Effect of Mooring Lines on the Responses of Spar Platforms

Spar platform, a competitive alternative structure for deepwater oil field development
is modelled as a rigid body with six degree -of-freedom, connected to the sea floor
by multi-component catenary mooring lines, which are attached to the spar platform
at the fairleads. Since this spar platform is quite new in deepwater exploration, a lot
of studies and researches still need to be done. Therefore in this project, the different
type of spar platforms as well as the dynamic responses of spar platform such as
surge, heave and pitch are being analyzed and compared by using comparison
method based on its different mooring lines configurations. The mathematical results
by using Linear Airy Wave Theory, Pierson-Moskowitz Spectrum, Morison Equation
and Motion Response Spectrum have been conducted. The frequency domain
analysis and time domain analysis have been performed by choosing frequency
within 0.05 - 0.3Hz and time series within 0 - 100 seconds. For Neptnne Spar
Platform, the maximum profile obtained were 1.9 - 2m for surge, 0.78m for heave
and 0.065radian for pitch. These values are within the permissible limits for offshore
operations. Also, parametric studies have been made by using different number of
mooring lines. It is shows that there is no significant effect on the surge and heave
responses even though the stiffness increases as the number of mooring lines
increases.