Seismic experience has shown that underground shaft structures are subjected to seismic threats and severe examples of damage have occurred. In order to obtain the seismic response of the shaft, the ‘beam-spring’ model was used to establish a system analysis model for the dynamic interaction between the large-diameter shaft and the soil based on the Pasternak foundation and the Timoshenko beam theory. On the basis of considering the normal earth pressure of site soil layer and shaft structure, the tangential shear force of site soil layer and shaft structure is further considered. The analytical solution of seismic response of large diameter shaft under horizontal earthquake was studied. The peak seismic response of the shaft along the depth direction is analyzed from the aspects of the ratio of the length to diameter of the shaft, the ratio of the inner and outer diameters, the ratio of the elastic modulus of the shaft to the site and the boundary conditions at the bottom of the shaft. The results show that the decrease of the ratio of the length to diameter of the shaft will lead to the increase of the peak response of the internal force of the shaft along the depth direction. The increase of the inner and outer diameter ratio of the shaft will reduce the peak internal force response of the shaft along the depth direction. With the increase of the ratio of the elastic modulus of the shaft to the site, the peak response of the internal force of the shaft along the depth direction will gradually increase. The displacement response of the shaft under the elastic soil foundation is larger than that of the rock-socketed foundation. The shear response under the rock-socketed foundation along the depth direction of the shaft is significantly larger than that of the elastic soil foundation, and the bending moment peak response of the rock-socketed shaft at the bottom position is larger.

The uncertainty of the combined incidence angle of seismic waves often has a significant effect on the dynamic response of faced rockfill DAMS. In this paper, the motion field of surface control points is decomposed by the principle of wave field superposition, and the time history of incident P and SV waves is obtained by two‑dimensional inversion. The angle of incident P wave and SV wave in the wave input model are randomly selected by the method of number theory. The influence of the uncertainty of combined incident angle on the seismic response of asphalt concrete faced rockfill dam is studied by the dynamic calculation of different combined incident angles. Taking a practical project as an example, by analyzing the mean value, coefficient of variation, 95% confidence interval limit and extreme value difference of the horizontal peak acceleration of foundation surface, panel stress and acceleration, dam body horizontal peak acceleration and permanent deformation, and other statistical laws and distribution type tests, and compared with the vertical incidence of seismic waves, The influence of random combination incidence Angle and input ground motion intensity on random response dispersion degree and obedience probability distribution is analyzed. The results show that considering the uncertainty of the combined incidence angle, the seismic response dispersion of the foundation surface of the dam will increase. The maximum principal tensile stress of the panel increases by at least 40% compared with the calculated result of vertical incidence. The influence of the horizontal peak acceleration on the dam crest and the panel crest is greater than that on the permanent deformation. Compared with the results of vertical incidence, the permanent deformation of the three groups of seismic waves has a transcendental probability of more than 70%. The statistical results of seismic response of dam body may not accord with normal distribution. The dispersion of seismic response results of overlay layer is greater than that of dam body.

Blind source separation (BSS) can be used to extract modal coordinate vibrations from structural vibration signals. Complexity pursuit (CP) is one of the classical methods for solving the BSS problem. To improve the computational efficiency of the CP algorithm, this paper proposes two enhancements： it uses the negative log function of a Gaussian distribution as a nonlinear function to estimate signal complexity and derives formulas for rapidly computing signal complexity and its gradient； it employs a subspace search-based gradient descent algorithm to calculate the optimal mixing vector in the reduced subspace. The new formulas only require the covariance matrix of mixed signals and the covariance matrix of time delays when computing complexity and its gradient, without using all signal data. Numerical examples and structural vibration data are employed to evaluate the proposed method. The results demonstrate that the fast complexity pursuit algorithm outperforms traditional methods in terms of computational efficiency and accurately separates structural modal coordinate vibrations.

The flexibility of gear teeth under cyclic varying loads can induce meshing impact and nonlinear vibration of gear pairs. Revealing the multi-state meshing characteristics and nonlinear dynamic characteristics of spur gear systems considering teeth flexibility lays the foundation for the safe and reliable operation of transmission systems. Based on the cantilever beam theory and gear meshing principles, the flexible deformation of meshing teeth is calculated, and the calculation method for flexible time-varying meshing parameters of gear pairs is derived； based on the contact states and loading conditions of the gear pairs, extract the characteristics of multi-state flexible meshing, and a nonlinear dynamic model of the spur gear system with multi-status flexible meshing is established； study the evolution laws of flexible time-varying meshing parameters and the distribution characteristics of flexible deformation of gear teeth under multi-parameters correlation, and uncover the global bifurcation and chaos characteristics of the system when the teeth flank clearance changes. The results indicate that the flexibility of the gear teeth reduces the double teeth meshing area, affects the meshing parameters and multi-status meshing characteristics of the gear system, and induces out-of-line meshing of the gear pair； the variation of teeth flank clearance causes the coexistence of periodic motions and chaotic motions, and incomplete bifurcation under multiple initial conditions is the fundamental cause for such dynamic behavior coexistence.

This paper proposes an accurate and efficient solution strategy for analyzing dynamic responses of flexible multibody systems. In the proposed strategy, flexible structures are modeled in the corotational frame, then the discrete mathematical model is solved by an optimized composite method. Due to the introduction of the corotational frame, some advanced linear elements can be directly employed, dramatically decreasing computational costs. For accurately calculating dynamic responses, an optimized three-sub-step composite method is developed wherein algorithmic parameters are optimized for minimizing local truncation errors. The optimized composite method achieves second-order accuracy, unconditional stability, and controllable stability. Some classical flexible dynamic systems are solved in this paper, and numerical results show that compared to the currently popular solution strategy based on the absolute nodal coordinate formulation and the Generalized-α method, under the same computational accuracy, our strategy has great superiorities in efficiency.

The non-uniform input of ground motion has a significant effect on the dynamic response of a concrete cut-off wall in deep overburden. In order to explore the response characteristics of the cut-off wall under non-uniform ground motion input at the overburden site, this study establishes the input method of P-wave three-dimensional oblique incident wave motion under any incident angle in space based on the wave field decomposition method and the viscoelastic artificial boundary method, and validates the input method. Nine non-uniform input conditions were designed to investigate the influence of different azimuthal and oblique incidence angles on the dynamic response of the cut-off wall under a combination of incidence. The results show that the maximum acceleration in the down-river direction of the cut-off wall at α=60° and γ=0° incidence is 3.89 times that of vertical incidence, and the maximum acceleration in the axial direction of the dam at α=60° and γ=90° incidence is 8.93 times that of vertical incidence. Non-uniform input causes a significant increase in the transverse riverward tensile stresses in the impermeable wall, up to 3.53 times that of the vertical incidence, with a significant change in the peak distribution region, and the vertical compressive stresses are significantly reduced at an oblique incidence angle of 90° incidence compared to the vertical incidence. The traditional vertical incidence method can ignore the expansion area of tensile stress of the cutoff wall under non-uniform input, so the non-uniformity of ground motion should be considered when analyzing the dynamic response of the cutoff wall in a deep overburden layer.

Aiming at the difficulties that the vibration response signal of the viscoelastic sandwich structure is strongly non-stationary and the change of vibration response signal caused by the change of aging state is weak, this paper proposes an intelligeat identification method for the aging state of the viscoelastic sandwich structure based on sparrow search algorithm (SSA) optimized variational mode decomposition (VMD) and adaptive neuro-fuzzy inference system (ANFIS）. The vibration response signals of different aging states of the viscoelastic sandwich structure are decomposed by the parameter-optimized VMD, and several intrinsic mode functions (IMFs) are obtained； The permutation entropy (PE) features of the obtained IMF components are computed, which are used to reflect the structural aging state change； The obtained permutation entropy features are constructed into feature vectors as inputs of ANFIS to realize the aging state intelligent iclentification of viscoelastic sandwich structure. The effectiveness of the method was verified through experiments, and compared with empirical mode decomposition (EMD) and ANFIS, parameter optimized VMD and radial basis function neural network (RBFNN) methods. The results show that the proposed method in this paper can more accurately identify the aging state of viscoelastic sandwich structure.

Ride comfort evaluation of high‑speed trains has vital importance for continuously improving the structural design and passengers’ ride satisfaction. This paper tries to evaluate the long‑term and momentary ride comfort of high‑speed trains in China in the light of the European standard EN 12299：2009, and discuss the applicability of the standard. Objective vibration test and subjective comfort evaluation were carried out in a comprehensive inspection train. Average comfort index and discrete events comfort index recommended by the EN 12299：2009 standard were briefly introduced, and the two indexes were selected for long‑term comfort evaluation and momentary comfort evaluation respectively. For the three kinds of track sections with different subjective feelings, based on the measured vibration acceleration data, the long‑time and momentary comfort evaluation indexes were calculated respectively, the comfort of high‑speed train and track quality were analyzed. Combined with the subjective evaluation results, the applicability of the corresponding indexes was analyzed, and attempts were made to put forward suggestions for improvement. according to which the comfort of high‑speed rail ride and the quality of the track into the standard is analyzed. The applicability of these indices was analyzed by referring to the subjective evaluation, and certain suggestion was proposed to modify the indexes.

To address the issue of unclear and challenging identification of non-contact rotating seal fault signals, this study established an experimental platform and acoustic emission testing system. It involved monitoring acoustic emission signals during various operational conditions, including normal operation and six typical fault scenarios of non-contact rotating seals. A total of 14000 feature samples were effectively collected. By applying the Bayesian optimization algorithm and incorporating continuous wavelet transform, an adaptive convolutional neural network classification model was constructed. Subsequently, the diagnostic performance of the fault recognition model was analyzed using confusion matrices and t-distributed stochastic neighbor embedding. The research results demonstrate that this model successfully classifies and identifies seven different operational conditions of non-contact rotating seals, including normal operation, dry friction, mixed lubrication, spring failure, end-face pitting, local spring failure, and end-face scratching, with an average recognition accuracy of 99.7023%. This achievement underscores the capability of effectively isolating and identifying seal fault sources from acoustic emission signals of non-contact rotating seals in non-stationary, complex, and overlapping environments, thereby establishing a solid theoretical foundation for practical engineering applications.

In order to obtain the main influencing factors of buffeting response calculation of Π‑shaped main girder cable‑stayed bridge, taking Qingzhou Minjiang River Bridge as the engineering background, the buffeting response characteristics of main girder displacement were analyzed by using three‑dimensional multi‑modal coupling buffeting calculation method on the basis of wind tunnel test. The significance of nine factors in buffeting response was tested by uniform experimental design and regression analysis method. The results show that the aerodynamic admittance, fluctuating wind correlation coefficient, vertical wind spectrum, average wind profile index, surface roughness height and air density have significant influence on the buffeting response of cable‑stayed bridge in the common range of values. The influence of structural mass and damping ratio is not significant, and its value deviation can be ignored in buffeting calculation. The horizontal wind spectrum only has a significant effect on the lateral buffeting response.