Design loads for wave impacts -- introducing the Probabilistic Adaptive Screening (PAS) method for predicting extreme non-linear loads on maritime structures

To ensure the safety of marine and coastal structures, extreme (design) values should be known at the design stage. But for such complex systems, estimating the magnitude of events which are both non-linear and rare is extremely challenging, and involves considerable computational cost to capture the high-fidelity physics. To address this challenge, we offer a new multi-fidelity screening method, Probabilistic Adaptive Screening (PAS), which accurately predicts extreme values of strongly non-linear wave-induced loads while minimising the required high-fidelity simulation duration. The method introduces a probabilistic approach to multi-fidelity screening, allowing efficient linear potential flow indicators to be used in the low-fidelity stage, even for strongly non-linear load cases. The method is validated against a range of cases, including non-linear waves, and ship vertical bending moments, green water impact loads, and slamming loads. It can be concluded that PAS accurately estimates both the short-term distributions and extreme values in all test cases, with most probable maximum (MPM) values within 10\% of the available full brute-force Monte-Carlo Simulation (MCS) results. In addition, PAS achieves this performance very efficiently, requiring less than 4\% of the high-fidelity simulation time needed for conventional MCS. These results demonstrate that PAS can reliably reproduce the statistics of both weakly and strongly non-linear extreme load problems, while significantly reducing the associated computational cost. The present study validates the statistical PAS framework; further work should focus on validating the full procedure including CFD load simulations, and on validating it for long-term extremes.