• Title/Summary/Keyword: Pressure Distribution

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Static Characteristics of Micro Gas-Lubricated proceeding Bearings with a Slip Flow (미끄럼 유동을 고려한 초소형 공기 베어링의 정특성)

  • Kwak, Hyun-Duck;Lee, Yong-Bok;Kim, Chang-Ho;Lee, Nam-Soo;Choi, Dong-Hoon
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 2002.05a
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    • pp.137-142
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    • 2002
  • The fluid mechanics and operating conditions of gas-lubricated proceeding bearings in micro rotating machinery such as micro polarization modulator and micro gas turbine are different from their larger size ones. Due to non-continuum effects, there is a slip of gas at the walls. Thus in this paper, the slip flow effect is considered to estimate the pressure distribution and load-carrying capacity of micro gas-lubricated proceeding bearings as the local Knudsen number at the minimum film thickness is greater than 0.01. Based on the compressible Reynolds equation with slip flow, the static characteristics of micro gas-lubricated proceeding bearings are obtained. Numerical predictions compare the pressure distribution and load capacity considering slip flow with the performance of micro proceeding bearings without slip f]ow for a range of bearing numbers and eccentricities. The results clearly show that the slip flow effect on the static characteristics is considerable and becomes more significant as temperature increases.

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Forecast on Internal Condensation at Ceiling of Super-high Apartment Building Faced with Open Air (외기에 면한 초고층 아파트 천정 내부결로 예측)

  • Ahn Jae-Bong;Song Young-Woong;Choi Yoon Ki
    • Proceedings of the Korean Institute Of Construction Engineering and Management
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    • autumn
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    • pp.626-629
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    • 2003
  • This study is to forecast possible occurrence of internal condensation around parpets and H-beam located at the inside of balcony ceilings on the uppermost floor of super-high apartment buildings faced with open air in order to provide dwellers with more comfortable environment in the related space and get rid of their uneasiness about the condensation. In this study, we estimated internal condensation. which vary in accordance with humidity pressure distribution, at curtain walls, stone panels or lower parts of slabs that constitute outer space of the residence and are weak against heat, through temperature forecast and temperature distribution interpretation program at normal two-dimension temperature.

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Characteristics of the Droplet Behavior in the Overlap Region of Twin Spray and in Single Spray (이중분무의 중첩영역과 단일분무에서 액적의 거동 특성)

  • Jung, Ji-Won;Cha, Keun-Jong;Kim, Duck-Jool
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.10
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    • pp.1300-1308
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    • 2000
  • The objectives of this study was to investigate the spray characteristics of single spray and twin spray in the overlap region such as mean axial velocity, mean radial velocity, mean droplet size and probability density function of droplet size. A phase doppler anemometer was used as the measurement system for droplet size and velocity. In case of single spray, injection pressure was varied from 0.2MPa to 0.7MPa. Mean axial velocity, mean radial velocity and droplet size were decreased as the distance below nozzle tip was increased. In case of twin spray, the spray characteristics were measured by varying the distance between two nozzles from 127mm to 155mm. In the overlap region, the boundary of the overlap region was determined by obtaining the distribution of mean axial and radial velocity. Droplet size was increased as the distance from nozzle tip was increased. It was found that the distribution of droplet size for twin spray in the overlap region was different to single spray.

A Study on the Bypass Flow Penetrating Through a Gas Diffusion Layer in a PEM Fuel Cell with Serpentine Flow Channels (사행유로를 갖는 고분자연료전지내부에서 가스확산층을 통과하는 반응가스 우회유동에 대한 연구)

  • Cho, Choong-Won;Ahn, Eun-Jin;Lee, Seung-Bo;Yoon, Young-Gi;Lee, Won-Yong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.33 no.4
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    • pp.288-297
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    • 2009
  • A serpentine channel geometry often used in a fuel cell has a strong pressure gradient between adjacent channels in specific regions. The pressure gradient helps some amount of reactant gas penetrate through a gas diffusion layer(GDL). As a result, the overall serpentine flow structure is slightly different from the intention of a designer. The purpose of this paper is to examine the effect of serpentine flow structure on current density distribution. By using a commercial code, STAR-CD, a numerical simulation is performed to analyze the fuel cell with high aspect ratio of active area. To increase the accuracy of the numerical simulation, GDL permeabilities are measured with various compressive forces. Three-dimensional flow field and current density distribution are calculated. For the verification of the numerical simulation results, water condensation process in the cathode channel is observed through a transparent bipolar plate. The result of this study shows that the region of relatively low current density corresponds that of dropwise condensation in cathode channels.

Formation of Silicon Particles Using $SiH_4$ pyrolysis at atmospheric pressure (상압에서 열분해법을 이용한 실리콘 입자 제조)

  • Woo, Dae-Kwang;Nam, Kyung-Tag;Kim, Young-Gil;Kim, Kwang-Su;Kang, Yun-Ho;Kim, Tae-Sung
    • Proceedings of the KSME Conference
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    • 2007.05a
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    • pp.126-129
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    • 2007
  • The particle formation using pyrolysis has many advantages over other particle manufacturing techniques. The particles by pyrolysis have relatively uniform size and chemical composition. Also, we can easily produce high purity particles. Thus, we studied the formation of silicon particles by pyrolysis of 50% $SiH_4$ gas diluted in Ar gas. A pyrolysis furnace was used for the thermal decomposition of $SiH_4$ gas at $800^{\circ}C$ and atmospheric pressure. The aerosol flow from furnace is separated into two ways. The one is to the Scanning Mobility Particle Sizer (SMPS) for particle size distribution measurement and the other is to the particle deposition system. The produced silicon particles are deposited on the wafer in the deposition chamber. SEM measurement was used to compare the particle size distribution results from the SMPS. Depending on the experimental conditions, particles of high concentration in the $30\sim80$ nm size range were generated.

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Analytical solutions for mechanical response of circular tunnels with double primary linings in squeezing grounds

  • Wu, Kui;Shao, Zhushan;Hong, Siyuan;Qin, Su
    • Geomechanics and Engineering
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    • v.22 no.6
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    • pp.509-518
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    • 2020
  • Multi-layered primary linings have been proved to be highly effective for tunneling in severe squeezing grounds. But there still has not existed well-established design method for it. Basically, there are two main critical problems in this method, including determinations of allowable deformation and distribution of support stiffness. In order to address such problems, an attempt to investigate the mechanical response of a circular tunnel with double primary linings is performed in this paper. Analytical solutions in closed form for stresses and displacements around tunnels are derived. In addition, the effectiveness and reliability of theoretical formulas provided are well validated by using the numerical method. Finally, based on the analytical solutions, a parametric investigation on the effects of allowable deformation and distribution of support stiffness on tunnel performance is conducted. Results show that the rock pressure and displacement are significantly affected by these two design parameters. It can be found that rock pressure decreases as either allowable deformation increases or stiffness of the first primary lining decreases, but rock displacement shows an opposite trend. This paper can provide a useful guidance for the design of multi-layered primary linings.

Do Phillips Curve Respond Asymmetrically to Unemployment? Evidence from Korea and the U.S.

  • Lee, Donghae;Lee, Sangki
    • The Journal of Industrial Distribution & Business
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    • v.9 no.3
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    • pp.19-29
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    • 2018
  • Purpose - This study empirically analyses the changes in unemployment rates to understand push factors of generating wage pressure and how it affects the aggregate demand in Korea and the United States. We use a structural macroeconomic model which is centered on the labor market and simultaneously explains the natural rate of unemployment and deviations. Research design, data and methodology - We attempt to empirically analyse the unemployment rates through two countries to analyse the economic effects of real wages and aggregate demand between 2000 and 2016. We introduce having estimated the whole model that the growth of unemployment into the part caused by each of these factors. Results - The results of this study show that in the long run, there is not only a natural level of employment but also a natural level of real demand are positively related. in the short run, demand can vary from bring about changes in employment by means of price or wage surprises. Conclusions - The pressure of demand in the labor market shows up strongly in both countries. The estimated labor-demand equation are consistent with this framework and generally have well defined real wage and demand effects.

Numerical simulations of interactions between solitary waves and elastic seawalls on rubble mound breakwaters

  • Lou, Yun-Feng;Luo, Chuan;Jin, Xian-Long
    • Structural Engineering and Mechanics
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    • v.53 no.3
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    • pp.393-410
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    • 2015
  • Two dimensional numerical models and physical models have been developed to study the highly nonlinear interactions between waves and breakwaters, but several of these models consider the effects of the structural dynamic responses and the shape of the breakwater axis on the wave pressures. In this study, a multi-material Arbitrary Lagrangian Eulerian (ALE) method is developed to simulate the nonlinear interactions between nonlinear waves and elastic seawalls on a coastal rubble mound breakwater, and is validated experimentally. In the experiment, a solitary wave is generated and used with a physical breakwater model. The wave impact is validated computationally using a breakwater - flume coupling model that replicates the physical model. The computational results, including those for the wave pressure and the water-on-deck, are in good agreement with the experimental results. A local breakwater model is used to discuss the effects of the structural dynamic response and different design parameters of the breakwater on wave loads, together with pressure distribution up the seawall. A large-scale breakwater model is used to numerically study the large-scale wave impact problem and the horizontal distribution of the wave pressures on the seawalls.

Application of the Level Set Method for Free Surface Modeling (자유수면의 모의를 위한 레블셑V 기법의 적용)

  • Lee, Hae-Gyun
    • The Journal of the Korea Contents Association
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    • v.10 no.10
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    • pp.451-455
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    • 2010
  • Hydraulics usually deals with flows with free surface. When the surface curvature is small, the assumption of hydrostatic pressure distribution is enough. However, in the case, when the curvature is big, the non-hydrostatic pressure distribution should be taken into account and the Navier-Stokes equations should be employed instead of the depth-averaged shallow water equations. For the simulation of two immiscible fluids with different characteristics (e.g. water and air, water and oil), the level set method is selected for this purpose. The developed model is applied to classical dam break problem and the computational results are compared with the experimental data. The effectiveness of the developed model is confirmed.

Combustion Characteristics of Full-scale Gas Generator for 30 ton Class Liquid Rocket Engine (30톤급 실물형 가스발생기 연소 특성)

  • Ahn, Kyu-Bok;Seo, Seong-Hyeon;Lim, Byoung-Jik;Kim, Jong-Gyu;Lee, Kwang-Jin;Han, Yeoung-Min;Choi, Hwan-Seok
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2008.05a
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    • pp.129-132
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    • 2008
  • Combustion characteristics of a gas generator for a 30 ton-class liquid rocket engine were studied. At the early stage of development, the combustion tests of the gas generator were performed by only using the nozzle which substitute for a turbine manifold exit. Then, the extension tube was applied between the gas generator and the nozzle for imitating the resonant mode of gas generator and turbine manifold. Finally, the hot-firing tests were performed on the condition of connecting the gas generator with the turbine manifold. In the paper, the step-by-step results such as temperature distribution and pressure fluctuations were analyzed.

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