【作者】 崔杰；

【导师】 张阿漫；

【作者基本信息】 哈尔滨工程大学 ， 船舶与海洋结构物设计制造， 2013， 博士

【摘要】 近年来，水下爆炸气泡、冲击波载荷及其对舰船结构的毁伤特性已经成为了国际上研究的前沿和热点。纵观国内外，在舰船远场水下爆炸、冲击波的传播特性、气泡的运动形态及结构响应等方面取得了丰硕的研究成果；对于近场水下爆炸，载荷情况较为复杂，冲击波压力、气泡脉动、气泡射流及近边界空化效应等都会对舰船结构产生恶劣的冲击环境。由于近场水下爆炸复杂的边界条件，加之载荷的特殊性和结构响应的强非线性，使得适用于远场水下爆炸的基本方程和假设都不适用，给近场水下爆炸的研究带来了极大的困难，迄今为止，近场水下爆炸载荷及其对舰船结构的毁伤机理仍未被完全揭示。实船试验作为水下爆炸研究的最好手段，发达国家及我国相继开展了一定数量实船水下爆炸的试验，经费虽然惊人但是可以开展；而近场水下爆炸实船试验由于破坏力较强，受到了技术因素和经济因素的双重制约，目前在我国较少开展，故开展舰船的模型试验及机理性试验对近场水下爆炸载荷和结构毁伤的研究尤为重要。为此，本文以舰船安全性为工程应用背景，以近场水下爆炸气泡载荷为研究对象，采用机理试验与模型试验相结合的方法，研究近场水下爆炸气泡载荷特性及其对结构毁伤。本文首先从水下爆炸分类及近场特性入手，确定了本文的研究内容及范围，从试验、理论及数值三方面回顾了国内外关于近场水下爆炸冲击波、气泡载荷的研究进展，以及其对舰船结构响应的研究进展，分析了现有研究中低压电火花气泡试验无法计入浮力影响因素以及近场气泡射流载荷对舰船结构毁伤研究中存在的不足。同时提出了开展近场水下爆炸气泡载荷及结构毁伤试验研究的必要性，为全文奠定了基础。通过对气泡动力学的经典理论和数值算法的回顾，提出本文气泡三维数值模拟方法，针对目前常压电火花试验无法计入浮力影响，而水下爆炸过程中浮力却又是影响气泡坍塌、上浮的重要因素这一问题，本文根据模型试验相似原理，建立了减压条件下电火花气泡生成方法，从而利用试验室的条件营造与水下爆炸浮力参数相似的强浮力环境，针对试验过程中边界的影响问题，本文论证了试验方法的可行性。采用减压条件下机理试验的方法，配合高速摄影技术，首先研究不同压力下无边界影响的自由场气泡表征运动形态的物理量：半径、周期、中心迁移、上下表面位移等，给出气泡周期、最大半径、射流速度随环境压力的变化规律。研究气泡脉动过程不局限于以往试验研究中的第一个周期，对气泡可见周期内的表征形态的物理量都进行了规律性的总结。在此基础上，一方面研究气泡作为边界时的融合、坍塌、对射流、反射流等现象，总结计及浮力影响的两个同相气泡之间的相互作用随距离参数和浮力参数共同影响的变化规律，得到两同相气泡处于水平和竖直位置时融合机理，为多发导弹发射方案提供参考；另一方面对计及浮力影响下气泡的―水幕‖（水冢）和射流现象进行分类，分析各种类型水冢和射流形成的原因，研究水冢形态、高度以及气泡射流速度、中心迁移高度、周期等随距离参数及浮力参数共同影响的变化规律，并将试验结果与Blake准则进行对比，为―水幕‖反导的设计提供参考。利用减压试验的方法研究计及浮力影响的复杂边界附近气泡运动形态，对气泡所受浮力与固壁的Bjerknes力同向、反向以及成90度角时，刚性壁面附近气泡动力学特性开展研究，通过对气泡周期、中心迁移及射流方向、角度、速度等物理量的研究，得出壁面上方气泡―撕裂区间‖及固壁侧方气泡射流角度与特征参数之间的关系。此外，还讨论了柱形边界、弹性边界、壁面与自由表面组合边界附近气泡动力学特性，为水中兵器的设计和使用提供参考。通过减压条件下气泡试验，营造不同浮力的环境来模拟真实水下爆炸气泡与边界相互作用过程，利用本文建立的气泡动力学数值模型与其减压条件下电火花试验对比研究气泡在无边界影响的自由场、自由表面、刚性壁面附近膨胀、坍塌、射流及撕裂等复杂的动力学行为，数值结果与试验吻合良好，从而完善了水下爆炸气泡三维数值方法。同时，利用减压试验的方法弥补了数值模型不能模拟超近壁面（距离参数小于0.5）及第一周期之后气泡的运动等局限性，从而为后文利用减压试验对舱段模型试验进行分析奠定了基础。通过开展实尺度舱段模型试验，对近场水下爆炸冲击载荷作用下舰船局部结构弾塑性动态响应进行研究，得到了气泡射流载荷对结构的影响范围及毁伤效果。利用机理试验与舱段模型试验对比分析的方法，对压力、应变及位移等物理量进行分析，得到了舰船在受到初始冲击波的打击后，气泡后续载荷对结构的毁伤特性，为近场水下爆炸载荷作用下舰船结构毁伤机理的研究提供参考。更多还原

【Abstract】 In recent years, the shock wave and the bubble of underwater explosions and theirdamage effects to ship structures have become the forefront and heated issues in theresearches internationally. Fruitful results have been achieved on the far-field underwaterexplosions, shock wave propagations, bubble dynamics and structure responses both at homeand aboard. The structural load is more complicated in the near field underwater explosionswhere impacts are caused by not only shock pressure but also bubble pulsations, jets andcavitation on the structures, and hence can be much severer. As a result of the complexboundary conditions, the specificity of the loads and the strong non-linearity of the structuralresponses, the basic formulations and assumptions for far-field explosions become invalid innear-field cases, hence immense difficulties arise in the researches. So far, the loadcharacteristics and the mechanism of structural damages in near-field underwater explosionsare still far from being fully revealed.As the best research method for underwater explosions, the full-scale test, despite itshigh cost, has been carried out in small amounts in China and some developed countries.However, there is much constraint to the full-scale test for the near-field explosion in bothtechnical and financial aspects due to its great destructive power, and it has been rarelyconducted domestically. Therefore, model tests and principle experiments become favorableand particularly important for the studies on the loads and structural damages in near-fieldunderwater explosions. In this paper, the loads and structural damages induced by theunderwater explosion bubbles are studied with a combined method of principle experimentsand model tests, with respect to the engineering in ship safety.A classification of underwater explosions and analysis on the characteristics of thenear-field cases were presented first, with which the scope and content of this study wasidentified. The research progress on shock wave and bubble load as well as ship structureresponses was then reviewed in three aspects, namely the experiments, analytical analysis andnumerical simulations. The major defect, i.e. the neglecting of buoyancy effects, in existingmedium and low voltage spark-discharge bubble experiments, as well as the deficiencies inthe researches on the damage effects of near-field bubble jets was analyzed. The necessity ofexperimental studies on bubble loads and structural damages in near-field underwaterexplosions were identified. All of these laid the foundation of this study.Based on a review of classical theories and algorithms of bubble dynamics, a3-D bubblesimulation method is proposed. Since the buoyancy effect, which atmospheric experiments fail to capture, is dominating the contraction and upward migration of the bubble in actualunderwater explosions, the spark-discharge bubble experiments in this study are conducted insub-atmospheric pressure; in this way, the strong buoyancy effect in full scale tests can bereproduced under laboratory conditions by adjusting the air pressure above the water.With the pressure reduction and a high-speed photographing system, principleexperiments were first conducted for bubble pulsations in free fluid field with differentpressures. Physical quantities representing bubble behaviors, including bubble radius,pulsation period and migrations of bubble center, top and bottom, etc., were obtained.Variations of the period, the maximum radius and jet speed with the fluid pressure werestudied. The measurements and analysis were carried out not only within the first pulsationperiod of the bubble, as in most of the previous works, but also in all visible periods thereafter.On this basis, the interactions of two in-phase bubbles were investigated, where one of thebubbles is seen as a special boundary for the other. The coalescence, contraction, counter jetsand reverse jets of the bubble and the variations of these behaviors with the distanceparameter and the buoyancy parameter were examined. The principles were obtained for thecoalescence of two bubbles located horizontally or vertically, and could be utilized in thedesign of launch schemes for multiple missiles. Besides, the "water curtain"(or the "waterspike") and the bubble jet, both strongly affected by buoyancy, were categorized into differenttypes. Their formation mechanisms were analyzed; the combined effects of both the buoyancyparameter and the distance parameter on the form and height of the water spike, the jet speed,the migration of bubble center and the pulsation period were studied. The results werecompared with the "Blake principle" and could be of use in the development of anti-missilewater curtains.Further, experiments were conducted on bubble behaviors near complex boundary underbuoyancy effect with reduced pressure. The dynamics of the bubble close to a rigid wall wasstudied with the direction of the Bjerknes force being the same, the opposite andperpendicular to that of the buoyancy. Through analysis of the pulsation period and themigration of the bubble and the direction, angle and speed of the jet, a "bubble splitting zone"over a horizontal wall, together with a relationship between the angle of the jet and the featureparameters, were identified. In addition, bubble dynamics were discussed near a rigid cylinder,an elastic boundary and combined boundaries of rigid wall and free surface, which could bereferred to in underwater weapon designs and utilizations.With the pressure reduction, different levels of buoyancy effect were obtained and thusfull scale underwater explosion bubbles and their interactions with different boundaries were simulated. The study on the complex bubble behaviors including expansion, contraction, jetand splitting in free field, near free surface or near a rigid wall was combined with numericalsimulations with the3-D dynamic bubble model constructed in this paper. The numericalresults were validated by the reduced-pressure experiments and contribute to the3Dnumerical methods for underwater explosions. The pulsations after the first period and thebehaviors of the bubble generated very close to the boundary (distance parameter less than0.5)were unable to be simulated numerically but can be easily observed in the experiments; thislaid the foundation for the following analysis on the model tests utilizing the reduced-pressureexperiments.A full scale cabin model was tested in near-field underwater explosion experiments tostudy the plastic dynamic response of local ship structures under explosion loads withdifferent impact factors; the structural damage due to the bubble jet and the area affected bythe jet were obtained. The results of the model test were combined with that of the principleexperiments in the analysis of pressure, strain, displacement, etc. of the structure; on this basis,the pattern of the structural damage induced by the bubble load preceded by the impact of aninitial shock wave was obtained. The results could offer references for researches on thedamage mechanism of ship structures under near-field underwater explosion loads.更多还原