• 한국음향학회지
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• 제41권4호
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• pp.419-425
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• 2022

본 논문은 양상태 소나의 음원과 수신기 배치를 위해 음향탐지성능을 평가하는 것을 목표로 한다. 단상태 소나와는 다르게 양상태 소나의 경우에는 배치를 위한 연산량과 복잡도가 크기 때문에 해양환경을 고려한 배치 연구는 진행된 바가 없다. 따라서 본 연구에서는 양상태 소나의 음원과 수신기 배치에 적용하기 위한 방법으로 해양환경의 변동성을 고려하면서도 연산량을 줄이는 평가 방법에 대해 제안한다. 본 연구에서는 천해와 심해의 대표 해양환경을 선정하였으며, 그 해역에서 음원과 수신기 간의 거리 및 센서 심도를 변경하며 신호초과를 계산하고, 그 결과를 제안하는 음향탐지성능 평가 방법과 비교 및 분석한다.

• Steel and Composite Structures
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• 제45권3호
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• pp.305-330
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• 2022

This article aims to investigate the static deflection and stress analysis of bi-directional functionally graded porous plate (BDFGPP) modeled by unified higher order kinematic theories to include the shear stress effects, which not be considered before. Different shear functions are described according to higher order models that satisfy the zero-shear influence at the top and bottom surfaces, and hence refrain from the need of shear correction factor. The material properties are graded through two spatial directions (i.e., thickness and length directions) according to the power law distribution. The porosities and voids inside the material constituent are described by different cosine functions. Hamilton's principle is implemented to derive the governing equilibrium equation of bi-directional FG porous plate structures. An efficient numerical differential integral quadrature method (DIQM) is exploited to solve the coupled variable coefficients partial differential equations of equilibrium. Problem validation and verification have been proven with previous prestigious work. Numerical results are illustrated to present the significant impacts of kinematic shear relations, gradation indices through thickness and length, porosity type, and boundary conditions on the static deflection and stress distribution of BDFGP plate. The proposed model is efficient in design and analysis of many applications used in nuclear, mechanical, aerospace, naval, dental, and medical fields.

• Advances in nano research
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• 제12권1호
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• pp.37-47
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• 2022

In this paper, the non-linear static analysis of Timoshenko nanobeams consisting of bi-directional functionally graded material (BFGM) with immovable ends is investigated. The scratching in the FG nanobeam mid-plane, is the source of nonlinearity of the bending problems. The nonlocal theory is used to investigate the non-linear static deflection of nanobeam. In order to simplify the formulation, the problem formulas is derived according to the physical middle surface. The Hamilton principle is employed to determine governing partial differential equations as well as boundary conditions. Moreover, the differential quadrature method (DQM) and direct iterative method are applied to solve governing equations. Present results for non-linear static deflection were compared with previously published results in order to validate the present formulation. The impacts of the nonlocal factors, beam length and material property gradient on the non-linear static deflection of BFG nanobeams are investigated. It is observed that these parameters are vital in the value of the non-linear static deflection of the BFG nanobeam.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.357-360
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• 2008

이 연구에서는 저형고의 콘크리트거더에 효율적으로 프리스트레스를 도입할 수 있는 Bi Prestressed Concrete Girder(이하 Bicon거더)에 대한 정적 구조성능을 검증하였다. Bicon거더는 거더 상연에 강봉(압축재)와 하연에 강연선(인장재)를 동시에 긴장하여 두 부재의 편심을 이용, 부재에 순수한 휨만을 도입할 수 있는 프리스트레싱 공법으로 제작된다. 구조성능검증을 위해 철도 LS-22하중으로 20m Bicon거더 시험체를 제작하였다. 프리스트레스 도입시 콘크리트 부재에 순수 휨의 도입여부를 계측하였고, 탄성 및 균열 후 거동, 파괴시의 극한거동을 평가하기 위해 정적 재하시험을 수행하였다. 시험결과 긴장시 중앙단면의 효과적인 휨모멘트의 도입을 확인하였고, 정적하중 재하시 균열은 사용하중의 약 1.2배의 하중에서 발생하였으며 극한강도는 최대저항모멘트보다 15% 이상 증가되는 결과를 보여 충분한 안전율을 갖고 있는 교량거더로 평가되었다.

• 한국음향학회지
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• 제22권6호
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• pp.472-481
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• 2003

천해에서 포물선 근사 (parabolic approximation)에 기초한 저주파 양상태 잔향음 모델 (LHYREV-B, Low-frequency Hanyang Univ. Reverberation model-Bistatic)을 제안하였다. LHYREV-B 모델에서는 해저와 해저지형 내의 상호작용을 포함하는 음향모델에 수평입사에 독립인 산란함수를 이용하여 양상태 잔향음을 계산하였다. 모델의 검증을 위하여 실측 잔향음 신호와 비교하였으며, 비교 결과 LHYREV-B 모델이 저주파 잔향음 예측에 적합함을 확인할 수 있다.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2000년도 KIASC Conference 2000 / 2000년도 학술대회 논문집
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• pp.128-129
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• 2000

The over-critical current behaviors for bare or insulated Bi-222 tapes with different matrix materials have been examined. The result shows that static resistances of the two bare tapes becomes similar for currents above 150 A but different for currents below. In the insulated A tape the first rapid temperature rise occurred around 180 A and eventually burned out about 190A.

• JSTS:Journal of Semiconductor Technology and Science
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• 제6권2호
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• pp.119-123
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• 2006

This work presents the fabrication and characteristics of $Bi_2O_3/Si$ heterojunction prepared by rapid thermal oxidation technique without any postdeposition annealing condition. The bismuth trioxide film was deposited onto monocrystalline Si and glass substrates by rapid thermal oxidation of bismuth film with aid of halogen lamp at $500^{\circ}C/\;45$ s in static air. The structural, optical and electrical properties of $Bi_2O_3$ film were investigated and compared with other published results. The structural investigation showed that the grown films are polycrystalline and multiphase (${\alpha}-Bi_2O_3$ and ${\beta}-Bi_2O_3$). Optical properties revealed that these films having direct optical band gap of 2.55 eV at 300 K with high transparency in visible and NIR regions. Dark and illuminated I-V, CV, and spectral responsivity of $Bi_2O_3/Si$ heterojunction were investigated and discussed.

• 정보저장시스템학회논문집
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• 제1권1호
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• pp.93-98
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• 2005

Rewritable optical disk is one of the essential data storage media in these days, which takes advantage of the different optical properties in the amorphous and crystalline states of phase change materials. As well known, data transfer rate is one of the most important parameter of the phase change optical disks, which is mostly limited by the crystallization speed of recording media. Therefore, we doped Sn/Bi to $Ge_2Sb_2Te_5$ alloy in order to improve the crystallization speed and investigated the dependence of phase change characteristics on Sn/Bi doping concentration. The Sn/Bi doped $Ge_2Sb_2Te_5$ thin film was deposited by RF magnetron co-sputtering system and phase change characteristics were investigated by X-ray diffraction (XRD), static tester, UV-visible spectrophotometer, electron probe microanalysis (EPMA), inductively coupled plasma mass spectrometer (ICP-MS) and atomic force microscopy (AFM). Optimum doping concentration of Bi and Sn were 5${\~}$6 at.$\%$ and the minimum time for crystallization was below than 20 ns. This improvement is correlated with the simple crystalline structure of Sn/Bi doped $Ge_2Sb_2Te_5$ and the reduced activation barrier arising from Sn/Bi doping. The results indicate that Sn/Bi might play an important role in the transformation kinetics of phase change materials..

• 한국군사과학기술학회지
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• 제21권2호
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• pp.158-165
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• 2018

Recently there is a great interest in the bi-static sonar. However, since the transmitter and the receiver operate on different platforms, it may be necessary to operate the system in a non-cooperative mode. In this situation, the detection and localization performance are limited. Therefore, it is necessary to classify the received pulse from the transmitter to overcome the performance limitation. In this paper, we proposed a robust automatic pulse classification method that can be applied to real systems. The proposed method eliminates the effects of noise and multipath propagation through post-processing and improves the pulse classification performance. We also verified the proposed method through the sea experimental data.

• 한국지진공학회논문집
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• 제27권6호
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• pp.237-244
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• 2023

This study analyzes the seismic response of traffic light poles, considering soil-foundation effects through nonlinear static and time history analyses. Two poles are investigated, uni-directional and bi-directional, each with 9 m mast arms. Finite element models incorporate the poles, soil, and concrete foundations for analysis. Results show that the initial stiffness of the traffic light poles decreases by approximately 38% due to soil effects, and the drift ratio at which their nonlinear behavior occurs is 77% of scenarios without considering soil effects. The maximum acceleration response increases by about 82% for uni-directional poles and 73% for bi-directional poles, while displacement response increases by approximately 10% for uni-directional and 16% for bi-directional poles when considering soil-foundation effects. Additionally, increasing ground motion intensity reduces soil restraints, making significant rotational displacement the dominant response mechanism over flexural displacement for the traffic light poles. These findings underscore the importance of considering soil-foundation interactions in analyzing the seismic behavior of traffic light poles and provide valuable insights to enhance their seismic resilience and safety.