• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.6
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• pp.454-460
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• 2009

To analyze the mixture formation process of evaporating diesel spray is important for emissions reduction in actual engines. Then the effects of change in density of ambient gas on spray structure in high temperature and pressure field have been investigated in this study. The ambient gas density was changed from ${\rho}_a=5.0kg/m^3$ to ${\rho}_a=12.3kg/m^3$ with CVC(Constant Volume Chamber). Also, simulation study by modified KIVA-II code was conducted and compared with experimental results. The ambient temperature and injection pressure are kept as 700K and 72MPa, respectively. The images of liquid and vapor phase in the evaporating free spray were simultaneously taken by exciplex fluorescence method. As experimental results, with increasing ambient gas density, the tip penetration of the evaporating free spray decreases due to the increase in the drag force from ambient gas. The spatial structure of a diesel spray can be verified as 2-regions consisted of liquid with momentum decrease and vapor with large-scale vortex. The calculated results obtained by modified KIVA-II code show good agreements with experimental results.

• Journal of Energy Engineering
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• v.24 no.3
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• pp.122-127
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• 2015

We carried out three-dimensional flow analysis in a clean room. Flow field in a robot experiment system, induced from the moving robot, is numerically studied in this paper. The effects of moving robot in a clean room are investigated in order to find the section of dust accumulation. Contamination on the bottom produced from the moving robot is predicted from the analysis results from the flow fields. Results show that a large swirl flow is formed around the moving robot. Consequently, the optimal flow condition can be obtained by controlling the fluid velocity through the fixing of inlet or outlet position.

• 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.4_1
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• pp.1-8
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• 1992

This paper presents a p-version finite element approach for modeling the stress distribution around a circular hole in a finite strip subjected to membrane and flexural behaviors. Also, same problem with a crack emanating from a perforated tension strip was solved by virtual crack extension method. The p-version of the finite element method based on integrals of Legendre polynomials is shown to perform very well for modeling geometries with very steep stress gradients in the vicinity of a circular cutout. Here, the transfinite mapping technique for circular boundaries was used to avoid the discretization errors. The numerical results from the proposed scheme have a good comparison with those by Nisida, Howland, Newman etc. and the conventional finite element approach.

• Journal of Korea Water Resources Association
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• v.49 no.8
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• pp.707-717
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• 2016

In this study we carried out laboratory experiments to investigate the three-dimensional turbulent flows around a spur dike installed in a straight open channel flume. The experiments are conducted under the two different Froude numbers, 0.100 and 0.185. The three-dimensional instantaneous velocities are measured using the Acoustic Doppler Velocimetry (ADV) to obtain the time-averaged velocities and the turbulence stresses. The measured flow field reveal the existence of the recirculation zones downstream of the dike, which is characterized by high turbulence stresses near its boundaries. The results show that although the overall mean flow patterns between the low and high Froude number cases are very similar to each other, there exist moderate changes in the maximum dimensionless turbulence stresses and the maximum dimensionless bed shear stress with the increase of the Froude number.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.1
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• pp.9-16
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• 2012

This paper describes a measuring apparatus that can be used to appraise the effectiveness of nanofluids as new heat-transfer-enhancing fluids. A couple of apparatuses using fine hot wires as sensors have been proposed for this purpose; however, they have a technical weakness related to the uncertain working conditions of the sensor. The present method uses the convective heat transfer coefficient from a hot wire as an indication of the heat transfer effectiveness of the nanofluid, where the temperature of the wire remains constant during the experiment. The operating principle and experimental procedure are explained in detail, and the validity of the system is tested with pure base fluids. The effects of particle concentration, velocity, and temperature on the heat transfer coefficients of the nanofluids are discussed comprehensively using the experimental data for graphite nanolubrication oil.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.4
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• pp.1-8
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• 1999

Numerical study is carried out to investigate flow characteristics around an axisymmetric body with and without an integrated propulsor. The incompressible Reynolds-Averaged Navier-Stokes(RANS) equations are also solved using the finite volume method and the standard $k-\varepsilon$ turbulence model for turbulence closure. In order to investigate the propulsor-hull interaction, the induced velocity calculated by surface panel methods is utilized for the boundary condition at the propeller plane. The calculated results are compared to the experimental results. It is considered that the present numerical code can be used for design of an integrated propulsor.

• Proceedings of the KOR-BRONCHOESO Conference
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• 1996.04a
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• pp.88-88
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• 1996

선천성 또는 외상등에 의한 후천성 기도 협착의 치료는 아직도 어려운 문제중 하나로서 해결하여야 할 많은 과제를 내포하고 있다. 특히 안정되고 유연한 구조적인 골격과 함께 호흡성상피로 피복되는 기관점막은 기관기능 보존에 있어 필수적 조건이다. 저자들은 현재까지 보고자에 따라 견해 차이가 있는, 이식연골막 및 이식점막의 운명에 대하여 시기에 따른 형태학적 변화를 관찰하고자 하였다. 즉 저자들은 혈행성 복합피판의 형태로 이식한 점막에 일어나는 변화를 형태학적으로 연구하였으며, 대조군으로는 혈행이 유지되지 않는 유리이식(free graft)으로 구성된 복합피판을 이용하였다. 또한 면역조직화학적 염색을 통해 이식 초기에 일어나는, 이식점막과 결손부 주변조직사이의 재생능의 차이를 비교하고자 하였다. 토끼 40마리를 두 군으로 나누어 각 군당 20마리씩으로 하였으며 술후 각각 2주, 4주, 6주 및 8주에 기관에 이식한 피판을 조직학적으로 분석하였다. 섬모의 재생상태는 주사현미경을 통해 관찰하였으며 각 군당 4마리의 토끼를 술 후 1일과 2일에 Brdu-Anti Brdu로 염색하여 결손된 점막의 주변부와 이식한 점막사이의 재생능이 복합피판의 구성에 따라 어떤 차이가 있는지 알아보았다. 1. 혈행성의 복합피판으로 구성된 구강점막은 원주상피로 화생(metaplasia)하는 경향을 보였으나 유리 연골막에 부착한 구강점막에서는 괴사가 진행되면서 주위의 점막에서 성장해 들어가는 양상을 보였다. 2. Brdu-Anti Brdu 염색의 결과, 복합피판의 구성에 따라 이식점막과 주위 기관상피의 염색양상에 유의한 차이를 나타내었다.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.3
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• pp.87-99
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• 1994

Reynolds Averaged Navier-Stokes equations are solved numerically for the computation of turbulent flow around a Wigley double model. A second order finite difference method is applied for the spatial discretization on the nonstaggered grid system and 4-stage Runge-Kutta scheme for the numerical integration in time. In order to increase the time step, residual averaging scheme of Jameson is adopted. Pressure field is obtained by solving the pressure-Poisson equation with the appropriate Neumann boundary condition. For the turbulence closure, 0-equation turbulence model of Baldwin-Lomax is used. Numerical computation is carried out for the Reynolds number of 4.5 million. Comparisons of the computed results with the available experimental data show good agreements for the velocity and pressure distributions.

• Journal of the Korean Chemical Society
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• v.46 no.1
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• pp.19-25
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• 2002

We measured the variations of potentials and current densities for several polymers. The results were carefully examined to identify various factors such as temperature and pH to influence the potential and rate. The Tafel slope for anodic dissolution was determined by the polarization effect under these conditions. The optimum conditions were established for each case. The second anodic current density peak and maximum current density were designated as the relative polarization sensitivity $(I_r/I_f)$. The mass-transfer coefficient value $({\alpha})$ was determined by the Tafel slope for anodic dissolution on the basis of the polarization effect under optimum conditions.