• Title, Summary, Keyword: harmonic loading

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Active-Sensing Based Damage Monitoring of Airplane Wings Under Low-Temperature and Continuous Loading Condition (능동센서 배열을 이용한 저온 반복하중 환경 항공기 날개 구조물의 손상 탐지)

  • Jeon, Jun Young;Jung, Hwee kwon;Park, Gyuhae;Ha, Jaeseok;Park, Chan-Yik
    • Journal of the Korean Society for Nondestructive Testing
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    • v.36 no.5
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    • pp.345-352
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    • 2016
  • As aircrafts are being operated at high altitude, wing structures experience various fatigue loadings under cryogenic environments. As a result, fatigue damage such as a crack could be develop that could eventually lead to a catastrophic failure. For this reason, fatigue damage monitoring is an important process to ensure efficient maintenance and safety of structures. To implement damage detection in real-world flight environments, a special cooling chamber was built. Inside the chamber, the temperature was maintained at the cryogenic temperature, and harmonic fatigue loading was given to a wing structure. In this study, piezoelectric active-sensing based guided waves were used to detect the fatigue damage. In particular, a beamforming technique was applied to efficiently measure the scattering wave caused by the fatigue damage. The system was used for detection, growth monitoring, and localization of a fatigue crack. In addition, a sensor diagnostic process was also applied to ensure the proper operation of piezoelectric sensors. Several experiments were implemented and the results of the experiments demonstrated that this process could efficiently detect damage in such an extreme environment.

A Study on Durability of Automotive Propeller Shaft by Fatigue and Vibration (피로 및 진동에 의한 자동차 추진축의 내구성 연구)

  • Cho, Jae-Ung;Kim, Sei-Hwan;Kim, Key-Sun
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.12 no.4
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    • pp.1495-1501
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    • 2011
  • Fatigue life and vibration can be analyzed at automotive propeller shaft during driving in this study. The york part is shown with the maximum equivalent stress and displacement of $1.3177{\times}10^3$Pa and $3.6148{\times}10^{-4}$m. The possible life in use in case of 'SAE bracket' is the shortest among the fatigue loading lives of 'SAE bracket', 'SAE transmission' and Sample history. There are the most frequency as 80% in case of 'SAE bracket and the least frequency as 5% in case of Sample history'. Maximum amplitude displacement is 0.00261m at 58 Hz at forced vibration. As the result of this study is applied by the propeller shaf, the prevention on fatigue damage and the durability are predicted.

Design and Fabrication of a X-band Voltage Control Dielectric Resonator Oscillator with The Low Phase Noise (낮은 위상잡음을 갖는 X-band 전압제어 유전체 공진형 발진기의 설계 및 제작)

  • 박창현;최병하
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.41 no.5
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    • pp.69-76
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    • 2004
  • In this paper, a VCDRO (Voltage Control Dielectric Resonator Oscillator) with low phase noise for X-band application has been designed and fabricated. A low noise and low flicker noise MESFET and a high Q dielectric resonator were selected to obtain good phase noise Performance. Also, a varactor diode having high Q, qualify factor was used to reduce the loading effects and a big Gamma of diode was chosen for linearity of frequency over voltage tuning range. The fabricated circuits was simulated with circuit design tools, ADS to provide the optimum performances. As the measured results of fabricated oscillator, the output power was 5.8 ㏈m at center frequency 12.05㎓ and harmonic suppression -30㏈c, phase noise -114 ㏈c at 100 KHz offset frequency, respectively, and the frequency tuning range as the function of valtage applied to varactor diode was 15.2 MHz and its power variation with frequency was 0.2 ㏈. This oscillator could be available to a local oscillator in X-band.

Comparative Study on Seismic Performance of Viscously Damped Self-Centering SDOF Systems with Elasto-Plastic SDOF Systems (점성 감쇠기를 가진 셀프 센터링 단자유도 시스템과 탄소성거동의 단자유도 시스템의 내진성능 비교에 관한 연구)

  • Kim, Hyung-Joon
    • Journal of Korean Society of Steel Construction
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    • v.22 no.6
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    • pp.553-561
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    • 2010
  • The purpose of this paper is to analytically find the approximate supplement damping ratio of the viscous damper installed in self-centering (SC) single-degree-of-freedom (SDOF) systems with maximum displacements that are similar to those of elasto-plastic (EP) SDOF systems. The behavior of an SC SDOF system under harmonic cyclic loading was first described. Then an analytical model that can capture the behavior of the viscously damped SC SDOF system was introduced. Analysis parameters that characterize the hysteresis of the EP and SC SDOF systems were chosen, and nonlinear time-history analyses were performed using 20 historical accelerograms. Most of the SC SDOF systems with viscous dampers with approximately 10-15% damping ratios presented mean maximum displacement values that were similar to those of the EP SDOF systems. To investigate in detail the seismic performance of both systems, three EP SDOF systems and six corresponding SC SDOF systems were selected. The analyses showed that all the SC SDOF systems eliminated the residual displacements after the end of their shaking, and that the SC SDOF systems with 15% damping ratios performed better than the EP SDOF systems in terms of maximum displacement and acceleration response.