Fatigue strength analysis of pontoon type VLFS using spectral method

Abstract

The fatigue strength analysis of VLFS is carried out by using a 3dimensional plate finite element model with a zooming technology which performs the modeling of wide portions of the structure by a coarse mesh but the concerned parts by a very fine mesh of t by t level. And a stepwise modeling technique for global loading conditions is applied which uses the motion response of the global structure from 2-D plate hydro-elastic analysis as the enforcing nodal displacements of the concern 3-D structural zooming model. Seven incident wave angles and whole ranges of frequency domains of wave spectrum are considered. In order to consider the effect of breakwater, the modified JONSWAP wave spectrum is used. Applying the wave data of install region, the long-term spectrum analysis is done based on stochastic process and the fatigue life of the structure is estimated. Finally some design considerations from the view point of fatigue strength analysis of VLFS are discussed. Copyright ？ 2006 by The International Society of Offshore and Polar Engineers.