Hao Chen

The two-bubble coupling dynamics near a boundary is always complicated due to the inter-bubble interaction and the boundary effect, and relevant research is still very limited. Benefit from the Lagrangian properties, smoothed particle hydrodynamics (SPH) has distinct superiority in handling the bubble fusion, tearing, and fragmentation. Using the SPH method, this work numerically simulates the nonlinear interactions of two large-scale underwater explosion bubbles near an upper wall and investigates the shock characteristics of the bubble pair. Given the superiority of Riemann solvers to handle discontinuities, an accurate multiphase Riemann-SPH method with the monotone upwind-centered scheme for conservation laws reconstruction is adopted. Through this method, the experiment of an out-of-phase bubble pair interaction near the wall is first modeled, and the reliability of the present model is proven by the comparison of the experimental data with the SPH results. Subsequently, the influence of several key factors, including the distance between the bubble pair (γbb), the distance from the bubble to the wall (γbw), and the phase difference of two bubbles (θ), on the dynamic bubble behavior, the jet mode, and the load characteristics are systematically discussed. In this study, four bubble jet patterns are discovered, namely, “merging-upward jet,” “merging-downward jet,” “upward-downward jet,” and “upward-counter jet.” Compared to the cases of θ = 0 and θ = 0.5, the bubble pair under θ = −0.5 always exerts a stronger impact on the wall regarding the pressure peak and impulse, with the upward-downward jet mode posing the greatest load to the wall.

The process of a damaged ship flooding is a complicated free surface flow problem. There is a complex coupling effect between the ship cabin and the flow inside and outside of the cabin. In this paper, a GPU (graphic processing unit)-δ+-SPH (smoothed particle hydrodynamics) numerical model for the cabin flooding in deep-water environments is developed based on GPU parallel acceleration technology and Nvidia's CUDA (compute unified device architecture). First, the computational accuracy and efficiency of this numerical model are verified by experiments results on the water flooding of a simple damaged cabin model. Furthermore, the flooding characteristics of a submarine cabin are analyzed, considering different numbers of damaged cabins, depths, and opening positions. Finally, the progressive flooding and the dynamic response characteristics of a full-scale submarine model are investigated. The results show that the process of progressive flooding in a submarine cabin is characterized by its rapidity and intensity. Different factors, for example, damaged cabin numbers, cabin depths, and opening positions, have great influences on the process of flooding and the motion of the submarine cabin. This study can offer valuable technical assistance in the post-damage remediation process.

In the rapid flooding process of a damaged ship, the air trapped in a damaged cabin will be compressed into an air cushion, which causes the air cushion effect (ACE). The ACE has a significant influence on the flooding process of an airtight cabin. In this paper, a three-cabin model is designed according to a parent ship, and a series of model experiments are carried out. First, the air-tightness ratio is defined by combining various air vents with different opening areas, and the flooding model experiments of different air-tightness ratios are carried out. The heeling and trimming angles of the model, the overpressure of the air cushion, and the water height inside the flooding cabin are recorded and analyzed, and the characteristics of ACE are summarized. Second, different forms of air vents with a same air-tightness ratio are designed, and the influence of the air vent distribution on the flooding process is analyzed. With the quasi-static method used for comparisons, the numerical results are compared with the experimental ones to check the effectiveness of the quasi-static method on the rapid flooding problems. The research on ACE can guide the design of ship subdivisions and provide a reference for the rescue of shipwreck accidents.