Multi-module floating ocean structures

Abstract

In this paper, we describe an analysis of the wave-induced motions and structural response of a very large floating structure made up of a number of modules, each of which is treated as a rigid body having six degrees of motion freedom. The modules are connected to one another by mechanical joints having elastic and damping characteristics. The platform may be held in its mean position by various means including catenary and taut cable mooring systems. Each module consists of a floating body of quite general geometry and the range of shapes may include ship- or barge-like bodies and wave-transparent bodies similar to semi-submersible platforms. The wave-induced forces and the motion responses are computed within the context of linear ship and platform motion theory. Provision is made for utilizing any procedure appropriate for the individual body geometry in computing the fluid forces on each module. Such procedures include two-dimensional strip and three-dimensional panel methods, both of which are based on ideal-fluid potential theory, and the Morison formula which includes some real fluid effects. Viscous forces are included by means of the method of equivalent linearization, with the necessary iteration built into the computer code. The results of the computation include the absolute and relative motion responses of the individual modules, the forces and reactions in the connecting structure, and the mooring and restraint loads. In addition, the relative motions between adjacent unconnected modules may be determined in order to simulate the assembly of the structure at sea.