A Framework for designing Offshore Mega Artificial Shelters: optimisation of breakwater layout and hydraulic properties under directional extreme waves

The growing demand for food production and marine space has created the need for large sheltered offshore areas. However, designing an Offshore Mega Artificial Shelter (OMAS) is challenging because the determination of the sheltered region is governed not only by breakwater configurations but also by the directional characteristics of the incident waves. This study proposes a framework for designing the geometric–hydraulic configuration of breakwater systems used to form an OMAS. Application to a real-world project shows that 32 incident-wave directions were sufficient for practical convergence. For 50-year design conditions, the optimised configuration reduced the total breakwater length from 8.35 km to 5.06 km, an approximately 40% reduction, while satisfying the prescribed minimum sheltered area of 20.2 km 2 , with a length-weighted mean transmission coefficient of 0.47. Increasing the design return period from 10 to 100 years increased the required breakwater length from 4.42 to 5.87 km. The originality of the proposed framework lies in integrating directional extreme-wave conditions with simultaneous optimisation of breakwater geometry and hydraulic performance, allowing the sheltered region to emerge as an outcome of each candidate design rather than being predefined, while automated mesh-quality improvement and high-performance computing enable its application to large-scale design problems.