Time domain hydrodynamic analysis of Semi-submersible platforms

Abstract
This paper presents the numerical hydrodynamic analysis for the motion responses of a moored semisubmersible
in regular sea waves. The semi-submersible is modeled as a rigid body made up of several cylindrical columns and twin rectangular pontoons. Airy wave theory and a hybrid approach incorporating Morison modified equation is used for evaluating the wave forces on the inclined and oscillating members of the platform. The linearized equation of motion is obtained in a common reference co-ordinate system fixed on the mean sea water level. The mass and stiffness matrices are evaluated at every time step and the equations of motion are formulated for the platform dynamic equilibrium. The equations are solved using an iterative incremental Newmark-Beta analysis method. The results agreed fairly well with the published experimental
data in the wave-period range.
Keywords: Semi-submersible platforms,
Hydrodynamic analysis, Degrees of freedom (DOF),
Morison modified equations, Equation of Motion
(EOM), Response Amplitude Operator (RAO).