Numerical analysis of the effects of mooring line configurations on the dynamic response of a truss spar platform in sea waves

In this paper, the effects of mooring lines configurations on the dynamic response on truss spar of Kikeh oil field off the coast of Malaysia near the Saba, was investigated. At first, the Aqwa code results were validated. Its results was then compared with Morison equation based DATspar code The RAO results showed that Aqwa software considering diffraction theory gives better results than DATspar code. It means that neglecting the diffraction phenomena leads to unrealistic results and modeling performed in this study is more accurate than previous work. The platform movements in three degrees of freedom in three different layouts of a four-line mooring, including the angles of 0, 22.5 and 45 degrees, respect to wave direction was investigated. The results showed that the effects of mooring configurations on the motions in regular waves in small and large amplitudes are insignificant and considerable respectively. Generally, by increasing the mooring line angle, the response amplitude is increased. For irregular waves, by increasing the mooring line angle from 0 to 22.5 and then from 22.5 to 45 relative to wave, the mean response amplitude of spar initially decreases and then increases. Nevertheless the minimum response amplitude occurs in 22.5 degrees.