Nonlinear Dynamic Analysis on Multi-Fishing Boats Anchored Together Based on Hilbert–Huang Transform

Fishing boats anchored away from the wharf or revetment are typically in side-by-side configurations due to their small size. Expanding on previous physical model tests investigating regular wave interactions with multi-boat and bow-and-stern-anchored fishing arrays, this study examines the hydrodynamic effects of irregular wave conditions. The Hilbert–Huang transform (HHT), an adaptive time–frequency processing technique, was applied to investigate multi-order nonlinear oscillatory elements in dynamic systems. It is found that the roll and heave motions of each boat are dominated by the wave-frequency components, whereas the sway motion is dominated by the low-frequency components. When multi-boats are anchored side by side, the roll and heave motion of the lee-side boat has a greater wave-frequency response compared with other boats, while for sway motion, the middle boat seems a little higher than others. The nonlinear dynamics of the roll and sway motion for a single boat is very large. An increase in the number of parallel boats has significant effect on reducing these responses. The variation trends of the three motion responses of the boat on the weather and lee sides are obviously different in each form.