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Abstract:To investigate the propagation characteristics of shock waves generated by underwater explosion constrained by different bottom sediments， this study designed 10 working-condition principle experiments of underwater explosion， covering three typical bottom sediment （concrete， sand， and clay） and varying burst heights.The shock wave pressure time-history curves of underwater explosion at different typical measuring points were collected， and the propagation characteristics were compared and analyzed. The experimental results show that when the dimensionless burst height parameter γ=0， There exists a positive correlation between the wave impedance of bottom sediment and the reflection effect of shock waves. The reflection coefficient of shock wave peak pressure on concrete markedly exceeds that of sand and clay， with corresponding maximum values of 1.337， 1.195， and 1.158 for the three sediments， respectively. Measurement azimuth exerts a significant effect on shock wave pressure propagation： the average reflection coefficient of shock wave peak pressure in the 60° direction is higher than that in the 30° direction， with the improvement amplitudes for concrete， sand， and clay reaching 25.01%， 16.44%， and 41.77%， respectively. For near-bottom explosions， the influence of bottom sediment gradually weakens with increasing burst height. When γ=0.5， the maximum reduction in the average reflection coefficient reaches 17.05% for concrete in both 30° and 60° directions and for sand and clay in the 30° direction， while the maximum increase reaches 6.65% for fine sand and clay in the 60° direction. When γ=1， the observed variation trend is consistent with that at γ=0.5， the maximum reduction in the average reflection coefficient reaches 21.37% for concrete in both 30° and 60° directions and for sand and clay in the 60° direction， while the maximum increase reaches 31.68% for sand and clay in the 30° direction， and the reflection coefficient in all directions approaches 1. Based on these results， it can be inferred that the influence of bottom sediment on shock wave pressure propagation will decrease rapidly when γ> 1.

Abstract:To clarify the evolution mechanism of the gas curtain flow field during underwater launch and optimize the in-tube drainage efficiency， this study investigates the effects of different injection pressure. A transient three-dimensional two-phase flow model was established for the drainage process during underwater gas-curtain launch. Based on a 40 mm supercavitating projectile and a spiral-grooved gas-curtain launch tube， numerical simulations of gas curtain evolution were performed under four different injection pressure conditions， and the effect of the pressurization rate on key evolution characteristics was analyzed. The results show that a higher pressurization rate results in better overall drainage performance， but it also induces higher pressure ahead of the projectile. Specifically， as the pressurization rate increases from 1 MPa·ms^-1 to 4 MPa·ms^-1， the drainage completion time （i.e.， the time required for the gas curtain front to reach the muzzle） decreases from 14.4 ms to 11.8 ms， achieving an 18.1% improvement in time efficiency and a 25.7% increase in drainage capacity. However， upon completion of drainage， the pressure on the projectile surface increases from 3.7 MPa to 4.96 MPa， and the average pressure inside the tube rises from 4.14 MPa to 5.47 MPa. In conclusion， although a high pressurization rate can significantly accelerate drainage， it substantially increases the subsequent in-tube motion resistance of the projectile. Therefore， in the practical matching design of propellant charge and projectile， it is necessary to comprehensively balance drainage efficiency and initial motion resistance， and reasonably control the injection pressure gradient.

Abstract:The synergistic reaction between boron and aluminum particles can ameliorate the ignition and energy release performance of boron components， thereby increasing the explosive energy of energetic charges. To optimize the structural combination and mass ratio of boron-aluminum mixed particles， a double-layer charge configuration consisting of an inner main explosive charge and an outer fuel layer was proposed in this work. The influences of particle size and mass ratio on the explosion performance of charges were systematically investigated via underwater explosion experiments. The experimental results show that when the outer fuel layer is composed solely of flake aluminum powder， micron boron powder or nano boron powder， the peak shock wave pressure of charges measured at a distance of 3 m is comparable， ranging from 10 to 10.2 MPa. Among these single-component systems， the flake aluminum powder exhibits a remarkable enhancement in explosion impulse. For boron-aluminum mixed particles with a mass ratio of 1∶1， the explosion impulse， shock wave energy and bubble energy of the charge are superior to those of pure micron boron powder and pure nano boron powder systems， while inferior to the flake aluminum powder system. The mixed system achieves the comprehensive optimal explosion performance at a boron-aluminum mass ratio of 7∶3. For the composite of micron boron powder and flake aluminum powder under this ratio， the peak shock wave pressure， explosion impulse and shock wave energy are increased by 17.6%， 15.8% and 28.7% respectively compared with the pure flake aluminum powder system， and its total energy accounts for 83.3% of that of pure flake aluminum powder. Further analysis reveals that the particle size of boron powder exerts a negligible effect on the energy distribution proportion of the system. This study demonstrates that rational gradation design of boron-aluminum particles can effectively improve the shock wave performance of energetic charges in underwater explosion and optimize the energy distribution structure.

Abstract:To improve the energy output characteristics of underwater explosives and clarify the influence law of the aluminum-oxygen ratio （R_Al：O） on the energy output performance of Al-3Li alloy-containing underwater explosives. HMX-based explosives containing pure aluminum （HAl） and Al-3Li alloy （HLi） with R_Al：O ranging from 0.2 to 1.0 were designed and fabricated. The surface morphology， phase composition and thermal decomposition properties of the prepared explosives were characterized via scanning electron microscopy （SEM）， X-ray diffraction （XRD）， and thermogravimetry-differential scanning calorimetry （TG-DSC）. The detonation parameters of the explosives were calculated using EXPLO-5 software， and underwater explosion tests were performed at detonation distances of 0.4， 0.6 m and 0.8 m to determine the shock wave energy （E_s） and bubble energy （E_b） of the two types of underwater explosives. The results indicate that the thermal decomposition process of the underwater explosives includes three successive stages： HMX decomposition， AP decomposition， and intense oxidation of metal powders. Compared with explosives filled with pure aluminum powder， HLi explosives exhibit a 53.81 ℃ advance in exothermic peak temperature and a 26.3% increase in mass gain. At a detonation distance of 0.4 m， the peak shock wave pressure of HLi explosives is 4.05% higher than that of HAl explosives. When the R_Al：O is in the range of 0.2-0.6， the E_s and E_b of HLi explosives are 5%-25% and 2.5%-11.4% higher than those of HAl explosives， respectively. For both explosives， the E_b reaches the maximum value at R_Al：O=0.6， while the total energy attenuates continuously with the increase of R_Al：O. The total energy of HLi explosives is up to 9.1% higher than that of HAl explosives. The energy output structure of underwater explosives changes significantly with the variation of R_Al：O. Specifically， low R_Al：O conditions are dominated by E_s， which accounts for 55.0% of the total energy， whereas moderate and high R_Al：O conditions are dominated by E_b， with a maximum proportion of 66.4%.

Abstract:Improving the utilization efficiency of Al-based metallic fuels and enhancing the energy output performance of composite explosives constitute a crucial research direction in the field of energetic materials. To explore the effects of Al-Li alloys on the safety and energy output characteristics of composite explosives， systematic investigations on the mechanical sensitivity， explosion heat， and underwater explosion performance of three composite explosives （E_Al， E_Al-2.3Li， and E_Al-5Li） containing pure Al， Al-2.3Li alloy， and Al-5Li alloy were carried out via the Langley D-optimization method， explosion heat tests， and underwater explosion experiments.The results show that under the condition of 50% ignition probability， compared with the EAl explosive， the impact energies of E_Al-2.3Li and E_Al-5Li are reduced by 33.02% and 42.36%， and their friction loads are decreased by 19.73% and 32.88%， respectively. The addition of Al-Li alloys increases the mechanical sensitivity of composite explosives， and the sensitivity to mechanical stimuli is further aggravated with the increase of Li content. In terms of explosion heat， Al-Li alloys can significantly improve the explosion heat of composite explosives. Among all formulations， E_Al-2.3Li exhibits the maximum explosion heat of 8.712 MJ·kg^-1， which is approximately 6.3% higher than that of E_Al. In the underwater explosion tests， the total energy of E_Al-2.3Li and E_Al-5Li reaches 7.177 MJ·kg^-1 and 6.954 MJ·kg^-1， increased by 8.33% and 4.97% compared with E_Al， which indicates that the incorporation of Al-Li alloys can effectively enhance the underwater energy release capacity of explosives.Comprehensive analysis demonstrates that the introduction of an appropriate amount of Li can effectively improve the comprehensive energy output performance of explosives， whereas the Li content has an optimal range. The E_Al-2.3Li explosive achieves an excellent balance between safety and energy output performance， presenting superior comprehensive properties. This study reveals the regulation law of Li content in Al-Li alloys on the safety performance and energy release characteristics of composite explosives， and provides theoretical basis and experimental references for the optimal design and engineering application of reactive metal fuels in high-energy metal-based explosives.

Abstract:In order to meet the multiple requirements of high safety， low cost， high temperature resistance， and high pressure resistance on the seismic source for deep oil exploration， a kind of high-voltage switch consisting of two gas discharge tubes （GDTs） was used to control the discharge of thin film capacitor， and S-type bridge foil was exploded into high-temperature and high-pressure gas/plasma to ignite the boron potassium nitrate （BPN） pellet and generate underwater shock waves. Then， the ignition threshold of the seismic source was determined by the up-down method， and the acoustic characteristics were also studied using pressure probe. The results show that the firing unit composed of a thin film capacitor （2 μF） and the high-voltage switch based on GDTs can reliably achieve pulse discharge， and work at the extreme underground environments such as high temperature and high pressure， and the cost is less than ¥10. Using the firing unit to stimulate the S-type Cu bridge foil， a firing voltage threshold of 1100 V and a critical peak current of 1847 A were determined. The measurements of underwater shock waves and acoustic source level （ASL） analysis show that the ASL excited by the seismic source is higher than 150 dB in the 50-800 Hz frequency band， meeting the requirements of underground seismic sources.

Abstract:Existing studies concerning the superposition characteristics of underwater explosion shock waves are mostly limited to the near-field range， while investigations on shock wave behaviors in the mid-near field remain insufficient. In this paper， the Arbitrary Lagrangian-Eulerian （ALE） method is adopted to conduct numerical simulations on the shock wave loading characteristics under the simultaneous detonation of two explosive charges. The reliability and computational accuracy of the numerical model are validated by comparing the simulated results of free-field single and dual-charge underwater explosions with theoretical solutions and experimental data. Through parametric analysis with variable charge separation distances， the influence law of charge spacing on shock wave loading characteristics is systematically explored. The results show that the shock fronts synchronously propagate and arrive at the symmetry plane of the two charges， inducing a prominent shock wave superposition effect. When the normalized spacing h/l exceeds 0.4， the superimposed peak pressure is higher than that generated by a single charge with an equivalent total mass， whereas an opposite superposition rule occurs when h/l ≤ 0.4. The maximum relative difference in peak pressure reaches 71.23% at a normalized spacing of h/l = 2. On the asymmetric plane， shock waves from the two explosion sources arrive asynchronously， forming a typical double-peak pressure curve. The first pressure peak is solely generated by the near charge， while the second peak， though similar to the pressure characteristic of the individual far charge， presents a pressure amplitude increase of 3.19%-13.41% and an advanced arrival time. Furthermore， for a fixed total charge mass， an optimal charge spacing exists that enables the peak pressure amplification on the symmetry plane and the secondary peak pressure enhancement on the asymmetric plane to be remarkably superior to those under other spacing conditions.

Abstract:To achieve favorable hole-opening performance against underwater armored protection and effective penetration in water medium simultaneously with a single shaped charge structure， and to overcome the single-functionality limitation of conventional underwater shaped charges， a finite element model was established based on the W shaped charge structure. The reliability of the simulation results was validated by comparison with jet formation and penetration experiments from the literature. The underwater formation mechanism and penetration performance of the multimode damage elements were further investigated. The results show that by controlling the initiation mode， the W shaped charge can form two types of damage elements： an explosively formed projectile （EFP） and an annular jet. The penetration depth of the EFP into water medium is proportional to the inner liner thickness （value a）， while the penetration hole diameter of the annular jet in the target plate is inversely proportional to value a. When value a increases from 3.2 mm to 7.2 mm， the penetration depth of the EFP in water medium increases by 239.2%， and the penetration hole diameter of the annular jet decreases by 30%. The penetration depth of the EFP into water medium is inversely proportional to the outer liner thickness （value b）， while the penetration hole diameter of the annular jet in the target plate is proportional to value b. When value b increases from 1.5 mm to 2.5 mm， the penetration depth of the EFP in water medium decreases by 63.5%， and the penetration hole diameter of the annular jet increases by 45.4%. This study can provide references for the design of underwater shaped charges and multimode shaped charges.

Abstract:To improve the energy release characteristics of aluminized explosives in underwater explosions， a micro / nano self-assembled composite aluminum powder structure was constructed in this study. The effects of aluminum powder configuration and nano-Al content on the energy release behavior of cyclotetramethylene tetranitramine （HMX）-based aluminized explosives were investigated. Scanning electron microscopy was used to characterize the microstructures of the composite aluminum powders， and underwater explosion tests and heat of explosion measurements were conducted to determine the shock wave energy， bubble energy， total energy， and heat of explosion of the explosive samples. The results show that the self-assembly process promotes the attachment of nano-Al particles onto the surface of micron-sized Al particles， forming a relatively stable micro / nano composite interface. In contrast， the physically mixed samples exhibit a more random distribution of nano-Al particles and more pronounced local agglomeration. The shock wave energies of different aluminized explosives show only slight differences， whereas their bubble energy and total energy vary significantly， indicating that aluminum powder configuration and nano-Al content mainly affect the afterburning energy release during the bubble expansion and pulsation stages. Among all samples， SA-Al-5% exhibits the best overall performance， with a total underwater explosion energy of 8.29 MJ·kg^-1， corresponding to 2.35 times that of an equal mass of TNT. Its heat of explosion reaches 8421 kJ·kg^-1， with a TNT equivalent of 2.04. The enhancement mechanism is attributed to the favorable interfacial contact between an appropriate amount of nano-Al and micron-sized Al particles. The early activation of nano-Al promotes the subsequent combustion of micron-sized Al， enabling the afterburning energy of aluminum to be more effectively coupled into the bubble expansion stage. When the nano-Al content increases to 10%， particle agglomeration， an increased oxide-shell fraction， and mismatched reaction timing weaken the effective energy release. These results indicate that a nano-Al content of 5% is well matched with the self-assembled micro / nano interfacial structure， providing a useful reference for optimizing metallic fuel configurations and enhancing bubble energy in aluminized underwater explosives.

Abstract:To calibrate the equation of state for the detonation products of the pressed HMX/FOX-7 composite explosive， a Φ25.4 mm probe cylinder test was conducted. The JWL equation of state parameters were calibrated based on the expansion displacement-time history of the cylinder wall. Additionally， underwater explosion tests of the HMX/FOX-7 composite explosive were performed to validate the effectiveness and applicability of the calibrated parameters. The results demonstrate that the coefficient of determination （R²） between the simulated and experimental displacement curves reaches 0.9999， indicating the high accuracy of the calibrated JWL parameters. Furthermore， numerical simulations of the underwater explosion tests were carried out using the calibrated equation of state. Compared with the experimental data at stand-off distances of 2.0 m and 2.4 m， the relative errors of the simulated peak overpressure are -2.34% and 4.37%， the relative errors of the impulse are 9.3% and 1.43%， and the relative errors of the specific shock wave energy are -1.1% and -6.4%， respectively. Moreover， for the first bubble pulsation period and the maximum bubble expansion radius， the relative deviations among the simulated values， experimental measurements， and empirical formula predictions are all within 10%. The strong agreement between the simulations and experiments across both the cylinder and underwater explosion tests confirms that the calibrated JWL parameters exhibit high precision and excellent applicability， providing a reliable foundation for further research on HMX/FOX-7 composite explosives in underwater applications.

Abstract:To predict the overall deformation and damage characteristics of ring-stiffened cylindrical shells subjected to underwater explosion loading， this study proposes a point-cloud displacement field prediction and deformation reconstruction method integrating a PointNet-based conditional diffusion model， K-nearest neighbor algorithm， graph neural network residual correction， and spatial interpolation. The deformation response data of the cylindrical shell obtained from numerical simulations are used for model training， and a deformation response prediction model for cylindrical shells under underwater explosion loading is established. The proposed model enables the prediction of three-dimensional deformation displacements and the reconstruction of complete surface deformation profiles under different charge masses， standoff distances， and time conditions. Error evaluation results show that the mean squared error， root mean squared error， mean absolute error， and coefficient of determination on the validation set are 0.0077 mm²， 0.0877 mm， 0.0548 mm， and 0.9858， respectively， indicating high displacement prediction accuracy. The reconstruction results can effectively reflect the deformation history and final overall deformation morphology of the cylindrical shell.

Abstract:Underwater blasting serves an indispensable construction technique for marine resource prospecting and ocean engineering construction. Nevertheless， the generated blast shock waves inflict varying degrees of damage on nearby reef-building corals and undermine the stability of coral reef ecosystems. Taking Cyphastrea japonica （Japanese cyphastrea） symbionts as the research object， this study reveals the physiological damage effects induced by underwater blast shock waves from three dimensions： coral host， symbiotic zooxanthellae and epibiotic microbial communities. The experimental results demonstrate that the critical shock wave resistance threshold of Cyphastrea japonica is 6.74 MPa. The total protein content of corals declines progressively with the increase of shock wave intensity， with a maximum reduction rate of 59.6%. When exposed to a blast shock wave of 11.01 MPa， the zooxanthellae density dropped by 87% and the photosynthetic capacity decreased by 49%， accompanied by obvious coral bleaching symptoms. Blast shock waves markedly suppressed the activities of superoxide dismutase （SOD） and catalase （CAT）， which meant the coral antioxidant defense system was impaired. After shock wave exposure， the epibiotic microbial communities presented significantly elevated diversity at the phylum taxonomic level and more complex community composition at the genus level. This work elucidates the stepwise damage evolution pathway of coral host–zooxanthellae photosynthetic system–microbial communities caused by underwater blast shock waves， and provides a scientific theoretical basis for coral reef ecological protection during ocean blasting engineering.