A study on motion responses of classic spar platforms subjected to short crested waves

The wind generated sea state 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 generated long crested waves that propagate to different directions. In this paper, experimental and numerical studies on the dynamic responses of the classic spar platforms subjected to short 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.