This study focuses on the hydrodynamic testing of a novel wave-propelled Autonomous and Surface Vehicle (ASV) called Demeter. The main objective of the study is to understand the vehicle performance in different wave conditions and its wave propulsion capability.
Experiments were conducted in the towing tank facility at the Kelvin Hydrodynamics Laboratory (KHL) at the University of Strathclyde. Qualisys system is used to capture the vehicle motion in waves. Both time domain and frequency domain analyses have been conducted. The results have shown that the vehicle velocity and response in waves are highly related to their natural frequency. The data collected in the study will also be used for further numerical simulations and design optimization.
Wave gliders or wave-propelled vehicles are a new type of autonomous surface vehicle (ASV) which harness wave energy to move the vehicle through the water. Its enduring appearance at sea serves as a long-standing platform for ocean research, surveillance, defence and etc. purposes. The renowned products include the wave glider by, AutoNaut and the "Black Pearl" (Sun et al., 2022) wave glider. The vehicle is made up of two primary parts: a surface float that floats on top of the water and houses the propulsion, navigation, and sensor systems, and a subsurface glider that is tethered to the surface float and uses wave motion to propel itself forward.
The wave glider transforms the vertical motion of the waves into horizontal propulsion through a process known as "heaving." While the surface float is largely immobile, the subsurface glider travels up and down with the waves. Following that, a series of mechanical or hydraulic linkages turn this motion into thrust.
Wave gliders are commonly used for extended oceanographic missions that involve monitoring ocean conditions, such as temperature, salinity, and pH levels, tracking marine life, and measuring ocean currents. They are also utilized in search and rescue operations, coastal surveillance, and oil spill monitoring. Their ability to run for extended periods without refuelling, thanks to their wave energy propulsion, makes them ideal for long-term missions. However, it's worth noting that traditional wave gliders are limited in speed. The general cruise speed is around 1 knot; some high-performing vehicles can reach 3kn. This limits its capability and operational efficiency for missions. Its core issue relates to a technology called wave propulsion, which was originally developed to propel large ships only by waves. But now wave-assisted propulsion is more used for energy saving and reducing ship motions at sea. To improve the performance of wave propulsion for gliders, Yang et. al first built a fully-coupled CFD model and attempted to use a torsional spring for tandem foils to enhance the propulsion force (Yang et al., 2019; Yang et al., 2018). However, traditional wave gliders normally have the surface body and the underwater body distanced to use the orbital velocity difference in different water depths. This creates a large drag body as it travels through a larger area of water. How to develop a wave glider with low drag and high propulsion is the research focus.
