Linearized Model for Subsea Installation Based on Natural KC Number

Abstract

Abstract The behaviour of subsea equipment has been widely studied by companies to minimise risks during subsea installation, which bring huge costs on the operation. The prediction of equipment motions typically is accomplished utilizing either commercial software or recommended practices from Classification Societies to comply with the minimum requirements on launching operations. This paper analyzes subsea installation in time and frequency domains using experimental, numerical and analytical approaches. Experiments have been carried out at Instituto de Pesquisas Tecnológicas (IPT) to investigate the dependency of drag andadded mass coefficients on Keulegan-Carpenter number and at Laboratory of Waves and Currents (LOC-COPPE/UFRJ) to study equipment and cable responses on the installation. A numerical model is made in OrcaFlex® for determining the transmissibility of displacement and force in function of frequency ratio, and the time series of manifold responses. Linearized models from DNV [1] and the so-called natural KC (proposed in the present paper) are taken in the investigation and compared to previous methodologies. The natural KC approach arises as an innovative way of investigating subsea equipment as the literature only provides parametric analysis considering an arbitrary KC value (i.e., Pestana et al. [3]). The analyses notice a good agreement among experiments, OrcaFlex® model and natural KC model whereas the curves found by DNV method usually overpredict the response of subsea equipment specially around resonance region.