Numerical Investigation of the Semi-Active Flapping Foil of the Wave Glider

Zhanfeng Qi,Yufeng Qin,Guofu Li,Jian Shi,Bo Zou,Jingsheng Zhai,Huiqiang Lu

doi:10.3390/jmse8010013

Zhanfeng Qi, Yufeng Qin + Show 5 more

Open Access

https://doi.org/10.3390/jmse8010013

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Abstract

A numerical investigation is conducted to study the propulsive performance of the semi-active flapping foil of the wave glider, where the heaving smotion is fully prescribed, and the pitching motion is determined by the hydrodynamic force and torsion spring. A mesh for two-dimensional NACA0012 foil with the Reynolds number Re = 42000 is produced, and a dynamic mesh and sliding interface are used in the computation. The influences of reduced frequency, spring stiffness, and critical pitching amplitude on the hydrodynamic characteristics of semi-active flapping foil are systematically investigated. We find that there is a critical reduced frequency: When the reduced frequency is lower than the critical value, the propulsive performance of flapping foil can be improved exponentially, and when the reduced frequency is higher than the critical value, the semi-active flapping foil cannot provide an effective thrust. For a greater reduced frequency, there is an optimal spring stiffness value, which corresponds to the maximum value of the output power coefficient. For a lower reduced frequency, the mean value of the output power coefficient monotonically decreases as the spring stiffness increases. We also notice that the propulsive efficiency of flapping foil monotonically decreases as the spring stiffness increases. Finally, we find that the appropriate critical pitching amplitude can improve the propulsive performance of semi-active flapping foil, especially for greater heaving amplitudes.

Highlights

The wave glider is a new class of wave-propelled, persistent ocean vehicle [1,2]
It consists of a surface boat and a submerged glider, which are connected by an umbilical cable
The hydrofoil flaps under hydrodynamic forces and continues to generate thrust [5,6]

Summary

Introduction

The wave glider is a new class of wave-propelled, persistent ocean vehicle [1,2]. It consists of a surface boat and a submerged glider, which are connected by an umbilical cable. The surface boat moves with the wave, and the submerged glider, with flapping hydrofoil, follows the movement. TThhee ddiissaaddvvaannttaaggee ooff ffuullllyy aaccttiivvee ffllaappppiinngg ffooiill iiss tthhaatt tthhee hheeaavviinngg aanndd ppiittcchhiinngg mmoottiioonnss rreeqquuiirree ccoommpplleexx mmeecchhaanniiccaall ssttrruuccttuurreess,, wwhhiicchh rreedduuccee tthhee uussaabbiilliittyy aanndd rreelliiaabbiilliittyy ooff tthhee ssyysstteemm [[2211]]. CCoonnvveennttiioonnaall sseemmii--aaccttiivvee ffllaappppiinngg ffooiill hhaass aa rriiggiidd bbooddyy,, aanndd ssoommee sscchhoollaarrss aallssoo ccaarrrriieedd oouutt rreesseeaarrcchh wwoorrkk oonnthtehheydhryoddryondaymnaicmpiecrfopremrfaonrmceaonfcfleexoifblfeleflxaipbpleingflahpypdirnogfoihl y[3d5r,o3f6o].ilLi[m35i,t3in6g]. ThLeimmiatignngituthdee magnitude of the pitching motion may reduce the propulsion efficiency of flapping foil [26,33]. Eng. 2019, 7, x FOR PEER REVIEW of the pitching motion may reduce the propulsion efficiency of flapping foil [26,33]. Where θ(t) is defined as the pitching velocity, while Fx(t) and Fy(t) represent the horizontal and vertical hydrodynamic forces of the flapping foil, respectively.

Numerical Method and Validation

Findings

The influence of the reduced frequency