Comparison Between Experiments and a Multibody Weakly Nonlinear Potential Flow Approach for Modeling of Marine Operations

Abstract

This paper presents validation tests for a new numerical tool for the numerical simulation of marine operations. It involves multibody dynamics modeling, wave-structure interactions with large amplitude body motion and cable’s dynamic modeling. Hydrodynamic loads are computed using the WS_CN weakly nonlinear potential flow solver, based on the weak-scatterer hypothesis. Large deformation of the wetted body surfaces can be taken into account. Firstly the ECN’s WS_CN solver capabilities are extended to multibody simulations. A first validation test is performed by comparing numerical results to the experimental data of [1]. Then, a second validation test is proposed. It consists in the ballasting operation of a spar. The experimental set-up is described.

Efficient Nonlinear Hydrodynamic Models for Wave Energy Converter Design—A Scoping Study

“…The WSA was pioneered by Pawlowski for nonlinear ship hydrodynamics in the early 1990s [178] but has only been applied to WECs in the past decade. The first usage is reported in Bretl [165] to assess the performance of a small scale data buoy equipped with an oscillating pendulum PTO, then in Merigaud et al [168] for a comparison against linear Cummins and NLFK models, and as then via the WSA code, under development at Ecole Central de Nantes (ECN) [170][171][172][179][180][181][182]. Letournel [179] developed a WSA model, for submerged bodies, and an early-stage comparison against an FNPF BEM solver is presented in [180], for the case of prescribed motion of a submerged cylinder, showing good agreement and roughly an order of magnitude speed increase.…”

“…In Bozonnet et al [171], the WSA model is then applied to a scaled Wavestar float, demonstrating similar results to experiments and an NLFK model. Wuillaume et al [170,182] couple the WSA model with an advanced multibody theory mechanical solver, inWave, to investigate simulating marine operations, performing a verification of the coupling procedure through a test case on a CETO type WEC in [170]. The method is extended in [182], to handle the case of multiple interacting floating bodies, by introducing a remeshing technique, which is validated against experiments for a test case involving two cylinders in regular waves.…”

Development of a Panel Cutting Method Coupled With an Unsteady Potential Flow Model Based on the Weak-Scatterer Approximation

“…In this section, the governing equations of the weakly nonlinear potential flow theory based on the weak-scatterer theory are described. More details may be found in [6,7,8].…”

“…Some slight differences are observed, probably due to the permanent remeshing process in the new mesh generator whereas, in the initial mesh strategy, the mesh is only deformed if the regeneration is not necessary. The remeshing involves an interpolation between the old and the new mesh as explained in [8] and so numerical errors may occur.…”

“…At Ecole Centrale de Nantes, a numerical tool, named WS_CN, based on the time-domain weakly nonlinear potential flow theory using the weak-scatterer hypothesis, has been under development since 2012. It has been used with single submerged bodies [6], single surface-piercing bodies [7] and has been extended to multibody simulations [8]. In these previous studies, the mesh generator of WS_CN is based on a 2 Copyright © 20xx by ASME semi-analytical approach.…”