Effects of overtopping structures on the hydrodynamic response of pile-supported enclosure

Pile-supported enclosure has represented one of the critical infrastructures in offshore aquaculture. Its structural resilience under extreme wave loads can directly govern economic viability and operational safety. It is often required for the non-overtopping structure in the complete containment of stock. Wave-induced loads can also be minimized for structural economy. Therefore, a tradeoff can be made between them. In this study, a semi-overtopping configuration was proposed to systematically evaluate and validate the pile-supported enclosure. Non-, semi- and full-overtopping configurations were selected to quantitatively assess the hydrodynamic performance, structure loads, and safety metrics. An optimal solution was identified to balance safety, functionality, and cost-effectiveness. A numerical framework was integrated to combine a three-dimensional potential flow solver for wave kinematics. A modified Morison equation was selected to calculate the hydrodynamic load on the slender structural members. A lumped-mass formulation was coupled with a finite element method (FEM) to simulate the dynamic response of the flexible netting. Nonlinear soil-structure interaction was incorporated for the piles using p-y curve models. The numerical model was validated using a series of physical tests. Experiments were conducted in a wave flume using a 1:20 scaled model of a pile-net enclosure. Both regular and extreme wave conditions were used to measure the wave forces on the central pile. A comparison was also made on the numerical predictions with the isolated and coupled pile networks. A high accuracy was validated with the deviations between simulated and measured forces of below 5%. Subsequently, full-scale simulations were evaluated under extreme wave condition (9 m wave height) in the period of 50-year return. In the pile system, the non-overtopping configuration resulted in extreme bending moments approximately four times greater than those in the full-overtopping ones, corresponding to a critically low bending safety factor of 1.24. In contrast, the semi-overtopping configuration was reduced about 62% in the maximum pile bending moment, compared with the non-overtopping ones. The factor of safety was elevated to 3.45, closer to the 6.19 for the full-overtopping ones. The peak tensions were concentrated in the upper regions of the net system for all configurations. The maximum net tension was 4.43 kN in the non-overtopping configuration, which was 30.9% higher than the 3.38 kN in the full-overtopping ones. The tensile safety factor was below 1.0 (0.89), indicating the high rupture risk. The semi-overtopping configuration exhibited the maximum tension of 3.62 kN, only 6.9% higher than the full-overtopping benchmark, with a safe tensile safety factor of 1.12. Furthermore, there was the different spatial distribution of high-stress zones: The failure risk was localized at the net-pile connections for the non-overtopping configuration, while it extended to the net-superstructure joints for the semi- and full-overtopping ones. Therefore, the semi-overtopping configuration was the optimal engineering. The extreme loads were dramatically reduced on the primary pile support system, thereby enhancing structural safety and potential cost savings. While the net tension levels and safety factors were maintained equivalent to the safest (full-overtopping) configuration, thus preserving essential anti-escape function. This finding can provide the quantitative framework for the high performance of offshore aquaculture enclosures in severe marine environments.