Abstract
Interest in renewable and clean energy over the past decade has motivated immense research on wind energy. The main issues in design of offshore wind turbines in regions of recent development have been aero- and hydro-dynamic loads; however, earthquake is a design concern in seismic areas such as East Asia and Western United states. This paper reviews the state of practice in seismic design of offshore wind turbines. It is demonstrated that wind turbines are in particular vulnerable to vertical earthquake excitation due to their rather high natural frequencies in vertical direction; however, inclusion of the radiation damping could contribute considerably reduce the earthquake loads. Moreover, it is demonstrated how soil nonlinearity could lead to settlement and permanent tilting of offshore wind turbines on caisson foundations or tripods. Using these cases, the paper demonstrates that the design of offshore wind turbines for earthquake loading is driven by performance-based considerations.
Highlights
For much of the twentieth century there was little interest in using wind energy for generation of electricity
The shake table did not have the possibility of including soil-structure interaction (SSI) for this large turbine; Prowell et al [30] used the finite element software OpenSees (Open System for Earthquake Engineering Simulation) [31] and conducted numerical studies of the 5 MW reference wind turbine developed by National Renewable Energy Laboratory (NREL) [29]
This paper has presented a brief history of the development and growth of wind turbines and offshore wind turbines (OWT)
Summary
For much of the twentieth century there was little interest in using wind energy for generation of electricity. The smoother surface at sea compared to land results in stronger and less turbulent wind that ensures a greater and more reliable power production It allows for the use of larger turbines and lower elevation above ground/water level. Throughout the 1990s small numbers of offshore wind turbines (OWT) were placed close to shore, until in 2002 the Horns Rev, 160 MW wind farm, about 20 km off the western coast of Denmark, was constructed This was the first project to use an offshore substation that increased the power collection voltage of 30–150 kV for transmission to shore. Other researchers have provided detailed account of general dynamic behavior of OWTs [11,12] They discuss the wind and wave power spectral densities, which essentially describe the frequency content of dynamic excitations from wind turbulence and waves. The means to produce more energy is to increase the rotor diameter and hub height
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