A Novel and More Efficient Oscillating Foil for Wave-Driven Unmanned Surface Vehicles

In the wave-driven unmanned surface vehicles (WUSVs), oscillating-foils are the most straightforward and widely used wave energy conversion mechanism, like the wave glider. However, WUSVs usually sail slowly compared with other types of USVs. Improving the thrust of the oscillating foil to increase its speed can help WUSVs improve their maneuverability and shorten the completion of ocean missions. This paper proposed a novel method to enhance oscillating foils’ thrust force using asymmetric cross-section shape and asymmetric oscillating motion. The thrust enhancement effect is verified by CFD simulation and pool experiment. The experimental results show that the asymmetric wing can enhance the propulsive force by at least 13.75%. The speed enhancement of WUSVs brought by this enhanced thrust is at least 7.6%, which has also been verified by simulation and sea experiment. The asymmetric foil only needs to make low-cost modifications on the traditional rigid symmetric foil to achieve the desired thrust enhancement effect.

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Figures
Float Cable Glider Figure S1. Conceptual diagram of the wave glider: It consists of float, cable, and glider. Figure S2. Example of one CFD simulation results: It can be seen that the thrust generated by the foil under the impact of water flow converges to the accurate value after a while.  Figure S3. Experimental control system framework: a host computer, a control board, a motor drive, a motor , a pressure sensor, a signal transmitter and power source. In the experiment process, the motion command is sent to the control board through the host computer. After receiving the command, the control board outputs pulse signals with different step sizes to the motor driver according to the command's content. After receiving the pulse signal, the motor driver will rotate the motor with corresponding steps to achieve speed control. In the process of wave simulation, the output interval of each pulse is different to control the motor to produce different speeds.      Figure S8. The control system of the prototype: The host processor is a Raspberry Pi board; Powered by a battery; The data collected by GPS module and IMU module is transmitted to the host processor; The host processor and remote computer are connected to a mini router to enter the LAN and communicate. GPS module will send multiple sets of data ($GPGGA, $GNGGA, $GPRMC, $GNRMC, ...), all following NEMA 0183 protocol. We only keep the sentence at the beginning of $GNRMC (multi-satellite integrated positioning data using GPS, BD2, and QZSS) and eliminate other data. The result of each location information is like "$GNRMC,045355.000, A,2234.4272,N,11432.7194,E,0.96,295.47,260321,,,A*7E". This sentence contains location information such as data header, sensor status, UTC, longitude and latitude, altitude, etc.  Includes segment ratio and bending angle. Optimize thrust force at the lower limit angle.
Randomly selected bending shape. The final value is consistent with the traditional foil.

In constant flow
Broad-range of flows Rotation time

Final effect
In waves The thrust force of the oscillating foil is simulated in a wide range of constant flow, including the upper and lower limit angles.
Determine the time relationship of each stage of asymmetric motion of oscillating foil.
Combine the above information to deduce the final thrust force enhancement. Figure S11. Key parameter establishment steps of the asymmetric oscillating foil..