• Smart Structures and Systems
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• v.17 no.1
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• pp.59-72
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• 2016

The Impact Echo method can be used to measure the thickness of concrete plate like structures. Measurements are based on the identification of a clear thickness resonance frequency which can be difficult in very thick or highly attenuative plates. In this study the detectability of the measured resonant frequency is enhanced by time domain summation of signals with different source receiver spacing. The proposed method is based on the spatial and temporal properties of the first higher symmetric zero group velocity Lamb mode (S1-ZGV) which are described in detail. No application dependent tuning or filtering is needed which makes the method robust and suitable for implementation in automatic IE thickness measurements. The proposed technique is exemplified with numerical data and field data from a thick concrete wall and a highly attenuative asphalt concrete layer.

• Journal of the Korean Association of Geographic Information Studies
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• v.4 no.3
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• pp.51-60
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• 2001

The travel behavior can be analysed microscopically using GPS because the travel characteristics can be found out by travelling two test cars loaded with GPS equipments. The speed difference and spacing variation between the lead vehicle and the following's in uninterrupted flow are the important variables related to capacity and safety. This study analysed these with data obtained by travelling the 4th Line and 28th Line of the national road. The variation width in speed difference in the run time is below 3.0%. But, related to the speed difference in the situation of acceleration and deceleration the difference after 4second is bigger than that just after the start. The spacing variation is similar to this. The spacing just before deceleration concerning safety was analysed. When the theoretical values by the modeling method and observed values were compared, the observed values were analysed 12.52% shorter than the other in average.

• 한국ITS학회:학술대회논문집
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• 2008.11a
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• pp.74-77
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• 2008

• Journal of the Korea Society of Computer and Information
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• v.9 no.3
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• pp.195-200
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• 2004

The change of traffic by the CDV is entered in a condensed form in UUC/NPC, overflowing the buffer of the net and possibly causing its congestion. For this reason this paper proposes the Cell Spacing Scheme. As the Cell Shaping Scheme, two method is proposed ; RAT based on the time in which cells enter the spacer and RDT based on the time in which cells come out from the spacer. This paper proposes the improved spacing sheme in which the departure time of the present cell determines the departure time of the next one, by combining with Leaky Bucket and on the traffic characteristics of ATM network.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.1
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• pp.140-148
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• 1999

Experiments on flame spread in an one-dimensional droplet array up to supercritical pressures of fuel droplet have been conducted In normal gravity and microgravity. Evaporating process around unburnt droplet is observed through high-speed Schlieren and direct visualizations in detail, and flame spread rate is measured using high speed chemiluminescence images of OH radical. Flame spread behaviors are categorized into three: flame spread is continuous at low pressures and is regularly intermittent up to the critical pressure of fuel. flame spread is irregularly intermittent and zig-zag at supercritical pressures of fuel. At atmospheric pressure, the limit droplet spacing and the droplet spacing of maximum flame spread rate in microgravity are larger than those in normal gravity. In microgravity, the flame spread rate with the increase of ambient pressure decreases initially, takes a minimum, and then decreases after taking maximum. This is so because the flame spread time is determined by competing effects between the increased transfer time of thermal boundary layer due to reduced flame diameter and the reduced ignition delay time in terms of the increase of ambient pressure. Consequently, it is found that flame spread behaviors in microgravity are considerably different from those in normal gravity due to the absence of natural convection.

• Journal of Energy Engineering
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• v.16 no.3
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• pp.113-119
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• 2007

The auto-ignition characteristics and combustion behaviors of one-dimensional array of water-in-fuel droplets suspended in a high temperature chamber have been investigated experimentally with various droplet spacing and number of droplets. The fuels used were pure n-decane and emulsified n-decane with water contents varied from 10% to 30%. All experiments have been performed at 920 K under the atmospheric pressure. The number of droplets in an array were fixed as 3 or 5 and its spacing was varied from 3 mm to 7 mm by 1mm interval. The imaging technique with a high-speed camera has been adopted to measure the ignition delay and flame life time. The micro-explosion behaviors were also observed. As the droplet array sparing increased, the ignition delay also increased regardless of water contents. However, the life time of droplet array decreased as the droplet spacing increased. The full combustion time in array of 3 droplets was found to be longer than that for 5 droplets case due to the longer ignition delay.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.4 no.4
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• pp.393-400
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• 2006

In design of a deep geological repository for the high level wastes, it is very important that the temperature of the bentonite block should not be over $100^{\circ}C$ to maintain the integrity of the bentonite buffer block from the decay heat. In this study, for the layout of the repository to meet the requirement, the analysis of the disposal tunnel and disposal pit spacing was carried out. To do this, based on the reference repository concept, several cases of cooling times and disposal tunnel and disposal pit spacing were compared. The thermal stabilities of the disposal systems were analyzed in terms of the cooling time and spacing. The results showed that it was more desirable to determine the layout of the repository in terms of disposal pit spacing than the disposal tunnel spacing. The results of these analyses can be used in the deep geological repository design. The detailed analyses with the exact site characteristics data will reduce the uncertainty of the results.

• Journal of Korea Foundry Society
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• v.17 no.6
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• pp.608-614
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• 1997

The effect of mold preheating temperature on the microstructure such as grain size, eutectic silicon morphology was investigated for the Al-7wt%Si-0.3wt%Mg alloy. Microstructural variations have been characterized as a function of Sr addition and cooling rate during solidification. Microstructures were correlated with cooling rate, local solidification time and eutectic nucleation temperature, etc. In this study, Sr addition caused increase of local solidification time, undercooling and reduction of eutectic plateau temperature. In logarithmic scale, local solidification time was in inverse proportion to cooling rate. Eutectic nucleation temperature was in inverse proportion to cooling rate of logarithmic scale. Increasing the cooling rate refined dendrite arm spacing and eutectic silicon. Dendrite arm spacing was logarithmically in inverse proportion to cooling rate. Without modifier addition, eutectic silicon was modified at cooling rate of $7^{\circ}C/s$ or higher.

• Polymer(Korea)
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• v.25 no.6
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• pp.818-825
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• 2001

Polycarbonate(PC)/montmorillonite (MMT) nanocomposites were prepared by solution and melt mixing methods. A d-spacing of the nanocomposites was measured by an X-ray diffractometer. Neat montmorillonite (MMT-Na) and MMTs modified by dodecyl ammonium (MMT-DA) or dimethyl hydrogenated tallow 2-ethylhexyl ammonium (MMT-25A) were used. The d-spacing value of PC/MMT-25A and PC/MMT-DA was higher than that of PC/MMT-Na. The d-spacing increased from around 12 to $37AA$ depending on the mixing method. PC was more readily introduced to the gallery of MMT as the molecular weight of PC reduced and the mixing time increased. PC/MMT-25A showed higher thermal stability by thermogravimetric analysis (TGA) than PC/MMT-DA and PC/MMT-Na.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.2
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• pp.76-84
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• 2003

Stereolithography is the technique using a laser beam to cure a liquid resin, a photopolymer, with three dimensional computer-aided design (CAD) data. The build parameters of stereolithography such as beam size, scan velocity. hatch spacing, layer thickness and etc. are determined by the accuracy of prototype, the build time and the cured properties of the resin. In particular, beam size is important processing parameter fur the other parameters. Therefore, this study observed the cured property to beam size. For this purpose, according to hatch spacing and beam size, the cure width and depth were measured on single cured line. Also, the cure width and depth were measured at single cured layer As a result of experiments. cure depth which varied from 0.23mm to 0.34mm was directly proportioned to beam radius. on the other hand, cure width which varied from 0.42mm to 1.07mm was inversely proportioned to beam radius. Surface roughness varied from 1.12 to 2.23 m for the ratio of hatch spacing to beam radius.