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In small sailboats, the bodyweight of the sailor is proportionately
large enough to induce significant unsteady dynamics
of the boat and sail. Sailors use a variety of techniques
to create sail dynamics which can provide an increment
in driving force, increasing the boatspeed. In this
study, we experimentally investigate the unsteady aerodynamics
associated with one such technique, called “sail
flicking”. We employ a two-part approach...
Fluid Structure Interaction in High Performance Catamaran C-Foils Under Load
An experimental technique to accurately quantify the deformation and the bend-twist coupling of high performance
composite foils under fluid loading is presented. The experimental results are reproduced in a Computational Fluid Dynamic (CFD)
environment to assess the impact of board deflection and changes in pitch angle on vertical force generated in the C-foils while
sailing under increased hydrodynamic pressure.
A three dimensional Digital Image Correlation (DIC) methodology suitable for use within a wind tunnel is developed. The technique
allows for the measurement of full-field deflection during fluid-structure interaction (FSI) experiments. Combined with DIC
technique, the C-foil tip vortex is investigated using Particle Image Velocimetry (PIV) to correlate the variation of the vortex position
and strength to the deflection of the board. These techniques, combined with CFD investigations allow potential changes in structural
behaviour to be assessed with regard to improving the performances of the foils in sailing conditions.
Experimental results are presented for a high performance curved foil from a NACRA F20 catamaran tested within the University of
Southampton RJ Mitchell wind tunnel. The fluid regime is chosen to have a Reynolds number equivalent to light upwind sailing
conditions (Rn=6.66x105: boat speed of 6 knots) with a fifth of the fluid loading experienced in the water. Curved foils provide both
a hydrodynamic side-force to counteract the aerodynamic forces of the sails and a vertical lift force to reduce the wetted surface area
and hence the resistance. It is therefore necessary to investigate from a sailor point of view the influences of the side force and
vertical coefficients that the change in effective angle of attack and of pitch will give to the stability and the performances of the
catamaran.
Numerical Study of a Flexible Sail Plan Submitted to Pitching: Hysteresis Phenomenon and Effect of Rig Adjustments
A numerical investigation of the dynamic fluid structure interaction (FSI) of a yacht sail plan submitted to harmonic pitching is presented to analyse the system's dynamic behaviour simplifications and rigging adjustments on aerodynamic forces.
Numerical Study of a Flexible Sail Plan: Effect of Pitching Decomposition and Adjustments
A numerical investigation of the dynamic Fluid Structure Interaction (FSI) of a yacht sail plan submitted to har-monic pitching is presented to analyse the effects of motion simplifications and rigging adjustments on aerodynamic forces. 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. These hysteresis phenomena do not result from a simple phase shift between forces and motion. Plotting the hysteresis loops in the appropriate coordinate system enables the associated energy to be determined. This amount of exchanged energy is shown to increase almost linearly with the pitching reduced frequency and to increase almost quadratically with the pitching amplitude in the investigated ranges. The effect of reducing the real pitching motion to a simpler surge motion is investigated. Results show significant discrepancies on the aerodynamic forces amplitude and the hysteresis phenomenon between pitching and surge motion. However, the superposition assumption consisting in a decomposition of the surge into two translations normal and collinear to the apparent wind is verified. Then, simulations with different dock tunes and backstay loads highlight the importance of rig adjustments on the aerodynamic forces and the dynamic behaviour of a sail plan.
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 – have 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