The time evolution of scour around offshore structures

Abstract

This paper describes the development of an engineering model to predict the development of scour evolution through time around an offshore structure under current, wave and combined wave–current flows. The model has been tested against a range of data as well as being run for idealised tests. From the results of these tests issues with respect to scour prediction have been highlighted. In particular, the initial growth rate of scour appears to be too rapid based on the large-scale laboratory tests and tidal field data against which the model has been compared. Application of the model to a field-scale study has been completed which shows that in shallow water depths storm waves dominate the scour process. In deeper water depths, currents generally dominate even under storm conditions, although this will be dependent on the wave height and period and the actual water depth. The scour time evolution predictor (Step) model can be applied to scour assessment studies where there is a requirement to have an indication of the time-history of scour. The model clearly has a role in offshore wind turbine studies, but it is not limited to this sector and can be applied to bridge scour situations or other situations where scouring around monopile structures is an issue. Furthermore, if the scour at other types of structures or objects needs to be evaluated then provided the equilibrium scour depth and time-scale functions are available these can be implemented within the framework of the Step model.