The boundary with an initial opening significantly affects shock wave propagation and bubble dynamics. To investigate the associated loading characteristics, this paper employs an axisymmetric Riemann-SPH method to simulate the shock wave and bubble near a single-layer deformable wall with an initial opening. The numerical model is first validated by simulating a spark-generated bubble experiment. Subsequently, the effects of plate deformation, opening radius, and stand-off distance on shock wave propagation, bubble pulsation, and jet evolution are systematically analyzed. The results show that plate deformation has little influence on shock wave propagation but significantly alters bubble pulsation and jet formation. At the opening center, the pressure history evolves from a double-peak to a single peak with increasing opening radius or stand-off distance. Bubble evolution presents three distinct jet modes: vertical jet, oblique jet tendency, and oblique jet. Small opening radii combined with short stand-off distances promote high-speed oblique jets and toroidal bubble formation, whereas increasing the stand-off distance weakens plate confinement, causing the bubble dynamics to gradually approach those in the free field. The study provides useful insight into shock wave propagation and bubble dynamics near non-intact plates and offers a reference for evaluating underwater explosion loading on damaged structures.

Artificial water surface jumpers hold great promises in a variety of application fields. However, it is still challenging to achieve a jumping performance that transcends the biological limit because the typical jumping processes involve deformation and the internal energy dissipation during the deformation processes often leads to low performances. Herein, inspired by the snapping shrimp, we report a tailor-designed, light-driven water surface jumper with a record-high jumping height (~910 body length), which is far superior to that of the best biological counterpart (~18 body length in case of pygmy mole crickets). The jumping process features an ultrafast take-off velocity (~14.9 m/s), a fast response time (~0.5 ms) and a high energy conversion efficiency (2.12%). The extraordinary jumping performance relies on a fundamentally different mechanism other than deformation that harnesses the synergy between the photothermal effect of the methyl-substituted polypyrrole nanoparticle constituent, the trapped air inside the surface micropores and the high stiffness of the jumper to generate high-pressure bubble and realize efficient propulsion. The excellent jumping performance and weight-carrying capability (~36 times of the jumper’s weight), together with the controllability over both jumping direction and height, make the light-driven water surface jumper reported in the current study potentially attractive for soft robotics and sensing applications.

Transient fluid-structure interaction (FSI) processes often involve strong impact loads and pronounced nonlinear responses. A typical example arises in near-field underwater explosions, which involve highly transient and nonlinear phenomena, including shock waves with strong discontinuities, pulsating bubbles undergoing drastic volume changes, and severe tearing and damage to ship structures. These processes entail complex FSI, placing stringent demands on both the accuracy and computational efficiency of numerical methods. To address the bottleneck in high-resolution, large-scale simulations, this study develops a fully meshless Riemannsmoothed particle hydrodynamics (SPH) and reproducing kernel particle method (RKPM) coupling method with GPU-acceleration for FSI analysis in underwater explosions. Within a unified GPU computing framework, the solutions of fluid dynamics, structural dynamics, and FSI are all organized using "particles" or "stress points" as fundamental parallel units. A unified data structure and a parallel optimization strategy based on a shared linked list are introduced, effectively reducing the overhead associated with neighbor searching and data access. The accuracy and computational efficiency of the proposed method are demonstrated through underwater explosion simulations involving a free-field shock wave, a double-layer cylindrical shell, and a full-scale submarine. Under the same spatial resolution, present single-precision implementation and computational configuration adopted in this study, the GPU-based parallel framework achieves an overall runtime reduction ratio of at least 31 times compared with the CPU-based parallel implementation in typical fluid-structure interaction scenarios. Moreover, it enables efficient large-scale, high-resolution simulations while substantially reducing total computational time.

Underwater contact explosions involve complex multi-phase moving interfaces under elastoplastic and damage-induced conditions. This study investigates shock wave propagation, bubble pulsation, and progressive damage evolution in plate structures subjected to underwater contact explosions. An experimental setup was established in a dedicated explosion water tank equipped with synchronized high-speed imaging and pressure sensors, complemented by arbitrary Lagrangian-Eulerian (ALE) simulations that account for fluid-structure interaction. The shock wave and bubble pulsation behaviors were compared between damaged and purely elastoplastic boundary conditions. The results show that both the reflection coefficient and impulse of the shock wave at the structural surface decay rapidly with decreasing stand-off distance, a trend that diminishes when the dimensionless stand-off distance γ exceeds 0.2. Plate rupture leads to bubble venting through the resulting cracks, which reduces internal pressure and attenuates secondary pulsation amplitude. Structural deformation and damage are primarily driven by shock-wave loading, while bubble-induced loads contribute up to 17

The formation of high-speed liquid jets is a defining feature of cavitation bubble dynamics near rigid boundaries. However, cavitation bubble inceptions naturally deviate from perfect spherical symmetry due to environmental disturbance, leading to elongated or teardrop-shaped geometries that complicate their dynamics. To systematically assess the influence of initial bubble geometry, we combine experimental observations with finite volume method (FVM) simulations, modeling the bubble as an initially ellipsoidal shape. We analyzed how the aspect ratio (q, = a/b), expansion ratio (7 = Rmax/R0), and standoff distance (y = d/Rmax) influence jet velocity. The simulations closely reproduce the experimental results, showing that variations in the initial shape cause less than a 1% change in bubble size and collapse dynamics but lead to a significantly larger difference - up to about 10% - in jet velocity. Parametric analysis shows that at 7 approximate to 22, the jet velocity first increases and then decreases with q,, causing a deviation of up to 39.1% in the peak velocity. This non-monotonic behavior arises from curvature variations during collapse, where regions of higher curvature experience stronger driving pressures, producing faster jets. The effect becomes more pronounced at smaller 7, while y exerts only a minor influence. Based on these results, we propose a polynomial correlation for jet velocity as a function of y and q,. These findings help explain some jet velocity differences between simulations and experiments and underscore the crucial role of initial bubble shape in cavitation modeling.

The interaction of a spark-generated cavitation bubble with an initially perturbed free surface is investigated experimentally, numerically and analytically. By exploiting contact-line pinning, we accurately prescribe an initial meniscus with a thin, hydrophilic-coated rod inserted into the liquid. A pronounced surface cavity, driven by the oscillating bubble, forms and penetrates downward to a scale comparable to the bubble itself. The coupled cavity-bubble system exhibits two distinct regimes - coalescence and non-coalescence - separated by a critical condition governed by the non-dimensional stand-off parameter $\gamma$ and the initial meniscus height $h_m$ . In the non-coalescence regime, the cavity evolves through inception, expansion and rebound/jetting. The maximum cavity length $h_{ extit{c}}$ follows a power-law scaling $h_{ extit{c}}\propto \gamma <^>{\alpha }$ with $\alpha =-2.7$ (experiments) and $\alpha =-2.6$ (simulations) for $1.5\lesssim \gamma \lesssim 3$ , where inertia dominates. Deviations emerge for $\gamma \lesssim 1.5$ (strong nonlinearity) and $\gamma \gtrsim 3$ (surface tension and viscosity become noticeable). An analytical model based on the Rayleigh-Plesset equation combined with nonlinear Rayleigh-Taylor instability theory captures the trend and confirms that $h_m$ plays only a secondary role relative to $\gamma$ . In the coalescence regime, atmospheric air vents into the bubble through the merged cavity, weakening the collapse intensity and reducing the associated pressure peak. We also examine air/liquid compressibility and boundary layer effects, whose significance grows as $\gamma$ decreases. These findings are relevant to surface-jetting technologies, cavitation-erosion mitigation and underwater-noise suppression.

This study experimentally, numerically, and theoretically investigates the cavity/bubble dynamics and radiated acoustics during the water entry of a centimeter-scale cylindrical projectile with a conical nose. Experiments were conducted in a laboratory tank, employing synchronized high-speed imaging and hydrophone measurements to characterize the cavity closure modes and their resultant acoustic signatures across a range of Froude numbers. The acoustic signal features a weak radiated signal upon impact, followed by significant pressure oscillations spanning more than 20 cycles in the flow field after cavity elongation and pinch-off. A numerical model based on the Finite Volume Method successfully captures these physical processes. Subsequently, a semi-theoretical model that incorporates the projectile's boundary effect is developed from potential flow theory. The model not only yields a dominant cavity oscillation frequency that agrees well with experimental data, but also reveals that the boundary effect leads to a cavity oscillation frequency markedly higher than the Minnaert frequency of an equivalent-volume ellipsoidal bubble containing an internal rigid core. The dominant cavity frequency falls nearly linearly with Fr, governed by nose geometry and projectile inertia. This study clarifies the underlying physics connecting cavity dynamics during water entry to underwater acoustic radiation.

This study presents a coupled thermo-mechanical SPH framework for simulating high-speed multimaterial impacts involving large deformations. The framework consistently integrates reaction heat release, heat conduction, and temperature-dependent constitutive laws and equations of state into the governing equations, enabling accurate modeling of plastic flow, thermal response, and damage evolution. For metallic materials, the Johnson-Cook constitutive model and failure criterion are employed, while a friction- and viscosity-dominated post-failure response is introduced to represent mechanical behavior after melting and fragmentation. To address tensile instability in conventional SPH methods, a novel physically based pressure-limiting technique coupled with temperature evolution is developed. Furthermore, a dynamic particle activation strategy is proposed to efficiently resolve only the shock-affected regions, greatly enhancing computational efficiency. Numerical results show that the proposed framework can robustly capture interface evolution, temperature distribution, and failure patterns in high-speed multimaterial impacts. The findings highlight the crucial role of thermal effects in impact-induced damage processes. Overall, the developed model achieves high accuracy and stability under extreme strain-rate conditions, offering a reliable computational tool for investigating coupled thermal-mechanical behavior and damage mechanisms in high-speed impact events.

ABSTRACT As the demand for deep-sea resource exploration continues to grow, the optimization of low-frequency performance has become a critical objective in the design and control of marine airgun sources. A damping screen, installed at the outlet of a large-scale airgun, was investigated as a method to shift the dominant frequency of the acoustic signal toward lower frequencies. Based on a validated numerical model of compressible airgun bubble dynamics, a systematic analysis was conducted to assess the impact of the damping screen’s geometric dimensions on bubble dynamic characteristics, the airgun’s pressure wavelet, and its sound pressure level spectrum. The damping screen effectively regulated the airgun’s performance by actively intervening in and reshaping the dynamic behavior of the bubble. A principal finding was that the damping screen successfully lowered the dominant frequency of the airgun, revealing a predictable, regulatory relationship between the screen’s dimensions and the source’s dominant frequency. Furthermore, the influence patterns of the damping screen’s dimensions on other key performance indicators, including the characteristics of the primary pulse, as well as the strength and period of the bubble pulse, were determined. A damping screen, therefore, shows promise as a novel approach for achieving targeted modulation of the dominant frequency in airgun source signatures.

When subjected to an underwater explosion, a ship may suffer severe structural damage and subsequent cabin flooding. This process is highly nonlinear, involving complex free-surface flows, structural fracture, and transient fluid-structure interactions. In this study, a fully meshless numerical framework is developed to simulate the entire fluid-structure interaction process of ship structures subjected to underwater explosion. This framework enables integrated simulation of the entire fluid-structure interaction (FSI) process from structure damage to cabin flooding. The fluid domain is modeled using a strongly compressible Riemann-SPH formulation during the explosive damage phase and a weakly compressible SPH model during the cabin flooding phase. Structural dynamics are resolved using the reproducing kernel particle method (RKPM), accounting for elastoplastic damage and crack propagation. At the fluid-structure interface, the normal flux method is employed to ensure compatibility in motion and dynamic conditions. The accuracy of the proposed framework is validated through comparisons with experimental results of underwater explosion-induced structural damage and cabin flooding, respectively. Furthermore, the entire process of structural damage and cabin flooding following an underwater contact explosion on a large-scale ship is successfully simulated. These results demonstrate the effectiveness of the established numerical framework in predicting the full sequence of events in underwater explosions.

Bubble pairs are effective modulators of liquid jets. We investigate the jetting of an air bubble driven by a laser-induced cavitation bubble using high-speed imaging, compressible volume-of-fluid (VoF) simulations and theoretical analysis. Three distinct jet types emerge, depending on the stand-off distance $\gamma$ and size ratio $\eta$ between the bubbles. Jet formation proceeds through two stages: an initial shock-induced acceleration followed by flow focusing on the concave liquid-air interface. We derive scaling relations, $V_0=1.1 p_0R_0/( ho cR_l)((\gamma (1+\eta )-1)/\eta )<^>{-1.6}$ for the shock-driven stage and $V_m={}(1+(0.8-0.5\gamma )\eta <^>{0.75})V_0$ for the flow focusing stage in the strong jet regime, both of which agree closely with experimental and numerical measurements. Here, $V_0$ and $V_m$ denote the velocity increments associated with shock-wave-induced acceleration and flow focusing stages, respectively. The variables $p_0$ , $R_0$ , $ ho$ , $c$ and $R_l$ represent the initial pressure and radius of the cavitation bubble, the fluid density, the speed of sound in the liquid and the maximum volume-equivalent radius of the cavitation bubble, respectively. A $(\eta ,\gamma )$ phase diagram delineates the weak, strong and explosive jets, with regime boundaries accurately captured by the theoretically derived transitions.

This study investigates the unsteady evolution of buoyant oscillating bubbles situated near a rigid boundary via a boundary integral (BI) approach, with a primary objective of identifying universal patterns in axial and annular jetting. We verify the BI simulation against several purposely conducted experiments on electric-discharge bubbles performed inside a depressurized tank. Four collapse patterns of the bubble are identified, namely, (i) downward jet towards the wall, (ii) upward jet, (iii) bubble pinch-off caused by an annular jet, and (iv) quasi-spherical collapse. We categorize them in a phase diagram in the γ-δ parameter space (0 ≼ γ ≼ 2, 0 ≼ δ ≼ 0.6), where γ and δ are the dimensionless standoff parameter and buoyancy parameter, respectively. A new ‘upward jet regime’ is found for a large-buoyancy bubble (γ ≽ 0.3) initially attached to or very close to the wall (γ ≼ 0.5), in which an annular focusing flow causes a complete detachment of the bubble from the wall and further drives an upward liquid jet. In the downward jet regime, the axial jet velocity is found to exhibit a power-law scaling in the maximum curvature of the bubble surface κ, i.e., Vjet = ηκ0.7±0.04, but with a different prefactor η depending on γ. As for the annular jet, the neck radius evolution of the bubble substantially deviates from the classic scaling Rn ∝ τ0.5, where τ represents the time remaining before the pinch-off event. A logarithmic correction, y = Rn(− ln Rn)1/4 (Gordillo et al., [Phys. Rev. Lett. 96, 194501 (2005)]), makes the effective exponent αy closer to 0.5, αy = 0.535 ± 0.004, but cannot account for all the deviations. Importantly, we demonstrate that the annular jet dynamics does not reach a universal regime. Instead, the extracted exponents depend on the specific simulation setup, falling between the theoretical predictions of Gordillo et al. [Phys. Rev. Lett. 96, 194501 (2005)] and Eggers et al. [Phys. Rev. Lett. 98, 094502 (2007)]. This non-universality highlights that the bubble pinch-off dynamics exhibits a weak dependence on the initial dimensionless parameters, a consequence of the slow logarithmic convergence of the governing dynamics.

A compressible axisymmetric physics-informed neural network (PINN) based on the volume of fluid (VOF) method is proposed to predict flow fields and infer unknown parameters of a pulsating bubble. Axisymmetric spatiotemporal coordinates serve as inputs, whereas velocity, pressure, and volume fraction are predicted as outputs. The governing equations are implemented in axisymmetric form to adhere to the underlying physical constraints. Density is computed from the predicted pressure using the equation of state (EOS) to ensure consistency between pressure and density. An adaptive sampling strategy is adopted to refine the regions around the bubble interface and the peak of the shock wave, thereby accurately capturing the steep and rapidly varying features around these regions. Specific activation functions are utilized in the output layer to strictly constrain the output range and ensure the stability of the training process. The proposed framework is validated by three representative cases: the forward and inverse problems for a bubble expanding in an unbounded liquid, and the forward problem for a bubble expanding near a rigid surface. Results demonstrate that the model can accurately predict flow field characteristics using only initial parameters and boundary conditions without additional data, and can reconstruct pressure and velocity fields from bubble interface information. This approach provides a novel framework for simulating axisymmetric compressible multiphase flow systems and offers a robust means of inferring unknown parameters that are challenging to measure in traditional experimental fluid mechanics.

This paper presents a model for the full-range formation and propagation process of near- and far-field underwater explosion shock waves. The model combines coordinate mapping with the discontinuous Galerkin method so that fast-moving discontinuities, including the shock front and the bubble interface, remain on subdomain boundaries and do not require conventional shock-capturing treatment. In the near field, the computational domain is divided into interior and exterior regions, and the boundary conditions are supplied analytically through a two-medium Riemann solver and the Hugoniot jump conditions. In the far field, a new equation for the evolution of a finite-strength shock is derived by simplifying the inward characteristic with theoretical analysis. The resulting far-field equation is much less stiff than the full Euler or wave equation system and has a substantially smaller characteristic speed, allowing larger time steps and efficient propagation to long distances. Validation against experimental data shows that the model reproduces both the primary and secondary shocks with good accuracy, and that the far-field model predicts the decay of the shock peak in close agreement with the fully nonlinear near-field solution. Finally, we examine how internal waves repeatedly reflect inside the bubble and generate multiple pressure fluctuations in the emitted pressure history. Through scaling analysis and numerical validation, we identify when internal-wave effects become dynamically important and show that ambient pressure is the dominant controlling parameter.

This study presents a physical model of bubble pulsation for a vacuum seismic source designed for deep-sea resource exploration. A comprehensive review of the published literature reveals that systematic theoretical analyses of vacuum seismic sources remain extremely limited to date. The vacuum seismic source investigated in this paper is a novel seismic exploration technology. By exploiting the energy difference between the deep-sea ambient environment and the internal state of the vacuum source, a deep-sea cavity is generated, producing high-energy pressure waves suitable for deep-water exploration. In this work, bubble pulsation models for both the conventional air gun and the vacuum seismic source are established, and a comparative analysis is conducted to elucidate the fundamental differences between these two types of seismic sources. The operating mechanism of the vacuum seismic source is thereby revealed. Furthermore, the influences of initial cavity volume, initial pressure, and excitation depth on how the vacuum seismic source performs are systematically investigated. The results provide critical theoretical foundations for improving the quality of exploration pressure waves generated by vacuum seismic sources and for optimizing their spectral characteristics and offer essential theoretical support for the transition from a conceptual vacuum source model to the development of a prototype system.

Soft robots, with their compliant bodies, minimal environmental disturbance, and ability to withstand ambient pressures, offer promising solutions for deep-sea exploration. However, a common challenge of stiffening in soft materials impairs their effective actuation in harsh conditions. In this work, we integrated a liquid dielectric plasticizer within an electrohydraulic soft robot, serving dual critical functions as a softening agent to maintain the softness of the polymer shell and an electrohydraulic fluid for efficient actuation. In addition, by using the surrounding seawater as alternating electrodes, we prevented charge retention in dielectric layers, enabling sustained actuation performance. Field tests at depths of ~1360, 3176, and ~4071 meters confirmed the robot's ability to sense the environment, navigate complex trajectories, and withstand unsteady disturbances. Our work offers a generalized and straightforward framework for developing soft materials tailored for deep-sea applications, paving the way for soft robots to execute real-world missions.

This study examines the impact of hydrostatic pressure on the dynamics of underwater explosion bubbles near a steel plate through numerical and experimental studies. We conduct underwater explosion experiments in a pressure tank, altering the air pressure within the tank using a pressure pump to change the hydrostatic pressure around the bubbles. The interaction between the bubbles and the plate is recorded with a highspeed camera, and we extract and analyze the jet velocity, bubble radius, and plate displacement as functions of hydrostatic pressure. Building on this, we design a numerical framework that encompasses hydrostatic pressures varying from 0.2 MPa to 20 MPa and dimensionless bubble-plate standoff parameters gamma from 0.6 to 2.5 for a more thorough investigation on the bubble-plate interaction. We find that both the maximum jet velocity and the maximum jet volume exhibit scaling relationships with hydrostatic pressure p(infinity) when p(infinity) > 1 MPa. Additionally, the dimensionless maximum jet volume shows a non-monotonic relationship with gamma, depending on the degree of bubble-plate interaction at the moment of jet impact. Across a certain span, the maximum plate displacement also follows a scaling relationship with p(infinity), where the exponent differs according to gamma. This work is intended to offer a foundation for the study of underwater explosion bubble dynamics and fluid-structure interaction characteristics under high hydrostatic pressure or deep water environments.

Bubble clusters are widely existed in nature and every single bubble will pulsate under its surrounding ambient pressure wave. To simulate the motion of bubble cluster under pressure wave is a great challenge for both algorithm robustness and calculation cost. This paper introduces a multi-scale method to simulate interaction between the pressure wave and bubble clusters comprising several thousand natural bubbles. In this model, the propagation process of pressure waves is simulated within a continuous Eulerian field, while the bubble clusters are depicted as Lagrangian points distributed in this field. The flow field information surrounding the bubbles is acquired by interpolation from the Eulerian field. Bubble oscillation and migration are accurately calculated using bubble theory. The variations of the bubble clusters are incorporated as source terms in the equations to achieve two-way coupling solution, which facilitates a more precise simulation of the interaction between underwater pressure waves and bubble clusters. Comparison with experimental data demonstrates the advantages and effectiveness of the computational model in simulating bubble cluster coupled with underwater pressure wave. Subsequently, this paper investigates the propagation process and attenuation mechanism of pressure waves among bubble clusters, analyzing the effects of pressure wave amplitudes and bubbles numbers and bubble sizes on pressure wave attenuation. Our results indicate that the pressure wave attenuation is dominated by the initial gas volume fraction of the bubble cluster and is not significantly affected by the pressure wave amplitude.

This work investigates the effects of fluid compressibility related to bubble migration. These effects are described based on a theoretical model for compressible bubble dynamics that considers phase transition and migration, as proposed by Zhang. Bubble experiments of different types are conducted to validate this theoretical model further. The model well captures experimental results near the wall and the free surface, illustrating that neglecting the compressibility effects of bubble migration results in overestimating the maximum radius and period during the second oscillating cycle. Disregarding the effects results in a higher peak migration kinetic energy during the second cycle but lower most of the time, which is related to the temperature, gas mass, and pressure inside the bubble. Furthermore, the discussion reveals that this migration-related compressibility can be enhanced by increasing the Mach number or vapor percentage.

Non-spherical bubble collapses near solid boundaries, generating water hammer pressures and shock waves, were recognized as key mechanisms for cavitation erosion. However, there is no agreement on local erosion patterns, and cavitation erosion damage lacks quantitative analysis. In our experiments, five distinct local erosion patterns were identified on aluminium sample surfaces, resulting from the collapse of laser-induced cavitation bubbles at moderate stand-off distances of $0.4\leqslant \gamma \leqslant 2.2$ , namely bipolar, monopolar, annular, solar-halo and central. Among them, the bipolar and monopolar patterns exhibit the most severe cavitation erosion when the toroidal bubbles undergo asymmetrical collapse along the circumferential direction during the second cycle. Shadowgraphy visualization revealed that asymmetrical collapse caused shockwave focusing through head-on collision and oblique superposition of wavefronts. This led to the variations in toroidal bubble radii and the positions of maximum erosion depth not matching at certain stand-off distances. Both initial plasma asymmetry and bubble–wall stand-off distance were critical in determining circumferential asymmetrical collapse behaviours. At large initial aspect ratios, the elliptical jet tips form during the contraction process, resulting in the toroidal bubble collapsing from regions with smaller curvature radii, ultimately converging to the colliding point along the circumferential direction. Our three-dimensional simulations using OpenFOAM successfully reproduce the key features of circumferentially asymmetrical bubble collapse. This study provides new insights into the non-spherical near-wall bubble collapse dynamics and provides a foundation for developing predictive models for cavitation erosion.