Objectives  In order to simplify the construction process and to reduce the weight of the structure, topology optimization and opening size optimization of solid floors in an outer tank of the pressure hull are conducted.

  Methods  In the study, Hyperworks/Optistruct is adopted to analyze the strength characteristic of the whole structure. The part of the solid floors 100 mm away from outer tank and pressure hull is defined as design space of the topology optimization. And the elements densities within the defined design space are taken as the design variables. The volume fraction of the design space and the typical stress values of the pressure hull and outer tank are assumed as design constraints while the objective is to minimize the maximum stress on the solid floors. Hyperworks/Optistruct is used to optimize the solid floor in outer pressure tank under full and empty loadings. Then, the size optimization of opening based on the Matlab and ANSYS is conducted. The von Mises and shear stresses of the solid floor are regarded as design constraints, and the weight of the solid floor including the stiffeners on them is treated as objective function to be minimized. A precise optimal scheme of openings is obtained through the above process.

  Results  The result of topology optimizations shows that holes should be placed on the middle to lower part of the solid floors. The result of opening size optimizations indicates that, compared with the initial scheme, the weight of the optimal solid floor with opening is decreased by 19% with the 38% increase in shear stress and equivalent levels of the other stresses.

  Conclusions  Both the optimization designs show that openings should be placed on the middle to lower part of the solid floor and their size should be gradually decreased from lower part to middle part of the solid floor.