Structural vibrations and radiation noise are common problems in the blade–shafting–shell coupled system. To research this problem, a coupled system consisting of a five-leaf blade, shaft, bearing, and shell was established using a dynamic equilibrium equation. To describe the dynamic behaviour, a blade excitation force model consisting of transverse and vertical excitation forces generated by the blade was established using a quasi-steady method. It was found that the transverse excitation force resulted in more complex frequency components than the vertical excitation force. The frequency components of the blade frequency doubling (2.5fr) and the blade frequency (5fr) in the spectrogram were mainly produced by the transverse excitation force (where fr is the rotational frequency of the shafting). In addition, in the acoustic analysis section of this paper, a finite element model of the coupled system was established. Blade excitation forces were applied to the model, and the vibrational response data of the coupling model's nodes were obtained. Using the acoustic boundary element method, the coupled system's acoustic response was calculated from the surface node vibration velocity data of the coupling model. The effects of the transverse and vertical excitation forces on the acoustic radiation of the coupled system were considered. Finally, dynamic and acoustic experiments of the blade–shafting–shell coupled system were conducted. The results verified the accuracy of the simulation model. © 2019 Elsevier Ltd

Accurate identification of prohibited items in x-ray security images is essential for ensuring public safety. However, current methodologies struggle to simultaneously address irregular deformation, multi-scale features, and background occlusion of prohibited items, leading to inadequate detection accuracy. To address these challenges, we propose an adaptive efficient focusing network (AEFNet) designed to target regions, thereby enhancing the automatic detection of prohibited items. Specifically, to accommodate the irregular deformation of target regions, we introduce the DACSP module, which dynamically adjusts sampling positions to enhance the network's adaptability and focus on occluded targets. To address detail loss and managing multi-scale features, we propose a multi-scale focus feature module and a focusing diffusion pyramid network (FDPN), which enable the fusion of semantic and perceptual features, improving the use of contextual information at different detection scales. Additionally, detail-enhanced convolution improves the efficacy of feature utilization at different scales, while facilitating a lightweight network design. Finally, we employ the PIoUv2 function to optimize localization loss, resulting in significant performance enhancement. Experimental results show that AEFNet performs effectively across various x-ray security image datasets (PIDray, CLCXray, OPIXray) achieving 74.7%, 61.3%, and 89.2% mAP respectively, and AEFNet also demonstrates strong generalization capabilities on the PASCAL VOC dataset in non-prohibited item detection scenarios.

In this paper, in order to solve the problem of unbalance vibration of rigid rotor system supported by the active magnetic bearing (AMB), automatic balancing method is applied to suppress the unbalance vibration of the rotor system. Firstly, considering the dynamic and static imbalance of the rotor, the detailed dynamic equations of the AMB-rigid rotor system are established according to Newton's second law. Then, in order to rotate the rotor around the inertia axis, the notch filter with phase compensation is used to eliminate the synchronous control current. Finally, the variable-step fourth-order Runge-Kutta iteration method is used to solve the unbalanced vibration response of the rotor system in MATLAB simulation. The effects of the rotational speed and phase compensation angle on the unbalanced vibration control are analysed in detail. It is found that the synchronous control currents would increase rapidly with the increase of rotational speed if the unbalance vibration cannot be controlled. When the notch filter with phase shift is used to balance the rotor system automatically, the control current is reduced significantly. It avoids the saturation of the power amplifier and reduces the vibration response of the rotor system. The rotor system can be stabilized over the entire operating speed range by adjusting the compensation phase of the notch filter. The method in the paper is easy to implement, and the research result can provide theoretical support for the unbalance vibration control of AMB-rotor systems.

Fault features extraction method for slight misalignment of rotor systems is researched in this paper. When a rotor system with faults is excited by harmonic inputs, system response will contain higher harmonic components. Phenomenon of these higher harmonics implies the presence of nonlinear features in a rotor system. When extracting these nonlinear features, traditional methods have certain limitations, and it is easy to ignore weak features of a rotor system. Nonlinear output frequency response functions (NOFRFs) can extract effectively nonlinear features of a rotor system from noise-containing vibration signals and are used in many fault diagnosis fields. However, as for weak damage to structures and in the early stages of a system faults, fault features reflected by high-order NOFRFs are not still obvious enough. Therefore, a new method, named variable weighted contribution rate of NOFRFs, is proposed in this paper. This method enhances the ratio of high-order output frequency response to total output response of a rotor system. Based on this method, a new index MR is proposed to detect the faults of a rotor system. In addition, lumped mass model is used in this paper to simulate misaligned rotor system with slight misalignment, and the sensitivities of the traditional methods and new index for slight misalignment fault features extraction are compared. The results indicate that the new index is more sensitive for the slight misalignment rotor system. Additionally, the rotor system with misalignment fault experiment table is built, and the effectiveness of this new index for detecting the slight misalignment fault of the rotor system is verified.
© 2019, Springer Nature B.V.

For the nonlinear vibration problem of spur gear transmission system caused by friction and gear backlash, the dynamic model of gearbox with 16-degree-of-freedom (16-DOF) considering timevarying meshing stiffness is established by Lagrange equation. The dynamic equations of the gear system are solved by the Newmark-beta method. The effects of friction coefficient, error fluctuation and meshing stiffness on the vibration response are investigated. In order to verify the validity of the model, a spur gear transmission rotor test bench was built by simulating the actual working conditions. The root mean square (RMS) is used to verify the accuracy of the model at multiple speeds, and makes up for the shortcomings of many researches without experimental argumentation. The experimental research can provide a reference for the research of gear transmission system.

Aiming at the analysis of the dynamic characteristics of the rotor system supported by deep groove ball bearings, the dynamic model of the double-disk rotor system supported by deep groove ball bearings was established. In this paper, the nonlinear finite element method is used combined with the structural characteristics of deep groove ball bearings. Based on the nonlinear Hertz contact theory, the mechanical model of deep groove ball bearings is obtained. The excitation response results of the rotor system nodes are solved by using the Newmark- numerical solution method combined with the Newton-Raphson iterative method. The vibration characteristics of the rotor system supported by deep groove ball bearings are studied deeply. In addition, the effect of varying compliance vibration (VC vibration) caused by the change in bearing support stiffness on the dynamics of the system is considered. The time domain and frequency domain characteristics of the rotor system at different speeds, as well as the influence of bearing clearance and bearing inner ring's acceleration on the dynamics of the rotor system are analyzed. The research shows that the VC vibration of the bearing has a great influence on the motion of the rotor system when the rotational speed is low. Moreover, reasonable control of bearing clearance can reduce the mutual impact between the bearing rolling element and the inner or outer rings of the bearing and reduce the influence of unstable bearing motion on the vibration characteristics of the rotor system. The results can provide theoretical basis for the subsequent study of the nonlinear vibration characteristics of the deep groove ball bearing rotor system.

The rub-impact between a rotor and a stator is a common fault of the rotor system. Various methods are available to detect the rub impact using vibration signals. However, the noise in vibration signals causes inconvenience when extracting characteristic signals. Nonlinear output frequency response functions (NOFRFs) comprise an effective method for using input and output signals to detect damage of a structure or system. A new evaluation method named the NOFRFs weighted contribution rate has been proposed in this paper. This method is an extension of traditional NOFRFs-based indexes and attempt to obtain a new index with higher recognition of faults. As a new index extracted by this method, the second-order optimal weighted contribution rate of the NOFRFs optimally amplify the extracted fault features. The characteristic signal after amplification is significantly enhanced. The new index is applied to the evaluation of a rub-impact fault. The simulation and experimental results demonstrate the sensitivity of the new index to rub-impact faults. Especially in the initial stage of the occurrence of rub-impact, the new index shows better superiority. The findings demonstrated that the second order optimal weighted contribution rate has a high application value in the fault diagnosis of rub-impact. © 2019 Elsevier Ltd

Rub-impact between the rotating and static parts is a more common fault. The occurrence of faults is often accompanied by the generation of nonlinear phenomena. However, it is difficult to find out because the nonlinear characteristics are not obvious at the beginning of the fault. As a new frequency domain-based method, nonlinear output frequency response functions (NOFRFs) use the vibration response to extract the nonlinear characteristics of the system. This method has a better recognition rate for fault detection. Also, it has been applied in structural damages detection, but the high-order NOFRFs have the characteristics that the signals are weak and the features are difficult to extract. On this basis, the concept of the weighted contribution rate of the NOFRFs is proposed in this paper. The variable weighted coefficients with orders are used to amplify the influence of high-order NOFRFs on the nonlinearity of the system so as to extract its fault characteristics. The new index RI is proposed based on Clenshaw-Curtis quadrature formula to eliminate the effect of artificially selected weighted coefficients on sensitivity. Especially in the early stage of the fault, the new index varies greatly with the deepening of the fault. Both simulation and experimental results verify the validity and practicability of the new index. The new index has certain guiding significance in the detection of mechanical system faults. © 2019 Yang Liu et al.

Ceramic coatings were prepared by plasma electrolytic oxidation (PEO) on four different surface roughness' of Ti-6Al-4V alloys. The effects of substrate roughness on the microstructure and fatigue behavior were investigated. Microstructural characterization was carried out by scanning electron microscopy (SEM) and a laser scanning confocal microscope. In addition, an X-ray diffractometer (XRD) and a U-X360 stress meter were used to analyze the phase composition and residual stress properties of the coatings. The microstructure of coatings revealed the growth mechanism of the coatings. The larger and deeper grooves of the substrate promoted the nucleation and growth of the PEO coating, but the defects (cracks and pores) of the oxide layer became more serious. The fatigue test indicated a significant influence of substrate roughness on the fatigue life under low cyclic stress. The fatigue damage of PEO coatings decreases as the surface roughness of substrates decreases because of the synergistic effect of the coating surface defects and coating/substrate interface roughness. Substrate roughness influences the quality and fatigue performance of the oxide layer.

The rub-impact fault of the rotor system is the research object in this paper, and the system is modeled by the finite element method. In the process of the study, the high-order harmonic components appear in the output response of the rotor system, which imply that the rotor system is nonlinear. Nonlinear output frequency response functions (NOFRFs) solve nonlinear problems in the frequency domain and explain these nonlinear phenomena. Based on NOFRFs, a method named weighted contribution rate of NOFRFs (WNOFRFs) is used to improve the weak high-order harmonic components proposed by the authors. In this paper, the multi-parameter optimized genetic algorithm is used to calculate the obstacle parameters of the stochastic resonance (SR) which is used to enhance weak signal components. In view of the fact that both WNOFRFs and SR can improve the weak signal components, a new method of weighted contribution rate of NOFRFs incorporating stochastic resonance (WNS) algorithm is proposed in this paper. Based on the algorithm, the variations of index WS show a trend of approximately linear growth, which indicates that index WS has certain advantages for the fault diagnosis of the rotor rub-impact. © 2020 Elsevier Ltd