Operational Vibration-Based Response Estimation for Offshore Wind Lattice Structures

The design for fatigue for offshore wind turbine structures is characterized by uncertainty, resulting from both loading specifications and numerical modelling. At the same time, fatigue is a main design driver for this type of structures. This study presents a strategy to monitor the accumulated fatigue damage in real-time, employing a joint input-state estimation algorithm. Measuring the operational vibrations at well-chosen locations enables the estimation of strain responses at unmeasured locations. The estimation algorithm is applied to a wind turbine on a lattice support structure, for which the response estimates of the lattice members are based on measurements on the turbine tower only. This restriction follows from the difficulty to reliably and robustly measure at locations on the lattice structure. Artificial measurement data is generated with a full-order finite element model, while the strains are estimated with an erroneous reduced-order design model, after inclusion of measurement noise. The strain estimates show that the main frequency content can be captured relatively accurately, except for a small bias and some high frequency disturbance, corresponding to a weakly observable higher mode. This second aspect shows the importance of a trade-off between the accuracy of the reduced-order finite element model and the ill-conditioning of the observability matrix.

[1]  M. Muskulus,et al.  Design Optimization of Wind Turbine Support Structures — A Review , 2014 .

[2]  Spyros G. Voutsinas,et al.  STATE OF THE ART IN WIND TURBINE AERODYNAMICS AND AEROELASTICITY , 2006 .

[3]  G. Roeck,et al.  Design of sensor networks for instantaneous inversion of modally reduced order models in structural dynamics , 2015 .

[4]  Eliz-Mari Lourens.  Force Identification in Structural Dynamics (Krachtidentificatie in structuurdynamica) , 2012 .

[5]  M.L.A. Segeren.  Influence of a boatlanding and j-tubes on wave loads and wall thickness of the monopile support structure design , 2011 .

[6]  Jason Jonkman,et al.  Verification of aero‐elastic offshore wind turbine design codes under IEA Wind Task XXIII , 2014 .

[7]  John M. Harris,et al.  The nature of scour development and scour protection at offshore windfarm foundations. , 2011, Marine pollution bulletin.

[8]  Claus-Peter Fritzen,et al.  An Integrated SHM Approach for Offshore Wind Energy Plants , 2011 .

[9]  Costas Papadimitriou,et al.  Prediction of Fatigue Damage Accumulation in Metallic Structures by the Estimation of Strains from Operational Vibrations , 2012 .

[10]  Costas Papadimitriou,et al.  Joint input-response estimation for structural systems based on reduced-order models and vibration data from a limited number of sensors , 2012 .

[11]  M. B. Zaaijer,et al.  Foundation modelling to assess dynamic behaviour of offshore wind turbines , 2006 .

[12]  Bart De Moor,et al.  Unbiased minimum-variance input and state estimation for linear discrete-time systems with direct feedthrough , 2007, Autom..

[13]  W. E. De Vries,et al.  Final report WP 4.2: Support Structure Concepts for Deep Water Sites: Deliverable D4.2.8 (WP4: offshore foundations and support structures) , 2011 .

[14]  M. Shinozuka,et al.  Simulation of Stochastic Processes by Spectral Representation , 1991 .

[15]  Patrick Guillaume,et al.  Verification of Joint Input-State Estimation by In Situ Measurements on a Footbridge , 2013 .

[16]  J. Jonkman,et al.  Definition of a 5-MW Reference Wind Turbine for Offshore System Development , 2009 .

[17]  N. Jenkins,et al.  Wind Energy Handbook: Burton/Wind Energy Handbook , 2011 .

[18]  W. G. Versteijlen.  Estimation of the Vibration Decrement of an Offshore Wind Turbine Support Structure Caused by its Interaction with Soil , 2011 .

[19]  M. B. Zaayer,et al.  Hydrodynamic loading on offshore wind turbine support structures , 2008 .

[20]  Guido De Roeck,et al.  Verification of joint input-state estimation by means of a full scale experiment on a footbridge , 2016 .

[21]  M. Kühn.  Dynamics and design optimisation of offshore wind energy conversion systems , 2001 .

[22]  Andrei V. Metrikine,et al.  Analysis of the fatigue life of offshore wind turbine generators under combined ice- And aerodynamic loading , 2014 .

[23]  W. Marsden.  I and J , 2012 .

[24]  W. G. Versteijlen,et al.  Assessing the small-strain soil stiffness for offshore wind turbines based on in situ seismic measurements , 2014 .

[25]  Ervin Bossanyi,et al.  Wind Energy Handbook , 2001 .