Efficient jib-mainsail fluid-structure interaction modelling – Validations with semi-rigid sails experiments

Abstract

The present work takes place in the framework of the “Jib Sea” project. The main purpose of the project is to develop a new sail design made of articulated composite panels, for large merchant ships. The French laboratory “ENSTA Bretagne, IRDL” is involved in this industrial project for its expertise on fluid-structure interactions modelling. A fast and robust approach to model fluid-structure interactions for yacht sails is presented. Specifically, interaction effects between the jib and the mainsail are considered in the flow model presented. This is achieved using the lifting-line theory combined with a discrete vortex method, involving distributions of lumped-vortex elements along sail sections. The flow model is coupled with a finite element analysis of the structure, using shell elements for the modelling of sail membranes, beam stringers for battens modelling and a quasi-static resolution based on a dynamic backward Euler scheme. The flow model based on the Lifting-Line Theory is presently validated by a commercial software tools using the Unsteady Reynolds-Average Navier-Stokes equations. Numerical comparisons with experiments are conducted on a 50 m2 composite mainsail prototype and a conventional jib, built and hoisted on an onshore balestron rig. Measurements, such as strain gauges or cable tensions, are synchronized with a wind sensor. These data collected together enable both global and local numerical-experimental comparisons for forces and moments, providing a validation of the proposed fluid-structure interactions modelling of ship sails. A good match between experimental and numerical modelling is observed on local comparisons as relative differences are all less than 25% for TWA∈[−20;20] and TWS<10 kn. Global comparison results exhibit validations with experiments for |TWA|<10 deg and TWS<10 kn, where numerical-experimental relative differences are less than 10%.