• 대한기계학회논문집
• /
• 제19권3호
• /
• pp.771-783
• /
• 1995

A simplified model for the so-called ACRT(accelerated crucible rotation technique) Bridgman crystal growth was considered in order to investigate the principal effects of the periodic variation of angular velocity. Numerical solutions were obtained for Ro=0.5, Ra=4.236*10$_{6}$ and E=2.176*10$^{-3}$ . The effects of spin-up process combined with natural convection was investigated as a preliminary study. The spin-up time scale for the present problem was a little larger than that observed for homogeneous spin-up problems. Numerical results reveal that over a time scale of (H$^{2}$/.nu..omega.$_{f}$)$^{1}$2/ the forced convection due to the formation of Ekman layer predominates. When the state of rigid body rotation is attained, natural convection due to buoyancy emerges as the main driving force and them the steady-state is approached asymptotically. Based on our preliminary results with simple spin-up, several fundamental features associated with variation of rotation speed are successfully identified. When a periodic variation of angular velocity was imposed, the system response was also periodic. Due to effect of mixing, the heat transfer was enlarged. From the analysis of time-averaged Nusselt number along the bottom surface the effect of a periodic variation of angular velocity on the interface location could be indirectly identified.d.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2006년도 정기 학술대회 논문집
• /
• pp.405-412
• /
• 2006

Among the various problems involved in the structural analysis of the Korean traditional wooden structure, the analytical model for the Kong-Po is controversial subject as usual. While some experiments are tried for establishing the basis of analytical models, most of these experiments are performed using scale down specimens. So, it is not possible to apply these experimental results to structural analysis of Korean traditional wooden structure directly. A numerical study for analogizing the stiffness of full scale Kong-Po structure is performed on the basis of experimental specimen. Some parameter studies using finite element method are made in this study. The finite element analysis used in this study is geometric material nonlinear analysis. The stiffness of Kong-Po structure found out in this study can be used for modelling the joints of the Korean traditional wood structure in frame analysis.

• Wind and Structures
• /
• 제29권6호
• /
• pp.405-416
• /
• 2019

Aerodynamic characteristic of a small scale wind turbine under the influence of an incoming uniform wind field is studied using k-ω Shear Stress Transport turbulence model. Firstly, the lift and drag characteristics of the blade section consisting of S826 airfoil is studied using 2D simulations at a Reynolds number of 1×10⁵. After that, the full turbine including the rotational effects of the blade is simulated using Multiple Reference Frames (MRF) and Sliding Mesh Interface (SMI) numerical techniques. The differences between the two techniques are quantified. It is then followed by a detailed comparison of the turbine's power/thrust output and the associated wake development at three tip speeds ratios (λ = 3, 6, 10). The phenomenon of blockage effect and spatial features of the flow are explained and linked to the turbines power output. Validation of wake profiles patterns at multiple locations downstream is also performed at each λ. The present work aims to evaluate the potential of the numerical methods in reproducing wind tunnel experimental results such that the method can be applied to full-scale turbines operating under realistic conditions in which observation data is scarce or lacking.

• 농촌계획
• /
• 제6권2호
• /
• pp.43-49
• /
• 2000

Buffer zone selection technique for natural purification of livestock wastewater within a small agricultural watershed was developed using Geographic Information Systems. The technique was applied to $4.12\;km^2$ watershed located in Gosan-myun, Ansung-gun which have 20 livestock farmhouses. As a necessary data for selecting process, feedlot site map, digital Elevation Model (DEM), stream network, soil and land use map were prepared. By using these data, wastewater moving-path tracing program from each feedlot to the stream was developed to get the basic topographic factors; average slope through the paths, distance to the nearest stream and watershed outlet. To identify the vulnerable feedlots for storm event, the grid-based storm runoff model (Kim, 1998; Kim et al., 1998) was adopted. The result helps to narrow down the suitable area of buffer zone, and finally by using subjective but persuasive conditions related to elevation, slope and land use, the suitable buffer zones were selected.

• 한국가시화정보학회지
• /
• 제18권2호
• /
• pp.28-34
• /
• 2020

In this study, we numerically investigated the thermal stratification in solar seasonal thermal storage tanks. The vertical in/out flows were unsuitable for the thermal stratification in a large scale. The effect of an aspect ratio (AR) on the thermal stratification was investigated. When AR was less than 2, water adheres and flows along the upper wall due to buoyance and the surface effect. Thereafter, hot water flows down and a large scale vortex occurs in entire tank. For high AR, jet flows ejected from the inlet pipe impinges to the opposite wall and splits. The divided flows create two vortex flows in the upper and lower regions. These different flows strongly influence temperature and thermal stratification. The thermal stratification was evaluated in terms of the thermocline thickness and degree of stratification. Compared to ARs, the maximum degree of stratification was obtained with AR of 5 having the minimum thermocline thickness.

• 천문학회보
• /
• 제38권1호
• /
• pp.40.1-40.1
• /
• 2013

The HI ring serendipitously found in the Leo I galaxy group is unique in size in the Local Universe. It is ~200kpc in diameter with MHI~$1.67{\times}109M{\odot}$, surrounding a pair of early type galaxies M105 and NGC 3384. Its origin is still under debate whether it is the remnant of formation of a galaxy group (primordial) or formed from stripped material during galaxy-galaxy interaction (tidal origin). Intriguingly a number of dwarf galaxies have been identified along the gas ring (with or without optical counterpart). Various properties of these dwarf galaxies such as dark matter content, color, and/or metallicity will allow us to pin down the origin of this large scale HI ring. We have obtained a mosaicked CFHT MegaCam image and the EVLA HI cube of the large scale gas ring. In this work we present optical and gas properties of dwarf galaxies identified in the CFHT data.

• 한국정보통신학회:학술대회논문집
• /
• 한국해양정보통신학회 2002년도 추계종합학술대회
• /
• pp.494-497
• /
• 2002

본 논문에서는 halo doping profile을 갖는 나노구조 LDD MOSFET의 문턱전압에 대한 시뮬레이션 결과를 나타내었다. 소자 크기는 generalized scaling을 사용하여 100nm에서 40nm까지 스케일링하였다. Van Dort Quantum Correction Model(QM)을 사용하여 정전계 스케일링과 정전압 스케일링에 대한 문턱 전압과 각각의 게이트 oxide 두께에 대한 direct tunneling 전류를 조사하였다. 게이트 길이가 감소할 때 정전계 스케일링에서는 문턱전압이 감소하고, 정전압 스케일링에서는 문턱전압이 증가하는 것을 알 수 있었고, 게이트 oxide두께가 감소할 때 direct tunneling 전류는 증가함을 알 수 있었다. 감소하는 채널 길이를 갖는 MOSFET 문턱전압에 대한 roll-off 특성을 최소화하기 위해 generalized scaling에서 $\alpha$값은 1에 가깝게 되는 것을 볼 수 있었다.

• Journal of Advanced Marine Engineering and Technology
• /
• 제32권4호
• /
• pp.498-505
• /
• 2008

Many researches have been studied on in-cylinder flow as one of dominant effects for an engine combustion. The combustion phenomena of reciprocating engine is one of the most important processes affecting performance and emissions. One effective way to improve the engine combustion is to control the motion of the charge inside a cylinder by means of optimum induction system design. It is believed that the tumble and swirl motion generated during intake breaks down into small-scale turbulence in the compression stroke of the cycle. However, the exact nature of their relationship is not well known. To know this relationship definitely, this paper describes analytical results of the tumble motion, swirl motion, turbulence intensity, turbulence inside the cylinder of marine engine. 3-D computation has been performed by using STAR-CD solver and es-ice.

• 대한조선학회지
• /
• 제21권2호
• /
• pp.9-17
• /
• 1984

Laminar and turbulent boundary layers on a rotating sector and a helical blade are calculated by differential method. The estimation of three dimensional viscous flows provide quite useful informations for the design of propellers and turbo-machinery. A general method of calculation is presented in this paper. Calculated laminar boundary layer on a sector shows smooth development of flows from Blasius' solution at the leading edge to von Karman's solution of a rotating disk at the down-stream. Eddy viscosity model is adopted for the calculation of turbulent flows. Turbulent flows on a rotating blade show similar characters as laminar flows. But cross-flow angle of turbulent flows are reduced in comparison with laminar boundary layers. Effects of rotation make flow structures significantly different from two-dimensional flows. In the range of Reynolds number of model scale propellers, large portion of the blade are still in the transition region from laminar to turbulent flows. Therefore viscous flow pattern might be quite different on the blade of model propeller. The present method of calculation is to be useful for the research of scale effects, cavitation, and roughness effects of propeller blades.

• 대한조선학회논문집
• /
• 제45권3호
• /
• pp.238-246
• /
• 2008

In the present study, the influences on the gap cavitaiton of the semi-spade rudder are investigated experimentally in the condition with propeller and hull wakes. To reduce the scale effect in the given experimental conditions, 1/28.5-scale-down models of propeller and rudder are manufactured. We have the propeller rotate ahead of the rudder, inducing the three dimensional effects originated from the propeller action. Experimental methods are composed of the cavitation observation using high speed camera, PIV (particle image velocimetry) measurements to visualize the cavitaition and flows around the gap. The propeller slipstream affects both of the gap flows and cavitation of the rudder.