Dynamic antiresonance vibration isolation technology is widely used in the vibration reduction system of helicopters, because its simple structure and high vibration isolation efficiency. In this study, a dual-frequency vibration isolation system with two anti-resonant frequencies has been established, which can adapt to the vibration characteristics of two main vibration frequencies caused by the variable speed of the new high-speed helicopter. The theoretical equation and transmissibility of the dual-frequency vibration isolation system are derived, and the variation law of the weight and other relevant parameters on the vibration isolation performance is explored. The accuracy of the theoretical results is verified by model tests. According to the installation form of the helicopter reducer, the structure of the dual-frequency vibration isolation system is preliminarily optimized, which provides technical support for the design of the vibration isolator of the helicopter with variable speed.

Using parameterized dynamic Bingham model to describe the relationship between active control actuator movement and damping force. SIMULINK emulation module of nonlinear actuator movement characteristics and compared with test data has been achieved by adopting MTLAB. According to the active system of displacement, velocity, acceleration and the desired damping force, the control current inverse model has been obtained based on fuzzy control theory. The validity and correctness of the simulation model are verified by the test results of variable current inverse. Fixed frequency excitation and real flying helicopters floor vibration data are adapted respectively to simulation, and the damping effect of the control system is obtained through simulation analysis.

In order to reduce the two main vibration frequency of the variable speed helicopter, an anti-resonance vibration isolator with double frequency vibration isolation is designed. First, the dynamic formula of the dual frequency vibration isolator was deduced based on the traditional dynamic anti-resonance theory. With the formula, the natural frequency, antiresonant frequency and transmissivity of the isolator are obtained. Then, the sensitivity of the performance and efficiency for the isolator is analyzed. The effects of design parameters such as secondary spring stiffness and secondary vibration isolation mass on the natural frequency and vibration isolation frequency of the isolator are obtained. The property test and vibration test are carried out. The calculation and test results show that the isolator has two vibration isolation frequency. The secondary vibration isolation efficiency is more than 60%, and the antiresonance frequency and efficiency of the isolator are both affected by the design parameters.

Considering the coupling effects of elastic wing, elastic blade, rigid nacelle and connection points between systems, the mathematical model of the coupling system including wing/nacelle/tilting rotor is established. Based on the eigenvalue method, the overall modal changes of the rotor installed on the wing and the effects of speed and offset on the dynamic characteristics of the system are studied. The results show that the wing joint motion mainly affects the backward and forward modes of rotor flapping. Different rotor rotation speeds cause varying degrees of modal frequencies of wings in different flight modes, especially the wing flapping mode. The nacelle tilt angle causes significant changes in wing waving frequency, and other modes are basically unaffected. The shaft length mainly affects the wing shimmy and torsional mode in vertical flight, and the offset basically does not affect the wing modes in the forward flight stage.

The combination resonance of size-dependent microbeams is investigated. Two harmonic forces act on the microbeam, and combination resonance is observed while the excitation frequencies differ from the resonant frequency. Microbeams with two different sources of nonlinearities including three kinds of boundary conditions, clamped-free (nonlinearity comes from large curvature and nonlinear inertial), clamped-clamped, and hinged-hinged (nonlinearity originates from mid-plane stretching-bending coupling), are taken into consideration to have a deep understanding of this phenomenon. A traveling load acting on the microbeam is presented as a special case of combination resonance. The modal discretization technique is applied to discretize the equations of motion, and then the Lindstedt–Poincare method, a perturbation approach, is employed to solve the resultant equations. The conditions for combination resonance are presented, and frequency-response curves and time histories at the resonance point are obtained for microbeams of each boundary condition. Results reveal that different sources of nonlinearities result in different performances of combination resonance. The free vibration part constitutes a large percentage of the final response. Furthermore, the situation of coexistence of combination resonance and superharmonic (or subharmonic) resonance is determined. The special case demonstrates a higher amplitude than the common combination resonance for all the boundary conditions. Parametric studies are then carried out to discuss the effects of the length scale parameter, excitation force as well as its position, and damping on the performance of the microbeam.