In this paper, we investigate the heave and pitch coupled motion of the cell spar platform through experiments. Free-decay tests are performed in a wave tank with a scaled model to determine the natural period and damping coefficient of heave and pitch. The motions in regular waves are measured to derive the transfer function. During the experiments, it is observed that pitch motions become unstable at a certain time range. It is thought that kinetic energy is transferred from heave mode to pitch mode due to nonlinearity. The experimental results agree well with the numerical results except for the time range of unstable pitch motion. It is found that the mooring effect is insignificant on the motion response.
With the increasing use of technologies such as third generation cell spar, new developments in the petroleum industry are beginning to invest in new reserves in deep-water and more efficient production of existing reserves.
Spar technology has been utilized in offshore structures such as research vessels, communication relay stations, and storage and offloading platforms. Recently its application has extended to deepdraft platforms for deepwater production (Halkyard, 1996; Glanville, 1991). Spar platform is a long hollow cylinder with a large diameter, which is normally moored by conventional spread chains.
The evolution of spar technology continues to open the door to deepwater deployment. Since the first spar platform was installed in the Gulf of Mexico in 1996, the spar has been regarded as a competitive floating structure for deepsea development. Spar technology has progressed from the classic design such as Neptune spar to the truss designs installed in Nansen, Boomvang and Gunnison, and further to the cell design. As the reserve threshold of oil fields is becoming smaller, it will no longer be economical to use the conventional floating facilities.
