• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.8
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• pp.677-684
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• 2007

In the Present Study, a 3-D viscous flow solver, based on unstructured hybrid meshses containing tetrahedra, prisms and pyramids, has been developed. A finite-volume discretization scheme is used for solving the compressible Navier-Stokes equations. A cell-vertex median dual volume is used for spatial discretization. The one-equation Spalart-Allmaras turbulence model has been adopted to evaluate the eddy viscosity. Validation were made by computing laminar and turbulent flows around a 3-D wing for steady flows and turbulent flows around an oscillating 3-D wing in harmonic motion for unsteady flows.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2012.04a
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• pp.66-69
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• 2012

Field Model에 의한 화재해석방법은 화재현상을 지배하는 망정식윤 직접 해석하기 때문에 Zone model에 비해 공간내의 상세 정보를 제공함과 동시에 다양한 화재형태에 내해 보편적인 적용이 가능하다. Field model은 해석영역을 구성하는 격자점에 대해 이산화된 지배 방정식을 해석하는 과정에서 차분방법이나 격자의 크기에 따라 수치오류가 발생할 수 있다. 특히 격자수는 계산시간에 영향을 미치는 가장 중요한 인자이기 때문에 효율적인 계산을 위해서는 격자크기의 최적화가 이루어져야 한다. 본 연구에서는 구획공간 화재의 최적 격자크기 선정을 위해 격자해상도(Grid Resolution)에 따른 해석결과의 독립성을 비교분석하고 이를 통해 구획공간화재에 대한 격자 최적화 방법에 대해 논의하고자 한다. 화재크기 및 특성 길이에 따른 격자의존성을 파악하기 위해 ISO-9705 표준화재실에 내해 적용된 격자크기는 최소 3 cm에서 최대 30 cm까지 총 7 종류의 격자크기에 대해 FDS 해석이 수행되었다. 해석결과, 환기량이 충분한 화재에 대해서도 격자해상도가 16보다 작은 경우 출입구의 유동은 격자에 따른 독립성을 확보하지 못하는 것으로 나타났으며 화재발열량이 증가함에 따라 독립적인 해석해를 얻기 위해서는 더 큰 격자해상도를 요구하는 것으로 나타났다. 따라서 현재 실무에서 격자최적화를 위해 사용되고 있는 격자선정법에 대한 재검토가 필요하며 화재특성 및 구획공간 조건에 따른 최적격자 조건을 도출하기 위한 추가적인 연구가 필요하다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.1
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• pp.159-170
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• 2005

The grid structure is parallel main girders intersected with crossgirder. It distribute the loads to adjoining main girder through the crossgirder when a girder is subjected to a load. grillage girder bridge has high load-carrying capacity, it can save materials and become more economical type of bridge. In this paper, the grillage girder bridge analysis program developed by using the transfer matrix method deals with following problems: the comparision with Leonhardt, Szabo, FEM yang and jung in the analysis of grillage girder bridges, quality of straight and curved bridges with skew angle, forces of straight and curved bridges according to skew angle and bending stiffness/torsional stiffness ratio.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.1-10
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• 2005

An unstructured parallel overset mesh method has been developed for the simulation of unsteady flows around multiple bodies in relative motion. For this purpose, an efficient and robust search method is proposed for the unstructured grid system. A new data-structure is also proposed to handle the variable number of data on parallel sub-domain boundary. The interpolation boundary is defined for data communication between grid systems. An interpolation method to retain second-order spatial accuracy and to treat the points inside the neighboring solid bodies are also suggested. A single store separating from the Eglin/Pylon configuration is calculated and the result is compared with experimental data for validation. Simulation of unsteady flows around multiple bodies in relative motion is also performed.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.9
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• pp.923-928
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• 2015

The FDS is one of the most used programs for fire analysis and needs an optimal grid selection for an accurate analysis. This study selected various grid aspect ratios (ARs) for selection of optimal grid and analyzed them with FDS v 6.1.2. A calculation time of 10 min. was used, which is enough to obtain the time average value of temperature changes. Temperature, visibility, and the time average value of mass balance are obtained from 200-600 s, which is a period of maintaining quasi-steady state. Two polyurethane fires of 1 [MW] and 2 [MW] in two enclosures of $10{\times}10{\times}3[m^3]$ and $20{\times}20{\times}3[m^3]$ were considered. Time variations of heat release rates, temperature, visibility, and mass balance were compared for ARs from 1-6. The heat release rates were accurate for all aspect ratios regardless of fire and enclosure sizes. The quasi-steady state temperature and visibility were well predicted for $AR{\leq}5$. Temperature drop and skewness of mass conservation, however, increased with increasing aspect ratio. Therefore, careful investigation of the grid size is recommended in performance-based design when $AR{\geq}3$, where temperature and visibility in early stage of a fire are important parameters. For accurate simulations of enclosure fires, grid sizes of 0.1~0.2 [m] and smaller in the vertical direction and $AR{\leq}2$ are recommended.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.34 no.6
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• pp.188-197
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• 2022

We develop a coastal wave forecasting system by using the unstructured grid based on sea wind data of Global Data Assimilation and Prediction System. The verification is performed to examine the performance and accuracy of the wave model. Since the conventional grid has limited wave forecasting on complex coastlines and bathymetry, the unstructured grid system is applied for precise numerical simulation, and applicability for operational support is evaluated. Both grid systems show similar prediction trends in offshore and coastal areas, and the difference in prediction errors according to the grid system is not large. In addition, the applicability of the operational wave forecasting system is confirmed by dramatically reducing the model execution time of the unstructured grid under the same conditions.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.57-60
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• 2006

This paper presents an assessment of vertex-centered and cell-centered finite-volume methods on unstructured meshes. The results indicate that the vertex-centered method is more reliable than the cell-centered method.

• Journal of Korea Multimedia Society
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• v.15 no.5
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• pp.672-676
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• 2012

This investigation relates generally to windows and doors for traditional Korean houses(Hanok) and, more particularly, to windows and doors for traditional Korean houses which have a lattice structure that can minimize heat loss in the winter. In order to accomplish the above objective, the present invention provides a door for traditional Korean houses, including a structure of a lattice door framed with vertical lattice frames and horizontal lattice frames which are arranged in a regular periodic pattern.

• Korean Journal of Optics and Photonics
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• v.10 no.4
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• pp.348-353
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• 1999

Ray-optics approach based on the rigorous coupled wave theory, called by the rigorous ray-optics method (RROM), is developed for the calculation of couling coefficients of waveguide grating devices. The coupling coefficients of several grating structures, such as rectangular, sinusoidal, triangle, and trapezoidal shapes, are determined by the RROM, and they are compared with those obtained by conventional methods of the ray-optics method (ROM) and the coupled mode method (CMM). In the case of rectangular gratings, the coupling coefficients is evaluated in detail by various depths and duty-cycles of the grating. We have found that the RROM gives more exact solutions for the coupling coefficients of even arbitrary shapes of diffractive waveguide grating devices than the other conventional methods.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.10
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• pp.669-676
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• 2022

In this paper, the carriage load analyses of stores installed on aircraft are conducted to validate the chimera grid method applied to an unstructured CFD solver, UMSAPv. First, the chimera grid method of UMSAPv is verified for the well-known Eglin Wing/Pylon/Finned store problem. Next, an angle of attack sweep of F/A-18C clean configuration is conducted at a subsonic speed. The computed results are compared with the results of the previous study using MSAPv, a structured CFD solver, to show the validity of Umsapv. Finally, the carriage of F/A-18C JDAM is carried out with a chimera grid as well as a single block grid. The computed results are compared with other computational, experimental and the flight tests.