A Study on Motion Responses of Classic Spar Platforms Subjected to Short Crested Waves

Abstract— The wind generated seastate in the real sea condition
is well represented by the short crested waves or the multidirectional
waves. The short crested waves are identified as the
linear summation of the randomly generatedlong crested waves
that propagate to different directions. In this paper,
experimental and numerical studies on the dynamic responses of
the classic spar platforms subjected toshort crested waves are
presented. The experimental study was performed in the
Offshore Laboratory of Universiti Teknologi PETRONAS. In
the study, the classic spar model was restrained by four mooring
lines and subjected to short crested waves. A MATLAB code was
developed to analyze the dynamic responses of the classic spar.
The classic spar was modeled as a rigid body with three degrees
of freedom in surge, heave and pitch motions. In each time step
of the analysis, the mass, damping and stiffness matrices were
computed. Newmark Beta method was employed to solve the
dynamic equations of motion. Response amplitude operators
(RAO) were estimated and compared with the measurements.
The results compared well.
Index Terms -Short crested waves; Model tests, Wave basin,
Response amplitude operator, Dynamic responses