Thrust Enhancement and Resistance Reduction of Ship Elastic Flapping Foil: A Study on Applicability of Different Vessel Types and Effect of Encounter Phase

Numerous studies indicate that a flapping-foil thruster installed at a ship’s bow can convert wave energy into propulsive power and reduce added wave resistance while improving dynamic stability. Based on the preliminary exploration of the drag reduction mechanism of an elastic bow-flapping-foil system in waves, this paper further compares the effects and universality of this system on the resistance and motion response of different ship types under similar operating conditions, using three classic ship types (DTMB 5415, KCS, and Wigley) as research objects. Using the ISIS-CFD solver in NUMECA software, the study simulates the ship coupled with a semi-active elastic flapping foil in head waves, analyzing the influences of spring stiffness, foil size, installation position, and encounter phase on system performance. Numerical results show effective wave energy harvesting, boosting propulsion and stability. Under optimized parameters, ship pitch and heave amplitudes decrease by up to 20.14%, resistance reduction reaches 9.60%, and DTMB 5415 achieves a comprehensive drag-reduction and thrust-increase ratio of 31.39%. Further analysis reveals that thrust performance does not rise proportionally with spring stiffness, whereas drag and heaving reduction improve with increasing stiffness. The system performs best at a wavelength-to-ship-length ratio of 1.2 and a foil encounter phase of −90°. This work supports parameter optimization for such systems based on practical application scenarios and requirements.