Simplified critical mudline bending moment spectra of offshore wind turbine support structures

Abstract

Offshore wind turbines are subjected to multiple dynamic loads arising from the wind, waves, rotational frequency (1P) and blade passing frequency (3P) loads. In the literature, these loads are often represented using a frequency plot where the power spectral densities (PSDs) of wave height and wind turbulence are plotted against the corresponding frequency range. The PSD magnitudes are usually normalized to unity, probably because they have different units, and thus, the magnitudes are not directly comparable. In this paper, a generalized attempt has been made to evaluate the relative magnitudes of these four loadings by transforming them into bending moment spectra using site-specific and turbine-specific data. A formulation is proposed to construct bending moment spectra at the mudline, i.e. at the location where the highest fatigue damage is expected. Equally, this formulation can also be tailored to find the bending moment at any other critical cross section, e.g. the transition piece level. Finally, an example case study is considered to demonstrate the application of the proposed methodology. The constructed spectra serve as a basis for frequency-domain fatigue estimation methods available in the literatur

Scour influence on the fatigue life of operational monopile‐supported offshore wind turbines

“…In summary, scour has been shown to influence the fatigue life (FL) of OWTs, and the effect of scour and backfilling on long‐term damage in a parked wind turbine has been researched . Due to the complexities associated with the fatigue analysis of OWTs, simplified methods have been proposed for this analysis . However, the quantification of the scour influence on the FL of an operational wind turbine and specific simplified methods for scour effects on fatigue analysis remain outstanding.…”

Predicting long term performance of offshore wind turbines using cyclic simple shear apparatus

“…Typical wave period will be in the order of 10sec (for North Sea) and will therefore have dynamic soil-structure interaction. A calculation procedure is developed in Arany et al [6] and the output of such a calculation will be relative wind and the wave loads and an example is shown in Figure 1. It is assumed in the analysis that the wind and wave are perfectly aligned which is a fair assumption for deeper water further offshore projects (i.e.…”

“…fetch distance is high). Analysis carried out by Arany et al [6] showed that the loads from 1P and 3P are orders of magnitude lower than wind and wave but they will have highest dynamic amplifications. The effect of dynamic amplifications due to 1P and 3P will be small amplitude vibrations.…”

An innovative cyclic loading device to study long term performance of offshore wind turbines

“…The loads acting on the foundation are typically one way cyclic and many of loads are also dynamic in nature. Further details of the loading can be found in Arany et al (2014). (b) It is well known from literature that repeated cyclic or dynamic loads on a soil causes a change in the properties which in turn can alter the stiffness of foundation, see Bhattacharya (2011, 2012).…”