Numerical study of the interactions between the pile-net aquaculture structures and extreme waves

Extreme waves are recognised as the governing loads for pile-net aquaculture structures (PNAS) widely serviced in China, yet the transient impact physics and distinct spectral features of the reciprocal interactions remain poorly quantified. The responses of a classic PNAS to the excitations of focused wave groups are studied using the open-source hydrodynamics toolbox REEF3D. Rigid piles are represented by the direct forcing immersed boundary method, while the responses of nets are modelled using the Lagrangian-Eulerian coupling algorithm. The framework is verified for free surface elevations and validated for impact forces against laboratory measurements. At the most exposed case, when the plunging jet first impinged, simultaneous horizontal peaks on piles and net reached 187.50 and 104.28 kN at full scale. The continuous wavelet transform identifies a broadband frequency excitation and energy spiking at impact. Local loads on the net are 3.72 to 3.87 kN maximally, and rise to about 21.46 kN when the solidities increase from 0.15 to 0.50. The non-linear interactions between the PNAS and extreme waves are further highlighted through the parametric studies, including the placement of the PNAS, wave parameters and net solidities. The findings of this study are expected to update the knowledge for designs and optimisations of the PNAS in the future.