An efficient method for unsteady hydrofoil simulations, based on Non-Linear Dynamic Lifting Line theory

This paper presents a Non-linear Dynamic Lifting Line (NDLL)-based method for analysing hydrofoil vessels in waves. The method is validated, and its utility is demonstrated in a case study. The NDLL accounts for dynamic and 3D effects through a panellized wake and allows the evaluation of the pressure distribution on hydrofoils. Improved models are presented for wake deformation, wake composition, hydrofoil interaction, and the viscous core of vortex wake models. Furthermore, an efficient way of accounting for Green function terms through a matrix interpolation method is presented. Validation is performed by comparison with aerodynamic and hydrodynamic experiments and new 3D RANS simulations. The RANS simulations focus on geometries and operating conditions deemed representative of hydrofoiling fast ferries. Predictions of steady and dynamic lift, drag, wake velocities and cavitation inception are evaluated, and results correspond well with the benchmark data. A simulator framework is introduced, which integrates the hydrodynamic model with kinetics, kinematics, and control system models. This enables analyses of free-running vessels under active control, including assessments of resistance, motions, and the hydrofoil pressure distribution. The case study constitutes a qualitative verification of the simulator and flight control tuning methods, and reveals the possibility of negative added resistance in waves.