Inverse estimation of breaking wave loads on monopile wind turbines

Abstract

Breaking waves occur in shallow water and cause large forces on offshore wind turbines, which can determine the design of the support structure. Due to the strong nonlinearity and statistical variability of breaking waves, the corresponding loads used in the design are generally characterized by large uncertainty. This paper presents a validation of an inverse method to estimate breaking wave loads on offshore monopile wind turbines based on wave basin tests. The accelerations measured on a scale model of a monopile wind turbine are passed to a force identification algorithm together with a dynamic model of the structure in order to identify the wave loads. In addition, the member forces in the support structure are estimated. Both the wave loads and member forces are estimated with a reasonable accuracy. The proposed methodology creates opportunities for operational monitoring of offshore wind turbines, hereby providing essential information to improve design guidelines for future wind turbines and allowing for a continuous fatigue assessment of the wind turbine during the operation.

Estimation of Wind Turbine Gearbox Loads for Online Fatigue Monitoring Using Inverse Methods

“…The first load estimation method is based on Kalman filtering, which has been widely studied [13,[15][16][17][18]21]. The Kalman Filter produces state estimates x of a system, that is governed by stochastic, linear state equations as formulated in Eq.…”

“…The most prominent applied methods in literature are Kalman filtering and least sqares estimators. Recent research has focused primarily on the identification of wind or wave loads on structural elements including aircraft [12], bridges [13], tall buildings [14][15][16] and wind turbine towers [17,18]. A few studies also worked on machine elements with multi-body dynamics such as railway vehicles [19,20], mining trucks [21] and diesel engines [22].…”

Experimental and numerical investigation of a jacket structure subject to steep and breaking regular waves

“…In order to identify the wave forcing levels directly from the dynamic response force measurements, it is necessary to filter the structural dynamics. Several methods have been proposed previously using either low pass filtering technique [8,27,28] or inverse force identification algorithms based on dynamic properties of the structure [24,29].…”

Vortex-induced vibration effect of extreme sea states over the structural dynamics of a scaled monopile offshore wind turbine

“…Also, the free surface (wave loading) aside from the structure was measured and did not consider wind loading and not reported the damping ratios of the rigid monopile. Maes et al (2018) analysed structural accelerations of a MWT under breaking wave loads. Wave elevations over the structure were measured and pointed out that they did not consider the hydrodynamic viscous effect because of the complexity of estimating the process.…”