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.

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.

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.

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.

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.

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.

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.

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.

To overcome the shortcomings of traditional base isolation technology, such as non-adjustable isolation parameters, limited low-frequency isolation effect, and inability to achieve vertical isolation, magnetic levitation technology is introduced to design a magnetic levitation vibration isolation bearing. The relationships between the levitation force of the electromagnet and the coil current and levitation gap are analyzed. The nonlinear model of the magnetic levitation vibration isolation bearing is established. Combining the advantages of terminal sliding mode and super-twisting algorithm and introducing an adaptive law to adjust the coefficients in the super-twisting algorithm, an adaptive super-twisting terminal sliding mode control strategy is proposed. Through experimental verification, the proposed control scheme can suppress the chattering phenomenon in the traditional sliding mode control, with high control accuracy and good steady-state and dynamic performance. The magnetic levitation vibration isolation bearing has excellent stability and disturbance-resisting performance.