Optimising scour protections for offshore wind
Expert(s) |
Pim van Steijn
In the experimental facilities, Deltares investigates how loose rock scour protections around offshore wind turbine foundations perform during storms and tides. The results help offshore wind developers make their designs more efficient. Pim van Steijn, expert in scour and scour protections at Deltares: “Every wind farm has a unique foundation design and therefore its own specific issues.”
In the Atlantic Basin, Pim van Steijn and his colleagues Minghao Wu and Ioanna Saxoni are building a setup to test scour protections around offshore wind turbine foundations. Various layouts will soon be placed on the sand bed around the foundation piles to prevent sand washout and deep scour holes.
The Deltares team is also examining the stability of a rock berm, which in practice is often placed over the power cables after they have been laid. This prevents the cables from moving too much, which could lead to failures and outages in part of the wind farm. Moreover, replacing cables is expensive.
Extreme waves or tide?
The rocks in the scour protections must be heavy and large enough to withstand a severe storm with high waves. Pim: “In this series of tests, we are focusing on the stability of the stones: do they stay in place during a storm with waves and currents that only occur once every fifty years? Does the protection change shape, causing sand to wash away underneath or leaving the power cable unprotected?”
Edge scour around the protections is also being investigated. Pim: “If the scour protection is too small, deep edge scour holes form, exposing power cables. This erosion process is often slow and mainly caused by tidal currents, much less by waves. Therefore, we simulate the tide in the basin to test how much sand washes away and advise on how far the rocks around the foundation should best be placed.”
Down to the millimetre
Using stereo photographs taken with a self-developed automated camera system, Pim and his colleagues monitor the deformation of the scour protections and the surrounding sandbed. “This way, we can see depth and measure bathymetry changes very accurately, down to the millimetre.”
From advice to research
Based on the test results, offshore wind developers gain a better understanding of the risks involved in building their wind farms. Pim has been working on this at Deltares for the past eleven years.
“It never gets boring. The basics may be the same, but the details are always different. Every wind farm is unique and therefore has its own questions. The core is to test and optimise the designs for wind farm developers and contractors, so they do not use too much stone, but can realise a robust and low-maintenance wind farm at minimal cost.”
Because Deltares has been doing this for a long time, our data is of high quality and reliable, and we have become a strategic cooperation partner for many offshore wind developers. In addition to direct client questions, broader knowledge questions often arise during projects.
Deltares organises 'Joint Industry Projects' together with the market for high-quality applied research. This knowledge can then be used by the entire sector to make wind farms more robust, efficient and cheaper. An important and recent example is the Handbook of scour and cable protection methods, which was created together with 20 partners from the industry.
Impact
With this work, you really make an impact, Pim says. “Because your advice is applied directly in the design and construction of offshore wind farms.” Pim also enjoys pioneering in practice.
“During my first scale tests 11 years ago, I was on my knees shifting sand myself. That was for Nordergründe, a wind farm on the edge of the German Wadden Sea. After it was built, I sailed around it.” He still receives field data from that project every year, which helps him to improve his next experiments.
