To effectively prevent explosion hazards during propylene production, storage, and utilization, the explosion limits of propylene in air under varying initial temperatures (20 ℃–180 ℃) and initial pressures (0.1 MPa–0.9 MPa) were measured using 12L explosion limit tester. The study revealed that as the initial temperature and pressure increase, the upper explosion limit (UEL) of propylene rises significantly, while the lower explosion limit (LEL) decreases slightly, resulting in a marked broadening of the explosion limit range. At an initial temperature of 180 ℃, with the pressure increases, the carbon powder content in the explosive products significantly increases during the UEL test, and the LEL decline transitions from a linear to a sliding-curve pattern. Analysis using CHETAH 11.0 software revealed that the increase in carbon powder content is closely related to thermodynamic properties under high-temperature and high-pressure conditions. When the pressure rises from 0.1 MPa to 0.9 MPa, the carbon powder content in the explosion products surges from 3.82% to 25.88%. This significant growth primarily stems from two factors: first, high-pressure conditions promote the Boudouard reaction toward carbon formation; second, the increased total amount of reactants under high pressure leads to a multiplicative rise in product quantities.Using CHEMKIN software, the combustion characteristics of propylene under lower explosion limit conditions were investigated. In the fuel-lean region, propylene undergoes free radical chain reactions, ultimately generating CO₂, which maintains the calculated adiabatic flame temperature (CAFT) above 1400 K. As pressure increases, CAFT gradually decreases. Meanwhile, with rising temperature, CAFT exhibits a pressure-dependent transition: at low pressures (<0.5 MPa), CAFT increases, whereas at high pressures, it decreases, with 0.5 MPa serving as the critical transition threshold. The coupling effects of initial temperature and pressure on explosion limits are far more pronounced than those of individual factors, with a stronger impact on the UEL than the LEL. The coupling effects caused a 108% increase in the UEL and an 18.05% decrease in the LEL. For individual factors, initial temperature alone led to a 3.8% UEL increase and a 3.41% LEL decrease, while initial pressure alone resulted in a 51.3% UEL increase and 2.44% LEL reduction.

The detonation-driven expansion and fracture behavior of single-layer and double-layer metallic cylindrical shells (with equal total thickness) were investigated via the DPS (Doppler pins system) array and high-speed photography. The velocity curves and high-speed photography images of the outer surface of the single- and double-layer cylindrical shells were obtained. The velocity curves show that spallation occurs at approximately 40% of the thickness from the outer surface in the single-layer cylindrical shell. In addition, the spallation part was caught up after ~1.89 μs by the fragments of the single-layer cylindrical shell, leading to the secondary impact loading. In the case of double-layer cylindrical shell, the inner and outer shells of the double-layer cylindrical shell separated quickly since they cannot withstand the tensile stress. The outer cylindrical shell expands freely with high velocity at initial stage. It is then caught up by the inner cylindrical shell after 26.13 μs, leading to the secondary impact loading. There is a significant difference in secondary impact loading times the single- and double-layer shell expansion experiments. The premature separation of the double-layer cylindrical shell hinders the crack penetration from the inside to the outside, and delays the crack penetration until the complete fracture of the whole cylindrical shell. In contrast to the widely investigated fracture behavior in a single-layer cylindrical shell, the detonation product leakage time is delayed when the outer layer of the double-layer cylindrical shell expands. The fragment size of a double-layer shell is obviously smaller than that of a single-layer shell. The distribution of the overflowing detonation product is relatively scattered and rare, and the overall crack of the outer cylindrical shell is clearly visible. The results of SPH (smoothed particle hydrodynamics) numerical simulations demonstrate that under certain conditions, the lower the spallation strength in single-layer cylindrical shells, the later the residual fragments catch up with the spalled layer during secondary loading, the less likely the occurrence of penetration fracture. Meanwhile, the interfacial gaps in double-layer cylindrical shells significantly inhibit the penetration and propagation of cracks.

To investigate the complex wake flow characteristics of multi-motor parallel rocket sleds, this study focuses on the mechanisms by which the nozzle horizontal spacing and the impingement height influence the flow structure and ground effect. A three-dimensional physical model was constructed for a dual-rail rocket sled system featuring three nozzles arranged in a triangular pyramid configuration. Four operating conditions were established, including large spacing (s=7d), small spacing (s=1d), low impingement height (h=2d), and high impingement height (h=5.5d). Here, s represents the horizontal center-to-center distance of the nozzles, h denotes the impact height, and d signifies the diameter of the nozzle outlet. The effects of nozzle center distance and impingement height on the flow field structure and ground effect were comparatively analyzed. Numerical simulations were performed using a computational fluid dynamics (CFD) method based on the Reynolds-Averaged Navier-Stokes equations, coupled with the Realizable k-ε turbulence model for transient solutions. The combustion chamber pressure-time curve derived from interior ballistic theory was applied to the nozzle inlet via a user-defined function (UDF). The sled velocity-time curve, determined from the exterior ballistic particle trajectory equation, was assigned as the far-field pressure boundary condition, enabling a coupled simulation framework of interior ballistics, exterior ballistics and flow field. The computational domain utilized a structured grid with refinement in the jet interaction region and near the ground to ensure calculation accuracy. The velocity and pressure fields obtained from numerical simulations were compared and validated against jet morphology, impingement height, and vortex core positions recorded by high-speed photography (2000 Hz). The flow field structure, pressure distribution, and thermal erosion behavior on the ground under different configurations are systematically revealed. The results indicate that the small-spacing nozzle arrangement triggers intense jet interference without ground effect participation, leading to a multi-peak and slow-recovery pressure evolution feature and substantially delays the flow field relaxation process. The coupling relationship between ground effect and jet interference is dominated by impingement height. At low impingement height conditions, the jet impinging on the ground induces intense reorganization and fragmentation of vortex structures, generating wall jets with velocities up to 960 m/s. Consequently, the peak ground surface temperatures reaches 1286.6 K with sustained high temperatures, which significantly elevates the risk of rail ablation. Conversely, a high impingement height effectively suppresses the ground effect, resulting in a more homogeneous and stable flow field structure. In this case, the peak ground temperature reduced by approximately 65% and maximum velocity reduced by 58%, significantly mitigating ablation risk. The initial phase (0－8 m) of the rocket sled is identified as the critical region subjected to the most severe thermomechanical loads. During this stage, the average acceleration reaches 832.7 m/s², and the specific action time per unit distance is prolonged to 1.84 ms/m. Coupled with the transient complex flow field, this constitutes an extremely high risk for rail ablation. The numerical simulation results show excellent agreement with high-speed photographic experimental data regarding flow field morphology, impingement height, and vortex core positions, thereby validating the reliability of the established coupled model. This study elucidates the complex flow mechanisms of multi-nozzle parallel systems under strongly constrained conditions, and provids important theoretical foundations and design parameters for structural layout optimization and thermal protection design in high-acceleration, heavy-load rocket sled test systems.

To investigate the effects of inlet pressure perturbations on the propagation characteristics of rotating detonation waves (RDWs), numerical simulations were conducted using the OpenFOAM platform and the two-dimensional Euler equations coupled with detailed chemical kinetics. A two-dimensional unfolded rotating detonation combustor model was established to represent the annular chamber. Periodic boundary conditions were applied in the circumferential direction, and non-reflecting boundary conditions were imposed at the outlet. Discretized premixed injection units were specified at the inlet to simulate the reactant supply process. High-frequency, small-amplitude pressure perturbations with a frequency of 5 kHz and an amplitude of 0.1 MPa were superimposed on the inlet total pressure with a mean value of 1 MPa, while the inlet total temperature was fixed at 300 K. Hydrogen–air mixtures with equivalence ratios ranging from 0.6 to 1.6 were considered to examine the influence of reactant composition on RDW behavior under perturbed inlet conditions. The governing equations were solved using a density-based compressible reacting-flow solver with a finite-volume discretization scheme. Convective fluxes were calculated using the KNP central-upwind scheme with a van Leer limiter, and time integration was performed using a second-order Crank-Nicolson method. A detailed hydrogen–air chemical reaction mechanism consisting of 27 elementary reactions was employed to capture detonation dynamics. The results indicate that the RDW wavenumber and propagation mode exhibit significant responses to inlet pressure perturbations at different equivalence ratios, which are mainly governed by the dual-wave collision process and the reactant replenishment characteristics ahead of the detonation front. The combustor adaptively balances the energy release and stable RDW propagation, allowing the system to stabilize at different wavenumbers through a nonlinear dynamic equilibrium. Under inlet pressure perturbations, flow parameters and RDW characteristics exhibit periodic responses at the perturbation frequency, with the RDW structure being more sensitive to the perturbations. The equivalence ratio and RDW propagation mode jointly determine the combustion heat release level and the outlet thrust, whereas the specific impulse is primarily controlled by the equivalence ratio and shows a weak correlation with the RDW wavenumber. High-frequency, small-amplitude inlet pressure perturbations mainly affect the wave structure and propagation mode of RDWs, while the mean performance parameters are only weakly influenced.

Traditional homogenization models have difficulty accurately capturing the mesoscale effects of aggregate distribution, aggregate particle size, and reinforcement configuration on stress-wave propagation paths and energy-dissipation mechanisms in concrete, thereby limiting an in-depth understanding of the blast-induced failure mechanisms of reinforced concrete slabs. To address this issue, a three-dimensional mesoscale finite element model of reinforced concrete slabs incorporating reinforcement, aggregates, and mortar matrix was established through the combined use of MATLAB and LS-DYNA. The aggregates were modeled according to actual aggregate gradation characteristics, the reinforcing bars were accurately arranged based on practical engineering layout parameters, and appropriate contact algorithms were adopted among the matrix, aggregates, and reinforcing bars to simulate interfacial effects. The model was validated against contact explosion tests, and the results show that it can predict the failure modes and crater dimensions of reinforced concrete slabs subjected to contact explosion loads with reasonable accuracy. On this basis, the effects of aggregate characteristics, including distribution pattern and particle size, and reinforcement arrangement on the blast resistance and stress-wave propagation behavior of reinforced concrete were investigated through parametric mesoscale numerical simulations. Regarding the aggregate parameters, the particle-size distribution pattern and aggregate size govern the evolution of stress waves and energy-dissipation characteristics, thereby affecting the geometric dimensions of the craters on the top surface and the spalling craters on the bottom surface of the concrete slab. When the aggregate particle size decreases from the top surface to the bottom surface, the expansion of the top-surface crater and the development of bottom-surface spalling can be effectively suppressed; in contrast, an increasing particle-size distribution aggravates surface cratering and internal spalling damage. In terms of aggregate size, the bottom-surface spalling craters of slabs containing small aggregates exhibit shallow and wide characteristics, whereas those containing large aggregates exhibit deep and narrow morphologies. Compared with aggregates, reinforcing bars exert a weaker influence on the overall failure mode and stress-wave propagation behavior of the slab. At a low reinforcement ratio, the reinforcing bars have little effect on the dynamic transmission of compressive stress peaks, whereas under high explosion loads, they suppress slab fragmentation, mitigate flexural damage, and improve the structural integrity and damage resistance of the slab.

To evaluate the crater damage effect of cylinder charge contact explosion on steel fiber reinforced concrete (SFRC) structures, a numerical model of an SFRC target was developed by the using the smooth particle Galerkin method and a structured arbitrary Lagrange-Euler (SPG-S-ALE) fluid-structure interaction algorithm. The failure modes and damage of the SFRC target under different charge mass Q and length-to-diameter ratios l/d were investigated. Based on contact explosion theory and dimensional analysis, cratering coefficients K₁ and K₂ were introduced to develop predictive models for the crater diameter D and depth H as functions of the effective charge mass Q_e. The results indicate that under the combined effects of charge mass and length-to-to-diameter ratio, the primary failure mode of the SFRC targets is cratering damage. Under constant charge mass conditions, as the l/d ratio increases from 1 to 5, both the crater diameter D and depth H decrease by approximately 50%. Within the range of effective charge Qₑ less than 16 kg, the K₁ and$ {\sqrt{{K}_{2}}} $ exhibit a power-law decay with increasing effective charge mass, while the crater diameter D and depth H show a power-law growth. For a given effective charge mass Qₑ, the cratering effect is more concentrated on the expansion of the crater diameter. The developed predictive model allows for rapid and reasonably accurate calculation of crater dimensions in SFRC with different strength grades and effective charge mass, providing a theoretical basis for the blast-resistant design of SFRC structures.

In order to compare the similarities and differences among the self-sharpening behavior as well as the corresponding ballistic performance of tungsten fiber/metallic glass matrix (WF/MG) composite long rod projectile with different fiber diameters, the deformation and failure characteristics of various WF/MG composite long rod projectile were investigated systematically integrated with related penetration test results and mesoscopic finite element (FE) simulation analysis. The two-dimensional (2D) and three-dimensional (3D) meso-scale FE geometric models of WF/MG composite long rod projectile were established according to the actual distribution characteristics of metallic glass matrix and tungsten fibers. A coupled ‘thermo-mechanical-free volume’ constitutive model was applied to characterize the high shear sensitivity as well as high strength of metallic glass matrix. Moreover, the transformation of deformation and failure modes of projectiles under different impact velocities was analyzed in detail. Related analysis demonstrated that due to the differences in the mechanical properties among the tungsten fibers with different diameters, i.e., bending resistance and shear resistance, etc., the corresponding composite long rod projectile exhibit different failure characteristics during the penetration process, which further affects their penetration/perforation performance. The impact velocity also plays an important role on the deformation and failure modes of composite long rod projectile and the corresponding penetration/perforation performance. When the impact velocity is relatively low, the fibers in the nose of composite rod projectile exhibits unstable buckling phenomenon and gradually disperse during the penetration process, which makes the projectile nose blunt at a certain extent. This induces the increase in the penetration resistance and decrease in the penetration performance. As the impact velocity increases, small-diameter fibers reflux along the nose periphery while large-diameter fibers fail in shear. The large-diameter fiber further strengthens the self-sharpening behavior as well as the penetration performance of projectile. When the impact velocity and fiber diameter reach a certain upper threshold values, the thickness of ‘edge layer’ in the rod nose is sharply reduced, and thus the self-sharpening performance is weakened, and the penetration capability of projectile is decayed again. Related research is beneficial to predicting the penetration/perforation performance of WF/MG composite long rod projectiles with different fiber diameters under different impact velocities, and optimizing the structural design of projectile as well as the impact velocity, etc.

Projectile’s structural vibration during high-speed penetration of hard targets is an important factor causing mixed overload signals and charge’s localized-deformation magnification issues, which restricts the destructive capability of projectiles. To accurately characterize the elastic vibration characteristics of the penetrating projectile, a refined theoretical modal modeling method for the projectile was derived based on the theories of variable cross-section rods. Furthermore, two 30-kg mass projectiles with the same mass and outline but different internal cavity structures were manufactured, together with an even hollow cylindrical bar with the same mass and outer diameter. Using these three structures as examples, theory test and simulation mode analyses were conducted to explore the modal features of the projectile from the perspectives of characteristic frequencies and their corresponding low-order tensile-compressive modes. The structural similarities and differences between projectile and even bar were compared, and the influence of charges on projectile modes was explored. Eventually, the vibration characteristics of the projectile penetrating semi-infinite and multi-layer concrete targets were deduced with the introduction of projectile’s modal characteristics measured separately. Research has shown that the Mindlin-Herrmann rod models have derived similar modal characteristic compared with simulation and test results, while the even bar model shows larger discrepancies. In weak load environments, the charge increases the structural damping, and the higher the modal order of the projectile, the weaker the coupling relationship between the projectile and the charge. However, the applicability of this conclusion in harsh load environments still needs to be explored. The low-order tensile-compressive modes dominate the vibration characteristics of the penetrating projectile, and the deformation and overload distribution are mostly affected by the first-order tensile-compressive mode, while the high-order modes supplement the vibration of the projectile. Benefiting from the variable cross-section effect, projectiles with short and concentrated inner cavities have better anti-vibration characteristics during ideal penetration. Projectile’s vibration characteristics obtained through modal analysis provides more reliable guidance for the design of the projectile-fuse-charge system.

To address the challenges posed by insufficient statistical sampling density and inherent irreducible uncertainties in multi-physical property detonation experiments, probability learning on manifold (PLoM) involving diffusion map and Itô projection sampling are used to generate sufficient dataset satisfying the detonation physical mechanism and therefore, to fulfill the uncertainty quantification of experiment. Firstly, scale transformation is implemented on the experimental data with multi-physical asset of insensitive high explosive PBX9502. The training set is obtained through the normalization of the scale matrix by means of principal component analysis. Secondly, an improved high-dimensional Gaussian kernel density estimation is utilized to calibrate the probability measure of the random matrix associated with the training dataset. Diffusion map is used to deduce the nonlinear manifold based on the training dataset. Sampling on the manifold is fulfilled through Itô-MCMC generator defined by a dissipative Hamilton system driven by the Wiener process. Finally, the learning set is obtained via inverse transformation. The result shows that the Gaussian statistics obtained from random numbers generated by PLoM coincide with the statistical information of density of PBX9502 calibrated in the literature. Furthermore, the double logarithm model related to the distance to detonation and initial impact stress is constructed through the data generated. It also holds for the relationship between the time of detonation and initial shock stress. Fitting precision of the curve is almost equivalent to the accuracy of result in literature, however the cost is negligible. More accurate digital test result is obtained through the learning and processing of existing experimental data via PLoM. The PLoM method demonstrates strong generalization capability, enabling its extension to detonation experiments with various types of explosive.

The research addresses the safety imperative of preventing flammable gas explosions in enclosed pipelines by establishing a predictive model for the critical quenching diameter within porous media flame arresters. A novel predictive framework was developed based on a comprehensive nine-dimensional feature space incorporating gas composition parameters (e.g., hydrogen equivalence ratio), pipeline geometry dimensions (length-to-diameter ratio), initial thermodynamic conditions (pressure), and porous medium structural characteristics (thickness, material thermal conductivity). A systematic investigation was conducted to identify the optimal hyperparameter configurations for both convolutional neural network (CNN) and Transformer architectures. Rigorous validation demonstrated that the Transformer model exhibits statistically significant superiority over the CNN model across all key performance metrics. Specifically, the model achieved a δ_MAE (mean absolute error, MAE) of 0.068, a δ_MSE (mean squared error, MSE) of 0.008, and an coefficient of determination R² of 0.928. The performance notably surpassed the CNN results (δ_MAE=0.079, δ_MSE=0.012, R²=0.906). Beyond evaluation indicators, detailed error distribution analysis confirmed the Transformer's enhanced predictive accuracy and reduced susceptibility to outliers. The superior performance is attributed to the Transformer’s intrinsic self-attention mechanism, which excels at dynamically identifying and weighting critical interdependencies among the diverse input features governing the complex quenching process. The capability enables more precise capture of the nonlinear phenomena defining the quenching limit. Furthermore, robustness testing involving diverse data normalization schemes revealed that the Transformer model exhibits greater stability. This resilience stems from its inherent layer normalization mechanism, which effectively decouples feature dependencies and mitigates sensitivity to input scaling variations. Consequently, the Transformer architecture is established as the definitive optimal model for this critical safety prediction task. Its significant advantage lies in the minimal data preprocessing required before deployment, a feature that greatly enhances its practical utility. The model provides robust quantitative decision-making support essential for formulating effective gas explosion mitigation strategies and optimizing the safety design parameters of pipeline flame arresters. By accurately predicting the critical quenching diameter across various scenarios, this work delivers a valuable tool for enhancing inherent safety in industries handling combustible gases within confined pipeline systems.