• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.3
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• pp.285-290
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• 2008

Pyrotechnic shock or pyroshock is characterized as a transient vibration phenomena which shows large acceleration and high frequency range up to 10kHz during the operation of separation devices where explosives are used. During the flight of a launch vehicle, pyro-shock is mainly generated at several events such as satellite separation, fairing separation and stage separation. In this paper, characteristics of pyroshock are introduced briefly, and PEEK washer shock absorber is applied for the reduction of pyroshock in the high frequency range. With some electronic devices, reduction characteristic of pyroshock using washer type shock absorber are studied. Random vibration tests are also performed for the verification of vibrational characteristics.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.4
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• pp.69-79
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• 2017

The purpose of this study is to reconsider the rating method for the floor impact sound insulation performance in current criterion. Although there are some arguments about proper standard heavy impact source with reproducibility of actual impact source in residence building, bang machine is adopted as the only standard heavy impact source in domestic criterion. To inspect the rating methods of evaluation criteria, this study conducted vibration test for both of standard heavy impact sources and actual impact sources. Using the test results, the floor impact sound insulation performance levels were assessed by each of several criteria. In addition, low frequency noise beyond current criteria was evaluated. Consequently, the floor impact sound levels have different performance levels according to adopted criteria, and measured floor impact sounds are bound to annoy the neighbors in the low frequency range. Current criteria does not consider the spectrum characteristics of floor impact sound according to impact sources and low frequency noise. This may cause the difference between the floor impact sound insulation performance level and human perception. Thus current criterion needs to be complemented to reflect the spectrum characteristics of floor impact sound levels according to impact sources and sound pressure levels in low frequency range.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.1227-1228
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• 2015

본 연구에서는 기계적 충격 방식을 통한 주파수 상향방식을 이용하여 저주파 진동원으로부터 충분한 에너지를 수확할 수 있는 압전 구동 방식의 광대역 에너지 수확 소자를 제작하고 평가하였다. 유연한 외팔보의 진동으로 인한 기계적 충격은 압전 외팔보에 큰 두 번째 힘을 전달한다. 변형률이 커지고 주파수 상향방식을 사용한 결과로 출력 전력과 동작 주파수의 대역폭 또한 향상되었다. 제작된 에너지 수확소자의 질량체 비율은 ${\mu}=5.8$, 스토퍼의 거리는 d = 0.5 mm이며, 17 Hz의 주파수, $30k{\Omega}$의 최적 부하저항에서 $449{\mu}W$의 최대 피크 전력을 전달하였다. 또한 1 g로 가진하였을 때 11 Hz부터 28 Hz의 주파수 대역에서 동작이 가능하였고, 저주파수의 무작위 진동에서도 효율적으로 에너지 수확이 가능하다는 것을 입증하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.10a
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• pp.487-488
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• 2010

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.15-23
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• 1996

강연의 내용은 주로 유동에 의하여 발생되는 소음으로 제한하지만 초음속 항공기에 형성된 충격파 소음인 Sonic Boom도 함께 간단히 소개하고자 한다.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.8 s.101
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• pp.962-967
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• 2005

The twin-impulse wave discharged from two parallel tubes is investigated to see flow patterns, compared with the single impulse wave. In the present study, the merging phenomena and propagation characteristics of the impulse waves are investigated by experiment and numerical computation. The Harten-Yee's total variation diminishing scheme is used to solve the unsteady, two-dimensional, compressible, Euler equations. The Mach number Ms of incident shock wave is lower than 1.5 and the distance between the tubes is between 1.2 and 4.0. In the shock tube experiment, the twin impulse waves are visualized by a Schlieren optical system in order to validate the computational result. It is shown that on the symmetric axis between two parallel tubes, the peak pressure produced by the twin impulse waves and its location strongly depend upon the tube distance and the incident shock Mach number, Ms. The predicted Schlieren images show a good agreement with the measured twin-impulse wave.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.1
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• pp.48-56
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• 2002

A computational work of the impulse wave which is discharged from the open end of a pipe is compared to the Lighthill\`s aeroacoustics theory. The second-order total variation diminishing(TVD) scheme is employed to solve the axisymmetric, compressible, unsteady Euler equations. The relationship between the initial compressure wave form and the resulting impulse wave is characterized in terms of the peak pressure. The overpressure, pressure gradient and wavelength of the initial compression wave are changed to investigate the influence of the initial compressure wave form on the peak pressure of impulse wave. The results obtained show that for the initial compression wave of a large wavelength and small pressure gradient the peak pressure of the impulse wave depends upon the wavelength and pressure gradient of compression wave, but for the initial compression wave of a short wavelength and large pressure gradient the peak pressure of the impulse wave is almost constant regardless of the wavelength and pressure gradient of compression wave. The peak pressure of the impulse wave is increased with an increase in the overpressure of the initial compression wave. The results from the numerical ana1ysis are well compared to the results from the aeroacoutics theory with a food agreement.

• Journal of Biomedical Engineering Research
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• v.24 no.5
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• pp.453-458
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• 2003

When the piezoelectric extracorporeal shock wave lithotripter is operated. sounds are generated. In this paper, we present a fact that the sounds are radiated undoubtedly from the object to be hit by the shock waves. For this results. we use the method to identify the sound source location of the radiated sounds by estimating the distance and the bearing from the sound source using one hydrophone. In addition. we investigate the relation between the radiated sounds and the vibrations of the objects using bronze models of disc type with clear vibrating characteristics and present the results of experiments to be analyzed.

• Journal of the Korean Geotechnical Society
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• v.16 no.6
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• pp.59-68
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• 2000

현재까지 진동이 양생중인 콘크리트에 미치는 영향을 알아보기 위해 수행된 대부분의 연구에서는 콘크리트 공시체나 콘크리트 블록에 대해 100Hz 미만의 주주파수를 가지는 충격진동이나 진동테이블을 이용한 진동을 가한 후 콘크리트의 강도 변화를 평가하는 방법이 사용되었다. 이 연구에서는 발파진동이 양생중인 라이닝 콘크리트에 미치는 영향을 알아보기 우해 실험실 충격진동 시험과 터널 현장에서의 발파진동 시험을 수행하였다. 터널발파진동과 유사한 100~300Hz의 주주파수를 가지 충격진동을 각각 재령 3, 7, 12 시간에 다한 실험실 시험결과 2cm/sec의 진동속도는 모르타르 라이닝의 P파속도를 증가시키지만, 5 cm/sec, 10cm/sec의진동의 모르타르 라이닝의 P파 속도를 감소시킬 수 있는 것으로 나타났다. 양생기간동안 2.5 cm/sec 이하의 발파진동이 가해진 양생중인 라이닝 콘크리트는 진동을 가하지 않고 양생시킨 콘크리트 공시체에 비해 압축강도가 더 큰 값을 나타내었다. 재령 5시간에 콘크리트 라이닝애 대한 소규모 시험발파로 발파진동을 가한 콘크리트 시료와 진동을 가하지 않고 터널 내에서 양생시킨 공시체에 대해 압축강도를 비교한 결과 콘크리트의 강도 및 탄성파 속도를 저하시킬 수 있는 진동수준은 3~4cm/sec 인 것 으로 나타났다.로 나타났다.

• Tunnel and Underground Space
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• v.9 no.1
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• pp.36-47
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• 1999

For cautious controlled blasting, it is necessary to understand characteristics of the blasting vibration. In this study, a series of tests were carried out to investigate the several characteristics of blasting vibration waveform by vibration time history analysis. Separation between impulse vibration and free vibration from blasting vibration, duration time, effects of overlap of free vibration upon the level of vibration and changes of waveform according to increase of charge weight per delay etc. were studied with waveform analysis.