• 전기학회논문지
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• 제67권6호
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• pp.702-707
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• 2018

In case of Lighting occurs in Domestic combined distribution line, normally the voltage for the neutral line increase dramatically. General connection for underground cable is bundled common earth type so the lightning over voltage increase at the concentric-neutral line is not big enough to give impact on cable sheath. But in case of Non bundled common earth type it is necessary to analyze the phenomena on cable sheath caused by lightening overvoltage. Especially pole and cable joint are the core factor to consider. In this paper concrete pole and cable joint were evaluated in case of Non bundled common earth type combined distribution Line. EMTP simulation model has been designed and several case study were made. Also several experimental test were made to verify the simulation result.

• 소성∙가공
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• 제23권5호
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• pp.275-281
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• 2014

Broaching is widely used for the machining of inner shaped slots in work-pieces. The broach tool is moved vertically (usually by hydraulic power) through the work-piece. Broaching occurs with the work-pieced fix while the broach tool traverses through material and shears it. To produce a T/F driven gear both an outside cutting and an inside cutting are needed. The outside cut determines the tooth profile and the inside cut determines the inner dimension. Broaching can cause problems with concentricity. In the current study, the characteristics of shearing along the cutting blade and the broaching of a T/F driven gear are considered.

• 태양에너지
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• 제7권1호
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• pp.53-60
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• 1987

Natural convection in the annulus between concentric inclined cylinders has been studied by the numerical analysis. Governing equations are numerically solved by means of successive over-relaxation methods for a range in orientation from horizontal to vertical. It is found that flow patterns can also be observed the co-axial double spiral. As the angle of inclination is increased, the center of the eddy is shifted into the lower part of annulus and flow structure is apparently changed. In the present study, the maximum local Nusselt numbers for the inner and outer walls at the vertical cylinder increase more than those at the horizontal cylinder by 71%, 42% respectively. Consequently the effect of inclination on the heat transfer is considerably large.

• 대한설비공학회지:설비저널
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• 제17권4호
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• pp.328-335
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• 1988

Natural convection in annuli between the horizontal and vertical concentric cylinders for ratio of the inner to the outer radius, $R_1$=0.85, 0.35 has been studied by the numerical analysis. Governing equations are numerically sloved by means of Successive over-relaxation methods. It is found that maximum local Nusselt number, $Nu_{1.max}$ at the inner cylinder and $Nu_{2.max}$ at the outer cylinder for $R_2$=0.35 have maxima at ${\phi}=0^{\circ}$, ${\phi}=180^{\circ}$ ${\xi}=0.4$, 1.6 for horizontal cylinder and at bottom, top for vertical cylinder, respectively. In the present study, mean Nusselt numbers at the vertical cylinder increased more than that at the horizontal cylinder by about 64% for $R_1$=0.35.

• 한국수소및신에너지학회논문집
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• 제32권1호
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• pp.63-67
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• 2021

Accurate measurements of the heat transfer coefficients of concentric annular space for the test section is important to measure the tube-side heat transfer coefficients of working fluids. This paper presents the annular side heat transfer coefficients of concentric annuli with variation of tube diameter ratios using Wilson plot method. The test facility has a straight, horizontal test section with an active length of 3.0 m. Inner/outer diameters of test tubes are 7.0/7.5 and 8.0/8.56 mm, respectively. An outer diameter of annulus side is 16.0 mm. The test results show that convective heat transfer coefficients in annuli increase with annular diameter ratio. The correlations for convective heat transfer coefficients in annuli are also developed.

• 대한설비공학회지:설비저널
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• 제15권2호
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• pp.196-203
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• 1986

The melting phenomena of horizontal cylindrical ice-bar immersed in water and air concentrically in the cylinder are experimentally investigated for the temperature range from $3.5^{\circ}C\;to\;2.5^{\circ}C$. The shapes of the melting ice-bar are recorded photographically by the shadowgraph method. The shadowgraphs of the melting ice-bar show that water adjacent to the bar flows upward for the temperature range from $3.5^{\circ}C\;to\;5.8^{\circ}C$ while above $5.8^|\circ}C$ the flow is downward direction. The local and average Nusselt numbers are obtoined with the recorded shadowgraphs and comparator. Melting shapes of the ice-bar in the air show the vortex motion in the bottom portion of the bar, whereas no vortex motion appears in the bottom portion when the bar is melted in the water.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2010년도 춘계학술발표대회
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• pp.135-138
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• 2010

무선 센서 네트워크 (WSN)를 구성하는 노드들은 그 크기가 매우 작고 보유 에너지 량이 한정되어 있는 등의 제약적인 환경 때문에 에너지 효율 및 보안적인 면에서 취약하다. EECCH (Energy-Efficient Clustering scheme with Concentric Hierarchy)는 WSN에서 동심원 기반의 계층화를 통해 에너지 효율을 높인 중앙 처리 방식의 클러스터링 기법이다. WSN에서 보안 위협에 대처하기 위해 키 분배 문제를 해결해야 한다. EECCH의 계층적인 환경에서 안전한 보안 기능을 제공하기 위해 여러 기법이 복합적으로 사용되어야 한다. 본 논문에서는 사전 키 분배 기법, 단일 해쉬 함수 등의 기법을 적용하여 기밀성, 무결성, 적시성 등의 보안 요구 사항을 제공하는 향상된 EECCH 기법을 제안한다.

• 대한설비공학회지:설비저널
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• 제16권4호
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• pp.383-391
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• 1987

An experimental investigation has been conducted to determine the flow pattern for two-component , two-phase mixtures which flow vertically upwards in concentric annuli based on the measurement for the local void fraction and the distribution of the local void fraction in various radial locations in the annular gap. The annular test section consists of a lucite outer tube whose inside diameter is 38mm and a stainless steel rod, The rod diameter is either :2mm,16mm or 20mm. It is demonstrated that the probability density function of the fluctuations in void fraction may be used as an flow pattern indicator and the local void fraction distribution depends on the flow pattern and radial location in the annular passage.

• 대한설비공학회지:설비저널
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• 제16권5호
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• pp.516-524
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• 1987

This paper presents experimental data of fluctuation characteristics of local void fraction of air-water two-phase flow which are associated with the flow pattern, annular gap size and radial location in vertical concentric annuli with coefficient of skewness and kurtosis. The annular gap widths are 13mm, 11mm, and 9mm for a 38m inner diameter as the lucite outer tube. A electrical conductivity probe was used to measure the local void fraction and traversed diametrically from inner wall to outer wall using radial increments of 2mm. It was shown that distribution of the coefficient of skewness and kurtosis, which is related that the one is the asymmetry and the other peakness of local void fraction distribution was influenced by flow pattern, annular gap size and radial location.

• 대한환경공학회지
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• 제34권2호
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• pp.103-108
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• 2012

연소과정 중에 발생하는 질소산화물을 저감하는 기술인 MILD 연소로는 연소용 공기 및 연료로 고온의 배기가스가 유입되는 양에 따라 질소산화물 저감 특성이 많은 영향을 받는다. 일반적인 MILD 연소로는 연료와 연소용 공기는 수직 상향방향이고 배기가스는 수직하향 방향으로 흐르면서 배기가스가 유입되는데 이러한 형태보다 더욱 배기가스의 유입량을 증가시키기 위한 방법으로 동심원관형태의 MILD 연소로를 사용하고 있다. 본 연구에서는 바깥 원통의 배기가스 통로에서 안쪽 원통의 연소통로 사이에 연결관을 설치하고 배기가스를 유입하기 위한 공기노즐을 동심원관 형태로 설치하여 공기분사속도, 노즐 직경, 배기가스측 압력과 연소로측 압력 차이의 변화에 따른 유입량 특성을 수치해석을 통해 살펴봄으로써 MILD 연소로에서 더욱 적극적인 배기가스의 유입량 특성을 파악하는 것을 연구하였다. 공기노즐 분사속도의 증가에 따라 유입량은 속도의 제곱근에 비례하는 것을 알았고 배기가스 측과 연소로 측의 압력차의 크기에 선형적으로 감소하는 것을 관찰하였다. 공기노즐 출구 위치의 변화는 유입량 변화에 큰 영향이 없음을 알 수 있었다.