Some Direct And Inverse Dynamic Problems On Damped Spacecraft Structure

With dynamic problems associated with the damped spacecraft structure analysis and design as a background, aiming at reducing the dynamic response of spacecraft structure, this dissertation systematically studies some computational and design methods of damped structural systems and their applications to spacecraft structure. The dissertation focuses on the methods of damping modeling, complex eigenvalue analysis, frequency response analysis, component mode synthesis, sub-structure model reduction and model modification methods. Some new or improved methods are proposed, which can be more effective in the application to the design of spacecraft structures. Main contents of this are as the following.Firstly, some representative damping measures which are often used in spacecraft structures are summarized. Based on the way of their implementation, these damping measures are classified into discrete damping and distributed damping. The former is usually used in some connections between diffrenent parts and can be treated as independent parallel stiffness and damping. While the latter is located at certain area and can not be treated as the former, thus it is necessary to study its mathematical modeling as an item in the daynamic equation of motions of spacecraft. A common character of these inductive dampings is the nonlinear damping ratio. In this dissertation, with the Metal Rubber Damping Material (MRDM for short, or metal wire mesh as called in some publications) and the Constrained Layer Damping (CLD) structure as examples, methods of accurately modeling the damping are studied.In order to meet the requirements of the large damped structure's dynamic analysis and design, algorithms of the complex eigenvalue problem are studied in detail. After some improvements on exsiting methods, a complete computation flow of the large complex eigenvalue problem is developed. Firstly, the damped structure's dynamic eigenvalue problem is transformed into standard eigenvalue problem by introducing partitional triangular decomposition method. Then, by introducing the Lanczos algorithm and other transform, the large-scale complex eigenvalue problem is equivalent to a small-scale real one which only contains the first several eigenvalues of the original system. The eigenvalues and the eigenvectors of the equicalent eigenvalue problem can be solved by using two-step QR algorithm. The proposed computation method is adapted to eigenvalue problem with different damping form, and has the merits of stability and efficiency. Aiming to reduce the computation difficulty of a system with huge number of degree of freedom (dof), the model dynamic reduction method for the damped sub-structure is studied. Based on the constrained modes, the model reduction coordinate transformation is accomplished. Then the half-decoupling system equation is reduced into selected dofs'physical coordinates, and the left dofs'contributions are presented by the model effective mass matrices. Because the model effectie mass matrices are rapidly convergent along with the increasing of the natural frequencies, the reduced model can achieve good precision by reserving only a few modes. The proposed reduced method can both assure the precision and stability and preseve the compatibility and physical meaning of the original sub-structure.The dynamic model modification method based on frequency response function (FRF) is studied. Firstly, one kind of improved model modification method is presented and introduced into the model synthesis of sub-structures with flexible connections. The above application combines the structural model modification with the sub-structure theory, and thus it can derive an explicit system dynamic function that can clearly reveal the dynamic relationship between every sub-structures and connections. Therefore, by introducing the sensitivity theory of FRF, a whole process of large damped structure's dynamic analsis and design is achieved.With consideration of static and dynamic requirements of satellite, a satellite design method which can simultaneously reduce structure's thermal deformation and dynamic response is presented. The principal idea of this method is to locate High Damping Flexible Connectors (HDFCs) in static and/or dynamic distortion transfer path to interesting parts. The flexibility of the HDFCs will release the thermal stress and the damping of the HDFCs will attenuate the jitter.