• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.04a
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• pp.52-54
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• 2009

A plane wave expansion method(PWEM) was applied for photonic band structure calculation. We examined zero group velocity modes in photonic crystals. The zero group velocity was obtained in second band along G-K direction. We expanded Brillouin zone, and investigated on zero group velocity.

• The KSFM Journal of Fluid Machinery
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• v.2 no.2 s.3
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• pp.5-12
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• 1999

This study presents the measured unsteady flctuation of impeller discharge flow for a centrifugal compressor in an unstable operating region. The characteristics of the blade-to-blade flow at rotating stall onset were investigated by measuring unsteady velocity fluctuations at several different diffuser axial distances using a hot wire anemometer. The flow characteristics in terms of the radial and tangential velocity components and the flow angle distribution at the impeller exit were analyzed using phase-locked ensemble averaging techniques. As a result, increase or decrease of the radial velocity component during the rotating stall is dominated by that of the suction side. The radial velocity distributions show the opposite trends in the regions where the radial velocity during rotating stall onset increases and decreases.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.8
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• pp.1931-1939
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• 1993

The wave propagation characteristics of laminated composites subjected to a transverse high-velocity impact of a steel ball is investigated. For this purpose, high-velocity impact experiments were conducted to obtain the strain response histories, and a finite element analysis based on the higher-order shear deformation theory in conjunction with the static contact law is used. Test materials for investigation are glass/epoxy laminated composite materials with $[0^{\circ}/45^{\circ}/0^{\circ}/-45^{\circ}]_{2s}$ and $[90^{\circ}/-45^{\circ}/90^{\circ}-45^{\circ}/90^{\circ}]_{2s}$ stacking sequences. As a result, the strain responses obtained from the experiments represented the wave propagation characteristics in the transversely impact, also the wave propagation velocities obtained from high-velocity impact experiments and wave propagation theory agree well.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.2
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• pp.185-192
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• 2000

Cam mechanism is one of the common devices used in many automatic machinery. Since the motion of the cam mechanism depends on the shape of the cam and the type of the follower, the shape design procedure must be well defined in order to determine the accurate shape of the cam corresponding to the prescribed motion of the follower. This paper proposes a new approach for designing the shape of disk cams. The proposed relative velocity method uses the relative velocity at center of the follower roller or at contact point between the cam and the follower for 4 different types of the disk cam systems. Also, the relative velocity method for determining the cam profile uses the geometric relationships of the cam and the follower.

• 유체기계공업학회:학술대회논문집
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• 1998.12a
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• pp.129-134
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• 1998

This study presents the measured unsteady fluctuation of impeller discharge flow for a centrifugal compressor in unstable operating region. The characteristics of the blade-to-blade flow at rotating stall onset were investigated by measuring unsteady velocity fluctuations at several different diffuser axial distances using a hot wire anemometer. The flow characteristics in terms of the radial and tangential velocity components and the flow angle distribution at the impeller exit were analyzed using phase-locked ensemble averaging techniques. As a result, increase or decrease of the radial velocity component during the rotating stall is dominated by that on the suction side. The radial velocity distributions show the opposite trends in the regions where the radial velocity during rotating stall onset increases and decreases.

• 유체기계공업학회:학술대회논문집
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• 1998.12a
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• pp.11-18
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• 1998

The present experimental study is focused on the application of multi-point simultaneous measurement by PIV(Particle Image Velocimetry) to rotor-stator region within centrifugal turbine pump. Six different kinds of rpm(120, 500, 1000, 1500, 2000 and 2500) are selected as experimental condition. Optimized cross correlation identification to obtain velocity vectors is implemented by direct calculation of correlation coefficients. Fine optical setup deeply concerned with PIV performance is arranged for accurate PIV measurement of high-speed complex flow. The instantaneous and time-mean velocity distribution and velocity profile are represented quantitatively at the rotor and stator region.

• Journal of Environmental Science International
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• v.7 no.1
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• pp.41-45
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• 1998

The feasibility of foam separation to remove protein in aquacultural recirculating water was investigated. From the results of batch foam separation on protein removal, superficial air velocity and initial protein concentration in bulk solution were found to be important operational factors In determining removal rates of protein. The protein removal rate by batch foam separation was proportionally increased with the superficial air velocity. Performance characteristics of continous foam separator were highly dependent upon the operating parameters of superficial air velocity, hydraulic retention time(HRT) and foam height. Removal effeciency of protein increases with increasing superficial air velocity and HRT, and independent on foam height. As DO concentration was increased with superficial air velocity, foam separator is also used for oxygen addition. It could be confinned that foam separator might offer better perspective for protein removal in aquacuitural recirculating water.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.11
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• pp.2011-2014
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• 2008

We measured the permittivity and electromagnetic wave propagation velocity of used insulation oil with wide frequency range including ultra-high frequency by time domain reflectometry. The permittivity or propagation velocity is essential for locating discharge faults of oil filled power transformer. We derived 2.21 as a permittivity and $2.03{\times}10^8 m/s$ as a velocity from the measurement of pulse travelling time along a coaxial line filled with used insulation oil or air. The permittivity measurement system we designed shows high measurement accuracy and the convenience for field use.

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.5
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• pp.639-645
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• 2013

The aim of the study is to investigate the method to estimate a storage life of propelling charge on the decrease of muzzle velocity by stochastic gamma process model. It is required to establish criterion for state failure to estimate the storage life and it is defined in this paper as a muzzle velocity difference between reference value and maximum allowable standard deviation multiplied by 6. The relationship between storage time and muzzle velocity is investigated by nonlinear regression analysis. The stochastic gamma process model is used to estimated the state distribution and the life distribution for storage time for 155mm propelling charge KM4A2 because the regression analysis is a deterministic method and it can't describe the distribution of life for storage time.

• Journal of Advanced Marine Engineering and Technology
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• v.25 no.6
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• pp.1308-1316
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• 2001

This paper described a numerical investigation performed to understand better the effects of flow parameters in an entrained flow combustor on the flow characteristics. The computational model was based on the gas phase Eulerian equations of mass, momentum and energy. The code was formulated with RNG $k-\varepsilon$ model for turbulent flow. The calculation parameters were the ratio of primary and secondary jet velocity and the height difference between primary and secondary jet As the secondary jet velocity increased, the upper recirculation 3one of the primary jet was strengthened. It was found that as the primary jet velocity increased, there was a critical jet Velocity at which the size of upper and lower recirculation zone was reversed.