Basic Theories and Key Technologies for the Deep-Sea Spherical Pressure Hulls

The research and development of advanced marine engineering equipment is one of the key areas in the implementation of marine power strategy. Manned submersibles, unmanned submersibles and other deep-sea equipment are the forefront and commanding heights. The research and development of deep-sea equipment has made great technological leaps in recent years. In order to further improve the development level, it is significant to continuously carry out theoretical system expansion and technological innovation. Pressure structures such as manned cabin, ballast tank, electronic cabin and their accessories including window frustums, hatch cover and penetration panels are key components and pressure bearing units, which play an important role in ensuring the normal operation of non-pressure equipment or personnel life safety.

Against this background, the authors' team of this book has been supported by 7 projects of National Natural Science Foundation of China (NSFC) and 2 projects of Shanghai municipal development programs, particularly as the key project of NSFC“Research on structural reliability of manned spherical hull of deep-sea manned submersibles", and the general project of NSFC"Research on design and life calculation method of deep-sea manned spherical hull made of maraging steel”. The research, development and application of key technologies for the design, manufacture and safety evaluation of deep-sea spherical pressure hulls are systematically carried out. The evaluation and verification methods of ultimate strength and fatigue strength are innovated, and valuable experience is accumulated. The research results can provide a theoretical basis for the research and development of deep-sea pressure structures.

Based on the research, this book systematically introduces the basic theories and key technical problems in the whole life cycle of deep-sea spherical pressure hulls, focusing on the material selection criterion based on the comprehensive properties of alternative materials, the theoretical basis and calculation method of linear and nonlinear buckling, and the dwell-fatigue model for life prediction of spherical pressure hulls. On this basis, the experience of evaluation, test and simulation methods of deep-sea spherical pressure hulls is summarized. Considering such contents, the book is divided into six chapters. Chapter l is a general introduction of deep-sea spherical pressure hulls; Chapter 2 introduces material selection method for deep-sea spherical pressure hulls; Chapter 3 introduces linear buckling mechanics of deep-sea spherical pressure hulls; Chapter 4 presents nonlinear buckling of deep-sea spherical pressure hulls; Chapter 5 summarizes fatigue life assessment theories for deep-sea spherical pressure hulls; and Chapter 6 gives the testing and numerical simulation techniques of deep-sea spherical pressure hulls. Among the contents, the small-time-domain crack growth model considering load-sustaining effect, the ultimate strength evaluation model of the spherical pressure hull made of ultra-high strength steel, and the design and analysis system of spherical pressure hulls covering the full-ocean-depth proposed by the authors' team creatively fill the gap of relevant research at home and abroad, expand the cutting-edge technology of deep-sea equipment, and have important academic value.

The key technologies presents in this book is appraised by the evaluation group of National Natural Science Foundation of China,“this study makes up for the blank of the material performance standard, structural failure mechanism and life prediction model of the pressure hulls, and puts forward a new direction for follow-up research.”Some research results have also been identified by Shanghai Shipbuilding and Marine Engineering Association in their evaluation results related to this book, "For the first time in the world, a unified method for fatigue life prediction of full-ocean-depth pressure cabin based on Generalized Probability Theory and the small-time-domain model of cyclic creep crack growth rate is proposed, which makes up for the shortcomings of traditional low-cycle fatigue life prediction method based on cumulative damage theory; the evaluation model of ultimate bearing capacity of ultra-high strength steel pressure cabin is innovated, the compression analysis method based on physical model is established.”Taking the achievements of this book as one of the innovation points, the research group won the second prize of Shanghai Scientific and Technological Progress in 2020.

This book is highly original, and practical. Readers can include teachers, postgraduates, scientific researchers and engineering technicians in many fields such as ship and marine engineering, marine technology and mechanical engineering at home and abroad. This book comprehensively and systematically introduces the basic theory and key technology of deep-sea spherical pressure hulls, which will provide a reference for the safety assessment of in-service deep-sea equipment, and the research and development of future's deep-sea equipment.

Chapter 1 General Introduction of Deep-sea Spherical Pressure Hulls 1

1.1Application scenario of deep-sea spherical pressure hulls 2

1.2 The design methodology of deep-sea pressure hull 6

1.2.1 Shape selection 6

1.2.2 Material selection 8

1.2.3 Hull thickness requirement based on the depth limit and safety factor 9

1.2.4 End closures design compatible with the hull and design requirement 9

1.3 Other considerations to ensure safety 10

1.3.1 Reliability 10

1.3.2 Fatigue and fracture 12

1.3.3 Model test 14

1.3.4 Seal design 16

1.4 Manufacturing process of deep-sea pressure hulls 17

References 21

Chapter 2 Material Selection for Deep-sea Spherical Pressure Hulls 23

2.1 Candidate materials for deep-sea spherical pressure hulls 24

2.1.1 Steels 26

2.1.2 Aluminium alloys 28

2.1.3 Titanium alloys 28

2.1.4 Acrylic plastics (polymethyl methacrylate) 29 2.1.5

Composites 30

2.2 Practice for material selection 31

2.2.1 Selection of titanium alloys 33

2.2.2 Selection of maraging steels 44

References 50

Chapter 3 Linear Buckling Mechanics of Deep-sea Spherical Pressure Hulls 53

3.1 Overview of current rules for spherical pressure hulls 53

3.1.1 Introduction of rules 53

3.1.2 Comparison of rules 59

3.2 Analytical analysis 62

3.2.1 Strength evaluation 62

3.2.2 Stability evaluation 69

3.3 Numerical analysis 76

3.3.1 Brief introduction of FEM principle 76

3.3.2 Numerical study of different methods 82

References 92

Chapter 4 Nonlinear Buckling of Deep-sea Spherical Pressure Hulls 94

4.1 Overview of current studies 94

4.1.1 Empirical formulae 94

4.1.2 Phenomenological models 104

4.2 Elastic-plastic buckling analysis 107

4.2.1 Titanium alloy spherical pressure hulls 107

4.2.2 Maraging steel spherical pressure hulls 124

4.3 Experimental study in laboratory scale 127

4.3.1 Materials and methods 128

4.3.2 Results and discussion 132

References 143

Chapter 5 Fatigue Life Assessment Theory for Deep-sea Spherical Pressure Hulls 146

5.1 Analysis methods for fatigue of spherical pressure hulls 147

5.1.1 Loading history of the spherical pressure hull 148

5.1.2 Low-cycle fatigue theory based on strain-cycles curve 152

5.1.3 Methods based on crack growth theory 158

5.1.4 A simplified life estimation method 185 References 192

Chapter 6 Testing and Numerical Simulation of Deep-sea Spherical Pressure Hulls 195

6.1 Verification testing 197

6.1.1 Ultimate compression-carrying capacity testing for scale model 198

6.1.2 Hydrostatic pressure testing for viewports 207

6.1.3 Function testing for hatch-cover opening and closing mechanism 209

6.2 Inspection testing 210

6.2.1 Material properties testing 210

6.2.2 Geometrical size measurement 213

6.3 Acceptance testing 214

6.3.1 Leakage testing 214

6.3.2 Hydrostatic pressure testing 215

6.4 Numerical Simulation 216

6.4.1 Structural strength calculation of the deep-sea spherical pressure hull using FEA method 

6.4.2 Numerical simulation on collapse of the deep-sea spherical pressure hull 221

6.4.3 The simulation of transient dynamic process of crushing 226

References 233