Two-objective structural optimization of space capsule with thin-walled cylindrical approximation

In this paper, the structural optimization of a space capsule has been discussed by approximating a thin-walled cylindrical shell with a certain length under the axial compression force and constant lateral pressure. Design variables include the outer diameter and cylinder thickness. The purpose of optimization is to minimize the mass and maximize the frequency of the first vibration shape mode of the cylinder. Design constraints include the buckling load multiplier (buckling safety factor) above 1.5 and Von Mises stress below 100 MPa. In this problem, first, according to the permissible limits of the design variables, a design of experiment and then a sensitivity analysis have been carried out to check the sensitivity of the objective functions and constraints to the design variables. After numerically solving the output values with the help of Ansys software and preparing the response surface, the optimal design point has been identified with the help of the Genetic algorithm. Then, with the numerical simulation of the optimal point, the accuracy of the values obtained from the response surface method was checked and their accuracy was confirmed. It has also been observed that at the selected design point, Von Mises stress is less than its allowed value, i.e. 100 MPa, and also the buckling load factor is more than twice its minimum allowed value. However, this point has the smallest distance from the origin and the optimum point has been chosen as the knee point.