Abstract To address excessive impact loads during high-speed water entry, a GPU-accelerated real-time fluid-structure interaction simulation system was developed. The system employs the VOF method to establish a two-phase flow model for high-speed water entry, combined with an explicit dynamics approach to simulate structural response. Real-time computational capability was achieved through parallel algorithms. System validation and application analysis were completed, yielding optimal parameter combinations for jet-induced load reduction. This provides an analytical tool for high-speed water entry load reduction design. Research demonstrates the system’s capability to accurately predict jet load reduction effects, highlighting its significant engineering application value.

Dispersion devices are widely applied in fields such as aerospace, forest firefighting, and unmanned aerial vehicle (UAV) deployment. The steel band, as a crucial component in the dispersion device that constrains the dispersed body, plays an important role in ensuring consistent dispersion velocities for multiple bodies. A dispersion test was conducted on a combustion-driven gasbag dispersion system, and the working process of the dispersion was described using high-speed camera. The fractured 1Cr18Ni9Ti steel band, which had undergone cold work hardening, was examined through metallographic and scanning electron microscopy (SEM) to observe the fracture morphology. The results indicate that the surface of the steel band consists of twinned austenite. The fracture surface features numerous oval shear dimples, some equiaxed dimples, and a few tear ridges. The fracture is entirely shear, with transgranular tearing observed. The steel band fracture exhibits ductile fracture caused by shear instability under plane stress conditions.

Deployable spacecraft have been widely used, while the motion state under the disturbance is still unknown. A test device is designed to simulate the motion of deployable spacecraft in this paper, and the ballistic characteristics of solid thruster are tested. The test results show that the total impulse deviation of the solid thruster can be effectively reduced by controlling the propellant mass, but the spacecraft would still produce a large precession angle and precession angular rate. The influence of launch disturbance and deployment disturbance on the spacecraft is larger than that of spinning thruster deviation. The ratio between the transverse moment of inertia and the axial moment of inertia should be increased as much as possible during the design of the spacecraft, otherwise a small disturbance would produce a large precession angle. The test results have certain reference significance for the study of the spacecraft micro-motion.

The core components of an aircraft and the source of its lift are its wings, but lift generation is disrupted by the high temperature and pressure generated on the wing surface when an aircraft gun is fired. Here, to investigate how this process influences the aerodynamic parameters of aircraft wings, the k-omega shear-stress-transport turbulence model and the nested dynamic grid technique are used to analyze numerically the transient process of the muzzle jet of a 30-mm small-caliber aircraft gun in high-altitude (10 km) flight with an incoming Mach number of Ma = 0.8. For comparison, two other models are established, one with no projectile and the other with no wing. The results indicate that when the aircraft gun is fired, the muzzle jet acts on the wing, creating a pressure field thereon. The uneven distribution of high pressure greatly reduces the lift of the aircraft, causing oscillations in its drag and disrupting its dynamic balance, thereby affecting its flight speed and attitude. Meanwhile, the muzzle jet is obstructed by the wing, and its flow field is distorted and deformed, developing upward toward the wing. Because of the influence of the incoming flow, the shockwave front of the projectile changes from a smooth spherical shape to an irregular one, and the motion parameters of the projectile are also greatly affected by oscillations. The present results provide an important theoretical basis for how the guns of fighter aircraft influence the aerodynamic performance of the wings. (c) 2025 Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Accurate modal analysis is essential for evaluating the dynamic characteristics of inflated beams, while modal analysis under vacuum conditions remains challenging. In this study, a vibration test platform for air and vacuum environments was developed to measure the modal characteristics of inflated beams under different inflation pressures. The average differences between the modal frequencies measured in air and vacuum were 26.141% for the first-order mode and 22.976% for the second-order mode, indicating that air effects cannot be neglected for thin inflated beams. A model considering the air added-mass effect was then proposed and validated experimentally. The average deviations between the predicted and experimental results were 1.46% for the first-order mode and 4.58% for the second-order mode. Acoustic–structure coupling simulations further verified the hydrodynamic pressure on the membrane surface, and the circumferential pressure distribution agreed well with the proposed model. Then the hydrodynamic pressure distribution along the beam axis was calculated, showing that the added mass is approximately uniformly distributed along the inflated beam. Finally, the distributed mass method was adopted to calculate the dry and wet modal characteristics of the inflated beam. The average deviations between the numerical and experimental results were 2.89% for the dry modal results and 2.35% for the wet modal results.

Collaborative technology for the remote, large-scale deployment of drones using dispersal systems holds significant potential in applications such as post-disaster rescue, which must balance low overload with high thrust, in addition to precisely controlling the separation attitude. To address these issues, this paper introduces a multi-gasbag propulsion system with a high aspect ratio that coordinates multiple gasbags to generate sufficient thrust. By adjusting the inlet size of the gasbag, the separation behavior of the release unit can be accurately controlled. A multidimensional two-phase flow model is established, accompanied by both combustion and flow experiments and a double-gasbag propulsion experiment. The results demonstrate that the proposed mathematical model is accurate, effectively captures the pressure fluctuations and spatiotemporal distribution of flow field parameters, and determines the separation attitude of the release unit. For the cases studied in this paper, the pressure at the gasbag inlet ( z = 650 mm) is the dominant factor during the gasbag propulsion response, causing the release unit to rotate counterclockwise when the gasbag inlet sizes are identical. Increasing the inlet size at z = 50 mm compensates for the adverse effects of uneven axial pressure distribution, thereby achieving a neutral separation for the release unit. When the radii r1 and r2 vary between 2 and 12 mm, the angular velocity and attitude angle of the release unit are found to range from-15.50 to 15.20 rad/s and from-0.109 to 0.106 rad, respectively.

Numerical simulations are utilized to model the shock wave dynamics at the outlet of a single-transition section shock tube. Using the Euler algorithm, the evolution of the shock wave generated by TNT detonation within the pipe is calculated, and the simulation results are validated by comparison with established empirical formulas such as Henrch, Садовский, and Chinese defense design standards. The effects of explosive parameters, including the explosive mass, arrangement, and shape, on the pressure at both the explosion room and test room outlets are discussed. The dispersed arrangement forms a higher-pressure zone in the initial stage of the shock wave compared to the concentrated arrangement, but both have consistent peak pressure and overpressure duration. Explosive shape only significantly affects the shock wave before full development, with little impact on outlet pressure. The results show that, under the conditions of this study, the explosive mass has the most significant impact on the peak overpressure and positive pressure duration of the shock wave. These results can serve as a reference for the structural design of explosive-driven shock tubes.

Increasing the initial velocity of large-caliber, high-mass projectiles remains a persistent challenge in military weapon design. To address this, we developed a novel main-auxiliary chamber configuration based on the balanced gun concept. An internal ballistic model incorporating this dual-chamber structure was established to evaluate its ballistic performance. By comparing the internal ballistic characteristics of the proposed design with those of a conventional balanced gun, we analyzed its acceleration capabilities. Additionally, we examined the effects of ignition delay time, auxiliary chamber charge mass, and shell mass on the internal ballistic behavior of the new structure. The results demonstrate that the dual-chamber balanced gun can significantly enhance the projectile ' s initial velocity without exceeding the maximum allowable chamber pressure. Specifically, within a suitable range of ignition delay times, reducing the delay leads to increases in both the projectile ' s initial velocity and the peak pressure in the auxiliary chamber. Furthermore, as long as the maximum pressure in the auxiliary chamber remains within safe limits, increasing the propellant charge improves projectile acceleration. Lastly, provided the structural integrity of the shell is maintained, reducing the shell mass of the auxiliary chamber further enhances the initial velocity. These findings offer valuable insights for both the theoretical study and engineering design of large-caliber balanced guns aimed at achieving higher muzzle velocities.

Davis gun as a representative experimental method for achieving hypersonic velocities in large-scale, high-mass systems effectively addresses the demands for scalable and reproducible dynamic experiments. However, due to the geometric constraints and operational principles inherent to Davis gun launch devices, the mechanistic interpretation of parameter interactions under multi-physics coupling effects remains challenging. To address this, the present study establishes a coupled gas-solid two-phase flow model for the interior ballistics of the Davis gun and employs a multi-objective optimization algorithm to conduct quantitative analysis of multi-parameter interactions. Comparative experimental validations across multiple caliber configurations demonstrate that the proposed two-phase flow model achieves remarkable prediction accuracy for chamber pressure and velocity fields, with computational results showing excellent consistency with experimental data (error margin within 5%). Transient analysis of combustion kinetics and propellant gas distribution characteristics reveals that the chamber flow field in the Davis gun exhibits a bidirectional expanding asymmetric distribution pattern, fundamentally differing from the unidirectional flow evolution observed in conventional launch devices. Multi-objective parameter optimization results indicate that the feasible design space exhibits pronounced aggregation characteristics. Through correlation analysis of the feasible region and coefficient matrix, a multi-parameter influence propagation pathway map is constructed, thereby providing a systematic technical pathway and engineering paradigm for multi-objective optimization design of Davis gun launch interior ballistics.

To address the challenge of predicting mass erosion during the penetration of kinetic projectiles into reinforced concrete, this paper proposes a coupled calculation method. This method is based on existing mass erosion theories regarding thermal melting stripping and thermal softening cutting, while simultaneously considering the shear-plastic hinge resistance encountered by the projectile during direct contact with the reinforcement. Solved via multi-scale discretization, this method discretizes the entire penetration process into microsecond-level steps (10−6 s) on a temporal scale and employs micro-scale grid division on the projectile surface layer on a spatial scale. The calculated results show good agreement with experimental data, with a deviation of 2.74% between the predicted and experimental penetration depths for reinforced concrete. The study finds that as the initial penetration velocity increases, the thermal melting mechanism dominates mass loss, although the proportion of mass loss induced by the cutting mechanism exhibits an increasing trend. The presence of reinforcement mitigates the total mass loss of the projectile during the penetration process. Furthermore, the proportions of cutting mass loss, melting mass loss, and total mass loss all demonstrate a decreasing trend as the projectile mass increases. Further analysis reveals the existence of critical thresholds for the projectile’s initial velocity and concrete strength concerning reinforcement protective efficacy; when both exceed these thresholds, the reinforcement’s contribution to the concrete’s anti-penetration protection becomes negligible. The coupled calculation method presented in this paper provides a design basis for optimizing reinforcement and enhancing cost-effectiveness.

Pipeline gelling presents a prevalent challenge in crude oil transportation. While hot water injection is widely employed to facilitate oil melting and transport, the intense shear stress from high-velocity flows frequently induces solid-liquid interfacial instability, yielding an irregular wavy interface. Currently, the complex effects of this morphology on heat transfer and flow dynamics remain poorly understood. To address this gap, this study establishes a three-dimensional numerical model coupling the Volume of Fluid (VOF) interface tracking method with the SST k-ω turbulence model to investigate the melting heat transfer and flow behaviors of gelled crude oil with a wavy interface. The results indicate that wave-induced near-wall disturbances effectively improve convective heat transfer compared to a flat interface, reducing the melting time by 20.7

To elucidate the flow field coupling mechanism during water entry of high-speed spinning cylinders, a comparative analysis was conducted on the evolution of the vertical water-entry flow field under non-spinning (omega = 0 rad/s) and varying spin angular velocities (omega = 40, 80, 120 rad/s) by combining a self-developed spinning launch apparatus with Large Eddy Simulation (LES), examining the influence mechanisms of high-speed spinning-induced cavity morphology reconstruction, vortex evolution, and motion characteristics. Experimental results demonstrate that the cavity surface of high-speed spinning cylinders exhibits helical topological structures. While the initial shedding depth of the tail cavity remains consistent across different spin rates, the spin angular velocity intensifies the severity of tail cavity shedding through enhanced wall shear effects. Regulated by tail cavity shedding characteristics, the velocity decay rate during water entry significantly decreases under spinning conditions. Numerical simulations further reveal that high-speed spinning increases the velocity gradient inside the cavity, thereby enlarging the pressure differential across the cavity interface and consequently intensifying vortex breakdown and cavity collapse. Simultaneously, high-speed spinning amplifies the pressure fluctuations and asymmetry on the cylinder surface, leading to more pronounced lateral deflection. These findings provide theoretical and experimental support for the design and motion stability control of Autonomous Underwater Vehicles.

During the storage and use of AlH3, a small amount of H2 is easily decomposed, forming a multiphase composite system that increases explosive hazard. This article discussed the AlH3 dust inducing low concentration H2 explosion and venting characteristics by a connected vessel. The results show that when the concentration of H2 was 1 % and 3 %, which was lower than the lower explosive limit of H2 (4 %), H2 was non-flammable, and the explosion was dust-driven explosion. At H2 volume fraction of 5 %, a dual-fuel-driven explosion dominated, culminating in the maximum explosion pressure, reduced pressure, venting flame length, and velocity. The microscopic reaction mechanism of AlH3 with H2 was explored using molecular dynamics simulations. Meanwhile, for the security strategy of AlH3 dust explosion venting with low H2 atmosphere, the NFPA 68 and EN 14491 standards predicted the venting flame length effectively, offering critical insights for the application and safety design of AlH3.

This paper proposes a two-mirror telescope alignment method based on the on-axis field of view coma and off- axis symmetrical field of view astigmatism, utilizing vector aberration theory based on the aberration field characteristics of a misaligned Ritchey-Chr & eacute;tien (R-C) telescope. A simulation alignment experiment is conducted on an R-C telescope, with random misalignments introduced into the secondary mirror. The alignment is successfully completed after three iterations using the proposed method, demonstrating its feasibility. An actual assembly experiment further validates the proposed method, achieving wave aberration values of 0. 07301 for the on-axis field of view and 0. 08081 and 0. 08341 for the two symmetrical off-axis fields of view, respectively. Experimental results indicate that the proposed method effectively aligns the R-C telescope, ensuring high imaging quality across all fields of view.

Thin-walled perforated structures are widely used in modern industry, where cracks may emanate from the hole edges due to structural loads and manufacturing processes, potentially reducing the reliability of the structure. This paper presents a general solution for stress intensity factors (SIFs) of two asymmetrical radial cracks emanating from a single hole in an infinite isotropic plate, utilizing complex variable theory. Hole shapes, including quasi-square, parabolic, and pentagonal, etc., are considered as instances, and SIFs at crack tips and stress distributions around the hole edge are provided. The analytical solutions are compared with existing literature and finite element method (FEM) results, which confirm the reliability. Under uniaxial tension or pure shear, for quasi-square, parabolic, and pentagonal shapes with equal crack lengths (a/H=0.5), the maximum stress occurs near the geometric vertices. As the crack length increases, the influence of the hole shape diminishes, causing SIF values to approach those of a Griffith crack.

Mixed charge effectively integrates the advantages of different propellant types. However, the irregular particle sizes inherent in this technology pose a challenge in achieving uniform mixing. Traditional two-fluid methods struggle to elucidate the mechanisms of particle dispersion and the resulting disparities in homogeneity. To address this issue, this study introduces the multiple particle element method (MPEM) and applies it to the internal ballistic modeling of mixed charges. Notably, a Gaussian distribution model is introduced to quantify the degree of mixing uniformity within the gun barrel. The internal ballistic process is simulated through coupled calculations between the particle element solver and a computational fluid dynamics solver. The computational results demonstrate that the MPEM accurately predicts the pressure and velocity characteristics within the chamber, aligning closely with experimental data, with deviations confined to within 1%. This study reveals that an increase in web thickness leads to prolonged burning times of the propellant surface, consequently protracting the overall burnout time of the combustion chamber and expanding the distribution range of burnout locations. As the difference in web thickness widens, this distribution disparity becomes more pronounced, accompanied by an escalating pressure wave amplitude. Furthermore, an increase in the standard deviation of mixing uniformity distribution broadens the pressure and velocity distribution ranges. While velocity variability exhibits a decelerating growth trajectory, pressure variability demonstrates an accelerating trend. The MPEM can effectively contribute to improving ballistic performance and safety.

The resin sealing parts obtained by 3D printing have been widely used in underwater sealing due to the ease of adjustment of size. To ensure the successful separation of seals, the blasting line separation technology is used. Numerical simulation and validation experiments are needed to investigate the damage law of resin sealing parts separated underwater. In the separation process of sealing parts, it is necessary to consider the influence of shock wave and hydrodynamic phenomenon generated by initial explosion in finite flow field. In this process, the aspects that need to be focused are the propagation process and damage mechanism of the blast shock wave in the sealed parts, the damage form, and damage mechanism of the hydrodynamic phenomenon on the sealing parts. Numerical simulation of the damage process was carried out using the fluid coupling algorithm in Autodyn, and the damage effects of sealing parts were obtained. The damage effects of the sealing parts were recorded by experiments. The damage effects fit well, verifying the credibility of the simulation. The damage process of sealing parts with different structures (conventional structure and structure with blast isolation groove) was compared, and the influence of structure on damage effect was analyzed. Finally, after validation experiments and simulations, we obtained and verified the damage law of the resin specimen. Besides, we also obtained the effect of the structure of the blast isolation groove on the impact resistance of the specimen.

The evolution form of the flow field generated via the impact of a muzzle jet on a constrained moving body changes from the state of fully free-spatial development to that of constrained development, and it involves the problem of interference, owing to the spatiotemporal coupling of various kinds of shock waves and vortices. Against this backdrop, the authors use the dynamic mesh method to establish two models for simulating the flow field and exploring the mechanism of development and the characteristics of propagation of disturbances induced via the shock waves as the muzzle jet impacts a constrained moving body. The results show that the muzzle jet exhibited a circumferentially asymmetric shape under the influence of the constrained track. The shock wave leaned towards the upper part of the muzzle, and its speed of propagation above the muzzle was higher than that below the muzzle. Meanwhile, the vortex that should have been present below the muzzle disappeared, and it was replaced with a separation line. Changes in the pressure of the flow field and important parameters of the moving body also became more complex due to the influence of the constrained track.

To enhance the prediction accuracy of energetic material combustion processes in balanced launching devices, this paper proposes a multi-physics coupling computational method. The methodology integrates an interior ballistic two-phase flow model with ABAQUS structural dynamics modules (VUAMP, VDLOAD, VDFLUX subroutines), comprehensively accounting for the transient heat transfer between high-temperature combustion gases and barrel structures, gas leakage effects of sealing bands, and the influence of barrel micro-deformation on chamber parameters. The gaseous phase energy equation is modified by incorporating heat loss terms and the dynamic leakage calculation, with the adaptive dynamic mesh technology implemented to address moving boundary challenges. The validation through 65 mm short-barrel balanced artillery experiments demonstrates excellent agreement between simulation results and measured pressure curves as well as muzzle velocities. The findings reveal that the heat loss contributes most significantly to the combustion pressure reduction, followed by the gas leakage, while the barrel micro-deformation has the least impact. This approach presents the quantitative characterization of energy conversion relationships under fluid-structure-thermal coupling effects, providing a high-fidelity analytical tool for the energetic material combustion simulation, with the substantial engineering value for the structural optimization and the safety assessment of launching systems.

To research the damage characteristics of image transmission modules in intense electromagnetic environments, an Electrical Fast Transient (EFT) pulse injection test system was established using a typical unmanned device image transmission system as the research subject. Injection tests were conducted by varying parameters including the injected pulse voltage, frequency, pulse count, and injection points. With an EFT output voltage of 4800 V, the peak current and voltage coupled to the power port, signal input port, and signal output port were measured as follows: $6.8 \mathrm{~A}, 752 \mathrm{~V}; 9.6 \mathrm{~A}, 1040 \mathrm{~V}$; and $17.3 \mathrm{~A}, 1300$ V, respectively. Experimental results indicate: The most vulnerable injection port in unmanned equipment is the signal input port. Under the conditions of 1000 kHz injection frequency, 50 pulse counts, and 116 ms burst intervals, repeated injections were performed. Damage probability increases inversely with injection voltage. The damage threshold of the image transmission module was determined to be 3000 V: At 3000 V, module damage occurred after $\mathbf{1 0} \mathbf{- 1 3}$ injections At 4000 V, damage occurred after 3-5 injections At $\mathbf{4 8 0 0 ~ V}$, damage occurred after 1-3 injections The findings of this study provide critical support and valuable references for developing attack and defense strategies against unmanned systems.