The Investigation Of Model Simplification Based On Parameter Optimization

In the field of aerospace, in order to control the flight attitude of aircraft, we need to obtain the dynamic characteristics of vehicle in the shortest possible time, and to adjust the flight attitude of the aircraft in a real time. Considering the kind of engineering problems from the model updating, it is how to obtain a modified model in which the computational efficiency can be improved effectively. The paper mainly explains the mathematical theory and method of dynamic model updating, and how to simplify the finite element model by using the model reduction method. The simplified finite element model is taken as the initial model for dynamic model updating, and the purpose is to make the parts of revised dynamic characteristics of the modified model as close as possible by using the optimization method. Specific approach is implemented in this paper consists of3main steps:First of all, in order to obtain a polycondensation matrix of the model, it uses Guyan condensation method to reduce the initial structure model of freedom. The Guyan condensation method does not consider the inertia influence on associate degree of freedom, and the dynamic control equation is simple, so it is more convenient to decrease the freedom of the initial theoretical model. Guyan condensation method has been widely used in finite element analysis software, and the polycondensation matrix of model can be extracted from the finite element analysis.Secondly, the objective of the paper is to build a simplified beam structure which can replace the initial theoretical model. The geometrical parameters of beam structure are based on the polycondensation matrix of the model and the formula of beam element. The replacement model is the initial model of updating model. In the process of model updating, the modified variables of the model are the radius and thickness, and the constraints are the first top3frequencies of the initial theoretical model. The best situation of the modified model is that the low order frequencies and modes of the initial theoretical model can be simulated.Finally, the initial theoretical model is divided into a plurality of sections, which are taken as a polycondensation structure model. According to the order of the polycondensation structure model and the simplified model of beam structure, the composite beam structure model can reflect parts of dynamic characteristics of the initial theoretical model by using the optimization methods, and can reduce the freedom of the initial theoretical model in the process of calculation. In this paper, we also have introduced some of the finite element software briefly to ensure the paper successfully completed. Patran is used for pre-processing and updating the size of model, and Nastran is used for post-processing. Isight provides solutions to optimization methods and Patran&Nastran integration.The dynamic characteristics of initial theoretical model can be simulated by using the proposed method of model simplification.In this paper, we build a finite element model to prove that our method is reasonable and easy to implement. The results show that the simplified model can reduce the computational complexity of computer and the practical value of the method is obvious.