The Hilbert resonance demodulation (HRD) technique is widely applied in bearing fault diagnosis. Current studies typically evaluate noise reduction methods based on the frequency components of envelope signals. However, there is a lack of quantitative analysis regarding the generation process of these frequency components. This might lead to misattributing HRD-induced effects to noise reduction methods during evaluation. In engineering, the empirical selection of test conditions and analysis parameters often results in missed diagnoses due to improper choices. To address these issues, this study constructs a fault signal model for vibration responses of rolling bearing outer race local faults. Through quantitative analysis of the Hilbert resonance demodulation process, the mapping relationship between signal parameters and envelope amplitude spectra is revealed. By investigating the influence of system physical parameters—such as natural frequency, damping ratio, and rotational speed—on signal characteristics, the correspondence between these parameters and the envelope amplitude spectrum distribution is established. This provides a clearer theoretical foundation for HRD applications. Simulated vibration signals processed by HRD demonstrate consistency with theoretical derivations, and experimental validation confirms the analytical conclusions based on the HRD demodulation mechanism.

Maximum correlated kurtosis deconvolution (MCKD), which uses correlated kurtosis as its deconvolution target, effectively extracts both periodic and impulsive features of mechanical faults. This is a widely used method for solving rolling bearing fault diagnosis problems. However, the performance of MCKD heavily relies on accurate prior fault period information. Existing solution often only focus on period estimation during the iterative process, making them ineffective under low signal-to-noise ration (SNR) conditions. To address this limitation, a period-refined maximum corrlated kurtosis deconvolution (PRMCKD) method is proposed. This approach refines the iteration period using time synchronous averaging (TSA) for reconolution, enabling accurate extraction of subtle bearing fault features even in strong noise environments. The method operates by first utilizing a filter bank for preliminary localization of the resonance frequency band, thus defining the correct deconvolution direction. With correlated kurtosis as the objective function, and leveraging the period information refined by TSA technology, the optimal filter coefficients are iteratively solved. Rolling bearing fault localization is achieved through the fault features present in the filtered signal. Simulation and experimental analysis results demonstrate that the proposed PRMCKD method offers significant advantages over traditional deconvolution methods for extracting weak fault features in rolling bearings.

The optimized layout of sensor measuring points is of significant importance for the condition monitoring, fault diagnosis and health management of mechanical equipment. Focusing on gear transmission systems, this paper investigates a method for optimizing vibration sensor placement based on the effective independent analysis of gearbox modes and frequency response functions. This method uses the fused signals from the optimized measuring points to monitor the vibration of the gear transmission system. A dynamic model of the gearbox is established, and modal analysis is performed to obtain the mode shapes of the gearbox. These mode shapes are utilized for effective independent analysis to determine an initial sensor layout. Harmonic response analysis is conducted to obtain the frequency response functions of these initial measuring points relative to the main bearing seats. The measuring points are further optimized using principal component analysis and effective independent analysis. The optimized measuring points most sensitive to gear fault excitation are selected. Spectral weighted fusion is performed based on the importance weights of the optimized measuring points. The fused spectrum then enables vibration monitoring of the gear transmission. Analysis of measured data from a bevel gear transmission test rig demonstrates that, compared to the fused spectra from arbitrarily selected measuring point groups, the fused spectrum from the optimized measuring point group exhibits a larger overall response amplitude. This indicates a superior monitoring effect for the oprational status of gear transmission.

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.

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.

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.

Flexible structures actuated by smart materials have been widely used in the fields of underwater bionic robotics, precision medical machines, micro/nano devices, and so on. It is still a challenging task to acquire the hydrodynamic force exerted on the oscillating flexible structure by the surrounding fluid. The fluid-structure coupled dynamic equation of the MFC-actuated flexible structure is established. A cantilever-based measurement system for the hydrodynamic force is proposed, and the performance indexes are also proposed. The characteristic parameters of the force measurement device are calibrated by experiments. Then, dynamic variations of the hydrodynamic forces exerted on the MFC-actuated flexible structure at different actuation levels are acquired using the proposed system. The measured hydrodynamic forces are decomposed into two components, namely, the added mass force and the hydrodynamic damping force. Moreover, the inertia and drag coefficients in the form of Morrison’s expression are obtained. Experimental results show that the underwater oscillating amplitude of the MFC-actuated structure increases from 3.67 mm to a maximum of 4.23 mm, as the excitation frequencies increase from 2.5 Hz to the resonant frequency of 3.1 Hz. Accordingly, the measured hydrodynamic force exerted on the oscillating structure increases significantly from 86.16 to 184.83 mN. However, the hydrodynamic force stays roughly unchanged, differing by no more than 15%. The proposed method and measurement system may be helpful for the design and application of the underwater flexible structure actuated by MFC and other smart materials.

To address the dynamics modeling of a single local damage fault in rolling bearings, a comprehensive approach based on Hertz contact theory has been developed.Specifically, a contact deformation retention factor is defined and a variable stiffness function using a static analysis method is proposed. This allowed us to establish and simulate a variable stiffness dynamics model for a single local damage fault in rolling bearings under radial load. The model was also experimentally validated. The research results show that when the rolling element enters the load zone its effective contact stiffness suddenly increases. Conversely, when it exits the load zone or falls into the fault position, the stiffness suddenly decreases. This change causes the contact force and contact deformation of other load-carrying rolling elements in the load zone to suddenly decrease or increase to rebalance the external load. However, this does not affect the effective contact stiffness of the rolling element itself. The effect is more pronounced for rolling elements near the center of the load zone. Additionally, these changes cause the total effective stiffness of the system to suddenly increase or decrease, leading to system vibrations. When the outer race has a fault, the change in total effective stiffness is of equal amplitude, resulting in an equal-amplitude time-domain vibration response. In contrast, when the inner race has a fault, both the change in total effective stiffness and the response amplitude are modulated by the rotation of the inner race, leading to significant variations. The proposed variable stiffness dynamics model is more consistent with reality and provides a certain theoretical basis for effective diagnosis of rolling bearing faults.

To achieve high-precision prediction of bridge-coupled extreme stresses, the wavelet multi-resolution analysis method is adopted to decouple the coupled extreme stresses. The decoupled low-frequency data is taken as the trend item information, where the high-frequency data is considered as the vehicle load effect information. The trend item, after subtracting its mean, is the temperature load effect information. A bivariate Bayesian dynamic linear trend model (BDLTM), which introduces a time-varying trend term, is built to predict and analyze low-frequency extreme stress. GRU neural network model is provided to predict and analyze high-frequency extreme stresses. The dynamic coupled extreme stresses are predicted. The monitoring coupled data from Tianjin Fumin Bridge is provided to illustrate the feasibility and application of the proposed BDLTM-GRU model, the accuracy of which is compared with the single BDLTM model and single GRU model for verifying the high precision of the BDLTM-GRU model.