Vibration Diagnostic of Rotor Mechanisms in Ships

L&/$>oN/33/0,2

1 Title Page

Vibration Diagnostic of

Rotor Mechanisms in Ships

G.G. Jayarathne

This Thesis was submitted to the Department of Mechanical Engineering of the University of Moratuwa en- the- in partial fulfillment of the requirements for the Degree of Master of Philosophy.

074441

University of Moratuwa

Department of Mechanical Engineering, University of Moratuwa, / L4-. u / - . / . Sri Lanka. November, 2001.

T H

7 4 4 4 1

Declaration

Here with, I certify that the work included in the Thesis in part or whole, has not been submitted for any other academic qualification at any institution.

(Candidate) (Supervisor)

ABSTRACT

In ships, there are so many sources of noise and Vibration such as propulsion engines and electric generators in restricted spaces and structures of ships, which are made of steel, transmit vibration well. By the reasons, noise and vibration of ships are very big by nature and reduction of noise and vibration is important subject for ships. Regarding noise reduction, reduction of noise cause by vibration has difficulty and the major part of such noise is structure born noise.

"Vibration" is not a problem. It is a physical manifestation of machinery imperfection. It is used to help find obvious and subtle deviations in machines. No machine runs perfect. "Diagnosis" is the Method of Detection. If, a fault develops and goes undetected, then, at best, the problem will not be too serious and can be remedied quickly and cheaply; at

T worst, it may result in expensive damage and down-time, injury, or even loss of life. There is no reason or excuse to have machinery operate unprotected. The areas of interest in vibration measuring in plant maintenance are general measurement, analysis, and corrective.

All rotor mechanisms in ships consist of shafts, bearings, couplings, gears etc. These machinery operate under various load conditions from light to heavy. Ship propulsion system comparatively works under very heavy load conditions with rolling and pitching of the ship which may tend to cause overstressing of shafts.

Objective of the Research: The aim of the project is to identify the vibration analysis of a ship transmission system. A ship transmission system is the link between the crank shaft (or thrust block) end and the propeller of the vessel. As it contains number of shafts, couplings and bearings it tends to cause severe vibrations due to various running and incipient defects. These defects can be diagnosed by measuring the level of vibration to the extent they excited.

Methodology Adopted: A Test Rig:

The test rig is a model of the transmission system of the ship "M/V Lanka Mahapola" made in to a scale of 1:10. Level and condition of lubrication maintained. Accelerometers are mounted over the bearing casings to trace the excitement of individual bearings.

Diagnosis of the misaligned and unbalanced shafts and defected sleeve (fluid film) bearings are done by using the "AUTOVIB" software package which is a vibration

* monitoring method introduce by this project.

Final Outcome of this research : Although spectrum analysis method is not in use, similar demodulation techniques, will be practical, for the diagnostics of Sleeve (Fluid Film) bearings.

Measurement of the vibrations excited by bearing friction forces present all the necessary information for Diagnostics of bearing condition including installation problems and the quality of lubrication.

iii

Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne

ACKNOWLEDGEMENT

I'd like to give special thanks to Dr. T.A. Piyasiri , Director/ITUM, who encouraged me for a M.Phil. Big tip of the hat to Dr. Piyasiri, for his help and valuable suggestions given.

A special thanks goes to Prof. P.A.de Silva, Ex. Head/Mechanical Engineering, for his grateful effort and valuable advices to make this success.

This project wouldn't have been possible without the concerted effort (on importing Vibration measuring equipment) of Former Dean/ Engineering Prof. L.L.Rathnayake.

I owe a debt of a gratitude to Head/ Mechanical Engineering, Dr. S.R. Tittagala who has provided feedback on early attempts, which has been incorporated to this successful one.

Thanks to all the current and former Supervisors of the project. In particular following individuals gave me their valuable advices and ideas in addition to proper guiding.

An extra special thanks goes to Dr. P.A.B.A. Ranjan Perera, a Supervisor of the Project, who after reading these chapters for several times an unerring eye for detail and manuscript editing support, must now know more than any other else.

Very special thanks go out to Dr. W.K.Wimalsiri, a Supervisor of the Project. His support continues to be invaluable. I appreciate the dedicated support of Dr. Wimalsiri, who provided ideas and advices through out the project.

Of course, Chairman/ Progress Review Committee Dr. Thusitha Sugathapala deserves special thanks for always keeping everything running smoothly and inspiring me when I didn't feel very inspired.

Thanks go to Mr. S.Ganesupiragash deciphering program properties and events in programming languages, providing useful suggestions.

I am specially appreciative the efforts of the Mr. Darshana Liyanage imparted to the hardware application.

Of course without the support of the staff in Maritime Division Mr. M.D.D. Gunathilake and Mr. Sunil Wickramasinghe, the Test Bed made for the project would be nothing more than a dream.

iv

Vibration Diagnostic of Rotor Mechanism in Ships By G.GJayarathne

C O N T E N T S

C O N T E N T S

LIST OF F IGURES A N D TABLES

P A G E

XIV - XX

LIST OF ABBREVIATIONS XXI - XXVIII

PREFACE XXIX - XXXVIII

CHAPTER I

I

LITERATURE SURVEYS CONDITION MONITORING AND FAULT DIAGNOSIS

INTRODUCTION . . . . .

PREVIOUS L ITERATURE REVIEWS AND SURVEYS

2 . I MASS UNBALANCE

2 . 2 BENT SHAFTS

2 . 3 CRACKED SHAFTS

2 . U CAN ONE AFFORD PLANT DOWNTIME ? .

2 . 5 WHAT IS 'CONDITION MONITORING'? .

2 . 6 WHERE CAN I T BE APPLIED

L ITERATURE SURVEY . . . .

3 . I APPLICATION OF SHOCK PULSE METHOD . (SPM) FOR ROLLING BEARING AND I T S DRAWBACKS AS A MONITORING METHOD

3 . 2 DIFFERENCE BETWEEN SHOCK PULSE AND IBRATION

PROCESSING SHOCK PULSE SIGNALS .

SHOCK PULSE PATTERNS

MEASURING OPERATION CONDITION

3

U

5

I - 13

2

3

6

8

9

9

10

10

10

10

II

12

13

CHAPTER II CODE ON NOISE LEVELS ON BOARD SHIPS \U - 18

II . I SCOPE . . . . . 15

II . 2 PURPOSE . . . . . . 15

II . 3 NOISE LEVEL L IMITS . . . . 15

V.


CONTENTS

C h a p t e r III ROTOR MECHANISMS IN SHIPS; . 1 9 - 2 0 CLASSIFICATION; ELEMENTS; SOURCES OF VIBRATION

III . I CLASSIFICATION OF SHIPS ROTOR ZO MECHANISMS

III . 2 ELEMENTS OF ROTOR MECHANISMS IN SHIPS 20

C h a p t e r IV MODES OF VIBRATION 2 1 - 2 5

IV . I TORSIONAL VIBRATION . . . . 22

IV . I . I HOLZER ANALYSIS OF TORSIONAL SYSTEM 23

IV . I . 2 DRIVE TRAIN ANALYSIS 23

IV . I . 3 VIBRATION AMPLITUDES ZU

IV . 2 RANDOM VIBRATION 2U

IV . 2 . I WHY DO WE CARE ABOUT RANDOM 25 VIBRATION?

IV . 2 . 2 WHAT IS FREQUENCY RESPONSE 25 ANALYSIS ?

CHAPTER V MAIN CAUSE OF SHIP VIBRATION 2 6 - 3 1

V . I INTRODUCTION . . . . . 27

V . I . I THE ACTION OF THE SEA 27

V . I . 2 VIBRATION IN SHIPS . . . 27

V . I . 3 OUT OF BALANCE FORCES IN 31 RECIPROCATING MACHINARY

CHAPTER VI VIBRATION ANALYSIS 3 2 - 3 5

VI . I INTRODUCTION . . . . . 33

VI . 2 ANALYSIS FREQUENCY IU

VI . 3 ADVANTAGES / LIMITATIONS . . . 35


CONTENTS

CHAPTER VII FOURIER ANALYSIS

VII . I CLASSIFICATION OF DATA

VII . I . I DIFFERENCES BETWEEN DETERMINISTIC AND RANDOM DATA

VII . I . 2 STATIONARY AND ERGODIC RANDOM . DATA

VII . I . 3 NON-STATIONARY DATA

VII . I . U NATURE OF TRANSIENT DATA

VII . I . 5 FREQUENCY SPACING AND LENGTH CONSIDERATIONS

VII . I . 6 PADDING WITH ZEROS .

VII . I . 7 EFFECT OF RECORD LENGTH .

VII . I . 8 COMPUTATIONAL VERSUS RESOLUTION BANDWIDTH

VII . I . 9 RESOLUTION L IMITS

VII . I . 10 NONZERO MEAN VALUES

VII . I . II TIME WEIGHTING FUNCTIONS AND SPECTRAL LEAKAGE

VII . I . 12 ANALYZING SHORT DURATION TRANSIENTS

VII . I . 13 E F F E C T S OF ZERO PADDING

VII . I . \U E F F E C T S OF RECORD LENGTH .

VII . I . 15 E F F E C T S OF TIME WEIGHTING FUNCTIONS . (WINDOWING)

VII . I . 16 HANDLING NON-ZERO MEAN VALUES .

VII . I . 17 PRACTICAL EXAMPLES USING DETERMINISTIC AND RANDOM TRANSIENT WAVE FORM

VII . I . 18 CONTINUOUS SINE WAVE

VII

VII

THE COMPLEX FOURIER TRANSFORMS

. 2 . 1 THE COMPLEX FOURIER TRANSFORMS (IN DETAIL)

VII . 2 . 2 TIME AND FREQUENCY REPRESENTATION

VII . 2 . 3 TIME AND FREQUENCY DOMAINS

36 - 75

37

37

38

38

38

U\

U2

U2

UU

UU

U5

U5

Ub

Ub

Ub

Ul

Ul

50

bU

5U

55

55


CONTENTS

VII . 3 DISCRETE FOURIER TRANSFORM AND THE F F T 59

* VII . 3 . I INTRODUCTION . . . 59

VII . 3 . 2 THE DISCRETE FOURIER TRANSFORMS. 59

VII . 3 . 3 FAST FOURIER TRANSFORMS . 61

VII . 3 . U F I L T E R S . . . . 62

VII. 3 . U . I FILTERING . . . 62

VII . 3 . U . 2 ANTI-ALIASING F I L T E R S 62

VII . 3 . 5 FOURIER TRANSFORM PROPERTIES 65

VII . 3 . 5 . I SCALING PROPERTY 65

* VII . 3 . 5 . 2 SHIFTING PROPERTY . 66

VII . 3 . 6 APPROXIMATION OF CONTINUOUS 66

TRANSFORMS WITH THE DFT

VII . U SAMPLING THEOREM . . . . 67

VII . 5 REAL TIME ANALYSIS . . . . 69

VII . 6 C-PROGRAM FOR FAST FOURIER TRANSFORMATION 70

CHAPTER VIII TYPES OF BEARINGS 7 6 - 7 9

VIII . I ROLLING BEARINGS . . . . 77

VIII . 1 . 1 DEEP GROVE BALL BEARINGS . 78

VIII . 1 . 2 SELF-ALIGNING BALL BEARINGS 78

VIII . 1 . 3 ANGULAR CONTACT BALL BEARINGS . 78

VIII . I . U NEEDLE ROLLER BEARINGS 78

VIII . 1 . 5 SPHERICAL ROLLER BEARINGS 78

VIII . 1 . 6 TAPER ROLLER BEARINGS 78

VIII . 1 . 7 THRUST BALL BEARINGS 79

* VIII . I . 8 CYLINDRICAL ROLLER T H R U S T BEARINGS 79

VIII . 1 . 9 NEEDLE ROLLER T H R U S T BEARINGS . 79

VIII . 2 HYDRO-DYNAMIC BEARINGS . . . 79

VIII . 3 SLEEVE BEARINGS . . . . 79

ix


CONTENTS

CHAPTER IX LIFE OF BEARINGS 8 0 - 8 7

IX . I INTRODUCTION . . . . . 81

IX . 2 IRREGULARITIES OF BALL BEARINGS 82

IX . 3 BEARING WEAR AND I T S CAUSES . . . 83

IX . 3 . I WEAR CAUSED BY ABRASIVE PARTICLES 83

IX . 3 . 2 WEAR CAUSED BY INADEQUATE 83 LUBRICATION

IX . 3 . 3 WEAR CAUSED BY VIBRATION . 8*.

IX . 3 . U SURFACE D I S T R E S S AND I T S CAUSES . 85

IX . 3 . 5 IONS AND T H E I R CAUSES 85

IX . 3 . 6 INDENTATIONS CAUSED BY FAULTY . 85 MOUNTING OR OVERLOADING

IX . 3 . 7 DAMAGE CAUSED BY THE PASSAGE OF . 85 ELECTRIC CURRENT

IX . U BEARING CRACKS . . . . 86

IX . U . I CRACKS CAUSED BY ROUGH TREATMENT 86

IX . U . 2 CRACKS CAUSED BY SMEARING 86

IX . U . 3 CRACKS CAUSED BY FRETTING CORROSION 86

IX . 5 BEARING CORROSSION . . . . 87

IX . 5 . I CORROSION . . . . 87

IX . 5 . 2 FRETTING CORROSION 87

CHAPTER X VIBRATION MONITORING . 8 8 - 9 1

X . I INTRODUCTION . . . . . 89

X . 2 CORRECTIVE MEASURES . . . . 89

CHAPTER XI CONDITION MONITORING AND 92 - 100 FAULT DIAGNOSTICS

XI . I MACHINE MONITORING SYSTEMS . . . 93

- MAINTANANCE PROCEDURE

XI . I . I PREDICTIVE MAINTANANCE 93

XI . I . 2 CONDITION MONITORING 9^.

XI , 2 FORMS OF TECHNICAL MAINTANANCE 98

XI . 2 . I METHODS FOR CONTROLLING THE 98 CONDITION OF MACHINES AND MECHANISMS

x


CONTENTS

CHAPTER XII VIBRATION MEASURING EQUIPMENT 101 - IU,

* ' XII . I INTRODUCTION . . . . . 102

XII . 2 ACCELEROMETERS \QU

XII . 2 . I THE PIEZOELECRIC EFFECT, THEORY, I0Z. DESIGN AND USAGE

XII . 3 CHARGE AMPLIFIERS . . . . 109

XII . 3 . I TIME CONSTANT AND DRIFT 110

XII . 3 . 2 FREQUENCY AND TIME DOMAIN 110 CONSIDERATION

XII . U LOW IMPEDANCE PIEZOELECTRIC . . . I l l TRANSDUCERS

XII . U . I TIME CONSTANT . . . 112

XII . 5 LOW IMPEDANCE POWER SUPPLY (COUPLER) 113

XII . 5 . I TIME CONSTANT . . . 113

XII . 5 . 2 SELECTION METRIX . . . 113

XII . 5 . 3 DUAL MODE CHARGE AMPLIFIERS 113

XII . 6 HIGH AND LOW IMPEDANCE SYSTEM \\U COMPARISON

XII . 6 . I SIMILARITIES \\U

XII . 6 . 2 HIGH IMPEDANCE SYSTEMS HIGH \\U

XII . 6 . 3 LOW IMPEDANCE SYSTEMS \\U

XII . 7 EXTERNAL IMPEDANCE CONVERTERS \\U

CHAPTER XIII VIBRATION MEASURING EQUIPMENT USED 115 - 119

XIII . I PIEZOELECTRIC ACCELEROMETER, DESIGN a U S E . 116

XIII . 1 . 1 MEASURING ACCELERATION 116

* XIII . 1 . 2 ACCELEROMETER MOUNTING . 118

XIII . 1 . 2 . 1 STUD MOUNTING 118

XIII . 1 . 2 . 2 ADHESIVE MOUNTING . 118

XIII . 1 . 2 . 3 TRIAXIAL MOUNTING 119

XIII . \ . Z . U STRAIN RELIEVING CABLE 119

XIII . 1 . 3 CALIBRATION TECHNIQUES 119

XIII . 1 . 3 . 1 ACCELEROMETERS 119

xi


CONTENTS

CHAPTER XIV VIBRATION MONITORING SYSTEM 120 - \ZU

XIV . I INTRODUCTION . . . . . 121

XIV . 2 WHY SEELVE BEARINGS ARE SELECTED ? 123

XIV . 2 . I COMMENT . . . . 123

XIV . 2 . 2 OBSERVATIONS: . . . \ZU

CHAPTER XV DATA ACQUISITION CARD : ACL - 8I2PG 125 - 130

XV . I INTRODUCTION . . . . . 126

XV . 2 A SELECTION OF MEASUREMENT LOCATION 127

XV . 3 SELECTION OF THE INTERVALS BETWEEN 127 MEASURMENTS

XV . U C-PROGRAME FOR CONVERSION OF ANALOG 127 SIGNAL INTO DIGITAL VALUES

XV . 5 PROJECT DATA . . . . . 127

XV . 6 CONVERSION OF DIGITAL VALUE TO 129 ACCELERATION UNITS

XV . 7 R E S U L T S OBTAINED FROM FAST FOURIER 130 TRANSFORMATION - ACCELARATION IN MM/S2

CHAPTER XVI 'AUTOVIB' - VIBRATION ANALYSING 131 - 137

PROGRAMME

XVI . I INTRODUCTION . . . . . 132

XVI . 2 'AUTOVIB' - VIBRATION ANALYSING PROGRAMME . 135

XVI . 3 EXAMPLES OF GRAPHS OBTAINED FROM . 135 'AUTOVIB' PROGRAM

XVII . U FAULT DETECTION IN ROTATING MACHINERY 136

XVII . 5 OVERALL MEASUREMENT AND SPECTRUM 136 COMPARISON

XVII . 6 HOW SPECTRUM CHANGES ARE RELATED 136 TO THE CONDITION OF A MACHINE

Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne ' < • \.-^

CONTENTS

CHAPTER XVII DATA ANALYSIS 138 - 168

XVII . I ENVELOPE SPECTRA OBTAINED FROM 139 ELECTRIC MOTOR (EM02, EMRI AND ECUP)

XVII . 2 COMPARISON OF GRAPHS Al B l l , AL.B2I . 144 AND AL-B3I

XVII . 3 THE MAIN FAULTS CAUSING VIBRATIONS AT 146 MACHINE ROTATING FREQUENCY

XVII . 4 FINDINGS . . . . . 165

CHAPTER XVIII CONCLUSION 169 - 173

CONCLUSION . . . . . . 170

A P P E N D I X - A C-PROGRAM FOR FAST FOURIER . 174 - 177 TRANSFORM

APPENDIX - B C-PROGRAME FOR CONVERSION OF 178 - 183 ANALOG SIGNAL INTO DIGITAL VALUES

APPENDIX - C 'AUTOVIB' - VIBRATION ANALYSING 184 - 194 PROGRAMME

APPENDIX - D AUTO SPECTRA AND ENVELOPE SPECTRA. 195 - 239 AT DIFFERENT CONDITIONS OF A MACHINE

APPENDIX - E ENVELOPE SPECTRA AT DIFFERENT . 240 - 285

CONDITIONS OF A MACHINE

APPENDIX - F VIBRATION MONITORING TEST BED 286 - 303

REFERENCES 304 - 311

G L O S S A R Y 312 320 GLOSSARY . . . . . . . 313


LIST O F FIGURES A N D T A B L E S

LIST O F FIGURES A N D T A B L E S

LIST OF FIGURES

F I G N O . F I G U R E P A G E N O .

FIG.

FIG.

FIG.

FIG.

FIG.

. 3 . 3 . 1 Shock Pu lse Transducer and i ts Vibration Signal II

. 3 . U . I Filtered Transducer S igna ls 12

. 3 . 5 . 1 Measurements using Shock Pu lse Meter 13

I . I Allowable Daily and Occasional No ise 16 Exposure Z o n e s

I . 2 Resonance Curve 17

FIG. VII . I . 10 . I S ine Shock Pu lse 44

FIG. VII . I . 17 . I Half Cycle S ine Pu lse , I ts Four ier T r a n s f o r m 48 Magnitude, and Imaginary Component (scale shifted).

FIG. VII . I . 17 . 2 One Cycle S ine Pu lse , and Its Four ier T r a n s f o r m 49

Magnitude.

FIG. VII . I . 17 . 3 S ine Wave and I ts Four ier Transformat ion 51 Curves

FIG. VII . I . 17 . U Four ier T r a n s f o r m of 1 H z 53

FIG. VII . 2 . 3 . I T i m e Domain Signal 56

FIG. VII . 2 . 3 . 2 Frequency Domain 56

FIG. VII . 2 . 3 . 3 Example of a Non - Harmonic Periodic Motion 57 (Piston Acceleration of a Combustion Engine)

FIG. VII . 2 . 3 . U Il lustration of How the Waveform can be 57 "Broken Up" into a S u m of Harmonically Related S ine -Waves


LIST OF FIGURES AND TABLES

4

FIG. VII . 2 . 3 . 5 Il lustration of How the Signal can be Described in T e r m s of a Frequency Spectrum

58

FIG. VII . u . 1 Undersampled, Oversampled, and Critically -Sampled Unit Area Gaussian Curves.

68

FIG. VII . 6 . 1 Recording an Array (Here of Length 8) by Bi t Reversal , (A) between T w o Arrays, v e r s u s (B) In Place.

73

FIG. VII . 6 . 2 Input and Output Ar rays for F F T 75

FIG. XI . 2 . 1 . 1 Measured Vibration f rom T e s t s of Periodic Conditions

99

FIG. XI . 2 . 1 . 2 A Typical Model of a Mechanism, in Absence of

Prophylactic Maintenance

99

FIG. XII . 2 . 1 . 1 T h i n Slab Representation of Crysta ls 106

FIG. XII . 2 . 1 . 2 Var ious Effects on Crysta ls 106

FIG. XII . 2 . 1. 3 Typical Frequency Response Curve 108

FIG. XII . 3 . 1 Simpli f ied Charge Amplif ier Model 109

FIG. XII . U . 1 P I E Z O T R O N Circuit & Coupler III

FIG. XIII . 1 . 1 1 Typical Compress ion Mode Accelerometer 116

FIG. XIII . 1 . 1 2 K - S H E A R Accelerometer 117

FIG. XIII . 1 . 2 . A . I Cable Strain Relief 119

FIG. XIV . 1 . 1 Vibration Monitoring S y s t e m 122

FIG. XIV . 2 . 1 . 1 Sleeve Bearing Assemb ly 123

FIG. XIV . 2 . 1 . 2 Ball Bearing Assemb ly 123

FIG. XVI . 1 . 1 Illustrating of View Por ts 13/.

FIG. XVI . 3 . 1 Example of Graph Obtained f rom A U T O V I B ' Program

135

FIG. XVI . 3 . 2 Example of Graph Obtained from ' A U T O V I B ' Program

135

FIG. XVII . 1 . I Characteristics of Electric Motor with No Speed 1̂ 0

FIG. XVII . 1 . 2 Characteristics of Electric Motor in Running \UZ

xvi



FIG. XVII . 1 . 3 Characteristics of Electric Motor with Coupling 143 attached

FIG. XVII . 2 . 1 Characteristics of Aligned Shaft - Vibration 145 Measured on F i r s t Bearing

FIG. XVII . 2 . 2 Characteristics of Aligned Shaft - Vibration 145 Measured on Second Bearing

FIG. XVII . 2 . 3 Characteristics of Aligned Shaft - Vibration 146 Measured on Th i rd Bearing

FIG. XVII . 3 . 1 Characteristics of Bearing No. 1 with Loosen I47

Coupling No. 1

FIG. XVII . 3 . 2 Characteristics of Electric Motor with Loosen I48

Coupling No. 2


Coupling No. 1

FIG. XVII . 3 . U Characteristics of Bearing No. 3 with Loosen I50

Coupling No. 2

FIG. XVII . 3 . 5 Typical Spectrum - S u m m a r y of 150

Graphs XVII . 3 . 2 , 3 and 4

FIG. XVII . 3 . 6 Characteristics of Bearing No. 1 without I5I

Lubrication

FIG. XVII . 3 . 7 Characteristics of Bearing No. 2 without I52 Lubrication

FIG. XVII . 3 . 8 Characteristics of Bearing No. 3 without I53

Lubrication

FIG. XVII . 3 . 9 Typical Spectrum - S u m m a r y of the Graphs I53 made Out of FIG. XVII . 3 . 6, 7 and 8


Coupling No. 1

Vibration Diagnostic of Rotor Mechanism in Ships By G. G. Jayarathne . / . " >• y^f'


FIG. XVII . 3 . II Characteristics of Bearing No. 2 with Loosen \5U

Coupling No. 2

FIG. XVII . 3 . 12 Characteristics of Electric Motor with Loosen 155

Coupling No. 2


Bearing No. 1


Bearing No. 2

FIG. XVII . 3 . 15 Characteristics of Bearing No. 1 with Loosen I58 Bearing No. 3

FIG. XVII . 3 . 16 Effects of Soft Foot I58


Cap No. 1


Cap No. 1

FIG. XVII . 3 . 19 Characteristics of Electric Motor with Loosen I60

Cap No. 1

FIG. XVII . 3 . 20 Characteristics of Electric Motor with Loosen I6I

Cap No. 2

FIG. XVII . 3 . 21 Characteristics of Bearing No. 1 with Loosen I6I

Cap No. 2


Cap No. 2

FIG. XVII . 3 . 2 3 Characteristics of Bearing No. 1 with Loosen I62

Cap No. 3

FIG. XVII . 3 . ZU Characteristics of Bearing No. 2 with Loosen I63

Cap No. 3

xviii



F I G . X V I I . 3 . 25 Characteristics of Bearing No. 3 with Loosen

Cap No. 3

F I G . X V I I . 3 . 26 Characteristics of Electric Motor with Loosen

Cap No. 3

F I G . X V I I . 3 . 27 Typical Spectrum - S u m m a r y of the Graphs

made Out of FIG. XVII . 3 . 1 8 , 1 9 , 2 0 , 2 1 , 2 2 and 23

xix Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne


LIST OF TABLES

T A B L E N O . T A B L E P A G E N O .

TABLE VII . I . U . I B A S I C F O R M S OF F O U R I E R UO

T R A N S F O M E

TABLE VII . 3 . U . 2 . I S Y M M E T R Y P R O P E R T I E S O F 6U T H E F O U R I E R T R A N S F O R M

TABLE XI . I . 2 . I MONITORING P A R A M E T E R S 97

TABLE XV . 5 . I D A T A O B T A I N E D A F T E R ANALOG 128 / D IG ITAL C O N V E R S I O N

TABLE XV . 7 . I R E S U L T S O B T A I N E D F R O M F A S T 130 F O U R I E R T R A N S F O R M A T I O N

XX


LIST O F ABBREVIAT IONS

LIST O F ABBREVIAT IONS CHAPTER I

dBsv Decibel shock value

dBi Initial shock value

dBN Normalized shock value

CHAPTER II

v impact velocity

dB(A) Vibration energy measurement

L Length of the structure

M Function of the mass at the structure and its distribution

I Second moment of area of the material of the structure

about its neutral axis.

f Frequency of applied force

In Frequency of Natural Structure

CHAPTER IV

m Mass or inertia (in Spring-mass system) ( kg )

i Mass or inertia (in Torsional system) ( kg m )

K m Spring (in Spring-mass system) ( Nm )

Kt Spring (in Torsional system) (Nm/rad )

c m Damping (in Spring-mass system) (Ns/m )

c r Damping (in Torsional system) ( Nms/rad )

a Acceleration (in Spring-mass system) ( m /s )

6 Acceleration (in Torsional system) ( rad/s 2 )

v Velocity (in Spring-mass system) ( m /s )

6 Velocity (in Torsional system) (rad/s )

y Displacement (in Spring-mass system) (m )

0 Displacement (in Torsional system) ( rad )

xxii Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne

LIST OF ABBREVIATIONS

CHAPTER VII

F(l) Fourier Transform - Time response function

T Periodic time

CO/ Angular velocity

/ Time

an, a„, b„ Fourier transform coefficients

n Integral multiplier

/ o Fundamental frequency (first harmonic)

Af Frequency interval

/(/) Fourier time response

N Number of discrete values

At Sampling interval

/ v Sampling rate

/ v , Nyquist frequency

F(f) Fourier Transform - Frequency response function

Boxcar time response function

Boxcar frequency response function

Number of padded zeros

Number of data values in time series

Af Frequency Increment

Be Resolution bandwidth

fmax Highest frequency

X(f) Fourier transform

x(i) Inverse fourier transform

k Integral coefficient

cik, bk Fourier transform coefficients

f(X). g(X) Original functions

F ( s ) . G(S) Function after convolution

X(mF) Discrete frequency transform function

xxlii Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne


x(nT) Time response function

realOut Array of coefficients of cosine waves in the Fourier formula.

imagOut Array of coefficients of sine waves in the Fourier formula.

h(l) Impulse response

x(t) Input time domain

y(l) Output time domain

X(f) Input frequency domain

Y(f) Output frequency domain

H(f) Impulse frequency domain

f(w) Fourier transform function

f(x) Continuous time function

E(x) Even part of function f(x)

O(x) Odd part of function f(x)

j*(-x) Imaginary Function

F*(-s) Complex Conjugate of Function f(x)

F(s) Fourier Transform function of f(x)

p c Cosine Transform

p s Sine Transform

/' Numerous

xo A Real constant

P = ( x - x 0 )

B A frequency in Hz

H„ Discrete Fourier transform of N-points

W A Complex Number

hk A Vector

Fk k l h component of fourier transform

F'/i k"' Component of Fourier transform of length n/2

dataf 1 ] Real part of/o

data[2] Imaginary part of fo

xxiv



CHAPTER IX

Basic rating life of bearing

Undamped natural (resonant) frequency (Hz)

Frequency at any given point of the curve (Hz)

Output acceleration

Mounting base or reference acceleration

Factor of amplitude increase at resonance

Transducer capacitance

Cable capacitance

Range (or feedback) capacitor

Time constant resistor (or insulation of range capacitor)

Insulation resistance of input circuit (cable and transducer)

Charge generated by the transducer

Output voltage

Open loop Gain

Time Constant

Charge generated by piezoelectric element

Input signal at gate

Transducer capacitance

MOSFET GATE capacitance

Force

Mass

Acceleration

XXV


Li„

CHAPTER XII

f

a„

0

c,

c,

R,

Ri

q v 0

A

TC q

Vi

Cc, CHAPTER XIII

F

m

a


CHAPTER XIV

xxvi

T l , T2, T3 Accelerometers

EM Electric motor

B1,B2, B3 Bearings

I S Tail shaft

IS Intermediate shaft

C1,C2 Couplings

CHAPTER XVII

N Motor speed (rps)

n Number of balls

d Ball diameter

D Pitch diameter

B Contact angle of ball

Z Number of polls

F L Line frequency

N s Synchronous speed

F r o t Rotational frequency

F S Slip frequency

F,, Pole frequency

F Z Slot frequency

F Z ± F R O , Side bands

F z - 2 F L ± F R 0 | Side bands

F M Main supply frequency

EMO Characteristics of electric motor at 0 rpm

ECUP Characteristics of electric motor running with attached coupling only

EMR Characteristics of electric motor running with shafting and propeller



CAP1_B11 Characteristics of bearing no. 1 with loosen cap no. 1

CAP1B21 Characteristics of bearing no. 2 with loosen cap no.l

CAP1B31 Characteristics of bearing no. 3 with loosen cap no.l

CAP 1 EMI Characteristics of electric motor with loosen cap no.l

CAP2B11 Characteristics of bearing no. 1 with loosen cap no.2

CAP2_B21 Characteristics of bearing no. 2 with loosen cap no.2

C A P 2 B 3 1 Characteristics of bearing no. 3 with loosen cap no.2

CAP2_EM1 Characteristics of electric motor with loosen cap no.2


CAP3_B21 Characteristics of bearing no. 2 with loosen cap no.3


CAP3_EM1 Characteristics of electric motor with loosen cap no.3

LB1_B11 Characteristics of bearing no. 1 with loosen bearing no.l



L B 1 E M 1 Characteristics of electric motor with loosen bearing no. 1

L B 2 B 1 1 Characteristics of bearing no. 1 with loosen bearing no.2


LB2_B31 Characteristics of bearing no. 3 with loosen bearing no.2

L B 2 E M 1 Characteristics of electric motor with loosen bearing no.2

LB3B11 Characteristics of bearing no. 1 with loosen bearing no.3

LB3_B21 Characteristics of bearing no. 2 with loosen bearing no.3


LB3_EM1 Characteristics of electric motor with loosen bearing no.3

LC1_B11 Characteristics of bearing no. 1 with loosen coupling no. 1

LC1_B21 Characteristics of bearing no. 2 with loosen coupling no.l

LC1_B31 Characteristics of bearing no. 3 with loosen coupling no.l

LC1_EM1 Characteristics of electric motor with loosen coupling no.

LC2B11 Characteristics of bearing no. 1 with loosen coupling no.2

LC2B21 Characteristics of bearing no. 2 with loosen coupling no.2

Jr xxvii


L I S T O F A B B R E V I A T I O N S

L C 2 B 3 1 Characteristics of bearing no. 3 with loosen coupling no.2

LC2_EM 1 Characteristics of electric motor with loosen coupling no.2

UM_B11 Characteristics of bearing no. 1 with unbalance mass

U M B 2 1 Characteristics of bearing no. 2 with unbalance mass

UM_B31 Characteristics of bearing no. 3 with unbalance mass

UM_EM1 Characteristics of electric motor with unbalance mass

N0L1_B11 Characteristics of bearing no. 1 without lubrication

NOL2_B21 Characteristics of bearing no. 2 without lubrication

NOL3_B31 Characteristics of bearing no. 3 without lubrication

ECUP Characteristics of electric motor with coupling attached

A L B 11 Characteristics of bearing no. 1 with shaft aligned

AL_B21 Characteristics of bearing no. 2 with shaft aligned

AL_B31 Characteristics of bearing no. 3 with shaft aligned

•A X X V I I I


t

P R E F A C E

P R E F A C E

A ship is the home of the crew for months at a time and of her

passengers perhaps for weeks. The influence of vibration upon comfort

is therefore extremely important and wil l be a factor in the reputation

of any passenger ship.

Vibration P r o b l e m s on s h i p s s u c h a s m a s t , founda t ion , a n d p rope l l e r shaf t

vibrat ion exc i ted by propuls ion s y s t e m f r e q u e n c i e s c a n lead to s t ruc tura l

fa t igue , d a m a g e to mach ine r y , a n d c a n b e a n n o y i n g , uncomfo r t ab l e , a n d

d a n g e r o u s for p e r s o n s on t h e sh ip .

Vibrat ion h a s b e e n a m a t t e r of c o n c e r n to sh ip d e s i g n e r s s i n c e t h e e n d of t h e

19th c e n t u r y a l t h o u g h its p r e s e n c e in sh ip cha rac t e r i s t i c s w a s k n o w n long

be fo re t ha t t ime a n d its i m p o r t a n c e h a s b e c o m e m u c h e m p h a s i z e d o v e r t h e

las t half cen tu ry . S o m e sailing w a r s h i p s , particularly t h e lightly-built f r igates ,

suf fered from s e r i o u s vibration aft w h e n driven hard , p r o b a b l y a s a resul t of

flow interact ion while t h e r e a r e a c c o u n t s of mas t / sa i l c o m b i n a t i o n s c a u s i n g

s u c h s e v e r e vibration tha t c r e w m e n w e r e th rown from their fee t or, w o r s e ,

from their m a s t - t o p pos i t ions .

T o d a y , a n inc reas ing n u m b e r of n e w or a l te rna t ive s h i p s is l a u n c h e d - very

l a rge a n d very fast c o n t a i n e r sh ip s , c ru i se s h i p s , t a n k e r s with m o d e r n

p ropu l s ion s y s t e m s . D u e to little e x p e r i e n c e with s u c h s h i p s , living cond i t i ons

c a n b e a d v e r s e l y affected by vibration if t h e f r e q u e n c i e s of major exc i t a t i ons

a r e c l o s e to a na tura l f r equency of t h e s u p e r s t r u c t u r e or a par t of it.

In s h i p s , t h e r e a r e s o m a n y s o u r c e s of n o i s e a n d Vibration s u c h a s p ropu l s ion

e n g i n e s a n d e lect r ic g e n e r a t o r s in res t r ic ted s p a c e s a n d s t r u c t u r e s of s h i p s ,

which a r e m a d e of s t ee l , t r ansmi t vibration well. By t h e r e a s o n s , n o i s e a n d

vibrat ion of s h i p s a r e very big by n a t u r e a n d reduc t ion of n o i s e a n d vibration is

impor tan t s u b j e c t for s h i p s .

M X X X


P R E F A C E

Effect of Vibration :

O n e c a n d is t inguish two a r e a s , w h e r e s t a n d a r d s h a v e b e e n d e v e l o p e d to

a s s e s s t h e effect of vibration, appl ied to t h e h u m a n body: vibration p a s s i n g to

h a n d a n d w h o l e body . T h e vibration p a s s e s to h a n d , c a n c a u s e t h e d i s e a s e ,

ca l led a s "white finger d i s e a s e , " t h e latter c a n lead to var ie ty of hea l th

p r o b l e m s , r ang ing from mot ion s i c k n e s s to t i s s u e d a m a g e s . It shou ld b e

n o t e d , t ha t t h e re la t ionship b e t w e e n e x p o s u r e a n d t h e d i s e a s e is c o m p l e x a n d

m a n y q u e s t i o n s in this a r e a , r ema in u n a n s w e r e d . A n u m b e r of s t a n d a r d s

incorpora t ing t h e la tes t s t a t e of k n o w l e d g e h a v e b e e n in t roduced o v e r t h e last

few y e a r s with t h e objec t of giving g u i d a n c e to t h o s e , w h o requ i red to a s s e s s

t h e i m p o r t a n c e of h u m a n vibration e x p o s u r e .

It is n o w gene ra l l y be l i eved tha t vibration c a u s e s d a m a g e to b lood v e s s e l s ,

which a r e t h u s m a d e i n c a p a b l e of circulating blood to t h e ex t remi t i e s . T h e r e is

n o known c u r e a n d s y m p t o m s , which a r e i r reversible . S o it is c lear ly impor tan t

to e s t a b l i s h t h e levels of vibration a n d t h e dura t ion of e x p o s u r e , which a r e

stat ical ly likely to c a u s e t h e d i s e a s e a n d to t a k e p r e c a u t i o n s .

Noise:

N o i s e h a s b e e n r e c o g n i z e d a s a n u i s a n c e (in t h e legal s e n s e ) for m a n y y e a r s .

N u i s a n c e c a n b e e i the r public or pr ivate . A pr ivate n u i s a n c e is c o m m o n l y

def ined a s a n unlawful in te r fe rence with a p e r s o n ' s u s e or e n j o y m e n t of land

or of s o m e right ove r it or in c o n n e c t i o n with it. A public n o i s e is a n unlawful

ac t or o m i s s i o n c a u s i n g in te r fe rence with t h e hea l th a n d sa fe ty of t h e publ ic a t

l a rge . A noisy ope ra t i on c a n b e both a public a n d a pr ivate n u i s a n c e . It is not

a l w a y s e a s y to a n s w e r t h e q u e s t i o n of w h e t h e r t h e n u i s a n c e c o m p l a i n e d of is

a public or a pr iva te o n e . If t h e n o i s e n u i s a n c e affects jus t o n e p e r s o n or a

h o u s e h o l d , it is clearly a pr ivate n u i s a n c e . If it affects a c l a s s of t h e public,

s u c h a s t h e r e s i d e n t s of a c o m m u n i t y or of t h e p a s s e r s - b y of a no isy factory, it

is likely to b e a public n u i s a n c e .

xxxi Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne

P R E F A C E

A pr iva te ac t ion c a n only b e b rough t by t h e o c c u p i e r of t h e land or by

s o m e o n e w h o h a s a legal in te res t in t h e land, a n d h e c a n only t a k e ac t ion

a g a i n s t t h e p e r s o n w h o c a u s e t h e n u i s a n c e . A public n u i s a n c e is a c r ime , a n d

p r o c e e d i n g s c a n b e t a k e n by public b o d i e s s u c h a s t h e local author i ty or

A t t o r n e y - G e n e r a l or both . All t h e criminal s a n c t i o n s a r e ava i l ab le to t h e court ,

a n in addi t ion it h a s p o w e r to i s s u e a n a b a t e m e n t o rder , which m a y t a k e t h e

form of restr ict ing t h e n o i s e to cer ta in hou r s , or levels , or to c e a s e entirely.

It is well known tha t m u c h of m o d e r n t e c h n o l o g y is de r ived from pro jec t s

o r d e r e d by t h e military industry of t h e d e v e l o p e d c o u n t r i e s . T h e d e e p e s t

r e s e a r c h of m a c h i n e s a n d e q u i p m e n t vibration is d o n e initially in c o u n t r i e s

with s t r o n g nava l fo rces , which h a v e impor tan t n e e d s to minimize n o i s e a n d

vibrat ion. A n u m b e r of nava l r e s e a r c h c e n t e r s tha t d e a l with us ing a n d

d e v e l o p i n g analyt ical too ls for vibration m e a s u r e m e n t a n d reduc t ion exis t in

D e v e l o p e d C o u n t r i e s . T h e s e c e n t e r s a r e e q u i p p e d with m o d e r n

i n s t rumen ta t i on for m e a s u r e m e n t a n d a n a l y s i s of s i g n a l s .most ly us ing

i n s t r u m e n t s p r o d u c e d by Bruel & Kjaer ( D e n m a r k ) a n d Kistler (Norway) . A

n u m b e r of highly qualified e x p e r t s work in t h e s e c e n t e r s a n d p r e p a r e

s p e c i a l i s t s for navy a n d shipbui lding industry.

T h e g r e a t e s t a d v a n c e s c a n m a k e in t h e condi t ion d i a g n o s t i c s of m a c h i n e s

us ing vibrat ion. , T h e AUTOVIB monitor ing m e t h o d for condi t ion d i a g n o s t i c s of

m a c h i n e s us ing vibration c a n b e success fu l ly u s e d in a n u m b e r of civil

i ndus t r i e s including e n e r g y , n u c l e a r p o w e r p lan t s , p a p e r a n d pulp , meta l lu rgy ,

t r a n s p o r t including s h i p s , aviat ion a n d ra i lways .

O n e of t h e main p r o b l e m s in Sri l anka is a g r e a t s h o r t a g e of s p e c i a l i s t s w h o

c a n efficiently u s e condi t ion monitor ing a n d d i a g n o s t i c s s y s t e m s , including

t h o s e with e x p e r t s y s t e m s tha t a r e supp l ied by t h e lead ing W e s t e r n

c o m p a n i e s . T o p r e p a r e t h e s e spec i a l i s t s would t a k e t oo m u c h t ime . Th i s fact

h a s def ined t h e main pecul iar i t ies of t h e vibration d i a g n o s t i c s in Sri l anka . T h e

s t r a t e g y of AUTOVIB, is to d e v e l o p a s y s t e m for condi t ion d i a g n o s t i c s of

s l e e v e b e a r i n g s (fluid film b e a r i n g s ) tha t c a n b e app l ied equa l ly for ball

b e a r i n g s a s well.

xxxii


P R E F A C E

The main problems peculiar to the Sri lankan market

T h e c h a n g e s a s s o c i a t e d with t h e introduction of m a r k e t re la t ions in t h e

n u m b e r of i ndus t r i e s in Sri lanka w e r e s t a r t ed a t t h e e n d of t h e 1 9 5 6 a n d after

1 9 8 0 s with t h e introduction of O p e n e c o n o m y . P l a n s for res t ruc tur ing t h e

e c o n o m y inc luded p l a n s to d e c r e a s e produc t ion c o s t s a n d e x c e s s l abour

e n e r g y . T h e d r a w b a c k s prevail in improving of t h e efficiency of p roduc t ion

p r o c e s s e s is b a s e d on t h r e e main a s s u m p t i o n s :

• T h e a b s e n c e of financial r e s o u r c e s in t h e coun t ry to r e n e w t h e m a c h i n e r y

a n d e q u i p m e n t in t h e majority of indus t r i es for a t l e a s t five to t en y e a r s .

T h e na tu ra l w e a r of t h e e q u i p m e n t shou ld significantly i n c r e a s e its

m a i n t e n a n c e c o s t s a n d t h e introduction of t h e condi t ion d i a g n o s t i c s

s y s t e m s is likely to b e t h e m o s t pract ical w a y to d e c r e a s e t h e s e c o s t s .

• Rela t ively high i n v e s t m e n t s ove r high level d i a g n o s t i c s y s t e m s (Automat i c

Condi t ion moni tor ing S y s t e m s ) p r e v e n t o w n e r s by utilizing s u c h a s y s t e m .

• Signif icant l imitations of exis t ing condi t ion d i a g n o s t i c t e c h n o l o g i e s from

l ead ing W e s t e r n c o m p a n i e s .

T h e following r e a s o n s tha t limit t h e u s e of m o d e r n condi t ion moni tor ing a n d

d i a g n o s t i c s s y s t e m s of A m e r i c a n a n d W e s t - E u r o p e a n p roduc t ion in Sri l anka

• T h e a b s e n c e in m o s t r e g i o n s of qualified p e r s o n n e l w h o c a n u s e t h e s e

s y s t e m s , d e s p i t e t h e e x i s t e n c e of a n u m b e r of scientific c e n t e r s with

e x p e r t s of h ighe r qualification. T h e p rob lem is t ha t to p r e p a r e a p e r s o n to

b e a qualified e x p e r t t a k e s s e v e r a l y e a r s a n d would requ i re significant

f inancial r e s o u r c e s .

• T h e high relat ive pr ice of t h e c o m m o n moni tor ing a n d d i a g n o s t i c s y s t e m s

in Import ing. For e x a m p l e , in t h e W e s t t h e pr ice of t h e d i a g n o s t i c

i n s t rumen ta t i on n e e d e d for a n e x p e r t to work on t h e e n t e r p r i s e is l e s s t h a n

or e q u a l to c o m p a r e d to t h e labor c o s t s of a n e x p e r t for t h e e n t e r p r i s e

dur ing a y e a r . In Sri lanka , taking into a c c o u n t t h e t ax policy, t h e pr ice for

t h e d i a g n o s t i c e q u i p m e n t e q u a l s t h e i n c o m e of a n e x p e r t for a b o u t t en

y e a r s . This m a k e s t h e survival of smal l c o m p a n i e s s p e c i a l i z e d in

d i a g n o s t i c s e r v i c e s imposs ib le .

xxxiii Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne

P R E F A C E

• O n e m o r e r e a s o n , which is a l s o e c o n o m i c is t h e high c o s t s of m o u n t i n g

p e r m a n e n t t r a n s d u c e r s on exis t ing e q u i p m e n t . Typically, t h e cons t ruc t ion

of uni ts shou ld b e r e d e s i g n e d to a s s u r e a p p r o p r i a t e m o u n t i n g a n d

pro tec t ion of t h e t r a n s d u c e r s s o a s not to d e s t r o y t h e m in t h e p r o c e s s of

s t a n d a r d m a i n t e n a n c e of t h e e q u i p m e n t .

• T h e last r e a s o n is c o n n e c t e d to t h e e x i s t e n c e of v a r i o u s s t a n d a r d s a n d

r egu l a t i ons tha t differ in e a c h industry t ha t def ine t h e r e q u i r e m e n t s for

different p a r a m e t e r s of t h e main e q u i p m e n t a n d m e t h o d s for their control .

T h e s e r egu la t i ons d o not allow mak ing a dec i s ion for m a i n t e n a n c e a n d

repa i r of t h e e q u i p m e n t without conduc t ing s t a n d a r d m e a s u r e m e n t s tha t

usua l ly requ i re t h e s h u t d o w n of t h e e q u i p m e n t a n d partial d i s a s s e m b l y of

t h e uni ts . T h a t ' s why t h e s e r egu la t ions m a k e it imposs ib l e to u s e m o d e r n

condi t ion moni tor ing s y s t e m s a n d u s e condit ion b a s e d m a i n t e n a n c e .

Th i s a n a l y s i s of t h e cur ren t s i tuat ion led to a r e c o m m e n d a t i o n to s p e e d up t h e

d e v e l o p m e n t of t h e m e t h o d s for m a s s condit ion d i a g n o s t i c s t ha t c a n b e

car r ied out by a u s e r with no spec ia l training in condi t ion d i a g n o s t i c s . T h e s e

m e t h o d s w e r e d e v e l o p e d ove r a per iod of s e v e r a l y e a r s b a s e d on t h e a n a l y s i s

of m a c h i n e v ibra t ions in t h e shipbui lding industry a n d t h e r e su l t an t ex t rac t ion

of d i a g n o s t i c information s igna l s . T h e m e t h o d s d e v e l o p e d w e r e i n t e n d e d to b e

u s e d for condi t ion d i a g n o s t i c s of s u p p l e m e n t a r y m a c h i n e s a n d e q u i p m e n t t h e

m a i n t e n a n c e of which w a s not g o v e r n e d by t h e exis t ing s t a n d a r d s a n d

r egu l a t i ons .

Th i s a n a l y s i s w a s t h e b a s e of this project . At t h e s a m e t ime, a n u m b e r of

p r o b l e m s b e c a m e ev iden t during t h e de ta i l ed m a r k e t r e s e a r c h s t a g e :

• T h e first p rob l em w a s t h e n e e d for appl ica t ion so f tware b a s e d on t h e

d e v e l o p e d m e t h o d s tha t would efficiently r e p l a c e a qualified expe r t . T h e

s y s t e m shou ld a s k t h e c u s t o m e r to d e s c r i b e t h e e q u i p m e n t for d i a g n o s t i c s ,

def ine w h a t d a t a shou ld b e m e a s u r e d , p r o c e s s t h e m e a s u r e d d a t a , m a k e

condi t ion d i a g n o s t i c a n d predict ion for t h e m a c h i n e s a n d e q u i p m e n t u n d e r

control .

xxxiv Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne

P R E F A C E

• T h e s e c o n d p rob l em o c c u r r e d after t h e s tar t of t h e exploi ta t ion by t h e

c u s t o m e r s of t h e a u t o m a t i c d i agnos t i c s y s t e m s cons i s t ing of t h e

m e a s u r e m e n t d e v i c e , p e r s o n a l c o m p u t e r a n d t h e appl ica t ion so f twa re .

Th i s w a s t h e p rob l em of t h e c u s t o m e r s s u p p o r t in t h o s e ra re s i t ua t ions

w h e n t h e a u t o m a t i c d i a g n o s t i c s did not a n s w e r e d t h e q u e s t i o n of w h a t is

t h e de fec t in t h e m a c h i n e a n d how d a n g e r o u s it is.

Noise Generated From Machine Vibrations

If you w a n t to r e d u c e m a i n t e n a n c e c o s t s you m u s t improve e q u i p m e n t

mainta inabi l i ty a n d reliability. T h e p r e m i s e be ing , if t h e e q u i p m e n t d o e s not

fail a s often, it c o s t s l e s s to repair . W h e n e q u i p m e n t d o e s fail, l onger life c a n

b e a c h i e v e d if p r o p e r r epa i r s a r e m a d e . P r o p e r r epa i r s m e a n s t h e c a u s e of

failure m u s t b e identified a n d e l imina ted . If this is not d o n e t h e e q u i p m e n t will

fail a g a i n . T h e s e ob jec t ives c a n b e a c c o m p l i s h e d dur ing t h e acquis i t ion p h a s e

of n e w e q u i p m e n t , t h e p u r c h a s e of s p a r e pa r t s , a n d a c c u r a t e d i a g n o s i s of all

rota t ing m a c h i n e r y p r o b l e m s . If e i ther of t h e s e i t ems a r e not proper ly

m a n a g e d t h e ob jec t ives m a y not b e a c h i e v e d . Execu t i ve e v a l u a t i o n s ,

p a y m e n t of b o n u s e s , p roduct ion ob jec t ives a n d o t h e r b rownie point s y s t e m s

t e n d to f o c u s m a n a g e m e n t ' s a t ten t ion on t h e shor t t e rm i n s t e a d of t h e long

t e r m . Th i s c a n a l s o affect maintainabil i ty a n d reliability.

In field b a l a n c i n g m a c h i n e s with high vibra t ions , t h e u s e of c o m m o n m e t h o d s

of d e t e r m i n i n g b a l a n c e w e i g h t s often d o e s not yield sa t i s fac tory r e su l t s . An

a n a l y s i s of t h e r e a s o n s for this s h o w s tha t t h e r e a r e two ma in g r o u p s of

c o n s t r a i n t s on t h e ba l anc ing efficiency: T h e fo rces of different n a t u r e from

s imp le u n b a l a n c e t ha t exc i t e vibration a t t h e rotat ing f r e q u e n c y a n d t h e

e x i s t e n c e of cer ta in d e f e c t s in t h e m a c h i n e tha t c a n c h a n g e t h e m e c h a n i c a l

p r o p e r t i e s of t h e m a c h i n e .

T h e t e c h n o l o g y on how to d i a g n o s e p r o b l e m s in rotat ing m a c h i n e r y is equa l ly

unpa ra l l e l ed . T h e t e c h n o l o g y h a s p r o g r e s s e d from a m p l i t u d e m e a s u r i n g a n d

t r end ing to us ing t h e t ime d o m a i n s ignal , p h a s e , a n d f r e q u e n c y d o m a i n

s p e c t r a for a c c u r a t e d i a g n o s i s of specif ic p r o b l e m s . In fact, it m a y b e t ime to

X X X V


P R E F A C E

p r o g r e s s to t h e next s t e p b e y o n d predict ive m a i n t e n a n c e to e q u i p m e n t

maintainabi l i ty a n d reliability.

C o n s i d e r a t i o n of t h e reliability a n d s e r v i c e life of a m a c h i n e s u g g e s t s t ha t low

f r e q u e n c y v ibra t ions p r e s e n t t h e g r e a t e s t s o u r c e of d a n g e r to a m a c h i n e . For

m a c h i n e s with rotat ing p a r t s (rotors) , this is typically a vibrat ion a t t h e rotat ion

f r e q u e n c y . Th i s vibration m a y significantly i n c r e a s e dur ing t h e m a c h i n e

o p e r a t i o n . Usually, w h e n t h e vibration level e x c e e d s cer ta in limits, t h e u s e r s

c o n d u c t m a i n t e n a n c e of t h e m a c h i n e . T h e inertial f o r ce s d u e to t h e u n b a l a n c e

of t h e rotat ing p a r t s relat ive to t h e rotation ax is a r e typically c o n s i d e r e d to b e

t h e r e a s o n s for t h e vibration i n c r e a s e . T h a t ' s why t h e u s e r s try field b a l a n c i n g

t h e m a c h i n e w h e n pos s ib l e . Unfortunately, a t t empt ing to b a l a n c e t h e m a c h i n e

m a y not a l w a y s p r o d u c e a c c e p t a b l e resu l t s . T h e main r e a s o n s for this a r e

o t h e r p r o b l e m s of t h e m a c h i n e or of its s u p p o r t s . T o e l imina te addi t ional

e x p e n s e s a n d d e l a y s , t h e c u s t o m e r shou ld h a v e t h e information a b o u t t h e

v a r i o u s p o s s i b l e d e f e c t s of t h e m a c h i n e tha t c a n b e r e s p o n s i b l e for t h e

m a c h i n e vibration a t t h e rotating f r equency a n d th is information s h o u l d b e

ava i l ab l e be fo re or a t l eas t during t h e ba l anc ing .

T h e factor, t h e vibration still r e m a i n s a s a n ac tua l p r o b l e m with i n c r e a s e in

s p e e d a n d load of m a c h i n e s in s h i p s . T h e t echn ica l d i a g n o s t i c is t h e p r o c e s s

of t e s t ing t h e m a c h i n e , in o rde r to t e s t t h e condi t ion of it. T h e r e f o r e t h e

t echn ica l d i a g n o s t i c h e l p s to d e t e c t t h e faults of m a c h i n e s while t h e y o p e r a t e .

T h e c h a n g e in condit ion of vibration of m a c h i n e s m a y c a u s e t h e c h a n g e in

t e chn i ca l condi t ion of sh ip m a c h i n e r y t h e n t h e condi t ion of t h e sh ip .

T h e t e r m Diagnostic is a G r e e k word , a n d m e a n s t h e ability to d i s c e r n . It is

u s e d in Medical S c i e n c e . T h a t is t h e sec t ion , which ind ica t e s t h e s y m p t o m s of

d i s e a s e s a n d m e t h o d s us ing to identify t h e d i s e a s e s .

Accurate Diagnosis

A c c u r a t e d i a g n o s i s of m a c h i n e r y p r o b l e m s p r o v i d e s t h e in te l l igence for n e w

e q u i p m e n t acqu i s i t ions , s p a r e p a r t s p u r c h a s i n g , a n d n e c e s s a r y r epa i r s . Th i s

is why this very impor tan t function m u s t b e par t of t h e E q u i p m e n t

Maintainabil i ty a n d Reliability g r o u p .

xxxvi


P R E F A C E

O n c e a p r o b l e m h a s b e e n identified t h e n e c e s s a r y m a i n t e n a n c e a n d

e n g i n e e r i n g ta len t m u s t b e ava i l ab le to d e t e r m i n e t h e p r o p e r fix. A c c u r a t e

d i a g n o s i s of m a c h i n e r y p r o b l e m s r e q u i r e s a lot m o r e t h a n condi t ion

moni tor ing a n d t r end ing . A c c u r a t e d i a g n o s i s r e q u i r e s t h e p r o p e r h a r d w a r e ,

so f tware , t e c h n o l o g y , a n d skilled p e o p l e . This i nc ludes t h e u s e of f r e q u e n c y

d o m a i n s p e c t r a , t ime d o m a i n s igna l s , a n d p h a s e r e l a t ionsh ips of f r e q u e n c i e s .

T h e first r e s p o n s e is "we can ' t afford that ." T h e fact is t ha t you can ' t afford not

to d o a c c u r a t e d i a g n o s i s .

If t h e right h a r d w a r e , sof tware , a n d t e c h n o l o g y a r e p l a c e d in t h e h a n d s of

skilled p e o p l e , t h e p a y b a c k per iod is t h e s h o r t e s t , a n d t h e re turn on

i n v e s t m e n t (ROI) is m o r e t h a n for a n y o t h e r i n v e s t m e n t t o d a y . T h e s e s a v i n g s

a r e rea l ized by a reduc t ion in m a i n t e n a n c e c o s t a n d i n c r e a s e d p roduc t ion .

M a n a g e r s s h o u l d rea l ize t h e y m a y h a v e to p u r c h a s e n e w e q u i p m e n t

a n a l y z e r s a n d t r a n s d u c e r s . High quali ty p e r s o n n e l s h o u l d b e a s s i g n e d to t h e

p r o g r a m . T h e s e p e o p l e m u s t b e t ra ined in t h e b e s t t e c h n o l o g y . P e o p l e ' s

a t t i tude s h o u l d b e c h a n g e d from condit ion monitor ing a n d t r end ing to a c c u r a t e

d i a g n o s i s with vibration a n a l y s i s . If t h e s e ob jec t ives a r e a c h i e v e d , t h e

i n c r e a s e in profits for a m e d i u m plant shou ld b e a t l eas t o n e million do l la r s p e r

y e a r .

I m b a l a n c e is a l inear p rob l em. Linear p r o b l e m s b e h a v e in a l inear m a n n e r . If a

m a c h i n e is ou t of b a l a n c e , you shou ld b e a b l e to b a l a n c e it in t h r e e or four

r u n s . If b a l a n c i n g is s o s imple , w h a t is t h e p r o b l e m ? T h e p r o b l e m is

i n a c c u r a t e d i a g n o s i s . T h e r e a r e a lot of vibration "expe r t s " t ha t c a n n o t tell t h e

d i f ference b e t w e e n i m b a l a n c e , l o o s e n e s s , b e n t shaft , m i sa l i gnmen t , softfoot,

b r o k e n rotor b a r s , a n d loading. All of t h e s e p r o b l e m s c a n c a u s e a high

a m p l i t u d e a t rotor s p e e d , h o w e v e r t h e s e p r o b l e m s c a n n o t b e so lved by

b a l a n c i n g .

T h e p r o g r a m "AUTOVIB" g i v e s a b road r a n g e of o p t i o n s to d i a g n o s e a b o v e

m e n t i o n e d d i s o r d e r s a n d irregulari t ies of t h e m a c h i n e r y .

xxxvii Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne

P R E F A C E

X X X V I I I


Documents

Vibration Diagnostic of Rotor Mechanisms in Ships