Research On Reduction Modeling And Time Delay Problems In Active Isolation System Of Typical Flexible Structure

In recent years, active vibration control has been widely used in aerospace, shipbuilding, automotive and other industries. However, due to the flexible structures of spacecrafts and ships are getting larger and more flexible, the vibration control of these structures becomes more and more difficult. One important reason is that it's difficult to establish a reliable mathematical model for the system: The scale of dynamic model built by finite element numerical method is usually too large to be used in controller design. And, the real system may have many components with different complexity, some of which can be analyzed with finite element method, while some others must be put into experimental modeling. So it need to be solved by integrated the finite modeling and experimental modeling together. Further more, the delay included in actuator, even it may be very small, could lead to a decline in control efficiency or even instability of the control system.For the above reasons, on the basis of a thorough review of existing researches, this thesis employs numerical simulation and experimental study to research on the problems of reduced modeling, setting up the full structure by combination of experimental model and finite element model and active control with time delay.First, by analyzing the deficiencies of the traditional modal synthesis method, a new free-interface component mode synthesis method was proposed based on the residual dynamic flexibility. This method can compensate for high-order truncate modes and could be easy used in experimental measurements. Then the free interface component mode synthesis method is used to set up the dynamic model of the full structure by coupling experimental model of component A and finite element model of component B. The method theoretically solves the condensation and mixed modeling of the flexible structure.Proposed reasonable solutions for four problems encountered in experimental modal synthesis method: the problem of the complex transfer function; the problem of getting mass matrix and stiffness matrix from the experimental data; the lack of displacements of rotation and the problem of spatial incompleteness. Finally, numerical examples and experimental model have demonstrated the validity and efficiency of proposed method.Based on the super-element dynamic condensation technology, finite element model of elastic body reduced in physical space. Taking into account the effect of actuators'delay, the study established delay active control model and numerical analysis maximum delay of the system and the stability of controller delay. Numerical calculations show that active control is necessary to consider the delay factor in order to avoid instability, the method proposed in this paper is easy to ensure control system performance and stability.