臺灣博碩士論文加值系統

Lubricant of hydrodynamic journal bearing substitutes the steel ball of ball bearing to support the shaft under rotating. The lubricant-film force, which is often defined by a set of linear stiffness and damping coefficients, plays a critical role in a hydrodynamic journal bearing. This study presents an experimental method to determine the stiffness and damping coefficients of herringbone grooved hydrodynamic journal bearing used in a cooling fan. In this work, we will discuss the static loading effects and rotating speed effects on the stiffness and damping coefficients.
The experimental rotating shaft used in this study is perpendicular to horizon. To simulate the traditional rotating shaft parallel to horizon, which needs to sustain the gravity of its weight and generates an eccentricity, we use an electromagnet to produce a static magnetic force attracting the rotor and generate the static eccentricity of the rotor. The experiments indicate that the using of the electromagnetic loading increases the stiffness and damping effects of hydrodynamic bearing. However, with the growth of the static loading, the values of the dynamic coefficients become more unstable. It means the nonlinear forces of the lubricant film become stronger under the larger loading and eccentricity.
From the rotating speed effects on the stiffness and damping coefficients, with the growth of the rotating speed, the stiffness coefficients become larger. However, comparing to the static loading effects, the static loading effects can affect the stiffness and damping coefficients of lubricant film of a hydrodynamic bearing more greatly.

Acknowledgement…………………………………………………I
Abstract…………………………………………………………II
Nomenclature…………………………………………………IV
Table of Content………………………………………………VI
List of Tables…………………………………………………VIII
List of Figures…………………………………………………IX
Chapter 1 Introduction 1
1.1. General Remarks 1
1.2. Motivation and Objectives 4
1.3. Literature Survey 5
1.4. Thesis Organization 7

Chapter 2 Theory of Dynamics of the Rotating System 13
2.1. Dynamics of a Rotor-Bearing System with Fluid Film 13
2.1.1. Equations of Motion of a Rotating System with Fluid Film 13
2.1.2. Definition of Dynamic Force Coefficients in Fluid Film Bearing….. 15
2.1.2.1. Lubricant Film Forces in the Bearing 15
2.1.2.2. Definition of the Stiffness and Damping Coefficients of Oil-Film…17
2.2. Measurement of Coefficients of Stiffness and Damping of Liquid-Film of Hydrodynamic Journal Bearing 19
2.2.1. Static-Load Method for Measuring Stiffness of Lubricant Film 19
2.2.2. Centrifugal Forces by Using Imbalance Mass for Measuring Damping Coefficients 24
2.3. Analysis of the Stability of Hydrodynamic Journal Bearing 28
2.3.1. Attitude Angle 28
2.3.2. Critical Mass and Critical Frequency 31

Chapter 3 Fabrication of the Experimental Equipments and Procedures………41
3.1. Design of Hydrodynamic Journal Bearing with Herringbone Microgrooves 41
3.2. Balance for the Rotor and Fabrication of the Experiment Fan 43
3.2.1. Residual Imbalance of the Rotor 43
3.2.2. Fabrication of the Experiment Fan 44
3.3. Experimental Equipments for the Measurement of Dynamic Characteristics 47
3.4. Experimental Procedures for the Measurement of Dynamic Characteristics 51

Chapter 4 Results and Discussion 84
4.1. Motion of the rotor under Static Loading by Using an Electromagnet 84
4.2. Effects of electromagnetic loading on the stiffness and damping coefficients 85
4.2.1. Repeatability Verification 86
4.2.2. Loading effects on the stiffness and damping coefficients 88
4.2.3. Verification of the Method for Measurements and Calculations of the Stiffness and Damping Coefficients 88
4.2.4. Nondimensional Analysis of the Stiffness and Damping Coefficients 90
4.3. Effects of Rotating Speed on the Stiffness and Damping Coefficients 92

Chapter 5 Conclusions and Future Prospects 113

References………………………………………………115

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