RIASSUNTO
ABSTRACT
Wave elevation around a cage array used in aquacultural engineering with different levels of biofouling are numerically investigated. The porous-media fluid model is introduced to model both the clean and the biofouled netting. An oscillating-boundary method is used to generate waves at one end of a tank partially filled with water. The flow motion of an incompressible, viscous fluid is described by Navier-Stokes equations and the free surface is tracked by volume of fluid (VOF) method. Validation of the numerical model is conducted and numerical results of wave elevation around cage arrays with different levels of biofouling are presented.
INTRODUCTION
The global aquaculture industry is in a stage of dramatic expansion with approximately half of all seafood eaten around the world being farmed. China has been responsible for most of the growth in fish availability owing to the rapid expansion in its fish production particularly from aquaculture (FAO, 2014). With the goal of more socially acceptable, economically profitable and environmentally friendly, developing aquaculture in fish farms located offshore and seeking superior environments for high-quality products are becoming inevitable trends (Aarsnes et al., 1990; Klebert et al., 2013; Zhan et al., 2006). When presented in offshore locations, cage arrays will attenuate incident waves by a combined action of blockage and dissipation. This attenuation in waves may alter the wave field around the fish farm, and thus needs to be taken into account in the design of the net-cage structure. Similar with other marine structures, the infrastructure of the cage array suffers significantly from the effects of biofouling. Biofouling, especially on netting, can lead to a rapid net aperture occlusion and significant changes of the porosity of the cage array (Braithwaite et al., 2007), which restricts the water exchange and aggravates the damping effect of the cage array on wave propagation. Thus, the investigation on wave propagating through the cage array considering the effect of biofouling is of great importance.