• Journal of the Korean Society for Precision Engineering
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• v.25 no.6
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• pp.99-107
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• 2008

In this paper, the stability of a cracked cantilever Timoshenko beam with a tip mass subjected to follower force is investigated. In addition, an analysis of the flutter instability(flutter critical follower force) and a critical natural frequency of a cracked cantilever Euler / Timoshenko beam with a tip mass subjected to a follower force is presented. The vibration analysis on such cracked beam is conducted to identify the critical follower force for flutter instability based on the variation of the first two resonant frequencies of the beam. Therefore, the effect of the crack's intensity, location and a tip mass on the flutter follower force is studied. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.6
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• pp.665-671
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• 2004

A mathematical model is presented to predict the frost properties and heat and mass transfer within the frost layer formed on a cold plate. The model consists of the laminar flow equations for air-side and the empirical correlation of local frost density. The correlation of local frost density used in this study is obtained from various experimental conditions by considering frosting parameters. The numerical results are compared with experimental data to validate the model, and agree well with experimental data within a maximum error of 9%.

• Journal of Mechanical Science and Technology
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• v.14 no.9
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• pp.997-1004
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• 2000

The experiments were conducted by using water and paraffin slurry to investigate the effect of a chip spacing in the multichip module on the cooling characteristics from an in-line $4{\times}3$ array of discrete heat sources which were flush mounted on the top wall of a channel. The experimental parameters were chip spacing in a multichip module, heat flux of simulated VLSI chip, mass fraction of paraffin slurry, and channel Reynolds number. The removable heat flux at the same chip surface temperature decreased as the chip spacing decreased at the first and fourth rows. The local heat transfer coefficients for the paraffin slurry were larger than those for water, and the chip spacing on the local heat transfer coefficients for paraffin slurry influenced less than that for water. The enhancement factor for paraffin slurry showed the largest value at a mass fraction of 5% regardless of the chip spacing, and the enhancement factors increased as the chip spacing decreased. This means that the paraffin slurry is more effective than water for cooling of the highly integrated multichip module.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.210-220
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• 2005

We have analyzed the stability for cut-slopes at main street 3-2 line section in Pa-ju local industrial complex. After studying an additional boring test, laboratory test and face mapping etc., we have determined the extent of reinforcement, slope inclinations and soil strength parameter from the analysis of test results. After changing the inclination of slopes for ground limit and carrying out the analysis of slope stability, we applied the Mass Nailing Method to the site because of need for reinforcement to soil and weathered rock slopes. In slope for soft and hard rock sections, we also reinforced the sections that are difficult to obtain the safety without reinforcement in alteration zone.

• Publications of The Korean Astronomical Society
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• v.25 no.3
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• pp.77-82
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• 2010

Recent results from large surveys of the local universe show that the galaxy-black hole connection is linked to host morphology at a fundamental level and that there are two fundamentally different modes of black hole growth. The fraction of early-type galaxies with actively growing black holes, and therefore the AGN duty cycle, declines significantly with increasing black hole mass. Late-type galaxies exhibit the opposite trend: the fraction of actively growing black holes increases with black hole mass. Issues of AGN selection bias and prospects for near-future efforts with high redshift data are discussed.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1458-1463
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• 2004

By using unique experimental techniques and careful construction of the experimental apparatus, the characteristics of the local heat transfer were investigated using the condensing R134a two-phase flow, in horizontal single mini-channels. The circular channels ($D_h=0.493$, 0.691, and 1.067 mm) and rectangular channels ($D_h=0.494$, 0.658, and 0.972 mm) were tested and compared. Tests were performed for a mass flux of 100, 200, 400, and 600 $kg/m^2s$, a heat flux of 5 to 20 $kW/m^2$, and a saturation temperature of $40^{\circ}C$. In this study, effect of heat flux, mass flux, vapor qualities, hydraulic diameter, and channel geometry on flow condensation were investigated and the experimental local condensation heat transfer coefficients are shown. The experimental data of condensation Nusselt number are compared with existing correlations.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.12
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• pp.837-845
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• 2012

The purpose of this research is to investigate the heat transfer enhancement by the multiple tripping wires installed on a flat plate. Naphthalene sublimation technique is used to measure the local mass transfer coefficients, and then heat transfer coefficients are calculated using heat/mass transfer analogy. Experiments are performed for the developed and developing flow conditions. Local and average heat transfer coefficients from the flat plate with three tripping wires are compared with those of no and one tripping wire. Remarkable heat transfer enhancements are found resulting from the boundary layer separation by the tripping wires, especially in the laminar boundary layer.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.63.2-63.2
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• 2016

One of the well-known problems in the lambda cold dark matter (${\Lambda}CDM$) models is a missing satellite problem. The slope of the mass function of low mass galaxies predicted by ${\Lambda}CDM$ models is much steeper than that based on the luminosity function of dwarf galaxies in the local universe. This implies that the model prediction is an overestimate of low mass galaxies, or that the current census of dwarf galaxies in the local universe may be an underestimate of dwarf galaxies. Previous studies of galaxy luminosity functions to address this problem are based mostly on the sample of galaxies brighter than Mv ~ -10 in the nearby galaxies. In this study we try to search for ultra-faint galaxies (UFDs), which are much fainter than those in the previous studies. We use multi-field HST ACS images of M60 in the archive. M60 is a giant elliptical galaxy located in the east part of the Virgo cluster, and hosts a large population of globular clusters and UCDs. Little is known about the dwarf galaxies in this galaxy. UFDs are much fainter, much smaller, and have lower surface brightness than normal dwarf galaxies so HST images of massive galaxies are an ideal resource. We present preliminary results of this search.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.8
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• pp.1029-1037
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• 2000

The present study investigates the local heat/mass transfer characteristics on a rotating disk which is the top disk covered with a shroud in HDD. The naphthalene sublimation technique is employed to determine the local heat/mass transfer coefficients on the rotating disk. Flow field measurements using Laser Doppler Anemometry (LDA) and numerical calculations are performed to analyze the flow patterns induced by the disk rotation. HDD has been developed for compactness and speedy data access, thus the rotating velocity of the disk is increased and the height of a hub is decreased. The experiments are conducted for the various hub heights of 5, 10 and 15 mm, for the rotating Reynolds numbers of $5.5{\times}10^4$ to $1.1{\times}10^5$ and for the effects of the presence of a read/write head arm. The results show that the heat transfer on the rotating disk is enhanced considerably for the decrease of the hub height and for the increase of the rotating Reynolds number. The head arm inserted in the cavity decreases the heat transfer despite the enhancement of tangential RMS velocity because of the deficit of the momentum in the flow field.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.97-102
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• 2003

An experimental study is conducted to investigate the effects of duct corrugation angle on heat/mass transfer characteristics in wavy ducts by using a naphthalene sublimation technique. The corrugation angles of the wavy ducts are $145^{\circ}$ , $130^{\circ}$ and $115^{\circ}$ . and the Reynolds numbers based on the duct hydraulic diameter vary from 300 to 3,000. At the low $Re(Re{\leq}1000)$, high heat/mass transfer regions are formed by the secondary vortex flows called Taylor-Gortler vortices on both pressure-side and suction-side walls. At the high $Re(Re{\geq}1000)$, the effects of these secondary flows are vanished. As corrugation angle decreases, the local peak Sh induced by Taylor-Gertler vortices are increased and average Sh also enhanced. More pumping power (pressure loss) is required with the smaller corrugation angle due to the stronger secondary vortex flows.