Optimal Layout of Gill Cells for Very Large Floating Structures

Abstract

A pontoon-type, very large floating structure (VLFS) undergoes uneven deformation when loaded unevenly. The resulting differential deflection may lead to a cessation of equipment operation, and even compromising the structural integrity of the VLFS. One cost effective solution for reducing the differential deflection is by introducing the innovative gill cells at appropriate locations in the VLFS. Gill cells are compartments in VLFS with holes or slits at their bottom surfaces to allow water to enter or leave freely. At these gill cell locations, the buoyancy forces are eliminated and this allows uneven buoyancy forces acting at the bottom hull of the VLFS to somewhat counterbalance the applied nonuniform loading. In this paper, we investigate the effectiveness of gill cells in pontoon-type VLFS in reducing the differential deflection and von Mises stresses as well as the optimal layout (i.e., the number and locations) of gill cells that minimizes the differential deflection subject to a draft constraint. As the decision variables, objective functions and the constraints are not continuous and differentiable, genetic algorithms are adopted as an optimization tool. The optimal layouts for gill cells are determined for various VLFS shapes such as square, rectangular and I-shape and loading configurations.