Abstract
In this study, the feasibility of vibration-based damage assessment in a wind turbine tower (WTT) with gravity-based foundation (GBF) under various waves is numerically investigated. Firstly, a finite element model is constructed for the GBF WTT which consists of a tower, caisson, and foundation bed. Eigenvalue analysis is performed to identify a few vibration modes of interest, which represent complex behaviors of a flexible tower, rigid caisson, and deformable foundation. Secondly, wave-induced dynamic pressures are analyzed for a few selected wave conditions and damage scenarios are also designed to simulate the main components of the target GBF WTT. Thirdly, forced vibration responses of the GBF WTT are analyzed for the wave-induced excitation. Then modal parameters (i.e., natural frequencies and mode shapes) are extracted by using a combined use of time-domain and frequency-domain modal identification methods. Finally, the variation of modal parameters is estimated by measuring relative changes in natural frequencies and mode shapes in order to quantify the damage-induced effects. Also, the wave-induced variation of modal parameters is estimated to relatively assess the effect of various wave actions on the damage-induced variation of modal parameters.
Highlights
E integrity of the structure-foundation system gets into danger when extreme loadings mix with local damage in critical subsystems. e worst scenario is that those unwanted situations mix with the inborn characteristics such as heavy self-weight and blade rotation-induced dynamic loading [2, 3]. erefore, it should be noticed that a variety of local damage types can occur in the subsystems. e slender tower damages as similar as local buckling, crack, or bolt loosening in segmental joints. e wave impact coupled with the armor stone can cause local damage like crack or hole in the concrete caisson, which results in the loss of infill sand
Local damage that occurs in the subsystems leads to the change of structural design parameters such as stiffness, mass, and damping, which result in the change of vibration characteristics of the gravity-based foundation (GBF) wind turbine tower (WTT) [5,6,7,8]
Damage Assessment Results: Damage Type 1. e variation of modal parameters of the GBF WTT was estimated for the bolt damage simulated in the tower flange (Figure 9 and Table 5)
Summary
All other layers in the foundation bed and the natural ground (i.e., 13 m depth assigned in Figure 1) were simulated using solid elements. Note that the dynamic effects of blades’ movement resulted by operating the wind turbine tower were not considered in this study
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