Abstract
To obtain reliable estimations of the dynamic responses of high-rising marine structures such as offshore wind turbines with obvious nonzero initial conditions, traditional frequency-domain methods cannot be employed because they provide only steady-state results. A novel frequency-domain transient response estimation method for offshore wind turbines is presented in this paper. This method builds upon a recent, significant theoretical development, which found that expressions of external loads in the frequency domain can be obtained by discretizing their eigenvalues and corresponding complex coefficients rather than directly by discrete Fourier transform (DFT) analysis, which makes it possible to deal with nonzero conditions in the frequency domain. One engineering advantage of this approach is its computational efficiency, as the motion equations of the system can be solved in the frequency domain. In order to demonstrate this approach, a case of a monopile-supported wind turbine with nonzero initial conditions was investigated. The numerical results indicate that the approach matches well with the time-domain method, except for a small, earlier portion of the estimated responses. A second case study of a sophisticated, jacket support wind turbine, involving practical issues such as complex external loads and computation efficiency, is also discussed, and comparisons of the results with the time-domain method and traditional frequency-domain method using the commercial software ANSYS are included here.
Highlights
The estimation of the dynamic responses of offshore wind turbine support structures, which transfer top loads to the surrounding soil, is one of the most important components in the design of wind turbine structures and may occupy up to 35% of the total installation costs (Arany et al., 2015) [1]
Building upon Liu’s work [16], this paper presents a further application of the aforementioned method to offshore wind turbines with transient responses, which involve practical issues, such as the complicated forms of wind turbine loads
A novel transient response estimation method for offshore wind turbines in frequency domain (FD) was presented in this paper
Summary
The estimation of the dynamic responses of offshore wind turbine support structures, which transfer top loads to the surrounding soil, is one of the most important components in the design of wind turbine structures and may occupy up to 35% of the total installation costs (Arany et al., 2015) [1]. A new generation of high-output wind turbines supported by tall and slender towers has been led by recent developments, which aim to obtain the most economic and productive configurations for wind turbines. These tall towers are generally regarded to be relatively flexible and lightly damped structures, as they are usually constructed with lightweight and high-strength materials. In order to simulate the loads on wind turbines, Seidel [9] adopted the sequential coupling and full coupling methods, and the measurement data from the DOWNVInD project was used to validate these methods
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