• Nuclear Engineering and Technology
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• 제53권1호
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• pp.79-92
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• 2021

Venturi tube is based on turbulent flow, whereby the microbubbles can be generated by the turbulent fragmentation. This phenomenon is common in several venturi bubblers used by the nuclear, aerospace and chemical industries. The first objective of this paper is to study the liquid-phase velocity field experimentally and develop correlations for the turbulent quantities. The second objective is to research velocity field characteristics theoretically. Stereoscopic PIV measurements for the velocity field have been analyzed and utilized to develop the turbulent kinetic energy in the venturi tube. The tracking properties of the tracer particles have been verified enough for us to analyze the turbulence field. The turbulence kinetic energy has a bimodal distribution trend. Also, the results of turbulence intensity along the horizontal direction is gradually uniform along the downstream. Both the mean velocity and the fluctuation velocity are proportional to the Reynolds number. Besides, the distribution trend of the mean velocity and the velocity fluctuation can be determined by the geometric parameters of the venturi tube. An analytical function model for the flow field has been developed to obtain the approximate analytical solutions. Good agreement is observed between the model predictions and experimental data.

• Water Engineering Research
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• 제1권4호
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• pp.293-298
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• 2000

Optimal values of $\alpha$ characterizing the linear dispersion property in the modified Boussinesq equations are determined by minimizing the combined relative errors of the phase and group velocities. The value of $\alpha$ is fixed in previous studies, whereas it is varying in the present study. The phase and group velocities are calculated by using variable $\alpha$ and compared to those of the linear Stokes wave theory and previous studies. It is found that the present study produces the best match to the linear Stokes theory.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2003년도 춘계전력전자학술대회 논문집(1)
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• pp.146-149
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• 2003

To control the position, velocity and torque of the ultrasonic motor, a great variety of method are proposed such as the amplitude, phase difference, frequency and so on. In the case of phase difference method, it has some advantages: it can control the direction and velocity of rotation only adjusting the phase difference and it has wide control-band. During the USM driving on adjusting phase difference, its characteristic was transformed by the change of resonance-frequency of stator, which means that the resonance frequency is different according to the phase difference. Consequently, we need to set up the most suitable driving frequency according to each phase difference.

• 비파괴검사학회지
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• 제28권2호
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• pp.112-118
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• 2008

본 논문에서는 유체에 포화된 다공성 매질에 적용되는 Biot 모델 및 modified Biot-Attenborough (MBA) 모델을 이용하여 해면질골에서 다공율 및 주파수에 대한 초음파 위상속도의 의존성을 예측하였다. 또한 선행 연구자들에 의하여 사람 및 소의 해면질골에서 측정된 값과 비교하였다. 해면질골에서 위상속도는 다공율 및 주파수가 증가함에 따라 감소하는 것을 알 수 있었다. 또한 전파각 효과를 포함하도록 수정된 Biot 모델 및 MBA 모델뿐만 아니라 Schoenberg 모델을 이용하여 해면질골에서 전파각에 대한 위상속도의 의존성을 예측하였다. 본 논문에서 이용된 이론적인 모델들은 초음파와 해면질골의 상호작용에 대한 물리학적인 이해를 증진시키는데 기여할 뿐만 아니라 골다공증을 진단하기 위하여 유용하게 이용될 수 있을 것으로 기대된다.

• 한국운동역학회지
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• 제12권1호
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• pp.221-231
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• 2002

The purpose of this study was to clarify the differences in service patterns of a forward and backward soft tennis players using 3D motion analyzer. Subjects were 4 forward players of $24.0\pm5.23$yrs and 4 backward players of $23.5\pm1.73$yrs. The results were as following: 1. There was no difference among each positions on swinging-time. The longest racket swinging-time was in the phase of takeback, the second one was in follow-through. The shortest one was in the phase of forward-swing so called force production phase, which had an influence on ball's velocity. 2. The racket speed on impact was 16.3m/s in forward subject and 19.53m/s in backward subject, when each velocity of balls was 44.6m/s, 52.9m/s. Although there was no significant difference along by positions, backward subject showed faster result. 3. The maximum speed of each performance was reached before the impact, and the speed at impact along by positions did not show any significant difference. The summation of velocity was measured in good order as following; hip, shoulder, elbow, wrist, top of racket. 4. In the angular velocity of all examine except one, the angular velocity of forearm was bigger than the one of racket top although there was no statistically significant difference between forward and backward subject. 5. The service grip of the forward players was shorter than that of backward players.

• 한국운동역학회지
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• 제13권3호
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• pp.1-14
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• 2003

This study was conducted to investigate the principles and motions for increasing the jumping height of Fosbury Flop. The subjects were three male jumpers who were former Korean national team players. Their jumping motions were analyzed using the DLT method of three-dimensional cinematography. The conclusions were as follows. 1. The horizontal velocity of approach run and decreasing of this velocity during the take off phase were increased as the jumping height was increased. Therefore, in order to increase the jumping height, the horizontal velocity of approachrun should be increased and decreased properly during the take-off phase. The average height of the analyzed Dials was 2.15m. The average horizontal velocity of approachrun was 7.49m/s and decreased to 4.16m/s at the instance of take-off. 2. The vertical velocity of the center of gravity was increased as the ascending height of the center of gravity during the take-off phase was increased. Therefore, the center of gravity at the instant of touch down should be lowered. This could be possible by increasing the length of the last stride and the backward lean angle of the body. The average length of the last stride was 111.1% of the standing height, the average height of the center of gravity was 46.6% of the standing height and the average backward lean angle of the body was 40.3 degrees.

• Korean Chemical Engineering Research
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• 제49권6호
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• pp.790-797
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• 2011

삼상유동층에서 수력학적 유사성을 규모인자(scaling factor)를 이용하여 해석하였다. 규모인자는 직경이 다른 두 종류의 삼상유동층간의 기체, 액체, 그리고 고체입자의 체류량과 단위면적당 유효부피흐름속도를 기준으로 정의하였다. 두 종류 삼상유동층의 직경은 각각 0.102 m와 0.152 m이었다. 여과된 압축공기, 물 그리고 밀도가 2,500 kg/$m^3$인 유리구슬을 각각 기체, 액체 그리고 유동고체입자로 사용하였다. 각 삼상유동층에서 각 상들의 체류량은 정압강하법에의해 결정하였다. 기체 및 액체의 유속 그리고 고체유동입자의 크기가 각 상들을 기준으로한 규모인자와 유효부피흐름속도를 기준으로한 규모인자에 미치는 영향을 검토하였다. 직경이 다른 두 삼상유동층에서 기체 체류량의 편차는 기체와 액체의 유속이 증가함에 따라 감소하였으나 유동입자의 크기가 증가함에 따라 증가하였다. 직경이 다른 두 종류 삼상유동층에서 액체 체류량 편차는 기체와 액체 그리고 고체유동입자의 크기가 증가함에 따라 감소하였다. 두 종류 삼상유동층에서 고체입자 체류량 편차는 기체유속과 유동입자의 크기가 증가함에 따라 증가하였으나 액체의 유속이 증가함에 따라 감소하였다. 직경이 다른 두 종류 삼상유동층에서 유효부피흐름속도를 매개로 한 규모인자는 기체유속과 유동입자의 크기가 증가함에 따라 감소하였으나 액체의 유속이 증가함에 따라 증가하였다. 본 연구에서 정의된 규모인자는 삼상유동층 공정의 수력학적 유사성을 해석하는데 효과적으로 사용될 수 있었다.

• 대한물리의학회지
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• 제15권3호
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• pp.117-125
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• 2020

PURPOSE: Aging causes changes in the postural alignment and gait due to changes in the nervous and musculoskeletal systems. On the other hand, the relationship between the changes in posture alignment and gait is unclear. This study examined the relationship between the postural alignment and spatiotemporal gait parameters in Korean elderly women. METHODS: Thirty-two-healthy elderly women participated in this study. All subjects were assessed for their posture alignment and gait ability. Stepwise multiple linear regression was performed to determine to what extent the postural alignments could explain the spatiotemporal gait parameters. RESULTS: Coronal head angle was moderately correlated with the velocity (r = -.51), normalized velocity (r = -.46) and gait-stability ratio (r = .58) (p < .05). The trunk angle was moderately correlated with the normalized velocity (r = -.32) and gait-stability ratio (r = .32) and weakly correlated with the velocity (r = -.28) (p < .05). The coronal shoulder angle was moderately correlated with the swing phase (r = -.57), stance phase (r = .56), single limb stance (r = -.56) and double limb stance (r = .51) (p < .05). The coronal head angle and trunk angle accounted for 36% of the variance in velocity, 33% variance in normalized velocity and 46% variance in the gait-stability ratio (p < .05). The coronal shoulder angle accounted for 32% variance in the swing phase, 32% variance in the stance phase, 31% variance in the single limb stance and 26% variance in the double limb stance (p < .05). CONCLUSION: Changes in posture alignment in elderly women may serve as a biomarker to predict a decrease in walking ability due to physical aging.

• 대한조선학회논문집
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• 제53권5호
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• pp.371-379
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• 2016

In the ship design process, ship motion and propulsion performance in sea waves became very important issues. Especially, prediction of ship propulsion performance during real operation is an important challenge to ship owners for economic operation in terms of fuel consumption and route-time evaluation. Therefore, it should be considered in the early design stages of the ship. It is thought that the averaged value and fluctuation of effective inflow velocity to the propeller have a great effect on the propulsion performance in waves. However, even for the nominal velocity distribution, very few results have been presented due to some technical difficulties in experiments. In this study, flow measurements near the propeller plane using a stereo PIV system were performed. Phase-averaged flow fields on the propeller plane of a KVLCC2 model ship in waves were measured in the towing tank by using the stereo PIV system and a phase synchronizer with heave motion. The experiment was carried out at fully loaded condition with making surge, heave and pitch motions free at a forward speed corresponding to Fr=0.142 (Re=2.55×106) in various head waves and calm water condition. The phase averaged nominal velocity fields obtained from the measurements are discussed with respect to effects of wave orbital velocity and ship motion. The low velocity region is affected by pressure gradient and ship motion.

• 설비공학논문집
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• 제5권4호
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• pp.235-242
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• 1993

The flow characteristics of developing turbulent pulsating flows are investigated experimentally in the entrance region of a square duct ($40mm{\times}40mm$ and 4,000mm). Mean velocity profiles, turbulence intensity and entrance length are measured by using a hot-wire anemometer system together with data acquisition and processing systems. It is found that the velocity waveforms are not changed in the fully developed flow region where that $x/Dh{\geq}40$. For turbulent pulsating flow, the turbulent components in the velocity waveforms increase as the dimensionless transverse position approaches the wall. Mean velocity profiles of the turbulent steady flows follow the one-seventh power law profile in the fully developed flow region. Turbulence intensity increases as the dimensionless transverse position increases from the center to the wall of the duct, and is slightly smaller in the accelerating phase than in the decelerating phase for the turbulent pulsating flows. The entrance length of the turbulent pulsating flow is about 40 times as large as the hydraulic diameter under the present experimental conditions.