Given the influence of flow instability, parameter uncertainty, and unpredictable disturbances in electro-hydraulic lifting systems, high-precision position control for electro-hydraulic lifting systems is challenging to achieve. This study proposes an observer–sliding mode control strategy to improve the control accuracy of the tractor electro-hydraulic lifting system. Firstly, the principle of the electro-hydraulic hoisting system is analyzed. Secondly, a mathematical model of the electro-hydraulic hoisting system is established, and the electro-hydraulic hoisting system is reduced to design an observer to achieve a real-time evaluation of the unknown system state and disturbance. The observer and the sliding mode control are then integrated into a controller to improve system response. Theoretical analysis demonstrates that the controller ensures that the actuator can achieve the desired control effect even under disturbing effects. Finally, a joint AMESim–MATLAB simulation and conducting pilot studies are carried out to compare the observer–sliding mode control with PID (Proportion–Integral–Derivative) control and sliding mode control. At the same time, in the process of the simulation and test, the symmetric structure as the electro-hydraulic lifting system was used to build a ploughing depth simulation system (changes in the hydraulic cylinder thrust simulate changes in ploughing depth values). The results show that the proposed observer–sliding mode control strategy can achieve a better position and pressure tracking and parameter change robustness than PID control and sliding mode control.

In this study, the influence of U-bends on the flow and pressure propagation characteristics of a gas–liquid two-phase flow in upstream and downstream straight pipes was investigated experimentally. The superficial velocities of the gas and liquid are 0.18–25.11 m/s and 0.20–1.98 m/s, respectively, covering plug flow, slug flow, and annular flow. The experiments were conducted in U-tubes with inner diameters of 9 mm and 12 mm and with a curvature ratio of 8.33. The U-tube was C-shaped. The pressure fluctuations at the axial measurement points of the straight tubes were measured. Flow images of the distal straight tubes and U-bends were obtained. The disturbance from U-bends in the two-phase flow in the vicinity of the bend is very obvious. The perturbation from U-bends in the fluid in the adjacent straight tubes is highly related to the incoming flow pattern. The slug flow has the most significant influence, whereas the effects of the plug and annular flows are small. Fundamentally, it mainly depends on the weight relationship between the gravity, centrifugal force, and inertial force of the gas–liquid two-phase fluid. The pressure fluctuation propagates in the form of a wave with the same dominant frequency in the straight pipes of the U-tube. The pressure pulsation energy in the straight tubes strengthens with decreasing distance from the 180° return bend. In addition, the pressure fluctuation energy downstream of the U-bend is greater than that upstream of the return bend.

Volatile Organic Compounds (VOCs) are pervasive environmental pollutants with significant implications for air quality and human health. The development of effective technologies for VOC degradation is essential to mitigate their adverse effects. Microwave plasma technology has emerged as a promising solution for VOC abatement due to its ability to generate highly reactive species at ambient conditions, enabling efficient decomposition of VOCs into harmless byproducts. Concurrently, Density Functional Theory (DFT) has become a critical tool for understanding the molecular-level mechanisms of VOC degradation, providing insights into reaction pathways and energy dynamics. This study explores the integration of microwave plasma experiments with DFT simulations to investigate the degradation mechanisms of VOCs under plasma conditions. DFT calculations of microwave plasma degradation for toluene are performed. The results show that on the one hand, toluene can undergo ring-opening. Then, these active molecules or groups react with active free radicals and are ultimately oxidized into CO₂ and H₂O. On the other hand, VOC gas molecules react with active free radicals (O, OH) generated by background gas (O₂ and H₂O) through oxidation reactions, generating organic intermediates such as benzene, benzyl alcohol, and benzoic acid, respectively, which are finally oxidized into CO₂ and H₂O. Our theoretical research results are expected to provide profound insights into the degradation mechanisms of these aromatic hydrocarbon VOCs through microwave plasma and also contribute to a better understanding of the further degradation mechanisms of air pollutants at the molecular level.