Efficient jib-mainsail fluid-structure interaction modelling based on an extended lifting-line theory ⇓validations with semi-rigid sails experiments

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 to provide 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 taken into account 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 structural finite element software, 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. 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 yacht sails. A good matching between experimental and numerical modelling is observed on local comparisons. Indeed, 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%.