Motor current monitoring systems have garnered significant attention due to their non-invasive and cost-effective advantages. However, conventional current spectrum analysis is susceptible to inherent harmonic and installation errors, and the high amplitude of the fundamental frequency can obscure fault characteristics. To reveal the frequency modulation patterns in motor current caused by reduced meshing stiffness due to gear faults, a motor current model incorporating faulty gear meshing stiffness is established, and its instantaneous frequency expression is derived. Addressing the limitation of traditional time-frequency analysis methods, which often suffer from low instantaneous frequency estimation accuracy, this paper proposes an instantaneous frequency polar view method based on high-order synchrosqueezing transform (HSST) for extracting gear fault features. This method intuitively demonstrates gearbox faults by detecting frequency modulation characteristics that are synchronized with the meshing period of faulty teeth. The instantaneous frequency polar view effectively avoids interference from inherent harmonics and fundamental frequency, offering a unique representation of gear fault characteristics. Analysis of motor current signals from an RV gearbox test rig validates the accuracy of the proposed motor current model and the distribution patterns of fault characteristics. It also confirms the effectiveness of the instantaneous frequency polar view method based on HSST for gearbox faults diagnosis.

Gear systems in precision machinery and aerospace applications are subjected to complex vibration problems due to mass eccentricity, time-varying backlash, and dynamic meshing parameter variations. A nonlinear dynamic model with six degrees of freedom is established, incorporating time-varying meshing stiffness, derived using the potential energy method and mass eccentricity. The Runge-Kutta method is employed to solve the system response under varying eccentricities and rotational speeds. Time-domain and frequency-domain analyses, phase portraits, and Poincaré maps are used to investigate the dynamic characteristics. The results indicate that mass eccentricity significantly influences system behavior, leading to the evolution from single-period to multi-period motions (e.g., 20-period cycles), and aggravates bifurcation and oscillation phenomena. The findings provide theoretical support for structural optimization and vibration control of gear transmission systems.

Gear transmission systems are critical for power delivery in major equipment, yet they are susceptible to diverse and unpredictable to diverse and unpredictable faults, compromising operational safety and service reliability. In practical engineering applications, the absence of fault samples and unknown fault locations pose significant challenges. To address these issues, this paper proposes an unsupervised hypersphere-based fault localization (UHFL) method empowered by mode component energy features. This method extracts mode component energy features that are not only related to the fault mechanisms of transmission components but also possess clear fault localization interpretability. These features then enable both unsupervised anomaly detection and interpretable fault localization. Specifically, an unsupervised data description model is constructed using the proposed features. An attribution explanation method is introduced to quantify the contribution of each feature to the anomaly detection result, thereby achieving interpretable fault localization of gear transmission system components under conditions lacking fault samples. The proposed method is validated through single-fault and compound-fault localization experiments conducted on a helicopter main reducer planetary stage test bench and an armored vehicle transmission system test bench. Experimental results demonstrate that the proposed UHFL method can accurately localize faults in transmission components without requiring any fault sample training. This method offers an effective solution for fault localization in gear transmission systems under data-scarce conditions, showcasing valuable engineering promotion potential and application prospects.

Planetary gear transmission systems are extensively used in industrial applications. Due to their compact and complex configurations, mechanical components are prone to failure during long-term operation. Compared to fixed-axis gear systems, planetary gear systems exhibit multiple excitation sources and time-varying signal transmission paths stemming from their intricate structural and kinematic characteristics. Consequently, condition monitoring techniques based on fixed vibration measurement points face significant challenges in compound fault diagnosis, especially when a planet gear fault is coupled with a bearing fault. To address these issues, this study proposes a non-contact torsional vibration monitoring and residual vibration analysis method utilizing laser doppler vibrometry (LDV). The laser beam is positioned on the low-speed shaft surface to directly acquire torsional vibration information from the gear system. To mitigate the impact of measurement noise on fault feature extraction, a hybrid denoising strategy combining cepstrum-based soft-threshold editing and median filtering is developed to suppress pseudo-vibration artifacts and random impulse noise, respectively. For different types of compound faults, a progressive residual vibration decomposition framework is established. This framework systematically peels off residual broadband response and residual meshing sideband components from the torsional vibration signal. Specifically, optimized filtering is applied to the broadband response obtained via cepstrum short-pass to extract the second-order cyclostationary features of bearing faults. Concurrently, a phase self-demodulation-based order domain resampling method is proposed to highlight gear fault features by reconstructing meshing sideband residual signals of different orders. Experiments involving tooth spalling on planetary gears and raceway spalling on the sun gear bearing demonstrate that the proposed method can effectively achieve non-contact compound fault diagnosis for planetary gear systems. Compared to conventional flexible synchronous averaging and accelerometer-based methods, the proposed approach exhibits superior performance in early-stage planet gear fault detection under varying speeds.

Based on the Biot’s dynamic consolidation equation and Novak’s plane strain theory, a coupled mechanical model of radially heterogeneous saturated soil and wedge-shaped pile was established under the horizontal vibration, by considering the construction disturbance effect of the surrounding saturated soil. Then, the analytical solution for the horizontal impedance of the pile head was obtained by using the potential function, Laplace transformation and variable separation methods, and the accuracy of the solution was verified by degenerating with the existing literature solutions. On this basis, the effects of the pile’s parameters and construction disturbance effect on the horizontal vibration characteristics of wedge-shaped pile are further discussed by conducting an extensive parametric analysis. The results show that: The horizontal impedance of the pile head tends to be stable when the number of pile-soil system layers reaches 100. With the increase of softening degree and range of surrounding saturated soil, the horizontal impedance of the pile head decreases, while both the horizontal displacement and bending moment of pile shaft increase. The reasonableness and reliability of the analytical model and solution proposed in this paper are verified by comparative analysis in many aspects.

In order to accurately reveal the impact of high-speed train operation on the vibration response of foundation, the out-of-round wheels and uneven rail surface were introduced to modify the quasi-static moving load. Based on the 2.5D finite element equation of nearly-saturated foundation, a train-track-quasi saturated foundation dynamic analysis model has been established. On this basis, the vibration response of nearly-saturated foundation under different train speeds and loads were analyzed. The results show that both of out-of-round wheels and uneven rail surface have little influence on the time history and peak value of displacement and acceleration at a low speed, whereas the vibration amplitude is significantly increased after the coupling of the two aspects. When the vehicle speed reaches the soil shear wave speed, the influence of out-of-round wheels and uneven rail surface on displacement and acceleration response gradually increases. Compared with the out-of-round wheels, rail surface unevenness has greater influence on nearly-saturated foundation vibration, and it is more sensitive to the change of vehicle speed. The pore water pressure decays rapidly within the range of 0~4 m below the center line of the track bed when the vehicle speed is low, and the pore pressure peak appears at 0.5 m below the track. After the vehicle speed increases, the peak value of pore pressure increases significantly under all kinds of modified loads, and the position of the peak value of pore pressure develops to the deeper part of the foundation under the condition of uneven rail surface and irregular wheel-rail. The vibration response of the nearly-saturated foundation under the irregular wheel-rail coupling condition is obviously greater than that under other load conditions. Therefore, the influence of out-of-round wheels and uneven rail surface should be considered simultaneously in the safety evaluation and foundation vibration response prediction of high-speed railway.

The strong surface impact loads caused by dynamic compaction and construction operations have significant implications on the surrounding environment. Traditional research methods often simplify the impact load as a triangular load for calculation. However, this simplification does not consider the energy loss during impact, leading to overestimation in the calculation results. This paper is based on the measured data from an actual dynamic compaction project. After validating the numerical method’s feasibility, a parametric analysis of key influencing factors is conducted. The paper proposes a reasonable reduction coefficient to modify the current triangular loading model. The objective is to improve the accuracy and applicability of the model for dynamic compaction projects. The calculation results indicate that the magnitude of impact energy and the soil parameters of the site are critical factors influencing the impact vibration response. It is suggested that for impact energy levels categorized as low, medium, and high, the reduction coefficients for medium-soft soil can be set as 0.85, 0.6 and 0.5, respectively. For medium-hard soil, the reduction coefficients can be set as 0.9, 0.7 and 0.6 for the corresponding low, medium, and high energy levels.

The ground motion of pulse type near fault has the characteristics of higher frequency, faster speed and more concentrated energy than that of a distant site, which has serious harm to engineering structures. With abundant water resources, frequent and high-intensity earthquakes occur in Western China, and many high dams are located near fault zones. The permanent deformation and slope safety of high dams under near-fault ground motion are very important. A random pulse ground motion model is established based on the pulse ground motion records of the Jiji near fault in Taiwan Province. Finite element analysis is carried out on the Gushui 250 m grade engineering panel dam, and stochastic dynamic analysis and reliability analysis are carried out on the displacement and slope slip of the high earth-rock dam by the direct probability integral method. The results show that pulse ground motion significantly affects on the vertical deformation and slope stability of high earth-rock dams. The seismic safety and seismic capability of high earth-rock dams near faults with high seismic risk are evaluated comprehensively.

To solve the problem of a lack of theoretical guidance in the simplification process of space pipe truss structure, the equivalent bending moment of inertia of space pipe truss structure was deduced by using the knowledge of material mechanics, and the corresponding calculation formula was put forward. Based on the principle of equal torsional strain energy, the formulas for calculating the equivalent thin plate thickness of the web members and the top and bottom lateral bracing of the pipe truss were derived, and the continuous equivalent section was constructed. The formula for calculating the equivalent torsional moment of inertia of the space pipe truss structure was proposed by using the thin-walled bar theory. The cantilever method was used to verify the accuracy of the calculation formula of equivalent moment of inertia. The equivalent analysis of the tennis court of Lanzhou Olympic Sports Center was carried out. The results show that the formula for calculating the equivalent moment of inertia is reasonable, and its error is within 4% compared with that of the cantilever method. Under the action of deadweight, the errors of the maximum displacement value and the maximum stress value between the original structure and the simplified structure of the tennis court are less than 9%. The vibration modes of the first five steps of the original structure are similar to those of the simplified structure, and their errors of the natural frequency are less than 4%, so the simplified structure has high accuracy.

The present study aims to improve the aerodynamic stability of a single-axis PV tracker. The effects of turbulence intensity, natural frequency and damping ratio on the aerodynamic stability of the single-axis PV tracker are studied by a sectional model wind tunnel test to reveal the sensitivity of these parameters. The results show unstable torsional vibration of the single-axis PV tracker system in a large tilt angle range with strong aerodynamic coupling and self-excited characteristics. The critical wind speed for the unstable vibration is low. The critical wind speed is high at 0° tilt angle (PV module is horizontal). The increase of turbulence intensity leads to the increase of the unstable vibration tilt angle range, which is not good for the aerodynamic stability. Increasing the damping ratio has an inconsiderable effect on increasing the critical wind speed at small tilt angles (0° and 5°). However, it works well when the tilt angle is larger than 15°. With the increase of natural frequency, the critical wind speed is significantly increased at all tilt angles.