• Structural Engineering and Mechanics
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• v.9 no.3
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• pp.289-304
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• 2000

This study discusses on the experimental and analytical results of the global buckling tests, carried out on aluminum alloy double layer space grids composed of tubular members, ball joints and connecting bolts at the member ends, with the purpose of demonstrating the effectiveness of a simplified analysis method using an equivalent slenderness ratio for the members. Because very few experiments have been carried out on this type of aluminum space grids, the buckling behavior is investigated experimentally over the post buckling regions using several space grid specimen with various values for the member slenderness ratio. The observed behavior duping the experiments is compared with the analytically obtained results. The comparison is made based on two different schemes; one on the plastic hinge method considering a bending moment-axial force interaction for members and the other on a method using an equivalent slenderness ratio. It is confirmed that the equivalent slenderness method can be effectively applied, even in the post buckling regions, once the effects of the rotational rigidity at the ball joints are appropriately evaluated, because the rigidity controls the buckling behavior. The effectiveness of the equivalent slenderness method will be widely utilized for estimation of the ultimate strength, even in post buckling regions for large span aluminum space grids composed of an extreme large number of nodes and members.

• Progress in Superconductivity and Cryogenics
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• v.18 no.1
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• pp.50-54
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• 2016

In this paper, a hybrid method is proposed to design an air-core superconducting solenoid system for 6 T axial uniform magnetic field using Niobium Titanium (NbTi) superconducting wire. In order to minimize the volume of conductor, the hybrid optimization method including a linear programming and a nonlinear programming was adopted. The feasible space of solenoid is divided by several grids and the magnetic field at target point is approximated by the sum of magnetic field generated by an ideal current loop at the center of each grid. Using the linear programming, a global optimal current distribution in the feasible space can be indicated by non-zero current grids. Furthermore the clusters of the non-zero current grids also give the information of probable solenoids in the feasible space, such as the number, the shape, and so on. Applying these probable solenoids as the initial model, the final practical configuration of solenoids with integer layers can be obtained by the nonlinear programming. The design result illustrates the efficiency and the flexibility of the hybrid method. And this method can also be used for the magnet design which is required the high homogeneity within several ppm (parts per million).

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.10
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• pp.17-25
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• 2005

A grid adaptation method within systems of chimera and patched grids is presented. Problem domains are divided into near-body and off-body fields. Near-body field is filled with curvilinear body-fitted grids that extend only a short distance from body surfaces and connected to other grid systems via chimera domain connectivity method. Off-body field is filled with patched uniform cartesian grids of varying levels of refinement. This method gives flexibility in grid generation and efficient adaptation capability. Several numerical experiments including 2D store separation were performed to show the performance of the proposed adaptation method.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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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.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.9
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• pp.805-813
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• 2015

This paper introduces the development of temperature mapping code between thermal mesh and structural mesh in KARI Satellite Design Software. Generally, temperature distribution of a satellite varies with the time by the space environment of the orbit, so thermal expansion of the structure should be analysed in design of the satellite. For the sake of the coupled thermal structural analysis, an interpolation algorithm between two finite element heterogeneous grids has been proposed by which temperature transfer is successively conducted.

• International Journal of Contents
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• v.6 no.1
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• pp.47-52
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• 2010

Skyline queries are an important new search capability for multi-dimensional databases. Most of the previous works have focused on processing skyline queries over static data set. However, most of the real applications deal with the dynamic data set. Since dynamic data set constantly changes as time passes, the continuous skyline computation over dynamic data set becomes ever more complicated. In this paper, we propose a multiple layer grids method for continuous skyline computation (MLGCS) that maintains multiple layer grids to manage the dynamic data set. The proposed method divides the work space into multiple layer grids and creates the skyline influence region in the grid of each layer. In the continuous environment, the continuous skyline queries are only handled when the updating data points are in the skyline influence region of each layer grid. Experiments based on various data distributions show that our proposed method outperforms the existing methods.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.1
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• pp.86-91
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• 2008

An integrated multidisciplinary analysis and design system plays a critical role in the preliminary design of an aircraft. In this work a system based on the CATIA is developed for multidisciplinary computational design; aerodynamics, elasticity, and radar frequency stealth. Common data base of geometry and rectangular grids is generated and used for aerodynamic and structural analysis, while derivative triangular grids are generated for the RCS calculation. The panel method (PANAIR), FEM (NASTRAN), and PO technique are used for aerodynamic, structural, and RF stealth computations, respectively, and several additional algorithms are developed for the effective communication of the common data.

• Journal of Power Electronics
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• v.15 no.2
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• pp.497-503
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• 2015

This paper analyses the harmonic pollution to power grids caused by several high-power rectifiers, summarizes the requirements for rectifiers in suppressing grid-side current harmonics and optimizes a new-type of current source PWM rectifier with a hybrid switch. The rectifier with a hybrid switch boasts significant current characteristics and cost advantages in the high-power area. To further enhance the working frequency of the current source rectifier with a hybrid switch for suppressing grid-side harmonics and reducing the inductance size, this paper proposes an optimal control strategy based on space vector. It also verifies that the optimal control strategy based on space vector can reduce the total harmonic distortion of the grid-side current of the rectifier with a hybrid switch via circuit simulation and experimental results.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.8
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• pp.907-914
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• 2014

A heuristic search algorithm is proposed to plan a collision free path for robots in an indoor environment. The proposed algorithm is to find a collision free path in the gridded configuration space by proposed heuristic graph search algorithm. The proposed algorithm largely consists of two parts : tunnel searching and path searching in the tunnel. The tunnel searching algorithm finds a thicker path from start grid to goal grid in grid configuration space. The tunnel is constructed with large grid defined as a connected several minimum size grids in grid-based configuration space. The path searching algorithm then searches a path in the tunnel with minimum grids. The computational time of the proposed algorithm is less than the other graph search algorithm and we analysis the time complexity. To show the validity of the proposed algorithm, some numerical examples are illustrated for robot.

• Korean Journal of Environment and Ecology
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• v.14 no.2
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• pp.154-161
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• 2000

The objectives of this study were to determine how land use pattern in Taejon the sixth largest city in Korea has changed with urbanization. Degree of green naturalness (DGN) was used to analyze land use pattern from 1990 to 1998. Number of 1km$\times$1km grids numbers of satistical land use data and compared rate of population increase quantified land use pat-tern. The rate of population increase of Taejon was 27.8% from 1990 to 1998. Eight degrees of DGN were identified with secondary forest(grade 7) occupied the largest area (203 grids: 37.5%) of the total 541 grids in 1998. The changes in land use were compared among 1990, 1994 and 1998. Grade 1 increased by 9 grids while grade 2 decreased by 6 grids. Likewise paddy field decreased by 10km2 from 62 to 52km2 dry field and forest also decreased by 4km2 and 1km2 respectively while residence and factories increased by 10km2 and 0.5km2 respec-tively. The green space was mostly distributes in a national park and greenbelts in the outer zone of the city. As a result paddy and dry fields in central area of the city have been changed to residential and industrial areas. The city environment in term of DGN reduced its quality and quantity.