To broaden the site selection for nuclear power plants，it is vital to assess the seismic safety of nuclear power structures in non-rock sites with pile foundations. Current pile-soil-structure interaction analysis methods，such as the Winkler foundation model and the p-y method，simplify the interaction problem and struggle to reflect complex foundation situations. While the integral finite element method can consider complex foundation situations，it is computationally intensive and inefficient. This paper introduces an efficient three-dimensional time-domain method，Partitioned Analysis of Soil-Structure Interaction （PASSI），which uses different time steps for pile foundation and soil to avoid unnecessary calculations. A three-dimensional finite element model of the pile-soil-nuclear power structure interaction is established，with the AP1000 nuclear island structure as the research object. The effectiveness of this asynchronous algorithm is verified by inputting pulse waves，and the characteristics of the maximum shear force and bending moment of the pile are analyzed by combining the kinematic and inertial interactions. The response of the pile-soil-nuclear power structure under the seismic wave input is then analyzed. Since the degrees of freedom of the pile are insignificant compared to the soil，the additional computational volume of the pile can be neglected when using the pile-soil asynchronous algorithm. This efficient method is expected to be used in the analysis of the dynamic interaction of large nuclear power structures with pile-soil-structures.

Current studies on the failure modes and safety evaluation of asphalt concrete core walls and dam bodies under the spatial oblique incidence of seismic waves are significantly lacking. This paper considers the spatial variability of the SH wave incident azimuth，and constructs the non-uniform free field on the foundation boundary based on the wave field superposition principle. It establishes a wave input method for SH waves with three-dimensional space oblique incidence. An empirical formula is then established for the change in the instantaneous tensile strength of asphalt concrete with the strain rate，based on the test results. A new method for core wall safety evaluation，based on instantaneous tensile stress and instantaneous tensile strength，is proposed to judge the tensile failure of elements. The influence of the incident azimuth on the dislocation between the transition material and the core wall，and the stress of the core wall，are analyzed. A shear failure evaluation of the dam body is carried out，and the seismic weak parts of the core wall and the dam body under different incident orientations are clarified. The results show that the seismic wave vibration direction parallel to the water flow direction is the most unfavorable excitation direction for transition material dislocation，core wall tensile stress，and local dynamic shear failure of the dam body. Compared with the vibration direction parallel to the dam axis direction，the horizontal detachment and vertical dislocation of the transition material increased by 19.25 times and 2.19 times respectively when the vibration direction was parallel to the water flow direction. The maximum tensile stress of the core wall increased by 1.8 times，and the dynamic shear failure depth of the upstream dam slope element deepened. Moreover，compared with the core tensile failure judgment method proposed in this paper，the traditional judgment method will lead to an overestimation of the damage degree of the core wall.

The study investigates the dynamic elastic modulus and damping ratio of sand and gravel under single and bidirectional cyclic loads using a large-scale vibration triaxial test. It also analyzes the effects of confining pressure and radial cyclic stress on the dynamic parameters of sand and gravel. The results show that in the bidirectional vibration triaxial test，the axial dynamic strain of sand and gravel is less influenced by the radial dynamic stress，with the dynamic strain primarily related to the applied axial dynamic stress. Under both unidirectional and bidirectional vibration，the dynamic elastic modulus of sand and gravel gradually decreases with the increase of dynamic strain. Under bidirectional vibration，the decay rate of dynamic elastic modulus of sand and gravel remains essentially unchanged，and the dynamic modulus of bidirectional vibration is lower than that of unidirectional vibration under the same dynamic strain. The damping ratio of sand and gravel under bidirectional vibration is larger than that under unidirectional vibration，and the dynamic strain energy consumed under bidirectional vibration is larger. Based on the analysis of the maximum dynamic elastic modulus and dynamic modulus ratio under the two test conditions，a conversion relation expressing the maximum dynamic elastic modulus under single and double direction test conditions and a correction model of the dynamic modulus ratio and dynamic strain in the bidirectional vibration test were established. The research results can provide a theoretical basis for the seismic design of sand and gravel in high earth-rock dams.

This paper proposes a fault diagnosis method for rolling bearings under variable speed conditions，based on the Adaptive Window Rotation Optimization Short-Time Fourier Transform （AWROSTFT）. This method addresses the issue of low energy concentration caused by the fixed window effect in Short-Time Fourier Transform （STFT）. Variational Mode Decomposition （VMD） is used to reduce the noise of the original vibration signal，and Particle Swarm Optimization （PSO） is employed to solve the complex problem of VMD parameter selection. A series of rotation operators are adaptively matched to the horizontal window in STFT using the tangent idea，aligning the rotation direction of the window with the instantaneous frequency modulation to improve the energy concentration of time-frequency representation. The instantaneous frequency，extracted by the spectral peak detection method，is divided by the frequency transformation curve. The result is matched with the fault characteristic coefficient of the bearing to achieve fault diagnosis of the rolling bearing under variable speed conditions. The results of simulation and experimental signals show that the proposed method effectively combines the advantages of PSO-VMD and AWROSTFT. Through the adaptive rotation window with the idea of tangency，the angle between the signal and the window function is globally reduced to zero，improving energy concentration，sharpening the time-frequency ridge line，and enabling fault diagnosis of rolling bearings under variable speed conditions.

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.

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.

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.

In the process of maneuvering flight，the aeroengine will bear very harsh working conditions，leading to irregular transient vibrations that can result in failure. In this paper，the effect of a semi-active magnetorheological damper （MR damper） on the dynamic characteristics of a rotor system under maneuvering flight is investigated. The finite element model of the rotor system with MR damper under maneuvering flight is established using the finite element method. The Newmark-β numerical method is used to solve the dynamic equations，and the dynamic characteristics of the rotor system during maneuvering flight are studied. On this basis，considering the effects of MR damper on the transient，the steady state responses of the rotor system under maneuvering flight are analyzed. The results show that transient impact is caused at the beginning and the end of maneuvering flight，which stimulates the first order modal response of the rotor system. The MR damper with suitable current can effectively suppress the amplitudes of transient and steady-state responses of the rotor system during maneuvering flight. In addition，due to the large eccentricity of the journal in maneuvering flight，the MR damper is prone to produce nonlinearity.

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.

Taking aircraft brakes as the research object，the problem of aircraft brake induced vibration was studied. Aiming at the influence of disc friction characteristics caused by the complex braking environment during aircraft skidding，a nonlinear dynamic analysis model of brake disc set was established considering the properties of the hydraulic system and disc material，with the model interface reserved for the development of new material technology. From the perspective of practical engineering research value，the influence of the above parameters on the stability of the system is studied by using numerical simulation，bifurcation theory，and other nonlinear analysis methods by considering key factors such as wheel speed，hydraulic system equivalent damping，brake disc surface damping and brake disc friction characteristics as control variables，and the range of structural parameters to keep the system stable is determined. It is convenient to parameterize the structure for rapid analysis and design. Based on the results of the model analysis，part of the causes of brake vibration were revealed，and corresponding optimization measures for vibration reduction were put forward from two aspects of structural parameters and brake control law. Then a comprehensive analysis method for aircraft brake induced flutter was formed，which provided a theoretical reference for the initial stage of aircraft brake design.