• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1997.10a
• /
• pp.841-844
• /
• 1997

Sandwich structure is widely used in various fields of industry due to its excellent strength and stiffness compared with weight. We studied the buckling and bending behavior with respect to the variation of design parameters such as length, height, and thickness of honeycomb sandwich core. We found that as the density and the thickness of core become higher, the value of critical bucking load increased significantly. We found that the effect of bending stress due to critical buckling load resulted in high bending stress and the value of bending stress decreased in half according to the increase of length of core. The effect by bending stress is dominant above the portion of the intersection line between bending stress and the effect of buckling is dominant below the potion of it. We could get proper thickness ratio and density of core according to applied load conditions.

• Nuclear Engineering and Technology
• /
• v.30 no.6
• /
• pp.485-495
• /
• 1998

Migration characteristics of tracers in a rock fracture in a case of line-source and line-collection was studied. The fracture plane was discretized into a square mesh to which variable apertures were assigned. The spatially varying apertures of a fracture were generated using a geostatistical method, based on a given aperture probability density distribution and a specified spatial correlation length. The flow potential and pressure at each node were computed. Calculations showed that fluid flow occurs predominantly through a few preferred paths. Hence, the large range of apertures in the fracture gives rise to flow channeling. The solute transport was calculated using a particle tracking method. The migration plumes of tracer between injection line and withdrawal line are displayed in contour plots. The elution curves are shown to be controlled by the aperture density distribution and to be insensitive to statistical realization and spatial correlation length.

• Journal of Hydrogen and New Energy
• /
• v.27 no.6
• /
• pp.727-736
• /
• 2016

Numerical simulations of n-heptane spray characteristics in a constant volume combustion chamber under diesel engine like conditions with increasing ambient gas density ($14.8-142kg/m^3$) and ambient temperature (800-1000 K) respectively were performed to understand the non-vaporizing and vaporizing spray behavior. The effect of fuel temperature (ranging 273-313 K) on spray characteristics was also simulated. In this simulation, spray modeling was implemented into ANSYS FORTE where the initial spray conditions at the nozzle exit and droplet breakups were determined through nozzle flow model and Kelvin-Helmholtz/Rayleigh-Taylor (KH-RT) model. Simulation results were compared with experimentally obtained spray tip penetration result to examine the accuracy. In case of non-vaporizing condition, simulation results show that with an increment of the magnitude of ambient gas density and pressure, the vapor penetration length, liquid penetration length and droplet mass decreases. On the other hand vapor penetration, liquid penetration and droplet mass increases with the increase of ambient temperature at the vaporizing condition. In case of lower injection pressure, vapor tip penetration and droplet mass are increased with a reduction in fuel temperature under the low ambient temperature and pressure.

• Journal of the Semiconductor & Display Technology
• /
• v.21 no.2
• /
• pp.38-44
• /
• 2022

Plasma density in semiconductor fabrication equipment becomes higher to achieve the improved the throughput of the process, but the increase of surface corrosion of the ceramic coated chamber wall has been observed by the increased plasma density. Plasma chamber wall coating with aerosol deposition prefer to be firm and uniform to prevent the potential creation of particle inside the chamber from the deformation of the coating materials, and the aerosol discharge nozzle is a good control factor for the deposited coating condition. In this paper, we investigated the design of the nozzle of the aerosol deposition to form a high-quality coating film. Computational fluid dynamics (CFD) study was employed to minimize boundary layer effect and shock wave. The degree of expansion, and design of simulation approach was applied to found out the relationship between the divergence angle and nozzle length as the key parameter for the nozzle design. We found that the trade-off tendency between divergence angle and nozzle length through simulation and quantitative analysis, and present the direction of nozzle design that can improve the uniformity of chamber wall coating.

• Journal of Aquaculture
• /
• v.1 no.1
• /
• pp.13-24
• /
• 1988

In order to investigate a reasonable rearing density and the possibility of high-density rearing, flounder, Paralichthys olivaceus, juveniles of 2.53$\pm$0.24 cm in total length and 1.12$\pm$0.12 cm in body height were used in this study. The initial rearing density of them was 10 (D10), 20 (D20), 30 (D30) and 40 (D40) individuals per 137.75 $cm^2$ of bottom area, respectively. Ranges of water temperature and specific gravity during the rearing period of 65 days were $21.0\~27.0^{\circ}C$ and 1.024$\~$1.026, respectively, showing relatively higher values than that of natural sea water. Dissolved oxygen during the rearing period was 5.4$\~$7.5 ml/$\iota$ and inorganic nitrate was 0.07$\~$0.48 ppm in $NH_4^+-N$, 0.006$\~$0.33 ppm in $NO_2^{-}-N$ and 3.89$\~$34.06 ppm in $NO_3^{-}-N$. Growth in total length and body height of the juveniles in four rearing density at the end of the experiment was 8.17$\pm$0.80 em and 4.16$\pm$0.39 em, the highest in D20 and 7.72$\pm$0.40 cm and 3.94$\pm$0.21 cm, the lowest in D10. Significant differences, however, were not recognized between the slope values of growth regressions in four rearing density. Slope values of the relative growth between total length and body height of the juveniles in four rearing density were 0.5346, the highest in D10 and 0.5165, the lowest in D30, but there were no significant differences in those values. Survival rate of juveniles at the end of the experiment was $90\%$ in D10, D20 and D30, but that of D40 was $75\%$. The relationship between total length X body height (X) and body surface area of ocular side (Y) to calculate the rate of Y to bottom area in rearing tank (covering rate) as an indicator of rearing density was expressed by a linear regression, Y=0.5994X+0.1840. Covering rate in four rearing density at the end of the experiment was ranged 1.2$\~$4.1 times. Judging from the covering rate above 4 times, it seems to be possible rearing the flounder juveniles in high-density.

• Journal of Aerospace System Engineering
• /
• v.10 no.3
• /
• pp.23-31
• /
• 2016

The intermediate mixing chamber is one of various methods for improving the regression rate and combustion efficiency of the hybrid rocket. The mixing chamber with its non-combustible material makes the propulsion performance increase, but it leads to a low fuel-loading density in the combustion chamber; therefore, this performance-related trade-off between the mixing chamber and the low fuel-loading density was studied. In this study, the trade-off was conducted by comparing the intermediate-mixing-chamber case with a w/o-mixing-chamber case. The small hybrid-sounding rocket is designed with internal ballistics for comparing the rocket length to the weight. In addition, an external ballistic analysis was conducted for comparing the performances of the w/- and w/o-mixing-chamber cases. As a result, the intermediate-mixing-chamber case shows that the length and the weight were decreased to 12 % and 8 %, respectively; furthermore, when compared with the normal cases, the estimated altitude result of the w/-mixing-chamber case was increased to approximately 75 m.

• Journal of The Korean Society of Grassland and Forage Science
• /
• v.12 no.1
• /
• pp.1-5
• /
• 1992

The purpose of this experiment was to determine the effect of soil phosphorus level on plant length, dry matter yield and competition in annual and perennial plants.The effect of phosphorus fertilizer on the plant length and dry matter yield was low in the perennial plant of Miscanthus sinensis, SaSa palmata and ilrtemlsia princeps, but was high in the annual plant of Polygonwn thunbergii and Echinochloa crus-galli.The plant length, density and dry matter yield of Italian ryegrass in individual natural community did not depend on relative photosynthetic photon flux density but on total and available phosphorus of soil.

• JSTS:Journal of Semiconductor Technology and Science
• /
• v.5 no.3
• /
• pp.187-194
• /
• 2005

An analysis of the 1/f or flicker noise in FD n-channel Double Gate SOI MOSFET is proposed. In this paper, the variation of power spectral density (PSD) of the equivalent noise voltage and noise current with respect to frequency, channel length and gate-to-source voltage at various temperatures and exponent $C(i.e\;1/f^c$ is reported. The temperature is varied 125 K from to room temperature. The variation of PSD with respect to channel length down to $0.1{\mu}m$ technology is considered. It is analyzed that l/f noise in FD n-channel Double Gate SOI MOSFET is due to both carrierdensity fluctuations and mobility-fluctuations. But controversy still exits to its origin.

• 한국방재학회:학술대회논문집
• /
• 2008.02a
• /
• pp.711-714
• /
• 2008

The objective of this study is to analyze the relationship between the watershed characteristics and the critical duration of design rainfall. For estimation of critical duration, adjustment Huff's method and ILLUDAS urban runoff model were applied to urban 21 areas. Watershed characteristics such as area, channel length, channel slope, shape factor, and pipe density were used to simulate correlation analysis. The conclusions of this study are as follows; it is revealed that critical duration is influenced by the watershed characteristics such as pipe density, area and channel length. Also, multiple regression analysis using watershed characteristics is carried out and the determination coefficient of multiple regression equation shows 0.972.

• JSTS:Journal of Semiconductor Technology and Science
• /
• v.8 no.1
• /
• pp.11-20
• /
• 2008

The structure of 2-bit/cell flash memory device was characterized for sub-50 nm non-volatile memory (NVM) technology. The memory cell has spacer-type storage nodes on both sidewalls in a recessed channel region, and is erased (or programmed) by using band-to-band tunneling hot-hole injection (or channel hot-electron injection). It was shown that counter channel doping near the bottom of the recessed channel is very important and can improve the $V_{th}$ margin for 2-bit/cell operation by ${\sim}2.5$ times. By controlling doping profiles of the channel doping and the counter channel doping in the recessed channel region, we could obtain the $V_{th}$ margin more than ${\sim}1.5V$. For a bit-programmed cell, reasonable bit-erasing characteristics were shown with the bias and stress pulse time condition for 2-bit/cell operation. The length effect of the spacer-type storage node is also characterized. Device which has the charge storage length of 40 nm shown better ${\Delta}V_{th}$ and $V_{th}$ margin for 2-bit/cell than those of the device with the length of 84 nm at a fixed recess depth of 100 nm. It was shown that peak of trapped charge density was observed near ${\sim}10nm$ below the source/drain junction.