The development of advanced composite structures for maritime and aerospace applications requires the ability to quantify their actual performance under known fluid loads. One example is the need to investigate the differences in fluid-structure response of passive adaptive composite structures. A wind tunnel based method is used to quantify the structural behaviour, and fluid response, of a flexible aerofoil under fluid loading. The technique measures the deflection of the structure, with high speed stereoscopic Digital Image Correlation (DIC). The tip vortex position is measured using high resolution stereoscopic Particle Image Velocimetry (PIV). The accuracy of the two full-field optical measurement systems is quantified and the effect of optical interactions is assessed. A flexible NACA0015 rectangular plan-form aerofoil of 0.9 m span and aspect ratio of two is subjected to aerodynamic loading within a closed circuit wind tunnel. The wind speed was varied from 10 to 25 m/s within a 3.5 m x 2.4 m working section. The structural response is measured simultaneously with the fluid flow field around the tip vortex. The tip vortex core, which moved by ≈ 62 mm at the highest wind speed, is directly compared to the deformation of the structure, which deflected by ≈ 58mm. A maximum foil twist of ≈ 0.6 deg was observed. The DIC accuracy is evaluated in static and transient conditions for translational and rotational movement. The DIC maximum error for translations, greater than or equal to 0.5 mm, is less than 3% and less than 0.6% in dynamic motions. The DIC total error for rotations is less than 5% in static motions and 1% in Email address: L.Marimon-Giovannetti@soton.ac.uk (L. Marimon Giovannetti) Preprint submitted to Journal of Fluids and StructuresOctober 21, 2016 dynamic rotations. The PIV uncertainty is quantified a posteriori providing the errors due to the correlation algorithm and the experimental setup. The mean in-plane velocity component uncertainties in the vortex region varied between 1.2% and 3.5% depending on flow speed (≈ 0.1 px) around the vortex structure. The mean out-of-plane velocity uncertainty around the vortex varies between 2% and 3.3% depending on flow speed.

Digital Image Correlation (DIC) is employed for the measurement of full-field deformation during fluid-structure interaction experiments in a wind tunnel. The methodology developed for the wind tunnel environment is quantitatively assessed. The static deformation error of the system is shown to be less than 0.8% when applied to a curved aerofoil specimen moved through known displacements using a micrometer. Enclosed camera fairings were shown to be required to minimise error due to wind induced camera vibration under aerodynamic loading. The methodology was demonstrated using a high performance curved foil, from a NACRA F20 sailing catamaran, tested within the University of Southampton RJ Mitchell, 3.5m x 2.4m, wind tunnel. The aerodynamic forces induced in the wind tunnel are relatively small, compared with typical hydrodynamic loading, resulting in small deformations. The coupled deflection and blade twist is evaluated over the tip region (80-100% Span, measured from the root) for a range of wind speeds and angles of attack. Steady deformations at low angles of attack were shown to be well captured however unsteady deformations at higher angles of attack were observed as an increase in variability due to hardware limitations in the current DIC system. It is concluded that higher DIC sample rates are required to assess unsteady deformations in the future. The full field deformation data reveals limited blade twist for low angles of attack, below the stall angle. For larger angles, however, there is a tendency to reduce the effective angle of attack at the tip of the structure, combined with an unsteady structural response. This capability highlights the benefits of the presented methodology over fixed-point measurements as the three dimensional foil deflections can be assessed over a large tip region. In addition, the methodology demonstrates that very small deformations and twist angles can be resolved.

The objective of this research is to explore the possibility of using Passive Adaptive Composite (PAC) on structures to help control the lift generated by hydrofoils on boats such as the International Moth. Intorducing composite fibres oriented at off-principal axis angles, allow a foil to passively control its pitch angle to reduce the lift generated at higher boat speeds helping to achieve a stable flight in a wide range of weather conditions. PAC utilises the inherent flexibility of a composite structure to induce a twist response under bending load which could be used to minimise the use of active control systems, or even improve the dynamic response of foils in waves. However, to design flexible foils requires numerical and experimental tools to assess the complex fluid structure interactions involved. This paper eveluates a simplified hydrofoil geometry designed to reduce its lift coefficient with increased flow speed. A coupled Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) methodology is presented to predict flexible foil performance. Validation of these numerical tools is achieved through the use of wind tunnel experiments including full field deformation measurements. Twist deformations resulted in a reduction in the effective angle of attack by approximately 30% at higher flow speeds reducing the foil lift and drag significantly.

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Abstract. For a sailing yacht, depowering is a set of strategies used to limit the sail force magnitude by intentionally moving away from the point of maximum forward driving force, potentially reducing the ship speed. The reasons for doing this includes among others; reduction of quasi-static heeling angle, structural integrity of masts and sails and crew comfort. For a wind powered cargo ship, time spent on a route is of utmost importance. This leads to the question whether there is a performance difference between different depowering strategies and if so, how large. In this research, a wind-powered cargo vessel with rigid wings is described in a Velocity Prediction Program (VPP) with four-degrees of freedom, namely surge, sway, roll and yaw, with a maximum heel angle constraint. The resulting ship speed performance for different depowering strategies are investigated and the implications in roll and pitch-moments are discussed. The wind conditions when depowering is needed are identified. A statistical analysis on the probability of occurrence of these conditions and the impact of the different depowering strategies on the required number of days for a round-trip on a Transatlantic route is performed.