Search Results (556)

This paper proposes a novel method for synthesizing a discrete optimization algorithm based on the moth–flame paradigm for application to the architecture of deceptive systems incorporating decoys and traps. Unlike existing approaches that primarily rely on continuous search spaces or static deception strategies, the proposed method enables the formation of a discrete search space with a coordinate-based representation of deception objects and system states. A spiral search trajectory is synthesized by modeling the dynamic interaction between moths and flames, which allows the algorithm to balance exploration and exploitation effectively and to mitigate premature convergence to local optima. The problem of selecting subsequent operational steps of a deceptive system, which includes the control and reconfiguration of decoys and traps in response to detected events, is formulated as a discrete optimization problem. The objective of this optimization is to increase the effectiveness of cyberattack and malware detection in corporate network environments. The decision variables include the sequence of deception actions, process models, and architectural characteristics of the system, while the constraints are defined by the operational conditions, resource limitations, and structural features of corporate networks. The proposed method supports the identification of an optimal sequence of deception actions under dynamically changing conditions and provides mechanisms for operational adaptation to attacker behavior in real time. This adaptability enables the creation of deceptive systems capable of long-term autonomous operation without continuous administrative intervention, while simultaneously increasing their resistance to adversarial reconnaissance and reverse engineering of their operational principles. The experimental results confirm the feasibility and effectiveness of the proposed approach and demonstrate the potential of integrating population-based optimization algorithms into deceptive system architectures. Comparative analysis shows that the proposed method outperforms its closest competitor, the genetic algorithm, achieving an improvement of 4.82% in terms of the objective function value. Future research directions include deeper integration of population-based optimization methods into decoy-and-trap architectures and the development of a comprehensive framework for organizing their operation in accordance with the proposed conceptual model. Overall, the results contribute to enhancing the cyber-resilience of corporate networks through intelligent, adaptive, and autonomous systems for countering modern cyberattacks and malware. Full article

Explosion venting is an important measure for mitigating gas explosion hazards in confined spaces; however, conventional venting processes often generate high speed, high temperature jet flames, leading to severe secondary hazards. To achieve flameless venting, an experimental study on methane explosions under the coupled effects of dual explosion vents and porous materials was conducted in a confined pipe. Porous silicon carbide foam ceramics with different pore densities (10, 20, and 25 PPI) were installed at the vent openings under various vent layout conditions. Combined with high-speed imaging and dynamic pressure measurements, the flame evolution, jet flame suppression, and explosion overpressure characteristics were systematically analyzed. The results indicate that porous materials effectively attenuate jet flame intensity without compromising venting efficiency and increasing pore density significantly enhances flame-quenching performance. In addition, explosion vents located closer to the ignition source facilitate earlier energy release, thereby improving the reliability of flameless venting. Full article

Advances in high-performance computing have expanded the use of computational fluid dynamics (CFD) for reacting-flow analysis; however, simulations involving detailed flame kinetics remain computationally intensive for many practical systems. Efficient modeling approaches are therefore essential for predicting flame behavior in swirl-stabilized combustors. This study examines the influence of main-stage swirl intensity on near-lean blow-off characteristics in a multistage swirl combustor using a hybrid RANS–LES framework. The Stress Blended Eddy Simulation (SBES) model, coupled with a Flamelet Generated Manifold (FGM) combustion formulation, is employed to capture key turbulence–chemistry interactions. Results indicate that reducing swirl intensity suppresses the formation of a swirl-stabilized flame, while excessive swirl negatively affects emission performance. For the baseline (S2) and high-swirl (S3) configurations, flame lift-off height increases by 21.0% and 11.96%, respectively, for every 0.1 reduction in equivalence ratio. The S3 case also demonstrates reduced combustion efficiency, with CO emissions rising by 156.4% relative to S2. Local flame extinction is observed in regions of strong droplet–flame interaction, highlighting enhanced quenching susceptibility under near-blow-off conditions. The present study investigates the flame dynamics in a multi-stage swirl combustor using high-fidelity CFD simulations. This study has yet to be validated through experimental analysis and the results presented in this work are entirely computational. Further experimental validation is necessary to verify the results. Full article

Aiming at the insufficient integration of real-gas effects and the unclear parameter influence mechanisms in predicting high-pressure hydrogen leakage flame length, this paper proposes a refined predictive model that systematically incorporates the real-gas critical flow factor ($C_r^{*}$). By dynamically correcting the mass flow rate calculation under high-pressure conditions, the model significantly improves prediction accuracy (relative error in mass flow rate < 3%). A parametric analysis reveals that the flame length is approximately three times more sensitive to the leakage orifice diameter than to the storage pressure ($L\propto D^{1.041}{P}_0^{0.347}$), providing a quantitative basis for inherent safety design. Validated by experimental datasets, the model demonstrates good accuracy. It can be employed for safety distance demarcation and risk assessment at hydrogen refueling stations and storage facilities. Full article

The paper presents computational fluid dynamics (CFD) simulations of a propane-fueled and under-ventilated fire in a reduced-scale corridor-like enclosure. The fire source is positioned at the closed end of the corridor. Due to the restricted inflow of oxygen, the flame lifts off from the gaseous burner and travels—along with unburned fuel—all the way to the open doorway at the opposite end of the corridor. Oxygen calorimetry shows that a quasi-steady state plateau is established, during which the heat release rate (HRR) within the enclosure is equal to the theoretical value ${\dot{Q}}_{in}=1500 A_o\sqrt{H_o}$ where $A_o\sqrt{H_o}$ is the ventilation factor. Then, external flaming occurs. CFD simulations with the Fire Dynamics Simulator (FDS) captured well the overall flame dynamics. More specifically, the HRR plateau is well predicted, provided that the actual autoignition temperature of propane, AIT = 450 °C, is prescribed instead of the default AIT = −273 °C. However, the occurrence time of external flaming remains significantly underestimated and is better predicted by setting AIT = 600 °C. This aspect of the modelling, linked to extinction and (re-)ignition, remains to be further investigated in the future. Full article

Trouble sleeping has become a global public health challenge. However, the relationship between organophosphate flame retardant (OPFR) exposure and trouble sleeping remains unclear. This study integrated epidemiological analysis, network toxicology, molecular docking, molecular dynamics simulations, and adverse outcome pathway (AOP) construction to identify OPFRs linked to trouble sleeping and attempted to elucidate underlying molecular mechanisms. We analyzed cross-sectional data from the U.S. National Health and Nutrition Examination Survey (NHANES 2013–2018) involving 4585 eligible adults. Logistic regression confirmed dibutyl phosphate (DBuP) as significantly correlated with trouble sleeping. Restricted cubic splines (RCSs) revealed a significant non-linear, J-shaped relationship between dibutyl phosphate (DBuP) levels and trouble sleeping. Weighted quantile sum (WQS) analysis determined that DBuP accounted for the majority contribution (58.23%) to the observed effects within exposure mixtures. These findings indicated that DBuP, a metabolite of tributyl phosphate (TnBP), was closely related to trouble sleeping, suggesting that the environmental health risks of TnBP may be jointly contributed to by itself and DBuP. We used network analysis to identify five core target genes (PPARG, MMP9, PTGS2, APP, EGFR) that interact with DBuP and its parent compound TnBP. Molecular docking predicted binding poses of TnBP and DBuP toward these five core targets; all showed moderate binding affinity (ΔG ≤ −5.0 kcal/mol) except MMP9, which exhibited weak binding. Molecular dynamics simulations further supported this putative binding. Enrichment analysis highlighted inflammatory response pathways. Ultimately, we elucidated the process from molecular exposure to trouble sleeping by constructing an AOP framework. In conclusion, we proposed that TnBP and DBuP may contribute to trouble sleeping through multi-target interactions, primarily through PPARG-driven inflammatory dysregulation. These findings suggest a potential link between OPFR exposure and trouble sleeping, providing insights that warrant further mechanistic investigation. Full article

High-velocity oxygen fuel (HVOF) spraying technology has been widely used to protect and repair the surface of mechanical parts and extend their service life. Spraying Fe-based amorphous alloy coatings can improve the corrosion resistance and fatigue resistance of the substrate. It is crucial to quantitatively elucidate the influence of process parameters on spraying behavior to achieve high-quality coatings. This study utilized a computational fluid-dynamics model to analyze the flight trajectories of flames and particles during HVOF spraying. Additionally, how parameters such as the O/F ratio, parallel barrel length, Laval nozzle diameter, and nitrogen flow rate affect flame and particle behavior was examined. These parameters were found to significantly impact the overall spraying process. As a result, the optimum structure and properties are obtained. In this study, the spray gun parameters were investigated to provide better guidance for the process and improve the quality and efficiency of the coating system. Full article

This study investigated premixed NH₃ combustion in a closed circular duct using two-dimensional numerical simulations. By varying the equivalence ratio and the oxygen volume fraction from 21% to 30%, the evolution of flame morphology, flame propagation velocity, flame surface area, as well as the temporal variations in duct-averaged temperature and pressure were systematically examined. In addition, sensitivity analysis and reaction-pathway analysis based on a detailed chemical kinetic mechanism were performed to clarify the coupling between local chemical reactions and global flow dynamics. The results showed that the flame generally evolves through a sequence of hemispherical, finger-shaped, wall-attached skirt, and planar finger- and tulip-shaped structures. Well-developed tulip flames are mainly observed under conditions close to stoichiometric composition with moderate to elevated oxygen enrichment, corresponding to an intermediate overall reactivity. As the oxygen volume fraction increases from 21% to 30%, flame propagation becomes markedly faster. The tube-averaged temperature and the peak overpressure show an overall increasing trend. This increase in overpressure is most pronounced at equivalence ratios of 1.0–1.2. This study identifies hazardous parameter ranges in oxygen-enriched NH₃ combustion that are prone to producing strong tulip flames and high overpressure, providing useful guidance for explosion risk assessment and safety-oriented design of NH₃-fueled combustion systems. Full article

Modern high-speed train compartments contain intricate internal configurations. In the event of a fire emergency, the propagation velocity of flames through the passenger cabin is determined by multiple factors, including compartment design, ignition source characteristics, and airflow conditions. This study employed computational fluid dynamics (CFD) and large eddy simulation (LES) to investigate the effects of fire source power, fire source location, and longitudinal ventilation velocity on the rate of flame progression. Unlike simplified homogeneous fuel models, this study incorporates the specific heterogeneous material layout of the CR400AF to capture realistic flame spread dynamics. The simulation results reveal that, under forward ventilation conditions, the magnitude of fire power has a minimal influence on flame propagation speed. However, stronger fire sources lead to earlier initiation of flame spread along the carriage. Central positioning of the ignition source results in bidirectional flame movement toward both ends of the carriage, with faster propagation rates than those of fires originating at the extremities. Longitudinal airflow patterns significantly influence the fire dynamics. When the airflow speed within the tunnel remains below 3 m/s, the impact of longitudinal ventilation on fire propagation speed in the train is minimal under forward ventilation conditions. Conversely, in reverse-ventilation scenarios, the rate of flame advancement shows a positive correlation with increasing ventilation speed. Nevertheless, once tunnel ventilation velocities exceed 3 m/s, combustion propagation within high-speed rail carriages becomes impossible due to intact windows, which create oxygen-deficient conditions that prevent the development of fire. This paper investigates the heat release rate and spread process of vehicle fires. It comprehensively considers the effects of fire source power, fire source location, and longitudinal ventilation rate on the rate of spread. The research results provide data support for the fire-resistant design of rail transit vehicles and for the formulation of emergency evacuation strategies for different fire scenarios, which are vital for enhancing rail vehicle fire safety and ensuring personnel evacuation safety. Full article

The rapid spread of fires underscores the urgency of high-accuracy fire smoke detection for public safety, but early fires pose major challenges—small flame/smoke targets, blurred boundaries, low contrast, and complex background interference—limiting the performance of existing models. To address these issues, this paper proposes SFFA-YOLO, an engineering-oriented improved algorithm based on the YOLOv11 framework for fire smoke detection, which achieves a balanced trade-off between detection precision, real-time performance, and lightweight deployment. The model integrates three synergistic optimization modules for targeted scene adaptation: (1) the FMFA module for cross-scale feature fusion to enhance thin smoke and small flame recognition; (2) the SGCA module for joint channel-spatial feature focusing to improve target localization accuracy; (3) the SDA-Loss function for dynamic weight adjustment based on target size and clarity to stabilize small target detection. Validated on the self-built FS-Blend dataset (supplemented with difficult samples such as distant thin smoke and backlit flames), SFFA-YOLO outperforms mainstream models (YOLOv8, YOLOv9, Faster R-CNN) in key metrics. Compared with the YOLOv11s baseline, it achieves a 2.5% Precision improvement and 3.9% mAP@0.5 improvement while reducing parameters by 12.8%, confirming its reliability as a real-time fire smoke detection solution. Full article

Accurately predicting molten steel carbon content plays a crucial role in improving productivity and energy efficiency during the Basic Oxygen Furnace (BOF) steelmaking process. However, current data-driven methods primarily focus on endpoint carbon content prediction, while lacking sufficient investigation into real-time curve forecasting during the blowing process, which hinders real-time closed-loop BOF control. In this article, a novel Transformer-based framework is presented for real-time carbon content prediction. The contributions include three main aspects. First, the prediction paradigm is reconstructed by converting the regression task into a sequence classification task, which demonstrates superior robustness and accuracy compared to traditional regression methods. Second, the focus is shifted from traditional endpoint-only forecasting to long-term prediction by introducing a Transformer-based model for continuous, real-time prediction of carbon content. Last, spatial–temporal feature representation is enhanced by integrating an optical flow channel with the original RGB channels, and the resulting four-channel input tensor effectively captures the dynamic characteristics of the converter mouth flame. Experimental results on an independent test dataset demonstrate favorable performance of the proposed framework in predicting carbon content trajectories. The model achieves high accuracy, reaching 84% during the critical decarburization endpoint phase where carbon content decreases from 0.0829 to 0.0440, and delivers predictions with approximately 75% of errors within ±0.05. Such performance demonstrates the practical potential for supporting intelligent BOF steelmaking. Full article

The liner temperature distribution of an aero-engine combustor is a critical parameter for evaluating its cooling effectiveness. It provides essential guidance for designing the combustor cooling flow field, assessing combustion performance, identifying critical regions, and predicting service life. However, current research on surface temperature field measurements in real or model aero-engine combustors remains limited. Existing studies focus primarily on the liner temperature measurement under near-steady-state conditions, with less attention to its dynamic changes. This study employs Laser-Induced Phosphorescence (LIP) thermometry to measure the effusion-cooled liner temperature field of an aero-engine model combustor under various CH₄/Air swirling premixed flame conditions and varying blowing ratios. Based on the geometric characteristics of the effusion-cooled liner, an optimization method for matching phosphorescence images of different wavelengths is proposed. This enhances the applicability of phosphorescence intensity ratio-based LIP thermometry in high-vibration environments. The study specifically focuses on the dynamic response of LIP thermometry for monitoring combustor liner temperature. The instantaneous effects of blowing ratio variations on liner temperature rise rates were investigated. Additionally, the influence mechanisms of a broad range of combustion conditions and the blowing ratios on the combustor liner temperature distribution and cooling effectiveness were examined. These findings provide theoretical and technical support for cooling design and dynamic liner temperature field measurement in real aero-engine combustors. Full article

This study presents a detailed numerical analysis of impinging propane flames within confined enclosures using the Fire Dynamics Simulator (FDS, v6.5.3). Two archetypal configurations were examined: (i) free buoyant plumes in unconfined environments, and (ii) ceiling-impinging flames under both open and confined conditions. The investigation encompassed a range of heat release rates (0.5–18.6 kW) and five degrees of ventilation confinement. The simulation results confirm that FDS reliably reproduces flame height evolution under free plume conditions, exhibiting strong consistency with Heskestad’s empirical correlation and available experimental benchmarks. Under ceiling impingement, confinement markedly influences the thermal field, the distribution of major gas species (O₂, CO₂, C₃H₈), and the accumulation of unburnt gas. Distinct from previous works primarily centered on unconfined plume dynamics, the present study systematically characterizes the onset of auto-ignition through combined lower flammability limit (LFL) and auto-ignition temperature (AIT) criteria for confined propane combustion. The highest auto-ignition risk was identified in partially confined configurations (Conf. 2 and Conf. 3) at an HRR of 18.6 kW, where unburnt propane concentrations locally exceeded the LFL (≈0.2%) and ceiling temperatures surpassed the AIT of propane (455 °C). The findings elucidate critical trade-offs between ventilation and safety. They also contribute to a validated FDS-based methodology for evaluating fire-induced flow structures, combustion behavior, and ignition hazards in confined spaces. Full article

In the present work, three-dimensional (3D) simulations have been performed for the characterization of a rectangular column for a uniform gas distributor with µm-sized holes at a ratio of 5. The model is first validated with experimental data from the literature. Simulations are then performed for a gas distributor with identical pitch but two different hole sizes, namely 600 µm and 200 µm. Three superficial gas velocities, namely 0.002 m/s, 0.004 m/s, and 0.006 m/s, were used for each distributor type. The gas movement in the fluid is found to be a strong function of hole size. For a 600 µm hole size, the operating condition has minimal impact on gas plume movement and moves centrally in a fully aerated regime. However, for a hole size of 200 µm, for all superficial velocities, the gas plume movement is dynamic and partially aerated. The plume moves along the right wall initially and then follows vertically. These characteristics are different from the meandering plume in centrally located spargers. The liquid mixing in the bulk is a function of time. During the plume development flow, different shapes are observed. Based on the analogy with the shapes found in nature, these shapes have been termed as balloon, cap, jet or candle flame, bull horn, mushroom, tree shape, and disintegrated mushroom shapes. Quantitative insights have been obtained in the form of time-averaged radial profiles of both volume fractions and liquid axial velocities. A symmetric parabolic shape for a hole size of 600 µm and skewed asymmetric shapes for a 200 µm hole size for three different axial positions, namely 0.1, 0.25, and 0.4 m, are observed. Correlations for gas holdup and liquid velocity have been proposed for low superficial velocities, which are in good agreement with the CFD simulation data, with a deviation of 15–20%. The deviations are partly due to the use of the k-ε turbulent model. The correlations perform better than the correlations available in the reported literature for similar superficial gas velocities. Full article

Three-dimensional computational fluid dynamics (CFD) simulation was performed using the eddy-dissipation concept coupled with detailed hydrogen oxidation kinetics and a reduced two-step methane mechanism for a newly proposed W-shaped radiant tube burner (RTB). The effects of the hydrogen volume fraction (0–100%) and excess air ratio (0%, 10%, 20%) on the flame morphology, temperature distribution, and NO_X emissions are systematically analyzed. The results deliver three main points. First, a flame-shape transformation was identified in which the near-injector flame changes from a triangular attached mode to a splitting mode as the mixture reactivity increases with the transition occurring at a characteristic laminar flame speed window of about 0.33 to 0.36 m/s. Second, NO_X shows non-monotonic behavior with dilution, and 10% excess air can produce higher NO_X than 0% or 20% because OH radical enhancement locally promotes thermal NO pathways despite partial cooling. Third, a multi-parameter coupling strategy was established showing that hydrogen enrichment raises the maximum gas temperature by roughly 100 to 200 K from 0% to 100% H₂, while higher excess air improves axial temperature uniformity and can suppress NO_X if over-dilution is avoided. These findings provide a quantitative operating map for balancing stability, uniform heating, and NO_X–CO trade-offs in hydrogen-enriched industrial RTBs. Full article