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.

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%.

The control of vibration and acoustic radiation in rectangular confined spaces has been an important challenge in engineering. In this study, a solution is proposed with a sensor-actuator control system consisting of a loudspeaker, a base and a piezoelectric ceramic sensor. This design has the advantages of lightweight, low natural frequency and integrated sensing/actuator design. However, the strain-integra control scheme used for the integrated sensor-actuator suffers from stability problems. To overcome these problems, this paper utilizes a control strategy with a band-pass filter. The study tests the mechanical properties of this home-made inertial actuator, and determines the structural modes that have the greatest impact on the acoustic performance. A band-pass filter control strategy is used to selectively modulate these structural modes. The experimental results show that the homemade inertial actuator can effectively generate inertial forces, while the band-pass filter can effectively reduce the structural vibration, especially in controlling the first two acoustic cavity modes in the low-frequency band, which exhibits a significant effect. This approach is more flexible in controlling low-frequency noise in confined spaces and provides an efficient solution to the problem of structural noise in engineering environments.

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 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.

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.

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.

The intrinsic characteristics of all-composite honeycomb core sandwich panels (ACHCSP) were investigated using a combined approach of theory and experimentation. A theoretical model of the ACHCSP structure was established based on the high-order shear deformation theory and Gibson equivalent theory. The dynamic characteristics of this structure were determined using the Rayleigh-Ritz method and orthogonal polynomial approach. A relevant experimental platform was constructed to conduct tests on ACHCSP as the research subject, thereby confirming the accuracy of the theoretical model. The results indicate that this theoretical model can accurately predict the natural frequencies of ACHCSP plates. Based on the established model, the influence of fiber layer thickness, honeycomb cell wall thickness, and wall length on the natural frequencies of ACHCSP structures is discussed.

Analysis of the instantaneous angular speed (IAS) has been proven to effectively detect bearing faults. To investigate the generation mechanism of IAS signal double-impulses phenomenon in ball bearings, a dynamic model is proposed in this paper based on the coupling characteristics between the normal, tangential forces and the time-varying impact excitation, in which the influences of the rolling resistance and the sharp edges of local defect on the dynamic behavior are considered. In this model, the elastic quarter-space method is adopted to calculate the additional deformation induced by the local spalled edges and its corresponding time-varying displacement excitation model is deduced. Additional contact forces and time-varying displacement excitations are considered when steel ball enter into and exit from the defect. The disturbances of normal and tangential forces in the bearing under sharp-edge excitations of local fault are studied, and the time-varying tangential force excitation model is also deduced. The nonlinear dynamic equation sets are solved using the Runge-Kutta numerical integration method. Comparisons between the simulation results and the actual measured results of outer race local fault bearings show the established dynamic model can effectively reveal the mechanism of double-impulses phenomenon based on IAS signals.

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.