• Title/Summary/Keyword: Expansion Method

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Application of Matched Asymptotic Expansion for Designing a Leading Edge of Super-cavitating Foil

  • Yim, Bo-hyun
    • Journal of Ship and Ocean Technology
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    • v.1 no.2
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    • pp.11-18
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    • 1997
  • The leading edge of a low-drag super-cavitating foil has been made to be thick enough by using a point drag which is supposed to be a linear model of the Kirchhoff lamina. In the present paper, the relation between the point drag and the Kirchhoff lamina is made clear by analyzing the cavity drag of both models and the leading edge radius of the point drag model and the lamina thickness of Kirchhoff\`s profile K. The matched asymptotic expansion is effectively made use of in designing a practical super-cavitating fool which is not only of low drag but also structurally sound. Also it has a distinct leading edge cavity separation point. The cavity foil shapes of trans-cavitating propeller blade sections designed by present method are shown.

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Identification Using Orthonormal Functions for Linear Dynamical Systems

  • Bae, Chul-Min;Wada, Kiyoshi;Imai, Jun
    • 제어로봇시스템학회:학술대회논문집
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    • 2000.10a
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    • pp.469-469
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    • 2000
  • The use of orthogonal functions with the aim of adapting the system and signal representation to the specific properties of the systems and signals has a long history. A least-squares identification method is studied that estimates a finite number of expansion coefficients in the series expansion of a transfer function, where the expansion is in terms of recently introduced generalized orthogonal functions. It is shown that there exist orthogonal functions that are generated by stable linear dynamical systems.

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Adhesion between the Nylon Cylinder and Steel Shaft by Expansion Fit and Induction Heating (나일론 실린더와 강축의 열박음과 유도가열에 의한 접합의 연구)

  • Choi Sin-Jin;Kang Suk-Choon
    • Journal of the Korean Society for Precision Engineering
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    • v.22 no.2
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    • pp.139-147
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    • 2005
  • The lubricant impregnated MC nylon has good frictional properties, but its mechanical strength is inferior to steel for the mechanical elements. For the tribological application Nylon as gears, sliding bearings, cam and etc, the steel shafts are fitted in pre-heated nylon cylinder by a process of interference expansion fit and bonded by induction heating method. The joint shear strength of the two materials was measured by a universal test machine. From the study, the adhesive shear strength between these two materials was affected by the factors of the interference between nylon and steel, the size of nylon cylinder, knurl of steel shaft and inducting heating conditions. The most effective jointing conditions were analyzed and decided for the practical application in the industry.

Thermal Expansion Analysis of the Ball Screw System by Finite Difference Methods (유한차분법을 이용한 볼스크류 시스템의 열팽창 해석)

  • Jeong, Seong-Jong;Park, Jeong-Gyun
    • Journal of the Korean Society for Precision Engineering
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    • v.9 no.4
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    • pp.44-57
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    • 1992
  • Ball screw systems have been used for positioning elements of machine tools and precision tables. In order to maintain the high rigidity and accuracy, a certain amount of preload is applied between the nut and the screw of ball screw systems. However, large amount of the preload oncreases the frictional heat. The temperature rises remarkably at the high speed motion, and the thermal expansion degrades the positioning accuracy. In this paper, a finite difference method is applied to analyse temperature distributions and thermal expansions of the ball screw system according to preload conditions and rotational speeds. Some simulation results show that the developed methodology is appropriate to study the thermal expansion characteristics of ball screw systems.

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Detection of urban expansion and surface temperature change using Landsat imagery (Landsat 영상을 이용한 도시확장과 지표온도 변화 탐지)

  • 손홍규;곽은주;방수남;박완용
    • Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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    • 2004.11a
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    • pp.161-166
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    • 2004
  • Seoul has experienced a rapid urban expansion over the past three decades. This paper reports an investigation into the application of Landsat imagery for detecting urban growth and assessing its impact on surface temperature in the region. Land cover/use change detection w3s carried out by using Landsat data. The results revealed a notable urban growth in the study area. This urban expansion had raised surface radiant temperature in the urbanized area. The method using remote sensing data based on GIS was found to be effective in monitoring and analysing urban growth and in evaluating urbanization impact on surface temperature.

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Calculations of the Thermal Expansion Coefficient for Rock-Forming Minerals Using Molecular Dynamics (MD) Simulation (분자동역학(MD) 시뮬레이션을 이용한 조암광물의 열팽창 계수 산정)

  • 서용석;배규진
    • The Journal of Engineering Geology
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    • v.11 no.3
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    • pp.269-278
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    • 2001
  • We describe the calculation of thermal expansion coefficients of $\alpha$-quartz, muscovite and albite using a MD simulation method. The selection of interatomic potentials is important for the MD calculation, and we used the 2-body interatomic potential function. The coefficients are calculated using a differential operation of the temperature dependence of the lattice constant obtained from the NPT-ensemble molecular dynamics simulation. Reasonable agreement is found between the analytical results and measured data.

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An experimental study about the water leakage structure of waterproofing layer performance demobilization method using of stick expansion type complex of flexible material (점착$\cdot$팽창성 유연형 복합소재를 이용한 누수구조물의 방수층 성능복원공법에 관한 실험적 연구)

  • Jang Hyok-Soo;Kang Hyo-Jin;Song Je-Young;Oh Sang-Keun
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2005.11a
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    • pp.79-83
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    • 2005
  • In the reinforced concrete structure, Even if speak that water leakage occurrence is no problem to material, there is a lot of reasons construction factor, material damage by behavior structure, properties of matter change by years and water leakage part by environment condition. so, waterproofing technological consideration should be gone ahead. In this research, we will study about stick performance, concrete surface adhesive, damage and blow. we will check all things and test it. The stick expansion type complex of flexible material passed on result of standard. It is conducive to concrete of durability by waterproofing layer performance demobilitation technology on the water leakage structure for solution of problem and repair

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Prediction of strongly swirling turbulent flow downstream of an abrupt pipe expansion (원관내 급확대부 하류의 강선회난류에 관한 수치해석)

  • Kim, K.Y.;Chang, Y.S.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.9 no.1
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    • pp.23-32
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    • 1997
  • Swirling turbulent flows downstream of an abrupt axisymmetric expansion in a pipe are analyzed numerically by a second-order turbulence closure. Predictions for the flows without swirl and with strong swirl are obtained. The governing differential equations are discretized by finite volume approach. The results show that the on-axis recirculation induced by the strong swirl is correctly reproduced. The predictions for mean velocity components and turbulent normal stresses agree well with experimental data far downstream of expansion, but show large discrepancies in wall-bounded recirculation zone.

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Behavior of Jointless Bridge of Steel Box Girder Type Due to Temperature Change (온도변화에 따른 무신축이음 강상자형 교량의 거동 분석)

  • 조남훈;이성우
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 1997.10a
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    • pp.95-102
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    • 1997
  • Jointless bridge is a new construction method applicable to bridge of short length. In the jointless bridge expansion of superstructure due to thermal effect was absorbed in the flexible pile-type abutment in stead of expansion joint in the conventional bridges. By removing expansion joint, it retards deterioration and extends life time of bridge. In this paper, jointless bridge of steel box girder type was studied through finite element analysis. Stress variations of superstructure and pile due to thermal effect was studied for the two span continuous integral bridge of 80m length and the results of analysis was presented.

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Calculation of Pressure Rise in a Thermal-expansion Type Arc Chamber (열팽창 분사식 가스차단부의 소호실내 압력상승 계산)

  • Choi, Y.K.;Oh, Y.H.;Shin, Y.J.;Park, K.Y.;Kim, H.J.;Choulkov, V.V.
    • Proceedings of the KIEE Conference
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    • 1998.07a
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    • pp.167-169
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    • 1998
  • Recently $SF_6$ gas circuit breakers utilizing the thermal-expansion principle are increasingly used in distribution power system. Active researches and developments have been conducted to reduce the size and weight, and to improve the interrupting performance of the circuit breakers. It was first developed a programme which could show the hot gas flowing into the thermal-expansion arc chamber. This programme, using so-called FLIC method basically, adopted 'Simplified Enthalpy Arc Model' which was somewhat modified to estimate the arc quenching process. The computation by it was compared with the measured results of the pressure rise in the chamber, and both showed fairly good agreement.

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