Mechanical metamaterials exhibit many counterintuitive mechanical properties by changing their internal geometry. We propose a mechanical metamaterial composed of gears as basic elements. The gear-based mechanical metamaterial proposed here is a multi-stable structure, which can be continuously converted between various stable states through the meshing of gear teeth. The continuous switching between states enables the mechanical metamaterial to exhibit in situ continuously tunable mechanical properties. The mechanical properties of the mechanical metamaterials were studied by using the finite element method. The results show that the gear-based mechanical metamaterials exhibited continuously adjustable stiffness, variable generalized shear stiffness, and adjustable acceleration transmissibility. These unique properties of mechanical metamaterials provide new ideas for creating programmable metamaterials with in situ continuously adjustable mechanical properties, and are expected to be applied in the fields of smart materials and engineering.

Vibration limit is one of the most essential contents in vibration serviceability research. Former studies showed that many factors, such as biological and environmental factors, significantly affected vibration limits deeply. As a reason of defects in traditional research, such as small scale data and unreal test environment, quantitative relationships between vibration limits and these factors stayed unknown. Based on data collected by crowd sensing in real environment, crest factor of vibration/ BMI/ human age/ floor of building were found key factors by using maximal information coefficient (MIC) in coefficient analysis. Functional relationship and 95% confidence intervals between vibration limits and key factors were proposed, respectively. Lilliefors test and normal probability plot show that residuals between fitted values of limits and measured ones follow a normal distribution. A novel approach of estimating vibration serviceability based on probability is proposed when key factors and vibration magnitude are known.

Artificial neural network modelling has been preliminarily employed to investigate effects on the biodynamic responses. In order to evaluate the vibration transmission characteristics of the seat‑occupant system, further quantitative research is needed. Drawing from a low frequency experimental investigation into whole body vibration, this study is aimed to develop an ANN model with the response surface method optimization. The age, stature, sitting height, knee height, buttock‑to‑knee, weight, gender, BMI, cushion thickness and frequency are used as network input to explore that these how to predict transmissibility from the seat base to the seat pan. Based on the interaction between hyperparameters, the mapping relationship between model hyperparameters and prediction performance indexes was established, and the optimal combination of hyperparameters was optimized and obtained. The results show that the resonance frequencies in the vertical inline and the fore‑and‑aft cross‑axis transmissibilities from seat base to seat pan decreased with increasing thickness of foam at the seat pan. BP‑ANN model has good performance in establishing the nonlinear relationship between the anthropometric, seat structure characteristics and vibration transmission characteristics of seat‑occupant system. Compared with BP‑ANN model, the error of RSM‑BP‑ANN model is reduced by 25% and 18% respectively in predicting vertical in‑line transmissibility and fore‑and‑aft cross‑axis transmissibility from seat base to seat pan. And this also provides an idea for adjusting the parameters of neural network models to improve the prediction accuracy of seat transmissibility.

To study the influence of the vibration characteristics of ballastless track on bridge under the failed fasteners, this thesis adopts an existing scale model of ballastless track-box girder structure. Under the random loading, the influence of different invalid fasteners conditions on the vibration response change of the track-box girder structure is discussed. The results show that the peak value of acceleration admittance increases and the peak frequency of admittance moves forward when the fastener fails, it appears in each component of the mid-span section of track-box girder structure, especially appears in the rail and track plate. At the same time, it is found that when the distance between the failure fastener and the observed section is different, the vibration response effect of the rail-box girder components is also different. When the distance between the failure fastener and the observed section within one fastener spacing, the acceleration admittance of each component of the track-box girder increases significantly, with the peak value at the track plate increasing by 1.48 times. When the distance between the failure fastener and the observed section is more than three fastener spacings, the acceleration response increase of each component of the box beam is within 5%. In addition, it is found that the dynamic response of various components of the track-box girder structure is directly proportional to the number of failed fasteners. For example, the peak acceleration admittance of the three fasteners with continuous failure at the track plate is 1.9 times higher than that without failure of fasteners. The maximum increase of peak admittance at the top plate and wing plate is 131% and 82% respectively, while the increase of peak admittance at the web plate and bottom plate of the box girder is approximately less than 25%.

In response to the problem of coupling vibration between equipment and coal rock during the anchoring drilling process of the comprehensive mining face in coal mines, considering the unevenness of the top and bottom plates of the working face, the mechanical characteristics of the anchoring drilling rig during the drilling process are mainly studied. Construct a dynamic model for synchronous anchoring operation of multi drilling rig anchoring drilling rig, and use numerical analysis methods to solve the vibration response characteristics of key components in the anchoring drilling rig. The results show that based on the time‑domain curve analysis, the maximum vibration radius of the drill pipe is 3.59 mm, and the minimum vibration radius of the drill frame is 1.51 mm； According to the frequency domain curve, it can be shown that the amplitude of the drill pipe reaches its maximum at around 11.94 Hz compared to other components of the drilling rig, with a maximum value of 392.6 mm； According to the vibration phase diagram, it can be shown that the overall stability of the power head, drilling frame, and crossbeam of the anchor drill is good during the vibration process. The vibration response characteristics of key components of the anchoring drilling rig during the drilling process were obtained through comparative experiments on the anchoring test prototype, which is basically consistent with the results of dynamic numerical simulation. This verifies the reliability of the theoretical analysis of drilling vibration characteristics of key components. The relevant theoretical results can provide a theoretical basis for the stability research of the anchoring drilling rig in the comprehensive excavation face.

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.

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.

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.

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.

Flexible cable supported photovoltaic are prone to be significant wind induced vibrations, which can lead to various structural safety and usability issues. Currently, the law of wind induced vibrations is not clear, and there are no corresponding vibration suppression measures. This study conducted wind tunnel tests on the full aeroelastic model of flexible cable supported photovoltaic. It synchronously measured the displacement and cable force of single-layer flexible cable supported photovoltaic, analyzed the effects of wind speed, inclination angle, and wind direction angle on displacement and cable force, proposed corresponding vibration suppression measures, and verified their vibration suppression effect through experiments. The results show that the flexible cable supported photovoltaic undergoes vertical and torsional coupled vibration under strong wind. The maximum displacement response occurs at wind suction and the maximum of cable force occurs under wind pressure. Therefore, wind suction is an unfavorable working condition for designing the joints. Meanwhile, wind pressure is an unfavorable working condition for designing columns and bases. The anchor cable has a significant mitigation effect on the vertical and torsional displacement at wind suction. The larger of the tilt angle is, the better mitigation effects. For the cable end force, the anchor cable can effectively reduce the fluctuation of cable force. The larger the tilt angle is, the more effective the cable force reduction.