Underwater Shock Research Articles

Directional enhancement of underwater impact and bubble loads in neighbor two-phase fluid domains charge

The loading characteristics of underwater explosions and the dynamic behavior of bubbles are directly related to the charge structure. This study proposes a unique charge structure in a gas–liquid two-phase fluid domain. Numerical methods are used to investigate the effects of fluid layer thickness and gas–liquid ratio on underwater explosion shock wave load, bubble dynamics, and bubble pulsation load. The results show that the two-phase fluid layer significantly enhances the directional release of shock wave energy and bubble pulsation load. During the shock wave phase, a lagging wave effect appears in the liquid layer direction, causing a secondary high-energy shock, significantly increasing the specific impulse. The gas layer direction may form a pressure relief channel effect, enhancing the shock wave peak pressure. For the bubble motion phase, differences in the physical properties of the fluid layer medium lead to irregular bubble boundary movements, promoting bubble tearing and rupture. The gaseous medium converts the accumulated shock wave energy into the internal energy of the bubble, increasing its volume potential. Although this characteristic reduces the pulsation frequency, it significantly increases the specific impulse. Altering the fluid layer medium can control explosion loads and bubble movement, offering new insights for ocean engineering applications.

Influence on micro-geometry and surface characteristics of laser powder bed fusion built 17-4 PH miniature spur gears in laser shock peening

Micro-geometrical errors, surface roughness, and surface integrity (microstructure, residual stresses, microhardness) play an important role in defining the quality of the gears as they directly affect their noise, vibration characteristics and service life during their use. In the present work, underwater laser shock peening (LSP) is employed to improve the quality of the laser powder bed fusion built 17-4 PH small-size spur gears (12 mm outside diameter). LSP was employed near the spur gear root, and effects were measured in terms of residual stresses, variation in microgeometry errors, surface roughness, porosity, microstructure, and microhardness. It was observed that LSP could impart compressive residual stresses up to 0.4 mm of measured depth, while the surface roughness has improved by 32%. Microgeometry and microhardness of gears showed minor variations. Additionally, LSP has shown an impact on the microstructure as the grain orientation was altered and grain size reduced by 15.6% due to shock wave transmission. The study paves the way to use LSP as a post-processing technique to modify the surface characteristics of LPBF-built miniature spur gears with minimal impact on the gear microgeometry.

Research on the response of underwater explosion liquid tank structure based on RKPM method

Abstract This work establishes a three-dimensional fluid-structure coupling calculation model for the response of SPH-RKPM underwater explosion structures and verifies its effectiveness. Using the established numerical model, the dynamic response of the water-containing liquid tank structure under underwater explosion shock wave load was modeled and calculated, and the response characteristics of the water-containing liquid tank under different detonation distances were discussed. The response law of the water-containing liquid tank structure under shock wave load is summarized.

Shock wave generated by composite energetic material driven by electrical non-penetrating wire explosion plasma.

Underwater shock wave technology can realize dynamic rock fracture, which is helpful to increase oil and gas reservoir permeability. It can realize the efficient exploitation of medium and low maturity oil and gas resources. In practical application, the shock wave parameters require not only high intensity but also safety and controllability. To meet these requirements, insensitive composite energetic materials driven by electrical wire explosion plasma were proposed, which is one of the most promising methods. However, when in use, the load assembly process containing wires and energetic materials is complex. In this paper, a new type of energetic material load is proposed, using non-penetrating wire to drive composite energetic material. It can simplify the production process of the energetic load and produce acceptable shock wave parameters. The test results show that both the energy deposition of the wire and the shock wave intensity decrease under a non-penetrating wire structure. However, the shock wave intensity is still higher than that of the underwater electrical wire explosion. Based on schlieren diagnosis, it is found that the composite energetic material is gradually driven, and the energy release is not concentrated. In addition, the "non-wire" structure driving condition was discussed in contrast. Under this condition, the process of ionization channel establishment in composite energetic materials is random. The shock wave intensity is weak because the composite energetic material is in the process of slow detonation.

A novel design of compact elastomer shock absorption system to protect sensitive objects from underwater shock for naval application

This research paper proposes a unique way to safeguard delicate systems on submerged platforms from the undesirable effects of underwater explosion shock loads. The underwater detonation of an explosive charge and mines produce devastating underwater shocks against underwater platforms. Shock load developed underwater has been analyzed, and a shock response spectrum (SRS) approach to compute shock peak responses has been adopted. SRS shock absorption frequency satisfies requirements for both shock absorption and delicate systems. The shock load was reduced to 2g by altering the delicate system stiffness and damping properties. The analytical model for a single DOF system was formulated, and simulation was carried out using ANSYS solver. The stiffness has been spread across various points along the length of the delicate system, allowing it to undergo translational oscillations when subjected to shock loads. This research paper presents an innovative design approach for a shock absorption system intended for underwater sensitive objects, emphasizing simplicity, distinctiveness, compactness, reliability, and electromagnetic compatibility. Experimental testing validated the shock absorption design on the prototype. Shock testing determined the absorber’s maximum displacement and sensitive object acceleration.

Underwater surface discharge characteristics and multi-physical effects with conductive coating load under fast electric pulse

Abstract Underwater pulsed discharges, where intense reactions between ionized gas and condensed-state water exist, can be a joint problem of both physics and chemistry. The study tries to build a comprehensive visualization of nanosecond-risetime discharge initiated by a conductive coating and its successive multi-physical effects. The scenario is established via a pair of thin-plate electrodes positioned on both sides of the coating, and diagnosed using high-speed backlight photography synchronized with electrical and optical measurements. For the sprayed Cu/Ag composite coating, the current density can achieve 20 A/mm2 which is high enough to induce the surface “electrical explosion” and breakup the conductive matrix within 500 ns. By increasing the discharge energy from 0.5 to 10 J, the explosion of coating can exhibit different discharge types as exploding wires. Adopting a thicker carbon foil or cermet sheet can reduce the current density and energy deposition rate, which converts the global explosion to partial ones, significantly increasing the lifetime. With the aid of the conductive coating, the breakdown delay diminishes, and hot plasma spots form in 100 ns due to non-uniform Joule heating of the pulsed current, which gradually evolve to a plasma bubble cluster above the lower-conductive coating (bypassing branch). Once the high-conductive plasma channel bridges two electrodes, it will be intensively heated (MW-level energy deposition rate) and rapidly expand, accompanied by underwater shock wave (102 kPa @30 cm) and bubble/cavity generation (20 mm maximum). Finally, microscopic characterization has been made, and the erosion morphology suggests typical arc erosion features (pits, cracks, etc.) and nanoparticles condensation from evaporated materials.

Shock Response of Water-Protected Spherical Explosion Containment Vessels

Abstract Explosion containment vessels (ECVs) are important equipment used for underwater explosion experiment research. In this paper, a method is proposed to improve the blast resistance of the ECV by placing it in the water medium. The shock response caused by the underwater explosion in a spherical ECV is studied. The single-layer thin-walled spherical vessel shell submerged in an infinite domain water medium is deduced and simplified as a single-degree-of-freedom elastic vibration system with viscous damping. The underwater explosion shock wave is simplified to an exponential shock loading, and the analytical solutions of the radial shock vibration of the spherical shell are obtained using Duhamel's integrals. Compared with the numerical simulation results, the accuracy of the theoretical model is verified. The study results show that the water medium radiates out vibration energy and plays an important role in eliminating vibration through damping. It is found that the vibration damping ratio can be controlled by adjusting the vessel radius and thickness, so that the vibration of the shell can be controlled within three periods and the impact fatigue can be reduced. In addition, the radiation damping of the water medium greatly reduces the maximum radial displacement of the spherical shell, which significantly improves the blast resistance of the spherical shell.

Removal of micro-nano particles based on water-assisted enhanced plasma shock wave

Foreign micro/nanoparticles can compromise the production and performance of semiconductors, high-energy laser systems, and other technologies. Owing to the strong adhesion (in GPa) of these particles to the surfaces of these devices, removing them using traditional methods such as ultrasound is difficult. Laser plasmas at high temperatures and pressures can effectively clean the micro/nanoparticles. Compared with traditional air media, laser plasma generates stronger shock waves and water flow erosion underwater, which can effectively clean these particles. In this study, we analysed the particle removal process under the action of laser plasma in water dielectrics, primarily the distribution characteristics of particles under spatial phase transition, final removal efficiency, removal thresholds, and optimal removal regions of particles with different sizes, as well as the corresponding academic analysis based on thermodynamic effects. We used a silicon wafer that was subjected to a high-energy laser beam to generate plasma shock waves underwater, which were used to remove micro- and nano-sized impurities. We found that the shock wave pressure of the plasma and water flow gradually decreased from the centre to the outside, and the corresponding action region could be divided into three areas, namely, 0–30°, 30–45°, and 45–50°, with particle removal rates of 96.93 %, 75.52 %, and 36.60 %, respectively. For particles in the 0–30° and 30–45° regions, the maximum removal rate corresponded to particle sizes ranging from 50–200 nm and greater than 200 nm, respectively. However, in the 45–60° region, the pressure of the shock wave was lower than the fragmentation threshold and, hence, had the worst particle removal effect owing to the lowest pressure. We believe that these findings will provide guidance for the subsequent development of particle removal technologies using underwater laser plasma shock waves.

Theoretical model and parameter sensitivity analysis of concrete slab vibration in concrete-face rockfill dams during underwater nuclear explosions

Large reservoir dams, which are carriers of energy and resources, have historically been the main targets of military conflict and terrorist attacks. A concrete-face rockfill dam (CFRD) is a competitive hydraulic structure widely used in large-scale water conservancy projects. However, the vibration response and damping paths of CFRDs under the influence of underwater explosion shock waves remains insufficiently understood. In this study, we created a theoretical model of slab vibration with four-sided free boundaries using Cole’s formula and the motion differential equation of a slab on an elastic foundation. Furthermore, a global sensitivity analysis of the vibration model parameters on the slab displacement was performed based on the Kriging surrogate model and Sobol method. The results showed that the antiseepage slabs experienced a void phenomenon, resulting in overall instability. The explosive distance and normal stiffness of the slab had the greatest influence on the void displacement of the slab, whereas the dam height and concrete density had insignificant effect. Moreover, increasing the dam height of the CFRD did not increase the risk of slab voids during underwater explosions, which was not the case under strong seismic loads. Therefore, the key factors for active and passive defense against blast resistance in CFRDs were identified, which can provide theoretical support for the blast-resistant design and research on CFRDs. In this study, the reliability of the theoretical model was verified by establishing a numerical analysis model.

Damage effect of underwater explosion bubble on concrete gravity dam

The underwater explosion bubble accounts for half of the total explosive energy and has been found to induce serious structural damage to ship structures. However, the existing research has commonly ignored the damage effect of an underwater explosion bubble on a concrete gravity dam. The current study aims to narrow this gap through high-fidelity numerical simulations and scale model tests. A fully-coupled numerical model is established first and is validated by small-scale centrifugal model tests. The bubble dynamics of underwater explosions near the perpendicular dam structure have been explored. The main focus is then on the sequential damage effects of the underwater explosion shock wave, bubble pulse, bubble jet, and bubble collapse on a concrete gravity dam. It is found that the shock wave causes a first attack, inducing tensile cracks in the vulnerable part of the dam. Subsequently, the bubble pulse generates a secondary attack, facilitating the penetration of the tensile crack throughout the entire dam structure. Additionally, the bubble jet driving the high-speed fluid flow and the bubble collapse causing the uplifted free water surface, united with the upstream reservoir water with huge hydrostatic pressure, largely accelerate the fracture of the dam, then facilitate the fractured dam to fall downstream leaving a breach with certain widths in the dam’s upper part, and finally speed up the discharge of the upstream reservoir water through the breach. It also finds that the underwater explosion bubble can generate no new cracks in the gravity dam, even in the pre-damaged area as long as there are no obvious pre-cracks by the shock wave. That is, the shock wave is the key trigger for dam failure, without which the dam failure will not happen, while the bubble, united with the upstream reservoir water, accelerates the process of dam failure.

The dynamic response of human lungs due to underwater shock wave exposure.

Since the 19th century, underwater explosions have posed a significant threat to service members. While there have been attempts to establish injury criteria for the most vulnerable organs, namely the lungs, existing criteria are highly variable due to insufficient human data and the corresponding inability to understand the underlying injury mechanisms. This study presents an experimental characterization of isolated human lung dynamics during simulated exposure to underwater shock waves. We found that the large acoustic impedance at the surface of the lung severely attenuated transmission of the shock wave into the lungs. However, the shock wave initiated large bulk pressure-volume cycles that are distinct from the response of the solid organs under similar loading. These pressure-volume cycles are due to compression of the contained gas, which we modeled with the Rayleigh-Plesset equation. The extent of these lung dynamics was dependent on physical confinement, which in real underwater blast conditions is influenced by factors such as rib cage properties and donned equipment. Findings demonstrate a potential causal mechanism for implosion injuries, which has significant implications for the understanding of primary blast lung injury due to underwater blast exposures.

The shock wave evolution of the laser-induced breakdown under non-spherical symmetry using a 1064 nm nanosecond laser

In acoustics-related interdisciplinary areas, the shock wave of laser-induced breakdown has garnered significant attention. However, research on the propagation of shock waves in non-spherical symmetry is insufficient in both theoretical and experimental aspects. This paper aims to thoroughly study the evolution of underwater shock wave directivity by employing the method of shadowgraph. The shock wave front is determined by the dark fringes in the shadowgraph image and the normal propagation speed of the shock wave is calculated using Huygens principle. Subsequently, normal propagation speed is converted to pressure in different directions by employing the equation of state of the medium. It has been found that the spherical plasma produces an isotropic shock wave, whereas filamentary plasma generates a highly anisotropic one. To evaluate the anisotropic property of the shock wave, we introduce pressure directivity, which is defined as the pressure at any direction normalized by the maximum value. The temporal evolution of shock wave pressure directivity is obtained based on the shadowgraph images. In the case of filamentary plasma, there is a sudden transition of the pressure directivity in the axial from 40 ns to 165 ns, after which the pressure directivity is consistent with the hydrophone measurement. Based on the moving breakdown model of the plasma and the superposition principle, we propose a theoretical model to explain the experimental result of the pressure directivity. The outcome of our model exhibits considerable consistency with the experiment.

Underwater Shock Wave-Enhanced Cavitation to Induce Morphological Changes and Cell Permeabilization in Microscopic Fungi

Since the discovery of extracorporeal lithotripsy, there has been an increased interest in studying shock wave-induced cavitation, both to improve this technique and to explore novel biotechnological applications. As shock waves propagate through fluids, pre-existing microbubbles undergo expansion and collapse, emitting high-speed microjets. These microjets play a crucial role in the pulverization of urinary stones during lithotripsy and have been utilized in the delivery of drugs and genetic materials into cells. Their intensity can be amplified using tandem shock waves, generated so that the second wave reaches the bubbles, expanded by the first wave, during their collapse. Nevertheless, there is little information regarding the control of microjet emissions. This study aimed to demonstrate that specific effects can be obtained by tuning the delay between the first and second shock waves. Suspensions containing Aspergillus niger, a microscopic fungus that produces metabolites with high commercial value, were exposed to single-pulse and tandem shock waves. Morphological changes were analyzed by scanning and transmission electron microscopy. Proteins released into the medium after shock wave exposure were also studied. Our findings suggest that, with enhanced control over cavitation, the detachment of proteins using conventional methods could be significantly optimized in future studies.

Numerical study of underwater explosion shock loading near a rigid dam

Numerical study of underwater explosion shock loading near a rigid dam

Cylindrical single-wall and double-wall structures with or without internal water subjected to underwater shock loading

A series of experimental studies were conducted for cylindrical structures subjected to underwater shock loading to understand their dynamic responses and failure characteristics. All tests were performed inside an anechoic water tank. The submerged test cylinders were freely suspended, and an underwater shock loading was generated by the Compressed Air Shock Pipe Underwater Release (CASPUR) system. Cylinders were made of two different materials. The first group of cylinders was fabricated from carbon fiber and resin using the filament winding technique. The winding angles were ± 45° resulting in the same properties along axial and hoop directions. The second group of cylinders was constructed using a 3-D printer with polylactic acid (PLA) material. The 3-D printed cylinders had an orthotropic material property with different values in the axial and hoop directions. Both single-wall and double-wall cylindrical structures were tested. The latter consisted of two concentric cylinders of different diameters with uniform spacing between them. In addition, within the single-wall cylinders and the annuli of double-wall cylinders, the water fill was varied at 0%, 50%, or 100%. Pressure and strain gages were used to measure the shock pressure and deformation of the cylinders. The number of cylinders such as single-wall or double-wall and the internal water resulted in significant effects on the measured dynamic response (i.e., strain gage response) as well as the failure loading and failure characteristics including major failure locations. Internal water reduced the strain on the cylinders and made them withstand greater shock loading for both single-wall and double-wall cylinders.

Damage Characteristics and Dynamic Response of RC Shells Subjected to Underwater Shock Wave

Underwater bottom-sitting shell structures face threats from underwater explosion shock waves. To investigate the damage characteristics and dynamic response of bottom-sitting shell structures under underwater explosion shock waves, three-dimensional numerical models of semi-spherical and semi-cylindrical bottom-sitting reinforced concrete (RC) shells under underwater shock waves were established based on the Arbitrary Lagrangian–Eulerian (ALE) algorithm using LS-DYNA software. The influences of the shock wave transmission medium, explosive equivalent, explosive distance, hydrostatic pressure, and reinforcement on the damage characteristics and dynamic response of semi-spherical and semi-cylindrical bottom-sitting RC shell structures were studied. The results indicated that the damage and center vertical deformation of RC shells under underwater shock waves are significantly greater than those under air shock waves. With an increase in explosive equivalent or decrease in explosive distance, the damage and center vertical deformation of RC shells are increased. The damage to the inner surface of RC shells is more severe than the outer surface. The damage and center vertical deformation of RC shells can be reduced by bottom reinforcement and an increase in the diameter of the steel bar. The ‘hoop effect’ caused by hydrostatic pressure restrains the horizontal convex deformation and slightly decreases the macroscopic damage and vertical center deformation of the semi-spherical RC shell with an increase in hydrostatic pressure within the range of 0–2.0092 MPa. The hydrostatic pressure restrains the horizontal convex deformation of the semi-cylindrical RC shell. However, inward concave deformation of the shell center is increased by hydrostatic pressure, inducing an increase in the damage to and center vertical deformation of the semi-cylindrical RC shell. These findings may offer a reference for the construction and design of protective measures for underwater bottom-sitting shell structures.

Numerical simulation of water jet load induced by spherical bubble collapse under underwater explosion

In this study, a numerical method combining the HLLC solver and FV-WENO scheme is proposed to accurately simulate the behavior of multiphase compressible fluids and investigate the formation process of water jets. The HLLC solver approximates the conservation equations of the fluid by using numerical fluxes from the approximate Riemann problem, while the FV-WENO scheme improves the accuracy of the numerical solution by employing the weighted essentially non-oscillatory (WENO) reconstruction method. The combination of these methods allows for a more accurate simulation of the behavior of multiphase compressible fluids, leading to an accurate depiction of the formation process of water jets. By simulating the interaction between underwater shock waves from explosions and single or multiple spherical bubbles, we study the generation, development, and collapse of water jets during the bubble collapse process. By revealing the characteristics of the load during the formation of water jets and the interaction mechanisms between bubbles, our study provides support for further research on water jet phenomena. The formation process of water jets is of great significance for understanding the propagation of underwater shock waves and structural damage. Through this study, we delve into the mechanism of water jet formation, providing a new perspective on the propagation of underwater shock waves and structural damage. Our research results demonstrate that the application of the HLLC solver and FVWENO scheme in water jet simulation effectively improves the accuracy and precision of the numerical solution.

A review of underwater shock and fluid–structure interactions

Abstract Underwater explosions are inherently complex and unique physical phenomena markedly distinct from those occurring above the surface. This distinctiveness is primarily attributed to the relatively incompressible nature of water, which fundamentally alters the propagation and impact of shock waves. The study of underwater explosions is paramount in applications such as underwater demolitions for construction and salvage operations. These applications require a comprehensive understanding in order to mitigate the disturbances’ impact on marine structures and ecosystems. Studying underwater explosions and their mitigation encompasses various disciplines, including fluid mechanics, materials science and structural engineering. The work reviewed in this study contributes significantly to enhancing safety measures in marine structures by providing critical insights into the behaviour of structures under extreme conditions. This includes understanding the behaviour of gas bubbles formed by explosions, the transmission of shock waves through different media and the resultant forces exerted on structures submerged in water. Consequently, this review is meant to aid in designing robust and resilient marine systems capable of withstanding severe loading conditions caused by underwater explosions by providing key engineering considerations. The continuous evolution of this research area is essential for advancing maritime technology, ensuring the safety of undersea operations and protecting marine environments from the adverse effects of extreme subaqueous loadings.

Dynamic compressive response of gradient truss–core sandwich structure subjected to underwater shock loading

The dynamic compressive responses of a multi–layer sandwich structures with the truss core were studied experimentally and numerically under the underwater explosion shock loading. A three–layer truss-core sandwich specimen was designed and fabricated from the stainless steel. The density gradient between core layers is realized by changing the cross-sectional size of the truss members in the core layer. A water tank explosion testing device was employed to carry out the underwater explosion experiment. The finite element method was used to investigate the influences of the layered strategy of structures and the density gradient between core layers on the dynamic response. The results reveal that the density–decreasing sandwich panels CBA has the optimal underwater explosion resistance, and the explosion resistance increases as the decrease of the density gradient ratio.

A recurrent neural network model for structural response to underwater shock

Simulating the dynamic response of structures to shock involves numerical models that can require significant effort and computational resources to create and solve. This can make accurate naval platform vulnerability analyses involving a large number of simulations impractical and motivates the development of efficient surrogate models for shock and blast effects. This paper presents a novel approach to predicting the response of a floating structure to underwater shock based on machine learning (ML). Velocity time-series for a rigid floating plate subjected to underwater shock and cavitation effects are calculated for a range of charge mass, standoff distance and plate mass per unit area values using a coupled Eulerian–Lagrangian (CEL) numerical model. The computed motions are used to train a recurrent neural network (RNN) to predict the plate response including the effect of reloading due to the cavitation closure pulse. The RNN predicts plate responses from a test set of CEL model instances with a mean value of mean-squared errors between the ML and CEL model velocities, normalized with respect to the velocity ranges, of 1.5 × 10-4.