Structural Modeling for Overall Structural Analysis of Very Large Floating Structures

Abstract

For the structural analysis of a Very Large Floating Structure (VLFS) of several thousand meters long, a hierarchical system of structural analysis must be established, in which a macroscopic structural idealization is performed first to make an overall structural analysis practicable and then the local structural analysis is performed using a zooming technique. A rational structural modeling for overall analyses is most important in such an analysis system, because it governs the accuracy of subsequent structural analyses for local structures.In this study, a two-dimensional grillage model is considered as one of the possible modeling for overall structural analysis of a VLFS, and a rational formulation of a torsional stiffness of grillage beam elements considering shear deformation of deck and bottom plating is discussed. Considering the characteristics of torsional deformation of plate-like structures and based on the concept of an equivalent strain energy, a new formulation of the equivalent torsional stiffness for beam elements is presented. Several static analyses of pontoon-type and semi-submersible type VLFSs are performed, and a validity of the proposed formulation is demonstrated.