• Proceedings of the KIEE Conference
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• 2003.07d
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• pp.2417-2419
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• 2003

이동성에 nonholonomic 제약을 받는 차륜 구동 이동 로봇의 불확실한 환경에서의 자율 주행 제어기를 제안하였다. 전체 시스템은 on-line으로 지역경로 계획을 하는 planner 부분과 차륜 구동 이동 로봇의 nonholonomic 제약을 극복하면서 계획된 지역 경로를 충실히 추종하기 위한 제어기 부분의 두 부분으로 구성하였다. Planner는 빠른 응답을 생성하고, 전역적인 정보를 사용하지 않기 위하여 반사적인 제어 방식에 의한 경로 생성 방식을 채택하였고, 제어기 부분은 비선형 posture feedback stabilizer로 설계하였다. 제안된 시스템은 단순한 형태의 제어 방식으로 완전한 자율적인 판단에 의한 장애물 회피와 목표 지점으로의 수렴 능력을 보여 준다. 본 시스템의 단순하면서도 효과적인 자율주행 능력은 반사제어 방식의 장점과 feedback 제어기의 증명된 안정성에서 기인한다. 시뮬레이션과 자체 구현한 차륜 구동 이동 로봇인 "MARI"로 실제 환경에서의 실험을 실시하여 제안된 제어기의 유효성을 검증하였다.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.4
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• pp.82-91
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• 2000

In this study, a numerical scheme based on physical optics method is developed to predict RCS of perfectly conducting body. The scheme is verified through the comparisons of numerical values of cylinder and sphere with analytical ones. It is also applied to compute RCS of a fast naval craft. Major reflection of this ship at threat angle of 0 degrees is found to be due to superstructure and stern part of main hull. In order to investigate the shaping effects on the ship. inclination angles of the stern of main hull and superstructure are set to 12 degrees. The RCS of the ship with shaping is proven to be much reduced in comparison with one without shaping.

• Proceedings of the Korea Water Resources Association Conference
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• 1985.07a
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• pp.275-281
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• 1985

The analytical procedure of the boundary element method on potential poblems is introduced and the method is used to analyze the wabe poblem which has the boundary condition based on the small amplitude wave theory. The accuracy of the computational scheme is investigated by comparing the results of progressive wave and standing wave on two dimensional (x-z plane) constant depth and the possibility about analyzing more complicated water wave theories using this method is discussed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.4
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• pp.242-251
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• 2020

In this study, the extraction efficiency and reflection coefficient by a two-dimensional OWC (Oscillating Water Column) WEC (wave energy converter) installed in front of a seawall was investigated for regular/irregular waves. The matched eigenfunction expansion method (MEEM) based on the linear potential theory was applied as an analytical tool. The diffraction problem by the incident wave in the open-chamber and the radiation problem by the oscillating pressure in the closed-chamber were solved to obtain the volume fluxes at the internal free-surface. Applying the volume fluxes into the continuity equation for the airflow in a chamber, we got the oscillating air pressure. The maximum extracted power and corresponding reflection coefficient were determined at the optimal turbine coefficient that maximizes the extracted power. OWC device designed for a high extracted efficiency simultaneously contributes to reduce reflected waves.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.9
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• pp.979-984
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• 2003

A reactive-loaded interstitial antenna(RLIA) is proposed for 2.45 GHz. It basically consists of a coaxial cable and a reactive load(RL). The RL is tipped at the end of the antenna and contributes to almost perfect matching and desirable heating area. For the almost perfect matching, a matching technique based on transmission line theory is suggested and the RLIA immersed in muscle phantom is designed, fabricated, measured and compared. The measured return loss of the RLIA is - 28.377 dB, which may be considered the best among those reported. Due to the excellent matching performance, the RLIA can also be applied for the treatment of deep-seated tumor or cancer with only one RLIA.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.12
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• pp.1308-1315
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• 2009

A full-polarimetric scatterometer(HPS: Hongik Polarimetric Scatterometer) for X-band is designed, fabricated, and verified using the theoretically well-known point-targets in this paper. The X-band full-polarimetric scatterometer consists of an OMT(Orthogonal-Mode Transducer)+horn antenna, the angle control part for the OMT+horn antenna, a transmitter/receiver with a network analyzer and a frequency-conversion circuitry, and a movable support of these parts. We use an inclinometer sensor to control the vertical and horizontal incidence angles. The full polarimetric data can be obtained because of the polarization switches and the OMT. The accuracy of the scatterometer system is verified by measuring the polarimetric RCS(Radar Cross Section) of one of the theoretically well-known point-targets, i.e., a corner reflector.

• Proceedings of the Acoustical Society of Korea Conference
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• 1993.06a
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• pp.174-178
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• 1993

초음파 변환기의 방사 컨덕턴스를 결정하기 위해서는 변환기로부터 방사된 음향파워와 입력전압의 정밀측정을 요구하게 된다. 음\ulcorner파워는 초음파를 거의 완전 반사시킬 수 있는 표적을 사용하여 변환기로부터 방사된 음압에 의해 표적에 가해진 힘을 수동맞저울과 레이저 간섭계로 측정하여 구하였으며, 입력전압을 열 변환기와 전압계를 한 시스템으로 하여 정밀 측정하였다. 방사 컨덕턴스의 최대 측정오차는 $\pm$4% 이내로 평가되었다.

• Geophysics and Geophysical Exploration
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• v.23 no.1
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• pp.38-49
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• 2020

Full-waveform inversion (FWI) is an optimization process of fitting observed and modeled data to reconstruct high-resolution subsurface physical models. In acoustic FWI (AFWI), pressure data acquired using a marine streamer has mainly been used to reconstruct the subsurface P-wave velocity models. With recent advances in marine seismic-acquisition techniques, acquiring multi-component data in marine environments have become increasingly common. Thus, AFWI strategies must be developed to effectively use marine multi-component data. Herein, we proposed an AFWI strategy using horizontal and vertical particle-acceleration data. By analyzing the modeled acoustic data and conducting sensitivity kernel analysis, we first investigated the characteristics of each data component using AFWI. Common-shot gathers show that direct, diving, and reflection waves appearing in the pressure data are separated in each component of the particle-acceleration data. Sensitivity kernel analyses show that the horizontal particle-acceleration wavefields typically contribute to the recovery of the long-wavelength structures in the shallow part of the model, and the vertical particle-acceleration wavefields are generally required to reconstruct long- and short-wavelength structures in the deep parts and over the whole area of a given model. Finally, we present a sequential-inversion strategy for using the particle-acceleration wavefields. We believe that this approach can be used to reconstruct a reasonable P-wave velocity model, even when the pressure data is not available.

• Journal of the Korean Geotechnical Society
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• v.31 no.6
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• pp.27-44
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• 2015

An analytical solution of dynamic responses for seabed in finite and infinite thicknesses including shallow has been developed under flow and partial standing wave with arbitrary reflection ration coexisting field at a constant water depth condition. In the analytical solution, a field was simply transited to a coexisting field of progressive wave and flow when reflection ratio was 0 and to a coexisting field of fully standing wave and flow when reflection ratio was 1. Based on the Biot's consolidation theory, the seabed was assumed as a porous elastic media with the assumptions that pore fluid is compressible and Darcy law governs the flow. The developed analytical solution was compared with the existing results and was verified. Using the analytical solution the deformation, pore pressure, effective and shear stresses were examined under various given values of reflection ratio, flow velocity, incident wave's period and seabed thickness. From this study, it was confirmed that the dynamic response of seabed was quite different depending on consideration of flow, which causes changing period and length of incident and reflection waves. It was also confirmed that dynamic response significantly depends on the magnitude of reflection ratio.

• Journal of Ocean Engineering and Technology
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• v.24 no.6
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• pp.34-40
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• 2010

Bragg reflection of nonlinear waves is simulated by a 2D fully nonlinear numerical wave tank (NWT). The developed NWT was based on the Boundary Element Method (BEM) with potential theory and the mixed Eulerian-Lagrangian (MEL) time marching scheme with Runge-Kutta 4th-order time integration. A spatial variation of wave elevations and their Fourier amplitudes of each component are compared to investigate the effect of sea bottom ripples and their relative heights. The incident waves over an undulated sea bottom are partially reflected and changed to partial standing waves due to Bragg reflection. The present results are verified with linear calculations and experimental data. It is found that the 1st-order wave component is mainly affected by Bragg reflection and its spatial modulation is significant in front of the bottom ripples.