Dynamics behavior for a submerged oscillating bubble is closely related to the physical properties of boundaries adjacent to the bubble. For an incomplete boundary, such as a ship structure broken by the shock wave from underwater explosion attack, the bubble load formed after the shock wave may cause secondary damage to it, and the jet characteristics generated during the bubble collapse are worth exploring. Based on the incompressible potential flow method, a boundary integral method with axisymmetric code is employed to investigate the jet features of the bubble under the combined action of a free surface above and a fixed plate with a centric circular opening below. For the numerical divergence caused by the expanding bubble infinitely approaching the rim of the circular opening, the bubble walls above and below the opening are, respectively, fused with the rigid wall, and the initial infinite flow field surrounding the bubble is then divided into two independent basins that are both required to be solved. Several experiments of a spark-generated bubble oscillating near a free surface and a rigid plate with a circular opening are conducted and the numerical results are validated. Following that, two typical cases with a dominant jet, respectively, directing upward and downward are analysed in detail, and some new phenomena are discovered. Additionally, another particular case that the upward and downward jet collides in the vicinity of the opening centroid is also presented. Finally, the initial bubble-free surface distance effects upon the bubble movement and the jet developments are analysed and discussed.

The interaction between an underwater explosion bubble and an elastic-plastic structure is a complex transient process, accompanying violent bubble collapsing, jet impact, penetration through the bubble, and large structural deformation. In the present study, the bubble dynamics are modeled using the boundary element method and the nonlinear transient structural response is modeled using the explicit finite element method. A new fully coupled 3D model is established through coupling the equations for the state variables of the fluid and structure and solving them as a set of coupled linear algebra equations. Based on the acceleration potential theory, the mutual dependence between the hydrodynamic load and the structural motion is decoupled. The pressure distribution in the flow field is calculated with the Bernoulli equation, where the partial derivative of the velocity potential in time is calculated using the boundary integral method to avoid numerical instabilities. To validate the present fully coupled model, the experiments of small-scale underwater explosion near a stiffened plate are carried out. High-speed imaging is used to capture the bubble behaviors and strain gauges are used to measure the strain response. The numerical results correspond well with the experimental data, in terms of bubble shapes and structural strain response. By both the loosely coupled model and the fully coupled model, the interaction between a bubble and a hollow spherical shell is studied. The bubble patterns vary with different parameters. When the fully coupled model and the loosely coupled model are advanced with the same time step, the error caused by the loosely coupled model becomes larger with the coupling effect becoming stronger. The fully coupled model is more stable than the loosely coupled model. Besides, the influences of the internal fluid on the dynamic response of the spherical shell are studied. At last, the case that the bubble interacts with an air-backed stiffened plate is simulated. The associated interesting physical phenomenon is obtained and expounded.

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