Research On The Structure Optimization Of The Pressure-resistant Shell Of Deep-sea Manned Submersible Based On Fatigue Life

Manned submersibles are subject to ever-changing cyclic loads during service,and the corresponding fatigue failure mode is the main threat to manned submersible pressure-resistant shells.From the perspective of most current studies,people usually only consider the check of strength and stability when they do the research on the structure optimization of the pressure-resistant shell,ignoring the fatigue damage caused by the cyclic load that the large-depth manned submersible bears in the process of diving.This paper studies how to takes the fatigue life of pressure-resistant shell of the manned submersible as the constraint condition and optimize it with the goal of minimizing the net volume of the structure.The detailed research work is as follows:The initial design parameters of the pressure-resistant spherical shell are determined.The strength of the pressure-resistant spherical shell is checked.Based on the theory of linear elastic fracture mechanics,the stress intensity factor of spherical shell surface crack is calculated.The unique curve model is used to predict the fatigue life of the pressure-resistant spherical shell under the extreme diving condition and the random diving condition.The results show that the fatigue life of the pressure-resistant spherical shell meets the design requirements in both conditions,and the fatigue life of the auxiliary viewport is lower than that of the main viewport in both conditions.The standard particle swarm optimization algorithm,the particle swarm optimization algorithm with improved inertia weight and the particle swarm optimization program with improved learning factor are respectively constructed by Matlab self-programming.Test functions are selected to compare and verify the accuracy,reliability,convergence and robustness of the self-programming algorithm.The results show that the improved particle swarm optimization algorithm with learning factors is more effective in solving the optimal value problems of most functions.In view of the constrained optimization problem in 3d,the influence of relevant control parameters on the algorithm performance is studied,and the reasonable control parameter values are given to provide reference for the optimization of the viewport of the pressure-resistant spherical shell.Parametric modeling is carried out for each viewport of the pressure-resistant spherical shell,and the finite element method is used to calculate the fatigue life of viewport with different parameter combinations.The upper bottom radius,lower bottom radius and height of the viewport are selected as design variables,and the net volume of the structure is the objective function.The fatigue life under the extreme diving condition and random diving condition are taken as constraint conditions respectively.Based on the principle of structure optimization,the minimum design sizes which meets the requirement of fatigue life are sought.The results show that the volume of the main viewport and the auxiliary viewport decreased by 14.19% and 8.29%respectively under the extreme diving condition.Under random diving conditions,evolume of the main viewport and the auxiliary viewport of the pressure-resistant spherical shell decreased by 13.83% and 7.09% respectively.