Model Reduction Method Of Stiffened Cylindrical Shell Structures And Its Application

The stiffened cylindrical shell structures are now widely used in the carrier rocket due to the high specific strength and specific stiffness.However,when the fine model is used in the finite element calculation,the complex structural details will lead a disadvantages of large computational scale and low computational efficiency.Especially in the dynamic optimization,a large number of times of dynamic analysis makes the optimization design face enormous challenges.The model reduction method could transform a fine model with larger calculation scale into a small calculation model that retains part of the main mechanical properties,which could improve the calculation efficiency while ensuring a high calculation accuracy.Therefore,the research on the method of model order reducing has important practical significance for improving the efficiency of the finite element analysis of the stiffened cylindrical shell structure.Among the common calculation methods of equivalent performance,the numerical implementation of asymptotic homogenization(NIAH)is based on strict mathematical theory,therefore it has a high calculation for accuracy equivalent performance.What's more,this method is easy to operate,and has little requirements to the type of reinforced form,which is an ideal method to be used in reducing the order of grid-stiffened cylindrical shells that consisting of a large number of periodic unit cells.In this thesis,the method of order reduce of grid-stiffened cylindrical shells based on NIAH method is studied.And the method is also combined with the proper orthogonal decomposition(POD)reduction method to be applied to structural dynamic characteristics optimization.In static model reduction,this thesis directly assigns the equivalent stiffness of the unit cell calculated by the NIAH method to the light tube structure to establish the reduced order model.The examples show that the reduced-order model has a high computational accuracy and computational efficiency in solving the response under static load.After that,the applicable conditions of this reduced-order method in the stiffened cylindrical shell with rectangular opening are also discussed.The modification method of using the fine model to replace the equivalent structure in the area near the opening is proposed,and obtained a good results.In dynamic model reduction,the NIAH method is combined with the equivalent density method or the additional mass method,respectively formed the NIAH-equivalent density method and the NIAH-additional mass method.The two methods are validated and compared by the related examples.The results show that the two methods both have high computational accuracy for the low-order global modes of the structure and can greatly improve the computational efficiency.The thesis is also proposes a fast method for solving the fundamental frequency of the structure based on the POD method.Finally,this thesis combines the NIAH-additional mass method and the POD,then constructs a structural dynamic characteristic optimization framework based on hybrid reduced order model,which can be used in the structural optimization of grid-stiffened cylindrical shells with target responses are specific overall vibration frequency and fundamental frequency.It is verified that the model reduction method adopted in this thesis can greatly improve the computational efficiency while maintaining a high computational accuracy.The optimized framework based on hybrid reduced-order model can effectively meet the optimization requirements and has a certain practical value.