Research On Dynamic Modeling And Vibration Characteristics Of Fiber-reinforced Air Vehicle Cabin Structure In Thermal Environment

The fiber-reinforced composite material is widely used in the structure deisgn of aerospace engineering,owing to its excellent properties such as light weight,high strength and good designability.The performance of air vehicle has been gradually improved with the application of fiber-reinforced composite material.At the same time,the air vehicle structure is also exposed to the more complex load environment induced by aerodynamic heating and different dynamic loads in the whole mission profile.Then some new difficulties are created in the initial design stage of air vehicle cabin structures due to the application of the fiber-reinforced composite material and the complexity of the load environment.They mainly include:1.The traditional design and analysis methods are difficult to satisfy the needs of rapid iterative design of fiber-reinforced air vehicle cabin structures because of the anisotropy property of fiber-reinforced composite material.So,there is a lack of reasonable and effective design methods;2.Since the influence of thermal load and dynamic loads on the cabin structures is intensified during the service process,the traditional analysis method is not suitable to predict the dynamic response of cabin structures under the complex conditions.Aiming at above problems,the thesis establishes the dynamic analysis model of the fiber-reinforced cabin structure in the thermal environment according to the research strategy from the cabin structure elements to the whole cabin structure.On this basis,the dynamic characteristics investigation related to the cabin structure is carried out.The main research works and conclusions are as follows:1.The dynamic unified analysis model of fiber-reinforced cabin structure elements,including conical shell,cylindrical shell,spherical shell,and annular plate,is established.And the research work sloves the problem of modeling separately for vibration analysis of different structure elements.Thus,the established model lays the foundation for the subsequent research on dynamic model and vibration characteristics analysis of the cabin structure.Firstly,different structure elements are obtained by changing the characteristic parameters of the double-curvature shell structure element.The constitutive relationship of structure elements is derived in the thermal environment by introducing the additional thermal stress into the shell theory.Then,the massless artificial springs are employed to simulate arbitrary boundary conditions and connection conditions at coupling boundaries of closed structural elements in circumferential direction.And displacement admissible functions of cabin structure elements are uniformly characterized by the spectrogeometric method(SGM).The energy equations of structure elements,such as kinetic energy and strain energy,etc,and the expression of work done by external force are derived.Finally,the dynamic discrete governing differential equation is obtained with the variational method.The validity and correctness of the dynamic analysis model is verified by numerical examples.2.The dynamic analysis model of the fiber-reinforced conical-cylindrical joined structure in the thermal environment is established.Firstly,continuity conditions of the conical shell and cylindrical shell at the connection location are satisfied by constructing the elastic coupler.And the elastic potential energy stored in the elastic coupler is derived.Then,combining elastic potential energy and the energy equations of conical shell and cylindrical shell,the lagrangian energy function is established.Finally,the dynamic discrete governing differential equation is derived with the variational method.Through the comparative analysis of numerical results,the validity of the dynamic analysis model is verified.3.The dynamic analysis model of the fiber-reinforced cabin structure(conicalcylindrical-spherical-annular plate joined structure)in the thermal environment is established.In the model,the elastic couplers are used to meet the continuity conditions at the connection locations of conical and cylindrical shell,cylindrical and spherical shell,and cylindrical shell and annular plate;the dynamic discrete governing differential equation of cabin structure is derived with the variational method.The validity and correctness of the dynamic model in predicting the dynamic response results of the cabin structure is verified by a series of numerical examples.On this basis,the parametric analysis on dynamic characteristics of fiberreinforced cabin structure is carried out.And the relevant analysis results can provide theoretical support for the design optimization of the related structures.