MSc ECE student Katie Corbett reports on the Coastal Seminar by Prof Richard Simons (UCL)
On Tuesday 27th November, Professor Richard Simons from the University College London gave a talk on ‘Seabed Scour around Offshore Foundations’ as part of the coastal seminar series. The focus was on the physical and theoretical models used to assess the vulnerability of offshore structures such as wind turbines to the effects of vibration and scour. This understanding is essential for their protection and to avoid large costs.
Scour is the erosion of sediment at the seabed around fixed offshore structures, for example at wind farms. Predicting scour is difficult though due to the complex forcings of winds, wave action and tidal currents. The design process is key to ensuring structures are set securely in place; enhancing their stability can be done by burying them deep into the seabed or placing large rocks around the base of the structure at the seabed. Recently there has also been research surrounding the shape of the monopile and its effect on scour and seabed stability. Scour depth varies with a number of factors, including the water depth, viscosity and sediment dynamics.
Richard Simons is a Professor of Fluid Mechanics and Coastal Engineering, with an interest in the effects of wave-current interactions and fluid effects on sediment, structures and seabed scour. Three pieces of experimental research were carried out at the University College London and were discussed in the seminar. The first of these explores the prediction of equilibrium scour depth around uniform and nonuniform cylindrical structures. The method was based on the depth-averaged Euler number which calculates pressure gradients at any level around structures. The equations used were derived from field data and experimental data from experiments and other published reports.
The second area of research was on the subject of scour around dynamically active monopiles in non-cohesive sediments. One of the experiments carried out investigated scour under a range of frequencies of cyclic loading and at two scales. The vibrating lead to uniform slumping of the material around the base of the structure; scour rate was initially reduced but had no overall effect for the equilibrium scour depth. The final area of research investigated the scour around monopiles subject to tidally reversing currents. Research was carried out at field scale, and the results showed that reversing tidal currents caused a 20% deeper scour hole in comparison to the hole formed under a unidirectional flow.
Professor Simons ended the seminar by reflecting on the risks associated with scale experiments and the steps researchers must take to avoid misconceptions and false results. The research undertaken in the field of scour is important economically and in terms of safety for industries such as offshore wind farms.