Hydrodynamic loads on an inclined monopile in the splash zone

Abstract

The thesis is about a relatively new installation method for monopile foundations for offshore wind turbines. For this method, the monopiles are upended from horizontal to vertical position using an upending tool and a crane, using one of the new vessels of Boskalis: the Bokalift. For large monopiles a part of the monopile will be partly in the wave zone during the upending process and therefore the overhanging part will be exposed to waves. The aim of the research is to determine the hydrodynamic loads on an open monopile when it is upended from horizontal to vertical position.

It is found that in addition to the loads that can be calculated using the first-order potential theory (calculated with programs such as AQWA), also a type of fluid resonance can play an important role, which is called piston-mode resonance (as presented on the figure). It is well-known that the loads calculated with a diffraction program such as AQWA overestimates the loads at resonance since viscous damping is neglected and therefore experiments at the Delft University of Technology are performed in order to validate the numerical results.

During the presentation, the experimental and numerical results are compared and several recommendations for further research will be presented.