• Explosives and Blasting
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• v.29 no.2
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• pp.51-58
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• 2011

Frequency is a very important factor in discussing the effect on facilities such as precision instruments and therefore, in evaluating the effect of blasting vibration, it is necessary to identity information on frequency in addition to maximum amplitude of vibration. This study collected rock samples in gneiss area to perform an indoor rock test and to identify frequency of blasting vibration according to priming location, performed of single hole test blasting. Then the study decided dominant frequency through FFT and analysed changes according to priming locations. Consequently frequency range according to priming location is indicated top priming is distributed high range, bottom priming is distributed high range, middle priming is distributed evenly range. Frequency trend according to priming location is indicated distance increase with frequency discrease in top priming, distance increase with frequency increase in bottom priming.

• Journal of Convergence for Information Technology
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• v.12 no.3
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• pp.151-157
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• 2022

The purpose of this study was to investigate the frequency characteristics of forced vibration considering the vehicle progress. And the vibration characteristics in frequency domain that occur, when vehicle passes the bump, were analyzed. The responses such as displacement, velocity and acceleration were obtained through numerical analysis, and FFT processing was performed to analyze the frequency response function(FRF) characteristics. In particular, the location of vehicle eigenmodes and external excitation modes was clearly shown and analyzed. In the forced vibration model by external force, the behavior of the eigenmode in power spectrum and real and imaginary parts were also analyzed. The mode characteristics were also analyzed in each FRF. It was approximated by assuming total excitation force by considering the exciting frequency using impulse and sine wave forces, which can give the amplitude and frequencies. The response characteristics of forced oscillations having different mass, damping and stiffness have been systematically discussed.

• Korean Journal of Optics and Photonics
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• v.13 no.1
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• pp.58-64
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• 2002

Using Mach-Zehnder type intensity modulator, we stabilized a 10 GHz harmonically mode-locked dispersion-compensated fiber ring laser using a feedback controlling system, and we measured its stability. The laser was stabilized for more than 16 hours by controlling the cavity length to suppress the relaxation oscillation frequency component which had caused the laser output instability. The ms timing jitter and ms amplitude noise were measured to be 260-524 fsec and 4~11.5%, respectively, and BER test measurement showed a value of 10$^{-13}$ .

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.7
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• pp.344-353
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• 2015

In the present study the characteristics of turbulent oscillatory flows in a square-sectional $180^{\circ}$curved duct were investigated experimentally. A series of experiments for air flow were conducted to measure axial velocity profiles, secondary flow velocity profiles and pressure distributions. The measurements were made by a Laser Doppler Velocimeter (LDV) system with a data acquisition and processing system which includes Rotating Machinery Resolve (RMR) and PHASE software. The results from the experiment are summarized as follows. (1) The maximum velocity moved toward the outer wall from the region of a bend angle of $30^{\circ}$. The velocity distribution had a positive value extended over the total phase in the region of a bend angle of $150^{\circ}$. (2) Secondary flows were generally proportional to the velocity of the main flow. The intensity of the secondary flow was about 25% as much as that in the axial direction. (3) Pressure distributions were effects of the oscillatory Dean number and respective region.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.12
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• pp.9-16
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• 1997

In this paper, a newly radial electronic shearography system was developed in order to study vibration characteristics of symmetrical objects. We utilized the electro-optic holography theory for quantificational analysis and a porror prism for shearing two inages radially in this study. These image data obtained by this shearography give us various distributions of the gradient of vibration amplitude, and they are useful informations to study vibrational characteristics of symmetrical objects. Finally this developed system with phase stepping and modulation was applied to fans and disks to inspect characteristics of the vibration and the blance of symmetrical objects and obtained good results.

• Progress in Medical Physics
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• v.18 no.2
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• pp.73-80
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• 2007

Fruitful findings have been produced from five out of sixty cells which were obtained from each 63 individual Aplisia caught at the Jeju coast. Spiking patterns of three out of five cells, such as relaxation oscillator, bursting within a short time of the inter-burst interval, chaotic bursting, period doubling sequences, bursting with long trains of action potentials separated by short silent periods, regular repeated beating or elliptic bursting, and silent states had been changed in order as the temperature was lowered to $10^{\circ}C\;from\;32^{\circ}C$. In the intervals of every about 40 minutes repeated ups and downs of temperature produced similar firing patterns at the allowable temperature ranges. The other two cells showed difference from these. The amplitudes of the action potentials of the two cells will not be highly decreased in 24 hours. Average spike frequencies, the inter-burst interval, peak to peak spike amplitude of action potentials, minimum potential values are compared and analyzed by using the computer programme. The spike frequencies according to temperature show the distribution of bell type, with maximal spike frequencies at intermediate temperatures and minimal ones at either end. The most common pattern consist of high spike frequency during failing and low one during rising temperatures.

• Journal of the Korean Society for Marine Environment & Energy
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• v.10 no.3
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• pp.173-180
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• 2007

Oscillating wave amplitude in a bottom-mounted OWC chamber designed for wave energy converter is investigated by applying characteristic wave conditions in Korean coastal water. The effects of shape parameters of OWC chamber in a view of wave energy absorbing capability are analyzed. Both experimental and numerical approaches are adopted and their results are compared to optimize the shape parameters which can result in a maximum power production under given wave distribution. The experiment was carried out in a wave flume under 2-D assumption of OWC chamber. The numerical scheme employed a hybrid Green integral equation which adopts the Rankine Green function inside chamber to take account of fluctuating air pressure, while it uses the Kelvin Green function in outer domain. Air duct diameter, chamber width, and submerged depths of front skirt and back wall of chamber changes the magnitude and peak frequency of wave absorption significantly.

• Journal of the Society of Disaster Information
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• v.18 no.3
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• pp.550-559
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• 2022

Purpose: Pipes are widely used as applied devices in many industrial fields such as machinery, electronics, electricity, and plants, and are also widely used in safety-related fields such as firefighting and chemistry. With the diversification of products, the importance of technology in the piping field is also increasing. In particular, when changing the existing copper pipe to stainless steel, it is necessary to evaluate safety and flow characteristics through structural analysis or flow analysis. Method: This study investigated the safety by flow analysis of the 6.35 inch socket model, which are integrated insert type connectors developed by a company, using CFD analysis technique. For CDF analysis, RAN model and LES model are used. Result: As results of the analysis, amplitude of the pressure fluctuation acting on the wall of the piping system is formed at a level of 3,780 Pa or less, which is a very small level of pressure compared with the operating pressure or design stress of the refrigerant piping. Conclusion: These results mean that the effect of vibration caused by turbulence on the structural safety of the pipe is negligible.

• Proceedings of the KSRS Conference
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• 2007.03a
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• pp.177-182
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• 2007

한반도 주변해역에서의 해수면 고도는 1993년부터 2005년까지의 기간 동안 연평균 3.89 mm $yr^{-1}$ 상승하였으며， 이는 전세계 해수면 상승률의 1.3배에 해당한다. 본 연구에서는 AVISO (Archiving, Validation and Interpretation of Satellite Oceanographic data)에서 제공하는 복합위성자료 (Topex/Poseidon, Jason-1, ERS, Envisat)인 DT-MSLA (Delayed Time - Maps of Sea Level Anomalies)를 이용하여 동해와 황해, 남해, 한국해협에서의 해수면 고도 변화를 연구하였다. 해수면 고도의 평균적인 변화는 증가하는 경향을 보임과 동시에, 여름에는 $4{\sim}5$년，겨울에는 3년의 주기성을 가지고 진동하였다. 조화분석을 통하여 해수면 고도와 해수면 온도의 연주기 모드와 반년주기 모드의 진폭과 위상을 나타내었다. 해수면 고도의 연주기 진폭은 한반도 주변해역에서 남동쪽이 높게，북서쪽이 낮게 나타나는 반면, 해수면 온도는 이와는 반대의 분포를 보였다. 월별 해수면 고도와 해수면 온도의 상관을 구한 결과，$6{\sim}8$월에 동해와 남해에서 1 / 2달 시간지연 일 때，상관계수가 0.7정도로 높게 나타났다. 이러한 결과를 통해 여름철 동해와 남해가 쿠로시오 해류의 영향을 크게 받고 있음을 짐작할 수 있다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.3
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• pp.127-136
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• 1985

A simplified single degree of freedom analog with mass-spring-dashpot is proposed in this study. The simplified analog can describe the dynamic behavior of a rigid circular footings whose contact pressures are parabolic. The analog proposed in this study shows remarkable agreement when compared with the elastic half-space theory the analog is also compared with vertical vibration test results of model concrete footings. For the vibration experiments, 11 circular footings with different mass ratio are constructed. The elastic half-space is represented by compacted sand layer. A constant force excitation vibrator is used for the dynamic loading. The frequency range for vibration tests is 30 to 100 Hz. From the dynamic experiments, it is found that the measured resonant frequencies agree very well with the analog results, however, the ratio of theoretical and measured resonant amplitudes vary between 0.5 and 1.7. It is also found that, when the dynamic force is increased, the resonant frequency is decreased slightly and the resonant amplitude is increased slightly.