Research On Dynamics Of Cylinderical Charge Underwater Explosion Bubble And Damage Of Jet Impact

Cylindrical charge is a common used charge construction on underwater weapons. Sincethe spheroid charge assumption is no longer appropriate in the study of close proximityunderwater explosion problem, the influence of charge structure and detonation mannershould be considered. Then, there are many different types of threats a naval ship canencounter. For ship survivability, the main threat comes from underwater explosions(UNDEX). The loading of UNDEX derives from shock wave and bubble motion. In the past,much more attention has been paid to understand the underwater explosion shock wave andits damage mechanism instead of the complicated loads induced by the bubble dynamics.However, recent prototype explosion tests and model experiment have all indicated thatunderwater explosion bubble can damage ship very badly, both hull and local structure.Review of investigation and development of non-contact underwater explosion shows thatlittle comprehension has been made on jet impacting problem, especially between thecharacteristic of jet loading and the damage response of structure.To understand the study of ship survivability and explosion analysis, underwater bubblesby cylindrical charge was made as the subject investigated in this dissertation. Bothexperimental investigation and numerical simulation were employed to study jet loading byunderwater explosion bubble and its damage on ship hull. Generally speaking, the main workof this thesis includes:1. Research progress about non-contact underwater explosion of ship structure was madefrom experimental, theoretical and numerical aspects respectively. Comprehensive review ofbubble dynamics research was also achieved, including methods, contents and developments.Significant differences between explosion bubble and cavitation bubble were pointed outbased on the summary of bubble dynamics studies. The necessity and feasibility to investigatenon-spherical bubble problems was also analyzed;2. Modes of spherically symmetric bubble and generalized bubbles were listed. Bycomparison advantages and disadvantages of each other, limitations between these twomathematical models were found out. It was shown that the identification of initial parameterson bubble restrict the application of these models only under initially spherical bubblecondition;3. Laboratory scale underwater explosion experiment method was established to studybubble dynamics by cylindrical charge, including the design of experimental facility, thechoosing of bubble generator and relevant measuring and testing technique. Data processing and accuracy analysis shows that the experimental method is feasible to study underwaterexplosion bubble phenomena;4. Multi-material Arbitrary Lagrangian/Eulerian finite element model and boundaryelement model were engaged to establish a non-spherical bubble dynamics model, which caninvolve real detonation process. As a result, the model can solve explosive with differentshape and detonation manner. The effectiveness and applicability of numerical modelvalidation shows that the numerical model has practical value;5. Global and local dynamics of bubble by cylindrical charges with different detonationmanner and length diameter ratio were obtained both experimentally and numerically. Theanalysis of bubble collapse and jet formation shows that jetting process is closely contact withthe non-spherical collapse of bubble, and the radius of curvature of initial bubble is a keyinfluence factor for bubble collapse;6. Dynamic characteristics of bubble by cylindrical charge near free surface and rigidwall were obtained by using the non-spherical bubble dynamics model, including bubbleperiod, bubble radius, shape evolution, migration and jets. Research results show that theinfluencing factors of jet features are detonation modes, boundary types, bubble depth and thedistance between bubble and boundary. Where detonation modes mainly affect the shape andinfluence area of jet, bubble depth mainly affects the shape and velocity of jet, boundary typesand the distance between bubble and boundary mainly affect the direction of jet;7. Characteristic of jet impact loading was investigated theoretically and numerically. Ajet impacting mode was established and was then used to simulate deformation and damageresponse of ship structure impacted by jet. Results show that the damage of jet impactingimposed on ship is mainly local failure. When a jet impacts on weak structural parts such asouter plate, most of the damage is concentrated in the cell plate and a cross shape petals willformed. As a result, the integrality of local structure will break down. While when a jetimpacts on strong structural parts such as floor plating and girder, crevasse of hexagon shapewill formed and the longitudinal strength of ship hull will break severely.