The present work concentrates on ship motion in random waves. The seakeeping performance of a typical tanker is observed in irregular waves, in particular severe ocean conditions. The computational tool is LAMP, which adopts the three-dimensional time-domain panel method. The numerical computation was carried out both the linear and nonlinear methods, and the results are compared. The statistical properties of random response are summarized, and the computation is extended to the prediction of green water. The result shows that the nonlinear effects are important in severe ocean condition, especially for the wave induced structural loads.
As oil exploration and production are going to deeper ocean, new concepts have been introduced for offshore structures. Those concepts include TLP, spar buoy, and FPSO. Nowadays, FPSO (Floating Production, Storage and Off-loading vessel) is getting to be popular. Basically FPSO's have the same hull forms with tankers, and many tankers have been converted to FPSO's. Some representative differences of FPSO with typical tankers are the positioning system, moon-pool effect and drift motion. In particular, since a FPSO stays at an installed position during her whole life, she may experience very severe ocean waves even phenomenal condition. In such ocean, the wave-induced loads can cause critical structural damage. In severe ocean, the nonlinearity of water waves and ship response are important. The nonlinearity of water wave makes the wave slope steeper and results in the nonlinear response of ship and offshore structure. In many cases, the nonlinearity of ship motion is stronger than that of water wave, and this fact has inspired to some researches on the nonlinear ship motion. Moreover, the inclusion of the body nonlinearity is easier to achieve than nonlinear waves in the theoretical and numerical studies.
