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.

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 human body’s perception of one stimulus may change due to the occurrence of another stimulus, which leads to the possibility of a masking effect between vibrations that successively act on the human body. Whether the masking effect is significant or not is related to many factors. This study designed and carried out a seated human vibration experiment to explore the impact of time-domain masking effects on vibration comfort of the seated human body. Designed variables include： intensity of masking signals (3 levels）, vibration interval (4 levels）, and masking sequence (forward and backward）. The experimental results show that these factors do have an impact on the overall comfort when subjected to whole-body vibration； comparing the effects of forward masking tests and backward masking tests, the discomfort caused by backward masking tests is stronger； with the increase of vibration time interval and the decrease of the masking signal strength, the influence of the masking effect on human body discomfort gradually weakens. It can be found that in addition to frequency domain weighting, the time domain characteristics of vibration amplitude also have a non-negligible impact on the evaluation of human vibration discomfort. Comfort prediction based on objective responses should consider the influence of more factors.

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 quantitative analysis of the effect of low-frequency vibrations on the sitting comfort has been a pivotal focus in the field of transportation engineering. In this study, the transmission of vibration through the human-seat system with different excitation conditions is predicted and analyzed using the finite element modeling. Individual finite element models for the human body and the seat, along with their respective contact properties, are constructed and integrated into an overall finite element model of the human-seat system. The model parameters are validated utilizing experimental data from static body pressure distribution at cushion and backrest locations, as well as the measured seat transmissibility obtained with the vertical excitation. The results indicate the finite element model, validated through the calibration, demonstrates a good fit with experimental data for the seat transmissibility under the fore-and-aft excitation. However, there is a deviation in the amplitude at the resonance frequency. Additionally, the model predicts that the resonance frequency of the seat transmissibility decreases with an increase in the excitation amplitude, and this trend aligns well with experimental results, particularly under the vertical excitation. The constructed model accurately reflects the dynamic response of the human-seat system with different conditions. It serves as a valuable reference for the seat design.

In order to explore the correlation between seated body pressure distribution and biomechanical loading, a setup scheme for the human-chair contact surface for human biomechanical modelling is proposed using body pressure information as a guide. The contact between the human body and the seat is simulated by a certain number of contact points, and based on the experimental body pressure distribution data, the relative contact strength is set as the relative magnitude of the average pressure in each partition of the body pressure cloud map. Through comparison, it is discovered that the average contact strength is set between 200~600, which can improve the solution accuracy and take into account the real muscle activation effect. At the same time, the scheme of different numbers of contact points was discussed, and it is more reasonable to choose to set 8 contact points in a comprehensive view. After comparing with the experimental data in the literature, it is shown that the contact scheme based on the body pressure distribution of the human chair biomechanical model can accurately reflect the muscle activation, joint force and other biomechanical indicators. Muscle activation and joint forces under hardwood planks and foam cushions were compared based on a contact scenario setup, explaining the reasons for more comfortable foam seating from a biomechanical point of view.

As a component widely used in various industries, the noise problem of fans has always attracted people’s attention. In equipment with relatively low noise energy levels, abnormal noise, such as whistling, or rattlesing, from fans are key factors that lead to user complaints. Taking laptop fans with various abnormal noises as an example, the correlation between the severity of fan abnormal noise and the main psychoacoustic parameters of sound quality was studied, and a linear regression model between the subjective score of abnormal noise and the objective parameters was established. The results show that loudness, sharpness, prominence ratio, and the frequency corresponding to the maximum value of pitch affect the subjective feeling of abnormal noise. The multivariate linear model including loudness and sharpness can better evaluate the subjective score of the severity of abnormal sound.

Limited by common situations of closely spaced modes and large structural dimension, damage identification based on modal parameter is difficult to perform in civil structures. A damage identification method based on multi-level modal group response reconstruction in the presence of close spaced modes is proposed. Several modes with small intervals are grouped together, and response of the entire modal group is extracted as damage sensitive characteristic. Based on the collected modal response, a multi-level damage identification strategy is adopted. In the super element level damage location, the original structure is first converted into a super element model with fewer DOFs through model reduction, and then the minimization problem is solved by defining the modal group response strain energy as a damage index to achieve the location of damaged super elements; In element level damage identification, the minimization problem is expressed as the discrepancy between reconstructed and actual modal group response to achieve elemental damage localization and quantification. A numerical simulation study and the experimental verification were conducted to demonstrate the operational process and feasibility of this method. Compared with traditional methods, the results show that the proposed method improves the accuracy and efficiency of damage identification through multi-level identification strategies and model reduction, and on the other hand, improves the shortcomings of modal-analysis-based methods that cannot accurately identify damage when faced with close spaced modes. Regardless of the presence or absence of close spaced modes. Damage identification can be performed based on multiple dynamic responses such as stress, strain, displacement, and acceleration of the structure.

Impacts between the flexible rotor and stator will excite the internal resonance of the forward and backward modes, resulting in asynchronous vibration, i.e, intermittent contact between the rotor and stator. To reveal the internal resonance mechanisms of the forward modes and backward modes, a mathematical model of the rotor system is established, Runge-Kutta numerical solution is used to solve the equation of motion, and the event detection function is used to detect the contact and non-contact motions. Through the coordinate system transformation, the Campbell diagrams of the rotor system under the stationary coordinate system and the rotating coordinate system are obtained, and the internal resonance speeds in the forward modes and backward modes are analyzed. Through the numerically calculated bifurcation diagram, the trajectory and frequency domain characteristics of the rotor when the asynchronous contact motion occurs are analyzed. The results show that the main resonance amplitude jumps at the critical speed, and there are two asynchronous contact response speed ranges. The rotor exhibits a closed continuous precession law in the stationary coordinate system and a periodic motion law in the rotating coordinate system, and there is a frequency doubling relationship in the rotation coordinate system, and the system has 2：1 and 3：1 internal resonance phenomena. The numerical simulation analysis verifies the correctness of the rotating speed predictions corresponding to the internal resonance, and the rotating speeds corresponding to the internal resonance can be predicted by this calculation method to avoid the internal resonance phenomenon caused by asynchronous contact.

Traditional computer vision methods usually focus on the in-plane dynamic response of structures. Therefore, this paper proposes an image phase-based stereo matching temporal analysis method to achieve targetless robust monitoring of three-dimensional structural deformation. This method uses 2D-Gabor filters and Gaussian pyramid gradient algorithms for image preprocessing, applies a phase-based dense optical flow tracking algorithm and an improved semi-global block matching (SGBM) algorithm to realize full-field measurement of structural displacement in the region of interest, and further proposes an intuitive displacement-strain conversion method to measure three-dimensional strain of structures. Through virtual reality experiments based on physics-based graphics models (PBGM), it is verified that the error of this method compared with 3D-DIC and finite element analysis deformation is less than 2%; in vibration tests of outdoor bridge structures in the laboratory, the deformation error compared with traditional testing methods can be controlled within 8%, meeting engineering application accuracy. Without compromising accuracy, this method achieves targetless robust monitoring of three-dimensional structural deformation, and better solves the problems of large environmental impact and high cost in traditional structural deformation monitoring.