• Journal of Power System Engineering
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• v.14 no.6
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• pp.75-82
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• 2010

In this study, the topics for free-surface wave simulation, nonlinear hydrodynamic force, and the critical resonance frequency of so-called ${\tau}=U{\omega}/g$=1/4 are discussed. A high-order spectral/boundary element method is newly adapted as an efficient numerical tool. This method is one of the most efficient numerical methods by which the nonlinear gravity waves can be simulated and hydrodynamic forces also can be calculated in time domain. In this method, the velocity potential is expressed as the sum of surface potential and body potential. Then, surface potential is solved by using the high-order spectral method and body potential is solved by using the high-order boundary element method. By the combination of these two methods, the wave-making problems by a submerged sphere oscillating with forward speed under the free-surface are solved in time domain.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.7
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• pp.661-668
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• 2009

The slosh natural frequencies, damping ratio, slosh mass and slosh force applying point of the liquid in cylindrical tank are estimated using the nonlinear least squares method in time domain. The estimated slosh model parameters are in good agreement with the results of the theoretical calculations for various liquid depths. Furthermore, this methodology will be applied to predict the sloshing parameters for a liquid propellant tank using ground experimental test-bed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.5
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• pp.28-33
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• 2005

Nonlinear aeroelastic characteristics of a two dimensional typical section model with bilinear plunge spring are investigated. Doublet-point method(DPM) is used for the calculation of supersonic unsteady aerodynamic forces which are approximated by using the minimum-state approximation. For nonlinear flutter analysis structural nonlinearity is represented by an asymmetric bilinear spring and is linearized by using the describing function method. The linear and nonlinear flutter analyses indicate that the flutter characteristics are significantly dependent on the frequency ratio. From the nonlinear flutter analysis, various types of limit cycle oscillations are observed in a wide range of air speeds below or above the linear flutter boundary. The nonlinear flutter characteristics and the nonlinear aeroelastic responses are investigated.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.4
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• pp.29-40
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• 2004

This paper reports the frequency characteristics and the time response of parallel adjacent-transmission lines, crossed adjacent-transmission lines and parallel adjacent-transmission lines which are on the different planes by using FDTD-PML method. In the parallel adjacent-transmission lines, the crosstalks as a function of horizontal distance are calculated and in the crossed adjacent- transmission lines, the crosstalks as a function of vertical distance are simulated. Also, the crosstalks as functions of horizontal and vertical distances are measured and analyzed in the parallel adjacent-transmission lines which are on the different planes.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.6 no.3
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• pp.3-14
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• 1995

The broadband input impedance, the input power and the radiation pattern of the monopole antenna attached to the handy phone operated at 800MHz are calculated by using the Finite Difference Time Domain(FDTD) Method. For the FDTD analysis of frequency characteristics of monopole antenna, the handy phone is modeled with the geometry that the monopole antenna is connected to a conducting box, and the modified FDTD algorithm[11] used the thin wire appproximation method and the Maxwell's integral equation from the original Yee algorithm is applied for the analysis of the wire structure. Also, by means of finding the current distribution directly from circumferencial magnetic filelds around the monopole antenna and the conducting box, the radiation pattern is calculated to observe the influence of the conducting box, and is compared with the results of the known mothod for the FDTD calculation of radiation pattern, For the experiments, the handy phone of which full length including antenna is .lambda. $\lambda$/2 is manufactured and we confirm that all computation results are agree well with the mea- sured values.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.3 no.3
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• pp.533-540
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• 1999

In this paper, a microstrip antenna is designed using a rectangular patch. To find characteristics of the antenna, computer simulations of the rectangular single microstrip patch antenna are performed with changing width and feed line. And we found characteristics of RHCP using axial ratio. Through the results, we found that the Finite Difference Time Domain(FDTD) method is an effective method for designing microstrip patch antenna. According to simulation the resonant point has been found it in the frequency received from GPS satellite. And these results were in relatively good accordance with the measured values.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.11
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• pp.1012-1018
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• 2016

We perform a electromagnetic analysis method for indirect effects of a high-conductive structure such as an aircraft exposed by lightning, by using the finite-difference time-domain(FDTD) method. The lightning waveform used to analyze indirect effects has low frequency spectrum and high-conductive materials such as aluminum and carbon fiber composite materials have very short skin depths, and thus, it requires large memory and long computation time using conventional three dimensional FDTD analysis method. We develop an efficient electromagnetic analysis method suitable for lightning and high-conductive structures. The developed analysis method is based on two dimensional FDTD and impedance network boundary condition(INBC) algorithms and we investigate the indirect effects on the structures exposed to lightning.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.8
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• pp.61-67
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• 2010

A characterization procedure for analyzing symmetric coupled MIS(Metal-Insulator-Semiconductor) transmission line is used the same procedure as a general single layer symmetric coupled line with perfect dielectric substrate from the extraction of the characteristic impedance and propagation constant for even- and odd-mode. In this paper, an analysis for a new substrate shielding symmetric coupled MIS structure consisting of grounded crossbar at the interface between Si and SiO2 layer using the Finite-Difference Time-Domain (FDTD) method is presented. In order to reduce the substrate effects on the transmission line characteristics, a shielding structure consisting of grounded crossbar lines over time-domain signal has been examined. Symmetric coupled MIS transmission line parameters for even- and odd-mode are investigated as the functions of frequency, and the extracted distributed frequency-dependent transmission line parameters and corresponding equivalent circuit parameters as well as quality factor for the new MIS crossbar embedded structure are also presented. It is shown that the quality factor of the symmetric coupled transmission line can be improved without significant change in the characteristic impedance and effective dielectric constant.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.574-577
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• 2007

본 논문에서는 실 시공 중인 PSC 교량에 대하여 풍하중에 의한 상시 진동 계측 자료을 기반으로, 교량의 동특성(고유진동수, 모드형상)을 추정하였으며, 이를 바탕으로 대상 교량의 탄성계수를 추정하여 정적 계측을 통한 탄성계수 결과와 비교하였다. 본 논문에서 사용한 동특성 추정 기법은, 대표적인 주파수 영역 해석 방법인 Frequency Domain Decomposition(FDD) 방법과 시간영역 해석 방법인 Stochastic Subspace Identification(SSI) 방법을 이용하였다. 탄성계수 추정은 유한요소모델과 계측 결과를 이용하여 두 개의 결과 차이가 수렴하도록 하는 반복 계산을 통해 탄성계수를 추정하였다. 우선, 탄성계수 추정 기법의 검증을 위해, 수치 해석을 통하여 그 기법을 검증하였으며, 해석 결과 정확한 탄성계수값을 추정하였으며, 이를 통해 본 논문에서 적용한 탄성계수 추정법에 대한 신뢰도를 확인하였다. 이를 바탕으로 사용된 추정 기법을 실 교량에 적용하기 위해 실제 상시 진동 계측 값을 바탕으로 실교량의 동특성 및 탄성계수를 추정하였다. FDD 및 SSI 기법을 통한 모드 해석 결과, 두 기법 모두 유사한 결과를 나타내어 FDD 및 SSI 두 방법에 대한 결과의 신뢰도를 확인 할 수 있었다. 추정 탄성계수 값은 거더 단면내 설치한 응력계 및 변형률계를 통한 계측 결과값의 범위 내에 있음을 확인하였다. 따라서 본 논문에서 적용한 교량의 상시 진동 데이터를 바탕으로 한동특성 및 탄성계수 추정법이 구조물의 대략적인 탄성계수 및 이에 따른 구조물의 전체적인 건전도를 파악하는데 도움이 되리라 생각된다.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.2
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• pp.31-40
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• 1999

Characteristics of monopole antenna and planar conductor structure mounted on handheld telephone are anlayzed by using FDTD method. Feeding of monopole antenna is implemented with lumped elements and plastic case is coated on the surface of conductor box. Otherwise, resonant frequency of handheld telephone mounting monopole antenna with no plastic case is 877MHz, when plastic case (${\varepsilon}_r=2$) is coated, the resonant frequency is down to 82MHz and the bandwidth is broadened about 1.5 times. Planar structure of handheld telephone mounted on the body makes to change far-field gain radiation patterns. In this case, radiation patterns are somewhat asymmetrical. Handheld telephone using PIFA(Planar Inverted F Antenna), instead of monopole antenna, is resonated at frequency 1.52GHz that is available onPCS. In the radiation pattern of this structure, azimuth that electric field intensity is presented below 20dB is 14$^{\circ}$.