Research On Dynamic Characteristics Of Rotating Internally Connected Blades

When some practical devices with internal flexible blades,such as centrifugal fan and shaftless pump,rotate in a large range,the stiffness of the system will change due to flexible accessories.In this thesis,it is abstracted as a rigid-flexible coupling system with flexible cantilever beam in rotating rigid ring.At the same time,a large number of experimental results show that the mechanical behavior of microstructure has obvious scale effect,and the classical continuum theory can not correctly describe its mechanical properties.In addition,such structures are usually in extremely complex environments,such as high temperature,high voltage,electric field,magnetic field and other physical fields.In order to meet the practical needs of engineering,it is very important to study the dynamic behavior of embedded flexible beam system in micro-scale and macro-scale respectively.In this thesis,a rigid-flexible coupling dynamic model of flexible cantilever beam with rotating rigid ring is established.Functionally graded material with strong heat resistance is selected to model the internal flexible blade from micro-scale and macro-scale respectively.at the same time,considering the influence of temperature field and blade section shape,it is verified by C++ and MATLAB programming and compared with related literature,and the numerical simulation is completed.The main research contents are as follows:First of all,the rigid-flexible coupling dynamic model of rotating internal flexible FGM beam is established,and the longitudinal shortening caused by transverse bending deformation is considered,that is,nonlinear coupling deformation.The deformation field of the flexible beam is discretized by the hypothetical mode method,and the rigid-flexible coupling dynamic equation of the system is derived by using the second kind of Lagrange equation,and the corresponding first-order approximate simplified model is given.Then the rigid-flexible coupling dynamic equations of the internal beam system considering scale effect,thermal effect and cross section are derived respectively.Secondly,through the numerical simulation example,the dynamic response of the internal FGM microbeam in the non-inertial system is analyzed,the difference between the first approximation model and the zero approximation model is compared,and the internal FGM microbeam is compared with the external FGM microbeam.At the same time,the effects of rotation angular velocity,functional gradient coefficient,scale parameters and diameter-length ratio on the dynamic characteristics of the internal FGM microbeam are studied.The natural frequency and critical speed of transverse bending are analyzed on the basis of constant angular velocity of rotation.Then,through a simulation example,the effects of various dimensionless parameters and temperature field on the natural frequency,critical speed and dynamic response of the system are studied in detail,and the influence of temperature field on the dynamic softening phenomenon of the internal FGM beam is pointed out,which provides a reference for studying the dynamic characteristics of the internal blade.Finally,combined with the practice of the blade model,the dynamic response of the internal conical FGM beam in the non-inertial system is studied by numerical simulation,and the effects of diameter-length ratio,section shape,taper ratio and functional gradient coefficient on the natural frequency and critical speed of the rotating internal conical FGM beam system are studied.