Abstract
Predicting wave slamming pressures on bulbous bows is essential for ship structural safety. This study employs an overset-grid RANS-VOF framework to investigate viscous scale effects on bulbous bow slamming loads. Multi-scale simulations were conducted across four geometric scale ratios of 1:50, 1:20, 1:15, and 1:10 (α = 50, 20, 15, 10) under critical pitch-heave resonant head waves (λ/LWL = 1.2). While global motion responses follow Froude similitude, local dynamic slamming pressures show notable scale disparities. Smaller physical models develop a relatively thicker viscous boundary layer that acts as a hydrodynamic cushion, reducing peak pressures while broadening pulse durations. Consequently, direct Froude scaling from small-scale models tends to underestimate full-scale impact loads. To account for these viscous scale effects, an engineering extrapolation approach based on multi-scale regression is proposed, which demonstrates a reasonable linear correlation across the investigated range (R2 = 0.88–0.99) in the primary impact region. This study provides physical insights into the scaling behavior of bulbous bow slamming and offers a practical reference for full-scale load estimation.