An automated airlift system for open ocean aquaculture

The University of New Hampshire has been investigating the feasibility of an automated airlift system for open ocean aquaculture net pens. This research proposes a prototype depth control device based upon automatic feedback control. The automated system aims to simplify operation of the airlift, as well as reduce the number of surface connections which weather poorly. The system is actuated via pressure regulators controlling the pressure differential between a ballast chamber and the ambient water, thus controlling overall buoyancy by controlling the mass flow rate into (or from) the chamber. The control device operates on ladder logic and allows the users to interact with it using a Human-Machine Interface (HMI) system and an associated Graphical User Interface (GUI). Through experimental prototype testing, it is determined that a PID and bang-bang controlled airlift system is an effective means of controlling the airlift system. The controller actuated hardware allows for precise depth set point values as well as real-time error and disturbance rejection.