• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.1 s.94
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• pp.63-71
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• 2005

In this study, structural vibration analyses of a composite smart unmanned aerial vehicle (UAV) have been conducted considering dynamic hub-loads of tilt-rotor. Practical computational structural dynamics technique based on the finite element method is applied using MSC/NASTRAN. The present smart UAV(TR-S2) structural model is constructed as full 3D configurations with both the helicopter flight mode and the airplane flight mode. Modal based transient response and frequency response analyses are used to efficiently investigate vibration characteristics of structure and installed electronic equipments. It is typically shown that the helicopter flight mode with the 90-deg tilting angle is the most critical case for the induced vibration of installed electronic equipments in the front.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.3 no.3
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• pp.9-18
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• 1983

In many geological investigation, a data sequence may be created which consisted of a succession of mutually exclusive state. However, now our interest lie in the nature of transition from one state to another, rather than in the position of states in the sequence. In this paper, authors studied for the deformation of HAEUNDAE beach by transition matrices and empirical eigenfunction method. In this paper, 5-yr. set of profile data from HAEUNDAE beach measured at several monthly or yearly intervals are analyzed by using the transition matrices and empirical eigen-function. Results of this study indicate that the transition matrices and empirical eigenfunctions are useful in the analysis of beach profile data and provide objective insight in the nature of profile configuration.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.6B
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• pp.1142-1148
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• 1999

In this paper, the characteristics of frequency dependent dispersion are analyzed for the phase shifters in Ku-band phased array antenna system using full-wave method, SDA(Spectral Domain Approach).The design technique of asymmetric coupled-line phase shifter with dielectric overlay is proposed. The compared results of phase responses are shown with conventional symmetric coupled-line Schiffman phase shifter. The experimental results verify the improvement of broadband characteristics by the increasing bandwidths and the decreasing phase deviations.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.10
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• pp.164-169
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• 1997

The aim of this paper is to present some results of sensitivity analysis in frequency domain. The sensitivity fonctions in frequency domain is not depend on the external excitation but depend on the frequency of the system's resonance. The sensitivity functions are determined as function of partial derivatives of system transfer functions taken with respect to system design parameters. The logarithmic sensitivity function is the dimensionless sensitivity funciton available, making it useful to compare the influence of various parameters on system variables. Two degree of fredom system is used to illustrate the procedure for sensitivity analysis proposed in this paper.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.1000-1007
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• 2007

In this study, structural vibration analyses of a smart unmanned aerial vehicle (UAV) have been conducted considering dynamic hub-loads of tilt rotor. Practical computational structural dynamics technique based on the finite element method is applied using MSC/NASTRAN. The present UAV(TR-S5-04) finite element model is constructed as a full three-dimensional configuration with different fuel conditions and tilting angles for helicopter, transient and airplane flight modes. In addition, the 3-dimensional supporting equipment structures of electronic devices are considered for vibration analysis. As the results of this study, transient structural displacements and accelerations are presented in detail. Moreover, vibration characteristics of structural parts and installed equipments are investigated for different fuel conditions and tilting angles.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.1
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• pp.77-85
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• 1988

A stochchastic analysis procedure of generating floor response spectra for proportionally damped linear systems subject to earthquake loading is presented. Theories of random vibration and mode acceleration method are used in the formulation of governing equations. The structure-oscillator interaction is not considered. It is assumed that the input motions and oscillator responses are stationary Gaussian processes with mean zero. The nonstationary characteristics of earthquake motion are incorporated in the peak factor which is based on Vanmarcke's theory. Floor response spectra for both resonance and non-resonance cases are calculated under the assumption that the peak factors for structure and oscillator are equal to that for ground response spectrum. The validity of this method is demonstrated by comparing the results obtained by proposed method with those by time history analyses. The results obtained by this method are conservative and accurate with tolerable precision. This method saves much computing time compared with time history analysis method.

• Proceedings of the KIPE Conference
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• 2018.11a
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• pp.80-82
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• 2018

위상천이 풀-브릿지 컨버터(PSFB converter)는 다양한 전원장치에 응용되고 있다. 하지만 2차측에 링잉(ringing)현상이 생겨 다이오드에 과도한 전압 스트레스를 유발하는 문제가 있다. 링잉 현상을 억제하기 위해 스너버 회로를 추가하여 사용해야 하지만 저항 값에 대한 주파수응답 해석이 이루어지지 않아 스너버 튜닝에 많은 시간이 소요되었다. 본 논문에서는 저항 값에 따른 스너버 회로의 주파수 응답특성 분석을 통해 링잉으로 인한 전압 스파이크를 최소화 할 수 있는 저항 값 선정 기법을 제안하며 PSIM/Matlab 시뮬레이션으로 검증한다.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1987.04a
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• pp.206-211
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• 1987

본 논문에서는 입력 신호인 정현파의 위상을 PGZC(positive going zero corssing)에 대해 한주기당 2회씩 추적하도록 하는 디지털 위상도기 회로(DPLL)을 제시한다. 제시된 루루프는 한 주기당 2번의 표본화를 갖도록 함으로써 한 주기당 하나의 표본을 취하는 기존의 DPLLqhek 정상 상태에서의 위상오차 변동범위가 전체적으로 1/2로 감소되었고, 연속 표본들간의 오차와 양자화 준위의 선택에 따라서 루우프의 천이 응답이 좋아짐을 알 수 있었다. 그 해석적 결과를 실제적으로 요구되는 조건류에 대하여 컴퓨터 시뮬레이션을 행함으로써 검증하였다.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.15 no.4
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• pp.24-32
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• 2007

In this study, computational structural vibration analyses of a smart unmanned aerial vehicle (SUAV) with tilt-rotors due to dynamic hub loads have been conducted considering detailed supporting structures of installed equipments. Three-dimensional dynamic finite element model has been constructed for different fuel conditions and tilting angles corresponding to helicopter, transition and airplane flight modes. Practical computational procedure for modal transient response analysis is successfully established. Also, dynamic loads generated by rotating blades and wakes in the transient and forward flight conditions are calculated by unsteady computational fluid dynamics technique with sliding mesh concept. As the results of present study, transient structural displacements and accelerations of the vibration sensitive equipments are presented in detail. In addition, vibration characteristics of structures and installed equipments of which safe operation is normally limited by the vibration environment specifications are physically investigated for different flight conditions.

• Computational Structural Engineering
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• v.11 no.4
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• pp.135-146
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• 1998

대형 시스템의 건전성 평가를 위한 동적 재하시험에 있어서 변위를 측정하는 것보다 가속도를 측정하는 것이 수월하나 대부분의 공학적 기준은 응력과 비례관계를 지니는 변화를 기준으로 하고 있다. 본 연구에서는 시스템의 재하시험시 측정된 가속도신호를 이용하여 변위응답을 산정하는데 그 목적을 두고 적분을 위한 신호처리시 발생되는 문제점을 정상상태 및 천이영역에 대하여 규명하였다. 기존의 연구에서 고려하지 못하였던 초기조건의 항을 도입함으로써 시간영역의 적분과 주파수영역의 적분결과가 일치함을 해석적으로 입증하였으며 이동하중을 받는 보의 동적거동에 대하여 제시된 타당성을 검증하였다.