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Aiming at the a UAV experience complicated dynamics environment under different conditions,firstly,the modal analysis of stress stiffening effect on the UAV main reducer is carried out,the natural frequency and mode shapes are obtained in different conditions.Then frequency response analysis of main reducer is carried out based on certain incentives implementing on the reducer.The research results show that the vibration modes of UAV are mainly torsion and modal natural frequency of UAV main reducer is increased with speed increasing.Through the frequency response analysis,the weak links of the main reducer structure design is predicted,some design references for the main reducer structural optimization are provided.

Abstract: In this study, the non-linear transverse vibrations of a system consisting of a beam with two piezoelectric actuators symmetrically bonded to its top and bottom surfaces are investigated. Due to the immovable end conditions the vibrating system is stretched. This stretching is modified by the residual in-plane stresses generated by the actuators, which are under the same in-phase voltages. A version of the Lindstedt–Poincare method is used to acquire the approximate solutions to the problem. The natural frequencies are computed from the solution to the linear problem, which is described by the equations of the first power of the small parameter. The orthogonality condition is applied to find the first correction of the linear frequency. The non-linear natural frequency of the system is derived depending on the vibration amplitude. Finally, the obtained solutions are applied to a steel beam with two piezoceramic layers. As the mass and stiffness of the piezoelectric elements are factors which affect the structure of the system, their influence on the natural linear frequency and the amplitude–frequency relationship is discussed. The main results concern the effect of the residual piezoforce on the non-linear vibration of the system. [Copyright &y& Elsevier]

An efficient method based on quadratic performance index and Lyapunov's second method is developed for the vibration reduction optimization of frame structure rotating at a constant angular velocity. Four optimization formulations and algorithms are studied for both low and high angular velocity. These formulations consider both linear vs nonlinear dynamic models as well as direct integration and Lypunov method to evaluate performance index. Three numerical examples are presented to compare the effectiveness of the four algorithms. Numerical results show that all the four optimization methods can reduce vibration at low rotating speed and find very similar optimal designs. However, at high rotating speed, dynamic model of rotating structure must consider nonlinear axial strain in order to obtain correct dynamic response. Since the Lyapunov's second method is not applicable for the nonlinear model and the NFTI (nonlinear dynamic model with nonlinear axial strain and time integration) method is very inefficient, the present study develops a perturbation method, linearizes the nonlinear dynamic model and establishes the LNFLA(linearized dynamic model with nonlinear axial strain, the Lyapunov's second method). Numerical examples show the optimization method LNFLA provides an efficient numerical method for vibration reduction of rotating frame structure with both low and high rotating speed. [ABSTRACT FROM AUTHOR]