• Journal of Advanced Marine Engineering and Technology
• /
• v.31 no.3
• /
• pp.272-281
• /
• 2007

A numerical simulation on nitrogen gas flow in a long parallel plate microchannel was performed to obtain the effect of compressibility and rarefaction on gaseous flow in microchannels. The simulation was based on steady. two dimensional compressible Navier-Stokes and energy equations with noslip and first order slip boundary conditions. The channel was $1.2{\mu}m$ deep and $3000{\mu}m$ long. The Reynolds numbers were in the range of order from $10^{-2}$ to $10^{-1}$. So the flow was assumed to be laminar. The computations were performed on various pressure ratios. The outlet pressure was fixed to atmospheric pressure. The outlet Knudsen number was 0.0585, consequently the flow was in the slip flow regime. The computations were performed with the assumption of isothermal channel walls. The results were compared with the experimental data. The agreement was good.

• 한국전산유체공학회:학술대회논문집
• /
• 2006.10a
• /
• pp.110-119
• /
• 2006

An accurate and cost efficient method PSE is used for the stability analysis of 2D or 3D compressible boundary layers. A highly accurate finite difference PSE code has been developed at a general curvilinear coordinate system using an implicit marching procedure to deal with a broad range of transition predictions problems. Evolution of disturbances in compressible flat plate boundary layers are studied for free-stream Mach numbers ranging from 0 to 1.5. The effect of mean-flow nonparallelism is found to be weak on two dimensional waves and strong on three dimensional waves. The maximum amplification rate increases monotonically with Mach number. The present PSE solutions are compared with previous numerical investigations and experimental results and are found to be in good agreement.

• 한국가시화정보학회:학술대회논문집
• /
• 2004.11a
• /
• pp.104-107
• /
• 2004

Most of the previous studies on natural convection were based on the numerical analysis, and some experimental studies considered the classic case of thermal convection. In this study, an adiabatic square body was located at the center of an enclosure between the bottom hot and top cold walls. And the measurement of the detailed temperature fields was conducted by the method of two-color Laser Induced Fluorescence using a Nd:Yag laser. As a result, heat transfer characteristics of natural convection with an adiabatic body was estimated as a function of time over a range of Rayleigh numbers.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2001.11a
• /
• pp.159-165
• /
• 2001

The fundamental fluid mechanics associated with the rotation of a smooth plane disk enclosed within a cylindrical chamber have been studied experimentally. In order to acquire systematic information pertinent to this problem torque and friction loss data were obtained over a wide range of disk Reynolds numbers for axial clearance-disk radius ratio H/R from 0.025 to 0.2 and radial tip gap-disk radius ratio s/R from 0.021 to 0.105. Loss analysis of hard disk drive(HDD) is presented to describe the contribution of windage loss of a rotating disk. The minimum loss from factor of HDD can be obtained from this analysis at each operation conditions.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.37 no.1
• /
• pp.65-72
• /
• 1995

This paper describes the applications of the SCS TR-20 hydrologic model for simula- tion of hourly inflow rates from sixty-six ungaged tributaries and subareas between the Naju station and the estuarin dam at the Yongsan River Basin. The model was tested for the ungaged conditions with fifteen storm events at Naju station. Hourly simulated run- off data were compared with the observed, and the results showed less correlationships between the two data than those from TANK model. The coefficients of correlation ranged from 0.74 to 0.87. The curve numbers and time of concentration were defined from topographic dta for each of sixty-six tributaries for the estuarine dam and used for TR-20 applications. The results were within an acceptable range of errors in simulating the inflow fluctuations for the flood forecasting at the estuarine dam.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.2 no.4
• /
• pp.268-278
• /
• 1990

Hydrodynamic stability equations are formulated for natural convection flows adjacent to a heated or cooled, inclined, isothermal surface in pure water at $4^{\circ}C$, where the density variation with temperature becomes nonlinear. The resulting stability equations, when reduced to ordinary differential equations by a similarity transformation, constitute a two-point boundary-value problem, which was solved numerically. It is found from the obtained stability results that the neutral stability curves are systematically shifted to have lower critical Grashof numbers, as the inclination angle of upward-facing plate increases. Also, the nose of the neutral stability curve becomes blunter as the angle increases. It implies that the greater the inclination of the upward-facing plate, the more susceptible of the flow to instability for the wide range of disturbance wave number and frequency.

• Journal of Wetlands Research
• /
• v.4 no.1
• /
• pp.33-41
• /
• 2002

Investigated was the ground-walking Coleoptera at the moor and adjacent forest at 800 m and rice paddies at lower level of 50 m in altitude. There were 5 species belonging to 5 genera and 2 families, 4 species belonging to 4 genera and 3 families, and 17 species belonging to 11 genera and 2 families respectively. Diplous depressus (Gebler) was the dominant species at the moor and forest in distinctive numbers, while Pheropsophus javanus (Dejean) was the one at the paddies. Three investigated sites supported independently their ground-walking Coleoptera groups. The moor group seemed to fail in establishing the resident Coleoptera community. The fact may imply to be related a kind of the pioneer species in early dry succession that D. depressus was found in a considerable range between forest and moor. The Coleoptera groups of moor and forest was different from that of paddies in species structure.

• Journal of the Society of Naval Architects of Korea
• /
• v.41 no.2
• /
• pp.70-78
• /
• 2004

The present study numerically investigates two-dimensional laminar flow past a circular cylinder in an aligned magnetic field using the spectral method. Numerical simulations are performed for flow fields with Re=100 and 200 in the range of 0$\leq$N$\leq$10, where Ν is the Stuart number that is the ratio of electromagnetic force to inertial force. The present study reports the detailed information of flow quantities on the cylinder surface at different Stuart numbers. It is shown that the vortex shedding can be controlled by the magnetic force representing the Stuart number. As Ν increases, the vortex shedding becomes weaker, resulting in drag reduction whose magnitude is the largest at a critical value. In addition, as the magnetic force increases, the lift amplitude decreases, reaching zero at the critical number.

• Journal of the Korean Home Economics Association
• /
• v.45 no.10
• /
• pp.97-111
• /
• 2007

This study examined the actual conditions of outdoor facilities and evaluated safety evaluations levels in playgrounds based on types of kindergartens. The samples for the survey were 100 kindergartens in Seongnam city Gyeonggi-Do province. Most outdoor facilities consisted of playgrounds with sand area and complex playing equipments, while wood-working area, sensory playing area, and mud playing area were less equipped than other facilities. In the case of outdoor playing facilities there were meaningful environmental differences within kindergartens. The public has less diversity in play areas and equipments and providing safety guidelines in playgrounds than privates. The score for the safety evaluations in the outdoor play environment was higher than average. As the range outdoor playing facilities increased, safety was dually considered, while kindergartens with a higher ratio of child-teacher numbers exhibited less consideration to playground safety.

• Proceedings of the KSME Conference
• /
• 2002.08a
• /
• pp.349-352
• /
• 2002

The time-development of the wake vortices of the unsteady viscous flow past a semicircular cylinder is simulated using the vortex particle methods for direct numerical simulations(DNS). The early wake behaviour of the flow behind an impulsively started a semicircualr cylinder is evaluated for a range of Reynolds numbers between 60 and 200 with opposite body configurations respectively. The diffusion scheme based on the particle strength exchange(PSE) is used to account far the viscous effect accurately. And the vorticity generation algorithm to enforce the no-slip boundary conditions is employed. In order to redistribute particles efficiently on the distorted Lagrangian grid the particle distribution technique is adaptively revised, while maintaining the uniform resolution. The results of the simulations are compared to other experimental results.