• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.5
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• pp.373-380
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• 1998

The prediction of bone strength by ultrasound velocity and broadband ultrasound attenuation was examined. Ultrasound velocity and broadband attenuation were measured for sixty specimens of human trabecular bone. Samples were divided into two equal groups and loaded in compression at the strain rates of $0.0004\;s^{-1}$ and of $0.08\;s^{-1}$. The ultimate strength was determined for each specimen. Specimens tested at $0.08\;s^{-1}$ had a mean value of strength 63% higher than the specimens tested at $0.0004\;s^{-1}$. Ultrasound velocity and broadband attenuation were significantly associated with compressive strength at both strain rates. Mechanical strength was also correlated strongly with a linear combination of ultrasound velocity and broadband attenuation for both the low and high loading rates. The use of ultrasound parameters may provide good clinical means for assessing the resistance of trabecular bone to both low and high energy trauma.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.2
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• pp.191-206
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• 2007

The general theoretical solutions for the wavespeed and damping derived in Part 1 of this work, are incorporated into the computer code. In this paper the code is used in a parametric study of the influence of excitation frequency and variations in material properties on propagation velocity and damping. Compressional wave velocity for waves of the first kind is shown to vary as a function of the frequency-permeability product, with a zone where wavespeed transitions from a lower bound value to a higher bound value with increasing values of the product. Damping is seen to be a maximum where the rate of change in wavespeed is greatest. Waves of the second kind also show a transition in wavespeed from near zero at low values of the frequency-permeability product to an upper bound value at higher values of the product.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.5B
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• pp.572-581
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• 2001

본 논문에서는 위성통신에서 강우감쇠에 따라 가변 부호화율을 적용시킬 수 있는 적응형 부호화 기법에 대한 연구를 하였다. 따라서, 3bit 연판정을 적용한 Viterbi 복호기를 이용하여 QPSK와 TC-8PSK 신호를 복호할 수 있는 pragmatic TCM과 LSB 부호화 알고리즘에 대해 여러 부호화율에서 성능분석을 하였다. 또한 구현을 위한 최적의 파라미터를 설정하여 부호화율 2/3를 가지는 pragmatic TCM을 VHDL 모델링 하였다. 구현결과 PLEX10KE100EQC208-1 CPLD 칩으로 구현 가능하였으며, 42.36 Mbps의 복호 속도를 가진다. 실제 ASIC 설계시 CPLD 속도보다 약 5∼6배의 고속화가 가능하므로, 200 MHz 트렌스 폰더를 갖는 Ka 대역 초고속 위성통신 시스템에서 강우 감쇠에 대처하기 위한 적응형 트렐리스 부호화방식에 적용할 수 있다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.426-432
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• 2017

An experimental and numerical study on shock attenuation in a solid by a subminiature flyer impact was conducted to determine the performance of a subminiature exploding foil initiator such as, flyer velocity and impulse loading. The obtained attenuation pattern shows the possibility to determine the critical flyer velocity for initiating the miniaturized pyrotechnic unit by figuring out shock intensity and duration according to flight characteristics.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.253-259
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• 1997

씨일의 마모에 따른 터빈펌프의 동적거동을 고찰하기 위해서 10단 터빈펌프를 대상으로 유한요소법에 의한 동특성 해석을 수행하였다. 베어링과 씨일의 동적계수를 회전속도의 하수로 계산하였으며, 이를 동적거동해석에 적용하였다. 해석결과 씨일들은 그 간극이 커질수록 강성 및 감쇠계수가 크게 떨어지고 누설량이 급격히 늘어남을 확인하였다. 따라서 1차 위험속도(1st Critical Speed) 이하에서 충분한 분리여유(Seperation Margine)를 가지고 정상운전되도록 설계된 터빈펌프라 할지라도 장기적 사용시 마모가 진전됨에 따라 계의 1차 위험속도가 변하여 운전속도에 접근할 수 있으며, 아울러 이 때 씨일의 감쇠가 크게 줄어들어 급격한 진동의 증가를 가져올 수 있음을 보였다.

• The Journal of Engineering Geology
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• v.6 no.2
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• pp.95-102
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• 1996

A study on the attenuation of ground vibration was carried out on the soil layer using seismic exploration method. A 12-channel engineering seismograph was used to acquire real digital amplitude data in field work. Frequency analysis of seismic data shows maximum spectrum amplitude around 40Hz. Relative amplitude decreases exponentially as the distance increases and the attenuation factors are n = 0.25 and a = 0.13-0.20. Internal attenuation indexes(a) are 0.13 and 0.20 in the wet soil zone and the vegatated soil zone, respectively. It means that ground vibration attenuates faster in vegatated soil zone than in wet soil zone. Average internal attenuation coefficient(h) was determined to be 0.094 from seismic velocity and frequency analysis.

• Journal of the Korean Society for Railway
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• v.16 no.4
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• pp.305-310
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• 2013

In general, it is difficult to measure dynamic responses of a bridge with stepwise increasing speed of a train during commercial service on a high speed railroad. However, before opening the 2nd stage of the Gyeongbu high speed railroad, there was an opportunity for field tests and measurements of the bridge with stepwise increasing speed(from 170km/ h to 315km/h). The measured responses were compared with the results of a developed bridge/train interaction analysis. Although good agreement was found throughout almost the entire range of speeds, relatively large differences were found in the vicinity of the critical speed at which resonance behavior of the bridge occurs. To investigate the cause of this, reanalyses are performed with re-estimated damping ratios from field tests.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.1
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• pp.20-25
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• 2013

Ultrasonic methods are widely used to degradation assessment. Remaining-life cycle of metal can be estimated by ultrasonic parameters because ultrasonic velocity and attenuation are affected by change of material properties with accumulated fatigue in the metal. Therefore, in this study, we will estimate overall change of material properties by 2D C-scan image. Fatigued aluminum alloy 6061-T6 samples from 0 to 85% were prepared for evaluating fatigue life cycle. Also, degraded image of materials using attenuation is proposed to estimate degree of material degradation for determining degraded area of fatigued samples. Finally, we will predicts process pf degradation with measured attenuation of fatigued aluminum alloy 6061-T6 samples.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.359-362
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• 2009

Damping characteristics of pressure oscillation induced by an orifice in fluid feeding line for are investigated numerically and experimentally. Assuming small pressure oscillation, acoustic damping effect of orifice is confirmed experimentally, and with the mean flow, damping characteristics of an orifice are investigated numerically. When an orifice is installed at the node of pressure oscillation corresponding to the anti-node of velocity oscillation, suppression of pressure oscillation is maximized and with the mean flow, the resonant frequency is decreased. And, it is found that the optimal position of an orifice for damping shouled be changed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.1
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• pp.109-119
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• 2004

A design procedure for velocity-dependent supplemental dampers, such as viscous or viscoelastic dampers, required to meet the desired performance objectives was developed using displacement spectra. The amount of supplemental damping required to satisfy given performance limit state was obtained first from the nonlinear static procedure using displacement spectra, then dampers were appropriately distributed throughout the stories to realize the required damping. The proposed method was applied to multi-story steel frames, and the structures were analyzed by time history analysis to validate the accuracy of the design procedure. According to the analysis results the maximum displacements of the model structures retrofitted by the supplemental dampers turned out to be restrained well within the given target values.