Geometric Accuracy Control of Very Large Floating Structures Considering Welding Distortion

Recently, the utility of VLFS (Very Large Floating Structures) attracts great deal of public attention. In order to construct VLFS, however, some technical problems remain. Because it is too large to build at any building dock or other site on the ground, the construction by joining floating units together on the sea is inevitable. Some advanced engineering for constructing operations on the sea are necessary, such as maintaining precise measurement of each unit, joining units in waves, underwater welding techniques.Demonstration with a large floating model was carried out by Technological Research Association of Mega-Float (TRAM) from 1995 to 2001. During construction of floating model, we found out it is important to estimate the welding distortion precisely, because it causes distortion of VLFS itself and the misalignment among units. Since complete restriction of the distortion at sea is impossible, precise estimation of the distortion become essential for super-sizing VLFS. In order to solve this problem, we had trial estimation by FEM analysis.In this paper, concerning on welding distortion, comparisons between experimental results and estimation by FEM analysis are shown. As a result, we show it is possible to estimate the welding distortion of VLFS under construction precisely. Moreover, we show FEM analysis can suggest the procedure to make geometrical inaccuracy and misalignment among units minimum by controlling the shapes of units and their placing position.