• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.21 no.10
• /
• pp.1350-1362
• /
• 1997

An experimental study has been performed on vortex pairing under fundamental and subharmonic forcing with controlled initial phase differences through hot-wire measurements and a multi-smoke wire flow visualization. For the range of St$_{D}$ < 0.6, vortex pairing was controlled by means of fundamental and subharmonic forcing with varying initial phase differences. Much larger mixing rate was achieved by two-frequency forcing with a proper phase difference than one frequency forcing. As St$_{D}$ decreased, vortex pairing was limited to a narrow region of the initial phase difference between two disturbances and higher amplitudes of the fundamental and its subharmonic at the nozzle exit were required for more stable pairing. As the amplitude of the subharmonic at the nozzle exit increased for fixed St$_{D}$ and fundamental amplitude, the distribution of the subharmonic mode against the variation of the initial phase difference changed from a sine function form into a cusp-like form. Thus, vortex pairing can be controlled more precisely for the former case. For St$_{D}$ > 0.6, non-pairing advection of vortices due to the improper phase difference was sometimes observed in several fundamental forcing amplitudes when only the fundamental was applied. However, when its subharmonic was added, vortex pairing readily occurred. As the initial amplitude of this subharmonic increased, the position of vortex pairing moved upstream. This was thought to be due to the fact that the variation of the initial phase difference between the fundamental and its subharmonic has less effects on vortex pairing in the region of fundamental-only vortex pairing.pairing.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.22 no.8
• /
• pp.1076-1082
• /
• 2018

This paper describes interferometer direction finder which measures the angle of arrival based on calculation of the phase difference of received radio signal from different antennas. Modern Electronic Warfare direction finder uses digital phase difference measuring techniques which have less effect on temperature variation and better performance under low Signal to Noise Ratio environment. In this paper, we analyze acceptable phase difference error for requirement of system's direction finding accuracy and introduce digital phase difference calculation techniques. We have investigated quantitative analysis on phase difference calculation according to sample number, SNR, interference injection. Through the simulation, frequency domain measurement technique is better performance than the time domain one at the environment of low SNR and interference injection. Proposed method can be used to determine the performance of interferometer direction finder.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2011.04a
• /
• pp.230-231
• /
• 2011

There is a merit a planetary gear set disperses a delivery load, and to decrease loss of friction and noise. But, in addition to meshing this internal and external gear simultaneously and phase difference by the tooth contact point and the time difference occurs asymmetric and symmetric sideband noise and vibration caused by the modulation in the vehicle. Existing planetary gear set research have progressed to reduce the cause of the sideband as run-out, pitch error and imbalance. In this paper presents a method for the design of the carrier phase difference by developing various theorys and experiments for gear noise.

• Journal of Power Electronics
• /
• v.16 no.1
• /
• pp.18-26
• /
• 2016

This paper proposes a compensation algorithm for reducing a specific ripple component on synchronous reference frame phase locked loop (SRF-PLL) in grid-tied single-phase inverters. In general, SRF-PLL, which is based on all-pass filter to generate virtual voltage, is widely used to estimate the grid phase angle in a single-phase system. In reality, the estimated grid phase angle might be distorted because the phase difference between actual and virtual voltages is not 90 degrees. That is, the phase error is caused by the difference between cut-off frequency of all-pass filter and grid frequency under grid frequency variation. Therefore, the effects on phase angle and output current attributed to the phase error are mathematically analyzed in this paper. In addition, the proportional resonant (PR) controller is adapted to reduce the effects of phase error. The validity of the proposed algorithm is verified through several simulations and experiments.

• The Journal of Korean Physical Therapy
• /
• v.25 no.5
• /
• pp.297-302
• /
• 2013

Purpose: This study was conducted in order to investigate the kinematic gait parameter of lower extremities with different gait conditions (level walking, stair, ramp) in hemiplegic patients. Methods: Ten hemiplegic patients participated in this study and kinematic data were measured using a 3D motion analysis system (LUKOtronic AS202, Lutz-kovacs-Electronics, Innsbruk, Austria). Statistical analysis was performed using one-way repeated measure of ANOVA in order to determine the difference of lower extremity angle at each gait phase with different gait conditions. Results: Affected degree of ankle joint in the heel strike phase showed significant difference between level walking and climbing stairs, and toe off phase showed significant difference between level walking and climbing stairs, ramps, and climbing stairs. Affected degree of knee joint showed no significant difference in all attempts. Affected degree of hip joint in the toe off phase showed significant difference between level walking, ramps and stairs, and climbing ramps. Swing phase showed significant difference between sides for level walking and stairs, climbing ramps. Affected ankle joint of heel strike and toe off, and affected hip joint of toe off and the maximum angle of swing phase in the angle was increased. Unaffected side of the ankle joint, knee joint, and hip joint showed a significant increase in walking phase. Conclusion: These findings indicate that compared with level walking, different results were obtained for joint angle of lower extremity when climbing stairs and ramps. In hemiplegia patient's climbing ramps, stairs, more movement was observed not only for the non-affected side but also the ankle joint of the affected side and hip joint. According to these findings of hemiplegic patients when climbing stairs or ramps, more joint motion was observed not only on the unaffected side but also on the affected side compared with flat walking.

• 한국전산유체공학회:학술대회논문집
• /
• 2003.10a
• /
• pp.181-182
• /
• 2003

A preconditioned numerical method for gas-liquid to-phase flow is applied to solve cavitating flow. The present method employs a density based finite-difference method of dual time-stepping integration procedure and Roe's flux difference splitting approximation with MUSCL-TVD scheme. A homogeneous equilibrium cavitation model is used. The method permits simple treatment of the whole gas-liquid two-phase flow field including wave propagation, large density changes and incompressible flow characteristics at low Mach number. By this method, two-dimensional internal flows through a venturi tuve and decelerating cascades are computed and discussed.

• Proceedings of the KSR Conference
• /
• 2011.10a
• /
• pp.1997-2004
• /
• 2011

The $2{\times}25kv$ AT electric power feeding method in the A.C. electric train adopts the one-phase power feeding method as the standard due to a voltage phase difference, and the distance between the two neighboring substations is 50km due to voltage drop. The one-phase power feeding method makes the system operation feasible, while making it unfavorable for power supply. Moreover, railroad involves large-capacity single-phase load, and if it is expected to continue to rise, it is necessary to research on measures to stabilize the supply of power to railroad cars with the existing facilities. In this study, a parallel power feeding method between neighboring substations is proposed to stabilize the supply of electric power to electric railroad cars under the 2*25kv AT power feeding method and the loop current induced by voltage phase difference between the two neighboring substations during parallel power feeding is investigated.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.11
• /
• pp.1610-1624
• /
• 1998

An axisymmetric jet is forced with two helical fundamental waves of identical frequency spinning in opposite directions and an additional axisymmetric sub harmonic wave. The subharmonic component rapidly grows downstream from subharmonic resonance with the fundamental, significantly depending on the initial phase difference. The variations of the subharmonic amplitude with the initial phase difference show cusp-like shapes. The amplification of the sub harmonic results in 'vortex pairing of helical modes'. Furthermore, azimuthal variation of the amplification induces an asymmetric jet cross-section. When the initial subharmonics is imposed with an initial phase difference close to a critical value, the jet-cross section evolves into a three-lobed shape. One lobe is generated by the enhanced vortex pairing and the other two lobes are generated by the delayed vortex pairing. Thus, it is confirmed that the initial phase difference between the fundamental and the subharmonic plays an important role in controlling the jet cross-section.

• Korean Journal of Applied Biomechanics
• /
• v.15 no.4
• /
• pp.67-74
• /
• 2005

The purpose of this study is to compare and analyze the muscle activations between the professional golfers without low back pain symptom and the professional golfers with low back pain symptom, and so identify the stress related to golf swings, and provide the basic data to minimize the low back pain and the injury risk. Using surface electrode electromyography, we evaluated muscle activity in 6 male professional golfers during the golf drive swing. Surface electrodes were used to record the level of muscle activity in the Abdominal Oblique, Elector Spinae, Rectus Abdominis, Gluteus Maximus muscles during the golfer's swing. These signals were compared with %RVC(Reference voluntary contraction) which was normalized by IEMG(Integrated EMG). The golf swing was divided into five phases: take away, forward swing, acceleration, early follow through, late follow through. we observed patterns of trunk muscle activity throughout five phases of the golf swing. The results can be summarized as follows: RES(Right Elector Spinae) had statistically significant difference in take away phase, LGM(Left Gluteus Maximus), LRA(Left Rectus Abdominis), LOA(Left Oblique Abdominal) had statistically significant difference in forward swing phase, RES(Right Elector Spinae), RGM(Right Gluteus Maximus), ROA(Right Oblique Abdominal) had statistically significant difference in acceleration phase, RES(Right Elector Spinae), RGM(Right Gluteus Maximus) had statistically significant difference in early follow-through phase, LES(Left Elector Spinae), RGM(Right Gluteus Maximus) had statistically significant difference in late follow through phase.

• Journal of the Korean Institute of Telematics and Electronics S
• /
• v.35S no.5
• /
• pp.11-16
• /
• 1998

DS/CDMA systems for the high speed communication require high code rats. In discrete time CDMA receivers, the performance degradation, caused by the phase difference between transmission code and reference code, increase the sampling frquency of the receiver. This increment of the sampling frequency makes hard to implement high speed CDMA systems. This paper analyzes the SIR(signal to interference Ratio) performance of the discrete time DS/CDMA system, based on the code phase difference. The results of this paper may be useful to study a low-sampling CDMA receiver.