In designing offshore mooring system, the dynamic behavior of mooring chains, wires and multi-component lines is of increasing importance. In order to investigate the global performance of deepwater floating system in South China Sea, nonlinear hull/mooring/riser coupled dynamic analyses of a truss spar designed for 1500-m waterdepth are conducted in the time domain. In addition, deepwater offshore basin and wind tunnel model tests of the truss spar were carried out. The vital wind coefficients for topsides and current coefficients for hull and truss section of Spar were gained from model tests. Discussion and comparison of mooring line tensions and global motions of hull/mooring/riser coupled system between the model tests and numerical simulations are provided.
So far, three competitive spar concepts have been proposed: classic spars using a deep-draft hollow vertical cylinder; truss spar using a combination of relatively shallow-draft hollow cylinder and truss structure extended to a soft tank; cell spar using combination of small diameter tubes. The floating spars have been increasingly popular as an economic and reliable oil production platform in deep or ultra-deep water, particularly in the remote areas of the Gulf of Mexico (Wichers, et al., 2004). As the offshore industry move into deeper water, the capacity to analyze and model test deepwater floating systems are challenged. The portion of the mooring line and riser mass becomes larger against the hull mass, and the resulting inertia and damping effects from them are expected to be important. As a result, it may lead to significant overestimation of mean and maximum pitch/roll responses. In this case, to accurately account for the inertia and damping effects of mooring lines and risers on the hull motions, hull/mooring/riser coupled dynamic analyses in time domain need to be employed (Kim, et al., 2001; Hansen, et al., 2004).