STRUCTURAL LIFE-CYCLE ENHANCEMENT OF NEXT-GENERATION ONSHORE AND OFFSHORE WIND FARMS

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The proposed research aims to develop an innovative mitigation device to protect the next-generation onshore and offshore wind farms from dynamic loading caused by extreme natural events.In 2020, 20% of the UK's electricity was obtained from wind using both onshore and offshore windfarms. In order to increase this percentage and help the UK address its climate change target, new wind farms, with taller and larger wind turbines, and situated in more extreme locations are planned. Projections of growth also indicate the expansion into emerging markets and construction of new wind farms in developing countries. Therefore, these next-generation wind turbines will have to cope with harsher climate conditions induced by stronger storms and taller sea waves, and extreme events such as earthquakes and tsunamis. Several simplifying assumptions used for the design of previous generations of wind turbines can no longer be applied and new critical factors and uncertainties linked to power-generation efficiency and structural safety will emerge, affecting their resilience and life-cycle. The particular area of focus of this research is the traditional transition piece of a wind turbine, which is a structural element that connects the tower with its foundation and will have to tolerate extreme stresses induced by dynamic loading during extreme natural events. The aim is to replace the traditional connector with a novel mechanical joint of hourglass shape, termed an Hourglass Lattice Structure (HLS). This innovation will combine the unique features of two proven technologies extremely effective in seismic engineering, namely the "reduced beam section" approach and the "rocking foundation" design. In particular, the proposed HLS device, because of its hourglass shape, will facilitate the rocking behaviour in order to create a highly dissipating "fuse" which will protect the wind tower and foundation.Performance of the novel proposed device on the structural life-cycle risk will be assessed through analytical, numerical, and experimental investigation by using, as a measure of efficiency, the levelized cost of energy (LCOE), namely the cost per unit of energy based on amortized capital cost over the project life.In addition, experimental testing of offshore small-scale wind turbines will be carried out by means of an innovative test rig, the first-ever underwater shake-table hosted in a hydraulic flume that will be deployed, calibrated, and used to simulate multi-hazard scenarios such as those recently discovered and dubbed "stormquakes".The successful outcome of this timely project will allow next-generation wind turbines to be more resilient and cost effective so that wind energy can develop as a competitive renewable energy resource with less need for government subsidy. The inclusion of industrial partners in all stages of the project ensures that the technical developments will be included in commercial devices for a medium-long term impact.