Advanced numerical modelling of scour and erosion

Abstract

Scour associated with anthropogenic activities in the marine environment has exercised the minds of scientists and engineers for decades. Despite the advances in understanding there remain areas of uncertainty which require further examination and challenges that require further research. Whilst real-life scour problems often help formulate the questions for detailed laboratory experiments, the associated information is less often used to answer some of those questions and yet the available data can offer the chance of exploring the scour at full-scale using real marine soils, albeit with all the inherent uncertainty associated with measurements obtained in the field. It can be argued that through the interpretation of these data, it forces the scientist and engineer to not only explore in more detail the limitations of the measurements but to engage in the full range of processes, whether physical (e.g. hydrodynamics and meteorological forcing) or biological (e.g. marine growth, benthic organisms) that impact on structures placed in what are often, very challenging environments.

Morphological evolution of a barchan dune migrating past an offshore wind farm foundation

“…Relative to the ambient seabed the scour depth progressed at a rate comparable to neighbouring monopiles, giving a maximum scour depth of 2.3m in 2015 in the seabed veneer and clay (Table 1, fifth column). This results in a ratio of scour depth to pile diameter of about 0.4, which is comparable to other sites in non-granular soils (Harris and Whitehouse, 2015). Even from the first survey time-step after the installation of the monopile (2013) the level at the base of the scour pit was deeper than the ambient bed-level, i.e.…”

“…This is comparable with empirical observations, which suggest a scour depth approximately 1.3 times the monopile diameter in sand (Sumer et al, 1992), which would give a depth of approximately 7.5m. This suggests that the scour depth through the barchan dune is similar to scouring in a flat bed of sandy sediments (Harris and Whitehouse, 2015). However, it is apparent that in the current situation, the seabed underlying the barchan is providing some element of geological control to the scour depth formation.…”

“…Whilst barchan dunes migrate at a rate of approximately 10 to 20m/yr, scour into loose sands can take place down to several metres with a timescale of a few days to weeks, potentially occurring within a few tidal cycles (Harris and Whitehouse, 2015). Noormets et al (2006) studied the scour taking place around a 1.65m diameter pile located in a field of bedforms within a tidal inlet.…”

The influence of physical cohesion on scour around a monopile

“…This variability and the inaccuracies of prediction can typically be attributed to a lack, or absence of, sedimentological and geological information within those predictive models (Van den Eynde et al 2010, Marine Management Organisation 2014) because certain sediments yield smaller scour depths than predicted. Indeed, post-installation data show that where geological, sedimentary and hydrodynamic conditions are similar, OWFs have similar responses in terms of scour (Harris and Whitehouse 2014).…”

Equilibrium Scour-Depth Prediction around Cylindrical Structures

“…This can partially explain the discrepancies between small scale laboratory experiments and 123 prototype scour measurements, the latter tending to have relatively small non-dimensional scour depths (Ettema 124 et al, 2006) whereas prototype observations of scour in the field with live-bed conditions can be large (i.e. scour 125 depth around 1.8D; Harris and Whitehouse, 2015). 126 Expression (7) shows that both the pile Reynolds number and the Euler number are of particular importance 127 when attempting to describe the processes involved in scour around uniform and complex structures.…”