Numerical modelling of dynamic responses of aquaculture net cages in waves: Snap load prediction and the effect of nonlinear added mass

Journal article, 2026

This study proposes an alternative time-domain model to simulate an aquaculture net cage equipped with a floating collar of circular cross-section and flexible nets. The hydrodynamic loads on the floating collar are calculated using a partially nonlinear strip theory, which incorporates the draft-dependent impulsive added mass of the cross sections along the floating collar to capture structural vibrations caused by water entry and exit. The structural responses are obtained in the time domain based on modal superposition, with the wave-radiation memory effects accounted for through Cummins-type equations. Results for regular waves show that the nonlinear added-mass loads excite high-frequency responses near the natural frequencies of the higher-order modes of the floater. An inextensible truss model is applied to simulate large-amplitude deformation of the nets. It is found that the phase difference in motion between the floating collar and the sinkers leads to transient snap loads. While the impulse of these loads has a limited impact on the motion of the floating collar due to the short duration, their peak tension poses a severe threat to the structural safety of the net structures. This study also clearly identifies the inherent limitations of the inextensible truss model in predicting the peak values of such snap-induced tensions. To address this limitation, we propose a straightforward extension of the original inextensible truss model. The enhanced extensible truss formulation accounts for the transient elastic response of the net, allowing it to replicate the snap-load phenomenon and thereby provide more reasonable and accurate predictions of the critical snap loads.