• 한국전산유체공학회:학술대회논문집
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• 1995.10a
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• pp.197-202
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• 1995

비정상(unsteady) 압축성(compressible) 유동에 의한 공력음향(aeroacoustics)을 모사하여 공력소음원을 해석하기 위해서는 고차(high order)의 정확도와 높은 해상도(resolution)를 가지며, 상대적으로 계산시간을 많이 필요로 하지 않는 외재적(explicit) 유한차분법이 필수적으로 요구된다. 이것은 주어진 차분방식과 격자계로써 공간과 시간상에 존재하는 미소크기의 파동성분들을 충분히 구현하여야 만족할 만한 수치해를 얻을 수 있기 때문이다. 본 연구에서는, 그러한 유한차분법 중 최근에 관심의 대상이 되고있는 삼각(tridiagonal)또는 오각(pentadiagonal) 집적유한차분법(compact finite difference scheme)이 최대의 해상도를 갖도록 하는 수학적인 방법을 개발하고, 이 방법으로써 새롭게 집적유한차분법을 최적화하였다. 개발된 최적화 방법은, 푸리에 해석법(Fourier analysis)을 통하여 파동수(wavenumber) 영역에서 수학적으로 계산된 위상오차(phase error)를 최소화하는 것이며, 이러한 개념과 방법은 본 연구에서 처음으로 집적유한차분법에 적용되었다. 여러가지 절단정확도(truncation order)에 대해서 최적화 된 집적유한차분법들이 실제 공간과 시간상에서 보여주는 정확도와 오차특성을 알아보기 위하여, 이 방법들을 1차원 선형파동방정식에 적용하였고, 이 결과를 통하여 가장 정확하고 효과적인 절단정확도의 집적유한차분법을 선별하였다. 특히, 오각(pentadiagonal)법에 비해 더욱 효율적인 6차 삼각(tridiagonal)법을 1차원 Euler방정식에 적용하여, 비선형 파동에 대한 모사를 수행할 수 있었다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.292-295
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• 2003

Moire topography method is a well-known non-contacting 3-D measurement method. the automatic 3-D measurement by moire topography has been required since the method was frequently applied to the engineering and medical fields. 3-D measurement using digital projection moire topography is very attractive because of its high measuring speed and high sensitivity. In this study, digital two-wavelength phase shilling moire is applied to the entertainment fields. recently. as promoting the growth of the VR-Game, display devices which attract public attention such as HMD or Projector are being appeared in order to deliver effectively the absorption sense. this study realized the Auto-calibrating system for arbitrary display surface using digital moire method which satisfied the shape measurement of display surface and the request of FOV(Field of View) output. also when large screen wasn't prepared, this auto-calibrating system was applied to enjoy games or movies at home with a projector and walls

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.04a
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• pp.255-259
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• 2003

Moire topography method isa well-known non-contacting 3-D measurement method as afast non-contact test for three-dimension shape measuring method. Recently, it's important to study the automatic three-dimension measurement by moire topography because it is frequently applied to the reverse engineering , the medical , the entertainment fields. Three-dimension measurement using projection of moire topography is very attractive because of its high measuring speed and high sensitivity. In this paper, the classical moire method is computerized-so called digital moire when a virtual grating pattern is projected on a surface, the captured image by the CCD camera has three-dimension information of the objects. The moire image can be obtained through a simple image processing and a reference grating pattern. and it provides similar results without physical grating pattern. digital projection moire topography turn out to be very effective for the three-dimension measurement of objects. Using different N-bucket algorithm method of digital projection moire topography is tested to measuring object with the 2-ambiguity problem. Experimental results prove that the proposed scheme is capable of finding measurement errors that decreased more by using the four-three step algorithm method instead of the same step in the phase shifting of different pitch.

• Journal of the Korean Institute of Landscape Architecture
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• v.27 no.4
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• pp.137-142
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• 1999

The purpose of this study is to develope a CAD-based tool for rasterization of polygonal vector map in AutoCAD. To identity the layer property of polygonal entity with user-defined coordinates as topology, algorithm in processing entity data of selection set that intersected with scan line was used, and the layers were extracted sequentially by sorted intersecting points in data-list. In addition to the functions for querying and modifying topology, two options for mapping were set up to construct plan projection type and to change meshes' properties in existing DTM data. In case of plan projection type, user-defined cell size of 3DFACE mesh is available for more detailed edge, and topological draping on landform can be executed in case of referring DTM data as an AutoCAD's drawing. The concept of algorithm was simple and clear, but some unexpectable errors were found in detecting intersected coordinates that were AutoCAD's error, not the utility's. Also, the routines to check these errors were included in algorithmic processing. Developed utility named MESHMAP was written in entity data control functions of AutoLISP language and dialog control language(DCL) for the purpose of user-oriented interactive usage. MESHMAP was proved to be more effective in data handling and time comparing with GRIDMAP module in LANDCADD which has similar function.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.9
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• pp.994-1000
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• 2004

We studied the characteristics of annular phase gratings as spatial frequency filters. We first calculated the Fraunhofer diffraction patterns of annular gratings and then got the modulation transfer function (MTF) from the zeroth order Hankel transform of the intensity distribution function. Binaryphase annular grating shows higher diffraction efficiency than binary phase rectangular grating. But the MTF decreases linearly in the low-frequency region as that of rectangular grating does. The diffraction pattern of 4-phase annular grating is similar to that of 2-phase grating and hence MTFs of the two are much alike. For 8-phase annular grating, the 7th order diffracted beam is the lowest one next to the first. Consequently, the diffraction efficiency is very high and the MTF graph is curved upward. The diffracted beams except the first order are negligible and hence the MTF characteristics are more improved in the case of 16-phase grating. But the degree of improvement becomes lowered c(Impaled with 8-phase grating. We made a 16-phase annular grating and measured its MTF. The experimental result agrees well with the calculated one.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.101-108
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• 2002

A numerical simulation of an incompressible cavity flow is conducted. Two dimensional Navier-Stokes equations are integrated using staggered grid and a finite volume method with C-QUICK scheme for spatial derivatives and fully implicit scheme for the time derivatives. SIMPLE-C algorithm is employed to solve the pressure field. Computational results show that the third eddy is generated in the shear layer mode but not in the steady mode. This signifies that the third eddy plays an important role in cavity flow stability. As a means to control the flow, jet blowing is applied to a position below the cavity upstream edge. Effects of flow control parameters on the stability such as the frequency, the phase, and the velocity magnitude are reported.

• The Journal of Korea Robotics Society
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• v.9 no.2
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• pp.104-110
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• 2014

Mapping is a fundamental element for robotic services. There are available many types of map data representation such as grid map, metric map, topology map, etc. As more robots are deployed for services, more chances of exchanging map data among the robots emerge and standardization of map data representation (MDR) becomes more valuable. Currently, activities in developing MDR standard are underway in IEEE Robotics and Automation Society. The MDR standard is for a common representation and encoding of the two-dimensional map data used for navigation by mobile robots. The standard focuses on interchange of map data among components and systems, particularly those that may be supplied by different vendors. This paper aims to introduce MDR standard and its application to map merging. We have applied the basic structure of the MDR standard to a grid map and Voronoi graph as a kind of topology map and performed map merging between two different maps. Simulation results show that the proposed MDR is suitable for map data exchange among robots.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.8
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• pp.1337-1345
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• 2000

In spite of the advantages of lightweight, low profile, and mass productions, microstrip array antenna has inherently the scan blindness problems in case of wide angle scan. And this scan blindness can be overcome by using cavity-backed microstrip radiator. In this paper, we presented the algorithm of analyzing skewed cavity-backed microstrip array and verified the validity of the proposed numerical results with those of reference papers. Finally, we show the effect of cavity-backed and skewed grid array structure.

• Geophysics and Geophysical Exploration
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• v.15 no.2
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• pp.75-84
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• 2012

The sea layer in marine Controlled-Source Electromagnetic (mCSEM) survey changes the conventional definition of apparent resistivity which is used in the land CSEM survey. Thus, the development of a new algorithm, which computes apparent resistivity for mCSEM survey, can be an initiative of mCSEM data interpretation. First, we compared and analyzed electromagnetic responses of the 1D stratified gas hydrate model and the half-space model below the sea layer. Amplitude and phase components showed proper results for computing apparent resistivity than real and imaginary components. Next, the amplitude component is more sensitive to the subsurface resistivity than the phase component in far offset range and vice versa. We suggested the induction number as a selection criteria of amplitude or phase component to calculate apparent resistivity. Based on our study, we have developed a numerical algorithm, which computes appropriate apparent resistivity corresponding to measured mCSEM data using grid search method. In addition, we verified the validity of the developed algorithm by applying it to the stratified gas hydrate models with various model parameters. Finally, by constructing apparent resistivity pseudo-section from the mCSEM responses with 2D numerical models simulating gas hydrate deposits in the Ulleung Basin, we confirmed that the apparent resistivity can provide the information on the geometric distribution of the gas hydrate deposit.

• Korean Journal of Optics and Photonics
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• v.17 no.1
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• pp.7-17
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• 2006

In this paper, we proposed an optical true time-delay (TTD) for planar phased array antennas (PAAs), which is composed of a wavelength-dependent optical true time delay (WDOTTD) followed by a wavelength-independent optical true time delay (WIOTTD). The WDOTTD is a fiber Bragg gratings (FBGs) Prism and the WDOTTD is a fiber delay-lines matrix of which each component consists of a certain length of fiber connected to cross-ports of a 2${\times}$2 MEMS switch. A 10-GHz 2-bit${\times}$4-bit two-dimensional optical TTD has been fabricated by cascading a WDOTTD with a maximum time delay of 810 ps to a WIOTTD of $\pm$50 ps. Time delay and insertion loss for each radiation angle have been measured. Time delay error for the WIOTTD has been measured to be less than $\pm$1 ps. We have also designed a two-dimensional 10-GHz PAA composed of 8${\times}$8 microstrip patch antenna elements driven by the proposed TTD. The radiation patterns of this PAA have been obtained by simulation and analyzed.