Study aims for deep water offshore wind viability

Deep water offshore wind turbines could be more economically viable following a project that will assess the stability of these turbines and their support structures.

Deep water offshore
CGI of deepwater offshore wind installation (Image Manchester Met)

To this end, academics from Manchester Metropolitan University have been awarded £124,000 to develop computer models to test the best methods for stabilisation and control in an aggressive offshore environment.

Lead researcher Dr Ling Qian, Reader in Computational Fluid Dynamics at the Centre for Mathematical Modelling and Flow Analysis, said: “If you want to locate wind turbines far away from the shore at a water depth of more than 50m, a fixed-bottom turbine becomes a very expensive and challenging engineering project.

“So we need to develop a floating offshore wind turbine that works in water deeper than 50m, but that leaves the top-heavy turbines exposed to being buffeted by high winds and rough seas even if the buoyant support system is attached to mooring lines anchored to the sea floor.”

Based on code developed in-house, Dr Qian and colleagues will use Manchester Met’s high-performance computer cluster to run a computer simulation of waves interacting with a platform based on an existing design for floating support structures. Representative waves from the North Sea will be used in the computer simulation.

The design comprises three connected columns 50m apart, creating a triangle frame in which the turbine sits, keeping most of the mast above the surface of the water. It is manufactured separately from the turbines – which are typically 130m high with a blade length of between 60m and 90m – and the two are joined on location.

Manchester Met’s model will incorporate two proposed stabilisation measures, namely a tuned liquid damper (a U-shaped tube filled with water that sloshes as the platform moves, acting as a counterbalance and helping to absorb rotational movements); and heave plates placed under the three columns, which suppress the up and down motion.

Dr Qian said: “Under extreme wave conditions such as during storms, floating platforms will undergo large movements and sometimes this movement is dangerous and leads to system damages. Therefore, we need to make sure the device can survive such storms with large waves. On the other hand, in order for the wind turbine to operate optimally we also need to control its motion.

“There is already one commercial floating offshore wind demonstration project in the UK, a test farm off the coast of Scotland near Peterhead, but to enhance the technical viability and to drive the cost down, further fundamental research is still needed.

“In this project, we will look at some novel and cost-effective techniques to stabilise a floating system so it can operate under high sea states and survive the worst impact.”

Once Dr Qian and his team have carried out their computer modelling, a 1:30 scale model of the turbine will be tested in a wave tank with research partners at Ningbo University in Ningbo, China.