Numerical Investigation on Dynamic Responses of Classic Spar Platforms: Long Crested Waves vs. Short Crested Waves

In the real sea condition, only multi-directional waves or
short crested waves are found. Short crested wave isdefined as
thelinear summation of various long crested waves propagated
tovarious angles, where the magnitude and direction generated
are randomly varied. In this study, the dynamic responses of
classic spar platform subjected to long crested and short crested
waves are investigated numerically and compared. Two
numerical simulations are developed by incorporating
Diffraction theory to obtain the wave forces for long crested
waves and short crested waves. The classic spar platform is
assumed to be rigid with three degrees of freedom surge, heave
and pitch, restrained by four mooring lines. For every time step,
the mass, damping and stiffness matrices are evaluated. The
equations of motion are formulated for the platform dynamic
equilibrium and are solved by using Newmark Beta method in
time domain. The results in terms of Response Amplitude
Operator (RAO) for surge, heave and pitch motionsare obtained
and compared.