Dynamic overset rans simulation of a wave-driven device for the oxygenation of deep layers

The most common methods of counteracting hypoxic events at the bottom sea layers are indirect measures aimed to reduce organic load introduced in the environment. No direct approach has been investigated except the WEBAP and OXYFLUX devices. The estimation of the surface water pumped from such devices is still largely based on physical or empirical methods. The present work adopts the CFD approach to the estimation of the pumped surface water as well as the analysis of the dynamic response of the OXYFLUX device. By means of a Reynolds-averaged Navier-Stokes code, through overset grid method, the 1:16 OXYFLUX model's dynamic response and pumping performance are evaluated under the action of 13 regular wave states. A grid sensitivity analysis is performed in order to define the best configuration able to describe the function of the device. The model is validated by comparing numerical and physical results of heave decay test, while systematic studies on the heave response and pumping performance under the action of regular waves are completed through the paper. The results demonstrate the importance of nonlinear effects, including viscous drag, wave overtopping and the interaction between heave and pitch modes. Moreover, the study shows also that nonlinear effects significantly decrease the dynamic response of the device and generate a second harmonic for pitch response, increasing the capacity of the OXYFLUX to be overtopped by small waves caused by the summer breeze typical of the hypoxic events.