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Sail Design
The main goal of this research activity is the investigation of non linear behaviour of sail rig under aerodynamic load. To this aim, a first computer code has been developed to perform the viscous aerodynamic analysis of a multi-sail system including mast effect. The code is based on 3D vortex lattice method coupled to 2D boundary layer solution along streamlines. Then the structural analysis is performed using a finite element code developed ad hoc able to predict non linear deformation and stresses on a muti-sail rig. The final ISTIA code couples the aerodynamic and structural solutions performing successive iterations.
The aerodynamic problem is faced using quadrangular vortex rings. Two-dimensional integral boundary layer, with separation bubble model, is used to evaluate viscous effects (including mast effect) on inviscid pressure distribution and on the final sail shape.
The structural behaviour of the sails is assumed to be similar to a membrane under pressure loads. Three nodes isoparametric triangular elements are chosen for the finite element method.
To validate the structural computer code an experimental test has been set up and a simple machinery has been built allowing shape measurements of a rectangular membrane under constant pressure load. Mechanical characterization of different fabrics used in the experiments has been done through tests on specimens performed using material testing machine.
The ISTIA code estimates the final shape of the multi-sail system set at a prescribed angle of attack, aerodynamic loads, all stresses, and the final aerodynamic and performances coefficients (like CL, CD, CPropulsion, etc.). It is also capable to analyse non isotropic material like those commonly used in sail fabric.
Since experimental tests on similar cases are unavailable up to date, the validation of the complete iterative coupling procedure inside ISTIA will be carried out through comparisons with wind tunnel tests. Accurately measurements of the shape of a small model of mast plus sail system will be performed.
