Offshore Wind Energy Powered Fish Feed Buoy
|Angela Pelletier||UNH - Department of Mechanical Engineering|
|Austin Ganly||UNH - Department of Mechanical Engineering|
|David Parker||UNH - Department of Mechanical Engineering|
|Gita George||UNH - Department of Earth Sciences|
|John Gagne||UNH - Department of Mechanical Engineering|
|Phillip Perrinez||UNH - Department of Mechanical Engineering|
As fish populations decline in the Gulf of Maine, alternatives to traditional fishing are being explored. One of these alternatives is open ocean aquaculture (OOA). The University of New Hampshire currently maintains an OOA facility near the Isle of Shoals. The goal of this facility is to eventually support four cages of cod and haddock with up to 50,000 fish per cage (Chambers, 2002). In order for these fish populations to survive they must have an adequate food supply.
An interdisciplinary undergraduate research design team was tasked with designing a buoy that will hold enough food to feed four full cages for one week and deliver the feed to the fish in a manner that can be controlled remotely. The team was charged with assessing feasibility from a technical standpoint.
One design goal was that the buoy be self-supporting in terms of its energy needs. A renewable power source for the pumps, valves and communication systems needed to be contained on the buoy. Because of continuous winds at the application site it was decided that a wind turbine would work well for the needs of this project. A vertical axis turbine, 1.8 meters in diameter and 4.4 meters tall, was designed by Windstream Power Systems. Eight marine batteries will be used to store the energy produced.
The feed delivery is comprised of a screw auger and four lines, one to each cage. Each line has its own valve so each cage can be fed independently. On board the buoy is a system of pumps and valves that allow ballast water in and out of the buoy to maintain a constant draft as food is added and removed. All of the systems are capable of being controlled remotely using 900 MHz cellular communications.
The buoy was required to store food for 200,000 mature fish for one week without being refilled. A spar shape (long and slender) was chosen for the design of the buoy because of its general independence of wave motion (Berteaux, 1991). Dimensions of the buoy were largely determined by the projected volume of feed required for a maximum number of fish during a stage in their growth when food consumption is greatest. The proposed buoy is three meters in diameter and 16.6 meters in length. Scale models of the buoy were built for testing. Early testing revealed that the damped natural frequency of the spar buoy as designed was the same as that of storm seas. A large disc nine meters in diameter with eight holes 1.5 meters in diameter spaced evenly around the vertical axis was placed on the bottom of the buoy, lowering the damped natural frequency and avoiding resonant loading conditions. Finite element analysis was conducted for the buoy structure and showed that the factor of safety for the buoy is 9.5.
UNH engineers have recently designed a mooring system suited for the proposed four fish cages. The design team needed to design a method for incorporating the feed buoy into this system. An extended bridle system was developed where four bridle lines extend horizontally from the feeder buoy to smaller surface buoys down to the grid, where a line extends from the bottom of the buoy to a chain on the sea floor. The purpose of the chain is to act as a restoring force, further reducing interaction between the waves and the buoy. Finite element analysis was also performed on the mooring grid and feed buoy system using Aqua-FE. Results showed stresses and displacements to be within acceptable ranges.
While the design of a feeder buoy capable of feeding 200,000 fish (50,000 fish per cage) for seven days is large, computational and physical tests show that it is possible. The structural integrity of the buoy and stability of the mooring system are sound. The buoy designed can withstand the harsh conditions in the Gulf of Maine. The project team asserts that this design is feasible; however, internal systems such as feed delivery and energy storage should be rigorously tested before construction.
Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant
- OSWEB - Offshore wind energy powered fish feed buoy (2003). Angela Pelletier, Austin Ganly, David Parker, Gita George, John Gagne and Phillip Perrinez. Advisor: Barbaros Celikkol.