Embedded very-low-frequency underwater acoustic acquisition technology and experimental study for underwater explosion monitoring

The dynamic and the whipping phenomena through an underwater explosion (UNDEX) experiments and simulations were verified. Furthermore, the comparison of the simulation and experimental results were conducted. The experiment was conducted at a reservoir and the MegaMEX was used as an explosive. The simulation was performed by combining the DAA-based USA code with the LS-Dyna which is a finite element analysis code, and for the gas bubble, the second-generation Geers–Hunter model was used. For the experiment, the natural frequency analysis of the structure was carried out to establish the explosion condition and four underwater explosion tests were carried out. Acceleration, velocity, strain and underwater pressures were measured by underwater explosion experiments, and acceleration, velocity and strain were compared. In this research, the whipping phenomenon by underwater explosion was confirmed through experiments and simulation. The results of this study are expected to contribute to the improvement of UNDEX simulation technique.

Assessment on shock pressure acquisition from underwater explosion using uncertainty of measurement

This study investigates the deformation characteristics of a ring-stiffened cylindrical shell induced by shock waves and coalesced bubbles in double-charge underwater explosions. A numerical model for coupling underwater multi-point explosion loads with the cylindrical shell is established by the Arbitrary Lagrange Euler method, and underwater explosion experiments with double charges are also conducted. The numerical model's effectiveness is validated by comparing shock wave superposition characteristics, bubble coalescence processes, and bubble pulsation periods with the experimental results. Based on the numerical model, the influences of detonation intervals and layout angles of charge on shock wave superposition effects, temporal and spatial distribution characteristics of shock waves, and the evolution process of coalesced bubbles in underwater explosions with double charges are explored. Additionally, the deformation characteristics of cylindrical shells induced by shock waves and coalesced bubbles for double charges with different detonation intervals and layout angles of charge are analyzed. The results indicate that double charges can induce more substantial deformation on the cylindrical shell at a specific detonation interval than a single charge with equal total mass. During the shock wave phase, the cylindrical shell's deformation decreases nonlinearly with an increased layout angle. Conversely, during the bubble load phase, the deformation of the cylindrical shell shows an approximately linear decrease with an increase in layout angle. A critical angle exists, below which the impact of double charges on the cylindrical shell is more substantial when detonated with an interval than simultaneous detonation.

Experimental and numerical investigation on saturated concrete subjected to underwater contact explosion

The fluid–structure interaction between elastic plates of varying thicknesses (4–20 mm) and underwater explosion bubbles was numerically studied via the finite element method. An underwater explosion experiment near a steel plate was carried out to verify the numerical approach. In addition to rigid body motion, it was observed that the substantial deformation of thin plates markedly impacts bubble collapse and jet formation. Specially, the deformation degree of the plate critically determines whether bubble pinching occurs. Such bubble pinching results in high-speed, needle-like jets, with their impact velocity rising as the vertical position of the annular necking region increases. This position is mainly dictated by plate motion and does not correlate monotonically with structural thickness. Once the plate thickness surpasses a critical threshold, the necking position gradually ascends until it vanishes.

Combined with the basic situation of submarine underwater acoustic countermeasure equipment at the present stage, this paper summarizes the countermeasure principle and suitable use time of main underwater acoustic countermeasure equipment in China, analyzes the development status of submarine underwater acoustic countermeasure technology, and looks forward to the development trend of submarine underwater acoustic countermeasure technology.

Numerical investigation on underwater explosion cavitation characteristics near water wave

Damage mechanisms of a typical simplified hull girder with thinner plates subjected to near-field underwater explosions

Early-stage dynamic responses of naval structures under underwater explosion shock loads exhibit high-frequency, intense amplitude fluctuations and short durations, serving as critical factors for the development of plastic deformation and other damage characteristics. These structural dynamics demonstrate prominent nonlinear and non-stationary features. This study focuses on the nonlinear evolutionary patterns of early-stage plastic shock responses in underwater explosion-impacted ship structures. Utilizing phase space reconstruction, unimodal mapping, and symbolic dynamics theory, we analyze the nonlinear and non-stationary characteristics along with their evolutionary patterns in experimental data. First, scaled model experiments under varying shock factors were conducted based on a stiffened cylindrical shell prototype, investigating the spatiotemporal evolution of nonlinear and non-stationary dynamic responses under different shock loads while characterizing their uncertainty features. Second, model tests were performed on deck-type cabin structures and plate frameworks derived from a naval vessel’s deck prototype, further analyzing the evolutionary patterns of early-stage plastic dynamic responses and verifying the method’s effectiveness and universality. Research findings indicate that (1) early-stage plastic shock responses of ships under underwater explosions exhibit multiple dynamical behaviors including chaotic motion, periodic motion, and quasi-periodic motion, and (2) during the initial plastic phase, orbital parameters approximate 0.8, providing guidance for test condition setup and initial parameter selection in underwater explosion experiments on naval structures.

In order to investigate the influence of rigid wall surface on the bubble characteristics of underwater explosion, the underwater explosion experiment under the boundary conditions of free surface and rigid wall surface was carried out on 2.5g cylindrical charge TNT in a 2×2×2m tank. The time history curves of shock wave and bubble pulsation were obtained by underwater pressure sensor, and the bubble pulsation process was observed by high-speed photography. The experimental results show that compared with the free surface underwater explosion, the shock wave peak pressure and the bubble pulse peak pressure in rigid wall surface underwater explosion are increased, and a large cavitation area appeared at the junction of rigid wall and water surface. After the bubbles contacted the rigid wall surface, the bubble morphology changed significantly, the first bubble pulsation period and the maximum radius of bubble expansion became larger. After the first bubble pulsation, the bubble partially collapsed and split into two parts, bubbles continued to pulsate in the direction of the rigid wall and the bottom of the water. Finally, combined with the experimental data of rigid wall surface at different explosion depths, the relationship between the first bubble pulsation period, the maximum bubble expansion radius and the explosion depth of 2.5gTNT under rigid wall conditions is given.

Numerical investigation on global responses of surface ship subjected to underwater explosion in waves

To investigate the dynamic response of a hollow cylindrical shell structure subjected to a near-field underwater explosion, underwater explosion experiments were conducted in a 2 × 2 × 2 m water tank, and high-speed cameras were used to record the interactions between the bubbles generated by the underwater explosion and the hollow cylindrical shell. The high-speed photography results showed that the cylindrical shell experienced a minor degree of deformation during the shock-wave stage. However, during the bubble-pulsation stage, the cylindrical shell experienced significant deformation that surpassed the deformation observed during the shock-wave stage. On this basis, combined with the damage results for the cylindrical shell, a numerical model for the hollow cylindrical shell subjected to an underwater explosion was established using LS-DYNA software. The dynamic process and damage mechanism of a hollow cylindrical shell that was subjected to a near-field underwater explosion were revealed by analyzing the pressures and strains of the shell elements, the velocities and displacements of the nodes, and the variations in the energy.

In this paper, comprehensive underwater contact explosion experiments are carried out on flat plates, aiming to substantiate the experimentally observed damage characteristics. Furthermore, the radius size during the bubble pulsation process is validated. Subsequently, a study on the damage characteristics of underwater explosion loads on double-layered cylindrical shells is conducted. The coupling mechanism between underwater explosion loads and elastoplastic structures is explored. The influences of factors such as explosion distance, water depth, and the type of fluid medium between the double-layered shells on the structural damage modes and damage effects are analyzed. The research shows that within a certain range, variations in the explosion distance mainly affect the destructive effects of shock wave loads on the structure, while the large temporal and spatial scales of bubbles make them less affected by the explosion distance. Changes in water depth primarily affect the destructive effects of bubble loads on the structure. As the water depth increases, the pulsation period and radius of the bubble decrease, and the energy dissipation during bubble pulsation also decreases. Consequently, the pulsating pressure generated by the secondary expansion of the bubble and the intensity of the water jet load can be effectively increased. In deep-water environments, the structural deflection is mainly determined by the bubble load. The water layer between the double-layered shells can effectively reduce the damage effects of shock waves and bubble loads on the structure.

Response of thin walled metallic structures to underwater explosion: A review

Black powder is still widely used in civil and scientific research fields, and it occasionally causes hazardous accidents. Thus, it is of great significance to describe its explosion effects. From a phenomenological perspective, this study uses the Jones‐Wilkins‐Lee (JWL) equation of state (EOS) to describe the explosion products of black powder, which makes it more convenient to conduct numerical simulations of black powder explosions. In order to accurately and quickly obtain the parameters of the JWL EOS for the explosion products, a calibration method combining underwater explosion shock wave data with an improved genetic algorithm is proposed. In practical applications, the peak pressure of the shock wave is the primary factor considered when evaluating hazards. Starting from the peak pressure of the shock wave obtained from underwater explosion experiments, the parameters are continuously optimized based on the combination of the genetic algorithm and numerical simulation, and finally, the EOS of the explosive explosion products is determined. The results show that the pressure‐distance attenuation curve calculated based on the parameters of the JWL equation after identification has a small deviation from the test data and the fitted empirical formula, with the coefficient of determination ( R 2 ) being greater than 0.98. At the same time, by changing the amount of explosive and comparing it with other test working conditions, the two are in good agreement, further demonstrating the effectiveness and accuracy of the proposed method.