Nonlinear wave induced loads on a flexible containership in head seas using advanced hydroelastic methods

Lakshmynarayanana, P. (Speaker), Hirdaris, S. (Contributor)

Activity: Talk or presentation typesConference presentation

Description

The ever-increasing size of ships and offshore structures has resulted in ‘softer’ structures that require hydroelastic effects to be taken into account when predicting wave-induced motions and loads. Numerical hydroelastic investigations use, by and large, linear to partially/fully nonlinear potential flow solvers. The success/accuracy of such numerical methods in capturing violent free surface flows and strong nonlinear effects is a function of their inherent assumptions and, accordingly, has shown modest improvements in the ensuing predictions. RANS solvers, on the other hand, can fully take into account the nonlinearities associated with free surface flows, as well as viscous effects if and when required, making them more realistic. Presently, wave-induced load calculations with RANS solvers predominantly use one-way coupling, where the ship is considered rigid in the fluid solver and the RANS fluid loads are mapped onto a FE model (or used to evaluate generalised forces which provide the generalised excitation to a multi-dof system of linear equations in terms of principal coordinates), thus omitting fluid-structure interactions which can be significant. A strong or two-way coupling between RANS/CFD and FEA codes has to be implemented to accurately model the hydroelastic behaviour of a vessel floating/travelling in a seaway.
This paper presents a two-way coupling between CFD (STARCCM+) and FEA (ABAQUS) codes to model the 3-D dynamic behaviour of a flexible S-175 containership advancing with a forward speed in regular head waves. A 3-D beam FE model is used to model the structure of the containership and 3-D modelling for the fluid-structure interaction. The Star-CCM+ mesh is build up on the past experience with refined meshing in regions such as free surface, wake and ship boundary, resulting in approximately 3.5M cells. The main emphasis is on the prediction of linear and non-linear wave loads. The effects of the nonlinearities are expressed in terms of the higher order harmonics and the asymmetry in sagging and hogging loads. The predicted wave bending moments, for a range of wave frequencies and positions along the hull, are compared with a number of experimental measurements and other published numerical predictions and demonstrate the capability of the two-way coupled CFD/FEA method in predicting the nonlinear effects even in relatively severe wave conditions. The influence of mesh refinement and structural damping on predicted responses is investigated for some operational conditions.
Period24 Sep 2019
Event titleThe Baltic Seas International Maritime Conference: European Maritime Research from Adriatic to Baltic
Event typeConference
LocationTurku, Finland
Degree of RecognitionInternational

Keywords

  • Hydroelasticity of Ships
  • Fluid-Structure interaction
  • RANS/CFD/FEA
  • Wave-induced loads
  • Springing