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A FEM Analysis of Dynamic Behavior for a Slider with Curvature Effect
임성근,임윤철,Lim, Sung-Keun,Rhim, Yoon-Chul 한국트라이볼로지학회 2004 KSTLE International Journal Vol.5 No.2
A new type slider with optical components is going to be introduced on market for portalbe and high capacity disk drive, and it will show a great potential for high performance drive in the paper the dynamic behavior and static characteristics of silder for a small form factor optical disk drive have been investigated numerically by an in-house simulation code using FEM. A curvature effect is found when a slider is applied to a relatively small disk, which makes rolling characteristics worse due to the negative pressured generated at the air bearing surface because of the curvature of small disk diameter.
오일윤활 빗살무늬 저널 베어링에 대한 정특성 및 안정성 해석
강경필,임윤철,Kang, Kyung-Phil,Rhim, Yoon-Chul 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.4
An oil lubricated Herringbone aroove jounal bearing(HGJB) with eight-circular-profile grooves on the non-rotating bearing surface is analyzed numerically and experimentally. The load carrying capacity, attitude angle, stiffness and damping coefficients are obtained numerically for the various bearing configurations. The onset speed of instability is also examined for the various eccentricity ratios. The configuration parameters of HGJB, such as groove depth ratio, groove width ratio, and groove angle, are dependent on each other because the grooves are generated by using eight small balls rolling over the inner surface of the sleeve with press fit. Therefore, it is not allowed to suggest a set of optimal design parameters such as the one for the rectangular profile HGJB. The overall results from numerical and experimental analysis prove that the circular profile HGJB has an excellent stability characteristics and the higher load carrying capacity than the plain journal bearing.
초미세 틈새의 기체 베어링 해석용 유효 점도의 표현식과 관련 계수들의 민감도 해석
김의한(Ui Han Kim),임윤철(Yoon Chul Rhim) 한국트라이볼로지학회 2014 한국윤활학회지(윤활학회지) Vol.30 No.1
A more accurate expression for effective viscosity is obtained using a linear regression of the data from Fukui-Kaneko’s model, which are obtained through numerical calculations based on the linearized Boltzmann equation. Veijola and Turowski’s expression is adopted as a base function for effective viscosity. The four coefficients in that equation are optimized, and sensitivity analysis is conducted for these coefficients. The results show that the coefficient for the first-order Knudsen number is the most accurate, whereas the coefficient in the exponential of the Knudsen number is the least accurate compared with Fukui-Kaneko’s results. The expression for effective viscosity is accurate within 0.02% rms of Fukui-Kaneko’s results for the inverse Knudsen numbers from 0.01 to 100 and surface accommodation coefficients ranging from 0.7 to 1.
초미세 틈색의 기체 베어링 해석용 유효 점도의 표현식과 관련 계수들의 민감도 해석
김의한(Ui Han Kim),임윤철(Yoon Chul Rhim) 한국트라이볼로지학회 2013 한국트라이볼로지학회 학술대회 Vol.2013 No.10
A most accurate expression for the effective viscosity is obtained using the linear regression of the data from Fukui-Kaneko’s model which are obtained through numerical calculations based on the linearized Boltzmann equation. Veijola and Turowski"s expression is adopted as a base function for the effective viscosity and four coefficients in that equation are optimized. The sensitivity analysis is conducted for four coefficients. As a results, the coefficient for the first order of Knudsen number is the most and the coefficient in exponential of Knudsen number is the least effective in error compared with the results of Fukui-Kaneko"s results. The expression for the effective viscosity is accurate within 0.02% rms of Fukui-Kaneko"s results for the inverse Knudsen number range from 0.01 to 100 and the range of surface accommodation coefficient from 0.7 to 1.
김재후 ( Jae Hoo Kim ),임윤철 ( Yoon Chul Rhim ) 정보저장시스템학회 2015 정보저장시스템학회논문집 Vol.11 No.1
An archive system is designed to store data for a long time without loss. However, many important factors such as temperature, dust, vibration, and humidity must be considered to design a successful archive system. Read/write devices, for example optical disk drives(ODDs), in an archive system generate heat while they are in operation. Fans are usually used to remove heat but the air flow accompanies dust into the system result in system failure. In this study, an archive system with six ODDs is chosen as an analysis model and flow together with temperature distributions are computed using a CFD simulation package. Flow analysis is focused on four cooling fans at the rear panel and temperature distribution is studied for various cases of fan operation. From the temperature point of view, fans give significant effects on 4th to 6th ODDs compared to the 1st to 3rd ODDs. Also, it is noticed which fan is the most important as far as cooling is concerned.
고속 회전 유연 디스크의 진동 저감용 공기 베어링 해석
이성호(Sung-ho Lee),임윤철(Yoon-chul Rhim) 한국트라이볼로지학회 2004 한국트라이볼로지학회 학술대회 Vol.39 No.-
Rotating disks are used in various machines such as data storage device, gyroscope, circular saw, etc. Transverse vibration of a rotating disk is very important for the performance of these machines. This work proposes a method to suppress transverse vibration of a very flexible rotating disk in non-contacting manner. A system considered in this study is a very flexible rotating disk with a thrust bearing pad which is located underneath the rotating disk. The pressure force generated in the gap between the rotating disk and the thrust pad pushes the rotating disk in the direction of axis of rotation while the centrifugal force and the elastic recovery force push the rotating disk in reverse direction. The balance between these forces suppresses the transverse vibration of the rotating disk. A coupled disk-fluid system is analyzed numerically. The finite element method is used to compute the pressure distribution between the thrust pad and the rotating disk while the finite difference method is used to compute the transverse vibration of a rotating disk. Results show that the transverse vibration of the rotating disk can be suppressed effectively for certain combination of air bearing and operating parameters.
극저온 환경용 볼베어링 시험장치 개발 및 터보펌프용 볼베어링 시제품의 성능평가
조준현(Jun Hyeon Jo),임윤철(Yoon Chul Rhim),이성철(Sungchul Lee),김충현(Choong Hyun Kim) 한국트라이볼로지학회 2012 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.28 No.4
The turbo pump of a liquid rocket engine is composed of three main parts: the oxidizer pump, fuel pump, and turbine. Liquid oxygen (LOX) is the working fluid in the cryogenic environment in the oxidizer pump, but tests are usually performed using liquid nitrogen (LN2), which has a boiling point similar to that of LOX but is comparatively safer and easier to use for the test. In this study, a bearing test rig is developed and its performance is evaluated using a cryogenic ball bearing with LN2 as the working fluid. Verifying the performance of the bearing test rig is crucial for ensuring correct working of the turbo pump unit in the liquid rocket engine. A stable test rig for the bearing in a cryogenic environment makes the bearing technology enhance its reliability. The test results show that the system operates stably and the requirement of performance time of 500 s is met. The test results of temperature, motor speed, and torque are discussed. The developed cryogenic bearing test rig is expected to help in widening knowledge and expanding research on ball bearings in the future.