Different offshore foundation options are discussed in terms of general layout, loading characteristics and related fundamental natural frequency. Offshore wind-power generation presents many engineering challenges including: limited guidelines available for analysis and design of foundation/support structures inadequate logistics for construction/fabrication and comparatively expensive operation and maintenance costs, which combined result in current levelised cost of energy approximately double that for onshore wind-power generation. Significant increases in wind-turbine dimensions, rated power-generation capacity and size of wind farm developments over the past two decades are projected to continue. This paper reviews various issues related to wind-power generation, one of the more popular forms of renewable energy, including attractions and challenges of electric power generation through onshore and offshore resources. The contents were presented and discussed at a dedicated hearing in which a wide pool of stakeholders participated, including representatives of the relevant technology platforms, industry associations and the Joint Programmes of the European Energy Research Associations. It has been produced by independent and renowned European materials scientists and energy technology experts, drawn from academia, research institutes and industry, under the coordination the SET-Plan Information System (SETIS), which is managed by the Joint Research Centre (JRC) of the European Commission. This report provides an in-depth analysis of the state-of-the-art and future challenges for energy technology-related materials and the needs for research activities to support the development of wind power technology both for the 2020 and the 2050 market horizons. It is intended to serve as a guide for developing specific research and development activities in the field of materials for energy applications over the next 10 years. The Materials Roadmap aims at contributing to strategic decisions on materials research funding at European and Member State levels and is aligned with the priorities of the Strategic Energy Technology Plan (SET-Plan). This scientific assessment serves as the basis for a materials research roadmap for wind power technology, itself an integral element of an overall "Materials Roadmap Enabling Low Carbon Technologies", a Commission Staff Working Document published in December 2011. Chris Golightly is a chartered civil engineer and works as an independent offshore oil and gas and renewables geotechnical and foundations consultant.
More worrying still, this was not an isolated incident and over 70% of offshore wind turbines were found to be affected, leading to subsequent costly repairs, consisting of cement filling, installation of elastomeric spring support bearings above the failed or at risk connections as well as a number of claims and legal disputes There is now a clear move towards direct none-grouted bolted flange connections, although some developers are persisting with the use of inclined none shear keyed monopile grout connections Dr. On closer inspection, this appeared to be due to the very high strength extremely brittle grout cracking as a result of tensile stresses being present as a result of repeated tower bending. However, in the UK and elsewhere, towards the end of 2009 these grouted connection joints, between the monopiles and connecting steel transition pieces were observed to be failing by slipping downwards and cracking at the top and bottom near the grout seals. The design guideline in use at the time mistakenly permitted this to be done without the use of reinforcing shear keys on the monopile and transition piece walls. The technique was sold as a quick, cost effective and apparently problem-free solution. In the early days of the offshore wind industry in Europe, an injection grouting technique was adopted as a supposed quicker and cheaper method of allowing wind turbine support towers to be placed close to vertical on non-vertically installed (~ 1o) steel large diameter (> 4 m) “monopiles”, in effect impact driven thin walled steel tubular shells.
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