Hydrodynamic forces in marine-fouled floating aquaculture cages: Physical modelling under irregular waves

Abstract

Marine fouling is a major concern in marine aquaculture industry. It changes the flow field around the cage, reduces water exchange across the nets and affects the current/wave-induced forces acting on the structure. The current/wave forces induced to marine-fouled planar net panels were studied by previous researchers. The current paper reports the results of a series of small-scale physical model tests conducted to study the wave forces induced to marine-fouled 3D aquaculture net cages. Using load cells fixed on the mooring lines, the time series of the forces generated by irregular waves propagating through the clean and fouled fish cage models were recorded. The artificial fouling was representative of hydroids, an important fouling organism in the aquaculture industry. Time and frequency domain analysis were performed on the in-line (surge) and cross-line (sway) wave force data.The experimental results showed that the surge force amplitudes increased up to around 160% and by the fouling. The sway force showed up to around 50% decrease by the fouling. The probability distribution of the force response to irregular waves was not significantly affected by the fouling. The force transfer functions from the time and frequency analysis were in reasonable agreements. The fouling, interestingly, increased the linearity of the wave-force interactions and provided stronger associations between the input forcing and the output response.