MARIN has taken the first step in creating a hydro- structural coupling using DIFFRAC - the hydrodynamic panel code used for offshore research - enabling more complex hull designs to be used in structural analysis.


Structural response calculations for a new FPSO concept for SHELL


Hydrodynamic tools are able to calculate ship motions based on the wave loads over the hull and the mass distribution of the ship. The pressure distributions and inertia loads solved by the hydrodynamic tool can also be mapped on a structural model of the ship, which is generally a Finite Element (FE) model. In combination with environ- mental and operational conditions, the stresses at selected critical details of the vessel can be calculated. The ultimate loads and fatigue loads can then be found.


Within MARIN, hydrodynamic solvers PRECAL_R and FATIMA are also used to per- form hydro-structural calculations. These have developed further but they are still only suitable for conventional hull shapes like monohulls or catamarans. However, a hydro-structural coupling with DIFFRAC enables more complex hull designs, with multiple floaters or moonpools, to be used.


Marcus Schiere & Wei Xu


m.schiere@marin.nl


Application on an FPSO concept design The hydro-structural coupling with DIFFRAC was used in calculations for a design of a new FPSO concept developed by SHELL. MARIN USA was already involved in the hydrodynamic studies for this concept. A simplified FE model of the ship was generated, before and after conversion and


the link between DIFFRAC and the FE solver was established. The goal of this study was to estimate the structural impact of the FPSO concept following its conversion from a Suezmax tanker. The material thicknesses for the main structural members in the FE model were based on Classification rules. Ultimate material stresses were calculated for both hulls in hurricane and storm con ditions. Additionally, the loads on the connectors between the hull and the mooring were calculated and included in the structural calculations.


This project shows the on-going efforts of MARIN to continuously develop the available numerical tools. This initiative facilitates the analysis of concept studies with innovative elements.


report 23


Part of the hull and maximum stress amplitude distrbutions calculated for the parent Suezmax hull in winter storm condition


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