W/Ta nanoscale metallic multilayer is a typical body-centered cubic/ body-centered cubic nanolayered composite，which is very promising for the application in nuclear fusion devices. Based on atomistic molecular dynamic（MD）simulations，we investigate the mechanical properties and plastic deformation mechanisms of W/Ta nanolayered composite under uniaxial tension，and further analyze the influence of modulation period on the mechanical response of W/Ta nanolayered composite. The results show that the W（110）/Ta（110）interface forms a misfit dislocation network，which can not only serve as the source for dislocation nucleation but also adsorb the dislocations in the metallic multilayer. The microstructure evolution analysis shows that，W/Ta nanolayered composite mainly experiences three deformation stages during stretching，i.e. linear elastic，plastic yield，and plastic flow stages. The dislocations firstly nucleate and propagate in the Ta layers，which leads to the sharp drop in the stress-strain curve. Subsequently，the dislocations in the Ta layers pass through the interfaces and enter into the W layers，and the propagation and slip of the dislocations in the W layers cause the yield of W layers. The yield of the sample is primarily determined by the Ta layers，and the plastic deformation in the flow stage is jointly governed by the dislocations and their evolution in both the W and Ta layers. With an increase of modulation period，the number of interfaces in the W/Ta metallic multilayer decreases，so that the nucleation of dislocations decreases as well as the amount of dislocations adsorbed by the interfaces decreases. In addition，the decreased number of the interface weakens the effect of hindering dislocations by interface. Therefore，the yield strength increases and the averaged plastic flow strength decreases.

The nonlinear dynamics of the bidirectional gear-driven friction nanogenerator（TENG）system is modelled by considering the time-varying meshing stiffness，time-varying support stiffness，transmission error，tooth side clearance and bearing clearance. The ode45 function is used to solve the vibration differential equations of system，and the time-varying meshing force diagram，time-frequency diagram，phase diagram，FFT spectrum diagram，Poincaré diagram，bifurcation diagram and three-dimensional spectrum diagram of the system are obtained，to explore the effect of the excitation frequency of the external load on the system dynamics characteristics. In addition，friction nano-generation technology is combined to obtain the output performance of TENG under different parameters，and to investigate the mechanism of the influence of external load excitation frequency and average engagement stiffness on the energy harvesting of the system. The results show that the bidirectional gear-driven friction nanogenerator mechanical transmission system has obvious nonlinear characteristics，and reasonable selection of the external load excitation frequency and meshing stiffness to avoid the control of unstable intervals can improve the mechanical energy conversion efficiency and increase the power generation capacity of TENG.

The transverse free vibration characteristics of a two-dimensional nanoplate with axial velocity are investigated based on the nonlocal strain gradient theory. The vibration control equations for the in-plane advection of the system are established according to the generalized Hamilton’s principle，and the intrinsic frequency of the nanoplate is derived by using complex modal analysis in the case of a four-ended simple support. The critical velocity of the system is determined by the equilibrium solution of the control equations，and the real and imaginary parts of the first-fourth-order modal functions are further analyzed for both the sub-critical and the supercritical velocities. The numerical results show that the scaling effect leads to a change in the self-oscillation frequency of the system at the micro- and nanoscale，and the nonlocal and strain gradient parameters have‘softening’ and‘hardening’ effects on the equivalent stiffness of the nanoplates，respectively，which affects the intrinsic frequency and the modal function of the nanoplates. This affects the intrinsic frequency and mode function of the nanoplates，and the higher order frequencies and vibration modes are more significantly affected by the size parameters.

A dynamic similitude design method is proposed for the problem of sudden unbalance of the rotor system. The dynamic differential equation requires the application of both equation analysis and dimensional analysis methods to establish the scaling laws, while also considering the damping scaling ratio. Based on the strain energy distribution criterion, a prototype rotor system is designed. The prototype is scaled according to the scaling laws to create a distorted model, and the dynamic similarity between the prototype and the distorted model is verified through simulation and test. The simulation results show that the distorted model exhibits high similarity to the prototype in terms of critical speed, strain energy distribution, and transient response. The errors for the first two critical speeds are 0.1% and 0.13%, respectively, and the error in peak amplitude is 3%. The test results show that the distorted model can accurately predict the critical speed and sudden unbalance vibration response of the prototype, with the errors for the first two critical speeds being 0.79% and 1.72%, respectively, and the error in peak amplitude being 5.98%.

Aiming at the vibration problem of rotating pre-twisted beams in engineering, an effective modeling method is proposed to study their vibration characteristics. Rotating experiments are designed to verify the accuracy of theoretical research. By adjusting the boundary spring stiffness, different boundary conditions are simulated. The displacement field is expanded using the modified Fourier series method, and the motion equation of the rotating beam is derived using the Rayleigh-Litz method. Based on the theoretical research, vibration tests of rotating straight beams and pre-twisted beams with different sizes are designed. The accuracy of this method is verified by comparing the theoretical calculations with finite element simulations and experimental results. The possibility of elastic boundaries is also verified through error analysis. The results show that the natural frequency of the beam increases with the increase in rotating speed and thickness. The increase in pre-twist angle has a minimal effect on the first-order natural frequency but significantly reduces the second-order natural frequency.

Parametric vibrations are commonly observed in microelectromechanical systems(MEMS) coupled with multi-physical fields. To study the parametric resonance nonlinear dynamics problems in electrostatically driven micromirror systems, a class of electrostatic comb-driven micromirrors is used as an example to study the parametric resonance response variation of the system under different factors by fitting a seventh-order polynomial to the comb capacitance variation and establishing a micromirror dynamics model. The influence of changes in the micromirror’s structural parameters on the torsion angle under static conditions is investigated. The multi-scale method is applied to analyze how system parameters affect the variation in resonance amplitude during the resonance state, and numerical verification of system parameter resonance is performed. Finally, the stability of subharmonic parametric resonance in the system is analyzed and verified using the Runge-Kutta method. The results show that subharmonic parametric resonance exists in the micromirror system. Factors such as excitation voltage and capacitance fitting parameters can affect the system’s resonance amplitude. Damping can alter the system’s instability region, increase the instability threshold, and influence the occurrence of subharmonic parametric resonance in the system.

To address the problem of contact between the slender rods and tubes immersed in fluid, a numerical method is established to model the coupling vibration and collision between slender rotating rods and the produced fluid, based on the overset mesh technique. The outer annulus fluid domain is divided into two overset subregions: a background mesh and a component mesh. The interpolation formula is derived to transfer fluid field boundary information in each overset region. The subdomain method is used to solve the coupling between the produced fluid domain and the rod solid domain. Additionally, the transfer method of physical variables and a normalized convergence criterion are established for the coupling interface. A coupling simulation device for a vertical rotating rod and produced fluid is established, and the numerical simulation results are compared with experimental results to validate the correctness of the numerical method presented in this paper. The coupled vibration and collision characteristics between the slender rods and tubes are studied under different fluid viscosities and rotational velocities. The results show that as fluid viscosity increases, the influence of viscous resistance on the motion of the rod becomes more pronounced, leading to lower contact pressure and reduced vibration. As the rotational speed of the rod increases, the vibration becomes more intense, the influence of torsional deformation on the rod’s motion becomes more significant, the normal acceleration during collision decreases, and the contact pressure decreases accordingly. When the collision occurs between the rods and tubes, the acceleration at each point of the rod changes abruptly, and the vibration intensity increases.

Clustering analysis is a commonly used unsupervised method in data processing. However, the difficulty in accurately determining clustering parameters limits the application of this method in structural damage identification. To address this issue, a non-parametric Bayesian clustering method is proposed in this study, which combines structural modal parameters for structural damage identification and quantitative analysis, thereby expanding the application range of the non-parametric Bayesian model.First, the natural excitation method is used to extract the natural frequency from the measured vibration data of the structure.Then, the non-parametric Bayesian clustering method is employed to cluster the data. Finally, maximum likelihood heteroscedastic Gaussian process regression and Bayesian factors are combined to quantitatively analyze the clustering results for damage quantitation analysis. The results of the damage identification method are verified by the actual engineering case of Yonghe Bridge in Tianjin. The results show that this method can accurately cluster the natural frequency data and identify the different damage states of the structure without the need to pre-set clustering parameters.

In order to evaluate the fatigue performance of the steel anchor box (SAB) when its stay cable experiences large-amplitude vortex-induced vibration (VIV) under in-service condition, continuous monitoring was conducted on a long-span cable-stayed bridge. The acceleration of the stay cable undergoing VIV and the stress at the SAB details were measured. The characteristic of stay cable vibration, as well as the stress at the SAB details due to VIV of the stay cable, vehicles loading, and thermal effects, were investigated in both time and frequency domains. Hence the loading mechanisms of VIV, vehicle loading, and thermal effects on the SAB were discussed. Based on the nominal stress method, the fatigue performance of the SAB under the joint action of VIV, vehicle loads and thermal effects were evaluated. The results show that the significant vibration of stay cable, characterized by the high-order multi-mode VIV, dominated by in-plane vibration with peak frequencies between the fifth and the seventeenth modes, occurring within a mean wind speed range of 2 m/s to 9 m/s, with observed maximum in-plane peak acceleration of 25 m/s².Thermal effects significantly contribute to the maximum stress range at the SAB details, although they only generate one stress cycle per day. Compared to the thermal action, the stress range generated by the passage of vehicles is relatively low, but trucks produce a large number of loading cycles. The inertial force generated by VIV of the stay cable applies very low stress to the SAB, making its effects on stress and fatigue negligible. It is concluded that the fatigue evaluation of the steel anchor box should consider the thermal effects. However, even when considering the combined effects of VIV loading, thermal effects and vehicle loading, the fatigue life at the critical details of the SAB—specifically the deck-side welds of the upper and lower plates to the outer web, as well as both weld ends of the bearing plate to the outer web of the steel box girder—exceeds 100 years. Therefore, the fatigue performance of the SAB under in-service conditions meets the bridge design requirements, even with large-amplitude VIV of the stay cable.

In complex hilly terrain, the wind field around interfered hills is influenced by nearby hills, which affects the wind-induced fatigue damage of the tension suspension-braced transmission structure. Therefore, the effect of occluding hills must be considered in the analysis of wind-induced fatigue. In order to analyze the influence of occluding hills on the wind-induced fatigue damage of the transmission structure in complex hilly terrain, wind tunnel tests on the wind filed characteristics of complex hilly terrain were first conducted. Based on the test results, the variation of the mean velocity correction factor and the fluctuating velocity correction factor of the wind field around interfered hills, with different slopes, heights and interval distances of occluding hills, were studied, and a corresponding distribution model was proposed. Next, a nonlinear finite element model for wind-induced vibration of the tension suspension-braced transmission structure considering the effect of occluding hills was established using the nonlinear finite element method. Then the time domain rain-flow method and the Miner’s linear cumulative damage theory were applied to estimate the wind-induced damage to the structure. Finally, a two-span tension suspension-braced transmission structure was selected as a case study, and considering the effect of occluding hills, the wind-induced fatigue damage was analyzed using the proposed model. The results show that: the fatigue damage in each part increases initially and then decreases as the slope of the occluding hills increases. The heights of occluding hills have little effect on the fatigue damage of each part, with no obvious trend. When the interval distances between occluding hills is between 0 m and 600 m, the fatigue damage in each part gradually decreases as the distance increases. However, when the interval distance is between 600 m and 800 m, the fatigue damage of each part suddenly increases as the distance increases. Under the influence of the same occluding hill, the fatigue damage of the end of the conductor and the supporting-conductor suspension cable is greater than that at the mid-span.