The damping box is the key device to improve the added water mass and the viscous damping effect for the cylindrical Floating Production Storage and Offloading (FPSO), which can effectively reduce heave and roll motion. The damping box is usually the cantilever box-like structure connected with the cylinder. The structural design and strength check of the damping box and its connection with the cylinder are critical to the structural design of the cylindrical FPSO. The maximum pressure and maximum damping force of the damping box are taken as the objective design load. It carries out the check and analysis of the structural strength of the damping box by using the sub-model method to check the structural strength of the damping box, taking the deformation obtained from the total strength analysis as the boundary condition, and the Morison method to simulate the viscous damping effect. It can provide reference for the structural design of the damping box.

Jacking holes of the jack-up platform leg are arranged in the entire length range of the leg, which directly affects the effective cross-sectional area of the leg and the overall bending performance of the leg. The reduction analysis method of the jacking hole for the overall strength and the buckling strength of the leg has been discussed in the current research. The sensitivity of the jacking hole to the plate thickness reduction degree or the reduction factor are discussed further according to the variation of the leg diameter, plate thickness and the size and space of the jacking hole. The analysis methods for the local strength of the jacking hole are compared in order to obtain the fast and effective calculation method of the local strength. It can provide a basis for the quick determination of the leg design scheme of the jack-up platform in the early design stage.