Jet velocities in water replenishment holes: A large-scale experiment

A large-scale experimental campaign in the GWK+ facility was performed for the description of the water replen-
ishment processes in monopiles (internal water level response, jet velocities, and their nondimensional response
amplitude operators, RAOs) for both regular and irregular sea states. The experimental scale was set to 1:15
with regular wave periods 𝑇 = [2, 6] s and irregular peak wave periods of 𝑇𝑝 ∈ [4.16, 9.00] s. The relevant statis-
tical measures for the RAOs were intestigated, and nondimensional prediction formulas were proposed for both
regular and irregular waves. The experimental data was furthermore applied to validate a numerical model for
prediction of the internal water level response and jet velocities. The numerical model was subsequently applied
to predict the number of individual occurrences of jets as a function of the vertical elevation of the water replen-
ishment hole, and the numerical approach was deemed applicable for design of offshore monopile foundations.
Application to field-scale shows that extreme jet velocities in excess of 9-10 m/s must be expected under North
Sea conditions.