Modelling and optimization of sails

The aim of this paper is to improve the quality and the performances of sails by using non-linear modelling, numerical experimentation and optimization methods. The sail is represented by a triangular structure made of composite materials (unidirectional or woven composite) well modelled by an orthotropic membrane behaviour. Under the wind pressure, the sail is submitted to large displacements and small strains. Initial pre-tension load which ensures that the surface is reasonably free of wrinkles is required. The numerical solution is carried out by means of a modified Newton–Raphson method. The mathematical problem of optimization relates to the displacement in the transverse direction of the sail. The parameter of design is the fiber orientation. The optimization method uses the Nelder–Mead algorithm, efficient to solve non-linear problems. The numerical data provided by the sail makers will ensure a comparison between the obtained results and the empirical techniques used by the sail designers.