The valve-controlled cylinder electro-hydraulic position servo system is a typical nonlinear system, which is affected by load variations, external disturbance forces and other factors during operation, resulting in a significant reduction in control accuracy. To improve the dynamic tracking accuracy of the system, a fractional-order sliding-mode control strategy based on an improved nonlinear extended disturbance observer is proposed. The improved nonlinear extended disturbance observer can effectively estimate the unknown external disturbances and their high-order derivatives in the electro-hydraulic position servo system. Moreover, the estimation accuracy of disturbances is improved and the chattering problem caused by traditional functions is solved by introducing nonlinear compensation terms and a new smooth nonlinear compensation function. On this basis, a fractional-order sliding mode controller is designed, and a fractional-order operator is introduced into the sliding mode surface, which provides more control degrees of freedom and can more effectively improve the system tracking accuracy and transient response. Finally, the designed controller is simulated and verified by MATLAB/Simulink, and the control effects of the system under different working conditions and signals are analyzed. The results show that the designed fractional-order sliding mode controller with the improved nonlinear extended disturbance observer can effectively improve the position-tracking accuracy, transient performance and anti-interference ability of the electro-hydraulic position servo system, and it has better robustness and control effects.
In this study, a semi-analytical method is established to solve the band gaps and vibration characteristics of anisotropic laminated beam structures. The energy functional of the beam structure is formulated based on the first-order shear deformation theory, and an improved Fourier series is adopted to represent the displacement functions of the structure. Artificial spring techniques are introduced to simulate periodic boundary conditions and typical boundary conditions. The Rayleigh–Ritz method is adopted to solve the band gap characteristics of the anisotropic laminated beam. The effectiveness of the proposed method is verified by comparison with the Transfer matrix method and results from published literature. Further parametric studies are conducted to reveal the influence mechanism of structural parameters and material properties on the band gaps of the unit cell. In addition, the equivalent conditions of band gaps for finitely periodic beam arrays and the robustness of boundary conditions to the band gap range are investigated, providing a theoretical basis for the vibration reduction design of anisotropic laminated beam structures.
Pumpkin seeds are widely valued for their nutritional and economic benefits; however, conventional grain separators used in centralized processing often suffer from low efficiency and high loss ratio due to the similar physical properties of seeds and pulp fragments. Furthermore, while discrete element method (DEM) simulations are widely used for generic vibrating screens, targeted theoretical and structural design studies addressing the unique material characteristics of pumpkin seeds remain scarce. To address this gap, this study systematically analyzes the relative motion constraints of particles on a vibrating screen to identify key factors governing screening behavior. Subsequently, a DEM model was established to simulate particle motion on a specialized double-layer rectangular perforated screen. A three-factor, three-level Box–Behnken response surface design was employed to construct regression models evaluating the interactive effects of vibration amplitude, deck inclination, and vibration frequency. Numerical optimization identified the optimum operating parameters as a 26 mm vibration amplitude, 2.5° deck inclination, and 4.0 Hz vibration frequency, yielding a predicted dynamic screening efficiency of 88.7% and a loss ratio of approximately 3.7%. Subsequent bench tests conducted under these optimized conditions demonstrated high consistency with DEM predictions, exhibiting small and stable deviations. Ultimately, unlike existing generic screening studies, this research provides a tailored equipment design paradigm and a collaborative parameter optimization framework specifically for pumpkin seeds, offering a reliable approach to resolve systemic bottlenecks in centralized processing.
Rayleigh-type waves are highly sensitive to the mechanical and interfacial properties of layered media, making their study important for characterizing composite structures and geophysical materials. The present paper investigates the characteristics of Rayleigh wave propagation in a magnetoelastic fibre-reinforced layer overlying a pre-stressed magnetoelastic fibre-reinforced orthotropic half-space under gravity. The main contribution of this study is the development of a unified analytical framework that simultaneously incorporates magnetoelasticity, fibre reinforcement, orthotropy, initial stress, gravity, and a Coulomb-friction interface. An analytical approach, the method of separation of variables, is used to obtain displacement fields, and the corresponding dispersion relation is derived using appropriate boundary conditions. Some limiting cases are also discussed to recover the classical Rayleigh wave equation and to validate the proposed formulation. Numerical results computed in MATLAB using parameter values from the existing literature illustrate that the Rayleigh wave phase velocity is significantly affected by the initial stress, gravity, electromagnetic and magnetoelastic parameters, fibre-reinforcement parameters, and interfacial bonding conditions. The results show that interfacial friction plays a significant role in modifying Rayleigh wave characteristics, emphasizing the importance of imperfect interface modelling in layered composite and geophysical media. This study provides valuable insights into wave propagation in complex frictionally bonded composites, offering useful information for engineering applications.
Wheel polygonal wear is a critical degradation phenomenon in metro systems, causing intensified wheel-rail interaction, abnormal vibration, and increased maintenance requirements. However, its formation mechanism remains insufficiently understood, particularly regarding the role of track structural dynamics in the resonance-driven evolution process. This study investigates the mechanism of metro wheel polygonal wear through an integrated approach combining field measurements, wheel-rail coupling analysis, and vehicle-track coupling modal analysis. Field measurements were conducted on an operating metro line using four trains with different service histories after wheel re-profiling. The results reveal that polygonal wear develops progressively with mileage and is predominantly characterized by the 7–9th orders, with the 8th order exhibiting the highest amplitude. These polygonal components generate periodic wheel-rail excitation, leading to abnormal axlebox vibration mainly within the 50–70 Hz frequency range. Frequency-response analysis based on wheel-rail coupling models identifies a pronounced resonance peak near 63 Hz, corresponding to the wheel-rail P2 resonance mechanism. Furthermore, finite element models incorporating vehicle-track coupling were developed for three representative track structures, including steel-spring floating slab track (FST), conventional slab track (CST), and trapezoidal sleeper track (TST). Modal analysis suggests that the P2 resonance frequency increases with structural stiffness, ranging from 63.36 Hz for FST to 95.72 Hz for TST and 126.91 Hz for CST. The frequency coincidence between FST resonance and polygonal excitation promotes dynamic amplification. Based on these findings, a resonance-driven regenerative mechanism is proposed, involving periodic excitation, wheel-rail P2 resonance amplification, initial wheel irregularity formation, and feedback-induced wear growth. The results suggest that wheel polygonal wear may be governed by the interaction among wheel condition, external excitation, and track structural dynamics. The proposed mechanism provides theoretical guidance for integrated condition monitoring and preventive maintenance of urban rail transit systems.
