Session: 06-03-06 Fluid-Structure, Multi-body and Wave-body Interaction VI

Paper Number: 128825

128825 - Assessment of Nonlinear Loads and Motions Through Response Conditioned Design Waves: Practical Application and Limits 

In the assessment of the extreme responses of marine structures during severe sea states, accuracy usually comes with a computational cost. Linear potential flow theory, which easily produces a response distribution at any desired probability, is known to have limited accuracy in large waves for such nonlinear quantities as the Vertical Bending Moment.

Extreme wave episodes are rare, the Unified Requirement S11 of IACS gives a design requirement for the Vertical Bending Moment corresponding to withstanding a 25 years return period in North Atlantic conditions. Long brute-force simulations or experiments are necessary to induce those extreme responses. It is , in most cases, cost-prohibitive for high-fidelity methods.

For this reason, the concept of Response Conditioned Waves  (RCW, a.k.a Equivalent Design Waves) has been developed, as a way of investigating solely wave patterns of short duration, that can be considered tantamount to brute-force simulations. If successful, it consists in computing short-time wave episodes that should cause a given target response of the quantity studied. The generation and propagation of such waves in the computational domain allow for short numerical simulations.

The paper presents a method that uses a fast nonlinear potential flow solver, specifically with a High Order Spectral (HOS) formulation to compute the RCW. This allows a quite easy reproduction of the wave in CFD and Experiments. This allows us to assess and validate the nonlinear responses.

The method is applied for the vertical bending moment (VBM) of a zero-speed containership and for the nacelle accelerations of a floating wind turbine. The strengths and limits of the methodology are discussed.

Presenting Author: Benjamin Bouscasse Ecole Centrale de Nantes

Presenting Author Biography: Senior scientist working at Ecole Centrale de Nantes. He is head of the IIHNE team of the LHEEA laboratory. He is active on both experimental and computational fluid dynamics.

Authors:

Benjamin Bouscasse Ecole Centrale de Nantes
Athanasios Dermatis Ecole Centrale Nantes
Shinwoong KIM Ecole Centrale de Nantes
Guillaume Ducrozet Ecole Centrale de Nantes
Guillaume De Hauteclocque Bureau Veritas
Marine Lasbleis Bureau Veritas