OC5 Project Phase II: Validation of Global Loads of the DeepCwind Floating Semisubmersible Wind Turbine

This paper summarizes the findings from Phase II of the Offshore Code Comparison, Collaboration, Continued, with Correlation project. The project is run under the International Energy Agency Wind Research Task 30, and is focused on validating the tools used for modeling offshore wind systems through the comparison of simulated responses of select system designs to physical test data. Validation activities such as these lead to improvement of offshore wind modeling tools, which will enable the development of more innovative and cost-effective offshore wind designs. For Phase II of the project, numerical models of the DeepCwind floating semisubmersible wind system were validated using measurement data from a 1/50th-scale validation campaign performed at the Maritime Research Institute Netherlands offshore wave basin. Validation of the models was performed by comparing the calculated ultimate and fatigue loads for eight different wave-only and combined wind/wave test cases against the measured data, after calibration was performed using free-decay, wind-only, and wave-only tests. The results show a decent estimation of both the ultimate and fatigue loads for the simulated results, but with a fairly consistent underestimation in the tower and upwind mooring line loads that can be attributed to an underestimation of waveexcitation forces outside the linear wave-excitation region, and the presence of broadband frequency excitation in the experimental measurements from wind. Participant results showed varied agreement with the experimental measurements based on the modeling approach used. Modeling attributes that enabled better agreement included: the use of a dynamic mooring model; wave stretching, or some other hydrodynamic modeling approach that excites frequencies outside the linear wave region; nonlinear wave kinematics models; and unsteady aerodynamics models. Also, it was observed that a Morison-only hydrodynamic modeling approach could create excessive pitch excitation and resulting tower loads in some frequency bands.This work was supported by the U.S. Department of Energy under Contract No. DEAC36- 08GO28308 with the National Renewable Energy Laboratory. Some of the funding for the work was provided by the DOE Office of Energy Efficiency and Renewable Energy, Wind and Water Power Technologies Office

Simplified wake modelling for wind farm load prediction

publishedVersio

Simplified wake modelling for wind farm load prediction

publishedVersio

Simplified wake modelling for wind farm load prediction

This paper presents a simple numerical wind farm model, where pragmatic choices are made in the modelling of underlying physical processes, with the aim of making useful power production and wind turbine load estimates. The numerical model decomposes the wind farm, inspired by the approach of the dynamic wake meandering model (DWM), into simple sub-models for a single wake deficit (1D Gaussian), wake meandering (statistical), and wake added turbulence (eddy viscosity based). Particular attention is given to selecting a momentum conserving wake summation method, because of its critical role in coupling the influence of individual wakes. Results are presented to illustrate the influence that wake summation methods have on equilibrium velocity and power production in a row of turbines, for different inter-turbine spacing and inflow velocities. Comparisons against published data from the Lillgrund wind farm illustrate that the suggested modelling approach reproduces important trends observed in the field data

Impact of foundation modelling in offshore wind turbines: Comparison between simulations and field data

The design of Offshore Wind Turbines (OWTs) relies on integrated simulation tools capable of predicting the system dynamic characteristics and the coupled loads and responses. Despite allefforts to develop accurate integrated models, these often fail to reproduce the measured naturalfrequencies, partly due to the modelling of the foundation. Several foundation models and ca-libration approaches have been proposed and compared with small or large scale field tests,where only the soil and the foundation are included. However, there is a lack of more integralvalidation where the interaction between the foundation and the structure is taken into account.The paper investigates the impact of the foundation model and calibration approach on the si-mulated response of a monopile-based OWT installed in the North Sea by comparing simulationsand full-scale field data. The OWT structure and the environmental actions are implemented inthe aero-servo-hydro-elastic code 3DFloat. Two foundation models and two calibration ap-proaches are evaluated. The results indicate that, with a conceptually correct foundation modeland a realistic calibration, it is possible to match the measured natural frequency and predictaccurate fatigue loads. More accurate predicted loads will reduce uncertainties in the estimatedfatigue lifetime and therefore reduce risk in the designImpact of foundation modelling in offshore wind turbines: Comparison between simulations and field dataacceptedVersio

Dependence of wind turbine loads on inlet flow field

publishedVersio

Impact of foundation modelling in offshore wind turbines: Comparison between simulations and field data

The design of Offshore Wind Turbines (OWTs) relies on integrated simulation tools capable of predicting the system dynamic characteristics and the coupled loads and responses. Despite allefforts to develop accurate integrated models, these often fail to reproduce the measured naturalfrequencies, partly due to the modelling of the foundation. Several foundation models and ca-libration approaches have been proposed and compared with small or large scale field tests,where only the soil and the foundation are included. However, there is a lack of more integralvalidation where the interaction between the foundation and the structure is taken into account.The paper investigates the impact of the foundation model and calibration approach on the si-mulated response of a monopile-based OWT installed in the North Sea by comparing simulationsand full-scale field data. The OWT structure and the environmental actions are implemented inthe aero-servo-hydro-elastic code 3DFloat. Two foundation models and two calibration ap-proaches are evaluated. The results indicate that, with a conceptually correct foundation modeland a realistic calibration, it is possible to match the measured natural frequency and predictaccurate fatigue loads. More accurate predicted loads will reduce uncertainties in the estimatedfatigue lifetime and therefore reduce risk in the desig

Impact of foundation modelling in offshore wind turbines: Comparison between simulations and field data

The design of Offshore Wind Turbines (OWTs) relies on integrated simulation tools capable of predicting the system dynamic characteristics and the coupled loads and responses. Despite allefforts to develop accurate integrated models, these often fail to reproduce the measured naturalfrequencies, partly due to the modelling of the foundation. Several foundation models and ca-libration approaches have been proposed and compared with small or large scale field tests,where only the soil and the foundation are included. However, there is a lack of more integralvalidation where the interaction between the foundation and the structure is taken into account.The paper investigates the impact of the foundation model and calibration approach on the si-mulated response of a monopile-based OWT installed in the North Sea by comparing simulationsand full-scale field data. The OWT structure and the environmental actions are implemented inthe aero-servo-hydro-elastic code 3DFloat. Two foundation models and two calibration ap-proaches are evaluated. The results indicate that, with a conceptually correct foundation modeland a realistic calibration, it is possible to match the measured natural frequency and predictaccurate fatigue loads. More accurate predicted loads will reduce uncertainties in the estimatedfatigue lifetime and therefore reduce risk in the desig

Dependence of wind turbine loads on inlet flow field

In wind farm simulations, the inflow wind field plays a crucial role in the accuracy of both power production, structural load predictions and the turbulent wake development behind wind turbines. Three different inflow wind field generation techniques, namely the Mann model, a reduced order based model described herein and LES data, are used in this study to characterise the relation between the inflow and the structural response of the wind turbine. In addition, the wake development under different inflow conditions are studied. The turbulence statistics of the reduced-order model and the LES data are similar to each other while the Mann turbulence has different turbulence profiles and spectral characteristics. An in-house developed aeroelastic code, 3Dfloat, is used for structural response analysis. The differences between the inflow fields are mainly attributed to the turbulence intensity profiles, and differences in their spectral characteristics