Adjoint Optimisation of Hydrofoils for Multiple Conditions

Hydrofoils in yacht racing are operated across a wide range of conditions. Between these conditions the state and the trim of the yacht changes significantly. This must be reflected in the optimisation of the hydrofoils. Previously, we have performed hydrofoil optimisations for a single condition. These were conducted using an adjoint velocity prediction program (VPP) in a gradient based optimisation routine. The method allows accurate optimisation with hundreds of design variables at a small computational cost. This framework is now extended to optimise foils for multiple conditions. Therefore, the VPP is solved for different conditions and returns the respective velocities made good (VMG) and gradients. The different VMG and the according gradients are averaged to enable the multi-condition optimisation within a single objective. The framework is used to optimise the hydrofoil of an America´s Cup yacht for six conditions derived from historical weather data. The optimal foil is perfectly smooth and exhibits the expected features. It is 7.2% faster than the initial foil in terms of average VMG. This amounts to an 81.9 second timesaving over a whole race. The multi-condition optimisation can be performed at no additional cost and demonstrates the immense capabilities of adjoint VPP-based hydrofoil optimisation.