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.

A numerical investigation on the propulsion performance of the semi-active flapping foil of the wave glider with different mass ratio and damping coefficient is investigated. The commercial CFD software Fluent is used to solve the URANS equations around the flapping foil by the Finite Volume Method. A mesh of 2D NACA0012 foil with the Reynolds number Re = 42,000 is used in all simulations. We first analyze the effect of the mass ratio on the mean output power coefficient and propulsion efficiency and note that with the variation of the mass ratio, the propulsion efficiency decreases slightly. Besides, we find that the mass ratio has a noticeable influence on the mean output power coefficient, and the influence is determined by the reduced frequency. For high reduced frequency, with the increase of the mass ratio, the propulsion performance of the flapping foil decreases monotonously. For low reduced frequency, the mean output power increases slightly. For critically reduced frequency, the mean output power coefficient of the foil firstly increases and then decreases via the mass ratio increase. Then, we examine the influence of the damping coefficient on the propulsion performance of the flapping foil and find that the damping coefficient has a severe adverse effect on the output power and propulsion efficiency. We conclude that the influence of the damping coefficient should be considered first when we design the propulsion device of the semi-active flapping foil. Meanwhile, we should also consider the sea conditions to choose the mass ratio to optimize the flapping foil.

This paper takes the wave glider as the research object. The wave glider is studied comprehensively from the aspects of motion mechanism, motion law and hydrodynamic performance. Firstly, based on the turbulence model of RANS equation, dynamic mesh method, the hydrodynamic performance of two-dimensional tandem hydrofoils is analyzed, which has been developed twice. The paper puts forward the a obstacle avoidance algorithm of wave glider based on fuzzy control. Combining the principle of line-of-sight navigation with the idea of fuzzy control, the path planning of wave glider is carried out. The simulation and experimental results show that the algorithm can provide real-time and stable motion path of the wave glider, effectively avoid obstacles and safely reach the target point.

Qi, Z.; Wang, B.; Qin, Y.; Shi, J., and Zhai, J., 2020. Planar path following control for wave glider and experimental study. In: Zheng, C.W.; Wang, Q.; Zhan, C., and Yang, S.B. (eds.), Air-Sea Interaction and Coastal Environments of the Maritime and Polar Silk Roads. Journal of Coastal Research, Special Issue No. 99, pp. 16-20. Coconut Creek (Florida), ISSN 0749-0208.This paper addresses a path following problem of Wave Glider along a predefined path in horizontal plane. The path following controller designing is challenging since Wave Glider is weak maneuvering, underactuated, inaccuracy mathematical model and large environmental disturbances. First, a planar curve path tracking error model is established in the Serret-Frenet coordinate frame. Based on the LOS guidance law and the virtual target method, a planar guidance controller for underactuated Wave Glider is presented to ensure the stability of the path following. And then, according to the classic feedback linearization PID controller and fuzzy controller, a fuzzy adaptive PID controller is developed. Fuzzy controller is used to achieve PID controller parameters online adaptive adjust, in order to improve the robustness of the control system under the influence of environmental disturbances and inaccuracy modeling parameters. Furthermore, analyzing the typical application scenarios of Wave Glider, we set two simulation path in horizontal plane named polyline path and circular path. Numerical simulation results illustrate the proposed control design is effective to deal with planar following problem of Wave Glider. Two sea trails show that the controller can achieve the path following task, however, the speed of Wave Glider is directly related to the accuracy of the path following.