Evaluation of flexible hull types for very large floating structures

Abstract

In this study, Very Large Floating Structures (VLFS) of different hull forms (semisubmersible and mat-like) are evaluated on the basis of their hull motions and structural responses. Some suggestions and recommendations are provided for selecting a configuration. The theory of linear hydroelasticity is applied to the analysis. The success of such an analysis of VLFS by means of available computers rests on the development of three efficient hydroelastic analysis methods that significantly reduce the CPU time and the required computational storage. The first method employs the modified Morison's equation and linear structural dynamic theory. The hydrodynamic coefficients in the modified Morison's equation, are obtained using the extended MacCamy & Fuchs' method for the columns and the strip theory for the pontoons, respectively. The method predicts better results at higher wave frequencies than does the Morison's equation method. In the second method, the simplified zero-draft Green function is employed in the hydrodynamic analysis and in the structural analysis a mat-like floating body is modeled as an equivalent floating plate. These two efforts result in significant CPU savings. The mathematical model of the last method employs a three-dimensional hydroelasticity theory. Two techniques are introduced to increase the computational efficiency of this method. One is related to the convergency of the Green function and the other involves the use of an iterative sparse solver for the linear system of equations. This method is especially efficient for the analysis of a VLFS in terms of CPU and storage. Hence, it has been possible to analyze the hydroelastic response of a VLFS with the available computer resources.