| The flexible bodies are widely used in many engineering application, such as aerospace, rotating machinery, vehicle engineering, military project equipment, robots and micro electro mechanical system(MEMS). The structural components in these engineering systems undergo large scale rigid motion as well as its elastic deformation, so the rigid motion and elastic deformation coupling problem for the flexible parts is involved. The kinematics and deformation coupling dynamics system contains the rigid-body dynamics and deformable mechanics, the dynamic process of the flexible body undergoing large scale rigid motion is very complicated. The precise forecast for the system operation process on different constraints, different loads and control factor have become a very important problem, as the scale of rigid-flexible coupling system become more and more large and the structure become more and more complex. Current researchs on the rigid-flexible coupling system dynamics are mainly focused on the construction for the dynamics modeling, calculation strategies, contacts and collision problems for the flexible multibody systems and the coupling effect for the multiple physical fields. However, it is very important to the dynamics modeling of the coupled system, which required the model can reflect the coupling effect, also can degenerate to the classical elastic mechanics when ignoring the rigid motion, and can degenerate to the rigid body dynamics when ignoring the elastic deformation. There has always been a dispute on the physical mechanism of the dynamic stiffness effect in the rigid-flexible coupling system, which involved the nonlinearity in geometry, motion and material, etc. To study on these questions is still a research emphasis and difficulties. The couple stress linear elastic theory can consider the rotational deformation of the elastic body. The research on rigid-flexible coupling system dynamics with considering the couple stress on the influence to the elastic body has become more and more attention, which brings a large breakthrough to the dynamics research on the microscopic size flexible body.First of all, the dynamic modeling, the numerical solution and the dynamic response of the mass-spring system are emphatically elaborated, the inertial effects and dynamic characteristics of the coupled system are analyzed. Also the centrifugal vibration compound experimental equipment is created to verify the theoretical model. Secondly, the rigid-flexible coupling model based on the couple stress theory with considering both translational deformation and rotational deformation is proposed, also the finite element calculation program for the model is established. Finally, numerical analysis the dynamic process of the rotating cantilever beam, the flexible hub-beam system, the rotor blades and the huge-type wheel crane's arm by using the rigid-flexible coupling dynamic model. The main works and conclusions in this dissertation are as follows:(1) The research is focused on the dynamic behaviors of the two-Dofs spring mass system. Dynamic equations are established under a given condition, and the analytical solutions are discussed systematically and in detail. Dynamic characteristic, dynamic response and the coupling mechanism are studied in depth. The change processes of various inertial forces with time are discovered. To verify the petals shape of the particle trajectory in rigid-flexible coupling system, a two-Dofs vibrating centrifugal experimental equipment is designed and created, the experimental datas show that the rigid-flexible coupling model proposed in this paper is correctly.(2) Based on the Midlin linear elastic couple stress, a generalized elasticity contains three material parameter is established. Combined the modeling approache of the single particle rigid-flexible system, the rigid-flexible coupling model is derived with Hamilton's principle, and the model can consider the relative inertia force,centrifugal force,Coriolis force and the tangential force. The finite element control equation is formulated for the generalized elastic body, based on the method of weighted residuals and the constrained variational principle,with both the displacement and rotational angle considered as independent variables. The 8-nodes and 48-Dofs hexahedron isoparametric element or 4-node and 24-Dofs tetrahedron isoparametric element is extended to the finite element formulation. The finite element method of the generalized elasticity can consider all kinds of inertial forces to influence on the distribution of the internal forces, which also can provide the change rule of the dynamic characteristics for the elastic body.(3) Numerical analysis the dynamic characteristics and dynamic response of the cantilever beam rotating around a fixed axis with variable speeds. The dynamic frequency curve of the rotating cantilever beam under various constant rotational speeds was calculated, also the equivalent stress, couple stress and the displacement responses of the beam under different rotating configuration and different rotational speed conditions are calculated and analyzed. The petals shape of the particle trajectory and the maximum rotation speed of the system are particularly pointed out. The dynamic characteristics and dynamic response of the rotating micro-beam are discussed, the results indicate that the influence to the micro-beam by considering the rotational deformation can't be ignored, the rigid-flexible coupling model considering the couple stress is correct and reasonable for the micro size structure.(4) Calculate the selection of the flexible hub-beam system, a further study on the maximum rotational speed of the rigid-flexible coupling system can provide a new approach for the structural control. The dynamics response of the rotating flexible beam in the whole process of the system is analyzed, also consider the flexible hub-beam system under different external force loads, it is more accurate and reasonable to simulate the dynamics process of the generalized elasticity. The rigid-flexible coupled mechanism of the system structure components is accurately analyzed, which can provide theoretical basis and technical guidance to be better numerical simulation the operation process for the engineering application and control the displacement and stress values of the rotating system.(5) Based on the rigid-flexible coupling dynamics model with the generalized elasticity rotating around a fixed axis, the dynamic process from starting stage to constant speed stage of rotor blades is numerically analyzed. The mechanics model of rotor blades is established and different dynamic responses under different load conditions are considered. This work can provide important reference value for simulating the dynamic process of the rotor blades more accurately and reasonably.(6) By use of the classical elastic theory, traditional beam element and bar element, the dynamic process of the rigid flexible multibody system is simulated preliminary. Furthermore, based on the dynamic process of the huge-type wheel crane's arm undergoing large overall motion, the flexible multibody dynamics model is established and the corresponding calculation program is completed. The process on the weight lifted by wire rope of the wheeled crane and then swung by the slewing crane jib is simulated numerically. Moreover, the curves changing with time for the deflection angle of the weight and the stress value of the crane jib's different location are obtained. Through the comparison and analysis, the numerical solutions are closely matched with the experimental measurement results. Thus, the correctness and rationality of the modeling thoughts and method in this dissertation are verified further. |
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