• Title/Summary/Keyword: rubbing direction

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A Study on the Performance of Slot Restrictor Bearing with a Variation in Circumferential Direction (원주방향 변화를 갖는 슬롯 레스트릭터 베어링의 성능 연구)

  • 박정구;김경웅
    • Tribology and Lubricants
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    • v.16 no.2
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    • pp.91-98
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    • 2000
  • A slot restrictor air journal bearing has high load capacity and high stiffness. The stability characteristics of the slot restrictor air journal bearing are studied theoretically and experimentally to forecast and to prevent the whirl instability. As for the high speed rotating machinery, the instability called'whirl'occurs when the rotor rotates at a speed more than twice the resonant speed. Once the whirl occurs, rubbing contact between the journal and the bearing occurs mostly and the bearing-rotor system is destroyed ultimately. Therefore, the forecasting and prevention of the occurrence of whirl instability is a very important subject especially to develop highly efficient high speed rotating machinery. The bearing with the slot restrictor that varies about circumferential direction is used for the purpose of the prevention of whirl instability.

Finite Element Analysis on the Dynamic Behaviors of a Disk-Pad Brake in High-Speed Trains (고속전철용 디스크-패드 브레이크의 동적거동 특성에 관한 유한요소해석)

  • 김청균;조승현
    • Tribology and Lubricants
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    • v.16 no.2
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    • pp.99-105
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    • 2000
  • Using a coupled thermal-mechanical analysis, the dynamic distortion of the ventilated disk brakes has been presented for a high-speed train. The offset ratio between the maximum and minimum values of the thermal distortions has been analyzed as a function of a braking number. The computed FEM results show that the offset ratios in radial direction are much greater than those of circumferentially distorted components. This means that the axial distortions in radial direction may dominantly produce thermally caused wears and cracks at the rubbing surfaces.

A study on performance of slot restrictor bearing with a variation in circumferencial direction (원주방향 변화를 갖는 슬롯 레스트릭터 베어링의 성능 연구)

  • 박정구;김경웅
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 1998.10a
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    • pp.350-357
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    • 1998
  • Slot restrictor air journal bearing has high load capacitance and high stiffness. Stability characteristics of slot restrictor air journal bearing are studied theoretically to forecast and to prevent the whirl instability. As for the high speed rotating machinery, the instability called 'whirl' occurs when the rotor rotates at a speed more than twice the resonant speed. Once the whirl occurs, rubbing contact between the journal and the bearing occurs mostly and the bearing-rotor system is destroyed ultimately. Therefore, the forecasting and prevention of the occurence of whirl instability is a very important subject especially to develop highly efficient high speed machinery. The bearing with the slot restrictor that varies about circumferencial direction is used for the purpose of the prevention of whirl instability.

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A Study on the Dynamic Behaviors of a Disk Brake for a High-Speed Train (고속전철용 디스크 브레이크의 동적거동 특성에 관한 연구)

  • 조승현;김청균
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 1999.11a
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    • pp.276-282
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    • 1999
  • Using a coupled thermal-mechanical analysis, the dynamic distortion of the ventilated disk brakes has been presented for a high-speed train. The offset ratio between the maximum and minimum values of the thermal distortions has been analyzed as a function of a braking number. The computed FEM results show that the offset ratios in radial direction are much greater than those of circumferentially distorted components. This means that the axial distortions in radial direction may dominantly produce thermally caused wears and cracks at the rubbing surfaces.

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Precise Measurement of Optical Anisotropy of Rubbed Polyimide on Patterned Glass and its Nanoscale Variation (패턴이 있는 유리기층 위 러빙된 Polyimide의 광학 이방성 미세변화 정밀 측정)

  • Kim, Ha-Rang;Kim, Sang-Youl
    • Korean Journal of Optics and Photonics
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    • v.20 no.5
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    • pp.281-287
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    • 2009
  • The optical anisotropy of rubbed PI(polyimide) film on patterned LCD glass substrate is analyzed using polarimetry. The direction of the optic axis and the magnitude of the very small retardation ($\sim$ 0.4 nm or less) is precisely measured by using a transmission ellipsometer. The variation of the optical anisotropy is presented as the curve of the optic axis versus the magnitude of the phase retardation and it is explained by using a simple optical model.

The Alignment of Liquid Crystals on the Film Surfaces of Soluble Aromatic Polyimides Bearing t-Butylphenyl and Trimethylsilylphenyl Side Groups

  • Hahm, Suk-Gyu;Jin, Kyeong-Sik;Park, Sam-Dae;Ree, Moon-Hor;Kim, Hyung-Sun;Kwon, Soon-Ki;Kim, Yun-Hi
    • Macromolecular Research
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    • v.17 no.12
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    • pp.976-986
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    • 2009
  • With the study goal of firstly elucidating the anisotropic interactions between oriented polymer chain segments and liquid crystal (LC) molecules, and secondly of determining the contributions of the chemical components of the polymer segments to the film surface topography, LC alignment, pretilt, and anchoring energy, we synthesized three dianhydrides, 1,4-bis(4'-t-butylphenyl)pyromellitic dianhydride (BBPD), 1,4-bis(4'-trimethylsilylphenyl)pyromellitic dianhydride(BTPD), and 2,2'-bis(4"-tert-butylphenyl)-4,4',5,5'-biphenyltetracarboxylic dianhydride (BBBPAn), and a series of their organosoluble polyirnides, BBPD-ODA, BBPD-MDA, BBPD-FDA, BTPD-FDA, and BBBPAn-FDA, which contain the diamines 4,4'-oxydianiline (ODA), 4,4'-methylenediamine (MDA), and 4,4'-(hexafluoroisopropylidene)dianiline (FDA). All the polyimides were determined to be positive birefringent polymers, regardless of the chemical components. Although all the rubbed polyimide films exhibited microgrooves which were created by rubbing process, the film surface topography varied depending on the polyimides. In all the rubbed films, the polymer chains were unidirectionally oriented along the rubbing direction. However, the degree of in-plane birefringence in the rubbed film varied depending on the polyimides. The rubbing-aligned polymer chains in the polyimide films effectively induced the alignment of nematic LCs along their orientation directors by anisotropic interactions between the preferentially oriented polymer chain segments and the LCs. The azimuthal and polar anchoring energies of the LCs ranged from $0.45{\times}10^{-4}\;-\;1.37{\times}10^{-4}\;J/m^2$ and from $0.86{\times}10^{-5}\;-\;4.26{\times}10^{-5}\;J/m^2$, respectively, depending on the polyimides. The pretilt angles of the LCs were in the range $0.10-0.62^{\circ}$. In summary, the soluble aromatic polyimides reported here are promising LC alignment layer candidates for the production of advanced LC display devices.

Annealing effect on LC alignment using the photo-depolymerization reaction (광분해 반응을 이용한 액정배향에서의 어닐링 효과)

  • Kim, Hyung-Kyu;Yu, Mun-Sang;Seo, Dae-Shik
    • Proceedings of the KIEE Conference
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    • 1999.07d
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    • pp.1762-1764
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    • 1999
  • We investigated the annealing effect on generating pretilt angle and aligning liquid crystal (LC) using the photo-depolymerization reaction in this study. In case of rubbing polyimide (PI) surface with the side chain, pretilt angle tends to increase with increasing the annealing time. It is considered because the steric interaction is increased by annealing which cause the side chain to come back to original position. For obliquely irradiating ultraviolet (UV) light on PI surface, pretilt angle shows to $0^{\circ}$ and is increased by annealing. The pretilt angle in rubbed PI surface is much higher than in photo-aligned PI surface. It is attributed to the steric interaction and the number of LC molecular arrangement on azimuthal direction. In addition. in case of obliquely irradiating UV light on PI surface. it showed LC alignment to increase by annealing. It can be regarded due to the fact that the re-alignment of LC molecule is improved to residual polymer direction by annealing.

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Homogeneous Liquid Crystal Alignment on Anisotropic YSnO Surface by Imprinting Method (임프린팅법을 이용한 YSnO 박막의 표면 이방성 획득과 액정 배향 특성 연구)

  • Oh, Byeong-Yun
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.33 no.1
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    • pp.21-24
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    • 2020
  • We investigated a solution-driven Yttrium Tin Oxide (YSnO) film that was imprinted using a parallel nanostructure as a liquid crystal (LC) alignment layer. The imprinting process was conducted at the annealing temperature of 100℃. To evaluate the effect of this process, we conducted surface analyses including atomic force microscopy (AFM). During imprinting, the surface roughness was reduced, and anisotropic characteristics were observed. Planar LC alignment was observed at a pretilt angle of 0.22° on YSnO film. Surface anisotropy induced by imprinting method forces LC to align along the direction of the parallel nanostructure, which is an alternative to conventional polyimide treated using a rubbing process.

Design of Butterfly Valve Disk to Minimize Interference at Opening and Closing (개폐 시 최소 간섭을 갖는 버터플라이 밸브 디스크의 설계)

  • Choi Young;Boo Kwangsuk;Yeo Hong-Tae;Hur Kwando;Kim Hokwan
    • Journal of the Korean Society for Precision Engineering
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    • v.21 no.12
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    • pp.140-145
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    • 2004
  • In this study, the design and analysis of a butterfly valve disk was performed to minimize the rubbing between the disk and the seat at opening and closing. The butterfly valve has double eccentric structure and the contact surface between the disk and the seat is a conical surface. At the instant of opening and closing the valve by the rotation of disk, the positions of zero contact point are changed. Also, if the cone surface is cut in the perpendicular direction to the rotation axis of the valve, the contour of cutting section is hyperbolic. Therefore minimum distance between the origin of the eccentric axis and the hyperbolic curve goes to the position of zero contact point. In order to consider the interferences between the disk and the seat, the thermal-structure coupled field analysis was performed by ANSYS.

A New Method for Measuring Azimuthal Anchoring Energy of Rubbed and UV-Exposed Polyimide Alignment Layers

  • Park, H.J.;Lee, W.K.;Kim, D.G.;Shin, D.C.;Woo, J.W.;Shin, H.H.
    • 한국정보디스플레이학회:학술대회논문집
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    • 2007.08b
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    • pp.1619-1621
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    • 2007
  • Novel optical measurement systems and improved cell configurations for measuring of azimuthal anchoring energies were developed. The difference between the mechanical rubbing direction and the optical easy axis that caused errors in the previous azimuthal anchoring energy measurement was compensated. In addition, the measurement accuracy of the twist angle and therefore the azimuthal anchoring energy was greatly enhanced. As a result, we were able to obtain valid azimuthal anchoring energy values for different alignment layers.

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