Abstract
Autonomous Underwater Vehicles (AUVs) are essential for a variety of marine applications but are typically constrained by battery capacity (limiting their range and duration) and necessary ancillary infrastructure. Recent advancements in Wave Energy Converter (WEC) technology offer the potential to extend AUV missions through docking and electrical power recharge. However, a significant challenge in utilizing wave-power for AUV systems is docking near the energetic ocean surface. This situation contrasts with traditional docking environments typically characterized by calmer, wave-minimal, deep-water conditions.
Scaled physical model testing provides a robust methodology for proof-of-concept testing. However, testing WEC-AUV docking in the laboratory presents a complex mixed-scale challenge. Firstly, in the laboratory, water depth and wave conditions are at model scale, whereas the dock and AUV remain at field scale. Secondly, unlike field conditions where the dock is physically connected to a WEC, laboratory setups cannot generally accommodate a field-scale WEC.
This paper presents a unique hardware-in-the-loop experimental methodology to replicate, in the wave tank, the dynamic interaction between WEC-AUV dock motions and ocean waves. This methodology includes the following real-time testing procedures:
- Run Distorted Wave Conditions in the Wave Flume: Laboratory experiments are conducted under distorted wave conditions derived from typical field wave scenarios. The distortion criteria are based on either acceleration amplitude matching or velocity amplitude matching to ensure hydrodynamic similarity.
- Measure Laboratory Wave Elevation in Real-time: During the experiments, wave elevation is measured upstream of the dock location in real time to capture and predict incoming waves.
- Convert Laboratory Wave Measurements to Field Scale: The measured model-scale wave elevation time history is converted into field-scale time history using wave distortion algorithms.
- Simulate WEC/Dock Displacement: The displacement of the WEC and dock is calculated in real-time through a hydrodynamic simulation (WEC-Sim, in this study), based on the field-scale wave input and precomputed impulse response functions between wave elevation and wave excitation forces.
- Convert Dock Displacement to Laboratory Scale: The resulting field-scale dock motion is then converted back to laboratory scale and used to physically actuate the dock during testing, ensuring consistency with the hydrodynamic forcing.
This hardware-in-the-loop approach offers a scalable and realistic framework for studying AUV docking under energetic wave conditions and supports future development of wave-powered AUV systems.