Researchers from Germany’s Fraunhofer Institute for Wind Energy Systems (IWES) are undertaking scale testing of suction bucket foundations in a bid to demonstrate the potential of the solution.
The team has said that this installation method for the foundations of offshore wind turbines is both fast and avoids pile driving noise, meaning it can also be employed for sites in regions subject to noise restrictions.
The technique consists in the pumping of water out of sealed steel buckets in order to build up a negative pressure, which draws the structure into the seabed.
According to the IWES team, the challenging aspects of a bucket installation include the distribution of the pressure as well as ensuring that the bucket remains level.
Following successful installation, the researchers are now investigating the tensile behaviour of suction buckets and the effects of extreme wave loads.
In a statement about the research, the team has said: “A stable position even in cases of extreme weather conditions is an absolute must for wind turbines in offshore farms. As such, not only the influence of the installation process on the subsequent stable position but also the interaction between the seabed and the steel structure, the effects of compressive and, above all, tensile loads are investigated in advance.
“The bucket foundation included in the research represents a bucket for a jacket support structure and measures 1.4m in diameter. In offshore applications, the same components can reach diameters of between 6m and 15m. Large-scale model tests such as these are performed in the foundation test pit, measuring 14m by 9m by 10m, which provides homogeneous testing conditions and a sandy model seabed representative of those typically found in the North Sea.”
During the scale testing, the steel cylinder was sunk just over a metre into the saturated sand.
“It is extremely important to monitor the negative pressure closely so as to avoid damaging the seabed and ensure the bucket remains level. For this reason, separate chambers are employed in the bucket during offshore installations, with the aim of regulating the pressure,” said IWES project manager Tulio Quiroz.
Tensile load testing is expected to start soon in order to simulate the effects of extreme waves on the structure.
IWES has said that the knowledge gathered will be made available to industry partners.