Underwater Explosion Experiments Research Articles

Computational investigation on damage of reinforced concrete slab subjected to underwater explosion

While the dynamic response of a variety of structures subjected to underwater explosion (UNDEX) has been studied for decades, investigations of the damage and failure of reinforced concrete (RC) structures are lacking. Here we present the results of a comprehensive computational study of the dynamic response of air-backed RC slabs exposed to UNDEX. To determine the loading produced by the explosion, a model involving parameters associated with the equations of state for water and explosive was validated by comparing its predictions with UNDEX experiments on a steel plate conducted in a centrifuge. This loading was then used to predict the response of an air-backed RC slab under UNDEX. Damage and failure of the RC slab were simulated using both continuum damage mechanics and peridynamics. The results of the two methods were consistent with each other and offer promise for assessing the damage experienced by RC slabs that are subjected to UNDEX.

Dynamics of an underwater explosion bubble near a sandwich structure

A numerical procedure that couples the Runge–Kutta discontinuous Galerkin method (RKDG), the boundary element method (BEM) and the finite element method (FEM) is developed to study the dynamics of an underwater explosion bubble near a sandwich structure efficiently and accurately. The numerical approach is validated by a near-field underwater explosion experiment. The numerical predicted bubble shape, cavitation and the free field pressure are in good agreement with the experimental results. The validated code is then used to determine the effects of the foam core strengths, the stand-off distances and the boundary condition of the back face sheet on the fluid response, the bubble behaviors, and the deformation of the sandwich structure. The results are beneficial for guiding the design of the protection structures.

A three-dimensional bistatic reverberation model of underwater explosion by interface scattering at variable sound speeds

Underwater reverberation is a main limitation of the sonar performance and thereby the reverberation level estimation becomes crucial. In this study, based on the Lambert law and ray theory, a model for predicting 3D bistatic reverberation performance by interface scattering at linear sound speed profile is established and then verified through the underwater explosion experiments. The Influences of source and receiver positions, and relative sound speed gradient on reverberation performance are further investigated. The results indicate that: (1) the proposed model can predict the short-range mean reverberation level effectively, with the deviation 2–4 dB and describe the whole reverberation level distribution in some details; (2) at the early reverberation phase, the interference effects between the interface scattering sounds are considerable and a dominating interface exists; the counterbalance between the losses by scattering, spreading and medium absorption results in the local high-intensity zones close to corresponding interfaces, respectively; (3) as the sound source moves towards some interface, associated local high-intensity zone gradually expands, while the other one shrinks; if the sound speed approaches are constant, an extra local high-intensity zone will appear between the previous two but with a lower magnitude.

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

Transient fluid-structure interaction (FSI) has always been a challenging problem in ship mechanics. Underwater explosion and its highly nonlinear impact on nearby structures are more complicated. In this paper, the global responses of a surface ship subjected to an underwater explosion in waves are numerically investigated considering the nonlinear coupling between the fluid and structure solvers. The fluid field is modeled with the boundary element method (BEM), while the potential decomposition theory is adopted to take the surface waves into account. The global responses of the ship structure are modeled with the mode superposition method. Then a FSI model is established using the mode decomposition method of the acceleration potential to consider the interaction. An underwater explosion experiment is carried out to validate the numerical model, which shows good agreement between the numerical and experimental results. With the presented model, the interactions between a ship and an underwater explosion bubble both in still water and waves are simulated. The dynamics of the ship global responses and the influence of the waves are analyzed which shows noteworthy nonlinearity.

The effect of explosive percentage on underwater explosion energy release of hexanitrohexaazaisowurtzitane and octogen based aluminized explosives

To control the explosion energy output by optimizing explosive components is a key requirement in a number of different application areas. The effect of different Al/O Ratio on underwater explosion of aluminized explosives has been studied detailedly. However, the effect of explosive percentage in the same Al/O Ratio is rarely researched, especially for Hexanitrohexaazaisowurtzitane (CL-20) based aluminized explosives. In this study, we performed the underwater explosion experiments with 1.2-kilogram explosives in order to investigate the explosion energy released from CL-20 and Octogen (HMX) based aluminized explosives. The percentage of the explosive varied from 5% to 30% and it is shown that: the shockwave peak pressure (pm) grows gradually; shock wave energy (Es) continues increasing, bubble energy (Eb) increases then decreases peaking at 15% for both formulas, and the total energy (E) and energy release rate (η) peak at 20% for CL-20 and 15% for HMX. This paper outlines the physical mechanism of Eb change under the influence of an aluminium initial reaction temperature and reaction active detonation product percentage coupling. The result shows that CL-20 is superior as a new high explosive and has promising application prospects in the regulation of explosive energy output for underwater explosives.

A Lab‐Scale Experiment Approach to the Measurement of Wall Pressure from Near‐Field under Water Explosions by a Hopkinson Bar

Direct measurement of the wall pressure loading subjected to the near‐field underwater explosion is of great difficulty. In this article, an improved methodology and a lab‐scale experimental system are proposed and manufactured to assess the wall pressure loading. In the methodology, a Hopkinson bar (HPB), used as the sensing element, is inserted through the hole drilled on the target plate and the bar’s end face lies flush with the loaded face of the target plate to detect and record the pressure loading. Furthermore, two improvements have been made on this methodology to measure the wall pressure loading from a near‐field underwater explosion. The first one is some waterproof units added to make it suitable for the underwater environment. The second one is a hard rubber cylinder placed at the distal end, and a pair of ropes taped on the HPB is used to pull the HPB against the cylinder hard to ensure the HPB’s end face flushes with loaded face of the target plate during the bubble collapse. To validate the pressure measurement technique based on the HPB, an underwater explosion between two parallelly mounted circular target plates is used as the validating system. Based on the assumption that the shock wave pressure profiles at the two points on the two plates which are symmetrical to each other about the middle plane of symmetry are the same, it was found that the pressure obtained by the HPB was in excellent agreement with pressure transducer measurements, thus validating the proposed technique. To verify the capability of this improved methodology and experimental system, a series of minicharge underwater explosion experiments are conducted. From the recorded pressure‐time profiles coupled with the underwater explosion evolution images captured by the HSV camera, the shock wave pressure loading and bubble‐jet pressure loadings are captured in detail at 5 mm, 10 mm, …, 30 mm stand‐off distances. Part of the pressure loading of the experiment at 35 mm stand‐off distance is recorded, which is still of great help and significance for engineers. Especially, the peak pressure of the shock wave is captured.

Explosion Performance of High‐Temperature Degraded Emulsion Explosives

AbstractExperiments were conducted to study the underwater explosion performance of emulsion explosives (EE) after hot water bath. Spherical charges of EE with different sensitizers and hot water bath were prepared and tested. As for as‐prepared charges, the detonation velocity experiments and underwater explosion experiments were carried out and the crystallization ratio was measured and calculated by the dissolution and neutralization method. The results showed an inverse relationship between explosion parameters (pressure peak, specific impulse, detonation velocity and specific total energy) and heating time. It also revealed that the effective explosive weight of EE was reduced with long time of hot water bath. Moreover, the crystallization ratio and the decreasing rate of explosion parameters of EE sensitized by NaNO2 were apparently higher than EE containing physical sensitizers (glass microballoon and perlite), which was attributed to the different destruction mechanism of EE. After 6‐hour hot water bath, the EE containing physical sensitizers still retained detonator sensitivity and more than 80 % of specific total energy. Meanwhile, the crystallization ratio was less than 20 %. Whereas, the EE sensitized by NaNO2 lost the detonator sensitivity and the crystallization ratio of EE was also above 40 %.

Study on the interactions between two identical oscillation bubbles and a free surface in a tank

A boundary element method based on the incompressible potential flow theory is adopted to investigate the interaction between two identical oscillating bubbles and a free surface in a tank. An axisymmetric numerical model is established, and certain numerical techniques are proposed to address coefficient matrix singularity and fluid-structure intersection. Experiments with spark-generated bubbles in a cylindrical tank recorded by a high-speed camera are conducted, and the numerical results are validated. On this basis, a typical case of bubbles interacting with a free surface in a tank with relatively small inter-bubble and bubble-free surface distances is carefully studied. A crown-shaped water column at the free surface is observed both numerically and experimentally. The maximum volume of the lower bubble is found to be much larger than that of the upper one. The effects of the inter-bubble and bubble-wall distances on bubble dynamics and free surface motion are analyzed. The results can provide a useful reference for underwater explosion experiments in the confined fluid field.

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

This study aims to verify experimentally the specifications of the data acquisition system required for the precise measurement of signals in an underwater explosion (UNDEX) experiment. The three data acquisition systems with different specifications are applied to compare their precision relatively on maximum shock pressures from UNDEX. In addition, a method of assessing the acquired signals is suggested by introducing the concept of measurement uncertainty. The underwater explosion experiments are repeated five times under same conditions, and assessment is conducted on maximum quantities acquired from underwater pressure sensors. It is confirmed that the concept of measurement uncertainty is very useful method in accrediting the measurement results of UNDEX experiments.

Effect of the Al/O ratio on the Al reaction of aluminized RDX-based explosives

Aluminum (Al) powders are used in composite explosives as a typical reducing agent for improving explosion performance. To understand energy release of aluminum in aluminized RDX-based explosives, a series of thermal measurements and underwater explosion (UNDEX) experiments were conducted. Lithium fluoride (LiF) was added in RDX-based explosives, as a replacement of aluminum, and used in constant temperature calorimeter experiments and UNDEXs. The influence of aluminum powder on explosion heat () was measured. A rich supply of data about aluminum energy release rate was gained. There are other oxides (CO, CO, and HO) in detonation products besides alumina when the content of RDX is maintained at the same levels. Aluminum cannot fully combine with oxygen in the detonation products. To study the relationship between the explosive formulation and energy release, pressure and impulse signals in underwater experiments were recorded and analyzed after charges were initiated underwater. The shock wave energy (), bubble energy (), and total energy () monotony increase with the Al/O ratio, while the growth rates of the shock wave energy, bubble energy, and total energy become slow.

The Effect of the Hydrogen Containing Material TiH2on the Detonation Characteristics of Emulsion Explosives

In order to improve the detonation performance of emulsion explosives, a new type of emulsion explosives with TiH2 powders is developed. The influences of the amount of sensitizers GMs and energetic additives TiH2 on explosion characteristics of emulsion explosives are studied to determine the optimum compositions. Underwater explosion and brisance testing experiments show that, compared to traditional GMs sensitized emulsion explosives, the shock wave specific impulse I and total energy E of GMs-TiH2 sensitized emulsion explosives are improved significantly, and the effect of TiH2 powders on improving the explosion power of emulsion explosives is better than that of Ti powders. The brisance of GMs-TiH2 emulsion explosives is 23.80 mm compression of lead block, 7.7 mm more than that of the emulsion explosives sensitized by GMs alone. Therefore, the hydrogen containing material TiH2 could be a promising energetic additive for developing high-power emulsion explosives.

Influence of booster size on the total energy of RBUL-1 explosive in underwater explosion

To investigate the influence of the booster size on the total energy of DNAN-based insensitive melt-cast explosive RBUL-1, six groups of underwater explosion experiments with varied booster sizes were carried out to measure the total energy of RBUL-1 explosive. Experimental results show that the booster size especially the booster diameter has a great influence on the total energy of RBUL-1 explosive. An expression was proposed and calibrated to illustrate the relationship between the total energy of RBUL-1 explosive and the booster size. Besides, the booster size used in the underwater explosion experiments was optimized to achieve higher total energy results. The present investigation has practical significance for the design of the booster sequence and warhead.

Small-charge underwater explosion bubble experiments under various boundary conditions

Small-charge underwater explosion experiments were performed to investigate bubbles subjected to gravity and various boundary conditions, including single boundary (free surface and rigid wall boundary), combined boundaries of free surface and solid wall, solid wall boundaries with a circular opening, and resilient wall boundaries. With high speed camera and pressure sensors, the behavior of explosion bubbles was studied and features of associated pressure pulses were analyzed. Detailed image analysis on the final stages of bubble collapse was carried out and revealed a possible explanation for the weakening of pressure waves at bubble rebound as the bubble approaches a wall boundary. Certain features also indicate that the magnitude of the pressure peaks induced by bubble rebound is related to the shape of the bubble shape during collapse. Pressure pulses arising from the two types of bubble behavior, specifically the collision of an annular jet and the impact of a jet with the wall boundary, were measured. Other curious types of bubble behavior were found, including jetting induced by suction when a bubble collapses covering a circular opening on a solid wall, and bubble splitting in interaction with a resilient wall boundary.

Numerical and experimental study on cyclotrimethylenetrinitramine/aluminum explosives in underwater explosions

Underwater explosion experiments were conducted to determine the optimal performance of cyclotrimethylenetrinitramine (RDX)-based aluminized explosives with an aluminum content of 0%, 15%, and 30%. Free-field blast output energies of the three types of explosives were measured between 0.3 and 0.8 m. The shock wave energy, bubble energy, detonation energy, and energy heat release rate were measured. A new calculation method was based on the experimental results to simulate the bubble pulse process and pressure changes inside the bubbles of non-ideal explosives. The specific distance at which maximum total energy was achieved for the underwater explosion was determined.

Investigation of bubble dynamics of underwater explosion based on improved compressible numerical model

A bubble jet with velocity of hundred meters per second forms at the final stage of bubble collapse, which makes the compressibility of flow field can’t ignore. Based on the spherical bubble model of Geers and Hunter, a compressible numerical model is improved for simulating non-spherical bubble dynamic in this paper. In the present implementation, the compressibility of external liquid and the wave effect of internal gas are considered by the first order external doubly asymptotic approximation and the first order internal doubly asymptotic approximation, respectively. In addition, the volume acceleration model is applied to calculate the initial condition of bubble. After that, the improved compressible numerical model is validated against the underwater explosion experiment data. The numerical result of bubble radius correlates well with the experiment data. Finally, based on the improved compressible numerical model, the influences of wave effect of internal gas and initial condition of bubble on bubble dynamics in free field and gravity field are investigated. The wave effect of internal gas makes bubble radius, radial velocity, translational displacement, jet velocity and remaining total energy decrease. The initial radial velocity, on the one hand, makes bubble radius, radial velocity, translational displacement, jet velocity and remaining total energy increase at the first bubble cycle; on the other hand, intensifies bubble radius, radial velocity, translational displacement, jet velocity and remaining total energy decay.

Damage characteristics of ship structures subjected to shockwaves of underwater contact explosions

The damage process of ship structures subjected to underwater contact explosions is characterized by strong nonlinearity, thus there are great challenges in solving such problems. Firstly, the full Smoothed Particle Hydrodynamics (SPH) method for the fluid and structure interaction (FSI) is established based on compressible SPH fluid dynamics and SPH shell. Furthermore, the normal flux method is introduced to treat the interface. However, given the immaturity of the SPH shell in dealing with the fracture of complex structures, an SPH-FEM (Finite Element Method) coupling method for FSI is proposed with the “glue” treatment applied at the interface. The above two methods are verified by an underwater contact explosion experiment. Afterwards, the pressure-time relationship within six charge radii is fitted based on the axisymmetric SPH simulation. On this basis, the flat plates subjected to underwater contact explosions are studied in detail with the application of a combined damage variable. Three stages in the damage process, namely localized bulging, discing and petaling, are observed, and the crack and deflection are found to be sensitive to the changes of peak pressure and impulse respectively. Finally, complex models of a stiffened plate and a ship are established to further study the damage characteristics.

A New Method for Determining the Equation of State of Aluminized Explosive

The time-dependent Jones—Wilkins—Lee equation of state (JWL-EOS) is applied to describe detonation state products for aluminized explosives. To obtain the time-dependent JWL-EOS parameters, cylinder tests and underwater explosion experiments are performed. According to the result of the wall radial velocity in cylinder tests and the shock wave pressures in underwater explosion experiments, the time-dependent JWL-EOS parameters are determined by iterating these variables in AUTODYN hydrocode simulations until the experimental values are reproduced. In addition, to verify the reliability of the derived JWL-EOS parameters, the aluminized explosive experiment is conducted in concrete. The shock wave pressures in the affected concrete bodies are measured by using manganin pressure sensors, and the rod velocity is obtained by using a high-speed camera. Simultaneously, the shock wave pressure and the rod velocity are calculated by using the derived time-dependent JWL equation of state. The calculated results are in good agreement with the experimental data.

Underwater detonation performance of the aluminum film explosive

A new aluminized explosive is proposed, and the approach is to replace the aluminum powder in the traditional aluminized explosive with an aluminum film. The purpose is not only to improve mechanical properties and lower the impact sensitivity of traditional aluminized explosives, but also to reduce environmental pollution in the aluminum particle production process. The pressure-time curves of the aluminum film explosive and RDX are measured in underwater explosion experiments. The peak pressure, impulse, shock wave energy, and bubble energy are obtained by analyzing the curves. The results of the study indicate that the peak pressure of the aluminum film explosive is lower than that of RDX. However, the aluminum film explosive maintains a high pressure for a longer period of time. The large amount of energy is found to liberate by subsequent reactions of the Al film with the primary detonation products. The increase in the explosion energy of the aluminum film explosive is based mainly on the increase in the bubble energy.

Effect of Aluminum Fiber Content on the Underwater Explosion Performance of RDX‐based Explosives

AbstractIn order to analyze the effect of aluminum fiber contents on the underwater explosion performance of RDX‐based explosives, the pressure‐time curves of composite explosives with different aluminum fiber contents are measured by underwater explosion experiments. Peak pressure, impulse, shock energy, and bubble energy were obtained by analyzing the curves. The results show that the peak pressures of composite explosives decrease with increasing aluminum fiber contents. The shock impulse of the 30 % aluminum fiber composite explosive is the highest in all composite explosives. The effects of the 20 % and 40 % composite explosives are nearly equal to that of the 30 % explosive, and the different values of shock impulse among them do not exceed 5 %. The specific shock energy of the 20 % aluminum fiber composite explosive is the highest in all composite explosives. The bubble energy and explosion energy of composite explosives increase with increasing aluminum fiber contents.

Explosion Power and Pressure Desensitization Resisting Property of Emulsion Explosives Sensitized by MgH2

Due to low detonation power and pressure desensitization problems that traditional emulsion explosives encounter in utilization, a hydrogen-based emulsion explosives was devised. This type of emulsion explosives is sensitized by hydrogen-containing material MgH2, and MgH2 plays a double role as a sensitizer and an energetic material in emulsion explosives. Underwater explosion experiments and shock wave desensitization experiments show that an MgH2 emulsion explosives has excellent detonation characteristics and is resistant to pressure desensitization. The pressure desensitization–resistant mechanism of MgH2 emulsion explosives was investigated using scanning electron microscopy.