Abstract
Wave glider is an unmanned surface vehicle that can directly convert wave energy into forward propulsion and fulfill long-term marine monitoring. A previous study suggested that the wave motion and stiffness of restoring springs mounted on the hydrofoil are the main factors affecting the propulsion performance of the wave glider. In this paper, the dynamic responses and nonlinear characteristics of the underwater propulsion mechanism considering the nonlinear stiffness of restoring springs are investigated based on a fluid–rigid body coupled model. Firstly, models of propulsion mechanism with different kinds of restoring springs are proposed, and the linear and nonlinear characteristics of the restoring spring are considered. Then, a fluid–rigid body coupled model of a wave glider is developed by coupling the rigid body dynamics model and hydrodynamic model. Dynamic responses are simulated by the numerical analysis method, and the nonlinear characteristics with different restoring springs are illustrated by the time/frequency domain motion response and phase diagram analysis. The effects of the wave excitation frequency, wave heights and the location of the connection point of springs on the propulsion performance of the wave glider are analyzed. The results show that multi-frequency responses occurred in the propulsion system, and the nonlinear restoring spring on the hydrofoil can provide a larger restoring moment to avoid excessive pitch angle and is more suitable for different sea conditions, which provides a reference for developing propulsion mechanisms with high performance in complex marine environments.
Highlights
IntroductionThe utilization of renewable energy for ocean exploration and environmental monitoring has become a focal issue
Liu et al [9] and Wang et al [10] studied the effects of wave parameters, foil number and flapping amplitude etc. on the propulsion performance of underwater flapping multi-foil, and found that multi-foil can produce higher propulsion than a single flapping foil due to the interaction of the multi-foil wake
Restoring springs mounted on the hydrofoil are usually used for controlling the pitch angle of the hydrofoil when wave glider operating in marine environment, there are many researchers studied the effect of restoring stiffness on the propulsion performance of wave glider
Summary
The utilization of renewable energy for ocean exploration and environmental monitoring has become a focal issue. Restoring springs mounted on the hydrofoil are usually used for controlling the pitch angle of the hydrofoil when wave glider operating in marine environment, there are many researchers studied the effect of restoring stiffness on the propulsion performance of wave glider. Yu et al [17] established a dynamic model of wave powered mechanism considered the spring limit, and obtained the relationship among the heave motion of the buoy, stiffness of the elastic components, and the forward speed. The effects of different restoring spring on the motion performance of the wave glider and the linear and nonlinear characteristics of restoring spring are investigated based on fluid-rigid body coupling method, and the influences of wave excitation frequency and wave heights are studied, which can provide references for optimization of propulsion performance of wave glider. The effects of different restoring spring on the motion performance of the wave glider and the linear and nonlinear characteristics of restoring spring are investigated based on fluid-rigid body coupling method, and the influences of wave excitation frequency and wave heights are studied, which can provide references for optimization of propulsion performance of wave glider. 2 Coupled Dynamics of Wave Glider
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