NUMERICAL AND EXPERIMENTAL STUDY ON MOTION RESPONSES OF SEMI-SUBMERSIBLE PLATFORMS SUBJECTED TO SHORT CRESTED WAVES

Keywords: Short crested waves, semi-submersible platforms, hydrodynamic analysis, wave
tank tests, Response amplitude operator.
Abstract. The effect of the short-crested waves on the motions of moored semi-submersible
platform is demonstrated from the results of the model tests, compared with the theoretical
calculations. The model tests were performed in the wave tank located in the Offshore Laboratory
of Universiti Teknologi PETRONAS. In the tests, model was moored in the head sea
with four linear springs fore and aft, and the motion responses subjected to multi-directional
waves were measured. The responses in three degrees of freedom (surge, heave and pitch)
are presented. A time domain numerical MATLAB code, incorporated with the short-crested
wave effect was developed. In each time step, the mass, damping and stiffness matrices were
calculated. The diffraction of short-crested wave force on circular cylinder was adopted, and
the equation of motion was solved by the Newmark Beta method. Responses in term of Response
Amplitude Operator (RAO) are presented and compared. Good agreement between
numerical and experimental results was achieved.