• Proceedings of the Korea Society of Information Technology Applications Conference
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• 2007.05a
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• pp.75-83
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• 2007

본 논문에서는 .NET 기반의 Remoting 시스템과 Socket 통신을 이용하여 이 기종 DB Server 간의 Data 동기화를 구현하였다. 이 시스템은 Client 의 웹 브라우저를 이용 Socket 통신으로 Data를 전송하여 데이터베이스에 저장하는 방식으로 구현하였고, Data 읽기는 Remoting 기술인 중계 어플리케이션 서버의 클래스를 원격으로 실행시켜 Data를 가져오는 방식으로 구현하였다. DB 동기화는 Data를 저장할 때 중계 어플리케이션 서버와 DB 서버의 Data 관리 어플리케이션 간 비동기 통신으로 DB 서버의 Data 처리 수준을 실시간으로 감시하여 중계 어플리케이션 서버에서 선택적으로 Data를 전송하고, 이후 Data 처리 수준이 정상화기 되면 다시 Data를 전송케 함으로써 이 기종 DB 서버간의 동기화를 구현하였다. 본 논문은 1 장에 서론, 2 장에 .NET Remoting 기술과 네트워크 프로그래밍, 3 장에 이 기종 DB 서버 간 동기화 시스템 설계 및 구현, 4 장에 결론을 기술하였다.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2000.11a
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• pp.203-204
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• 2000

도시협곡 내에서 형성되는 전형적인 유동장은 협곡내부에서 형성되는 회전류(vortex)이다(Berkowicz, 1998). Oke(1988)에 따르면 단면비가 큰 경우 (W/H＞2.5), 도시 협곡내 유동장은 isolated roughness flow, 단면비가 중간인 경우(1.538

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.2
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• pp.122-127
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• 2000

Microstructural evolutions in ceria-stabilized zirconia (Ce-TZP) and alumina-dispersed Ce-TZP ceramics were investigated as functions of doping and annealing conditions. All of sintered specimens showed the relative density over 99 %. Sintered specimens had linear grain boundaries and normal grain shapes, but ceria-doped specimens had irregular grain shapes and nonlinear grain boundaries due to the diffusion-induced grain boundary migration during annealing at $1650^{\circ}C$ for 2 h. Mean grain boundary length of Ce-TZP with irregular grain shapes was higher than that of normal grain shapes, and was a value of 23pm at the maximum. Alumina particles dispersed in Ce-TZP inhibited the grain growth of zirconia particles. $Al_2O_3$Ce-TZP doped with ceria and annealed at $1650^{\circ}C$ for 2 h showed irregular grain shapes as well as small grain size. Added alumina particles showed the grain growth during sintering or annealing, and they changed the position from grain boundary to inside of the grains during the annealing. The specimens with normal grain shapes showed an intergranular fracture mode, whereas the specimens with irregular grain shapes showed a transgranular fracture mode during the crack propagation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.2
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• pp.10-16
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• 2003

The unsteady supersonic flow over tandem cavities has been analyzed by the integration of Navier-Stokes equations with the k-$\varepsilon$ turbulence model. The unsteady flow is characterized by the periodicity due to the mutual relation between the shear layer and the internal flow in cavities. The upwind TVD scheme based on the flux vector split with the van Leer limiters is used. The results show the principal frequency is very reasonable. The principal frequency of the rear cavity due to the front cavity has been analyzed by the combination of the several aspect ratios of cavities. In the case of the front cavity of low aspect ratio, the frequencies of tandem cavities are almost same, because two shear layers developed from each cavity are mixed and developed to one shear layer. However, in the case of the front cavity of high aspect ratio, the characteristis of frequency are very different, because the second shear layer is developed in the diffused first shear layer.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.75-75
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• 2011

본 논문에서는 진동중인 교량 거더에 작용하는 풍하중을 산정하고 그에 따른 플러터 발생풍속을 예측하기 위하여 분산형 전산환경을 활용한 수치해석 연구를 수행하였다. 분산형 전산환경은 웹 포탈을 기반으로 수치해석 환경을 제공하는 수치풍동 시스템으로서, 전산유체역학(CFD : Computational Fluid Dynamics)에 대한 전문지식이 부족한 사용자들도 격자생성, 수치해석자를 이용한 계산, 가시화 등의 전 과정을 편리하게 수행할 수 있는 차세대 토목분야 연구 환경이다. 본 시스템은 그리드스피어(GfidSphere)를 기반으로 구성되었으며, 기본적으로 사용자 관리, 세션 관리, 그룹 관리, 레이아웃 관리 등을 제공하여 사용자가 포탈을 통해서 다양한 서비스를 쉽게 사용할 수 있는 환경을 구축하도록 도와준다. 수치해석을 위한 유체 지배방정식은 2차원 비정상 비압축성 RANS(Reynolds-Averaged Navier-Stokes) 방정식이며, pseudo compressibility 방법을 적용하였다. 비정상 유동장을 해석하기 위하여 이중시간 전진법(dual time stepping)을 사용하였으며, 수렴가속화를 위해 Multi-grid 기법을 적용하였다. 또한 난류 유동장 해석을 위해서 $k-{\omega}$ SST 난류 모델을 사용하였으며, 난류 천이 과정에서의 유동을 모사하기 위하여 Total stress limitation 방법을 적용하였다. 교량 거더의 연직과 회전방향의 2자유도 움직임을 모사하기 위하여 동적격자 기법을 도입하였다. 교량 거더 주변의 비정상 유동해석 결과를 통해, 거더 표면에서 떨어져나가는 크고 작은 와류의 영향으로 양력 및 모멘트 계수 그래프가 중첩된 진폭과 주기를 갖고 주기적으로 나타나는 것을 확인할 수 있었다. 또한 계산된 비정상 공기력을 적용한 2자유도 플러터 방정식을 통하여 플러터 발생풍속을 산정하였다. 최종적으로 본 연구에서 계산된 결과의 타당성을 검증하기 위하여 수치적으로 구한 플러터 발생풍속과 기존의 실험 및 수치해석 결과를 비교하였으며, 결과는 잘 일치하였다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.3
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• pp.126-132
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• 2002

The nanocrystalline zirconia powder with anisotropic shapes was synthesized by hydrothermal treatment of the tetragonal zirconia prepared by aging the zirconium hydroxide precipitate, which was obtained from the reaction between $ZrOCl_2{\cdot}8H_2O$ and KOH solutions under the fixed pH of 13.5, at $100^{\circ}C$ for 24 h. With increasing the hydrothermal reaction temperature and time, the fraction of tetragonal phase with spherical zirconia decreased, whereas, relatively the fraction of monoclinic phase with spindle-like and rod shape zirconia increased. As increased concentration of the NaOH solution it promoted the particle size to become larger and the crystalline phase to transform tetragonal to monoclinic. However, the specific surface area at the early stage of the reaction increased and subsequently decreased because of grain growth in powder with longer reaction time.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.7
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• pp.1-8
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• 2005

For study on the unsteady wall interference effect, flows around a circular cylinder in closed test-section wind tunnels have been numerically investigated by solving compressible Navier-Stokes equations. The numerical scheme is based on a node-based finite-volume method with the Roe's flux-difference splitting and an implicit time-integration method coupled with dual time-step sub-iteration. The computed results showed that the unsteady pressure gradient over the cylinder is enhanced by the wall interference, and as a result the fluctuations of lift and drag are augmented. The drag is further increased because of the lower base pressure. The vortex shedding frequency is also increased by the wall interference. The pressure on the test section wall shows the harmonics having the shedding frequency contained in the wall effect.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.437-442
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• 2015

The swirl ratio in a SI engine is investigated in a steady flow bench according to the measurement methods: an impulse swirl meter and particle image velocimetry (PIV). When measuring the swirl ratio using the PIV, the torque is evaluated based on the cylinder center and swirl center, respectively. The position of the measurement plane is considered. As a result, in the upstream, the swirl ratio measured by the impulse swirl meter is estimated to be larger than that from the PIV measurements due to the unstable vortex motions. Regarding the PIV measurements, the swirl ratio based on the cylinder center has been found to be lower than that based on the swirl center. On the other hand, the difference in swirl ratio has decreased smaller as the measurement plane moved downstream due to the stabilization of the vortex motion.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.97-103
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• 2003

Numerical research has been done for the transverse jet behind a rearward-facings step in turbulent supersonic flow without chemical reaction. Purpose of transverse jet is to enhance mixing of the fuel in the combustor. Two-dimensional unsteady flowfields generated by slot injection into supersonic flow are numerically simulated with the Navier-Stokes equations with two-equation k-$\varepsilon$ turbulence model. Numerical method is used high-order upwind TVD scheme. Eight cases are computed for different slot momentum flux ratios and slot position at downstream of the step. The flow is very similar to the cavity flow, because the jet acts as an obstacle. The numerical results thus show the periodic phenomenon.

• Korean Journal of Ichthyology
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• v.2 no.2
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• pp.138-148
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• 1990

The influence of starvation on morphological change of the red sea bream larvae was examined at Song-ji fish hatchery, Tongyong-Gun, Kyongnam Provice in July 1988. The results obtained are as follows: 1) The larvae of red sea bream began to feed on rotifers in 2 days after hatching. In case of non-feeding, all of the larvae died in 5 days after hatching and the larvae which feeding delayed 1 and 2 days from normal first feeding schedule also died 100 in 6 days after hatching. 2) With the exhaustion of the yolk, the total length, body length, myotome height and gut height of unfed larvae decreased. 3) The ratio of height to myotome height in unfed larvae has declined most rapidly compare to other demensions while starving. At 5 days after hatching, the ratios of these of starving larvae and fed larvae were 0.306 and 0.010, respectively. 4) The morphology of starving larvae at 6 days after hatching are characterized as sharpened jaw, projected edge of lower part of clavicle and slender gut.