Modeling And Updating Method On Stitched Thermal Protection Structure

Thermal protection structure is a key subsystem to guarantee flight safety of hypersonic aircraft, which can provide extra structural strength and stiffness to retain the aerodynamic shape and avoid the vehicle interior from extremely high temperature, ensuring complete the flight tasks under harsh circumstance. Finite element modeling plays an important role in numerical simulation of thermal protection systems, the accuracy of which will strongly effect on veracity of the structural dynamics response. Therefore, in this paper, finite element modeling and updating approaches are investigated for constructing numerical model of a newly design stitched thermal protection structure.Firstly, numerical modelling of a stitched thermal protection structure is conducted. The characteristics of the stitched thermal protection structure are analyzed and the equivalence method is used to gain the equivalent elastic properties of the refined model. The effectiveness of the equivalent model is verified by comparing with the refined model. The influences of stitching thread to the structure performance are studied, including the influences of the preload of stitching thread, the stitching gap, the space between stitching steps and so on. Results show that the stitching threads are employed to enhance the through-the-thickness elastic properties.Secondly, Parameter identification technique is adopted to reduce the errors in parameter estimation of stitched thermal protection structure. Modal data are measured by vibration test and model updating method is used based on the experiment data. A multi-stage model updating method is proposed to deal with the situation that the number of parameters is more than the experiment data in the model. Parameters are divided into groups and modified in certain iteration sequences. The thermal elastic parameters are fitted and the sensitivity of the fitted parameter is calculated by difference method under high temperature, consequently, model updating method based on thermal modal data is achieved.At last, model updating method using structural dynamic response is investigated.Several improved methods focused on the selected method of parameters and frequency points are adopted to enhance the stability of the iteration by improve the condition of the sensitivity matrix. The frequency points are picked based on the MDI method and the multi-stage model updating method is adopted to increase the accuracy of modification results.