臺灣博碩士論文加值系統

水下爆炸的現象引發眾多研究者之興趣，由於各種原因，特別在軍事領域，水下爆炸會造成其附近之結構嚴重損害。了解此現象，有助於提高海軍艦艇及和潛艦之生存能力。水下爆炸發生後，爆震波徑向向外傳播，伴隨而來為含熱氣體之高壓氣泡脈衝，通過水介質傳播之高速爆震波會對結構造成相當大的損傷。雖然爆震波將產生高壓之負荷，然其持續時間甚短，反之氣泡脈衝則導致相對低壓的負荷，而其出現則會維持一個相當長的時間。因此，此氣泡脈衝之振盪將會導致在整體結構損壞；此外在氣泡收縮崩潰階段所形成高速噴流亦會引致附近結構之局部損傷。
由於水下爆炸氣泡脈衝現象為系列複雜行為所構成，本論文研究分為兩個階段。第一階段的研究，針對數值模型進行實驗及理論分析之驗證。隨即針對已驗證之系列氣泡模型，考慮不同邊界情況下進行分析。第二階段研究則主要集中模擬結構受氣泡脈衝之高速衝擊效應。其中包括衝擊壓力及受影響之結構響應特性。為了克服古典有限單元方法於此類型問題所招遇之難題，如大變形，流體及氣體模擬等，本論文應用ABAQUS中之歐拉分析方法進行研究。此方法可模擬一元素多材料行為，並且應用藕合歐拉-拉格朗日方法來求解決流-固藕合行為。
透過層流，不可壓縮黏性流體，非黏性流體行為，以及爆炸氣體之理想化之簡化工作，及與實驗及經驗公式之比較，本論文所發展之數值分析方法，可以用來評核及分析由爆震噴流衝擊所造成之結構損傷，以及水下爆炸引致氣泡脈衝之重要關鍵特性，包括如氣泡脈衝之漂移，壓力脈衝以及氣泡崩潰形成噴射行為。此外，本論文亦針對變形平板及簡化類船結構為對象，研究氣泡脈衝與結構距離及結構勁度受水下爆炸後之影響進行研究，研究成果亦可用於不同型態或大小之炸藥種類以及設置爆炸深度之研究

Underwater explosion phenomenon is of interest of numerous researchers for various reasons, particularly in the area of military, because such phenomenon can cause serious damage to any nearby structure. Understanding this phenomenon helps improve the survivability of naval ships and submarines. After detonation, the shockwave radially propagates outwards and this is followed by a high-pressure bubble containing hot gaseous products of the explosion. The shockwave travels out through the water at high speed and can cause considerable damage on structures. Although the shockwave generates high-pressure load but its duration is very short, whereas pulsating bubble induces low-pressure load but it occurs for a substantially long time. Therefore, the oscillation of the bubble can result in global damage on structures. Furthermore, the formation of high-speed water jet during the bubble collapse can also cause local damage on nearby structures.
Because an underwater explosion bubble phenomenon consists of a complicated sequence of events, the present study approached this phenomenon in two separated phases. In the first phase of the study, numerical models were introduced and verified by the experimental and theoretical data. Then, those models were applied for investigating the behavior of the bubble in the vicinity of different boundaries. In the second phase, the research focused on simulating the impact of a separated high-speed water jet on a flat plate. In which, the characteristics of impact pressure as well as the response of impacted structures were interpreted. To overcome the difficulties regarding the classical finite element method; such as large deformations, and flow simulation of fluid and gas, the Eulerian analysis in ABAQUS software was applied. This method allowed simulating multi-materials in an element, and the coupled Eulerian-Lagrangian technique helps solving the fluid-structure interaction (FSI), in which the Eluerian-Lagrangian contact contrains are enforced using penalty method.
Despite of limitation relating to the simplifications such as laminar, incompressible viscous, and inviscid flow behaviors, as well as the idealization of explosion gas products, the comparison to experimental and empirical results shows that the numerical model enable to estimate the damage of structures due to the impact of water jet, and reliably reproduced crucial characteristics of the underwater explosion bubble, including the migration of the bubble, pressure pulse, and the formation of water jet in the bubble collapse. The results show that the wall has the effect of slow down the collapse rate of the bubble, the standoff distance factor and the stiffness factor affect the behavior of the bubble as well as the development of water jet in different ways. The highest impact pressure induced by water jet impact at the center of the impact area and the stagnation pressure scatters quite uniformly on the area of diameter of the jet head. The quantitative characterization of the UNDEX bubble model is suitable for other explosive charge types, masses, and depths.

Inside Front Cover
Signature Page
中文摘要 ...iii
ABSTRACT ...v
ACKNOWLEDMENTS ...vii
TABLE OF CONTENTS ...viii
LIST OF FIGURES ...xi
LIST OF TABLES ...xvi
NOMENCLATURE ...xvii
ABBREVIATION ...xx

Chapter I: INTRODUCTION ...1
1.1 Underwater explosion phenomenon and motivation of research ...1
1.2 Literature review ...6
1.2.1 Underwater explosion bubble phenomenon ...6
1.2.2 Water jet impact phenomenon ...10
1.3 Research objective and scope ...13
1.4 Research framework and process ...15

Chapter II: THEORETICAL BACKGROUND ...18
2.1 Review of bubble equation ...18
2.1.1 Continuity equation ...18
2.1.2 Laplace equation ...21
2.1.3 Rayleigh - Plesset equation ...23
2.2 Water jet impact theory ...26
2.3 Numerical background ...27
2.3.1 ABAQUS General Description ...27
2.3.2 ABAQUS/Explicit ...28
2.3.3 Coupled Eulerian Lagrangian technique ...30
2.3.4 Equation of State ...34

Chapter III: SIMULATION OF AN ISOLATED UNDERWATER EXPLOSION BUBBLE ...38
3.1 Numerical model description ...38
3.1.1 Finite element model ...39
3.1.2 Initial conditions ...43
3.2 Results and discussion ...46
3.2.1 Expansion and contraction of bubble ...46
3.2.2 Migration of bubble ...51
3.2.3 Water jet formation ...53
3.2.4 Pressure pulse ...55
3.3 Summary and concluding remarks ...56

Chapter IV: THE INTERACTION BETWEEN AN UNDERWATER EXPLOSION BUBBLE AND STRUCTURES ...58
4.1 Bubble in the vicinity of a wall ...58
4.1.1 Numerical description ...58
4.1.2 Results and discussion ...61
4.2 Bubble below a ship surface ...71
4.2.1 Numerical model description ...71
4.2.2 Result and discussion ...75
4.3 Summary and concluding remarks ...80

Chapter V: SIMULATION OF WATER JET IMPACT ...83
5.1 Numerical model description ...83
5.2 Results and discussion ...90
5.2.1 Impact pressure ...90
5.2.2 The influence of impact angle on the impact pressure ...99
5.2.3 The deformation of impacted target ...103
5.3 Summary and concluding remarks ...109

Chapter VI: CONCLUSION AND FURTURE DIRECTIONS ...111
6.1 Conclusion ...111
6.2 Directions for future research ...114
REFERENCES ...115
APPENDIX ...121

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