Machinery Vibration and Rotordynamics E-Book

John M. Vance

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 504

Veröffentlichungsjahr: 2010

Beschreibung

An in-depth analysis of machine vibration in rotating machinery

Whether it's a compressor on an offshore platform, a turbocharger in a truck or automobile, or a turbine in a jet airplane, rotating machinery is the driving force behind almost anything that produces or uses energy. Counted on daily to perform any number of vital societal tasks, turbomachinery uses high rotational speeds to produce amazing amounts of power efficiently. The key to increasing its longevity, efficiency, and reliability lies in the examination of rotor vibration and bearing dynamics, a field called rotordynamics.

A valuable textbook for beginners as well as a handy reference for experts, Machinery Vibration and Rotordynamics is teeming with rich technical detail and real-world examples geared toward the study of machine vibration. A logical progression of information covers essential fundamentals, in-depth case studies, and the latest analytical tools used for predicting and preventing damage in rotating machinery. Machinery Vibration and Rotordynamics:

• Combines rotordynamics with the applications of machinery vibration in a single volume

• Includes case studies of vibration problems in several different types of machines as well as computer simulation models used in industry

• Contains fundamental physical phenomena, mathematical and computational aspects, practical hardware considerations, troubleshooting, and instrumentation and measurement techniques

For students interested in entering this highly specialized field of study, as well as professionals seeking to expand their knowledge base, Machinery Vibration and Rotordynamics will serve as the one book they will come to rely upon consistently.

Leseprobe

Table of Contents

Title Page

Copyright Page

Dedication

PREFACE

Chapter 1 - FUNDAMENTALSOF MACHINE VIBRATION AND CLASSICAL SOLUTIONS

THE MAIN SOURCES OF VIBRATION IN MACHINERY

THE SINGLE DEGREE OF FREEDOM (SDOF) MODEL

USING SIMPLE MODELS FOR ANALYSIS AND DIAGNOSTICS

SIX TECHNIQUES FOR SOLVING VIBRATION PROBLEMS WITH FORCED EXCITATION

SOME EXAMPLES WITH FORCED EXCITATION

SOME OBSERVATIONS ABOUT MODELING

UNSTABLE VIBRATION

REFERENCES

EXERCISES

Chapter 2 - TORSIONAL VIBRATION

TORSIONAL VIBRATION INDICATORS

OBJECTIVES OF TORSIONAL VIBRATION ANALYSIS

SIMPLIFIED MODELS

COMPUTER MODELS

TORSIONAL VIBRATION MEASUREMENT

FRENCH’S COMPARISON EXPERIMENTS

A SPECIAL TAPE FOR OPTICAL TRANSDUCERS

TIME-INTERVAL MEASUREMENT SYSTEMS

REFERENCES

EXERCISES

Chapter 3 - INTRODUCTION TO ROTORDYNAMICS ANALYSIS

OBJECTIVES OF ROTORDYNAMICS ANALYSIS

THE SPRING-MASS MODEL

SYNCHRONOUS AND NONSYNCHRONOUS WHIRL

ANALYSIS OF THE JEFFCOTT ROTOR

SOME DAMPING DEFINITIONS

THE “GRAVITY CRITICAL”

CRITICAL SPEED DEFINITIONS

EFFECT OF FLEXIBLE (SOFT) SUPPORTS

ROTORDYNAMIC EFFECTS OF THE FORCE COEFFICIENTS—A SUMMARY

ROTORDYNAMIC INSTABILITY

EFFECT OF CROSS-COUPLED STIFFNESS ON UNBALANCE RESPONSE

ADDED COMPLEXITIES

GYROSCOPIC EFFECTS

EFFECT OF SUPPORT ASYMMETRY ON SYNCHRONOUS WHIRL

FALSE INSTABILITIES

REFERENCES

EXERCISES

Chapter 4 - COMPUTER SIMULATIONS OF ROTORDYNAMICS

DIFFERENT TYPES OF MODELS

BEARING AND SEAL MATRICES

TORSIONAL AND AXIAL MODELS

DIFFERENT TYPES OF ANALYSES

EIGENANALYSIS

LINEAR FORCED RESPONSE (LFR)

TRANSIENT RESPONSE

SHAFT MODELING RECOMMENDATIONS

EXAMPLE SIMULATIONS

REFERENCES

Chapter 5 - BEARINGS AND THEIR EFFECT ON ROTORDYNAMICS

FLUID FILM BEARINGS

FIXED-GEOMETRY SLEEVE BEARINGS

VARIABLE-GEOMETRY TILTING PAD BEARINGS

FLUID FILM BEARING DYNAMIC COEFFICIENTS AND METHODS OF OBTAINING THEM

LOAD BETWEEN PIVOTS VERSUS LOAD ON PIVOT

INFLUENCE OF PRELOAD ON THE DYNAMIC COEFFICIENTS IN TILT PAD BEARINGS

INFLUENCE OF THE BEARING LENGTH OR PAD LENGTH

INFLUENCE OF THE PIVOT OFFSET

INFLUENCE OF THE NUMBER OF PADS

BALL AND ROLLING ELEMENT BEARINGS

CASE STUDY: BEARING SUPPORT DESIGN FOR A ROCKET ENGINE TURBOPUMP

SQUEEZE FILM DAMPERS

APPLICATIONS OF SQUEEZE FILM DAMPERS

INSIGHTS INTO THE ROTOR - BEARING DYNAMIC INTERACTION WITH SOFT/STIFF BEARING SUPPORTS

INFLUENCE ON NATURAL FREQUENCIES WITH SOFT/STIFF BEARING SUPPORTS

EFFECTS OF MASS DISTRIBUTION ON THE CRITICAL SPEEDS WITH SOFT/STIFF BEARING SUPPORTS

INFLUENCE OF ERHUNG MASS ON NATURAL FREQUENCIES WITH SOFT/STIFF SUPPORTS

INFLUENCE OF GYROSCOPIC MOMENTS ON NATURAL FREQUENCIES WITH SOFT/STIFF BEARING SUPPORTS

REFERENCES

EXERCISES

APPENDIX: SHAFT WITH NO ADDED WEIGHT

Chapter 6 - FLUID SEALS AND THEIR EFFECT ON ROTORDYNAMICS

FUNCTION AND CLASSIFICATION OF SEALS

UNDERSTANDING AND MODELING DAMPER SEAL FORCE COEFFICIENTS

ALFORD’S HYPOTHESIS OF LABYRINTH SEAL DAMPING

CROSS-COUPLED STIFFNESS MEASUREMENTS

INVENTION OF THE POCKET DAMPER SEAL

POCKET DAMPER SEAL THEORY

ROTORDYNAMIC TESTING OF POCKET DAMPER SEALS

IMPEDANCE MEASUREMENTS OF POCKET DAMPER SEAL FORCE COEFFICIENTS (STIFFNESS AND ...

THE FULLY PARTITIONED PDS DESIGN

EFFECTS OF NEGATIVE STIFFNESS

FREQUENCY DEPENDENCE OF DAMPER SEALS

LABORATORY MEASUREMENTS OF STIFFNESS AND DAMPING FROM POCKET DAMPER SEALS AT ...

FIELD EXPERIENCE WITH POCKET DAMPER SEALS

DESIGNING FOR DESIRED FORCE COEFFICIENT CHARACTERISTICS

SOME COMPARISONS OF DIFFERENT TYPES OF ANNULAR GAS SEALS

REFERENCES

Chapter 7 - HISTORY OF MACHINERY ROTORDYNAMICS

THE FOUNDATION YEARS, 1869 - 1941

REFINING AND EXPANDING THE ROTORDYNAMIC MODEL, 1942-1963

MULTISTAGE COMPRESSORS AND TURBINES, ROCKET ENGINE TURBOPUMPS, AND DAMPER ...

NEW FRONTIERS OF SPEED AND POWER DENSITY WITH ROCKET ENGINE TURBOPUMPS

SHAFT DIFFERENTIAL HEATING (THE MORTON EFFECT)

REFERENCES

INDEX

This book is printed on acid-free paper.

Copyright © 2010 by John Wiley & Sons, Inc. All rights reserved.

Published by John Wiley & Sons, Inc., Hoboken, New Jersey

Published simultaneously in Canada

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Library of Congress Cataloging-in-Publication Data:

Vance, John M.

Machinery vibration and rotordynamics / John Vance, Brian Murphy, Fouad Zeidan. p. cm.

Includes bibliographical references and index.

ISBN 978-0-471-46213-2 (cloth)

1. Rotors-Dynamics. 2. Rotors-Vibration. 3. Machinery-Vibration. 4.

Turbomachines-Dynamics. I. Murphy, Brian, 1956- II. Zeidan, Fouad. III. Title.

TJ177.V36 2010

621.8’ 11—dc22 2009045963

The first author gratefully dedicates his part in this book to his loving wife Louise, who made the book possible by her unselfish support of the task and devotion to her husband while it was being written.

John M. Vance

PREFACE

This book follows the first author’s book Rotordynamics of Turbomachinery in its practical approach and style. Much of the material in that book has been updated and extended with new information, new examples, and a few corrections that reflect what has been learned since then. Of particular interest and significance are the new chapters (4, 5, and 6) on bearings, seals, and computer modeling contributed by the co-authors Dr. Fouad Zeidan and Dr. Brian Murphy. Dr. Zeidan is the president of two companies that design and manufacture high performance bearings and seals. These products often require the design and modeling of the complete rotor-bearing system to ensure reliable operation and compatibility. Dr. Murphy is the author of XLRotor™, one of the most widely used computer programs for rotordynamic analysis. Chapters 1 and 7 are also completely new. Chapter 1 describes the classical analytical techniques used by engineers for troubleshooting vibration problems. Chapter 7 gives a history of the most important rotordynamics analysis and experiments since 1869.

The authors have noted (with some surprise) for many years that the subject material of this book is not taught in most engineering colleges, even though rotating machines are probably the most common application of mechanical engineering. The book is organized so that the first three or four chapters could be used as a text for a senior or graduate college elective course. These chapters have exercises at the end that can be assigned to the students, which will greatly enhance their understanding of the chapter material. The later chapters will serve the same students well after graduation as reference source material with examples of analysis and test results for real machines, bearings, and seals. But for the majority of engineers assigned to troubleshoot a rotating machine, or to design it for reliability, and having no relevant technical background, this entire book can be the substitute for the course they never had.

It is the author’s hope that this book will make a significant contribution to the improvement of rotating machines for the service of mankind in the years to come.

John M. Vance Fouad Y. Zeidan Brian T. Murphy

1

FUNDAMENTALSOF MACHINE VIBRATION AND CLASSICAL SOLUTIONS

This chapter is focused on practical applications of mechanical vibrations theory. The reader may want to supplement the chapter with one of the vibration textbooks in the reference list at the end of the chapter if he has no background in the theory.

THE MAIN SOURCES OF VIBRATION IN MACHINERY

The most common sources of vibration in machinery are related to the inertia of moving parts in the machine. Some parts have a reciprocating motion, accelerating back and forth. In such a case Newton’s laws require a force to accelerate the mass and also require that the force be reacted to the frame of the machine. The forces are usually periodic and therefore produce periodic displacements observed as vibration. For example, the piston motion in the slider-crank mechanism of Fig. 1-1 has a fundamental frequency equal to the crankshaft speed but also has higher frequencies (harmonics). The dominant harmonic is twice crankshaft speed (2nd harmonic). Figure 1-2a shows the displacement of the piston. It looks almost like a sine wave but it is slightly distorted by higher-order harmonics due to the nonlinear kinematics of the mechanism. Fig. 1-2b shows the acceleration of the piston, where the 2nd harmonic is amplified since the acceleration amplitude is frequency-squared times the displacement amplitude.

Figure 1-1 Slider-crank mechanism.

Another type of machine vibration problem, less common but more difficult to deal with, can come from the characteristic natural vibration frequencies (eigenvalues) of the machine structure and its supports, even if no imbalance or excitation is present. Natural frequencies die out in static structures due to the energy dissipated by damping, but in rotating machines they can grow larger with time. This is known as self-excited instability or rotordynamic instability. It is an innate potential characteristic of some rotating machines, especially when fluid pressures are present (e.g., bearings, impellers, turbine wheels, or seals).

Every real structure has an infinite number of natural frequencies, but many machinery vibration problems involve just one of these frequencies. That is why the simple single degree of freedom (SDOF) model (with just one natural frequency) presented in vibration textbooks [1-3] can be useful for analyzing vibration in machines. In fact, a SDOF model, consisting of one rigid mass, one spring, and one damper can be constructed to represent the vibration characteristics of any real machine in the neighborhood of a particular natural frequency of interest. This is called a modal model. To make physical sense out of complex machinery vibration data, or from realistic computer simulations of machinery vibration, the details of the SDOF mathematical model, its variations, and its solutions must be burned indelibly into the mind of the vibration engineer.