Dynamic Behaviour of a Flexible Yacht Sail Plan

• Dynamic fluid structure interaction of a sail plan is modeled in harmonic pitching • Aerodynamic forces oscillations show hysteresis phenomena • Neglecting the structural deformation underestimates the forces oscillations • Both aerodynamic and structure inertia affect loads in the rig.A numerical investigation of the dynamic Fluid Structure Interaction (FSI) of a yacht sail plan submitted to harmonic pitching is presented to address both issues of aerodynamic unsteadiness and structural deformation. The FSI model | Vortex Lattice Method uid model and Finite Element structure model | has been validated with full-scale measurements. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces presented as a function of the instantaneous apparent wind angle show hysteresis loops, suggesting that some energy is exchanged by the system. The area included in the hysteresis loop increases with the motion reduced frequency and amplitude. Comparison of rigid versus soft structures shows that FSI increases the energy exchanged by the system and that the oscillations of aerodynamic forces are underestimated when the structure deformation is not considered. Dynamic loads in the fore and aft rigging wires are dominated by structural and inertial effects. This FSI model and the obtained results may be useful firstly for yacht design, and also in the field of auxiliary wind assisted ship propulsion, or to investigate other marine soft structures.This work was supported by the French Naval Academy

Experimental validation of unsteady models for wind / sails / rigging fluid structure interaction

The aim of this paper is to present the work of experimental validation elements of the aero elastic and unsteady model ARAVANTI. Numerical and Experimental results comparison is made on the rigging and sails of a J80 sail boat. Yacht modelling demands to consider unsteady phenomena resulting from the sea state, variations of wind speed and direction, yacht motion or trimming by the crew. A dedicated instrumentation is developed to measure the loads in shrouds and tension points of the sail, the apparent wind, the yacht motion, the sails flying shape and the navigation data. A special effort is made on sensors calibration, physical measurement comprehension and data synchronisation. Comparison with numerical results shows that the loads and flying shapes are well predicted by the model

A metapopulation model to simulate West Nile virus circulation in Western Africa, Southern Europe and the Mediterranean basin

In Europe, virological and epidemiological data collected in wild birds and horses suggest that a recurrent circulation of West Nile virus (WNV) could exist in some areas. Whether this circulation is permanent (due to overwintering mechanisms) or not remains unknown. The current conception of WNV epidemiology suggests that it is not: this conception combines an enzootic WNV circulation in tropical Africa with seasonal introductions of the virus in Europe by migratory birds. The objectives of this work were to (i) model this conception of WNV global circulation; and (ii) evaluate whether the model could reproduce data and patterns observed in Europe and Africa in vectors, horses, and birds. The model was calibrated using published seroprevalence data obtained from African (Senegal) and European (Spain) wild birds, and validated using independent, published data: seroprevalence rates in migratory and resident wild birds, minimal infection rates in vectors, as well as seroprevalence and incidence rates in horses. According to this model, overwintering mechanisms are not needed to reproduce the observed data. However, the existence of such mechanisms cannot be ruled out

Experimental validation of unsteady models for wind / sails / rigging fluid structure interaction

International audienceThe aim of this paper is to present the work of experimental validation elements of the aero elastic and unsteady model ARAVANTI. Numerical and Experimental results comparison is made on the rigging and sails of a J80 sail boat. Yacht modelling demands to consider unsteady phenomena resulting from the sea state, variations of wind speed and direction, yacht motion or trimming by the crew. A dedicated instrumentation is developed to measure the loads in shrouds and tension points of the sail, the apparent wind, the yacht motion, the sails flying shape and the navigation data. A special effort is made on sensors calibration, physical measurement comprehension and data synchronisation. Comparison with numerical results shows that the loads and flying shapes are well predicted by the model

Wave energy dissipation by vegetation in TOMAWAC

Water Qualit