This work presents a full scale experimental study on the aero-elastic wind/sails/rig interaction in real navigation conditions with the aim to give an experimental validation of unsteady Fluid Structure Interaction (FSI) models applied to yacht sails. An inboard instrumentation system has been developed on a J80 yacht to simultaneously and dynamically measure the navigation parameters, yacht's motion, and sails flying shape and loads in the standing and running rigging. The first results recorded while sailing upwind in head waves are shown. Variations of the measured parameters are characterized and related to the yacht motion (trim mainly). Correlations between the different parameters are examined. In the system's response to the dynamic forcing (pitching motion) we attempt to distinguish between the aerodynamic effect of varying apparent wind induced by the motion and the structural effect of varying stresses and strains due to the motion and inertia. The dynamic full scale measurements presented underline the necessity of considering the unsteadiness of phenomena to correctly simulate a yacht's behavior in actual sailing conditions. The simulation results from the FSI model compare very well with the experimental data for steady sailing conditions. For the unsteady conditions obtained in head waves, the first results show a good agreement between measurements and simulation.

This paper describes an experiment that was carried out in the Twisted Flow Wind Tunnel at The University of Auckland to measure a detailed set of pressure distributions on a rigid 1/15 th scale model of a modern asymmetric spinnaker. It was observed that the pressures varied considerably up the height of the spinnaker. The fine resolution of pressure taps allowed the extent of leading edge separation bubble, pressure recovery region, and effect of sail curvature to be observed quite clearly. It was found that the shape of the pressure distributions could be understood in terms of conventional aerodynamic theory. The sail performed best at an apparent wind angle of about 55°, which is its design angle, and the effect of heel was more pronounced near the head than the foot. Analysis of pressure time histories allows the large scale vortex shedding to be detected in the separation region, with a Strouhal number in the range 0.1-0.3, based on local sail chord length.

The dynamics of defects in a pattern of traveling inclined rolls has been investigated. Two regimes were identified in the neighborhood of defects: a diffusive regime, with a negative phase diffusion coefficient, and a coalescence regime in which the phase gradient diverges in time following a power law behavior. The observed periodic nucleation of defects is related to the frequency inhomogeneity induced by the disymmetry of the wave amplitude. Amplitude holes have been observed in the secondary modulated pattern. PACS. 47.20.-k Hydrodynamic stability -47.20.Lz Secondary instability -47.54.+r Pattern selection; pattern formation 142 The European Physical Journal B

The secondary instability mode and transition to a weak chaotic regime in a one-dimensional roll pattern have been investigated in the Taylor-Dean system. The spatiotemporal modulation of a roll pattern, called a triplet state in Phys. Rev. Lett. 64, 1729 ͑1990͒, is quantitatively characterized using the demodulation technique by the Hilbert transform. A triplet pattern arises from the primary structure by a periodic modulation of the phase both in space and time. The amplitude of the modulation, chosen as an order parameter, has been measured, and it grows as a square root of the reduced control parameter. The correlation length and time of the triplet pattern are maximal near the threshold, and decrease to values comparable to the size and period of a triplet in the chaotic regime. In the chaotic regime, regular oscillations of triplets are observed with a finite frequency, suggesting a phase modulation of the triplet pattern itself.

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 fluid 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