Challenges and recent advances in offshore scour modelling

In recent years, progress has been made on the understanding and description of scour around offshore structures. For simple geometries, such as cylindrical piles and triangular structures, empirical formulae have been developed. This makes it possible to predict scour depth and time rate depending on site-specific conditions with reasonable accuracy. However, the jack-up industry does not (yet) have validated and generally applicable tools to predict scour development for almost all existing jack-up footing designs. This has triggered the initiation of the joint industry project “OSCAR” (Offshore SCour Assessment and Remedial measures), which has started in autumn 2008. Oil companies, drilling rig owners, designers and research companies joined forces to develop engineering tools for jack-up specific scour assessments. This paper outlines major challenges in scour assessments for jack-ups and introduces recent developments and innovations in scour modelling. Their successful application to offshore monopiles offers a large potential to tackle and resolve a number of key challenges on jack-up scour: x Online monitoring with cameras allows gathering time-dependent information, the identification of the equilibrium scour depth and insight into the behaviour of scour protection. x Development of transfer functions from model scale to reality and verification of these functions with field data allow for improved reliability of scour predictions. x Fundamental research on the dynamic behaviour of scour protection beyond the threshold for initiation of motion allows to predict the performance of the scour protection and to conceptually design scour protection layouts.