Large-scale experimental study on scour around both slender and large monopiles under irregular waves

Offshore wind power plays a crucial role in energy strategies. The results of traditional small-scale physical models may be unreliable when extrapolated to large field scales. This study addressed this limitation by conducting large-scale (1:13) experiments to investigate the scour hole pattern and equilibrium scour depth around both slender and large monopiles under irregular waves. The experiments adopted Keulegan—Carpenter number (N_KC) values from 1.01 to 8.89 and diffraction parameter (D/L, where D is the diameter of the monopile, and L is the wave length) values from 0.016 to 0.056. The results showed that changes in the maximum scour location and scour hole shape around a slender monopile were associated with N_KC, with differences observed between irregular and regular waves. Improving the calculation of N_KC enhanced the accuracy of existing scour formulae under irregular waves. The maximum scour locations around a large monopile were consistently found on both sides, regardless of N_KC and D/L, but the scour hole topography was influenced by both parameters. Notably, the scour range around a large monopile was at least as large as the monopile diameter.