An Automatic Ball Balancer （ABB） can entirely eliminate the unknown imbalance of the rotor above the critical speed. However，it has the disadvantage of causing large amplitude resonance response and unstable oscillation near the critical speed. To overcome these shortcomings and improve its vibration suppression performance，this paper proposes the addition of a Dynamic Vibration Absorber （DVA）. Using the Jeffcott eccentric rotor model as the research object，dynamic equations are established to control the unbalanced vibration of the rotor when the DVA and ABB are used either separately or in combination，based on the Lagrange equation. The harmonic balance method is used to solve the amplitude expression of the new coupling system，and the influence laws of each parameter on the steady-state amplitude-frequency curve are analyzed to obtain more suitable parameters. The steady-state amplitude-frequency characteristic diagram and the transient amplitude time-domain change curves are obtained using the Runge-Kutta numerical calculation method. The comparison results show that the new scheme of combining the two methods effectively reduces the vibration level of the rotor when passing through the critical resonance region，and causes the rotor to attenuate to zero amplitude above the critical speed. This new scheme achieves the goal of combining the advantages of the two methods and provides superior vibration suppression.

Vision-based modal analysis techniques have gained attention due to their non-contact，full-field measurement capabilities，making them particularly suitable for the dynamic testing of large-scale or thin-walled structures. However，these techniques often require cameras to be fixed to the ground to avoid coupling with the vibrations of the test structure，a requirement that can be too restrictive in real-world applications. This paper proposes a method to compensate for camera motion using homography transformation，followed by the extraction of the test structure’s movement by applying the dense optical flow method to the stabilized video. The procedure involves transforming the video captured by a moving camera using feature matching algorithms，where a homography matrix compensates for six degrees of camera motions. Several "virtual vision sensors" are selected on the edges of the structure，and their vibrations are estimated using optical flow methods. Structural modal parameters are then extracted from the output-only data using stochastic subspace identification algorithms. The proposed procedure was applied to videos recorded using a moving smartphone to conduct an operating modal analysis of a 2 m cantilevered beam. To validate the procedure，the vision-based analysis results were compared with measurements taken with a Scanning Laser Doppler Vibrometer. The results show an average discrepancy of 0.4% and 11.5% for the first five natural frequencies and damping ratios of the beam，respectively. The mode shapes also show strong correlation between the two measurement techniques，as indicated by the diagonal MAC values greater than 98%. Therefore，the proposed procedure effectively cancels out camera motions and achieves accurate estimation of structural modal parameters.

A segmented damping device is designed using a cam mechanism in this study. Based on the traditional Voigt dynamic vibration absorber，this device is installed between the main system and subsystem of the dynamic vibration absorber，and the dynamic equation of the vibration absorber is established. Using the principle of equivalent damping energy dissipation within one vibration period，the equivalent damping coefficient of the segmented damping device at the same vibration frequency is obtained. The theoretical solution of a dynamic vibration absorber with piecewise damping characteristic is derived and verified by numerical solution. The vibration absorption characteristics of undamped，traditional linear damping，and dynamic absorber with piecewise damping are compared and analyzed. The results show that the amplitude frequency characteristics of the dynamic vibration absorber with piecewise damping characteristics integrate the characteristics of undamped and traditional linear damping dynamic vibration absorbers. This ensures that the amplitude of the main system at the anti-resonance point is very low，and the suppression effect of the resonance amplitude of the main system is close to that of the traditional linear damping dynamic vibration absorber.

This paper introduces a method of using indicial functions （IFs） to simulate the time-domain expressions of self-excited aerodynamic loads of bridge decks，and studies the precision of this simulation. A modern genetic optimization algorithm is proposed to identify the parameters of IFs based on the tested flutter derivatives. During the simulation process，the equivalent relation between flutter derivatives and IFs parameters is first established. Then，the genetic optimization algorithm is implemented to identify all the IFs parameters using the MATLAB software. Based on the obtained IFs parameters，the fitted flutter derivatives are calculated according to the relation expression between IFs parameters and flutter derivatives. Finally，the simulation precision is evaluated by comparing the fitted and tested flutter derivatives. Numerical results indicate that the genetic optimization algorithm has high computational efficiency and is not affected by the number or range of parameters. The number of IFs parameters greatly influences the fitting precision of the flutter derivative. When the number of IFs parameters is small，the fitting precision is not ideal for complex flutter derivative curves. As the number of IFs parameters increases，the fitting precision significantly improves. The difference in fitting precision directly affects the critical wind speed of flutter obtained by the subsequent time-domain flutter analysis. Therefore，it is necessary to carefully select the number of IFs parameters based on the properties of flutter derivative curves. This allows for the simulation of a high-precision time-domain self-excited aerodynamic loads model，which can accurately evaluate the flutter stability of long-span bridges.

The paper proposes a time-frequency ridge index algorithm for gearboxes under variable speed conditions，based on Dynamic Path Planning of Barycenter （DPPB）. This algorithm addresses the challenge of estimating the instantaneous frequency of signals in a high-noise environment. The algorithm builds upon the analysis of the Multi-Path Matching Pursuit （MMP） ridge index algorithm and its limitations under high noise. By adding windows to the ridge set obtained by the MMP algorithm，a ridge barycenter sparse matrix of the signal is constructed. A dynamic path planning function is then designed for the barycenter sparse matrix to index the barycenters on the ridge line. The optimal time-frequency ridge line is calculated based on the values of the ridge line cost function. The similarity coefficient Ra and confidence σRa are used as measures of the ridge extraction effect. Simulations and experiments indicate that the DPPB algorithm can effectively extract the time-frequency ridge of signals in high-noise environments，and it is more reliable and robust than the peak index algorithm and the MMP algorithm under various noise intensities.

In pursuit of the ideal power-to-weight ratio，supercritical transmission shaft systems are increasingly used in the design of helicopter structures，which leads to the generation of violent vibrations driving through its critical speed. To suppress the excessive transcritical vibration，dry friction dampers are usually employed. In this study，a supercritical transmission shaft system with a dry friction damper is investigated. The governing equations are established and the boundary characteristics of various rub-impact responses of the system under eccentric excitation of the transmission shaft are analyzed. Firstly，the nonlinear governing equations of the damper/shaft system are constructed. Secondly，typical response characteristics are determined using frequency sweep，and the boundaries of impact occurrence and stability conditions for the synchronous full annular rub are solved using analytical methods. Finally，the derived response boundaries are verified by the Runge-Kutta method，and the relationship between the response boundaries and the system parameters is further explored.

It is usually difficult to establish the dynamic model of a launch vehicle that accurately describes its time-varying characteristics. Therefore modal identification techniques are particularly necessary to obtain the time-varying dynamic characteristics of launch vehicles under flight conditions. Aiming at the problem of in-flight modal identification of launch vehicles，an output-only recursive identification method based on the time-dependent autoregressive moving average model is developed by using exponentially weighted mechanisms to track the time-varying characteristics. Without measuring the natural excitation forces，the proposed method can accurately and quickly identify the time-varying modal parameters of launch vehicles by exclusively using the measured response signals. Taking the CERES-1 launch vehicle as an example，time-varying modal parameters before liftoff and during the flight phase are accurately estimated by processing the flight telemetry data. Identification results are consistent with the variation of the finite element analysis results，demonstrating the high achievable accuracy of the proposed method. The proposed in-flight modal identification method can obtain the full-cycle modal information of launch vehicles，which meets the engineering requirements for the finite element model updating and attitude control system design.

In recent years，acoustic black hole （ABH） has shown an extremely broad application prospect in the fields of structural vibration and noise suppression，acoustic wave control，energy recovery，etc，due to its excellent performance. However，the truncation of ABH edge will lead to the existence of non-zero reflection coefficient，thus weakening the acoustic black hole effect. In this paper，the constrained layer damping is introduced into ABH plates. Under the framework of Rayleigh Ritz method，Gaussian function is selected as the basis function，and the distribution of basis function is determined according to the shape of ABH plate to avoid the singularity of mass matrix and stiffness matrix. A semi analytical model of ABH plate with constrained layer damping is established. By comparing with the results of finite element analysis，the correctness of the semi analytical modeling method is verified. The influence of structural parameters of constrained layer damping on the bending vibration characteristics of ABH plate is studied，and the damping mechanism and energy dissipation of constrained layer damping are revealed. The experiment further verifies the damping effect of ABH plate with constrained layer damping. The research provides a design reference for the application of constrained layer damping in ABH structures.

The large number of aero-engine rotor components and the large computational volume of high-dimensional complex models lead to difficult dynamic analysis and long computation times，which are disadvantageous to the efficiency of rotor structure design and dynamics verification. Based on the component modal synthesis method，a novel multi-stage modal reduction strategy is proposed for the modal reduction of a large complex system with many components. The internal freedom degrees of each sub-structure are reduced in parallel using fixed interface modal reduction，while the couplings between the substructures are retained completely. By defining a new level of substructure through substructure combination，the multi-stage modal reduction is applied to an additional reduction，and the hybrid mode synthesis is subsequently combined to construct the branch mode and significantly reduce the dimensionality of the rotor FEM model. Meanwhile，the dynamic characteristics of key substructures and the key dynamic characteristics of the vibration system are preserved. This computational strategy is used to establish a low-dimensional reduced model of a missile engine rotor system，and the reduced model is used to improve the efficiency of rotor dynamics analysis and accelerate the design optimization of bearing stiffness parameters. The results show that the time required for rotor dynamics analysis is reduced by 99.5%，and the accuracy error does not exceed 0.1% compared with ANSYS calculations. The computational strategy can be used for rapid analysis of multi-component high-dimensional complex systems.

The windowed synchronous averaging （WSA） is commonly applied to the fault detection of planetary structures since it can overcome the problem of time-varying transfer path. However，it is unsuitable for the fault feature extraction of the planet gear at the first stage in a two-stage planetary gearbox due to the vibration coupling caused by the two-stage planetary structures. To address the issue，an angle compensation synchronous averaging scheme is proposed in this paper. In the proposed scheme，the speed fluctuation of the observed vibration is eliminated by equal-angle resampling. The second-stage interference from the sun gear at the second stage is constructed by applying the synchronous averaging to the resampled vibration based on the angle compensation strategy. The second-stage interference is removed by subtracting it from the resampled vibration. The corresponding envelope signal is extracted by the envelope analysis from the residual vibration. The WSA is utilized to construct the synthetic envelope signal of the planet gear at the first stage. The envelope synchronous averaging is used to suppress the asynchronous interference and extract the fault feature of the planet gear. According to the experimental results of a two-stage planetary gearbox test rig，the effectiveness of the proposed method is verified.