Normally, the design slamming pressure on the bottomof a semi-submersible-type floating rig is determined in a simple way using the relative speed obtained from an air-gap analysis. However, few studies have taken a thorough, robust, and deep-background approach to the estimation of design pressure. To investigate the slamming pressure on the bottom of a semi-submersible rig, a simplified deformable stiffened plate of a zero-degree deadrise angle is simulated using the nonlinear FEM software LS-DYNA, which can take the influence of fluid-structure interaction (FSI) into account. Various parametric studies are carried out to examine the effects of structural flexibility, coupling stiffness, mesh size, velocity, stiffener size, and air cushion. The pressure response on the plate by the coupling of fluid and structure is studied and the FSI effect of each parameter is discussed. Then, equivalent transient and static loads that result in the same maximum or permanent deformation as FSI are evaluated for design purposes through a series of parametric studies.

Normally design bottom slamming pressure of semi-submersible type floater is determined in a simple way using a relative speed obtained from an air-gap analysis. However, there are few studies on a robust background on the estimation of the design pressure. In this study, to investigate the slamming pressure on the bottom of semi-submersible rig, a simplified deformable stiffened plate with 0° dead rise angle is simulated by using nonlinear FEM software, LS-DYNA which can take the influence of Fluid-Structure Interaction (FSI) into account. To simulate the slamming condition of semi-rig in a similar way, water hitting the structure with fixed boundary conditions is proposed. Various parametric studies are carried out to examine the effect of structural flexibility, coupling stiffness, mesh size, velocity, stiffener size, and air cushion effect. To further investigate the effect of horizontal velocity, the model is expanded and simulated with various horizontal water velocities. Pressure response on the plate by the coupling of fluid and structure is studied and the hydroelastic effect of each parameter is discussed.