Abstract
A wave glider can convert vertical wave motion into its forward propulsion. There are many factors affecting the propulsion performance of a wave glider. The swing amplitude of hydrofoil can affect the efficiency of hydrofoil to capture wave energy, and the pull direction of an umbilical cable can affect the transmission efficiency of wave energy. In this paper, an optimized hydrofoil mechanism with a self-adjusting lower limit (SALL) was proposed by analyzing the un- synchronized movement between the submerged glider and the surface float. This mechanism was able to transfer the movement of umbilical cable to the hydrofoil swing mechanism through the linkage to control the lower limit of hydrofoil swing (maximum swing angle of hydrofoil in a counterclockwise direction). Firstly, the user-defined function (UDF) was written to control the motion of hydrofoil in the fluid domain. The lower limit swing angle and the heave direction of the hydrofoil were both set in the UDF, and the forward thrust generated by the passive swing of the hydrofoil in the fluid domain was able to be obtained by the simulation. Secondly, the prototype was designed by introducing a parallelogram mechanism on a conventional submerged glider, and a wave simulation test platform was built to verify the propulsive performance of the prototype. The results showed that, in comparison with the conventional submerged glider, the forward thrust of the SALL submerged glider was able to be improved by 1.50%, 17.78%, 7.42%, and 20.70% under the stiffness coefficients of torsion spring set to K = 2, K = 4, K = 6, and K = 8 in the simulation experiment, respectively. The forward thrust of the SALL submerged glider was able to be elevated by 9.99% with torsion spring K = 8 in the tank experiment. The advantage of the SALL mechanism was verified by comparing the results of the simulation and the tank experiment. Finally, the feasibility of the SALL submerged glider was verified in actual sea conditions by a sea trial.
Highlights
The wave glider is a new type of unmanned mobile observation platform, consisting of a surface float, a submerged glider, and an umbilical cable, the latter of which is used to connect the surface float and the submerged glider [1]
A novel type of the self-adjusting lower limit (SALL) submerged glider was proposed to improve the forward thrust of the wave glider
The existence of the umbilical cable inclination angle changed the direction of wave energy transmission and reduced the conversion efficiency of wave energy
Summary
The wave glider is a new type of unmanned mobile observation platform, consisting of a surface float, a submerged glider, and an umbilical cable, the latter of which is used to connect the surface float and the submerged glider [1]. The effects of the difference connection structures between the surface float and the submerged glider on the propulsive performance of the wave glider were studied [7]. Various connection types such as rigid rod cable, multi-link chain, and elastic rod were used to connect the surface float and the submerged glider. The propulsive performance of the wave glider was analyzed by using the numerical method under the difference connection structure types. The effects of the umbilical cable, the structure, and the swing mode of the hydrofoil on the propulsive performance of the wave glider were analyzed. When the surface float falls, the submerged glider will sink be-
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