Efficient estimation of remaining volume in gravity-type fish cages using field data and numerical simulations

Abstract

An effective approach to estimating the remaining volume of net cages in natural sea conditions is essential for the cage aquaculture industry. However, harsh sea environments impede the use of imaging technology or acoustic sensors. This study aims to develop an alternative method using four depth meters to overcome this obstacle. From 2020 to 2023, a series of field measurements were performed on net cages in Taiwanese waters, focusing on mooring line tension and net cage volume. To validate the practicality of this method, an in-house developed time-domain model based on the lumped-mass approach, along with a screen force model for fullscale net cages, was used. Results indicate that the trends observed in the measurements and simulations for the mooring load and remaining volume exhibit considerable similarities despite the high variance present in the measurements. Furthermore, during typhoon conditions, the frequency domain results reveal that once the net cage is submerged, there is no considerable change in volume response in the wave frequency region. This suggests that the submersible function effectively mitigates net volume deformation. In conclusion, this study shows that the proposed method can accurately capture volume changes under both typical and extreme weather conditions, although further enhancements in accuracy are needed.