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 replenishment 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 $T_p\in [4.16,9.00]$ s. The relevant statistical 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 replenishment 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.