Bearings are critical mechanical components in industrial equipment, and damage detection is of great significance for effectively preventing prolonged downtime and catastrophic accidents. Nevertheless, the extraction of weak damage characteristics at the early stage of bearing degradation remains challenging under harsh operating conditions. To address this issue, an initialization parameters guided adaptive chirp mode decomposition (IPGACMD) method is proposed. First, the envelope spectrum crest factor diagram (ESCFgram) is developed to guide the selection of the optimal frequency band, and a bandwidth empirical expression is further introduced to guide penalty parameter selection. IPGACMD is constructed by integrating these two schemes, which can extract bearing damage characteristics without requiring any prior knowledge or subjective experience. The feasibility and superiority of IPGACMD are verified using experimental bearing damage signals. Comparative analysis results demonstrate that IPGACMD outperforms other methods in bearing damage characteristic extraction. Furthermore, IPGACMD is also applied to bearing condition assessment, achieving accurate extraction of degradation characteristics. Combined with the Chebyshev inequality threshold strategy, it provides early warning of the initial degradation moment of bearings.
This study presents the development of a disc spring–supported seismic friction damper (DSS-SFD) aimed at mitigating earthquake-induced structural damage and potential loss of life in reinforced concrete structures. Quasi-static loading tests were conducted based on the number of cycles and displacement values specified in BS EN 15129:2009 (2009). For comparative evaluation and to highlight the differences from the proposed device, a conventional seismic friction damper (SFD) was also tested under identical conditions. In addition, the influence of DSS-SFD dampers on the seismic performance of hypothetical existing reinforced concrete buildings was evaluated in accordance with the Turkish Building Earthquake Code 2018 (TBEC 2018). The contribution of the DSS-SFD device to the residual story drift ratio of the structure was also investigated by comparison with the SFD device. Within the experimental program, pre-tension forces were applied to both DSS-SFD and SFD devices using bolt torques of 50 Nm, 100 Nm, and 200 Nm (torque sets). Force–displacement responses were experimentally obtained and compared at 25%, 50%, and 100% of the design displacement ( d b d ). The experimental results showed that sliding forces remained constant in the SFD, whereas they increased with displacement in the DSS-SFD. Variations in loading velocity, period, and frequency had no significant effect on the force–displacement relationship. Performance assessment of the existing reinforced concrete structure showed that 83.33% of ground-story columns and 16.67% of second-story columns failed to meet the life safety performance level. After DSS-SFD implementation, all columns and beams satisfied the life safety requirements. The DSS-SFD–retrofitted structure also exhibited a 34.39% lower residual story drift ratio at the base floor than the SFD-retrofitted structure under the selected earthquake record. Overall, the DSS-SFD system enhanced seismic performance and reduced residual story drift.
Efficiently harvesting ultra-low-frequency vibration energy from human motion to power electronic devices remains challenging. This study presents a compact magnetically coupled energy harvester (MCEH) that integrates piezoelectric (PEH) and electromagnetic (EEH) modules through a shared reciprocating center magnet. The center magnet simultaneously produces electromagnetic induction and excites the piezoelectric cantilevers through nonlinear magnetic repulsion, enabling dual-path energy conversion and magnetic frequency up-conversion from excitation below 10 Hz. A coupled lumped-parameter electromechanical model was established and evaluated using numerical simulations and experiments, including frequency-response, load-matching, human-motion, and sensor-powering tests. At 6.5 Hz, the PEH reaches an RMS voltage of 3.56 V with magnetic coupling, versus only 0.0383 V for the no-center-magnet reference, showing an approximately 93-fold enhancement. Under the matched loads, the system delivers a total output of 1,147.88 μ W and a normalized power density of 31.89 μ W/ cm 3 . The prototype also powers a temperature-humidity sensor under the tested motion conditions, demonstrating the feasibility of the proposed approach for low-power wearable sensing.
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.
