Zi-Fei Meng

In this study, we systematically focus on the coupling mechanism between the free surface and array bubbles. The method of underwater electric discharge was utilized to synchronously generate the array bubbles. The current array design consists of three collinear bubbles arranged horizontally beneath the free surface. High-speed photography shows distinct bubble dynamics and water spike evolution patterns for different bubble-free surface stand-off distances of γb and γf. Numerous distinct and novel phenomena were identified. Quantitative analyses are performed on the jet velocities of array bubbles and the width and rising velocity of the water spikes at different stand-off distances. It is shown that for small γb less than 1.0, the bubbles would merge as well as the water spike being formed. As γb increases, the integrated water spike is observed to be separated, resulting in three water spikes arising on the free surface. Rich shapes of water spikes with the required width or height can be produced by controlling the stand-off distances associated with the array bubbles. The findings can provide a probable reference for predicting dynamics of the water spikes caused by array oscillating bubbles.

The interplay of coupling and entanglement among underwater bubbles exerts a pronounced impact on bubble dynamics, as well as the propagation characteristics of pulsations and velocities. Herein, both horizontal and vertical arrangements were considered. A double-bubble mathematical model was employed to emphasize the interactions between a pair of oscillating bubbles, with a single-bubble scenario serving as the control group. Spatiotemporal correlation analysis was conducted between the bubble motion patterns and flow-field instabilities. The results indicated that, within the double-bubble system, the predominant oscillation duration of the left-hand bubble was prolonged by over 50% in comparison to that of a single bubble. As the liquid level increased in depth, there was a notable delay in both the oscillation and migration of the bubbles, and the flow instability induced by the bubbles gradually diminished. Moreover, the acceleration of bubble oscillation and the viscous force emerge as the primary factors governing the momentum propagation. In contrast, the bubble radius and migration velocity exert only a negligible influence on the flow field. The current study provides new theoretical insights and quantitative tools for future research in multiphase flow and underwater bubble control strategies.

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 acoustic cavitation oscillation behavior of a single bubble and the resulting characteristic pressure evolution is a complex dynamic phenomenon. The coupling mechanisms among many characteristic pressures that affect the oscillation characteristics are still ambiguous. A correlation method is applied to analyze the degree of correlation between characteristic pressures and bubble oscillations. The effects of ambient pressure, bubble state, and propagation of driving acoustic pressure on bubble oscillation and size were investigated. The results indicate that the viscosity is the dominant factor affecting bubble oscillating velocity during the growth or collapse processes. The surface tension is strongly correlated with the bubble oscillation, and the oscillating velocity of a bubble greatly suppresses the effect of the viscosity on the bubble oscillation. In particular, the sinusoidal variation in driving acoustic pressure strongly correlates with bubble radius oscillation, and its correlation with bubble acceleration increases linearly. Moreover, two linear relationships between the ambient pressure and the frequency to the characteristic radius are obtained.

The present study aims to provide a deep understanding of curved wedge water entry. It involves a numerical simulation investigation into the kinematic and dynamic properties of water entry for two curved wedges with deadrise angles of 25° and 35°. The meshless Riemann-smoothed particle hydrodynamics (SPH) model embedded with an acoustic damper is developed to simulate these violent water entries. The validation of the Riemann-SPH accuracy is confirmed through comparison with experimental data, and subsequently, we make a systematical simulation study on curved wedge water entry, including a comparative study of free surface evolution and pressure distribution at different curvatures and drop heights. Furthermore, the kinematics analysis of velocity and displacement of curved wedges and time domain characteristics of slamming pressure loads on both sides of the wedge are investigated. It is revealed that the pressure distribution is symmetrical, with high-pressure regions forming near the bottom of the wedge and gradually propagating outward. The free surface profiles are symmetrical, with deeper depressions formed by sharper wedges. The entry depth and velocity are correlated with the initial theoretical entry velocity, and the rate of speed decline varies with the curvature of the wedge. The slamming pressure loads exhibit distinct time-domain patterns, with lower pressure loads by sharper wedges.

With the limited resources and high cost of lithium‐ion batteries (LIBs) and the ever‐increasing market demands, sodium‐ion batteries (SIBs) gain much interest due to their economical sustainability, and similar chemistry and manufacturing processes to LIBs. As cathodes play a vital role in determining the energy density of SIBs, Mn‐based layered oxides are promising cathodes due to their low cost, environmental friendliness, and high theoretical capacity. However, the main challenge is structural instability upon cycling at high voltage. Herein, Mg is introduced into the P2‐type Na_0.62Ni_0.25Mn_0.75O₂ cathode to enhance electrochemical stability. By combining electrochemical testing and material characterizations, it is found that substituting 10 mol% Mg can effectively alleviate the P2–O2 phase transition, Jahn‐Teller distortion, and irreversible oxygen redox. Moreover, structural integrity is greatly improved. These lead to enhanced electrochemical performances. With the optimized sample, a remarkable capacity retention of 92% in the half cell after 100 cycles and 95% in the full cell after 170 cycles can be achieved. Altogether, this work provides an alternative way to stabilize P2‐type Mn‐based layer oxide cathodes, which in turn, put forward the development of this material for the next‐generation SIBs.

High-pressure bubble dynamics often involves many complex issues, including large deformations and inhomogeneities, strong compression, moving interfaces, and large discontinuities, that bring challenges to numerical simulations. In this work, an axisymmetric Riemann–smoothed particle hydrodynamics (SPH) method is used to simulate high-pressure bubbles near different boundaries. This Riemann–SPH can adopt the real sound speed instead of the artificial one for the air phase in the bubble. Therefore, the real compressibility of the air phase can be considered, and the corresponding time step is significantly increased. To avoid unphysical interface penetration and maintain relatively homogeneous particle distribution, a new and simple particle shifting scheme for multiphase flows is proposed. Additionally, to minimize the influence of the unphysical boundary on the bubble, a large fluid domain with an optimized initial particle distribution is adopted to reduce the particle number. Several high-pressure bubbles under different boundary conditions are considered, including in a free field, near a free surface, near a solid boundary, and near a rigid sphere. Numerical results show that these bubble dynamic behaviors can be reproduced with satisfactory accuracy.