Environmental microvibration affects the accuracy of precision instruments, making microvibration measurement and assessment crucial. Microvibration level measurement is based on the octave spectrum of the velocity signal. However, the frequency-domain FFT method used in traditional octave analysis suffers from shortcomings such as fixed resolution and low-frequency spectrum leakage. Therefore, a complex-analysis ZFFT correction algorithm based on ratio correction was proposed. Simulations show that this algorithm improves spectral resolution while maintaining the same number of FFT analysis points. While maintaining the same number of sampling points, the computational effort is significantly reduced, and the spectrum amplitude error is as low as one thousandth. Frequency-band octave analysis is employed to suppress low-frequency spectrum leakage and increase the number of spectral lines. A microvibration monitoring and analysis system was developed, comprising a low-frequency microvibration sensor, the MI-7208 intelligent measurement device, and microvibration level measurement and assessment software. Field measurements verified the system's ability to detect VC-F-level microvibration signals and its long-term measurement stability.

Real-time hybrid test has been applied to the performance test of high-speed train running on the bridge in recent year. In order to avoid the damage of specimens or loading systems caused by instability, it is necessary to study the stability of real-time hybrid test on traveling train-bridge system. The time-varying characteristic of the traveling train-bridge system poses challenges to the stability analysis of real-time hybrid test. Therefore, it is necessary to develop suitable stability prediction methods for the time-varying system. Firstly, the time-varying discrete state space equation of the real-time hybrid test on traveling vehicle-bridge system was established, which can accurately describe the changes of all state quantities of the test system over time. Then a stability criterion based on the spectral radius of the cumulative state transition matrix was proposed, and then by combining the stability criterion with the dichotomy method, a relative stability prediction method for the time-varying real-time hybrid test was developed. A serial of practical real-time hybrid tests on traveling vehicle-bridge system was conducted based on a shaking table. The results show that the critical stability obtained by the practical tests was in good agreement with the predicted results based on the developed stability prediction method. The developed method can accurately predict the stability of RTHT on vehicle-bridge coupled system.

The fractional nonlinear Zener model is used to describe the nonlinear and viscoelastic constitutive relation of the vibration isolation system. The variation law of system amplitude-frequency response and backbone under the combined action of constant excitation and harmonic excitation is discussed, and the influence of constant excitation on the dynamic behavior of vibration isolation system is discussed significantly. The fractional-order derivative term is made equivalent to a term in the form of trigonometric function, the steady-state response of the system is solved by harmonic balance method, and the results are compared with a variety of other methods. The influences of different parameters on the coexistence frequency band range of the amplitude-frequency response multi-state solution are summarized, and the dynamic behaviors of the system under the combined excitation are obtained by using numerically simulation. The results show that there are five solutions co-existence region in the amplitude-frequency response solution under the combined effect of constant excitation and harmonic excitation, and the system shows a phenomenon of coexistence of softening characteristic and hardening characteristic, and the backbone of the amplitude-frequency curve is tilted firstly to the left and then to the right. Additionally, it is found that the periodic motion and chaos coexist in the system under the combined excitation, and the transition laws of the polymorphic coexistence region and its adjacent regions are summarized explicitly. Affected by constant excitation, the diversity of periodic motion of the system under the combined excitation is significantly different from the dynamic behavior under the action of simple harmonic excitation alone, and the transition rules of periodic motion of the system under the action of combined excitation are summarized based on the Lyapunov exponent.

Tuned Liquid Damper (TLD) is a simple and effective passive vibration control device. By adding thickening agents to the TLD, the effect of liquid viscosity on the damping ratio and frequency of the TLD system is studied. Firstly, the relationship between thickener concentration and liquid viscosity is measured by a viscometer. Then, rectangular, circular, circular and U-shaped TLD tanks are designed and tested on a unidirectional harmonic excitation vibration table.The influence of parameters on the performance of the TLD is analyzed, such as thickener concentration, water depth ratio of the tank, external excitation frequency, relative excitation amplitude and placement time. Finally, CFD numerical simulation of TLD system is carried out to study the influence of tank size. The results show that increasing the concentration of thickener can effectively improve the damping ratio of TLD, and has little effect on the frequency of TLD. Water depth ratio has little effect on frequency and damping ratio of TLD. The external excitation amplitude and frequency have little effect on the frequency and damping ratio of the TLD system, but can significantly change the liquid surface wave height. The TLD placement time of the thickener liquid increased, resulting in a decrease in the viscosity of the liquid in the TLD, resulting in a decrease in the damping ratio of the TLD, partial volatilization of the liquid in the TLD, and a decrease in the water depth ratio, resulting in a phenomenon of TLD frequency mismatch. As the size of the tank decreases, the TLD damping ratio gradually increases, and the damping ratio remains basically stable when the size is larger.

With the development of performance-based earthquake engineering, the ‘risk-probabilistic’ oriented performance evaluation method has gradually gained the attention of researchers, an important part of which is seismic vulnerability analysis. At this stage, there are different kinds of vulnerability methods, and more researches focus on how to combine probability theory with earthquake engineering, but the reasonable comparison for the accuracy and applicability of different methods still requires further research. Based on the nonstationary random mainshock-aftershock sequences, this paper compares three methods commonly used in seismic vulnerability at this stage: linear fitting method, maximum likelihood estimation, and Monte Carlo method. Then, based on a reinforced concrete frame, a case study is carried out, and the applicability of these three methods as well as the influence of random aftershocks are discussed. Generally speaking, the results obtained by the three methods are similar, and the development trends are relatively consistent, which also proves the effectiveness of these three methods to a certain extent. The Monte Carlo method has a long calculation period, the maximum likelihood estimation is more suitable for the performance level of minor damage, and the linear fitting method is more accurate after excluding the scattered points in the collapse state. After considering non-stationary random aftershocks, the obtained structural vulnerability shows an overall left-shifting trend. If the influence of random aftershocks is not considered, the probabilistic risk caused by earthquake sequences will be greatly underestimated.

Since current loudness models are unable to predict loudness under round window stimulation，a loudness model for round window stimulation is proposed in this paper. The loudness model consists of a peripheral auditory model and a data processing back-end. The peripheral auditory model that is able to calculate basilar membrane velocities under free-field acoustic stimulation and round window stimulation and the back-end that transforms basilar membrane velocities into loudness are constructed. The reliability of the peripheral auditory model is verified by comparing the model-predicted results with the experimental data on the outer ear transfer function，middle ear transfer function and stapes velocities under acoustic stimulation，round window stimulation transfer function，frequency selectivity and frequency response of the basilar membrane，and basilar membrane displacement. The reliability of the loudness model is verified by comparing the model-predicted results with the experimental data on equal-loudness contours，bandwidth noise loudness，loudness level of tone with frequency masking，and threshold for complex tones. The results indicate that the loudness model accurately calculates basilar membrane velocities under acoustic stimulation and round window stimulation，and is able to predict the loudness of pure tone，complex tones，and bandwidth noise under acoustic stimulation and round window stimulation.

Recent earthquake damage investigations found that a large number of reinforced concrete frame buildings were heavily destroyed at beam-column joints and columns，without forming the beam-hinging mechanism expected in the design. Installing reinforced concrete wing walls beside the existing columns remains a fundamental and effective strengthening method，by improving seismic performance of both the columns and the joints，while promoting a beam-yielding mechanism. Two 1/2-scale frame specimens were manufactured，and one of them was strengthened by post-installation wing wall. By quasi-static tests，hysteretic behaviour，deformation capacity，energy dissipation power and failure mode of the two specimens were examined. The results show that the stiffness，bearing capacity and energy dissipation capacity of the strengthened frame were significantly improved. After strengthening，failure mode of the frame was changed from joints shear failure to expected beam-hinging. The efficiency and applicability of wing wall installation method were validated for strengthening existing frame structure buildings with seriously weak beam-column joints.

Helicopter cabin noise negatively impacts cabin environmental comfort and safety. In this paper，non-dominated sorting genetic algorithm Ⅱ is used to solve the electro-acoustic device placement problem of the active control system applied in the cabin. An appropriate spatial discretization of the sound field of the confined space is preformed，and then the electro-acoustic devices placement optimization problem，quantity optimization problem，and secondary source sound intensity optimization problem are further transformed into a combinatorial optimization problem. Taking the minimun value of the sum of the squares of the acoustic pressures at the measurement points as the control objective，the multi-objective optimization algorithm combined with the active control algorithm is adopted to solve the optimal placement of electroacoustic devices in the system. Considering the noise control system’s complexity and feasibility and limited space inside the cabin，the control system’s secondary sound sources and error sensors are selected as a 4-channel configuration. The optimization program is repeated several times independently，and the most frequently occurring positions of electroacoustic devices are counted，based on which computer simulation and experiment are conducted，and the results show that the optimization results can make the noise reduction at the height of the head of the cabin personnel in the sitting position reach up to 24.9 dB，and the global noise reduction reaches 19.4 dB.

In order to improve the intelligence of fastener disease diagnosis，a fastener condition diagnosis method is proposed based on vehicle dynamic response data and generalized demodulation time-frequency analysis combined with sparrow search algorithm-support vector machine （SSA-SVM） model. The acceleration signals of the normal and abnormal sections of the fastener are collected，and the short-time Fourier transform and the maximum overlapping discrete wavelet packet transform are used to preprocess the signal data. The generalized demodulation time-frequency analysis method is used to decompose the signal，and the effective value，energy contribution rate and wavelength of the main information components are calculated as the characteristic index. The characteristic index is trained by the joint SSA-SVM model to construct the classification model. The results show that the accuracy of the method is 97.50%，and several evaluation indicators are used to verify that its effectiveness and accuracy can meet the actual needs.

The tire deformation traveling wave characteristics vary at different vibration frequencies and speeds，and are influenced by the coupling of landing gear structural vibration，resulting in continuous changes in tire lateral deformation modes. The tire models for previous traditional landing gear shimmy analysis are quasi-static restoring force model，which assumes that the functional relationship between tire lateral force，self-aligning moment and lateral deformation is fixed. Based on the tire stretched string theory，a time delay tire model coupled with landing gear shimmy is established to analyze the dynamic changes in tire lateral deformation modes，and the real-time lateral deformation distribution of the tire and the nonlinear dynamic behavior of the landing gear during shimmy are obtained. The time delay is introduced to calculate the tire deformation traveling wave，and the stability of the landing gear tire coupled shimmy model is studied by the bisection method. The testing methods for the parameters of time delay tire shimmy model is provided. Using the methods presented in this paper，the landing gear shimmy analysis and experimental test of a certain aircraft are conducted. The calculated vibration frequency and shimmy stability region are consistent with the analysis results of traditional tire models and test results.