Reliability Analysis And Reliability-based On Design Optimization Of Spacecraft Stiffened Cylindrical Shell Structure

As the main structural components of space vehicles and missiles,the reliability evaluation and design optimization of the stiffened cylindrical shell structure are especially important,which is the main basis for determining whether the structural is safe and economical or not.The rationality and reliability of structural reliability evaluation and optimization design depend on the accuracy of finite element analysis,the adequacy of random variables considered in reliability analysis,the accuracy of reliability analysis methods,and the global convergence of optimization algorithms.In this paper,the nonlinear stability of the stiffened cylindrical shell structure is first studied,and the quasi-static analysis of explicit dynamics is used to solve the nonlinear response and limit load of the structure to overcome the problem of convergence of the Newton-Raphson method and the Arc Length method.The mesh accuracy of finite element and the analysis loading time of the quasi-static response are obtained,through the study of the mesh accuracy and the total loading time.Based on the nonlinear finite element model of the explicit dynamics method,the influence of modal defection,internal pressure and external pressure loads,and structural design parameters on the ultimate load is analyzed.The results show: the amplitude of modal defection,internal and external pressure loads,thickness of skin and the longitudinal stiffened parameters have a significant impact on the ultimate load.The ultimate load decreases significantly and then stabilizes with the increasing of the defection’s amplitude.The internal pressure load can increase the ultimate load,and the external pressure load can reduce the ultimate load.Generally,the ultimate load can be increased by increasing the structural design parameters.Secondly,for the spacecraft stiffened cylindrical shell structure,considering its three failure modes of ultimate load,maximum displacement and yield stress failure,and considering the structural design parameters,material elastic modulus,first-order modal defection amplitude and load as random variables,and then establish the Kriging model of failure modes.Based on the Kriging model,performing the structural reliability and sensitivity analysis of the stiffened cylindrical shells under pure axial compression and combination of external pressure and axial load by the HL-RF method and the MCS method,and then comparing the reliability of the structure under different load distributions.Then,considering the correlation between the three failure modes,the reliability analysis of the series system is carried out.The reliability and sensitivity analysis results show that the calculation results of the HL-RF method and the MCS method are highly consistent and meet the requirements of analysis accuracy.Structural failure modes are highly correlated,and the system failure probability depends entirely on the failure mode with the largest failure probability.It can be seen from the dimensionless sensitivity coefficient that the axial load,material elastic modulus,thickness of skin,external pressure load and defection amplitude have significant effects on structural reliability.Finally,based on optimized framework of the Kriging proxy model,the reliability-based design optimization of the stiffened cylindrical shell structure under combined external and axial compression loads is performed.The optimization of the safety factor of 1.5,the reliability-based design optimization of the load following the normal distribution,and the reliability-based design optimization of the load following the extreme value I distribution were carried out respectively,and the three optimizations were compared.The analysis results show that the deterministic optimization of 1.5 times safety factor has a certain redundancy compared with the reliability-based design optimization of the load following the normal distribution,while the load following the extreme value I distribution does not meet the reliability requirements of the spacecraft structure.Therefore,the reliability-based optimization design is more reasonable than the deterministic optimization design,and can provide guidance for the selection of structural safety factors.