Increasing the life of Marine Turbines by Design and Innovation

Host Institution: Cambridge University

Principal Investigator: Dr Robert Miller

Unsteady loads on tidal turbines are much larger than in wind turbines because of the high density of water and the high levels of unsteadiness in offshore marine environments. In addition the welded mild steel structures normally used to support marine turbines have a low fatigue life in salt water. This can lead to life of 30 months or less instead of the design requirement of 30 years. In addition fatigue life limits the number of locations where tidal turbine can be deployed, limiting the overall practical UK tidal resource. This project aims to develop innovative technologies which will reduce the unsteady loads which result from flow unsteadiness and thus increase the longevity of a marine turbine by an order of magnitude.

Two technologies will be developed. The first uses innovative hydraulic drive trains, developed in the UK, to reduce the unsteady loads created by large length unsteady ‘gusts’, those larger in size than the machine diameter. The hydraulic drive train allows the speed of the turbine to respond quickly to the ‘gust’ ensuring that the load on the machine remains constant. The second innovative technology is designed to reduce the unsteady loads created by short length unsteady ‘gusts’, those smaller than the machine diameter. The technology is similar to that used in aircraft to stop sudden changes in aircraft lift as the wing is hit by an air ‘gust’. The technology uses ‘spoilers’, ‘fluid ejection’ or ‘flaps’ on the wing to automatically hold the blade lift constant as the ‘gust’ moves over it. This technology will be employed on tidal turbine blades to reduce unsteady loading due to short length scale unsteady ‘gusts’. Once developed this second technology could also be used as an alternative to variable pitch mechanisms to avoid peak loads being exceeded.