Hydrodynamic and dissolved oxygen transport characteristics of an upper and lower water exchange device with regular waves

Dissolved oxygen (DO) plays an important role in seawater environment and fish farming systems. Its vertical distribution is usually non-uniform with relatively high and low values in surface and bottom water, respectively, due to the effects of natural factors including wave, seawater stratification, and eutrophication. Based on our previous study (Zhang et al., 2020), an upgraded upper and lower water exchange device was presented for strengthening the vertical water exchange and DO transport performance. A series of experiments were conducted, and a 3-D mathematical model, comprising of hydrodynamics and DO transport, was developed to investigate the characteristics of the device effect under regular waves. It was observed that wave overtopping and pressure difference are dominant factors in the water movement inside the device. The relative wave height and net flow rate inside the device are significantly dependent on the wave parameters and geometrical parameters of the device. The relative wave height increases with increases in pipe diameter and length, but decreases as wave steepness increases. The oxygen transfer coefficient roughly increases as wave height increases, and it decreases with increasing wave period and the initial average temperature in the entire water body.