A dynamic model to evaluate the influence of the laying or retrieval speed on the installation and recovery of subsea equipment

Abstract

A new model for the dynamics of a cable-mass system representing the installation or retrieval of subsea equipment is analyzed. It considers a one-degree of freedom system, which is able to account for the variation of the cable’s length during the time, simulating the equipment laying or recovering process. Also, the cable’s mass is included in the analysis and the hydrodynamic forces are modeled by the Morison’s equation. The resulting nonlinear equation of motion is integrated over the time domain via a predictor-corrector Newmark β-method. Firstly, the proposed model is compared with an Orcaflex model on fixed and variable length scenarios. The results show that the proposed model give accurate solutions in comparison with the finite element model through all the depths evaluated, even at zones where superharmonic response occurs. Secondly, the influence of payout speed on the dynamics of the system is assessed. Here, the system presents a variation on the static and dynamic forces, especially at the resonance zone. Finally, an operational weather window is generated for a specific case, which shows that the acceptable sea states change depending on the laying or retrieval speed considered. This highlights the importance of using models that account for the payout speed when analyzing subsea equipment installation and retrieval operations.