ABSTRACT
The objective of structural design is to develop a structure that fulfils serviceability and safety requirements in a cost-effective manner. For a novel structure like a very large floating structure (VLFS), the structural design needs a first-principle approach that is based on a rational structural response analysis and explicit design criteria. Hydroelastic response analysis is an essential process for predicting the
global response of deformation and stresses in VLFSs. In the initial stage of the structural design of a VLFS, a uniform plate model is generally used for the hydroelastic response analysis. Such a simple structural model is effective for the determination of global stiffness parameters to meet design requirements. For the subsequent design stage, however, a more detailed structural model that can deal with structural member behaviors is needed in order to determine the structural member arrangement and configuration. Owing to its huge structural size, the applicability of three-dimensional (3D) finite element (FE) modeling to the entire VLFS is rather limited. Therefore, simple and rational structural modeling techniques need to be developed. Furthermore, hydroelastic response analysis should ultimately furnish the local stress response of detailed structures, as well as global responses. A hierarchical system of structural analysis that includes a zooming technique is needed. The design limit states for marine structures include the ultimate limit state
(ULS), the fatigue limit state (FLS), the serviceability limit state (SLS), and the progressive collapse limit state (PLS). ULS refers to the ultimate event in which structural resistance has an appropriate reserve. PLS refers to the progressive failure of structures when subjected to accidental or abnormal load effects (DNV 1997). PLS for accidental load effects is also called the accidental collapse limit state (ALS) (Moan 2004). ULS corresponds to component design verification based on the elastic behavior of the structure, and thus can be examined by the hydroelastic response analysis. But PLS needs a progressive collapse analysis that considers nonlinear structural behaviors such as buckling and yielding.
