Jingang Liu

When small multirotor unmanned aerial vehicles (UAVs) undergo uncontrolled descent following low-altitude failures, inadequate impact protection can cause airframe damage and injuries to people on the ground. Inspired by the feline paw pad, whose central palm pad bears the primary load and the surrounding digital pads provide coordinated support, this study proposes a bioinspired main–auxiliary composite airbag configuration comprising a central main airbag and three concentric annular auxiliary airbags. Starting from a fully deployed airbag configuration, a two-stage approach combining the arbitrary Lagrangian–Eulerian (ALE) and control-volume (CV) methods was developed to model the entire process of free fall and touchdown cushioning. The ALE model was assessed against a theoretical estimate, whereas the CV model was validated against drop-test results. The cushioning results showed that the main airbag carried most of the impact load during initial touchdown. The annular auxiliary airbags then progressively shared part of the load and, together with the outer skin, restrained further airframe rotation, consistent with the cushioning mechanism of the feline paw pad. Even at large touchdown inclination angles, the composite configuration effectively suppressed airframe tip-over and promoted gradual attitude recovery. Parametric analysis showed that the peak center-of-mass acceleration first decreased and then increased as either the vent-opening pressure threshold or the initial pressure of the main airbag increased. Increasing the vent area generally reduced peak acceleration, although further increases provided limited additional improvement. These findings provide guidance for emergency protection and cushioning airbag design for small multirotor UAVs.

Farmland in the hilly and mountainous regions of southern China is characterized by complex terrain and highly variable operating loads. Conventional diesel-powered tracked harvesters are constrained by high crop losses, excessive impurity rates, frequent blockages, and low overall energy-use efficiency. Distributed electric drive provides a promising solution; however, threshing cylinder blockage, high-frequency load transients, and slope operation make it difficult for conventional energy-management strategies to simultaneously ensure dynamic responses, fuel economy, and battery state of charge (SOC) stability. This study therefore proposes a deep deterministic policy gradient (DDPG)-based reinforcement learning energy-management strategy (RL-EMS) for a range-extended, distributed-drive hybrid tracked combine harvester. First, a full-vehicle dynamic model incorporating eight electric-drive units and strong electromechanical coupling is established. Second, power allocation is formulated as a Markov decision process (MDP), with a multi-objective reward function that accounts for fuel consumption, SOC tracking, and boundary violations; the load-rate-of-change is introduced as a feedforward state. Finally, a supervisory physical layer comprising feasible power projection, safety filtering, and rate limiting is inserted between the policy network output and the physical plant so that the executed command satisfies range extender power, battery SOC, current, and power-slew constraints. Under the standard 1000 s cycle, SOC-corrected energy-equivalent comparison shows that the RL-EMS reduces fuel consumption by 1.5% relative to the adaptive equivalent consumption minimization strategy (A-ECMS) and by 26.6% relative to the constant-torque energy-management strategy (CT-EMS). Under an unseen complex random cycle, the RL-EMS reduces fuel consumption by 5.1% relative to A-ECMS. It also suppresses DC-bus voltage sag during a threshing cylinder blockage transient, demonstrating favorable electromechanical transient response. The proposed method provides a modeling and control reference for the intelligent energy management of range-extended, distributed-drive agricultural machinery.

To address uneven surface hardness distribution in 65Mn external tooth friction plates after furnace quenching and disc mold tempering, we adopted an integrated quenching and forming process, using an internal-circulation mold. By simultaneously implementing pressure forming and quenching within the internal-circulation mold, the hardness uniformity of the friction plate during forming was improved, effectively suppressing warping deformation. A multi-field coupled model of the friction plate quenching in the internal-circulation mold was established to simulate the dynamic evolution of the temperature field, the microstructural transformation, and the stress field, thus obtaining the complete heat treatment response of the martensitic transformation. The experimentally observed microstructure agreed well with the simulation results. Data analysis showed that after quenching in the internal-circulation mold, the surface hardness difference of a single friction plate was reduced from 3 HRC to 0.9 HRC, and the end face runout decreased from 0.1–0.15 mm to no more than 0.06 mm, significantly improving the product’s dimensional accuracy and performance consistency.

To investigate the influence of soil parameters on the cushioning performance of landing airbags, a landing airbag cushioning dynamics model considering soil characteristics was established based on the control volume method and a crushable foam model. Experimental validation was conducted for both the airbag cushioning model and the soil impact model, respectively, with good consistency between simulated and experimental results. Based on the established model, the influence of soil on the cushioning performance of landing airbags was analyzed. The analysis results indicate that soil absorbs energy through compressive deformation during the cushioning process, thereby exhibiting a certain degree of cushioning performance. Softer soil absorbs more energy, and the payload is less prone to rebound. However, excessively soft soil causes the airbag to sink into the soil, hindering the venting of gas outward and resulting in hard landings for payloads. Therefore, three indicators—airbag peak pressure, payload maximum acceleration, and maximum drop height—are used to comprehensively evaluate the cushioning performance of airbags, and the influence laws of soil parameters are quantitatively researched. The research shows that the soil density, shear modulus, and yield parameters A₁ and A₂ significantly influence cushioning performance. Specifically, the shear modulus and yield parameter A₁ exhibit logarithmic growth relationships with the three cushioning performance indicators, while the yield parameter A₂ and soil density show linear growth relationships with the three cushioning performance indicators.

Power-split hybrid electric vehicles (power-split-HEVs) exhibit significant engine torque fluctuations due to their mechanical coupling with the driveline, leading to pronounced torsional vibration issues in the drive shaft. This study investigates an active torsional vibration suppression strategy based on drive motor control. First, a dynamic model of the power-split-HEV driveline is established, and its intrinsic characteristics are analyzed. Subsequently, an engine excitation torque model is developed to identify the dominant response orders, while a vehicle dynamics model is constructed to elucidate the torsional vibration mechanisms in both hybrid and pure electric driving modes. Next, a torsional vibration feedback control framework is proposed, utilizing the electric motor as a secondary-channel torque disturbance compensator. Furthermore, a novel frequency-decoupled dual-loop control framework is proposed, with rigorous derivation of the sufficient conditions for decoupling. Based on this framework, two distinct vibration suppression algorithms are developed for the secondary-loop controller, each tailored for specific operational modes. Finally, the proposed algorithms are validated through simulation and hardware-in-the-loop (HIL) testing. The results demonstrate a torque fluctuation suppression ratio of up to 72.2%, confirming that the active suppression algorithm effectively mitigates driveline torsional vibration induced by engine harmonic torque disturbances.

In this paper, gears made of 18Cr2Ni2MoVNbA steel were taken as the research object, and their cooling curves under different flow rate conditions were determined. By calculating the corresponding heat transfer coefficients, a finite element simulation method was used to study the temperature field distribution law of different flow rate combinations on the gears in the cooling process of pressure quenching. The results show that among the four representative flow combinations, the working condition 1 (A + (A − b − c) + (A − b − c)) has the smallest temperature difference between the inner and outer gears, and can better reduce the temperature difference between the inner and outer parts. Furthermore, in the pressure quenching process of gears, the appropriate extension of the quenching time can keep the quenched gear with a lower average temperature, while promoting the martensitic transformation on the surface of the workpiece. Comparing the simulation results with the experimental data, the reliability of the pressure-quenching temperature field model is verified, which can provide theoretical guidance for the optimization of the pressure quenching process.

To improve the wear resistance of TC4 titanium alloy, two types of wear-resistant coatings were applied to the surface using laser melting: Ni60 + 50% WC and d22 powder priming. The phase composition and microstructure of the coatings were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and energy spectroscopy (EDS). The mechanical properties of the coating were tested using an HV-1000 micro-Vickers hardness tester, an HRS-2M high-speed reciprocating friction and wear tester, and a WDW-100D electronic universal testing machine. The results show that Ni60 + 50% WC composite coating and d22 priming + (Ni60 + 50% WC) composite coating mainly consist of W₂C, TiC, Ni₁₇W₃, Ni₃Ti, and Ti_xW_1−x phases. Compared to the TC4 substrate, the microhardness of both coatings is significantly higher, approximately 2.8 times the microhardness of the substrate. In frictional wear experiments, the average friction factors of the two coatings and the TC4 substrate are 0.476, 0.55, and 0.865, respectively, and the wear of the two coatings is only 0.0559–0.0769 that of the TC4 substrate, with a significant increase in wear resistance, nearly 17 times higher than that of the substrate. The coating shows flaking, shallow abrasion marks, and granular debris, dominated by adhesive wear and fatigue wear, while the TC4 substrate shows more furrows on the surface, dominated by abrasive wear. The shear bond strengths of the Ni60 + 50% WC composite coating and the d22 powder primed + (Ni60 + 50% WC) composite coating were 188.19 MPa and 49.11 MPa, respectively. Conclusion: both coatings significantly improve the hardness and wear resistance of the TC4 titanium alloy substrate surface, with the Ni60 + 50% WC composite coating performing better in hardness, wear resistance, and bond strength.

Urban safety production is a core component of social safety and is associated with the production, storage and transport of hazardous chemicals, which are potential sources of disaster in an urban area. Chemicals’ locations in a city present a hidden site of danger, which can easily become disaster sites if supervision is inadequate. Aiming to improve the processes and typical scenarios of the production, storage, transportation and use of hazardous chemicals, this paper proposes an intelligent-technology-empowered active emergency command strategy (ITAECS) for urban hazardous chemical disaster management (UHCDM) in smart–safe cities. This paper aims to provide a strategy for active emergency command that takes into account the disaster source; hidden danger site; or disaster site of hazardous chemicals such as natural gas, gasoline and hydrogen energy based on five aspects: intelligent perception technology and equipment, a dynamically perceived IoT system, the accurate deduction of disaster posture, virtual reality emergency rescue rehearsal and an immersive emergency command platform. This research is conducive to the safety, efficiency and greenness of the whole industrial chain, such as the production, storage, transportation, operation and use of hazardous chemicals. There are difficulties and challenges in introducing ITAECS to urban hazardous chemical production safety and emergency management, such as the need for joint promotion of enterprises, industries and governments; uneven technological development; and several scientific–technological issues to be solved, as well as non-uniform standards. Overall, this paper helps improve the emergency management of urban hazardous chemical safety production.

To overcome the detrimental effect of residual stress in welded joints, which affects the overall performance of the welded structure, this paper studies the magnitude and distribution of residual stress after welding and local post-weld heat treatment (PWHT). The coupled thermo-metallurgical-mechanical model for welding 6 mm thick Ti-6Al-4V (TC4) titanium alloy plates was established, the evolution of the SSPT and its effect on the residual stress were quantitatively analyzed, and a parametric analysis of local PWHT was performed. The results demonstrated that there was good agreement between the numerical results and the experimental data. Due to the cooling rate reaching 327 °C/s, the volume fraction of α^、 in the fusion zone (FZ) reached 0.218 after welding and decreased by 90.83% after PWHT when the heating temperature was 700 °C. The peak value of the longitudinal residual stress can reach 686.4 MPa after welding with SSPT, which was 11.38% lower than that without SSPT, and it decreased by 65.6% after PWHT when the heating temperature was 900 °C. The research results demonstrate that SSPT has a significant effect on residual stress, and PWHT can obviously reduce the residual stress, which provides a certain reference for welding TC4 titanium alloy plates.