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.

When the finite element method is employed to calculate the mechanical behaviors of a corrugated sandwich panel structure, the numerical model occupies a large amount of computational resources, which usually causes the problem of long-time solution. In order to reduce the scale of the finite element model and to quickly perform the dynamic analysis of such type structures, in this paper the middle corrugated sandwich layer is simplified into a homogeneous orthotropic plate. Then, based on the third-order shear deformation theory, the equivalent stiffness matrix of the corresponding laminated plate element is formulated from adequate performance analyses of the corrugated sandwich plate. Afterwards, the natural frequencies of two corrugated sandwich plate structures in typical boundary status are obtained respectively through the test and numerical calculation. By comparing with the experimental results, the effectiveness of the equivalent finite element model is verified. It turns out that the obtained results are much better than those based on the first-order shear deformation model. Moreover, the method proposed in this work can be utilized efficiently for modal parameter computations of the corrugated sandwich plates with the high accuracy.

It is often difficult to suppress vibration of flexible rotors at high-order critical speeds through conventional low-speed balancing, especially in the case of the rotor with initial bending. In this paper, a low-speed dynamic balancing method for flexible rotors with initial bending is presented first. Combining the modal information of the rotor with the measurement data at speeds below the critical speeds, the low-speed dynamic balancing method is able to balancing the critical speeds without directly measuring the vibrations at the critical speeds and the initial bending of the rotor. Based on this, a mode-by-mode forward higher-order-extra-trial-weight-free method is proposed for balancing the higher modes simultaneously. In the proposed method, the lower-mode balancing weights on different balancing planes are used as trial weights and linked by the modal ratios of the measuring points. This avoids the potential severe vibration when pass through the critical speeds if any additional trial weights are used for balancing the higher-order modes. The proposed method is validated by numerical simulation and experimental tests respectively. The results show that the proposed method is better than the traditional influence coefficient method in balancing performance. In addition, it also avoids potentially high resonant vibration response, thus providing a safer approach for the high order dynamic balancing of flexible rotors.

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.

The wedge-shaped oil film in sliding bearings induces uneven heating effects on the journal of a rapidly rotating rotor, resulting in circumferential temperature variations in the journal. The thermal bending caused by these temperature differences exacerbates rotor vibration, leading to a phenomenon known as ‘Morton effect’ or rotor thermal instability. This effect is particularly severe in cantilevered rotors. Initially, an elliptical bearing’s thermal fluid lubrication model is established, and its dynamic coefficients and oil film temperature field are calculated. Subsequently, based on Fourier heat conduction theory, using the obtained oil film temperature as a boundary condition, a finite element method is employed to solve the three-dimensional transient temperature field of the journal to determine the thermal deformation and thermal stress. The thermal stress is then integrated to obtain an equivalent moment for rotor dynamic analysis. Additionally, the sliding bearing oil film thickness is updated based on thermal deformation. Repeating these steps completes the fluid-solid-thermal multi-field coupling analysis of the rotor-bearing system, and the effectiveness of the simulation model is validated against experimental data. Finally, parameter analysis is conducted on the rotor-bearing system with the rotor’s cantilever length and suspended mass as variables. The results indicate that reducing the cantilever length or decreasing the suspended mass effectively reduces system vibration.

In order to effectively control the vibration transmitted by the elastic supports of the aero-engine rotor, an active magnetic dry friction damper (AMDFD) is employed to tune the support damping. On the basis of the traditional dynamics model of the dual rotor system, an AMDFD-dual rotor-bearing seat dynamics model that can characterize the transmitted vibration of the support is established. The effectiveness of AMDFD in suppressing the transmitted vibration of the rotor supports is simulated by using a speed interval switching controller and a model-free adaptive controller, and the intrinsic principle in realizing suppression is elucidated. Using the AMDFD-twin-rotor system test rig, the test of transmitted vibration control when rotor passes through the multi-order critical speeds was carried out. The results show that the AMDFD controlled by aforementioned two controllers can effectively reduce the transmitted vibration at each bearing position, and the reduction is more than 52%.

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.

Bearing fault diagnosis is an important research topic in aviation engine prediction and health management. Signal processing algorithms and deep learning models in this field rely on datasets. However, publicly available datasets generally cover narrow speed ranges, large speed intervals, single loads, and a lack of composite fault data, making it difficult to support the practical development of fault diagnosis methods. This article discloses a vibration dataset of aircraft main shaft bearings with a wide speed range. In addition to providing single fault data, this dataset also provides multiple composite bearing fault data, covering multi-channel bearing vibration signals with a wide speed range under different loads. The dataset well supports the research of classic fault diagnosis algorithms, and due to the large speed range covered by the data and high-speed sampling rate, it is more conducive to training deep learning fault diagnosis models.

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.