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.

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.

To ameliorate the low-frequency sound absorption performance of bulk porous materials, a theoretical model for predicting the sound absorption of the composite structure incorporating flexible ultra-thin and bulk porous materials is derived. The model integrates Johnson-Champoux-Allard (JCA) model and acoustic impedance model for flexible ultra-thin materials, employing non-woven fabric and melamine cotton as illustrative instances. The accuracy of this model is validated through experimental verification, and particle swarm optimization (PSO) is employed to optimize the parameters of the composite structure. The analysis results indicate that the addition of a layer of non-woven fabric on the surface of traditional bulk porous materials significantly enhances the low-frequency sound absorption performance. This paper provides a theoretical foundation for the determination, analysis and optimization of the sound absorption performance of the composite sound-absorbing structure composed of flexible ultra-thin and bulk porous materials, Additionally, it presents an effective method for improving the low frequency sound absorption performance without changing the thickness of the original sound absorber.

A method of product sound quality classification and limit value evaluation based on satisfaction is proposed for the quantitative evaluation of product noise level by product manufacturers, product quality evaluation institutions, consumers and other stakeholders. Through subjective evaluation experiment and questionnaire survey, the relationship between product noise quality index and satisfaction degree was obtained. After comprehensive consideration of the current production level of the industry, affordability and consumer interests and other factors, the sound quality classification and limit assessment were carried out. The method is applied to household appliances and ships, and the product noise quality classification and limit evaluation are carried out to verify the effectiveness and applicability of the proposed method. The characteristics and problems needing attention when the method is applied to different fields and scenarios are discussed.

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 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.

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.