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. 
Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
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 
Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
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 
Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
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 
Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
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 F MACHINES AND MECHANISMS 
x 
Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
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 
Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
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 
Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
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 
Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
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 1^ 0 
FIG. XVII . 1 . 2 Characteristics of Electric Motor in Running \UZ 
xvi 
Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
LIST OF FIGURES AND TABLES 
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 
FIG. XVII . 3 . 3 Characteristics of Bearing No. 2 with Loosen I49 
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 
FIG. XVII . 3 . 10 Characteristics of Bearing No. 1 with Loosen I54 
Coupling No. 1 
Vibration Diagnostic of Rotor Mechanism in Ships By G. G. Jayarathne . / . " >• y^f' 
LIST OF FIGURES AND TABLES 
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 
FIG. XVII . 3 . 13 Characteristics of Bearing No. 1 with Loosen I56 
Bearing No. 1 
FIG. XVII . 3 . 14 Characteristics of Bearing No. 1 with Loosen I57 
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 
FIG. XVII . 3 . 17 Characteristics of Bearing No. 1 with Loosen I59 
Cap No. 1 
FIG. XVII . 3 . 18 Characteristics of Bearing No. 3 with Loosen I60 
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 
FIG. XVII . 3 . 22 Characteristics of Bearing No. 2 with Loosen I62 
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 
Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
LIST OF FIGURES AND TABLES 
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 FIGURES AND TABLES 
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 
Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
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 
LIST OF ABBREVIATIONS 
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 
Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
LIST OF ABBREVIATIONS 
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 
Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
Li„ 
CHAPTER XII 
f 
a„ 
0 
c, 
c, 
R, 
Ri 
q 
v 0 
A 
TC 
q 
Vi 
Cc, 
CHAPTER XIII 
F 
m 
a 
LIST OF ABBREVIATIONS 
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 
Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
LIST OF ABBREVIATIONS 
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 
CAP3B11 Characteristics of bearing no. 1 with loosen cap no.3 
CAP3_B21 Characteristics of bearing no. 2 with loosen cap no.3 
CAP3B31 Characteristics of bearing no. 3 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 
LB1_B21 Characteristics of bearing no. 2 with loosen bearing no.l 
LB1_B31 Characteristics of bearing no. 3 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 
L B 2 B 2 1 Characteristics of bearing no. 2 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 
L B 3 B 3 1 Characteristics of bearing no. 3 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 
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Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
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 
Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
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 
Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
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 
Vibration Diagnostic of Rotor Mechanism in Ships By G.G.Jayarathne 
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 . 
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• 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 
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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 . 
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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 . 
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