Numerical and experimental study on the drainage and collapse of a floating flexible bag structure

Abstract This paper addresses the possible drainage and collapse of closed flexible cages in sea-based fish farming. A closed flexible cage is a floating bag structure containing water that is enclosed from the ambient water. Possible density stratification in typical fjord locations can cause buoyancy driven discharge from the containment if damages occur under special operational conditions. The discharge may in turn cause drainage and collapse of the closed flexible cage. A combined structural and hydrodynamic model was developed to study the process of drainage and collapse of a floating closed flexible bag structure. Scaled physical model experiments with buoyancy-driven drainage of a hemispherical bag structure was conducted and compared with results from numerical simulations. Good comparison was observed for the flexible deformations and the drainage time. Main characteristics of the drainage process and performance of the numerical model are discussed. Implications from the present results on the design of closed flexible cages are suggested. To the best of the authors’ knowledge, the present study is the first to consider the drainage and collapse of a floating flexible bag containment structure through both numerical and experimental methods.