineering
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• v.11 no.2 s.33
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• pp.62-66
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• 2006

In this paper an automated hole-finding method for overset grids is introduced which uses recursive octree-cell division. A graphic program which enables the user to do the hole-cutting with ease is also introduced. Using this program it is found that there is an optimum combination of the level of octree division and vector calculation for the efficient and fast hole finding.

• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.83-86
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• 2004

In this paper an automated hole-finding method for overset grids is introduced which uses recursive octree-cell division. A graphic program which enables the user to do the hole-cutting with ease is also introduced. Using this program it was found that a proper combination of the level of octree division and vector calculation should be used for efficient and fast hole finding.

• 한국전산유체공학회:학술대회논문집
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• 1998.11a
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• pp.175-184
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• 1998

본 연구에서는 제한된 수로를 운항하는 선체주위의 유동특성에 관한 연구를 수행하고자 하였다. 일반적으로 운하 또는 하천을 운항하는 선박의 경우 제한된 수심의 영향으로 천수효과가 발생하게 된다. 이러한 천수의 효과와 제한된 폭의 영향으로 선수부분에서 선체보다 선행하는 파도가 전파되어 나아가기도 하며, 이로 인하여 선박은 보다 많은 조파저항을 받게 된다. 본 연구에서는 임의의 형상을 갖는 선체가 폭과 수심이 제한된 운하를 임계속도 근처에서 운항하는 경우에 관하여 폭과 수심을 변화시켜가며 수치계산을 수행하여, 제한수로에서의 임의의 선체주위의 유동특성을 관찰하고자 하였다. 수치계산은 MAC(Marker And Cell)법을 기초로 한 유한차분법(Finite Difference Method)을 사용하였으며, 계산에 사용된 격자계는 임의의 형상에 관하여 격자생성이 용이한 직사각형 격자계(Rectangular Grid System)를 사용하였다.

• Korean Journal of Optics and Photonics
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• v.14 no.4
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• pp.392-398
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• 2003

We present a novel concept of a phase-shifting diffraction-grating interferometer, which is intended for the optical testing of concave mirrors with high precision. The interferometer is configured with a single reflective diffraction grating, which performs multiple functions of beam splitting, beam recombination, and phase shifting. The reference and test wave fronts are generated by means of reflective diffraction at the focal plane of a microscope objective with large numerical aperture, which allows testing fast mirrors with low f-numbers. The fiber-optic confocal design is adopted for the microscope objective to focus a converging beam on the diffractive grating, which greatly reduces the alignment error between the focusing optics and the diffraction grating. Translating the grating provides phase shifting, which allows measurement of the figure errors of the test mirror to nanometer accuracy.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.189-196
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• 1990

In the present study, a new method of generating boundary-fitted coordinates systems controlled by control function is introduced. Application of the method to a three-dimensional simply-connected region is the demonstrated. The numerical grid generation has following feat ures, (a) The generated boundary fitted coordinates is well concentrated in near wall region and satisfied orthogonality, (b) The grid control function is fully automatic and well controlled in sharp convex boundary.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.3
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• pp.561-565
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• 1988

In the present study, a new method of generating a nearly orthogonal boundary-fitted coordinate systems with automatic grid spacing control is introduced. Applications of the method to a two dimensional simply-connected region is then demonstrated. The nearly orthogonal boundary-fitted method has the following features, (a) Strong grid control in the .eta.-direction can be made, (b) The generated boundary-fitted coordinates are nearly orthoronal, (c) Both the .xi.-and .eta.-direction control function are mathematically derived. Especially the .eta.-direction control function is derived under the assumption that the .eta.-direction grid spacing is by far smaller than the .xi.-direction grid spacing when the .eta.-direction grid line is strongly clustered. (d) The grid control functions are dynamically adjusted by the metric scale factors imposed on the boundary. The control function is fully automatic and eliminates the need of user manipulation of the control function.

• Journal of the Mineralogical Society of Korea
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• v.8 no.2
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• pp.57-72
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• 1995

춘천 지역 선캠브리아기의 구봉산층군 내의 백운석질 대리암에는 광역변성작용의 산물로서 조립질의 투각섬석이 주된 규산염 광물상을 이루며 산출된다. 이들은 배태 층준과 원암의 조성에 따라 두 가지 유형으로 구분된다. : (1) 투각섬석(흑회색)+방해석+백운석+활석, (2)투각섬석(백색)+금운모+백운석+방해석+K-장석, 백색의 투각섬석이 흑회색형보다 상대적으로 높은 Al과 알칼리 함유도를 보이지만, 전반적으로 모두 Mg-단종에 가까운 화학 조성을 갖는다. 투각섬석들이 격자 구조상의 결함 구조를 갖지 않는데 비해서, 금운모는 1M 구조형을 이루고 저면 격자 간격상에 녹니석 단위의 빈번한 개재에 의한 격자상의 구조적 결함이 흔히 관찰된다.방해석-백운석 지온계에 대한 연구와 TWEEQU 프로그램을 이용한 상평형도 작성을 통해서, 투각섬석들은 500~$600^{\circ}C$의 온도 범위, 8kb 정도의 압력 및 Xco2=0.2~0.5 조건에서 생성된 것으로 해석하였다. 이 지역의 투각섬석은 위와 같은 조건에서 지속적으로 평형 상태가 유지되고 상안정도가 증대되므로서, (1) 투휘석을 수반하지 않고, (2) 격자 구조상의 결합을 갖지 않는, (3) 자형의 큰 결정을 이루게 된 것으로 해석된다.

• Journal of Korea Foundry Society
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• v.43 no.6
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• pp.302-309
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• 2023

In general, castings often have complex shapes and significant variations in thickness within a single product, making grid generation for simulations challenging. Casting flows involve multiphase flows, requiring the tracking of the boundary between air and molten metal. Additionally, considerable time is spent calculating pressure fields due to density differences in a numerical analysis. For these reasons, the Cartesian grid system has traditionally been used in mold filling simulations. However, orthogonal grids fail to represent shapes accurately, leading to a momentum loss caused by the stair-like grid patterns on curved and sloped surfaces. This can alter the flow of molten metals and result in incorrect casting process designs. To address this issue, simulations in the Cartesian grid system involve creating a large number of grids to represent shapes more accurately. Alternatively, the Cut Cell method can be applied to address the problems arising from the Cartesian grid system. In this study, analysis results based on the number of grid in the Cartesian grid system for a casting flow analysis were compared with results obtained using the Cut Cell method. Casting flow simulations of actual products during various casting processes were also conducted, and these results were analyzed with and without applying the Cut Cell method.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.655-659
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• 2008

본 연구에서는 3차원 수치모의를 통하여 횡방향 하상형상 및 격자형 이차흐름 구조의 생성 메커니즘을 분석하였다. 이를 위해 곡선좌표계에서의 지배방정식을 구성하고, 난류 폐합을 위해 Speziale(1987)가 제안한 비등방성 k-$\varepsilon$모형을 이용하였다. 또한 Exner 방정식을 이용하여 시간에 따른 하상변동을 예측하였다. 그 결과 바닥과 측벽 사이에서 발생되는 바닥 이차흐름의 하향류에 의해 측벽 부근부터 하상이 침식되고, 침식된 유사량은 이차흐름의 횡방향 유속에 의해 이동되어 퇴적되어, 결국 횡방향으로 연속적인 언덕 및 저면과 같인 하상형상이 생성되는 것으로 나타났다. 또한 시간에 따른 이차흐름 및 바닥 전단력, 하상고의 변화에 대해 살펴보았다.