Dynamic behaviour of a large flexible net with local biofouling subjected to irregular waves

Abstract

In deep-sea aquaculture facilities, flexible nets are widely used and are easily colonized by marine organisms. Once fouled by these organisms, the flexible nets experience increased weight and greater hydrodynamic forces due to waves and currents. This paper presents a theoretical model developed to simulate the three-dimensional vibrations of a large-area flexible net subjected to irregular waves, considering three different types of local biofouling. The marine organisms are modelled as adhering to the net near the boundaries, on a rectangular ring, and within the central rectangular region, respectively. The irregular waves are described using the Jonswap spectrum. Employing the lumped-mass method, the nonlinear vibrations of the net are solved. The theoretical model is validated by comparing it with experimental results. Using the present model, the effects of different types of biofoulings on the vibrations of a flexible net under the action of irregular waves are examined. The results indicate that the distribution of dynamic tensions of net twines on the whole net is different for different regions and as the extent of biofouling increases, the dynamic tensions of net twines also increase.