Unsteady model of sail and flow interaction

We present an analysis and a numerical method for predicting the response of a two-dimensional sail in unsteady flow. The fluid is considered inviscid and incompressible so that the perturbation of the uniform inflow can be treated within vortex sheet theory. Due to the very small thickness of the sail, the assumption of the ideal flexibility can be made, and a nonlinear membrane model is used to solve the dynamics of the sail. Energy considerations on the complete system provide a variational formulation of the flow-structure interaction problem, which can be solved by using the boundary element method and a point vortex approximation of the wake. Numerical simulations for harmonic perturbation of the trailing edge and random inflows exhibit the nonlinear response of the sail.