• Title/Summary/Keyword: Surface geometry

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Survival of the Insulator under the electrical stress condition at cryogenic temperature

  • Baek, Seung-Myeong;Kim, Sang-Hyun
    • Progress in Superconductivity and Cryogenics
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    • v.15 no.4
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    • pp.10-14
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    • 2013
  • We have clearly investigated with respect to the survival of the insulator at cryogenic temperature under the electrical stress. The breakdown and voltage-time characteristics of turn-to-turn models for point contact geometry and surface contact geometry using copper multi wrapped with polyimide film for an HTS transformer were investigated under AC and impulse voltage at 77 K. Polyimide film (Kapton) 0.025 mm thick is used for multi wrapping of the electrode. As expected, the breakdown voltages for the surface contact geometry are lower than that of the point contact geometry, because the contact area of the surface contact geometry is lager than that of the point contact geometry. The time to breakdown t50 decreases as the applied voltage is increased, and the lifetime indices increase slightly as the number of layers is increased. The electric field amplitude at the position where breakdown occurs is about 80 % of the maximum electric field value. The relationship between survival probability and the electrical stress at cryogenic temperature was evident.

A Study on the Inverse Shape Design of a Turbine Cascade Using the Permeable Boundary Condition and CFD (침투경계조건과 CFD를 이용한 터빈 역형상 설계에 관한 연구)

  • Lee, Eun-Seok;Seol, Woo-Seok
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.3116-3121
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    • 2007
  • In this paper, the inverse shape design is introduced using the permeable wall boundary condition. Inverse shape design defines the blade shape for the prescribed Mach numbers or pressure distribution on its surface. It calculates the normal mass flux from the difference between the calculated and prescribed pressure at the surface. A new geometry can be achieved after applying the quasi one-dimensional continuity equation from the leading edge to the trailing edge. For validation of this method, two test cases are studied. The first test case of inverse shape design illustrates the cosine bump with a strong shock. After seven geometry modifications, the shock-free bump geometry can be obtained. The second example concerns the redesign of a transonic turbine cascade. The initial isentropic Mach distribution has a peak on the upper surface. The target isentropic Mach number distribution was imposed smoothly. The peak of Mach distribution has disappeared at the final geometry. This proposed inverse design method has proven to be an efficient and robust tool in turbomachinery design fields.

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Effects of seed geometry on the crystal growth and the magnetic properties of single grain REBCO bulk superconductors

  • Lee, Hwi-Joo;Park, Soon-dong;Jun, Bung-Hyuck;Kim, Chan-Joong;Lee, Hee-Gyoun
    • Progress in Superconductivity and Cryogenics
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    • v.19 no.3
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    • pp.33-39
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    • 2017
  • This study presents that the orientation and the geometry of seed affect on the growth behavior of melt processed single grain REBCO bulk superconductor and its magnetic properties. The effects of seed geometry have been investigated for thin $30mm{\times}30mm$ rectangular powder compacts. Single grain REBCO bulk superconductors have been grown successfully by a top seed melt growth method for 8-mm thick vertical thin REBCO slab. Asymmetric structures have been developed at the front surface and at the rear surface of the specimen. Higher magnetic properties have been obtained for the specimen that c-axis is normal to the specimen surface. The relationships between microstructure, grain growth and magnetic properties have been discussed.

Optimization of a geometric form and cutting conditions of a metal slitting saw by experimental method (실험적 방법을 통한 Metal slitting saw의 형상 및 절삭 조건의 최적화)

  • 정경득;고태조;김희술
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2000.05a
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    • pp.934-938
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    • 2000
  • Built-up edge affects the surface integrity of the machined surface and tool wear. Tool geometry and cutting conditions are very important factors to remove BUE. In this paper, we optimized the geometry of the metal slitting saw .1nd cutting conditions to remove BUE by the experiment. In general, the metal slitting saw is plain milling cutter with thickness less of a 3/16 inch. This is used for cutting workpiece where high dimensional accuracy and surface finish are necessary. The experiment was planned with Taguchi method that is based on the orthogonal array of design factors(coating, rake angle, number of tooth, cutting speed, feed rate). Response table was made by the value of the surface roughness, the optimized tool geometry and cutting conditions through response table could be determined. In addition. the relative effect of factors were identified by the variance analysis. filially. coating and cutting speed turned out important factors.

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Analysis of Cutting Edge Geometry Effect on Surface Roughness in Ball-end Milling Using the Taguchi Method (다구찌 방법을 통한 볼 엔드밀 절삭날 형상이 가공면 거칠기에 미치는 영향 분석)

  • Cho, Chul Yong;Ryu, Shi Hyoung
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.23 no.6
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    • pp.569-575
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    • 2014
  • In this study, the effect of cutting edge geometry, such as helix and rake angles, on surface roughness in ball-end milling is investigated by using the Taguchi method. A set of experiments adopting the $L_{27}(3^{13})$ design with an orthogonal array are conducted with special WC ball-end mills having different helix and rake angles. Analysis of variance (ANOVA) is performed to analyze the effects of tool geometry and machining parameters, such as cutting speed, feed per tooth, and depth of cut, on surface roughness. The ANOVA results reveal that helix and rake angles are critical factors affecting surface roughness; the interaction of helix angle and cutting speed is also important. This research can contribute to novel cutting edge designs of ball-end mills and optimization of cutting parameters.

The Characteristic of Hydrogen Generation on the Structure of Plasma Reactor Using the Streamer Discharge in the Water (수중 스트리머 방전용 플라즈마 반응기 구조에서 수소발생 특성)

  • Park, Jae-Youn;Kim, Jong-Seok
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.20 no.4
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    • pp.37-42
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    • 2006
  • The effect of arc like streamer discharge is investigated on the hydrogen generation using the multineedle-plate electrode geometry plasma realtor(MPER) and the needle-plate electrode geometry plasma reactor(NPER). In order to restrict waves at the water surface when the high voltage applied, two kinds of the insulator such as the rectangular mesh or the hole mesh type are installed under the water surface. The discharge assistant of the two type(the saw type and the $TiO_2$ pellet type) was placed under the water surface to investigate the effect of the water surface conditions. The experimental results are compared in case of the reactor with and without the discharge assistant on the water surface.

The Effect of Network Geometry on Three- Dimensional Analysis in Close-Range Photogrammetry (근접사진측량의 망구성이 삼차원 위치해석에 미치는 영향)

  • 이진덕;강준묵
    • Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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    • v.8 no.1
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    • pp.15-22
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    • 1990
  • The purpose of this study is to suggest possibility to analyze the three-dimensional positions of the whole surface of an object simultaneously and precisely by close-range photogrammetry. For this purpose, the geometry of network, namely imaging geometry and control configuration etc was considered, and then the whole surface of the object was analyzed by bundle adjustment through forma. lion of strip and block with which cover the whole surface of the object. As a result, we were able to prove possibility of the whole surface analysis of an object and to extract characteristics of accuracies in accordance with the number and configuration of control points. Also as desirable accuracies were able to be acquired even by employing configuration of only a few control point stationed on a limited surface, it is expected that the difficulties of control surveying will be able to be reduced considerably.

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Parametric Modeling of a Screw Fabricated by Turning (선삭가공으로 제작되는 나사형상의 3차원 파라메터릭 모델)

  • Kim, Ho-Chan;Ko, Tae-Jo
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.11 no.6
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    • pp.62-68
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    • 2012
  • Geometry of a screw fabricated by a turning process determined by the shape of the tool, feed rate of the tool and rotation speed of the spindle. Therefore, computing the exact geometry of the screw is very important to perform a simulation on machining or an evaluation of the workpice quality. In this paper, a new mathematical geometry model of the 3 dimensional screw is fabricated by turning process introduced for the exact geometry computation. Becasue model has a parametric formulation, it is easy to process for a CAD geometry or apply for a machining simulation. Also, it can be applied to process planning because it gives precise machined geometry on whole the 3 dimensional surface of the screw. This paper introduces a new parametric model of a geometry for screw fabricated by turning process. As an application, a simulation software for the 3 dimensional screw surface is developed and evaluated for several manufacturing parameters.

Study on the Design of End Mill Geometry for the High Speed Machining (고속 가공용 엔드밀의 형상설계에 관한 연구)

  • 이상규;배승민;고성림;김경배;서천석
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2001.04a
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    • pp.67-70
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    • 2001
  • The tool geometry parameters and cutting process have complex relationships. Until now, numerous cutting tests were needed to acquire optimal design of end mill for the purpose of high speed machining, due to the insufficient knowledge about cutting process in high speed machining. Using various tools with different geometry, relationships between tool geometry parameter(rake angle, clearance angle, length of cutter) and cutting process(cutting force, surface accuracy, surface roughness) have been studied. Acquired data can be used to design optimal tool for high speed machining

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Development of Geometric Design S/W for High Speed End Mill (고속가공용 엔드밀 형상설계 S/W 개발)

  • 한창규;고성림;서천석;김경배
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 2004.10a
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    • pp.422-427
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    • 2004
  • The tool geometry parameters and cutting process have complex relationships. Until now, various cutting test were needed to acquire optimal design of end mill for the purpose of high speed machining, due to the insufficient knowledge about cutting process in high speed machining. Using various tools with different geometry, relationships between tool geometry parameter (rake angle, clearance angle, length of cutter) and cutting process (cutting force, surface accuracy, surface roughness) have been studied. Acquired data can be used to design optimal tool for high speed machining and to develop a software for design of end mill geometry.

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