Research On Multi-Mode Coupled Vibration Characteristics And Stability Of The Rotating Composite Structures In Complex Environments

The composite structures have excellent mechanical properties,such as high strength,light weight,corrosion resistance,thermostability,fatigue resistance,and so on.These structures are used increasingly in many engineering applications.Rotating composite beams are one important example of the composite structures in industrial applications like wind turbine blades,helicopter blades and aircraft propellers.According the previous studies on the rotating beams,the rotating motion will induce various modes of vibrations including edgewise bending(vibration in the rotating plane),flapwise bending(vibration perpendicular to the rotating plane),torsion(vibration about the axis of the structure itself)and axial extension.These modes of the rotating beam are generally coupled with each other due to the anisotropy of composite materials.The combined effects of rotation,design parameters,external environment and other factors aggravate the complexity of the composite structure dynamic behaviors.Therefore,the study on the vibration characteristics of these composite structures is of great theoretical significance and practical value.The main work in this paper is to establish the bending-bending coupled nonlinear vibration governing equation of the rotating composite beam in complex external environment.The coupled vibration characteristics and nonlinear dynamic behaviors are studied by means of numerical methods,and the influences of various parameters on the coupled vibration characteristics,stability and bifurcation characteristics are analyzed as follows,Comprehensively considering the influences of rotating effects,coupling factor,design parameters and fiber orientation,the governing equation of the rotating laminated composite beam bending-bending coupled nonlinear vibration in hygrothermal environment based on D'Alembert principle and the constitutive equation of one single layer material due to the hygrothermal effects.On further reflection of the aerodynamic effect,the governing equation of the rotating composite thin-walled beam bending-bending coupled nonlinear vibration subjected to aerodynamic force and hygrothermal environment by means of Hamilton's principle.The accuracy and usability of the above two rotating composite beam models are verified compared with the existing model.A numerical approach based on Green's functions is presented to handle the bending-bending coupled vibration characteristics problem of the rotating laminated composite beam.It is focused on the influences of the rotation and hygrothermal environment combined effects on the composite beam.The numerical results are presented to discuss the effects of coupling factor,rotational velocity,temperature,humidity,setting angle,pitch angle and fiber orientation angle on the coupled vibration characteristics of the system.The bending-bending coupled vibration governing equation of the rotating composite thin-walled beam under aerodynamic force and hygrothermal environment are solved by the method of Galerkin truncation.The partial differential equations are discretized into ordinary differential equations.The complex frequencies of the coupled vibrations via solving eigenvalue problem of the system.Finally,the influences of the coupling and some parameters such as rotational velocity,design parameters,hygrothermal environment and aerodynamic effects on the complex frequencies of the coupled vibration.The flapwise nonlinear parametric vibration of the rotating composite thin-walled beam under aerodynamic force and hygrothermal environment is studied,and the nonlinear dynamic behavior and stability of the system are analyzed.Based on the governing equation established,the partial differential equation is discretized into differential equations through the method of Galerkin truncation.Then,the steady-state response and amplitude of the system nonlinear parametric vibration are obtained by the method of multiple scales and the stability conditions of trivial and untrivial solutions of the system are solved via Routh-Hurwitz criterion.The numerical results are used to further describe the influences of rotational velocity,hygrothermal environment,aerodynamic effects,design parameters and fiber orientation on the frequency response cures and instability regions of the system are studied.Employing the multiple scales method and Galerkin truncation,the flapwise nonlinear forced vibration of the rotating composite thin-walled beam under aerodynamic force and hygrothermal environment is investigated.The stability conditions and bifurcation characteristics are obtained through Routh-Hurwitz criterion in the low-frequency primary resonance and high-frequency primary resonance.Eventually,the influences of external excitation amplitude,rotational velocity frequency,hygrothermal environment,aerodynamic effects,design parameters and fiber orientation on the frequency response cures of the system are analyzed.Finally,the research content,research methods and research results of this dissertation are summarized,and the prospects for the future research are given.