Researchers Jen-Ping Chu, Mitul Luhar, and Patrick Lynett, affiliated with the University of Southern California, have conducted a study examining the interactions between internal solitary waves and floating canopies. Their work, published in the Journal of Fluid Mechanics, explores how these interactions can affect wave dynamics and energy transfer, which has potential implications for the energy industry, particularly in offshore and marine renewable energy sectors.
Internal solitary waves are large, slow-moving waves that occur beneath the ocean’s surface, often in regions with strong tidal currents or where different water masses meet. These waves can interact with floating structures, such as seaweed farms, floating wind turbines, or other marine energy devices, which can be represented as “canopies” in the context of this study. The researchers investigated how these interactions can alter the waves’ behavior and energy characteristics.
The study involved both laboratory experiments and computer simulations. In the experiments, the team created internal solitary waves of varying amplitudes using a jet-array mechanism. They then observed how these waves interacted with floating canopies of different lengths and porosities. The researchers measured pycnocline displacements, phase speeds, and velocity fields using advanced imaging techniques.
In the simulations, the canopy was represented as a porous zone with specific porosity and hydraulic conductivity, determined using the Kozeny-Carman model. The researchers validated this model by comparing simulated and measured horizontal velocity profiles.
The findings revealed that higher-porosity canopies, which allow more water to pass through, resulted in minor amplitude reduction and negligible wave energy dissipation. However, lower-porosity, or “dense,” canopies led to more complex interactions. The shear layer developed at the bottom edge of these canopies grew to a strength comparable to the shear sustained by the internal solitary wave profile at the pycnocline. This interaction generated a vortex pair that accelerated the upper-layer fluid beneath the canopy, leading to significant wave transformation and energy transfer between kinetic and potential energy.
When the canopy length was extended, the internal solitary waves settled to a quasi-steady state with a significant phase speed reduction. Upon exiting the canopy, flow separation at the downstream edge paired with the shear at the pycnocline, inducing an intensified jet. This complex interaction further influenced the wave’s energy characteristics.
The practical applications of this research for the energy sector include better understanding and predicting the interactions between internal solitary waves and floating structures, such as marine renewable energy devices. This knowledge can aid in the design and optimization of these structures to enhance their efficiency and durability in real-world conditions. Additionally, the study’s findings can contribute to improving the accuracy of ocean models used for energy resource assessment and environmental impact studies.
Source: Chu, J.-P., Luhar, M., & Lynett, P. (2023). Interactions between internal solitary waves and floating canopies. Journal of Fluid Mechanics.
This article is based on research available at arXiv.