DYNAMIC RESPONSE OF MARINE PROPULSION SYSTEMS UNDER MULTIAXIAL RANDOM LOADS
VIKASH KUMAR SATYAM
DEPARTMENT OF APPLIED MECHANICS INDIAN INSTITUTE OF TECHNOLOGY DELHI
AUGUST 2010
© Indian Institute of Technology Delhi (IITD), New Delhi, 2010
DYNAMIC RESPONSE OF MARINE PROPULSION SYSTEMS UNDER MULTIAXIAL RANDOM LOADS
M
Vikash Kumar Satyam
DEPARTMENT OF APPLIED MECHANICS Submitted
in fulfillment of the requirements of the degree of Doctor of Philosophy
to the
INDIAN INSTITUTE OF TECHNOLOGY DELHI
August 2010
Acknowledgements
I would like to thank Professor Suhail Ahmad and Professor NT( Gupta for their guidance, constant encouragement and mentorship throughout my doctoral studies. Their suggestions, comments and many hours of enthusiastic discussions have been instrumental in enhancing my understanding and appreciation of the subject.
I am grateful to Professor Kshitiz Gupta and Professor SN Singh for their insightful comments on my work during discussions. I wish to thank Professor Puneet Mahajan for his help and his suggestions with reference to part of the work carried out using the finite element packages. Thanks are also due to my doctoral committee members, Professor RK Mittal and Professor DK Sehgal, for some of their suggestions during my comprehensive test, which had prompted me to look at the problems considered from a different perspectives.
During my stay at IIT Delhi, I have been fortunate enough to have the opportunity to interact with many faculty members, discussions with whom have been an enriching experience. Specifically, I wish to thank Dr. S Hegde, for his ready willingness to help and who has never said no to any of my requests. Thanks are also due to my colleagues Captain Kulkarni, CDR R Vijayakumar, LCDR Amit Ray, LCDR SK Rao and LCDR Swaminathan for many discussions, technical and otherwise. Inquisitive students at all levels that is research scholars, postgraduate and undergraduate kept me inspiring all the time.
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My stay at IIT Delhi has been an enjoyable and enriching experience and for that, credit goes in no small measure, to many people with whom I had the privilege to get acquainted and become friends.
I am indebted to my family for their constant encouragement and for being extremely supportive in all my decisions. Words are not sufficient to express my gratitude for all the difficult decisions they had to make in their life on account of me and for being there always whenever I needed them specially with ever changing dynamic IT environment.
Finally, I would like to thank my wife who has been my best friend and strongest critic.
I am grateful for her willingness to discuss problems related to my research at any time, for all her suggestions and for her constant support, encouragement and patience.
Vikash Kumar Satyam August 2010
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ABSTRACT
Engineering design of real systems consists of breaking the system into smaller components in time and space, analyzing them under different types of loads and synthesis of the system. Such practice has evolved with experience in design. In order to benefit from past experience, time tested standards and engineering codes are used. However, actual simulation of the design in real time in natural working conditions considering multiaxial loads under random environment remains a serious challenge.
As the technological innovations in the field of digital computation and computer simulation are growing, possibility to analyze service life under different loading scenario for component design has improved. Powerful simulation supported by finite element methods with mathematical techniques make it possible to take better decisions at very early stages of design resulting in better utilization of resources.
This thesis is study about dynamic response of the marine propulsion system under multiaxial random loads. Components of propulsion shafting system are subjected to torsion, axial, bending and lateral loadings during operations. Torsional vibration analysis of the propulsive shaft is an important task in the ship design in order to ensure smooth propulsion power transmission to the propeller from the prime mover and the thrust generated by propeller to move the ship. Propeller shaft undergoes severe loading during conversion of rotational motion by propeller to translatory motion of the ship. Torque, thrust, self-weights of shaft and weight of the propeller has to be supported by the outer most part of the shafting system creating a multiaxial loading scenario. Designers have been using limited analysis using
transfer matrix method or analytical and numerical combined methods. Structural designs based on correlations with uniaxial test data or limited multiaxial test data supplemented with safety
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factor based on statistics is nonconservative as far as reliability of the system is concerned. A detailed analysis covering multiaxial loads can equip designer with better information in respect of the service life of the component under design. A three-dimensional finite element analysis complemented by reliability assessment has been carried out to study the durability of the propeller shaft.
Based on the propeller induced vibrations and available means to improve stealth of a submarine has been examined. Interesting facts have emerged out for the future research on the subject. Using basics of the dynamic response under multiaxial loading propulsion system of a powerful nuclear submarine has been investigated.
Reliability studies include the comparative service life grading based on the reliability index and probability of failure. At early stages of design such reliability analysis can ensure specified performance of the propulsion system or probable failure can be predicted and future surprises can be avoided.
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CONTENTS Page No.
CERTIFICATE i
ACKNOWLEDGEMENTS ii
ABSTRACT iv
CONTENTS vi
LIST OF FIGURES x
LIST OF TABLES xiv
NOMENCLATURE xvi
CHAPTER
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I 1-15INTRODUCTION 1
1.1 Historical Perspective 1
1.2 Present Scenario 1
1.3 Marine Propulsion System 3
1.4 Organisation of the Thesis 8
Figures 1.1 to 1.8 12-15
CHAPTER —II 16-40
LITERATURE REVIEW 16
2.1 Need for the Present Study 37
2.2 Scope and Objective of the Study 38
CHAPTER
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III 41-79DYNAMIC RESPONSE OF PROPELLER SHAFT UNDER 41 MULTIAXIAL RANDOM LOADS
3.1 Introduction 41
3.2 Propeller induced excitation 41
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3.2.1 Simulation of the random loads due to propeller and fluid interaction 42
3.3 Finite element modeling 45
3.3.1 Mathematical model for the propeller shaft 46
3.3.2. Dynamic Analysis 46
3.3.3 Natural frequency analysis 47
3.4 System configuration 48
3.5 Numerical study 49
3.5.1 Validation studies -general 49
3.5.2 Validation of the static response 50
3.5.3 Validation of dynamic behavior 50
3.5.4 Eigenvalue analysis 51
3.5.5 Response time history of the propeller shaft 52 3.5.6 Dynamic response under the multiaxial random loads 52
3.6 Discussion of results 54
3.6.1 Dynamic response under the synchronous random loads 55 3.6.2 Dynamic response under the random loads in rough seas 57 3.6.3 Dynamic response under the non synchronous random loads 57
3.6.4 Transient maneuver (Case IV) 58
3.7 Conclusion 59
Tables 3.1 to 3.5 60-64
Figures 3.1 to 3.28 65-79
CHAPTER —IV 80-89
VIBRATION ANALYSIS OF THE MARINE PROPULSION SYSTEM 80
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4.1 Introduction 80 4.2 Mathematical Model to Minimize the Vibrational Losses 82
4.3 Conclusion 88
CHAPTER — V 90-115
SUBMARINE STEALTH UNDER RANDOM LOADS 90
5.1 Introduction 90
5.2 Active and passive SONAR 91
5.3 Submarine stealth 92
5.4 Submarine propulsion system 93
5.5 Parameters of the propellers 94
5.6 Vessel speed characteristics 94
5.7 Propeller model 95
5.8 Numerical studies 96
5.8.1 Speed of deterrence 97
5.8.2 Propeller configurations 97
5.8.3 Time histories and operational requirements 98
5.8.4 Operational scenarios 98
5.9 Results and discussions 99
5.10 Conclusion 100
Tables 5.1 to 5.5 101-105
Figures 5.1 to 5.14 106 —115
CHAPTER — VI 116 —142
FATIGUE RELIABILITY OF MARINE SHAFT 116
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6.1 Introduction 116
6.2 Fatigue Reliability Formulation 117
6.2.1 Limit State Function 117
6.2.1.1 S-N Curve Model 118
6.2.1.2 Fracture Mechanics Model 122
6.3 Numerical Study 125
6.3.1 Characteristics of Random Variable 126
6.4 Results and Discussion 128
6.4.1 Probability of Failure and Reliability Index 128
6.4.2 Effect of Service Life 128
6.4.3 Design Point or Most Probable Failure Point (MPP) 129
6.4.4 Sensitivity Analysis 129
6.4.5 Effect of Random variables on Reliability index by FORM 131
6.5 Conclusion 132
Tables 6.1 to 6.11 134 —137
Figures 6.1 to 6.10 138 -142
CHAPTER — VII 143 —146
CONCLUSIONS 143 —146
REFERENCES 147 —155
BIO — DATA OF THE AUTHOR 156
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