• Title/Summary/Keyword: Boundary effect

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A Boundary Protection for Power Distribution Line Based on Equivalent Boundary Effect

  • Zhang, Xin;Mu, Long-Hua
    • Journal of Electrical Engineering and Technology
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    • v.8 no.2
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    • pp.262-270
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    • 2013
  • A boundary protection method for power distribution line based on equivalent boundary effect is presented in this paper. In the proposed scheme, the equivalent resonance component with a certain central frequency is sleeve-mounted at the beginning of protected zone. The 'Line Boundary' is built by using boundary effect, which is created by introducing impedance in the primary-side of line. The 'Line Boundary' is significantly different from line wave impedance. Therefore, the boundary protection principle can be applied to power distribution line without line traps. To analyze the frequency characteristic corresponding to traveling-waves of introducing impedance in the primary-side of line, distributed parameters model of equivalent resonance component is established. The results of PSCAD/EMTDC simulation prove the obvious difference of voltage high frequency component between internal faults and external faults due to equivalent resonance component, and validate the scheme.

Effect of Boundary Layer Thickness on the Flow Characteristics around a Rectangular Prism (직사각형 프리즘 주위의 유동특성에 대한 경계층 두께의 영향)

  • Ji, Ho-Seong;Kim, Kyung-Chun
    • Proceedings of the KSME Conference
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    • 2001.11b
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    • pp.306-311
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    • 2001
  • Effect of boundary layer thickness on the flow characteristics around a rectangular prism has been investigated by using a PIV(Particle Image Velocimetry) technique. Three different boundary layers(thick, medium and thin)were generated in the Atmospheric Boundary Layer Wind Tunnel at Pusan National University. The thick boundary layer having 670mm thickness was generated by using spires and roughness elements. The medium thickness of boundary layer$(\delta=270mm)$ was the natural turbulent boundary layer at the test section with fully long developing length(18m). The thin boundary layer with 36.5mm thickness was generated by on a smooth panel elevated 70cm from the wind tunnel floor. The Reynolds number based on the free stream velocity and the height of the model was $7.9{\times}10^3$. The mean velocity vector fields and turbulent kinetic energy distribution were measured and compared. The effect of boundary layer thickness is clearly observed not only in the length of separation bubble but also in the reattachment points. The thinner boundary layer thickness, the higher turbulent kinetic energy peak around the model roof. It is strongly recommended that the height ratio between model and approaching boundary layer thickness should be a major parameter.

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The Effect of Exposure in Elevated Temperatures on Bending Properties of Wood

  • Park, Joo-Saeng;Lee, Jun-Jae
    • Journal of the Korean Wood Science and Technology
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    • v.27 no.4
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    • pp.20-29
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    • 1999
  • Temperature has important effect on mechanical properties of wood. These effect needs to be understood and taken into account in the structural use of wood. Furthermore, the effect of cooling after exposing to high temperature must be explained. In this study, the effect of temperature, exposure time, specific gravity, and cooling on bending properties were investigated. The boundary temperatures at which bending MOE and MOR reduced rapidly were approximately $200^{\circ}C$ and $150^{\circ}C$, respectively. This boundary temperature was nearly constant with independence of species(specific gravity), exposure time, and cooling. Above the boundary temperature, the effect of exposure time was increased with temperature and the reduction of bending MOE and MOR for Japanese Larch with relatively higher specific gravity was smaller than that of Hem-fir. The recovery of bending MOE and MOR after cooling was also more significant above the boundary temperature than below. The degree of cooling effect was larger for MOR than MOE. Consequently, bending properties of wood in elevated temperatures should be considered in terms of the boundary temperature, $200^{\circ}C$ for bending MOE, $150^{\circ}C$ for MOR, and these boundary temperatures must be considered an important factor. Furthermore, to evaluate the safety of structure, the recovery after cooling should be considered.

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Turbulent Flow Simulations on 2-Dimensional Ground Effect Part II. Study on the Effects of Ground Boundary Conditions (2차원 지면효과에 대한 난류 유동장 해석 Part II. 지면경계 조건의 영향에 대한 연구)

  • Kim, Yoon-Sik;Lee, Jae-Eun;Kim, Eu-Gene;Kwon, Jang-Hyuk
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.35 no.8
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    • pp.670-676
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    • 2007
  • A comparative study on ground boundary conditions for the airfoil in ground effect has been carried out. The objective of the present study is to clarify effects of the ground boundary conditions so that it will be helpful to analyse results of wind tunnel tests using the fixed ground board or the image method. A low Mach number preconditioned Navier-Stokes solver using the overlap grid method has been applied. It has been turned out that results with the symmetric boundary condition are almost the same to those with the moving boundary condition. Results with the fixed ground boundary show discrepancy to those with the moving boundary condition when flow separation on the ground board takes place.

Effect of Interconnected Boundary Between Journal and Thrust Bearings on the Performance of Self-Acting Air-Lubricated Bearings (저널-스러스트 베어링 사이의 상호 연결 경계가 동압 공기 윤활 베어링의 성능에 미치는 영향)

  • Kang, Ji-Hoon;Kim, Sung-Ki;Kim, Kyung-Woong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.4
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    • pp.608-613
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    • 2003
  • In this paper, the effect of interconnected boundary between journal and thrust bearings on the performance of self-acting air-lubricated bearings is investigated. When journal and thrust bearings have common boundary, conventional boundary condition which assumes that the boundary pressure is equal to atmosphere is no more valid. Instead, new boundary condition by mass conservation at interconnected boundary is needed. To do this, a duct model satisfying mass conservation at interconnected boundary is developed. Using this model, pressure distribution at interconnected boundary is numerically analyzed with changing the volume of interconnecting part. As a result, it is shown that load capacity of thrust bearing can be greatly increased when journal and thrust have a common boundary.

The Effect of Microstructure on the Ionic Conductivity in the $Bi_2O_3-CaO$ System ($Bi_2O_3-CaO$계에서의 미세구조가 이온 전도도에 미치는 영향)

  • 백현덕
    • Journal of the Korean Ceramic Society
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    • v.32 no.3
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    • pp.359-365
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    • 1995
  • The grain boundary effect on the ionic conductivity was investigated using a.c. admittance analysis in (Bi2O3)0.715(CaO)0.285 oxygen-ion conducting solid electrolyte. As a separated arc representing grain boundary polarization was not observed in the admittance plane, bulk conductivity was measrued for samples with various grain sizes in the temperature range from 48$0^{\circ}C$ to 72$0^{\circ}C$ and the conductivity distribution between grain interior and grain boundary was determined by the reported analytical methods. In the above temperature range, grain boundary worked as a high conductive path instead of blocking layer and ionic conduction through grain boundary was significant. The activation energy for conduction through grain and grain boundary was 78 and 106 kJ/mol, respectively.

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A study on the relation between space boundary system and spatial effect -focused on the space analysis case of Korean traditional houses- (경계구조 유형과 공간적 효과의 상관관계에 대한 조사연구 - 서울경기 소개 조선후기 상류주택을 중심으로 -)

  • 윤갑근;이시웅
    • Korean Institute of Interior Design Journal
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    • no.26
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    • pp.42-48
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    • 2001
  • This study is on the relations between space boundary system and spatial effects. The system is consist of circulation axis & territory and vision axis & vision limit. The former is the spatial characteristic and the later is the time one. The purpose of this case study is confirm the correlation of the both and the spatial effect which is caused by space boundary system. Boundary is enable us to cognize 'territory' and intermediary of each territories. The facts that forms space boundary system are circulation axis & territory and vision axis & vision limit. The space boundary system could be categorized by congregation of these facts. and categorizing is determined with agreement degree of each couple of facts. Categorizing facts on the space boundary system are relevant to spatial effect, especially territory, directness, continuity and concentration.

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Effect of Boundary Layer Thickness on the Flow Around a Rectangular Prism (직사각형 프리즘 주위의 유동구조에 대한 경계층 두께의 영향)

  • Ji, Ho-Seong;Kim, Kyung-Chun;Lee, Seung-Hong;Boo, Jeong-Sook
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.6
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    • pp.893-901
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    • 2002
  • Effect of boundary layer thickness on the flow characteristics around a rectangular prism has been investigated by using a PIV(Particle Image Velocimetry) technique. Three different boundary layers(thick, medium and thin)were generated in the Atmospheric Boundary Layer Wind Tunnel at Pusan National University. The thick boundary layer having 670 mm thickness was generated by using spires and roughness elements. The medium thickness of boundary layer($\delta$=270 mm) was the natural turbulent boundary layer at the test section floor with fairly long developing length(18 m). The thin boundary layer($\delta$=36.5 mm) was generated on the smooth panel elevated 70cm from the wind tunnel floor. The Reynolds number based on the free stream velocity(3 ㎧) and the height of the model(40 mm) was 7.9$\times$10$^3$. The mean velocity vector fields and turbulent kinetic energy distributions were measured and compared. The effect of boundary layer thickness was clearly observed not only in the length of separation bubble but also in the location of reattachment point. The thinner the boundary layer thickness, the higher the turbulent kinetic energy Peak around the model roofbecame. It is strongly recommended that the height ratio between the model and the approaching boundary layer thickness should be encountered as a major parameter.

Effect of Boundary Conditions on the Stability Characteristics of a Nanotube with Scale Effect (Scale Effect를 고려한 경계조건에 따른 나노튜브의 안정성 해석)

  • Choi, Jong-Woon;Yun, Kyung-Jae;Kim, Sung-Kyun;Park, Sang-Yun;Song, Oh-Seop
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2012.04a
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    • pp.923-928
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    • 2012
  • In this paper, static and oscillatory instability of a nanotube conveying fluid and modelled as a thin-walled beam is investigated. Analytically nonlocal effect, effects of boundary conditions, transverse shear and rotary inertia are incorporated in this study. The governing equations and the two different boundary conditions are derived through Hamilton's principle. Numerical analysis is performed by using extend Galerkin method which enables us to obtain more exact solutions compared with conventional Galerkin method. Variations of critical flow velocity for different boundary conditions of a nanotube with analytically nonlocal effect, partially nonlocal effect and local effect of a nanotube are investigated and pertinent conclusion is outlined.

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Absence of Distinctively High Grain-Boundary Impedance in Polycrystalline Cubic Bismuth Oxide

  • Jung, Hyun Joon;Chung, Sung-Yoon
    • Journal of the Korean Ceramic Society
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    • v.54 no.5
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    • pp.413-421
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    • 2017
  • In this work, we studied a fluorite structure oxides: Yttria stabilized zirconia, (YSZ); Gd doped $CeO_2$ (GDC); erbia stabilized $Bi_2O_3$ (ESB); Zr doped erbia stabilized $Bi_2O_3$ (ZESB); Ca doped erbia stabilized $Bi_2O_3$ (CESB) in the temperature range of 250 to $600^{\circ}C$ using electrochemical impedance spectroscopy (EIS). As is well known, grain boundary blocking effect was observed in YSZ and GDC. However, there is no grain boundary effect on ESB, ZESB, and CESB. The Nyquist plots of these materials exhibit a single arc at low temperature. This means that there is no space charge effect on ${\delta}-Bi_2O_3$. In addition, impedance data were analyzed by using the brick layer model. We indirectly demonstrate that grain boundary ionic conductivity is similar to or even higher than bulk ionic conductivity on cubic bismuth oxide.