Submergible cage farming and technology improves reliability of cage sinking-floating process by means of process control, automation and remote controlling
Main expected result: Create and improve existing cage systems, feeding systems, nets and mooring as one submersible unit in order to be used offshore.
1) Nets: Depth, twine and mesh size, requirements for access, submerged and in surface position, positioning of the net roof in surface position, system to maintain the net volume, cleaning system
Results and discussion
Experiments: A cage sinking and lifting concept was tested in the Hirtshals lab (Figure 1). Different cage positions were obtained by moving the loads (black dots) along the mooring lines and the behaviour of the cage was studied by increasing the flow velocity. Stresses were measured along each line and cage deformations due to currents were recorded with a 3D camera system.
The combination of the load positions and the current flow velocity produced different strains in the anchoring lines in the front and back of the cage and resulted in different angles of rotation of the cage (Figure 2)
Figure 1. Concept of the system to sink conventional cages: a) floating and b) submerged cage.
FIgure 2. Example of submerged cage behaviour in the flume tank.
Simulation tool: Mathematical models of three different submersible cage concepts are being develop to allow simulations to performing stability analyses of the models. All models are fully dynamic and in 3D, based on a common basic model of the cage, but with different concepts for the submergence process. These three concepts are: 1) movable point mass on the (only) top bridle line; 2) fixed mass on the bottom bridle line at various positions, connected to the bottom ring; and 3) variable buoyancy devices attached to the bottom ring. This model is still under development.
Next generation submersible cage concepts: Phase two of the project will explore alternatives for next generation cages, with a focus on fish welfare. The concept aims to address the critical aspects for cage performance and innovate new solutions. Ideas and concepts are under development. The final concept is taking shape and is expected to be ready for testing before the mid-2009.
Alf Kristian Fjelldal (AKVA group ASA)