• Title, Summary, Keyword: Radial Clearance

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Analysis of Dynamic Characteristics of a Piston for a Linear Compressor Considering Changes in Groove Geometry (리니어 압축기에서 그루브 형상 변화에 따른피스톤의 동특성 해석)

  • Noh, Sangwan;Oh, Wonsik;Park, Kyeongbae;Rhim, Yoonchul
    • Tribology and Lubricants
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    • v.31 no.5
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    • pp.221-228
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    • 2015
  • It is possible to prevent a piston from contacting the cylinder by changing the shape of the piston or by applying micro-textures, such as micro-grooves or micro-holes, over the piston surface. Usually, the minimum radial clearance reaches its minimum value at the beginning of the suction stroke because the pressure around the piston is low and almost axisymmetric such that the net pressure force on the piston is not sufficiently high to support the piston from touching the cylinder. In this study, we apply a series of saw-tooth-shaped grooves on the piston surface, and numerically investigate the effects of groove depth, groove angle, and the number of grooves with radial clearance variations using a finite difference method. We conduct a dynamic analysis of the piston for various changes in groove geometries to obtain the minimum radial clearance variation for the entire compression cycle. The minimum radial clearance increases while friction loss decreases when we apply the series of saw-tooth-shaped grooves on the piston. In addition, we analyze the impact of the change in the groove shape variable due to changes in radial clearance. Leakage variations are relevant to radial clearance, but have almost no effect on the groove parameters.

Machining Characteristics of Micro-EDMed Holes According to Dielectric Fluid, Capacitance and Ultrasonic Vibrations (방전가공을 이용한 미세구멍 가공 시 절연액, 축전용량과 초음파 부가에 따른 가공특성)

  • Seo, Dong-Woo;Yi, Sang-Min;Chu, Chong-Nam;Park, Min-Soo
    • Journal of the Korean Society for Precision Engineering
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    • v.24 no.12
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    • pp.42-49
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    • 2007
  • When micro holes are machined by EDM, machining characteristics of machined holes are changed according to the machining conditions. Typical machining conditions are the kind of dielectric fluids, capacitance and ultrasonic vibrations. They influence electrode wear, machining time, radial clearance and taper angle. In this paper, machined holes whose depths are 300, 500, $1000\;{\mu}m$ are observed for each machining conditions. Using deionized water as a dielectric fluid makes electrode wear small, machining time short, radial clearance large and taper angle small. High capacitance makes electrode wear high. Ultrasonic vibrations make electrode wear large, machining time short, radial clearance small and taper angle small. From the results of experiments, the optimal machining conditions were obtained to machine highly qualified micro holes.

Dynamic Behavior Analysis of a Orbiting Scroll in Scroll Compressor with Tangential Leakage (접선방향의 누설이 고려된 스크롤 압축기 선회 스크롤의 동적 거동 해석)

  • 김태종;한동철
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • pp.41-46
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    • 1996
  • For a vertical type crankshaft-journal bearing system used in scroll compressor, nonlinear transient response analysis is applied includung nonlinear fluid film reaction forces of journal beatings. By a connected behavior analysis of crankshaft and orbiting scroll, the radial clearance of scroll wraps is calculated. Considering tangential leakage for this clearance, a coupled analysis model for leakage and dynamic behavior of the orbiting scroll is made, and analyzed by iterative calculation. By regarding clearances of main, sub bearing of crankshaft and orbiting scroll shaft bearing clearance as design parameters, the radial clearance of scroll wraps is analyzed.

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Numerical Analysis of Tip Clearance Effects in a Micro Radial Inflow Turbine

  • Watanabe, Naoki;Teramoto, Susumu;Nagashima, Toshio
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.622-627
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    • 2004
  • There are many difficulties in realizing Ultra-micro gas turbine system. Among them, the effects of tip clearance upon the micro turbine flowfield are discussed in this paper. The flowfield was investigated numerically with the Reynolds-averaged three-dimensional thin-layer Navier-Stokes equations. Calculations were conducted with clearance height from 0% to 10% of the passage height. Leakage mass flow and deterioration of efficiency are proportional to the clearance height for the clearance height larger than 4%. However, in the case of 2% clearance, leakage flow is significantly reduced due to relative motion of the casing and as a result deterioration of efficiency is very small. It is difficult to control tip clearance in micro turbines, but the results of this study indicate that if the clearance height is controlled within a few per-cent of passage height, deterioration of stage performance will be small.

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Finite Element Analysis on the Shaft Fitting to Inner Raceway of Radial Ball Bearing (레이디얼 볼베어링의 내륜 끼워맞춤에 관한 유한요소해석)

  • Ko, Byung-Du;Lee, Ha-Sung
    • Journal of the Korea Society of Die & Mold Engineering
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    • v.6 no.1
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    • pp.45-51
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    • 2012
  • The main goal of this paper is to establish an interference tolerance for determining optimal amount of clearance in the shaft-bearing system supported by radial ball bearings. The 2-D frictional contact model was employed for the FE analysis between the shaft and the inner raceway. Several examples were simulated using different material properties for the solid shaft. Efforts were focused on the deformation applied in the radial direction to select suitable bearings. The analysis results showed that the initial axial preload applied on the bearings plays a significant role to reduce bearing fatigue life. The proposed design parameters obtained by numerical simulations can approximately predict a rate of bearing life reduction as a function of shaft diameter ratio. This analysis can also be used to calculate the optimal initial radial clearance in order to obtain a shaft-bearing system design for high accuracy and long life.

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Micro-Hole Machining Using MEDM According to Machining Depth (미소구멍의 가공 깊이에 따른 미세방전 가공특성)

  • 김재현;김보현;류시형;주종남
    • Journal of the Korean Society for Precision Engineering
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    • v.20 no.7
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    • pp.227-232
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    • 2003
  • In order to make a deep and precise micro-hole, electrode wear and clearance between the electrode and the workpiece are important parameters using micro-electrical discharge machining. In this study, experiments were carried out to show the characteristics of electrode wear and radial clearance with respect to the depth of machined hole. Electrode wear varied with respect to the depth of hole. With deeper machined hole, bigger clearance was observed. Also it was found that the diameter of electrode influences machining characteristics of deep holes.

Clearance and preload effects on NRRO of miniaturc ball bearings with waviness

  • Kim, Y.C.;Choi, S.K.;Yoon, K.C.
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • pp.303-304
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    • 2002
  • This paper presents theoretical analysis of the NRRO(the non-repeatable run-out) for a ball bearing with geometric imperfection. This imperfection contains ball size error, ball waviness, outer race waviness and inner race waviness. The 3D dynamic analysis of a ball bearing using the Newton-Raphson method is performed to calculate the displacement of shaft center. The radial and axial NRRO are simulated, and preload and clearance effects are investigated. Preload and clearance have significant effects on radial and axial NRRO of for miniature ball bearings.

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Radial Performances of Spiral-Grooved Spherical Air Bearings (나선홈을 갖는 반구형 공기 베어링의 반경 방향 성능 측정)

  • Park, Keun-Hyung;Choi, Jeong-Hwan;Choi, Woo-Chon;Kim, Kwon-Hee;Woo, Ki-Myung;Kim, Seung-Kon
    • Journal of the Korean Society for Precision Engineering
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    • v.16 no.2
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    • pp.23-30
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    • 1999
  • This paper investigates the radial performance of self-acting spiral-grooved air bearing, used to support small high-speed rotating bodies. Repeatable runout, nonrepeatable runout, stiffness and supporting load are selected as the performance. The clearance between rotor and stator, the stator groove depth, and the rotating speed are chosen as three main parameters affecting the performances. Force application and displacement measurement are done in a noncontact manner, in order not to disturb operation: electromagnetic force is applied to the rotor and gap sensors are used to measure the displacement of the rotor. Experimental results show that repeatable runout decreases as speed, groove depth and clearance decrease. Nonrepeatable runout decreases as clearance decreases, and it has a minimum value at $5.5{\mu}m$ of grove depth and a maximum value at speed of 18.000rpm. Stiffness increases as speed increases and clearance decreases, and has a maximum value around $5.5{\mu}m$ of groove depth. The relationship between force and displacement is linear for small displacement, but becomes nonlinear for large displacement. Supporting load is linearly proportional to the stiffness, and it is a maximum value around $4.75{\mu}m$ of clearance.

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Performance Prediction and Flow Field Calculation for Airfoil Fan with Impeller Inlet Clearance

  • Kang, Shin-Hyoung;Cao, Renjing;Zhang, Yangjun
    • Journal of Mechanical Science and Technology
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    • v.14 no.2
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    • pp.226-235
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    • 2000
  • The performance prediction of an airfoil fan using a commerical code, STAR/CD, is verified by comparing the calculated results with measured performance data and velocity fields of an airfoil fan. The effects of inlet tip clearance on performance are investigated. The calculations overestimate the pressure rise performance by about 10-25 percent. However, the performance reduction due to tip clearance is well predicted by numerical simulations. Main source of performance decrease is not only the slip factor but also impeller efficiency. The reduction in performance is 12-16 percent for 1 percent gap of the diameter. The calculated reductions in impeller efficiency and slip factor are also linearly proportional to the gap size. The span-wise distributions of phase averaged velocity and pressure at the impeller exit are strongly influenced by the radial gap size. The radial component of velocity and the flow angle increase over the passsage as the gap increases. The slip factor decreases and the loss increases with the gap size. The high velocity of leakage jet affects the impeller inlet and passage flows. With a larger clearance, the main stream moves to the impeller hub side and high loss region extends from the shroud to the hub.

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Effect of Clearance between a Rotor and Stator of a Disk-Type Drag Pump on the Pumping Performance (고속 회전하는 원판형 드래그펌프 회전익과 고정익 사이 간극이 배기 성능에 미치는 영향)

  • Kwon, Myoung-Keun;Lee, Soo-Yong;Hwang, Young-Kyu
    • Proceedings of the KSME Conference
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    • pp.1640-1645
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    • 2004
  • The pumping characteristics of a single-stage disk-type drag pump ( DTDP ) are calculated,for the variation of the vertical clearance between a rotor and stator and of the radial clearance between a rotor and casing wall, by the three-dimensional direct simulation Monte Carlo (DSMC)method. The gas flow mainly belongs to the molecular transition flow region. Spiral channels of a DTDP are cut on the both the upper and lower sides of a rotating disk, but the stationary disks are planar. As a consequence of results, the vertical and radial clearances have a significant effect on the pumping performance. Experiments are performed under the outlet pressure range of 0.4 $^{\sim}$ 533 Pa. When the numerical results are compared to the experimental data, the numerical results agree well qualitatively.

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