Experimental investigation of volume deformation of fish cage models with different sinking systems subjected to current and wave

Abstract

Aquaculture net cage consists of mainly supple structural components nets, ropes (mooring lines) and rigid or elastic structural elements including floating collar, buoy and sinkers. There are different kinds of net cages. Fixed, floating, submersible, and submerged that have different designs and shapes. Cage models that are considered under this study are floating type. In this paper, our study mainly focused on variable sinking systems. To do so, two physical cage models with different sinking systems were used, one test model is with bottom weight sinkers, and the other one is with sinking collar. Both sinkers have the same gravitational forces and other structural components including net, collar and mooring systems. The deformation of those two kinds of cages was investigated through the experiments under the action of wave and current in different tank systems. The responses of the model cages by the action of water current were measured using tension meter at mooring line. Additionally, cross-sectional area of the cages was determined from 2D displacement of selected points on netting system using digitizer. The data that were obtained from digitizer help to analyze volume reduction of the cage by the action of water current in flume tank. Similarly, the responses of test models by the wave action in towing tank were carried out. The two cage models were subjected with the same regular water waves at specific direction with variable wave parameters. The data generated from tension meter was homogenized by removing noises and further analyzed. Based on the test result, it was concluded that the reaction force of the cage with sinking collar was higher than cage with weight sinkers at identical current and wave conditions. Moreover, Former model possessed less volume reduction coefficient than later under the action of current.