Ultimate Strength Investigations of Pressure Hull Structures Subjected to External Hydrostatic Pressure
- Alternative Title
- 외부 정수압을 받는 압력 선체구조물의 최종강도 평가
- Abstract
- A submarine, which is a naval fleet vessel, is a complex ship due to its ability to dive beneath the water surface to reasonable operating depths even deeper under battle conditions.
The pressure hull is the primary structure of a submarine to withstand the hydrostatic pressure.
In practice, the typical element for pressure hull structures is consisted of a ring-stiffened cylinder, blocked off by hemispherical shell at the front and ring-stiffened conical at the rear section. These hulls are designed to withstand a specific pressure within a limited range of tolerance. It is reasonable to state that this collapse pressure is the most important parameter to ensure the safe performance of the platform and its crew living inside. Hence, this study has been initiated by the need to establish an understanding of the behavior of the collapsing of pressure hull structures subjected to hydrostatic pressures.
Within this dissertation, a detail of experimental study, fabrication of test model, test procedures, test results, non-linear finite element analyses, and ultimate strength formula assessment are briefly reported. The experimental investigation identified the collapse pressure and structural failure modes. The empirical formula is then developed using the test data, taken into account the parameter of failure mode. Subsequently, non-linear FEA is performed by employing the measured geometry and material characteristics from the test models. The quantitative and qualitative validation of the numerical simulation is obtained from the test data of ring-stiffened cylinder, ring-stiffened conical shell, and hemispherical shell. From the studied results, the distinctive failure mode: shell yielding, inter-frame, and/or overall failure can be easily predicted using the characteristic pressure calculated from the structure scantling. Moreover, The LFEA was found to be an accurate tool to simulate the buckling behavior when the parameter of geometric imperfections and the residual stress is well defined.
In the last test campaign of this topic, an investigation of dynamic implosion behavior of cylindrical shells that represent the collapse of the external sub-structure of the submarine is also provided both in experimental and numerical ways. The experiments prove that the implosion test using compressed nitrogen can successfully replicate the constant highpressure condition. The extent of damage to adjacent structures caused by the implosion shock wave is also investigated. It is confirmed that the main cylinder could collapse at a pressure lower than the design pressure due to the implosion of the additional/ sub-structure.
In order to provide comprehensive research focused on the ultimate strength of ringstiffened cylinder as the main structural member of the pressure hull, the optimization study aiming the lightest structures with a greater volume and a maximum collapse strength as possible have also been conducted. The multi-objective optimization for steel-welded ringstiffened cylindrical shell is also carried out using a genetic algorithm (GA) scheme. In this study, the benefits of GA with design constraint to find the best optimum in collapse pressure and buoyancy coefficient are demonstrated. It is also identified that the upper and lower bounds were profoundly influencing the control selection of the initial population. Moreover,
the sensitivity studies employed with different material shows that the higher strength material has a smaller buoyancy coefficient as the design operating depth increases. In other words, weight savings can be achieved when a higher strength material is used, particularly at the deeper design depths.
- Issued Date
- 2020
- Awarded Date
- 2020. 8
- Type
- Dissertation
- Keyword
- Ring-stiffened cylindrical shell ring-stiffened conical shell hemispherical shell ultimate strength test implosion test collapse pressure failure mode design formula NLFEA
- Publisher
- 부경대학교
- Affiliation
- Pukyong National University, Graduate School
- Department
- 대학원 조선해양시스템공학과
- Advisor
- Jung Min Sohn
- Table Of Contents
- I. Introduction 1
1. Background and Motivation 1
2. Scope and Objectives 6
3. Outline of the Thesis 7
II. design Overview on Pressure Hull Structure 8
1. Introduction 8
2. Buckling Theory and Design Formulation 8
2.1 Yield Pressure 8
2.2 Local Buckling Pressure 10
2.3 Overall Buckling Pressure 10
2.4 Tripping Pressure 11
3. Research on Ultimate Strength of Pressure Hull Structure 11
3.1. Ring-stiffened Cylindrical Shells Subjected to External Hydrostatic Pressure 11
3.2. Ring-stiffened Conical Shells Subjected to External Hydrostatic Pressure 13
3.3. Hemispherical Shells Subjected to External Hydrostatic Pressure 16
3.4. Dynamic Implosion Experiments 17
4. Final Remarks 19
III. Strength Assessment of Steel-welded Ring-stiffened Cylindrical Shell 20
1. Introduction 20
2. Ultimate Strength Test Benchmark 20
3. Non-linear Finite Element Analyses 21
3.1. Imperfection Assessment 23
3.2. Numerical Validation 24
4. Failure Mode Interaction Formula 25
5. Discussion 27
5.1. Effect of Overall Length Variation 28
5.2. Effect of Shell Thickness Variation 30
5.3. Effect of Stiffener Height Variation 32
5.4. Effect of Stiffener Spacing Variation 33
6. Final Remarks 35
IV. Strength Assessment of Steel-welded Ring-stiffened Conical Shell 36
1. Introduction 36
2. Review of Experimental Works 36
2.1 Preparation before the Test 37
2.2 Apparatus and Testing 38
3. Test Results 39
4. Non-linear Finite Element Analyses 42
4.1. Imperfection Modelling Strategies 42
4.2. Numerical Procedures 44
5. Ultimate Strength Formulation 45
5.1. Conversion Parameter of the Conical Shell 45
5.2. Proposed Formulation 48
6. Discussion 50
6.1. Numerical Prediction on Local Failure 50
6.2. Numerical Prediction on Overall Failure 51
6.3. Comparison of Ultimate Strength Formulation 52
6.4. Effect of residual stresses and initial imperfection 53
7. Final Remarks 54
V. Strength Assessment of Steel-welded Hemispherical Shell
1. Introduction 55
2. Welded Segment and Crown Hemisphere Test Model 55
2.1 Preparation before the Test 57
2.2 Apparatus and Testing 59
3. Test Results 61
3.1. Pressure and Strain Evaluation 61
3.2. Failure Mode Evaluation 62
4. Non-linear Finite Element Analyses 63
4.1. Numerical Procedures 63
4.2. Numerical Validation 64
5. Discussion 67
5.1. Numerical Prediction on Hemisphere Test Model 67
5.2. Comparison of Ultimate Strength Formulation 69
5.3. Effect of residual stresses and initial imperfection 69
6. Final Remarks 70
VI. Dynamic Implosion Investigation of Thin Cylindrical Shell 71
1. Introduction 71
2. Model Geometry and Measurements 71
2.1 Description of Test Model 71
2.2 Material characterization 74
3. Details of Experiments 76
3.1. Single Implosion Test 76
3.2. Serial Implosion Test 78
4. Test Results 79
4.1. Single Implosion Test 79
4.1.1. Model C1 to C6 Series 79
4.1.2. Model C7, CR3, CR5 Series 81
4.1.3. Model C8 to C13 series 83
4.2. Serial Implosion Test 87
5. Non-linear Finite Element Analyses 89
5.1. Single Implosion Test 89
5.1.1. Model C1 to C6 Series 89
5.1.2. Model C7, CR3, CR5 Series 92
5.1.3. Model C8 to C13 Series 94
5.2. Serial Implosion Test 97
6. Discussion 102
6.1. Evaluation on Single Dynamic Implosion Histories 102
6.1.1. Model C6D 102
6.1.2. Model C7C with End-Tapered Section 103
6.1.3. Model CR3-C, Ring-Stiffened Model with End-Tapered Section 104
6.2. Evaluation on Serial Dynamic Implosion Histories 105
6.2.1. Model C9B and C10B 105
6.3. Evaluation on Negative and Positive Pressure Impulse 107
6.4. Effects of Pressurising Rate to the Ultimate Strength 108
6.5. Effects of Pressurising Media to the Dynamic Implosion Pressure 109
7. Final Remarks 111
VII. Optimal Design of Pressure Hull Structure 112
1. Introduction 112
2. Design of a Steel-Welded Pressure Hull Structure 112
3. Genetic algorithm method for multi-objective optimization 113
4. GA Operation 116
4.1. Initial Model Category 116
4.2. Fitness Function 116
4.3. Multi-objective Constraints 118
5. Nonlinear FEA of the pressure hull 120
5.1. Model Idealization 120
5.2. Analysis of the Previous Pressure Hull 121
6. Results and Discussion 124
6.1. Convergence of the Fitness Function 124
6.2. Unconstrained Optimization 126
6.3. Constrained Optimization 130
6.4. Sensitivity Studies 134
7. Final Remarks 136
VIII. Conclusions and Recommendations 137
1. Conclusions 137
2. Recommendations 141
국문요약 143
References 145
Acknowledgements 152
- Degree
- Doctor
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- 대학원 > 조선해양시스템공학과
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