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Bubble pulsation is a characteristic multiphase compressible flow, which involves periodic oscillation and strong pressure wave and is vulnerable to boundary conditions. The smoothed particle hydrodynamics (SPH) has limitations in imposing the fluid boundary suitable for such problems, which have been verified first with the state-of-the-art SPH boundaries. It brings challenges to the three-dimensional modeling. Then, we propose to combine SPH with the finite volume method via the spatial coupling to deal with this problem. The accuracy of the coupled method has been validated by comparisons with other numerical methods and the theoretical equation from the spherical pulsation to the more complex bubble oscillations. Good agreements are obtained in terms of the bubble radius and the pulse pressure peak. The conclusions drawn in this work and the computational framework lay the foundation for the further complicated study on the bubble dynamics, the complete process of underwater explosion, and the related fluid–structure interaction problems. [ABSTRACT FROM AUTHOR]

Particle propulsion by an attached acoustic cavitation bubble under strong ultrasonic wave excitation occupies the core of many applications, including ultrasonic cleaning, ultrasonography, targeted therapy, and microbubble motors. However, the driving capacity and mode of bubbles in the field of ultrasonics are far from being well understood, which severely limits its applicability in a variety of fields. In this study, a fluid–structure interaction model based on the boundary integral method is proposed to simulate complex interactions between a suspended spherical particle and an attached cavitation bubble. A one-to-one comparison between the numerical results and experimental data demonstrates the distinct advantage of our model over conventional approaches. Thereafter, we systematically investigate the dependence of bubble–particle interactions on the governing parameters, including the amplitude and phase of the ultrasonic wave, particle density, and particle-to-bubble size ratio. We also document different types of bubble dynamic behaviors under various governing parameters. Finally, we obtain scaling laws for the maximum displacement of the particle with respect to the governing parameters. [ABSTRACT FROM AUTHOR]

High-speed water entry is a transient hydrodynamic process that is accompanied by strongly compressible flow, free surface splash, cavity evolution and other nonlinear hydrodynamic phenomena. To address these problems, a novel fluid–structure interaction (FSI) scheme based on the immersed boundary method is proposed which is suitable for strongly compressible multiphase flows. In this scheme, considering the multiphase interfaces at the immersed boundary, an improved immersed boundary method for effectively suppressing the non-physical force oscillation is proposed. Additionally, a quaternion-based six degrees of freedom motion system is used to describe rigid body motion, and the multiphase flow Eulerian finite element method is applied as the fluid solver. Using analytical solutions, experimental data and literature data, the accuracy and robustness of the FSI scheme are validated. Finally, the high-speed water entry of the slender body with different noses is investigated, and the hydrodynamic loads including the axial and normal drag forces and the bending moment are extensively discussed. The hydrodynamic load and motion trajectory are determined by the nose configuration. The tail slamming phenomenon is the primary focus, and it is revealed that its formation is primarily related to the pitch moment formed at the stage of crossing the free surface. Tail slamming also causes violent impact loads, especially bending moments, which may cause slender projectiles to break off. Finally, to combine the features of the flat and hemispherical noses, the water entry of the projectile with a truncated hemispherical nose is simulated and discussed. [ABSTRACT FROM AUTHOR]

In this work, we established a novel theory for the dynamics of oscillating bubbles such as cavitation bubbles, underwater explosion bubbles, and air bubbles. For the first time, we proposed bubble dynamics equations that can simultaneously take into consideration the effects of boundaries, bubble interaction, ambient flow field, gravity, bubble migration, fluid compressibility, viscosity, and surface tension while maintaining a unified and elegant mathematical form. The present theory unifies different classical bubble equations such as the Rayleigh–Plesset equation, the Gilmore equation, and the Keller–Miksis equation. Furthermore, we validated the theory with experimental data of bubbles with a variety in scales, sources, boundaries, and ambient conditions and showed the advantages of our theory over the classical theoretical models, followed by a discussion on the applicability of the present theory based on a comparison to simulation results with different numerical methods. Finally, as a demonstration of the potential of our theory, we modeled the complex multi-cycle bubble interaction with wide ranges of energy and phase differences and gained new physical insight into inter-bubble energy transfer and coupling of bubble-induced pressure waves. [ABSTRACT FROM AUTHOR]

This paper aims at presenting a general-purpose-oriented and fully parallelized meshless framework to simulate complex Fluid–Structure Interaction (FSI) problems in ocean engineering. In this framework, a Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) solver is combined with several advanced pre- and post-processing techniques. Based on the framework, we have been developing our in-house WCSPH-FSI package named SPHydro for solving hydrodynamic problems involving complex FSI processes in an accurate, efficient, and convenient manner. Three benchmarks are performed to qualitatively and quantitatively validate the accuracy and convergence of SPHydro. In addition, several practical applications are also provided to further highlight the generality and applicability of SPHydro in ocean engineering simulations. It is demonstrated that SPHydro holds satisfactory performance in solving complex FSI problems in ocean engineering and that the present framework can be further developed to tackle more complex FSI problems for general engineering applications due to its high flexibility and extensibility. [ABSTRACT FROM AUTHOR]

Solid object water entry is a common problem in various natural, industrial and military applications, which involves large deformation of free surfaces and violent fluid–structure interactions. In computational fluid dynamics (CFD), this is a type of problem that tests the robustness and capacity of any CFD numerical algorithm. In this work, the newly-developed updated Lagrangian particle hydrodynamics (ULPH) method, which is a fluid version of peridynamics, is enhanced and applied to simulate solid object water entry problems. ULPH method is Lagrangian meshfree particle method that can ensure the specific free surface conditions automatically satisfied. The density filter and artificial viscosity diffusion are adopted in the ULPH scheme to stabilize and smooth the pressure field. In the process of a rigid body entering water, it may induce negative pressure in some areas of impact region, which can cause spurious tensile instability in some meshfree particle simulations, such as SPH and ULPH. A tensile instability control technique based on the ULPH framework has been developed to overcome the numerical instability. To validate the stability and accuracy of the ULPH approach in simulating water entry problems, several 2D and 3D examples of water entry have been carried out in this work. The necking and cavity pinch-off phenomena are visible in the numerical results. The simulation results of the ULPH method are well compared with experimental data and other numerical solutions. The water crown, cavity shapes and stream pattern formed around the rigid body entering the water can be well captured. The computation results show that the ULPH method has the ability to simulate the complex solid object water entry precess accurately. [ABSTRACT FROM AUTHOR]

The physics of cavitation bubbles in water has been extensively studied for over a century. However, our understanding of bubble dynamics in binary immiscible fluids, such as a water-oil system, is limited. These systems have recently gained a lot of interest due to their relevance in modern medical treatment, emulsification, and the food industry. In this study, we establish an accurate and inexpensive three-dimensional boundary integral (BI) model for inertial cavitation bubble dynamics in binary immiscible fluid systems. Our novel scheme for solving velocities on the flow boundaries, expressed in a matrix form, can be easily extended to complex situations where multiple bubbles are generated in different phases. Additionally, we employ a density potential method and a weighted moving least-squares method to maintain a high level of mesh regularity. Our results demonstrate that the proposed 3D model is comparable in accuracy to a 3D axisymmetric model by comparing it against analytical solutions and the results obtained from an axisymmetric model. Furthermore, we compare our numerical simulations against a purposely conducted experiment for the bubble-droplet interaction, and excellent agreement is achieved. For the first time, we present simulation results of two-bubble interactions with an initially flat fluid-fluid interface and inside a droplet surrounded by a second fluid. We also reveal the dependences of the two-bubble morphologies, flow patterns, and jet velocities on the density ratio between the two phases. Finally, we find a significant difference in the mechanism of fluid mixing by multiple bubbles compared to that of a single bubble case. • We established a 3D model for inertial bubbles in binary immiscible fluids. • Our 3D model has shown comparable accuracy to an axisymmetric model. • We reproduce the essential physics in an experiment of bubble-droplet interaction. • We unveil novel fluid-mixing mechanisms with multiple bubbles. • We explore the dependencies of two-bubble interactions on the density ratio. [ABSTRACT FROM AUTHOR]

In this paper, we establish a fluid-structure interaction (FSI) model to investigate the dynamic interactions between the underwater explosion (UNDEX) shock wave and a movable sphere near the free surface. We utilize the local discontinuous Galerkin (LDG) method to capture the propagation of the shock wave in the fluid domain and employ the pressure cutoff model to calculate cavitation effects. The fluid elements at the fluid-structure interface are directly coupled to the structural dynamic model, and the structural transient dynamic responses are coupled with fluid acoustic pressure at the fluid-structure interface in the governing equation. The validity of the present FSI model is verified by comparing with the continuous Galerkin method. Due to the advantage of the LDG method in capturing the discontinuous wave, the present model shows better properties than the traditional coupled acoustic-structural model. With the present FSI model, we investigate the interaction between the UNDEX shock wave and a submerged and floated sphere. Under the combined effects of the free surface and structure, the UNDEX shock and cavitation loading characteristics are analyzed, and the influences of complicated cavitation effects on dynamic responses of the sphere are discussed. [ABSTRACT FROM AUTHOR]

The propagation of the shock wave across multilayer structures during underwater explosion is a very complex physical phenomenon, involving violent fluid-structure interaction (FSI) problems. In this paper, the coupled Eulerian–Lagrangian (CEL) method in AUTODYN is used to simulate the process of shock wave propagation and solve FSI problems. Firstly, the governing equation and the treatment of fluid and structure interface of the CEL method are briefly reviewed. Afterwards, two underwater explosion numerical models are established, and the results are compared with the empirical formula and experimental data, respectively, to verify the reliability of numerical solutions. The results obtained by this method show good agreements with those of the empirical formula and experiment. Furthermore, the model of the multilayer structures composed of two hemispherical shells and the fluid filled between the shells subjected to underwater explosion is established, and the pressure characteristics of the shock wave propagating across the multilayer structures are analyzed regarding the wave reflection and transmission. Finally, the effects of the shell thickness and the filled fluid type among the multilayer structures on the wave reflection and transmission are studied. [ABSTRACT FROM AUTHOR]

The present work is dedicated to the enhancement and application of the recently developed δ + -SPH scheme for two and three dimensional water entry problems. The cylinder surface presents a circular shape and therefore the position where the flow separation happens is tightly related to the implementation of the boundary condition. A special treatment for the particle shifting between fluid and solid wall is highlighted. Adaptive particle refinement (APR) is applied in this work to reduce the computational cost. It is found that, APR and the δ + -SPH scheme benefit to each other. That is to say the former reduces the computing cost of the latter while in return the latter solves the problem of particle disorder of the inactive particles of the former. Thanks to the combination of APR and δ + -SPH especially in three dimensional (3D) cases, the overall computational cost is significantly reduced while sufficiently fine particle resolution can be obtained in the flow region characterized by large pressure gradient close to the structure surface. The fairly good agreements between the SPH results and the experimental data prove the present SPH model to be a reliable tool in accurately solving the fluid–structure interacting problems in ocean engineering. [ABSTRACT FROM AUTHOR]

In numerical simulations of fluid dynamics based on the smoothed particle hydrodynamics (SPH) method, the formula for the viscosity term is always complicated since it is a second-order derivative term. In this paper, for Newtonian fluids, a novel formula for the viscous force satisfying the Stokes hypothesis is proposed in the weakly compressible framework. Because of the ease of adopting only a single layer of particles to enforce the boundary condition, the normal flux method is implemented for a solid wall boundary, which should be suitable for complex geometries and thin structures. The normal flux method can mitigate the decrease in numerical accuracy caused by the lack of neighbouring particles at the boundary. Meanwhile, the kernel function at the boundary is modified to satisfy the normalization condition. The accuracy and robustness of the proposed algorithm are verified by a series of cases of numerical fluid simulations, paving the way for SPH simulations coupled with complex thin shell structures for fluid–structure interaction problems. • A novel viscous force that satisfies Stokes hypothesis is derived. • The viscous force near the single-layer boundary is presented. • Kernel function correction technique is proposed to ensure consistence near the single-layer boundary. [ABSTRACT FROM AUTHOR]

A hydroelastic fluid–structure interaction (FSI) solver entirely based on the Riemann-SPH method is proposed. In this scheme, the Riemann-SPH method is incorporated to model elastic structures, which is performed by proposing a new treatment on Cauchy stress. The present structure solver can avoid the use of the artificial viscous force and can obtain good results. For the fluid, the conventional Riemann-SPH with a low-dissipation limiter is adopted to simulate incompressible free surface flows. The structure solver is coupled with the fluid solver by a simple coupling way considering the force balance. The developed structure solver is verified by three benchmarks, namely a free oscillating cantilever plate, stress concentration problem of a plate and wave propagation in a cable. Subsequently, through several 2D and 3D typical hydroelastic FSI tests, the accuracy and robustness of the present FSI solver are verified/validated by comparing with analytical solutions and experimental results. • The Riemann-SPH method is incorporated to be an elastic structure solver. • A unified hydroelastic FSI solver based on the Riemann-SPH method is proposed. • The present FSI solver can reproduce typical FSI problems with superior accuracy. [ABSTRACT FROM AUTHOR]

Water entry problem is common in ocean engineering, including complex fluid–structure interaction (FSI) phenomena at the interfaces. As a Lagrangian and mesh-free particle method, the smoothed particle hydrodynamics (SPH) method owns great advantages in dealing with FSI problems. However, solid boundary treatment has always been one of the main issues affecting the accuracy of the SPH method. Through combining the dummy particle boundary and the normal flux method, an improved solid boundary treatment technology is proposed in this paper. After fully validated by a series of 2D and 3D water entry cases, the boundary treatment method is applied to simulate the water entry of a lifeboat. The results indicate that the SPH model in this paper can provide a reliable numerical prediction for water entry problems with 3D complex geometries. • An improved solid boundary treatment technology is proposed. • Strict numerical validations are carried out using both 2D and 3D water entry cases. • The improved boundary treatment is applied to the water entry of a lifeboat. [ABSTRACT FROM AUTHOR]

In the present paper, the penalty immersed boundary method is improved to resolve the transient fluid–solid interaction problems. The Eulerian finite-element method is chosen as the fluid solver, and the conservation of the total energy is solved to ensure the correct results for discontinuous problems. The penalty immersed boundary method is adopted to couple the fluid and the submerged solid body, which is improved by considering both the normal and tangential relative velocities of the solid surface with an upwind scheme when updating the penetrated depth. With the present model, the simulated results of a 1-dimensional moving piston problem in the ideal gas are compared with the exact solution and the results from the Abaqus to validate the capability of the present method in dealing with shocks. Then, several 3-dimensional problems are simulated and analyzed, including a bubble–sphere interaction problem, and three high-speed water entry problems. The results are compared with experiments and show good agreements. • The penalty immersed boundary method is improved to resolve the fluid–solid interaction problems. • The Eulerian finite-element method is modified to ensure the conservation of the total energy. • The present method perform well in several test cases of fluid–structure interaction. [ABSTRACT FROM AUTHOR]

A 2D fluid–structure interaction (FSI) solver based on Smoothed Particle Hydrodynamics (SPH) and RKPM is established in this paper. Since we focus on the incompressible flow problem, the WCSPH is adopted to simulate the fluid. Meanwhile, the structure is modeled by the RKPM beam formulation, in which the plane strain hypothesis is adopted, and only a column of particles is needed to discretize the beam. Since the support domain of the fluid particle near the FS interface is truanted, the so-called normal-flux method is adopted to consider surface integration terms. Moreover, we propose a new excess pressure for the incompressible fluid flow based on Bernoulli's principle, which is more accurate for the simulation of incompressible FSI problems. Besides, the particle shifting scheme near the fluid–structure interface is modified. Finally, the accuracy and stability of the present FSI solver are verified by several numerical examples. [ABSTRACT FROM AUTHOR]

In the present work, numerical simulation of structural damage subjected to the near-field underwater explosion is carried out by coupling the SPH and RKPM. The fluid solver is established based on the compressible SPH method, while the dynamic response of the structure is calculated based on the RKPM shell formulation. Since large deformation with contact will occur in the underwater explosion problem, a contact detection algorithm for the RKPM shell formulation is proposed. The contact force is calculated based on the volume strain. The fluid-structure interaction solver is established by adopting the normal-flux method, in which the structure is treated as a moving solid boundary for the fluid domain, while the fluid pressure is considered as the load act on the structure surface. Thus, the numerical model for the simulation of structural damage analysis in the underwater explosion is obtained, which is a part of the FSLAB software developed by the FSI laboratory of Harbin Engineering University. Finally, several numerical examples are studied to verify the robustness and accuracy of the present numerical model. • Propose a 3D FSI solver by coupling the SPH and RKPM. • A contact detection algorithm for the RKPM shell formulation is developed. • Fracture of the ship structure subjected to underwater explosion is simulated. • The accuracy and robustness of the FSI solver are verified. [ABSTRACT FROM AUTHOR]

In this paper, by combining the boundary element method (BEM) and peridynamics (PD), a bubble-ice interaction model is established, which can investigate the dynamic interactions between a high-pressure bubble and an ice plate with particular focus on the mechanical behaviors of ice breaking. The bubble dynamics are solved by BEM based on the potential flow theory. Ice cracks initiation and propagation are simulated by the bond-based peridynamics which is validated by a three-point bending test. The fluid–structure interaction (FSI) is achieved by matching the normal velocity and hydrodynamic loads at the fluid–structure interface. To validate the proposed FSI model, an experiment is carried out in which an oscillating bubble is generated under an ice plate by underwater discharge system. The whole interaction process is captured by a Phantom V711 high-speed camera. Qualitative agreements are achieved between the numerical and experimental results. The underlying mechanism of cracks initiation, propagation, branching, and coalescence of the ice plate is found to highly depend on three parameters, i.e., bubble–ice distance, ice thickness and bubble size. The present study is expected to provide further assists in the understanding of ice breaking problems. [ABSTRACT FROM AUTHOR]

A combined RKDG-FEM approach, using the Runge-Kutta discontinuous Galerkin (RKDG) method [1,2] for fluid simulating and the finite element method (FEM) [3,4] for structure simulating, is developed to study the complex interactions between compressible multiphase flows and deformable steel and composite structures in near-field early-time underwater explosion (UNDEX). The level set method (LSM) [5,6] and the real ghost fluid method (RGFM) [7,8] are applied to capture and treat the moving gas-water interface, respectively. A GFM-based interface treating scheme [9,10] is adopted to treat the fluid-structure interface, achieving the coupling by solving simultaneously the fluid characteristic equation and the structure equation of motion at the material interface to satisfy the kinematic compatibility and pressure equilibrium conditions. The isentropic one-fluid cavitation model in [11] is employed to capture the transient flow cavitation. Accuracy and effectiveness of the combined RKDG-FEM approach are validated by five benchmark cases, and then it is applied to simulate early-time UNDEX problems near a submerged aluminum foam-cored sandwich plate and a monolithic steel plate of equivalent mass. Numerical results show that the sandwich plate has a higher underwater explosion load resistance through absorbing plastic energy by the foam core than the monolithic steel plate of equivalent mass, and that the foam core plays an important role in the fluid-structure interaction (FSI) and flow cavitation effects, which can be exploited to improve the UNDEX mitigation capability of composite sandwich structures. • A combined RKDG-FEM approach is developed for simulating UNDEX problems. • UNDEX involving shock-bubble-structure interactions and flow cavitation is simulated. • Comparison study of UNDEX near steel and composite sandwich structures is conducted. [ABSTRACT FROM AUTHOR]

Abstract The bubble-sphere interaction beneath a free surface is investigated experimentally and numerically, which is associated with underwater explosion and cavitation. We use the electric discharge technique to generate an oscillating bubble that is set above a movable sphere and below a free surface. The transient fluid-structure interaction (FSI) is recorded by high-speed imaging. We identify three distinctive bubble jet impact patterns, i.e., (i) jet impacts on the sphere top with water layer between them; (ii) the bubble partly envelops the sphere at first and then the jet impacts on the sphere top without water layer; (iii) the jet impacts on an annular ring, splitting the bubble into a toroidal bubble and a new singly-connected bubble. Such transient FSI events are modeled by the boundary integral method and the foregoing bubble splitting is modeled by an improved vortex ring model. The bubble, free surface, and sphere dynamics in experiments are found to be captured extremely well by numerical simulations. The bubble dynamic behaviors are associated with three dimensionless parameters and a systematic study of these parameters are provided. Lastly, the two types of cavitation phenomena on sphere surface are discussed and the detailed physical mechanisms are analyzed. Highlights • The bubble-sphere interaction beneath a free surface is investigated experimentally and numerically. • We identify three distinctive bubble jet impact patterns, which are classified in a graph according to two parameters. • A full coupling model based on boundary integral method reproduces the experimental observations well. • An improved vortex ring model is established to study the splitting of a bubble into a torus and a singly-connected bubble. • Two types of cavitation phenomena on sphere surface during the rebounding phase of the bubble. [ABSTRACT FROM AUTHOR]

Dynamic buckling prediction of submerged structures under impact loads is a challenging problem for both theoretical and numerical approaches, and the experimental data is very limited. In the present paper, dynamic buckling of grid-stiffened cylindrical shells submerged in a large opening pond at a depth of 5 m and subjected to radial intermediate-velocity impact was experimentally investigated. In order to increase load durations under the condition of fixed peak pressure, explosive depth and standoff distance, airbags composed of O 2 and C 2 H 2 were used and exploded underwater to generate impact load. Amplitudes and durations of shock waves and pulsating bubbles were characterized by using pressure transducers. Measurements of hoop and axial strains reveal that global buckling of skin and stiffeners of the grid-stiffened cylindrical shell occurred under bubble pulsation loads, which features mutation and separation of strains and a sudden change in the vibration period of the stiffened shell with a small increment of impulse. 6 half waves and 1 half wave are observed along the circumferential and axial directions of the shell, respectively. Larger bubble pulse impulse, greater deformation and vibration of the shell under larger impact are the main reasons for global dynamic buckling of the grid-stiffened cylindrical shell. [ABSTRACT FROM AUTHOR]

This paper established a novel Riemann SPH–RKPM fluid–structure interaction numerical model, which is more stable and has lower dissipation than the traditional method. Firstly, an improved dissipation limiter is proposed and applied to Riemann SPH to simulate fluid motion, effectively reducing dissipation while ensuring computational stability. Secondly, an improved method to treat the fluid–structure interaction (FSI) force is proposed, which introduces the Riemann solver into the normal flux method to solve the FSI force. This improvement ensures the smoothness of the flow field pressure at the fluid–structure interface and then improves the stability of the violent impact fluid–structure interaction problem. This paper used the RKPM to solve the large deformation of the structure. Several benchmark tests and one improved example are used to verify the convergence and accuracy of the numerical model. The results calculated in this paper agree with experiment and other numerical methods, proving that the Riemann SPH–RKPM fluid–structure interaction numerical model is effective and has high accuracy. • This paper proposed an improved dissipation limiter for Riemann SPH. • This paper introduced the Riemann solver into the normal flux method to solve the fluid–structure interaction force. • This paper established a completely meshless Riemann fluid–structure interaction numerical model based on the SPH–RKPM model. [ABSTRACT FROM AUTHOR]

This work presents a multi-resolution fluid–structure interaction (FSI) solver for hydroelastic issues by coupling the Weakly Compressive Smoothed Particle Hydrodynamics (WCSPH) method and the Finite Element Method (FEM). The fluid is simulated by the SPH method, and the structure response is considered by the FEM beam. The normal flux method is employed to calculate the coupled force between the fluid and structure by considering the surface integration term in SPH approximation equations. A multi-resolution technology is proposed by discretizing the fluid and structure with different resolutions. The resolution of beam elements can be either coarser or finer than that of SPH particles. Finally, the accuracy, robustness and efficiency of the current FSI solver are strictly validated by several typical benchmarks, including the hydrostatic, free-surface flow and water entry problems. • We developed a coupled SPH-FEM method for fluid–structure interactions. • Different spatial–temporal resolution is employed for fluid and solid structure. • The accuracy, efficiency, and robustness of the FSI solver are strictly validated. [ABSTRACT FROM AUTHOR]

Lifeboats can be launched through free-fall in extreme maritime accidents to fast leave the hazardous area, which deserves particular attention because it is tightly related to the safety of lifeboats and the carried passengers as well. This paper, within the framework of a fully 3D and multi-resolution Smoothed Particle Hydrodynamics (SPH) model, aims at investigating the water entry dynamics of a free-fall lifeboat with different water entry angles. First of all, two rigorous model validations are performed to demonstrate the accuracy, stability and convergence of the present SPH model. Furthermore, the water entry dynamics of the lifeboat with respect to different water entry angles, including the motion characteristics and cavity evolutions, is investigated and discussed in detail based on the SPH results. It is clearly demonstrated that the present SPH model possesses (1) satisfactory accuracy for predicting the water entry dynamics of a lifeboat, and (2) a better ability to capture the splashing jets and scattering droplets than mesh-based solvers thanks to its entirely Lagrangian nature. In addition, it is also demonstrated that the water entry angle exerts significant effects on the water entry dynamics of a lifeboat, which should be taken into account in the design stage to provide safer productions. • A multi-resolution and fully 3D SPH model for water entry problems is presented. • A simple procedure to generate uniform particles is applied for complex geometries. • The present SPH model is shown to be superior in simulating water entry problems. • The water entry angle exerts significant effects on lifeboat's water entry dynamics. [ABSTRACT FROM AUTHOR]

This paper is dedicated to (1) emphasizing the importance of removing the Tensile Instability (TI) induced by negative pressures in Smoothed Particle Hydrodynamics (SPH) simulations, and (2) proposing new modifications for the Tensile Instability Control (TIC) and Particle Shifting Technique (PST) to simulate Fluid–Structure Interaction (FSI) phenomena with violent free-surface evolutions. Four numerical benchmarks associated with classical FSI problems characterized by negative pressures are simulated to show how the tensile instability destroys an SPH simulation without any TI prevention strategies. Therefore, PST and TIC are adopted into the SPH simulations for the sake of suppressing the tensile instability. However, different combinations of TI prevention strategies, i.e. different combinations of PST and TIC, lead to different results, and hence detailed investigations and discussions are provided. It is demonstrated that when negative pressures are moderate, solely using either PST or TIC works well. Nonetheless, it is in favor of using both PST and TIC if an SPH simulation is characterized by extremely strong negative pressures. Furthermore, for the problems with a convex-shaped structure penetrating a free-surface, special modifications are necessary for both PST and TIC in order to obtain accurate SPH results. • Importance of removing the tensile instability in WCSPH simulations is stressed. • New modifications for PST and TIC at boundaries are presented for FSI problems. • Solely using PST could fail to suppress the tensile instability. • Solely using TIC is hard to achieve homogenous particle distribution. • PST, TIC and their modifications at boundaries should be used simultaneously. [ABSTRACT FROM AUTHOR]

In the present study, the nonlinear bubble–plate interaction is investigated via boundary integral (BI) simulations with a particular focus on the effect of fluid–structure interaction (FSI). A series of experiments of electric discharge cavitation bubbles are also conducted to gain more physical insights. Good agreement between BI simulations and high-speed recordings is obtained. The effects of two geometrical parameters including the normalized stand-off distance γ and the plate-bubble size ratio θ (both scaled by the maximum bubble radius) are investigated systematically. We find four types of distinct bubble collapse patterns, namely, contacting jet that impacts the plate directly, non-contacting jet that impacts a layer of liquid, collision of two axial jets and no evident jet. A detailed phase diagram for the bubble collapse pattern is given in a large parameter space. Through the comparison of bubble dynamics near a movable and a fixed plate, the FSI effect is found to induce a significant increase in the jet impact velocity and the corresponding impact pressure. We also give a criterion condition for neglecting the FSI effect. Finally, we find two scaling laws for the plate motion with respect to γ , which can be explained using a semi-analytical model. • The transient fluid–structure interaction between a pulsating bubble and a movable plate is investigated. • Four types of distinct bubble collapse patterns are identified in a large parameter space. • The effect of FSI on the jet impact velocity and the structural pressure load is unveiled. • A criterion condition for neglecting FSI effect is given. • We find two scaling laws for the plate motion. [ABSTRACT FROM AUTHOR]

The recently developed FSI-SPH model (Sun et al., 2019c), by combining the multi-resolution δ + -SPH scheme and a Total Lagrangian SPH method, is further extended for more complex three-dimensional (3D) Fluid Structure Interaction (FSI) problems. The FSI-SPH model is strengthened with advanced numerical techniques, in which a combination of the Particle Shifting Technique (PST) and the Tensile Instability Control (TIC) is adopted to prevent flow voids induced by the tensile instability. The Adaptive Particle Refinement (APR) is used to refine particles in the boundary layer region and coarsen particles in the far-field to increase local accuracy but reduce overall computational cost. Moreover, the δ + -SPH and Total Lagrangian SPH solvers are coupled through a Modified Sequential Staggered (MSS) algorithm which, on one hand, ensures the numerical accuracy and stability and, on the other hand, improves the efficiency when magnitudes of time steps between the two solvers differ from each other significantly. In the numerical results, challenging 2D and 3D FSI cases are simulated to test the accuracy of the proposed FSI-SPH model. A new FSI benchmark with free-surface is proposed to highlight the advantage of this FSI-SPH model in simulating free-surface viscous flows. In addition, 3D effects in the FSI dam-breaking and sloshing cases are investigated. • Multi-resolution δ+-SPH model is accurately and efficiently coupled with the Total Lagrangian SPH model. • Complex three-dimensional (3D) Fluid Structure Interaction (FSI) problems are simulated and validated. • A new benchmark named FSI4 is proposed. • The 3D effects in the FSI dam-breaking and sloshing cases are highlighted. [ABSTRACT FROM AUTHOR]