Session: 06-12-04 Ship Hydromechanics IV

Paper Number: 128033

128033 - Procedure to Include the Dynamic Loads of Catenary Shaped Risers on FPSO Roll Motion Assessments 

This work describes a proposed procedure to incorporate vertical dynamic loads of catenary shaped risers to the roll motion assessment of a FPSO in the frequency domain. The proposed procedure involves the application of the Aranha-Pinto (2001) formulation for the dynamic tension in the top of the risers. It is assumed, as an approximation, that the riser tensions are harmonic when the floating body (FPSO) is under the action of regular waves (this hypothesis is related to the assumption that the quadratic hydrodynamic damping is linearized in the Aranha-Pinto (2001) formulation). Since the dynamic tension are amplitude dependent, the described procedure is iterative. From the hull “point of view”, the effect of the riser vertical loads can be considered to be equivalent to additional roll inertia and damping. It is shown that the riser vertical dynamic load, according to the application of the chosen analytical formulation, has a component that is in phase with the vertical acceleration of the point that connects the riser to the hull and a component that is in phase with the vertical velocity of such point. The roll RAOs calculated with the proposed procedure have a good agreement with the roll motions calculated with a coupled time-domain model in Orcaflex.

Presenting Author: Carlos Chads Petrobras

Presenting Author Biography: Naval architect working at the Petrobras Research Center (CENPES) since 2011 in the field of naval architecture and offshore engineering, with experience in hydrodynamics, mooring and stability of offshore platforms. Masters Degree in Ocean Engineeing in the Federal University of Rio de Janeiro (2015), with a thesis in second order roll assessment of a barge shaped FPSO.

Obtained in 2015 a Masters degree in Ocean Engineering from the Federal University of Rio de Janeiro (UFRJ), with the thesis focused on the area of second order roll assessment of a Floating Production, Storage, and Offloading (FPSO) vessel.

Currently undertaking a doctoral program in Ocean Engineering in the Federal University of Rio de Janeiro (UFRJ).

Authors:

Carlos Chads Petrobras
Paulo Esperança Federal University of Rio de Janeiro