Helicopter tail rotors adopt a segmented driveline connected by flexible couplings, and dry friction dampers to suppress resonance. Modeling for this system can provide a basic foundation for parameter analysis. In this work, the lateral-torsional vibration equation of the shaft with continuous internal damping is established. The static and dynamic effects caused by flexible diaphragm couplings subject to parallel and angular misalignment is derived. A novel dual rub-impact model between the shaft and dry friction damper with multiple stages is proposed. Finally, a model of a helicopter tail rotor driveline incorporating all the above elements is formulated. Numerical simulations are carried out by an improved Adams–Bashforth method following the design flowchart. The dynamics of multiple vibration suppression, and the static and dynamic misalignment are analyzed to illustrate the accuracy and characteristics of the model. The coeffect of the rub impact and the misalignment on shafts and dampers are presented through the results of simulation and experiment. It provides an accurate and comprehensive mathematical model for the helicopter driveline. Response characteristics of multiple damping stages, static and dynamic misalignment, and their interaction are revealed.

This study investigates the stability and phase difference of a shaft mounted a dry friction damper with effects of viscous internal damping and gyroscopic moment. The equations of the system with the vibration reduction effect of the dry friction damper on the shaft are derived in the form of the rectangular coordinate and polar coordinate in the vicinity of critical speed. The phase difference characteristics in the rub-impact process and its physical mechanism are analyzed by mathematical derivation. The characteristic equation is studied to investigate the stability of the periodic solution. Effects of different parameters of the system, especially viscous internal damping of the composite shaft and gyroscopic moment on the phase difference and stability regions are presented in detail by analytical and numerical simulation based on a helicopter tailrotor driveline. The experimental investigation is conducted in a test rig to validate theoretical formulas and simulation analysis. The analysis results show that rub impact delays the change of phase difference, viscous internal damping improves the stability of synchronous full annual rub solution, and gyroscopic moment affects the increase of the phase difference.

Extracting weak fault features from vibration signals contaminated with strong noise, especially non-Gaussian noise, is a challenging task for early fault diagnosis of bearings. In this paper, a novel adaptive orthogonality-constrained robust dictionary learning (AOCRDL) method for bearing fault diagnosis is developed to address this issue. Firstly, an α-divergence based robust dictionary learning (RDL) approach was introduced to enhance the capability of sparse representation techniques in handling non-Gaussian noise. Secondly, orthogonalization process of atoms is embedded into the dictionary learning process to obtain an optimized dictionary for recovering impulse sequences related to faults. Thirdly, the adaptive determination method of key parameters in the AOCRDL was developed to ensure optimal performance of the approach. Simulations and experimental results demonstrate that AOCRDL method can effectively extract early bearing fault features, especially in scenarios with strong non-Gaussian noise.