Search Results (619)

Current understanding of the load-transfer mechanism in the skeletal contact state of asphalt mixtures and its influence on macroscopic mechanical properties remains insufficient. This knowledge gap leads to difficulties in accurately predicting the performance of designed mixtures, thereby restricting the service life of asphalt pavements and the sustainable development of road engineering. This study investigated the skeletal contact characteristics, coarse aggregate movement, and crack propagation of three asphalt mixture types—Stone Mastic Asphalt (SMA), Asphalt Concrete (AC), and Open-Graded Friction Course (OGFC)—under loading. The methodology incorporated Computed Tomography (CT) technology, a Voronoi diagram-based skeletal contact evaluation method, and discrete element numerical simulation. The research aimed to elucidate the influence mechanisms of different skeletal structures on macroscopic performance and to validate the efficacy of the skeletal contact evaluation method. The findings revealed that under splitting load, the tensile stress contact force chains within the asphalt mixture’s skeleton were predominantly distributed along both sides of the specimen’s central axis. For all three gradations, compressive stress contact force chains (points) accounted for over 65% of the total, indicating that the asphalt mixture skeleton primarily bore and transmitted compressive stresses. The interlocking structure formed by coarse aggregates significantly enhanced the stability of the asphalt mixture skeleton, reduced its displacement under load, and improved the mixture’s resistance to cracking. In the three gradations, shear stress-induced cracks outnumbered those caused by tensile stress, with shear stress cracks accounting for over 55% of the total cracks. This suggests that under splitting load, cracks resulting from shear failure were more prevalent than those from tensile failure. SMA-20 demonstrated the best crack resistance, followed by AC-20, while OGFC-20 performed the poorest. These conclusions are consistent with the results of the Voronoi diagram-based skeletal contact evaluation, confirming the correlation between the contact conditions of the asphalt mixture skeleton and its mechanical performance. Specifically, inadequate skeletal contact leads to a significant deterioration in mechanical properties. The research results elucidate the influence of skeletal contact characteristics with different gradations on both mesoscopic features and macroscopic mechanical behavior, providing a crucial basis for optimizing asphalt mixture design. Full article

Electromagnetic Railguns Face Severe Ablation and Melting Risks Due to Extremely High Transient Thermal Loads During High-Speed Launching, Directly Impacting Launch Reliability and Service Life. To address this thermal management challenge, this study proposes and validates the effectiveness of spray cooling technology. Leveraging its high heat transfer coefficient, exceptional critical heat flux (CHF) carrying capacity, and strong transient cooling characteristics, it is particularly suitable for the unsteady thermal control during the initial launch phase. An experimental platform was established, and a three-dimensional numerical model was developed to systematically analyze the dynamic influence mechanisms of nozzle inlet pressure, flow rate, spray angle, and spray distance on cooling performance. Experimental results indicate that the system achieves maximum critical heat flux (CHF) and rail temperature drop at an inlet pressure of 0.5 MPa and a spray angle of 0°. Numerical simulations further reveal that a 45° spray cone angle simultaneously achieves the maximum temperature drop and optimal wall temperature uniformity. Key parameter sensitivity analysis demonstrates that while increasing spray distance leads to larger droplet diameters, the minimal droplet velocity decay combined with a significant increase in overall momentum markedly enhances convective heat transfer efficiency. Concurrently, increasing spray distance effectively improves rail surface temperature uniformity by optimizing the spatial distribution of droplet size and velocity. Full article

This paper investigates frequency regulation of an airport microgrid (AIM) through the application of an integral absolute error (IAE)-assisted control approach. The islanded AIM is initially captured using a linearized transfer function model to accurately reflect its dynamic characteristics. This model is then simplified using a first-order plus dead time (FOPDT) approximation derived via a reaction-curve-based method, which balances between model simplicity and accuracy. Two different proportional–integral–derivative (PID) controllers are designed to meet distinct objectives: one focuses on set-point tracking (SPT) to maintain the target frequency levels, while the other addresses load disturbance rejection (LDR) to reduce the effects of load fluctuations. A thorough comparison of these controllers demonstrates that the SPT-mode PID controller outperforms the LDR-mode controller by providing an improved transient response and notably lower error measures. The results underscore the effectiveness of combining IAE-based control with reaction curve modeling to tune PID controllers for islanded AIM systems, contributing to enhanced and reliable frequency regulation for microgrid operations. Full article

Against the backdrop of global climate change, extreme weather events are increasingly challenging the safe and stable operation of power distribution networks. These events can cause sudden load fluctuations, equipment failures, and disruptions in power transfer. To address these, this paper proposes an optimal control strategy for distribution network power transfer, integrating Long Short-Term Memory (LSTM) networks and dynamic optimization models. By fusing meteorological data with grid characteristics, the LSTM model predicts load demand and fault probability, capturing complex system behaviors under extreme conditions. Combined with Mixed-Integer Linear Programming (MILP), a decision-making model is developed, and a deep-reinforcement-learning-based algorithm handles uncertainties in weather, load, and equipment faults, enabling accurate control. Validation on a 33-bus system shows the method enhances reliability under extreme weather, providing practical value. Furthermore, typhoons, as extreme weather events, can severely damage infrastructure, disrupt power lines, and affect grid stability. In the 33-bus system, typhoons can cause tower collapses and line failures, impacting power transfer. This paper explores the impact of typhoons on a bus model integrated with renewable energy, proposing optimal control strategies to ensure power supply to critical loads while minimizing equipment damage. Full article

Cracking is a critical distress that reduces an asphalt pavement’s service life, and fiber reinforcement is an effective strategy to enhance anti-cracking capacity. However, the effects of fiber type, morphology, and length on key cracking modes remain insufficiently understood, limiting rational fiber selection in practice. This study systematically evaluated the influence of four representative fiber types on the anti-cracking performance of Stone Mastic Asphalt (SMA) mixture, combining mechanical testing and microstructural analysis. The fibers included lignin fiber (LF); polyester fiber (PF); chopped basalt fiber (CBF) with lengths of 3 mm, 6 mm, 9 mm; and flocculent basalt fiber (FBF). Key mechanical tests assessed specific cracking behaviors: three-point bending (low-temperature cracking), indirect tensile (tensile cracking), pre-cracked semi-circular bending (crack propagation), overlay (reflective cracking), and four-point bending (fatigue resistance) tests. A scanning electron microscopy (SEM) test characterized fiber morphology and fiber–asphalt interface interactions, revealing microstructural mechanisms underlying performance improvements. The results showed that all fibers improved anti-cracking performance, but their efficacy varied with fiber type, appearance, and length. PF exhibited the best low-temperature cracking resistance, with a 26.8% increase in bending strength and a 16.6% increase in maximum bending strain. For tensile and crack propagation resistance, 6 mm CBF and FBF outperformed the other fibers, with fracture energy increases of up to 53.2% (6 mm CBF) and CT_index improvements of 72.8% (FBF). FBF optimized reflective cracking resistance, increasing the loading cycles by 48.0%, while 6 mm CBF achieved the most significant fatigue life improvement (36.9%) by balancing rigidity and deformation. Additionally, SEM analysis confirmed that effective fiber dispersion and strong fiber–asphalt bonding were critical for enhancing stress transfer and inhibiting crack initiation/propagation. These findings provide quantitative insights into the relationship between fiber characteristics (type, morphology, length) and anti-cracking performance, offering practical guidance for rational fiber selection to improve pavement durability. Full article

In deep-sea oil and gas development scenarios, deep-sea dual-channel connectors often face the risk of seal failure due to internal and external temperature difference loads. To address this issue, this paper systematically establishes equivalent heat transfer models for the key parts of the connector based on the third-type boundary condition. On this basis, the quantitative correlation between the equivalent thermal conductivity, composite heat transfer coefficient and temperature of each part is explored. Using the finite element numerical simulation method, the transient temperature field of the connector under three working conditions (heating, cooling and temperature shock) is simulated and analyzed, revealing the temperature distribution characteristics and temperature change trends of the maximum temperature difference of each key component of the connector; combined with thermal–structural coupling simulation, the temperature field is converted into static load, to determine the behavior of the contact stress on the sealing surface under different temperature–pressure coupling working conditions; in addition, by placing the test prototype in a high-low temperature cycle chamber, the seal performance tests under pressurized and non-pressurized working conditions are carried out to verify the reliable sealing performance of the connector under variable temperature conditions. The results of this paper provide comprehensive theoretical support and an experimental basis for the thermodynamic optimization design of deep-sea connectors and the improvement of the reliability of the sealing system. Full article

Identifying suitable catalyst types and efficient loading methods remains a key research challenge for implementing the in situ catalytic pyrolysis of tar-rich coal. This study investigated a lignite and a gas coal, employing NiCl₂ solution for Ni²⁺ catalyst loading via room-temperature impregnation and hydrothermal treatment on coal particles sized 6–13 mm. The efficiency of Ni²⁺ loading through hydrothermal treatment and the characteristics of pyrolysis product distribution and composition before and after treatment were examined. The results indicated that after NiCl₂ solution impregnation, the Ni²⁺ content in lignite increased from nearly undetectable to over 20 mg/g, whereas in gas coal, it only rose to less than 2 mg/g. Ion exchange is hypothesized to be a primary pathway for Ni²⁺ loading into coal. After hydrothermal treatment at 170 °C, the Ni²⁺ loadings in lignite and gas coal reached 33.6 and 1.45 mg/g, respectively. The loaded Ni²⁺ exhibited distinct catalytic effects on the two coals. For lignite, Ni²⁺ catalyzed the deoxygenation of oxygen-containing compounds and the aromatization of aliphatic hydrocarbons. For gas coal, hydrothermal treatment with NiCl₂ solution at 170 and 220 °C promoted hydrogen transfer reactions, resulting in an increase in tar yield from 10.67% to 11.30% and 11.64%, respectively. Also, the H₂ yield decreased, accompanied by a decrease in aromatic hydrocarbons and an increase in phenolic compounds within the tar. Full article

The air turbine starter (ATS) of an aero-engine incorporates a high-speed, high-energy rotor. An uncontained failure of the ATS could lead to catastrophic consequences, making containment capability research critically important. This study proposes a comprehensive evaluation methodology for ATS containment. A full-scale finite element model of the whole structure of an ATS was established to analyze containment characteristics and structural deformation patterns. Furthermore, an experimental method for ATS containment testing was designed to investigate the containment process and critical structural damage. By integrating simulation and experimental results, the load transfer paths and structural dynamic response of the ATS were systematically analyzed. The results demonstrate that sudden high-energy loads primarily follow two distinct transfer paths, each causing completely different structural damage behaviors. After the turbine wheel is broken, the resulting unbalanced load causes turbine shaft oscillation, which, in turn, compresses the bearings and damages their inner and outer rings. This research provides valuable guidance for the structural design of air turbine starters. Full article

The fast and accurate calculation of the internal temperature rise in the oil-immersed transformer is the premise to realize the thermal health management and load energy evaluation of the in-service transformer. In view of the influence of nanofluids on the heat transfer process of transformer, a numerical simulation algorithm based on lattice Boltzmann method (LBM) and finite difference method (FDM) is proposed to study the heat and mass transfer process inside nano-modified oil-immersed transformer. Firstly, the D2Q9 lattice model is used to solve the fluid and thermal lattice Boltzmann equations inside the oil-immersed transformer at the mesoscopic scale, and the temperature field and velocity field are obtained by macroscopic transformation. Secondly, the electric field distribution inside the oil-immersed transformer is calculated by FDM. The viscous resistance in LBM analysis and the electric field force in FDM analysis, as well as the gravity and buoyancy of particles, are used to explore the motion characteristics of nanoparticles and metal particles. Finally, compared with the thermal ring method and the finite volume method (FVM), the relative error is less than 5%, which verifies the effectiveness of the numerical model and provides a method for studying the internal electrothermal convection of nano-modified oil-immersed transformers. Full article

Rail transport is widely regarded as an efficient and environmentally sustainable mode of mobility, although lifecycle emissions from infrastructure can diminish its ecological benefits. This study assesses a novel slab track system design that replaces conventional concrete components with recycled polymeric composite sleepers, supporting circular economy objectives. Analytical calculations (per EN 16432-2 and EN 13230-6) and finite element analysis (FEA) were conducted on a 2.6 m polymeric composite sleeper model under static vertical loading. The results demonstrate that bonded base layers comprising asphalt and hydraulically bound materials reduce bending stresses within the sleeper to 1.307 N/mm², substantially below the 5.50 N/mm² observed without bound layers and well below both characteristic fatigue limits. Laboratory validation via strain-gauge measurements corroborates the numerical model. Despite minor torsional effects from first-batch production, the polymeric composite sleeper design is structurally viable for slab track applications. The methodology is directly transferable to alternative composite designs, allowing material-based adaptation of mechanical performance. These findings support the use of recycled polymeric composite sleepers in slab track systems, combining structural adequacy with enhanced circularity. Further research can base itself on the findings and should incorporate long-term durability testing. Full article

Optimization dispatch with flexible load participation in new power systems significantly enhances renewable energy accommodation, though the potential of flexible loads remains underexploited. To improve renewable utilization efficiency, promote wind/PV consumption and reduce carbon emissions, this paper establishes a low-carbon economic optimization dispatch model for active distribution networks incorporating flexible loads and tiered carbon trading. First, a hybrid SSA (Sparrow Search Algorithm)–CNN-LSTM model is adopted for accurate renewable generation forecasting. Meanwhile, multi-type flexible loads are categorized into shiftable, transferable and reducible loads based on response characteristics, with tiered carbon trading mechanism introduced to achieve low-carbon operation through price incentives that guide load-side participation while avoiding privacy leakage from direct control. Considering the non-convex nonlinear characteristics of the dispatch model, an improved Beluga Whale Optimization (BWO) algorithm is developed. To address the diminished solution diversity and precision in conventional BWO evolution, Tent chaotic mapping is introduced to resolve initial parameter sensitivity. Finally, modified IEEE-33 bus system simulations demonstrate the method’s validity and feasibility. Full article

Tire contact imprint characteristics and pressure distribution directly affect their lateral mechanical characteristics under rolling conditions, which are the key influencing factors for vehicle handling stability. Based on the nonlinear finite element method, an explicit dynamic model of radial tires is established using Abaqus, and its contact process is simulated through phased load transfer and kinematic inversion. The modified mathematical model of contact pressure distribution is introduced from the geometric evolution law of contact imprint and the nonlinear characteristics of contact pressure distribution. The corrected lateral force and aligning torque and contact imprint behavior are analyzed. The results show that in the low roll-angle range, with the increase in the roll angle, the contact imprint shrinks asymmetrically, the pressure center shifts to the outer shoulder of the roll direction, and the lateral force and aligning torque show linear growth characteristics. At the critical value ±8°, the growth rate is significantly slowed down due to the stress saturation effect of the shoulder area. The research analyzes the evolution mechanism of the lateral mechanical characteristics of the contact imprint geometry and pressure distribution drive tires under roll conditions, providing theoretical support for vehicle handling stability optimization and tire structure design. Full article

This paper presents an analysis of the mechanical characteristics of bridge structures during both construction and operation phases, with a focus on stress distribution patterns and the impact of vehicle loads on structural safety. The monitoring during the construction phase indicates that the compressive stress of the main beam segments is mainly controlled by prestress, and the maximum compressive stress meets the specification requirements; the maximum tensile stress of the main beam occurs in the stage when the tension reinforcement of the top pier is under stress, and the tensile stress value is within the allowable range of the specification. Under the negative bending moment of the pier top, the tensile stress at the upper edge reaches the peak simultaneously with the pre-pressurization stress. In contrast, the tensile stress at the mid-span joint transfers to the lower edge, and the corresponding bending moment significantly decreases. Based on the maximum tensile stress theory, when the stress of the structure caused by the earthquake wave reaches the ultimate tensile strength of the concrete, it is prone to cause structural damage. Therefore, it is necessary to limit the vehicle weight and driving speed to reduce the vibration impact. According to the “Regulations on the Management of Over-limit Transport Vehicles on Highways” issued by the Ministry of Transport (the total designed load shall not exceed 55 tons), after calculation, it is known that the maximum allowable driving speed of a 60-ton vehicle is 81.4 km per hour, which exceeds the safety limit of the specification. The research shows that in actual operation, the driving speed needs to be dynamically controlled according to the vehicle weight to ensure the long-term safety and durability of the bridge structure. Full article

To address the limitations of conventional magnetically coupled resonant wireless power transfer (MCR-WPT) systems in multi-frequency multi-load applications—specifically inadequate load power independence and high complexity inconstant-voltage/constant-current (CV/CC) control—this paper proposes a variable-structure dual-frequency dual-load wireless power transfer system by first establishing its mathematical model and implementing hybrid-frequency modulation for multi-frequency output, then developing an improved T/LCC hybrid resonant topology by deriving parameter design conditions for compensation network reconfiguration under CV/CC requirements, subsequently employing an orthogonal planar solenoid coupling mechanism and frequency-division demodulation to achieve load-independent power regulation across wide load ranges for enhanced stability, and finally constructing a 120 W dual-frequency dual-load prototype to validate the system’s CV/CC characteristics, where simulations and experimental results demonstrate stronger consistency with theoretical predictions. Full article

The rising need for sustainable building technologies and passive ventilation strategies has sparked renewed research interest in traditional building practices. In this regard, Roman thermal buildings are notable for their incorporation of sophisticated ventilated facade systems. Nevertheless, the structural performance of these buildings remains poorly understood. This study presents a numerical analysis of Roman ventilated facade systems, focusing on the Forum Women’s Thermal Baths in Pompeii. A nonlinear finite element model is developed in Straus7 to examine the dynamic response and establish baseline dynamic properties essential for future structural performance assessments. Modal analysis identified characteristic frequencies related to the horizontal translation modes. The numerical model will give insight into the load transfer pattern between the individual tegulae and the supporting structures. The results will provide a quantitative database on dynamic characteristics for these traditional systems and set out a verified computational procedure applicable in the fields of heritage conservation and current design practice. The current study combines archaeology and engineering in order to obtain valuable insights into ventilation strategies still applicable in the design of sustainable buildings. Full article