Accurate and efficient modeling of complex offshore wind turbine support structures using augmented superelements

Abstract

Traditionally, wind turbine dynamics are analyzed using computationally efficient but geometrically coarse aeroelastic models. With ever larger offshore turbines being installed in deeper waters, the wind industry is gradually moving toward more complex foundation types such as jackets and tripods. Even the simplest models of such structures have many more degrees of freedom (DoFs) than the complete wind turbine model, leading to excessive computation times. To cope with this, we can employ reduced ‘superelement’ modeling of the support structure. However, since these structures are subjected to hydrodynamic loading at a large portion of their DoFs, traditional reduction methods fail to properly describe the response to this excitation. In this paper, we therefore propose to combine superelement modeling with the concept of modal truncation augmentation, which consists in extending the reduction basis by adding ‘residual vectors’. Furthermore, we use principal component analysis to find the predominant hydrodynamic loading on the support structure.A case study is performed on a reference wind turbine model on a jacket structure, revealing both the need for coupled dynamic analysis and the shortcomings of traditional superelement models for offshore support structures. Most importantly, this case study shows that the proposed augmented superelement approach allows to create very compact yet accurate models of the complex support structure, thereby enabling efficient integrated simulation of offshore wind turbines.Copyright © 2013 John Wiley & Sons, Ltd.

Dynamic Models for Load Calculation Procedures of Offshore Wind Turbine Support Structures: Overview, Assessment, and Outlook

“…In this method, fixed interface vibration modes are added to the Guyan reduction basis (10) in order to include the dynamic response of the internal DoFs. The reduction basis hence becomes:…”

“…Therefore we will reduce the model of the UpWind reference jacket design [6] using three different reduction methods, namely Guyan reduction [7], the Craig-Bampton method [8] and an augmented Craig-Bampton method [9,10]. Thereafter we will evaluate different methods for reconstructing the response of the jacket substructure from the results obtained with the reduced models.…”

Structural topology optimization of the transition piece for an offshore wind turbine with jacket foundation

“…Under the PalmgreneMiner linear damage accumulation hypothesis, the accumulated damage sum, D, from the fatigue strength calculation should not exceed the value D max , i.e. : (10) where N i is the tolerable number of stress cycles obtained from the relevant SeN curve for a constant stress range of value g M Ds i and g M is the partial safety factor for fatigue verification. Hence the accumulated damage D from a fatigue strength calculation is dependent on the material, type of loading and structural geometry.…”

“…Using the results coming from the time simulation, the final amount of damage was calculated by applying the PalmgreneMiner linear damage accumulation method (10). The damage evaluation was done by considering a typical service life of 20 years.…”

“…Simulating the dynamic response of an OWT mounted on a jacket foundation is a complex fluid-structure interaction problem where the waves and the large-scale wind blades cause bending moments on the support structure owing to the complicated aerodynamic loads and the nonlinear hydrodynamic forces acting on the structure [9,10]. Dynamic simulations of this complexity contain high levels of uncertainty [11e13] and are normally obtained from time-domain numerical coupled aero-servo-hydroelastic codes which have been validated for the design of OWTs, both in terms of the accuracy of the dynamic simulation and the predictability of a wide range of design cases for different support structures [14e19].…”