Design Of Gradient Layer And Optimization Of Integrated Thermal Protection Structure

Integrated thermal protection structure with composition of thermal protection material and lightweight thermal-insulation material, simplifying the design of thermal protection structure and heat insulation structure of thermal protection system and having the advantages of light weight and short preparation period, is one of the important directions in the development of thermal protection system. However, due to performance mismatch between different materials, there is a great thermal stress in the structure, even leading to the failure of the structure in the process of structural service. To solve this problem, the gradient layer is added between different materials, and the design of gradient layer and the optimization of the whole structure are studied in this paper.The finite element model of integrated thermal protection structure with gradient layer has been established, and the response characteristics are analyzed, which has confirmed the effect of the gradient layer. The influence of structural parameters and the spatial distribution of volume fraction of constituents of the gradient layer on the structural response, based on parameter study, are analyzed.Furthermore, to improve the efficiency and reduce the structure weight, a multi-objective optimization model of integrated thermal protection structure is established. The critical response is determined through the trend revealed by the relationship between structure response and heat flux, which has improved the computational efficiency. Based on the simplex method, the volume fraction of constituents at each control point of the gradient layer is optimized, which makes the stress level of the structure significantly reduced. And on this basis, the corresponding solution method of the multi-objective optimization model is established based on neighborhood cultivation genetic algorithm, with taking structure dimension parameters as design variables. The corresponding optimization results shows that the obtained 30 Pareto optimal solutions are all close to the critical state and the Pareto front is distributed widely in the space of objective functions.With considering the uncertainties of load conditions, material properties and structural dimension parameters, the reliability of the minimum thickness design scheme of multi-objective optimization results is analyzed using Monte Carlo simulation method. Meanwhile, the impact of the random input variables on the random output response is also investigated. A neural network approximation model of the input parameters and the output response is established using the radial basis function. And on this basis, the reliability-based optimization of integrated thermal protection structure is carried out using six sigma based probabilistic design optimization approach, which makes the structural efficiency further improved by comparing with the results of multi-objective deterministic optimization.