• The Journal of the Acoustical Society of Korea
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• v.27 no.4
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• pp.178-182
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• 2008

In measurements of the vibration of structures underwater with a laser Doppler vibrometer, the surface vibration is measured by means of detecting the phase change of the laser beam due to the structural vibration. The laser beam passes through the sound field radiated from the vibrating structures underwater. It experiences an additional phase change due to the change in refractive index in the radiated sound field. This phase change due to the sound field may cause the error in surface vibration measurements. In this paper, this phase change due to the radiated sound filed has been analyzed. The numerical simulation has been peformed to evaluate the phase change in sound field radiated from an infinite cylindrical structure vibrating underwater.

• Progress in Medical Physics
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• v.5 no.1
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• pp.25-39
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• 1994

To measure the velocity of heart wall and local flow transctaneously in blood vessels, we have developed a single channel 3.1 MHz pulsed ultrasonic Doppler velocity meter. Ultrasound pluse width and repetition frequency (PRF) used in the velocity meter is 1 ${\mu}$sec 6kHz reapectively, and the Doppler shift of the backscattered echo signal is sensed in a phase detector by coherent demodulation method. From the output of the phase detector, the Doppler signal corresponding to the mean velocity of acoustic wave scatterers over a small region is obtained by using a range gate, sample holder and band-pass filter. Mean frequency of Doppler signal is estimated by zero-crossing counter and the instantaneous velocity of scatters is displayed as a function of time. It is possible to estimate velocity profile, volume flow and flow acceleration of vessels in man if the number of channels and range resolution in increased.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.1039-1049
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• 1994

The intermitternt and transient fuel spray have been investigated from the simultaneous measurement of droplet sizes and velocities by using Phase/Doppler Particle Analyzer(PDPA). Measurement have been done on the spray axis and at the edge of the spray near nozzle at various gas-to-liquid density ratios(.rho./sub g//.rho./sub l/) that ranges from those found in free atmospheric jets to conditions typical of diesel engines. Probability density distributions of the droplet size and velocity were obtained from raw data and mathematical probability density functions which can fit the experimental distribations were extracted using the principle of maximum likelihood. In the near nozzle region on the spray axis, droplet sizes ranged from the lower limit of the measurement system to the order of nozzle diameter for all (.rho./sub g/ /.rho./sub l/) and droplet sizes tended to be small on the spray edge. At the edge of spray, average droplet velocity peaked during needle opening and needle closing. The rms intensity is greatly incresed as the radial distance from the nozzle is increased. The probability density function which can best fit the physical breakage process such as breakup of fuel drops is exponecially decreasing log-hypebolic function with 4 parameters.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.167-169
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• 2014

Spray combustion has been used in many industrial fields, for instance, such as diesel engines, gas turbines and industrial furnaces, and furthermore various measurement techniques have been applied to elucidate the phenomenon of spray combustion. In order to measure simultaneously the droplet velocity and the droplet size of spray, Phase Doppler Anemometry (PDA) was frequently used in spray combustion. However, the measurement error is occurred due to existence of flame, which is considered as influencing the precision of measurement. Therefore, the purpose of this study is experimentally to conduct the systematic evaluation on the measurement error when PDA measurement is applied to combustion field.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.287-290
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• 2002

'Backhole' is an extra empty volume where is located behind the tangential entries at the rear par of the vortex chamber in the swirl coaxial injector. With the backhole, there are three major hydraulic characteristics. First, mass flow rate is increased about $15{\%}$ compared with the case without the backhole. Second, with the backhole, the center region of the injected flow has more large volume than that of without the backhole. The last, some range of the cone angle can be controlled by the backhole Experiments are conducted by using a PDPA apparatus, a mechanical patternator, stroboscopic photography and etc. With the backhole, based on cold-flow tests, the model swirl injector has some Improvement in its performance.