A Non-Linear BEM–FEM Coupled Scheme for the Performance of Flexible Flapping-Foil Thrusters

Abstract

Recent studies indicate that nature-inspired thrusters based on flexible oscillating foils show enhanced propulsive performance. However, understanding the underlying physics of the fluid–structure interaction (FSI) is essential to improve the efficiency of existing devices and pave the way for novel energy-efficient marine thrusters. In the present work, we investigate the effect of chord-wise flexibility on the propulsive performance of flapping-foil thrusters. For this purpose, a numerical method has been developed to simulate the time-dependent structural response of the flexible foil that undergoes prescribed large general motions. The fluid flow model is based on potential theory, whereas the elastic response of the foil is approximated by means of the classical Kirchhoff–Love theory for thin plates under cylindrical bending. The fully coupled FSI problem is treated numerically with a non-linear BEM–FEM scheme. The validity of the proposed scheme is established through comparisons against existing works. The performance of the flapping-foil thrusters over a range of design parameters, including flexural rigidity, Strouhal number, heaving and pitching amplitudes is also studied. The results show a propulsive efficiency enhancement of up to 6% for such systems with moderate loss in thrust, compared to rigid foils. Finally, the present model after enhancement could serve as a useful tool in the design, assessment and control of flexible biomimetic flapping-foil thrusters.

Hydroelastic analysis of flapping-foil thrusters using a partitioned BEM-FEM

“…However, the weak coupling approach does not permit the prediction of the phase lag between the prescribed flapping motions and the wing's response in terms of bending deformation; which would improve the prediction capabilities of the computational tool significantly. In a recent work by the author's [15] the fully coupled 2-D BEM-FEM scheme is proposed for the hydroelastic analysis of flapping-foil thrusters and it is found to be in excellent agreement with experimental data found in the literature. Finally, the tools developed for the present work serve as the building blocks for the fully coupled 3-D BEM-FEM scheme for hydroelastic analysis and optimization that is currently under study.…”

Hydrodynamic Optimization of Actively Deforming Flapping-Foil Thrusters for Auv Propulsion

“…with emphasis on the effects of a superposition of chordwise and spanwise bending on the propulsive performance of the thruster. The phase differences that contribute to efficiency enhancement for this setup have been determined in previous work by the authors (Anevlavi, Filippas and Belibassakis 2023), as ψc=180deg and ψb=0deg respectively. The frequency of motions is kept the same.…”

“…The code includes GP-GPU acceleration features targeting the computationally demanding numerical integration for the calculation of the induced coefficients using the processors of an NVIDIA graphics card and the CUDA API, which significantly reduces the computational time of the simulation. The present solver that has been used in a previous work by the authors (Anevlavi, Filippas and Belibassakis 2023),  enables numerical calculation of the wing body velocities using backward finite differences with GPU parallelization.  re-generates the surface mesh at each time-instance to simulate a deforming wing  re-calculates of the induced coefficients (DtN) matrix at each time-step  calculates the propulsive performance metrics targeting flapping-foil thrusters…”

“…This friction coefficient increases at higher angles of attack leading to better predictions. In (Anevlavi, Filippas and Belibassakis 2023) the comparison between the GPU-BEM and the experimental data from (Heathcote, Wang and Gursul 2008)…”

Investigation of Submergence Depth and Wave-Induced Effects on the Performance of a Fully Passive Energy Harvesting Flapping Foil Operating Beneath the Free Surface

“…Many studies have taken place, either experimental [8,9] or numerical (a collection can be found here in [4]), showing the applicability of these devices and highlighting their advantages and disadvantages over conventional devices. Incorporating chord-wise flexibility also seems promising as increases in performance are significant, as shown in [10]. Importantly, this device can be simplified by attaching the heaving degree of freedom (DOF) to a spring and damper, and imposing the motion of the pitching DOF, creating the semi-passive flapping foil [11].…”