To improve the hydrodynamic performance of conventional semi-submersible platform (SEMI), the large individual column was divided into several small columns, and the hydrodynamic performance of the SEMI with multiple small columns (MSC) was numerically investigated in this paper. For a comparative study, a series of MSC SEMI models together with a conventional SEMI model were established and the displacement of them were kept constant. Detailed parametric studies were carried out in frequency domain to investigate the influence of column number and column diameter on structural hydrodynamic performance of MSC SEMI. The numerical results indicated that the concept of multiple small columns can not only weaken the hydrodynamic load on structure but also improve structural hydrodynamic performance significantly as expected.
The recent emphasis on deep and ultra-deep water hydrocarbon exploration and production, the floating systems, such as the tension leg platform (TLP), Spar platform, and semi-submersible platform (SEMI), are progressively replacing conventional gravity systems to exploit oil and gas in deep water (Low and Langley, 2007; Jiao, 2007). Different from the gravity system, the motion response of floating system is the limiting factor. The motion response of TLPs and Spars are very small, especially in heave direction, due to the tendons of TLP and the deep draft and damping members of Spar (Zeng et al., 2013). However, the TLP tendon design and installation become challenging when the water depth beyond about 1500m (Mansour, 2009; Williams et al., 2010). The Spar's available deck space is constrained by its hull diameter, and thereby pushing designers to stack the deck vertically to provide enough space (Jacobs, 2013). In addition, the topside-hull integration cannot be performed at quayside due to the deep draft of Spar. The topside and hull should be wet towed to the installation site and an extra derrick barge is needed to upending the hull and install the topside. These operations not only introduce greater risks but also incur costly on-site hook up and commission (Chen et al., 2008).