• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.103-106
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• 2004

Impact location monitoring is one of the major concerns of the smart health monitoring. For this application, multipoint ultrasonic sensors are to be employed. In this study, a multiplexed FBG sensor system with wide dynamic range was proposed and stabilization controlling system was also developed for the maintenance of maximum sensitivity of sensors. For the intensity demodulation system of FBG sensors, Fabry-Perot tunable filter(FP-TF) with 23.8nm FSR(free spectral range) was used, which behaves as two separate filters between $1530 \~ 1560$ nm range. Two FBG sensors were attached on the bottom side of the graphite/epoxy composite beam specimen, and low velocity impact tests were performed to detect the one-dimensional impact locations. Impact locations were calculated by the arrival time differences of the impact longitudinal waves acquired by the two FBGs. As a result, multiplexed in-line FBG sensors could detect the moment of impact precisely and found the impact locations with the average error of 1.32mm.

• 한국광학회지
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• 제33권4호
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• pp.137-145
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• 2022

광집적회로(photonic integrated circuits) 소자의 기본적인 부품 중 하나인 방향성 결합기 소자는 두 개의 인접한 광도파로 사이에서 일어나는 모드 간 광결합에 의해서 광파워를 분배하는 기능을 가진다. 본 논문에서는 방향성 결합기 소자를 제작하기 위한 설계 과정에 대하여 살펴보고 실제로 제작된 소자의 특성으로부터 설계 결과의 정확도에 대하여 확인하는 과정을 수행한다. 빔전파기법(beam propagation method, BPM) 시뮬레이션을 통하여 방향성 결합기 소자를 설계하는 과정에서, 유효굴절률 계산을 통하여 2차원 평면 구조로 변환된 소자에 대한 이차원 BPM 설계를 하여서 소자 구조를 확정하고, 실리카 광도파로 방향성 결합기 소자를 어레이 형태로 제작한 뒤 특성을 측정하였다. 실험 결과와 차이를 보이는 2D BPM 설계 결과를 보완하기 위하여 계산량이 훨씬 많은 3D BPM 설계를 수행하였으며 그 결과는 실험 결과에 더욱 근접하였다. 실험 결과와 일치하는 설계 결과를 얻기 위하여 3D BPM에 사용된 광도파로 코어 굴절률을 미세하게 보정하였으며 이를 통하여 실험치를 정확히 예측 가능한 BPM 설계를 수행하는 방법을 확립하였다.

• 전자공학회논문지A
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• 제29A권11호
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• pp.40-48
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• 1992

The wave-kinetic numerical method is used in simulating the irradiance scintillations of optical wave through a two-dimensional random medium containing weak Gaussian fluctuations of the refractive index. The results are compared to existing analytical or numerical results. The wave-kinetic method is a phase-space ray-tracing method for certain key ray trajectories, and the irradiance is calculated by reconstructing the entire beam from these trajectories. The strength of the wave-kinetic method lies in the fact that it can be applied to any type of random media.

• Journal of Magnetics
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• 제2권2호
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• pp.58-66
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• 1997

Recently, artificially modulated magnetic multilayer materials, for examples giant magnetoresistant magnetic head materials and magneto-optic recording materials in the wavelength of a blue laser beam, attract great attention in the electronics industry due to their unique properties derived from the modulated multilayer structure. Since the multilayer structure as well as amorphous structure, is non-equilibrium state in terms of free energy, an assessment of the thermal staibility in the multilayer structure is crucially importnat both for basic research and applications. In this review paper, effective microscopic interdiffusion process in the two dimensional multilayer structure will be described in terms of steep concentration gradient effect, strain effect and magnetic transition effect.

• Journal of Welding and Joining
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• 제10권2호
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• pp.19-31
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• 1992

A numerical study was performed to investigate the flow field and the heat transfer characteristics occurring in high power density welding which is important in many fields of engineering applications. A two dimensional quasi-steady state of keyhole welding model is simulated by using the finite volume methods. It is shown that the shape of isothermal line is elliptic and the temperature gradient is very steep compared with other welding method and the welding speed has on welding width and observed beam power.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2005년도 추계학술대회 논문집
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• pp.1261-1267
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• 2005

At this paper Dynamic respones of bridges for the Korean high-speed railway are analyzed by a modal analysis. To control vibration of bridges, Tuned Mass Damper(TMD) that is passive type control device is used. Opimize and prove it. Newmark method is used for a numerical analysis. In case of vehicle is modeled for moving mass that considers the effects of the moving. Also this paper is assumped as the simple supported Bernoulli-Euler beam and considered two dimensional Interaction motion between vehicle and bridge.

• 한국전산구조공학회논문집
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• 제28권5호
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• pp.467-475
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• 2015

본 논문에서는 구조물에 작용하는 하중의 크기와 진동수에 따른 거동의 비선형성을 확인하고 정확한 예측을 위한 방법을 모색하기 위하여 외팔보의 정적 및 동적해석의 수행에서 선형, 비선형 해석의 결과를 비교하는 연구를 진행하였다. 우선 보의 자유단에 수직방향의 정적 및 동적 하중을 가한 상황을 예측하였다. 선형 해석방법으로 고전 외팔보 이론을 적용하였고, co-rotational dynamic 유한요소해석 기법을 개발하여 비선형 해석방법으로 사용하였다. 먼저 정적해석에서 외력의 크기가 달라질 때 선형 및 비선형 해석 예측이 어떠한 차이를 보이는지 비교하였다. 그리고 동적해석을 통해 가진 진동수의 변화에 따른 보 끝단의 무차원화된 변위의 양상을 연구하였고, 공진진동수 근방에서의 상당한 변위가 발생함을 보였다. 마지막으로 주파수 지연현상을 조사하기 위해 특정 진동수에서의 시간 경과에 따른 보의 변위를 확인하였다.

• 한국음향학회:학술대회논문집
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• 한국음향학회 2000년도 하계학술발표대회 논문집 제19권 1호
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• pp.385-388
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• 2000

Electromagnet ic wave falling on solid surface acts on the medium with a force. This force brings about a redistribution of surface charges and the surface potential is varied. By measuring this potential variations, the surface electrical properties on conductors, semicionductors and dielectrics can be tested. In this paper, two dimensional photocharge voltage on the $LiNbO_3$ wafer induced by He-Ne laser beam, the temperature characteristics and the capacitive coupling test structure for the photocharge voltage measurement for the dielectrical materials are shown.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.353-356
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• 2002

Planar laser induced fluorescence(PLIF) has been widely used to obtain two dimensional fuel distribution. Preliminary investigation was performed to measure quantitative air excess ratio distribution in an engine fueled with LPG. It is known that fluorescence signal from acetone as a fluorescent tracer is less sensitive to oxygen quenching than other dopants. Acetone was excited by KrF excimer laser (248nm) and its fluorescence image was acquired by ICCD camera with a cut-of filter to suppress Mie scattering from the laser light. For the purpose of quantifying PLIF signal, an image processing method including the correction of laser sheet beam profile was suggested. Raw images were divided by each intensity of laser energy and profile of laser sheet beam. Inhomogeneous fluorescence images scaled with the reference data, which was taken by a calibration process, were converted to air excess ratio distribution. This investigation showed instantaneous quantitative measurement of planar air excess ratio distribution for gaseous fuel.

• 한국터널공학회:학술대회논문집
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• 한국터널공학회 2005년도 학술발표회 논문집
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• pp.213-224
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• 2005

The safety factor of a tunnel considering the failure of supports is important because the failure of supports might cause the collapse of the tunnel. In the previous studies, shotcrete was modelled as beam elements and the failure of the shotcrete was checked according to the allowable working stress concept. In this study, shotcrete was modelled by both beam elements and continuum (elasto-plastic) elements. Safety factors of tunnels were estimated by two dimensional numerical analysis with varying rock mass class, coefficient of lateral pressure, thickness of shotcrete, rock bolt reinforcement and excavation method. Also the study suggested not only a proper amount of supports but also modelling method.