Analysis of the hydrodynamic characteristics of chain-link woven copper alloy nets for fish cages

• The hydrodynamic characteristics of chain link woven copper alloy intended for use in fish cages have been examined.
• The lift and drag coefficients were calculated, and the flow characteristics were determined by PIV.
• The trends in the coefficients have been found to be similar for both copper alloy and fabric nets.
• The differences in coefficients for fabric and copper alloys caused by flow attack angle and current speed have been compared and explained.

Copper alloy nets have drawn attention from researchers and fishermen as an alternative to fabric nets for fish cages, due to such advantages as protection from predators, better cage volume retention, and good resistance to bio-fouling. The drag and lift coefficients of nine chain-link woven copper alloys and three knotless fabric nets were derived using a circulating water channel and structural analysis of the nets. The flow through one copper alloy net was visualized using particle image velocimetry (PIV) to understand better the hydrodynamic characteristics necessary for the use of the net in a fish cage. The trends in behavior of the drag and lift coefficients for the copper alloy nets based on various attack angles and current speeds were highly similar to those of the fabric nets. The coefficients of the copper alloy nets were larger than those of the fabric nets for attack angles less than 30°. For angles greater than 30°, the coefficients of the fabric nets were larger than those of the copper alloy nets. These results might be attributed to structural differences between the two nets, as well as the roughness of the surfaces. The hydrodynamic characteristics of the alloy nets were illustrated using PIV, and a difference in the structure of the net was observed to reduce the resistance when the net was set against the current with an attack angle of 90°.