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.

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.

Traditional algorithms are difficult to effectively separate and extract the composite fault features of bearings with overlapping resonance bands, an adaptive rolling bearing composite fault feature separation and extraction method combining adaptive variational mode extraction (AVME) and optimized multi-point optimal minimum entropy deconvolution adjusted (OMOMEDA) is proposed in this paper. The initial value of the center frequency of the VME parameter is determined by using the autocorrelation energy spectrum of S transform spectrum, and the desired modes related to the fault are extracted. Then the desired modes are linearly superimposed to reconstruct the original signal to realize the noise reduction of the signal. Extract periodic pulse signals from the reconstructed signal using OMOMEDA, and obtain fault characteristic frequencies by combining with envelope demodulation. The simulation and test signals verify that the method can effectively separate and extract the composite fault features of bearings with overlapping resonance bands. And compared with four other existing algorithms such as VMD-MCKD, the superiority of the proposed method is demonstrated.

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.

In this paper, a new concentrated mass-bent beam model of aircraft pylon is proposed, which is an effective mode reduction method for the analysis of vibration characteristics of continuous structures of pylon. Firstly, according to the periodic structure and the stress characteristics of pylon structure under actual working conditions, pylon structure is simplified into a concentrated mass-bent beam model which consists of 12 mass elements and 11 beam elements in series by using the concentrated mass method. The two simply supported boundary conditions reflect the true constraints of pylon-wing front and rear lifting points. The transfer equation and characteristic equation of the model are established based on the transfer matrix method. After using the parameter sensitivity method to correct and optimize the uncertain parameters of bending stiffness, the effectiveness of pylon concentrated mass-bent beam model is verified by comparing with the lower order natural frequencies of the finite element model. On this basis an engine is connected to the front and rear lifting points of pylon-engine through the installation section as the basic excitation, and engine-pylon concentrated mass-bent beam coupled model is established. Transfer matrix method is applied to study the natural frequency of the coupled model and the vibration response of pylon structure under the take-off, cruise and flight idle conditions of the engine. The vibration envelope lines of pylon structure mass elements under different conditions and different times and the vibration response of the representative mass element are obtained. In addition, the effectiveness of the new model is further verified by comparing with the finite element method. The research results provide theoretical support for the vibration reduction design of the pylon structure.

With the advantages of small size, light weight, flexible design and excellent frequency selectivity, surface acoustic wave devices are widely used in radar, communication, non-destructive testing, electronic countermeasures, TV signal processing and other fields. For exploring the application of surface acoustic wave (SAW) devices in mass sensing, the Love wave propagation in a piezoelectric layered structure is systematically investigated from perspectives of theoretical analysis and numerical examples. As for the theoretical model consisting of an additional mass layer, a piezoelectric sensing layer and a semi-infinite elastic half-space, the exact solution that simultaneously satisfy the dynamic governing equations and the continuous conditions between layers is established, and the phase velocity of Love waves is obtained.Then,the three-layer structure is degenerated into two-layer structure by stepwise degradation method, and the correctness of the theory is verified by comparing with the results of previous paper. After validation, the influence of structural and material parameters of the additional mass layer on Love wave phase velocity is conducted, including the thickness, shear modulus, density, and dielectric coefficient. Finally, an approximate method with only consideration of the inertial effect of the additional mass layer is developed, with its applicable condition demonstrated. It is revealed via numerical examples that the Love wave is very sensitive to the thickness of the additional mass layer, while the dielectric coefficient has minimal influence on the phase velocity. Additionally, the phase velocity decreases linearly when the density of the additional mass layer increases. The approximate method proposed in this paper exhibits good universality, which simplifies the wave solving, and can possess high computational accuracy when the additional mass layer is thin. The results and methods in this paper can provide guidance for the application of SAW devices in mass sensing.

The vibration and radiation noise caused by the mechanical power equipment running on the ship have great harm, and seriously reduce the stealth performance and combat ability of the ship. The feedforward control algorithm which depends on the precise model will fail due to the adverse factors such as the long running of the power plant without stopping or the external impact. The traditional method of on-line system identification using auxiliary white noise not only reduces the control performance, but also increases the convergence time of the identification process. The method proposed in this paper uses the control signal to model the controlled system required by the FxLMS algorithm online in the noise frequency band, with faster convergence speed and identification accuracy. When the controlled system changes abruptly, that is, when the phase frequency characteristics of the controlled system change beyond ±90°, the algorithm can also track the changes of the system in real time and maintain the stability of the control. The active vibration control of the single-layer power unit vibration isolation platform was studied. The experimental results showed that the online identification of FxLMS control algorithm achieved 20.44 dB noise reduction at the motor operating frequency (50 Hz) when there was no secondary path model. The on-line identification algorithm can also maintain the control stability and quickly identify the changes in the phase frequency characteristics of the system after the mutation of secondary path.

Considering the random uncertainty of landing gear parameters in design and manufacturing, this study conducts a quantitative study on the random response of carrier-based aircraft landing impact and the buffering performance of landing gear. This study established a dynamic model of the landing vibration of a carrier-based aircraft’s main landing gear. Based on the statistical characteristics of some filling parameters of the landing gear buffer (such as the initial volume of the air chamber, pressure oil area, oil shrinkage coefficient, etc.), the representative point set is divided by the direct probability integration method (DPIM), and the deterministic structural equation and probability density integration equation on the representative point set are solved. At the same time, the accuracy of DPIM application in the landing gear stochastic model is demonstrated by using the Monte Carlo Simulation (MCS) method. By outputting the buffer stroke of the landing gear, the vertical tire force, and the axial force of the strut, the mean value, standard deviation, probability density function, and related features of these responses are obtained. It is found that although the distribution of these responses are concentrated near the mean value, there is still a possibility of significant responses leading to system failure. Therefore, a functional function is defined using the buffer stroke, vertical tire force, and the axial force of the strut, and a reliability evaluation study is conducted on the landing gear structure under different threshold values.

With the continuous development of aerospace industry, the load transfer structure of spacecraft is getting more and more complicated. In practical engineering, how to distribute the loads in a reasonable way is of great significance for the lightweight design of spacecraft and the guarantee of structural load carrying capacity, and it is also necessary to take into account the non-ideal boundary conditions of the overall structure to the local structure in the process of dynamic load transfer structure design. Based on this, this paper proposes a dynamic topology optimization design method for dynamic load transfer structure based on structural boundary condition equivalence, which can fully consider the influence of the overall structure on the local structure while designing the load transfer structure. The method firstly simplifies the connection boundary between the local structure and the overall structure into a spring unit and a centralized mass unit, optimizes the unit parameters through genetic algorithm to achieve the equivalence of boundary conditions, and finally establishes a topology optimization model of the load transfer structure based on the unit density variable in conjunction with the design objective of the dynamic compliance of the structure. Numerical examples verify the effectiveness of the new method and obtain the optimization design results with the variation of volume fraction, external load frequency and load constraint interval.

A novel data-driven method for simulating non-Gaussian stochastic processes is proposed in this paper. The sample conversion model and power spectrum conversion model are established by using artificial neural network models respectively. A neural network model is constructed based on sample data to transform Gaussian samples into non-Gaussian samples. The distribution function of the samples is modeled using the shifted generalized lognormal distribution, and the latent Gaussian power spectrum is directly obtained through the backpropagation neural network model. The Gaussian stochastic process samples are generated using the spectral representation method, and then transformed into non-Gaussian process samples using the sample conversion neural network model. This method is capable of generating non-Gaussian stochastic process samples based on limited sample data, addressing the challenge of determining latent Gaussian power spectrum, and solving the problems such as poor accuracy and limited application range of the central moments-based transformation models. Through numerical simulations and validation in turbulent wind fields, the accuracy and effectiveness of the proposed method are further demonstrated.