An Aeroelastic Implementation for YachtSails and Rigs

Sammanfattning: An aeroelastic model has been developed to determine the elastic response of sailing yachts’ rigs and sails due to the aerodynamic pressure induced on the sails by the wind. A vortex-lattice method (VLM) is used to determine the aerodynamic pressure. The structural response is calculated with a non-linear finite element method (FEM). In the aeroelastic model, pressures are calculated using the VLM module and applied to the finite element representation of the sail. Displacements are calculated and the new shape is used to determine a new pressure distribution. The procedure is iterated until the pressure distribution has converged. A comparison of a fixed and elastic rig is presented which shows the importance of using a fully aeroelastic model when studying the behavior of yacht sails. The VLM-implementation uses vortex ring elements with two different wake models: a fixed wake aligned with the free-stream and a force free wake. The VLM-implementation shows good correlation to commercial VLM-codes as well as with model tests. Results show minor differences between the fixed- and the free wake model. Three types of finite elements have been implemented to model the various parts of the rig: nonlinear bar elements for stays and boom, nonlinear triangular membrane elements for sails and linear beam elements for mast and spreaders. The Newton-Raphson method is used to solve the non-linear structural problem for displacements. The structural implementation show good correlation to other FEM-implementations and analytical solutions.