Horizontal T-foils allow for maximum lift generation within a given span. However, the lift force on a T-foil acts on the symmetry plane of the hull, thereby producing no righting moment. It results in a lack of transverse stability during foil-borne sailing. In this paper, we propose a system, where the height-regulating flap on the trailing edge of the foil is split into a port and a starboard part, whose deflection angles are adjusted to shift the centre of effort of the lift force. Similar to the ailerons which help in steering aircraft, the split-flaps produce an additional righting moment for stabilizing the boat. The improved stability comes, however, at a cost of additional induced resistance. To investigate the performance of the split-flap system a new Dynamic Velocity Prediction Program (DVPP) is developed. Since it is very important for the performance evaluation of the proposed system it is described in some detail in the paper. A complicated effect to model in the DVPP is the flow in the slot between the two flaps and the induced resistance due to the generated vorticity. Therefore, a detailed CFD investigation is carried out to validate a model for the resistance due to the slot effect. Two applications of the split-flap system: an Automated Heel Stability System (AHSS) and a manual offset system for performance increase are studied using a DVPP for a custom-made double-handed skiff. It is shown that the AHSS system can assist the sailors while stabilizing the boat during unsteady wind conditions. The manual offset enables the sailors to adjust the difference between the deflection angles of the two flaps while sailing, thus creating a righting moment whenever required. Such a system would be an advantage whilst sailing with a windward heel. Due to the additional righting moment from the manual offset system, the sails could be less depowered by the sailors resulting in a faster boat despite the additional induced resistance. It is shown in the paper that the control systems for the ride height and the heel stability need to be decoupled. The paper ends with a description of a mechanical system that satisfies this requirement.
<p>Tidal turbines harnessing power from tidal currents, have the prospective to become an important source for renewable energy production. The tidal power plant studied here, the Deep Green, rather than being fixed like conventional horizontally mounted axial tidal turbines, uses a &#8216;flying&#8217; kite with a turbine attached to it. The kite, which is tethered to the bottom, converses in a lemniscate trajectory (&#42830;) perpendicular to the direction of the tidal current. In the trajectory, the apparent flow velocity experienced by the turbine is several times the tidal flow, thereby allowing utilization of sites with lower tidal current velocities than most traditional tidal power plants. To study the operation of single power plants and for designing efficient arrays of tidal power plants Computational Fluid Dynamics (CFD) are used.</p><p>Through previous studies, the Deep Green is modelled using Large Eddy Simulations (LES) and the Actuator Line Model (ALM). While using ALM, the Deep Green wing and its turbine are represented as a momentum source that moves in a prescribed trajectory (lemniscate). Using the numerical simulations, the impact of the Deep Green on the tidal flow is studied by analysing the changed velocity field and turbulence characteristics downstream of the power plant. Before conducting large-scale numerical studies on the design of arrays, the numerical model needs to be validated against observations.</p><p>The measurements used for this study were performed by Minesto AB in the site Holyhead deep using a vessel mounted ADCP (Acoustic Doppler Current Profiler) downstream of the kite. A domain and boundary conditions similar to the measurements are set up in the numerical simulation. The velocity downstream of the power plant is compared with the measured velocity data, and the preliminary study shows good agreement between ADCP observations and output from the CFD model. The results of the validation will be helpful to strengthen the methods used in numerical modelling in order to conduct sound tidal power array analysis.</p>
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