• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.4
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• pp.53-62
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• 2006

Two-dimensional steady flowfields generated by transverse injection jets into a supersonic mainstream are numerically simulated. Fine-scale turbulence effects are represented by a k-${\omega}$ SST two-equation closure model which includes $y^+$ effects on the turbulence model. Solution convergence is evaluated by using Grid Convergence Index(GCI), a measure of uncertainty of the grid convergence. Comparison is made with experimental data and other turbulence models in term of surface static pressure distributions, the length of the upstream separation region, and the penetration height. Results indicate that the k-${\omega}$ SST model correctly predicts the mean surface pressure distribution and the upstream separation length for low static pressure ratios. However, the numerical predictions become less consistent with experimental results as the static pressure ratio increases. All these results are taken within 1% error band of grid convergence.

• Composites Research
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• v.29 no.3
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• pp.104-110
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• 2016

This paper reports a novel method for simultaneous exfoliation of graphene and dispersion of carbon nanotube by using intercalation method. In common, graphene flake and carbon nanotubes can be produced through individual exfoliation or debundling process, but the process require significant amount of time. Here, potassium sodium tartrate was thermally intercalated into graphite and carbon nanotube bundle for simultaneous exfoliation and dispersion of graphene and carbon nanotubes. We confirmed expansion of interlayer distance via XRD, and also found that oxidation level of the exfoliated materials were significantly low (below 8.3 at%). The produced materials are fabricated in to conductive composite film via vacuum filtration and spray deposition to show enhancement of conductive properties.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.287-292
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• 2005

The flowfields generated by gaseous slot injection into a supersonic flow at a Mach number of 3.75 and a Reynolds number of $2.07{\times}10^7$ are simulated numerically. Fine-scale turbulence effects are represented by a two-equation(k-w SST model) closure model which includes $y^+$ effects on the turbulence model. Grid convergence index(GCI) is also considered to provide a measure of uncertainty of the grid convergence. Comparison is made with experimental data and other turbulence model in term of surface static pressure distributions, the length of the upstream separation region, and the penetration height. Results indicate that the k-w SST model correctly predicts mean surface pressure distribution and upstream separation length. However, it is also observed that the numerical simulation over predicts the pressure spike and penetration height compared with experimental data. All these results are taken within $1\%$ error band of grid convergence.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.226-226
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• 2003

일반적으로, 고분자 매트릭스에 층상 점토광물이 분산되어 얻어지는 복합재료는 세가지 형태를 이룬다. 첫째 통상의 복합재료는 고분자 매트릭스 내에 점토입자가 고루게 분산된 상태를 말하며, 둘째 점토 층 사이에 고분자 모노머나 올리고머가 일부분 삽입된 삽입형 복합재료(intercalated composite)이며, 셋째 점토 층 사이에 삽입된 모노머나 올리고머의 경화 또는 중합반응을 통해 점토내의 한층 한층 균일하게 매트릭스 내에 분산된 박리형 나노복합소재(exfoliated nanocomposite) 이다. 이들 복합재료들 중 박리형 나노복합소재는 적은 양의 점토가 단위 층으로 고분자 매트릭스에 완전히 분산되어 다양한 물성의 향상이 기대되는 재료이다. 따라서 최근 고분자의 기계적 강도, 팽윤 저항성 그리고 차폐특성 둥 전반적인 물성을 향상시키는 방법으로 층상 점토광물의 층 사이에 다양한 유기물을 삽입하여 층간거리를 확장시킨 유기 점토광물을 제조하고 이를 고분자 소재에 첨가하여 박리형 나노복합소재를 제조하는 방법이 많은 연구가 수행되고 있다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.2
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• pp.153-160
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• 2011

The characteristics of supersonic coaxial/off-axis jet impingements on a slanted kerf surface were experimentally studied, to investigate the role of the assist gas that removes molten materials from cut zone formed by laser machining. In this parametric study, hundreds of high-resolution schlieren images were obtained for various gas pressures, distances between nozzle exit and kerf surface, kerf widths, and alignments of off-axis nozzle. It was noticed that simply increasing the assist gas pressure was not effective in eliminating the flow separation that occurs downstream of the kerf surface. However, it was also observed that by increasing the kerf width and utilizing off-axis nozzles, the separation of the assist gas on the kerf surface can be weakened. The effect of the distance between the nozzle exit and the kerf surface on the characteristics of separation occurring on the kerf surface was found to be lower in the case of supersonic nozzles than that in the case of sonic nozzles.

• Journal of Navigation and Port Research
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• v.27 no.5
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• pp.473-478
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• 2003

Numerical study was made on the flow characteristics around a circular pipeline between parallel walls. The incompressible Navier-Stokes equations were solved by using a third-order upwind differential scheme. When the distance near a wall is small enough, the vortex shedding is almost completely suppressed because of the interaction with the wall boundary layer separation. This study aims to clarify the characteristics of the vortex shedding regime as the body approaches a wall as Reynolds number varies. The feature of separated vorticity dynamics is analyzed at different conditions with particular attention to the interaction between the pipeline wake and the induced separation on the plane walls.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2000.05a
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• pp.522-523
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• 2000

우리나라에서 건강식품으로 널리 알려져 있는 참전복은 불로장수의 식품으로 널리 애용되고 있을 뿐만 아니라 발암억제 물질인 paolin을 함유하고 있어, 세계적으로 상품가치가 인정되고 있다. 이러한 중요성에도 불구하고 참전복 부착치패의 성장 및 생존율 제고는 아직까지도 해결되어야 할 문제로 남아 있는 실정이다. 참전복 부착치패의 먹이선택성 및 유인성에 관한 기존의 연구를 보면 Viana et al. (1994)은 평균 각장 4.2 cm인 치패를 이용하여 배합사료의 9가지 원료에 대한 유연성을, Harada and Kawasaki (1982)는 각장 2.4 cm 이상인 치패를 대상으로 해조류 3종(미역, 톳, 파래)의 유인효과에 관하여 보고하였다. 그러나 이와 같은 보고들은 전복 종묘생산 현장에서 보다 빠른 시기에 박리하여 해조로 먹이 전환을 하기 위한 노력과는 어느 정도의 거리가 있다고 판단된다. 따라서 본 연구에 있어서는 평균 각장 5.0$\pm$1.0 mm인 치패를 박리하여 Navicula spp., 해조 2종(다시마, 파래) 및 자체 제조한 사료를 공급하여 먹이별 유인효과를 관찰하였다. (중략)

• Polymer(Korea)
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• v.30 no.6
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• pp.492-497
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• 2006

The epoxy composites are prepared with mixing temperature of epoxy/montmorillonite (MMT) melt master batch and the dielectric properties of the composites are also compared with intercalation of MMT. The exfoliation mainly occurrs iii the low content of MMT composites, while in the composites with high content of MMT the interspacing distance increases as the mixing temperature of epoxy/MMT master batch is increased. Class transition temperature of the composite which the MMT are effectively exfoliated is increased with the appropriate postcuring condition. Since the orientation polarization of dipoles in the epoxy molecules is restricted by the clay nanolayers exfoliated, the dielectric constant and dielectric loss of the composites are reduced. Furthermore, the dielectric properties could be improved by controling the mixing temperature and time of epoxy/MMT master batch as well as postcuring condition.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.384-384
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• 2009

에폭시 수지에 유기화된 층상실리케이트 나노입자를 1wt% 충진한 경우 나노콤포지트와 마이크로 입자를 50wt% 충진한 경우 마이크로 콤포지트를 제조하였다. 초음파 분산법을 이용하여 나노 및 마이크로입자를 120분 동안 분산시킨 에폭시- 나노/마이크로 콤포지트이다. 나노콤포지트와 마이크로콤포지트의 단시간 교류절연파괴특성을 조사하기 위해 와이블 분포 plot을 통하여 나타내었다. 와이블 plot은 기울기로서 형상파라미터를 나타낸 경우로서 이는 파괴강도의 균질성을 의미하게 된다. 63.2% 누적분포함수를 나타낸 경우 척도파라미터로서 나타내어진다. 마이크로 콤포지트의 경우 형상파라미터가 2.99, 나노콤포지트는 8.96를 나타내었다. 또한 마이크로 콤포지트 및 나노콤포지트 스케일 파라미터는 164.25kV/mm, 245kV/mm를 얻었다. 또한 B10수명의 경우 마이크로콤포지트와 나노콤포지트의 경우 77.57kV/mm, 139.3 6kV/mm로서 나노콤포지트의 경우 완전하게 박리가 일어난 경우이다. 마이크로 입자를 분산시켜 입자간거리와 나노입자를 분산시켜 박리가 일어난 경우 입자간거리는 대단히 큰 차이를 나타내고 있다. 나노입자가 교번전계 하에서 주입된 전하 및 케리어 이동을 억제하는 경우로 이와같은 결과를 얻을 수 있다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2007.12a
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• pp.125-126
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• 2007

In this paper, the floating body with vertical plate is introduced with a study on the flow patterns and characteristics in around the floating body by using 2 frame particle tracking method. This paper introduce an analysis method to predict the characteristics if flow around the neighboring fields if Floating Body with vertical plate in order to investigate a high performance model. Flow visualization has conducted in a drcu1ating water channel by a high speed camera and etc. Flow phenomena according to turbulence intensity distribution and flow separation around the floating body with vertical plate were obtained by two-dimensional PIV system.