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Dynamic Stability Analysis Of The Ultra-Thin Gas Film Between Magnetic Head And Disk In Computer Data Storage System

Posted on:2005-01-05Degree:DoctorType:Dissertation
Country:ChinaCandidate:H X ChenFull Text:PDF
GTID:1118360152967560Subject:Fluid Mechanics
Abstract/Summary:PDF Full Text Request
The computer proceeds to increase storage density and improve stability. In data storage system, it is valuable to study the dynamic lubrication behavior of ultra-thin film between the slider and disk to improve stability of the disk system.It's needed to take Knudsen number, defined as a ratio of the molecular mean free path to gas film characteristic height, into account for stability analysis of ultra-thin film. The Fukui's general gas lubrication equation including thermal creep flow is applicable to cases of arbitrary Knudsen number. This work adopts the Fukui's equation to investigate gas lubrication behavior and film stability. The flow rate coefficients, accounting for gas rarefaction, are approximated as polynomial interpolations based on database. The numerical examples of nano nutcracker slider were presented in this paper.The operator splitting /finite element method with unstructured triangular grids are used to solve the general gas lubrication equation and the perturbation method is adopted to analysis the stability of the coupling system of air film and slider. The numerical results indicate that the operator splitting method effectively suppresses numerical oscillations in the cases of high air bearing number. The numerical results show that both air lift force and pitch moment increase with the ratio of the slider's rail height to the air film characteristic height and the air bearing number, and finally reaches to stable value. Moreover, it's shown that increasing disk rotation speed cannot increase air lift force unlimitedly.In this work pressure perturbation equations are developed due to the film thickness disturbance and head velocity disturbance, respectively. The solution of perturbation pressure is used to calculate air bearing's stiffness and damping coefficients. The air bearing's stiffness coefficients are much greater than mechanical suspension stiffness coefficients, while the damping coefficients are less than that of suspension. By superposition of the stiffness and damping of air bearing and suspension, the coupling system's damping rate, natural frequencies and modal shapes were obtained, and the stability of the coupling system are analyzed. The natural frequencies of coupling system decrease with increase of the film thickness, and are not sensitive to disk rotation speed. It is shown the first vibration mode of the system is a uncoupled mode of the pitch motion, the second mode is a uncoupled mode of the roll motion, and the third mode are coupled mode of heaven and pitch. It is also found that the natural frequencies and damping rates of coupled vibration mode are much smaller than those of the uncoupled modes.This paper presents a resonance coefficient to predict resonance possibility of disk system. The numerical results show that the system stability can be improved in cases of thinner gas film and slower disk rotation speed.A comparison of stability of nano and pico sliders is also made in this paper. The primary conclusions are made in this paper. (1) The air bearing has lower natural frequencies in thicker air film. The natural frequencies of the disk system do not significantly vary with disk rotation speed. The system's damping rates are higher as the disk rotation speed is lower. (2) The resonance coefficient is small in cases of thinner gas film and slower disk rotation speed. The higher damping rate and better stability can be achieved by combining the slider with smaller dimension and bigger damping suspension.
Keywords/Search Tags:Magnetic Disk Stability, Finite Element Method, Operator- Splitting Method, Ultra-Thin Gas Film Lubrication
PDF Full Text Request
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