A GPU-accelerated 3dBEM supporting the optimization of actively morphing flapping-foil thrusters with application to AUV propulsion

In recent years, flapping thrusters have been getting attention as an eco-friendly alternative to conventional propellers for autonomous underwater vehicles (AUVs) mainly due to their low-frequency operation, advanced maneuverability, and high efficiency. Their operating principle mimics the thrust-producing kinematics found among efficient swimmers in the aquatic environment. The present work focuses on the analysis and optimization of flapping systems with active morphing features for increased performance. The two optimization studies refer to a realistic AUV propulsion scenario for a wing thruster with active hydrofoil-section adjustment, spanwise bend and twist morphing capabilities. A gradient descent approach based on sequential quadratic programming (SQP) is used for optimal tuning of design variables (planform shape, kinematics) targeting efficiency maximization under thrust and effective angle of attack constraints. For the evaluation of each candidate thruster the unsteady boundary element solver 3dBEM is developed and used for wing performance prediction. The solver exploits GPU parallel computation techniques to reduce computational time and enable fast optimization. Results indicate that the optimal thruster with chordline/spanwise bending is 25% more efficient, whereas the same result for the wing with spanwise bending and twist profiles is up to 8.8%. The 3dBEM solver can support the preliminary design process of morphing flapping-foil thrusters.