Hydrodynamic damping contributions for an advanced floating production system design

Abstract

Catenary moored floating vessels used for hydrocarbon production and storage exhibit low frequency, large amplitude resonant motions predominantly in the surge direction. These motions are caused by slow drift forces resulting primarily from random wave action. Accurate predictions of the damping forces are required in order to design fit for purpose moorings. This paper considers the contribution caused by hydrodynamic damping on an innovative floating production system design that is actively being evaluated by the offshore industry. The design consists of a relatively shallow draught surface piercing monohull attached by short rectangular connectors to a fully submerged lower hull positioned below the water surface. Theoretical methods are developed to predict a lower bound on the hydrodynamic damping contributions caused by fluid interaction with the connectors. The lower bound prediction is of relevance because it provides an upper bound estimate on the large amplitude vessel surge motions and hence the maximum mooring line loads. Comparisons with experimental data are provided for model tests performed on a typical vessel and a deep draught monohull design without connectors.