• 대한전자공학회논문지TC
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• 제42권12호
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• pp.165-170
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• 2005

본 논문은 임펄스 전파 채널 측정에 있어서, 사용된 초광대역 (Ultra Wideband) 안테나가 시간 및 주파수 영역에서 임펄스 전파 채널에 미치는 영향을 기술하고자 한다. 임펄스 전파 채널에서의 초광대역 안테나의 영향을 해석하기 위해, 우선 초광대역 안테나의 임펄스 응답을 구하였고, 이를 이용하여 초광대역 안테나의 영향이 배제된 임펄스 전파 채널 해석 방법을 제시하였다. 이론적 증명을 위해, 임펄스 전파 채널 측정을 위한 변형된 초광대역 코니컬 모노폴 안테나를 설계, 제작하였고 무반향 반사실에서의 전달 특성을 측정하여 초광대역 안테나의 임펄스 응답을 도출하였다. 또한, 임펄스 전파 채널 상에서의 초광대역 안테나에 대한 영향을 해석하기 위해, 무반향 반사실에서 다중경로 환경을 만들어 주파수 영역에서 벡터 회로망 분석기를 사용하여 전달 특성을 측정하였다. 주파수 영역에서 측정된 데이터는 신호 처리 과정을 거쳐 시간 영역의 신호로 변환하였다. 측정된 결과로부터, 안테나의 특성이 임펄스 전파 채널에 영향을 미침을 확인하였다. 또한, 초광대역 안테나의 임펄스 응답을 사용하여 순수하게 다중경로 채널에 의한 임펄스 응답을 구하였다.

• Earthquakes and Structures
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• 제9권1호
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• pp.173-194
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• 2015

Site response analysis is an important topic in earthquake engineering. A time-domain numerical method called as one-dimensional (1D) finite element artificial boundary method is proposed to simulate the homogeneous plane elastic wave propagation in a layered half space subjected to the obliquely incident plane body wave. In this method, an exact artificial boundary condition combining the absorbing boundary condition with the inputting boundary condition is developed to model the wave absorption and input effects of the truncated half space under layer system. The spatially two-dimensional (2D) problem consisting of the layer system with the artificial boundary condition is transformed equivalently into a 1D one along the vertical direction according to Snell's law. The resulting 1D problem is solved by the finite element method with a new explicit time integration algorithm. The 1D finite element artificial boundary method is verified by analyzing two engineering sites in time domain and by comparing with the frequency-domain transfer matrix method with fast Fourier transform.

• 디지털콘텐츠학회 논문지
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• 제11권3호
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• pp.331-339
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• 2010

네트워크 보안에서의 효율성은 침입차단 성능과 시스템 performance로 대표된다. 네트워크 보안의 성능 향상을 위해서는 네트워크 인프라스트럭쳐에서의 기능적인 효율성을 우선 확보해야 한다. 그동안 네트워크 보안 효율성 제고 달성에 관한 많은 방법론들이 연구되었다. 이 같은 연구의 목적은 인프라스트럭쳐에서의 효율성 메커니즘 구현을 통해 빠른 응답시간내에 보다 우수한 침입차단을 실현하는 것이다. 이를 위해서 네트워크 보안 도메인 효율성 구조를 설계하고 구조별 효율성 측정방법을 연구함으로써 인프라스트럭쳐상에서의 보안방법론 모델을 제안하였다. 본 연구에서 제안한 방법론을 통해 체계적인 도메인 설계와 측정방법을 실시할 경우 운용인프라스트럭쳐 시스템상에서 보안 효율성 확보가 가능함이 입증되었다.

• 대한조선학회논문집
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• 제51권4호
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• pp.274-282
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• 2014

Time series of the dynamic response of a slender marine structure was predicted using quadratic Volterra series. The wave-structure interaction system was identified using the NARX(Nonlinear Autoregressive with Exogenous Input) technique, and the network parameters were determined through the supervised training with the prepared datasets. The dataset used for the network training was obtained by carrying out the nonlinear finite element analysis on the freely standing riser under random ocean waves of white noise. The nonlinearities involved in the analysis were both large deformation of the structure under consideration and the quadratic term of relative velocity between the water particle and structure in Morison formula. The linear and quadratic frequency response functions of the given system were extracted using the multi-tone harmonic probing method and the time series of response of the structure was predicted using the quadratic Volterra series. In order to check the applicability of the method, the response of structure under the realistic ocean wave environment with given significant wave height and modal period was predicted and compared with the nonlinear time domain simulation results. It turned out that the predicted time series of the response of structure with quadratic Volterra series successfully captures the slowly varying response with reasonably good accuracy. It is expected that the method can be used in predicting the response of the slender offshore structure exposed to the Morison type load without relying on the computationally expensive time domain analysis, especially for the screening purpose.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1996년도 추계학술대회 논문
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• pp.6-10
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• 1996

This paper presents an overview of research results obtained by the authors in a series of publications. Methods are developed both for time-varying and time-invariant for linear and nonlinear. for time domain and frequency domain . and for discrete-time and continuous-time systems. Among the topics presented are: 1. Learning control based on integral control concepts applied in the repetition domain. 2. New algorithms that give improved transient response of the indirect adaptive control ideas. 4. Direct model reference learning control. 5 . Learning control based frequency domain. 6. Use of neural networks in learning control. 7. Decentralized learning controllers. These learning algorithms apply to robot control. The decentralized learning control laws are important in such applications becaused of the usual robot decentralized controller structured.

• Nuclear Engineering and Technology
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• 제39권6호
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• pp.717-724
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• 2007

A measurement-based time-domain noise simulation of radiation detector-preamplifier (front-end) noise in nuclear spectroscopy is described. The time-domain noise simulation was performed by generating "noise random numbers" using Monte Carlo's inverse method. The probability of unpredictable noise was derived from the empirical cumulative distribution function via the sampled noise, which was measured from a preamplifier output. Results of the simulated noise were investigated as functions of time, frequency, and statistical domains. Noise behavior was evaluated using the signal wave-shaping function, and was compared with the actual noise. Similarities between the response characteristics of the simulated and the actual preamplifier output noises were found. The simulated noise and the computed nuclear pulse signal were also combined to generate a simulated preamplifier output signal. Such simulated output signals could be used in nuclear spectroscopy to determine energy resolution degradation from front-end noise effect.

• Wind and Structures
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• 제28권3호
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• pp.171-180
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• 2019

This paper presents a restart iterative approach for time-domain flutter analysis of long-span bridges using the commercial FE package ANSYS. This approach utilizes the recursive formats of impulse-response-function expressions for bridge's aeroelastic forces. Nonlinear dynamic equilibrium equations are iteratively solved by using the restart technique in ANSYS, which enable the equilibrium state of system to get back to last moment absolutely during iterations. The condition for the onset of flutter instability becomes that, at a certain wind velocity, the amplitude of vibration is invariant with time. A long-span suspension bridge was taken as a numerical example to verify the applicability and accuracy of the proposed method by comparing calculated results with wind tunnel tests. The proposed method enables the bridge designers and engineering practitioners to carry out time-domain flutter analysis of bridges in commercial FE package ANSYS.

• 한국방재학회 논문집
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• 제11권1호
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• pp.7-13
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• 2011

지진에 대한 장대 교량의 정확한 반응 해석은 지진 방재에 있어서 중요한 역할을 한다. 본 논문은 비동기 다지지점 지진입력에 의한 교량의 반응을 진동수 영역방법과 시간 영역방법으로 해석하였으며 그 결과를 동기 입력 결과와 비교하였다. 시간영역방법에서는 선형모드 중첩 법으로 최대반응 값을 계산하였다. 진동수영역방법에서는 선형랜덤진동 이론을 사용하여 교량 성능에 영향을 미치는 모드와 다지지점 지진입력의 상호상관관계를 고려한 반응의 제곱평균근(RMS값)을 계산하였다. 교량 성능 반응 중, 변위 및 부재의 내력에 대한 시간 영역해석 결과와 진동수영역 해석 결과로부터 최대반응 값과 RMS값의 비로 정의된 최대반응 계수의 실용적인 값과 계산 방법을 요약하였다. 신뢰 있는 최대 반응계수가 있으면, 교량의 성능기반설계에서 구체적인 임의의 입력을 고려한 시간영역방법보다 결과의 일반성 및 수치적인 장점을 갖은 진동수영역방법이 더 효율적이다.

• Structural Engineering and Mechanics
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• 제22권4호
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• pp.469-481
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• 2006

A new method called fuzzy factor method for the stationary stochastic response analysis of fuzzy truss with global fuzzy structural parameters is presented in this paper. Considering the fuzziness of the structural physical parameters and geometric dimensions simultaneously, the fuzzy correlation function matrix of structural displacement response in time domain is derived by using the fuzzy factor method and the optimization method, the fuzzy mean square values of the structural displacement and stress response in the frequency domain are then developed with the fuzzy factor method. The influences of the fuzziness of structural parameters on the fuzziness of mean square values of the displacement and stress response are inspected via an example and some important conclusions are obtained. Finally, the example is simulated by Monte-Carlo method and the results of the two methods are close, which verified the feasibility of the method given in this paper.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1995년도 봄 학술발표회 논문집
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• pp.136-143
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• 1995

The problem of the structural identification becomes important, particularly with relation to the rapid increase of the number of the damaged or deteriorated structures, such as highway bridges, buildings, and industrial facilities. This paper summarizes the recent studies related to those problems by the present authors. The system identfication methods are generally classified as the time domain and the frequency domain methods. As time doamin methods, the sequential algorithms such as the extended Kalman filter and the sequential prediction error method are studied. Several techniques for improving the convergences are incorporated. As frequency domain methods, a new frequency response function estimator is introduced. For damage estimation of existing structures, the modal perturbation and the sensitivity matrix methods are studied. From the example analysis, it has been found that the combined utilization of the measurement data for the static response and the dynamic (modal) properties are very effictive for the damage estimation.