bluuebunny/crossref_metadata_2025_split huggingface dataset:
Automatic detection and correction of aerodynamic and inertial rotor imbalances in wind turbine rotors
Authors: Bertelè M. , Bottasso C.L. 
Published: June 2022

Abstract
In this work, a novel rotor rebalancing algorithm is tested in a simulation environment to evaluate its performance when facing both aerodynamic and inertial imbalances. The algorithm, starting from a generic measurement collected on the wind turbine fixed frame, is capable of remotely minimizing once per revolution vibrations, avoiding the need for on-site inspections, and without requiring detailed information about the machine. Indeed, once access to the pitch system is granted, this algorithm simply iteratively computes the pitch angle that needs to be applied to each individual blade in order to rebalance the rotor.
Several turbulent time histories, with changing mean inflows, were simulated with the goal of testing the proposed method in realistic field conditions. Overall, the algorithm proved capable of significantly reducing the desired once per revolution vibrations in 3 to 4 iterations, irrespective of the imbalance root cause, its severity and its location. The method also appeared quite robust, showing that the found rebalanced configurations guarantee reduced vibrations no matter the machine operating point.
FLORIDyn - A dynamic and flexible framework for real-time wind farm control
Authors: Becker M , Allaerts D , van Wingerden J W 
Published: June 2022

Abstract
This paper presents a new framework of the FLOw Redirection and Induction Dynamics (FLORIDyn) model. It is able to dynamically simulate the wake behaviour in wind farms under heterogeneous and changing environmental conditions at a low computational cost. The novelty of this work is the improved segregation of wake dynamics and wake influence: the framework creates Observation Points (OPs) at each turbine, which propagate wind field states and turbine states downstream and follow the wind direction of the free stream velocity. These observation points cover the dynamic aspects of the simulation. The OPs, along with the stored states, are now used to derive so-called Temporary Wind Farms (TWF), which approximate the effective intra-farm wind conditions at a given location. Within these TWF, the flow conditions are homogeneous and steady state. This way, arbitrary wake models can be used to calculate the farm influence on the location. The FLORIDyn framework also provides interfaces to flow field estimators, which is tested with an effective wind speed estimator. A nine turbine case is used to highlight the quality and performance of the simulation result. Compared to its predecessor, the new FLORIDyn framework decreases the computational cost by one to two orders of magnitude, which makes it a promising candidate for real-time model predictive dynamic wind farm control.
Serial-Refine Method for Fast Wake-Steering Yaw Optimization
Authors: Fleming Paul A. , Stanley Andrew P. J. , Bay Christopher J. , King Jennifer , Simley Eric , Doekemeijer Bart M. , Mudafort Rafael 
Published: June 2022

Abstract
In this paper we present the Serial-Refine method for quickly finding the optimal yaw angles in wake steering. The method optimizes turbine angles serially from upstream to downstream using a small number of candidate angles. The presented results show that Serial-Refine finds solutions that are at least as good as former conventional optimization approaches but that require much less computation time.
Aeroservoelastic stability of a floating wind turbine
Authors: Vanelli T , Rinker J , Zalkind D S 
Published: June 2022

Abstract
The problem of negative damping undermines the aeroservoelastic stability of floating offshore wind turbines. The negative damping problem is most prevalent around rated wind speed, where the sensitivity of thrust to wind speed is the largest. This paper investigates the implementation of peak shaving, a controller feature that limits the rated thrust by pitching the blades before rated wind speed is reached. Two controller designs are investigated: a de-tuned controller and a nacelle-feedback controller. A time-domain metric is defined, inspired by Lyapunov theory, in order to compute and assess the stability of floating offshore wind turbines. The model of the International Energy Agency 15-MW reference wind turbine mounted on the University of Maine VolturnUS-S floater is simulated in HAWC2 with the National Renewable Energy Laboratory reference open-source controller. Peak shaving is applied to the two controller designs and stability is assessed. According to the chosen metric, peak shaving does not improve the stability of the system. This is due to the trade-off between loads and error tracking: although the loads and displacements in the fore-aft direction of the turbine are reduced, the rotor-speed tracking is poorer, which increases the shaft torsion fatigue load.
A novel Nonlinear Model Predictive Controller for Power Maximization on Floating Offshore Wind Turbines
Authors: Pustina Luca , Biral Francesco , Serafini Jacopo 
Published: June 2022

Abstract
Reducing the Levelized Cost of Energy is the main objective of wind turbine industry, in particular for the emerging sector of floating offshore turbines. In this work, a novel Economic Nonlinear Model Predictive Control (ENMPC) strategy is developed to maximize the power production of floating offshore wind turbines. The control problem is solved through an indirect method, which achieves the computational efficiency required to apply it in real world cases. A non-linear Reduced Order Model of the floating turbine predicts aerodynamic power, generator temperature and platform motions inside the controller. A set of constraints, including a bound on the generator temperature, the thrust and platform velocities are imposed. Simulations using the open-source engineering tool OpenFAST on the 5MW NREL wind turbine supported by the OC3 spar buoy platform [1] are performed to validate the turbine model and then to assess the controller performances in realistic wind and sea state conditions. With respect to the standard controller, a 4.3% increase of generated power in rated conditions is achieved with a more stable generator temperature.
A comprehensive code-to-code comparison study with the modified IEA15MW-UMaine Floating Wind Turbine for H2020 HIPERWIND project
Authors: Kim Taeseong , Natarajan Anand , Lovera Anaïs , Julan Emricka , Peyrard Christophe , Capaldo Matteo , Huwart Guillaume , Bozonnet Pauline , Guiton Martin 
Published: June 2022

Abstract
An extensive code-to-code comparison among DIEGO, DLW and HAWC2 has been performed on a floating wind turbine (modified version of UMaine floater with IEAWIND 15MW wind turbine). In total, 10 cases are compared, and a few key results of this comparison are reported in this paper. From the comparisons, it is clearly seen that the results predicted by the three codes are generally agreed well despite some differences in specific degrees of freedom like roll, sway and yaw for the extreme load case, which requires additional investigations.
Efficient multibody modeling of offshore wind turbines with flexible substructures
Authors: Steinacker Heiner , Lemmer Frank , Raach Steffen , Schlipf David , Cheng Po Wen 
Published: June 2022

Abstract
Offshore wind turbines, especially floating wind turbines, are often simulated assuming rigid substructures to obtain computationally efficient simulation models for preliminary parameter variation studies. This causes large errors in the determination of coupled natural frequencies and internal loads, particularly with increasing turbine sizes. Finite Element models for flexible substructures were developed by several researchers, often resulting in a high simulation effort. In this paper, a modally reduced Finite Element model, precomputed by the SubDyn module of OpenFAST, is directly included in the generalized Equation of Motion of the Simplified Low Order Wind turbine model SLOW. The approach was tested with the DTU10MW reference wind turbine mounted on a flexible monopile. It shows a high agreement with the former beam-based Multibody System in the calculated coupled natural frequencies and steady state results both for the linear and nonlinear model. A basis has been established to integrate flexible bodies of any shape even into computational efficient Multibody Systems of reduced order, such as SLOW, without coupling of two modules as in OpenFAST. This might improve numerical stability due to unified equations of motion.
Parametrisation Scheme for Multidisciplinary Design Analysis and Optimisation of a Floating Offshore Wind Turbine Substructure – OC3 5MW Case Study
Authors: Ojo Adebayo , Collu Maurizio , Coraddu Andrea 
Published: June 2022

Abstract
The development of novel energy technologies is considered imperative in the provision of solutions to meet an increasing global demand for clean energy. Floating Offshore Wind Turbine (FOWT) is one of the emerging technologies to exploit the vast wind resources available in deeper waters. To lower the levelized cost of energy (LCOE) or optimise the performance response associated with a FOWT system, a detailed understanding of the different disciplines (Aero-Hydro-Servo-Elastic) within the system and the relationship between the FOWT system and the dynamics of the marine environment is required. This requires an efficient Multidisciplinary Design, Analysis and Optimisation (MDAO) framework for FOWT systems to reduce the capital cost and increase dynamic performance. A key component of any MDAO framework is the shape parameterisation scheme, as it enables the modelling of a large array of platform designs with different geometric shapes using limited number of parameters. This work focuses on the B-Spline parameterisation modelling technique of OC3 spar-buoy and the use pattern search optimization algorithm to select the optimal design variants. The parametrisation technique is implemented in an analysis framework, where a B-spline library from Sesam GeniE is used to model each design representation, and a potential flow frequency domain analysis solver (HydroD/Wadam) is used for the hydrodynamic analysis. Validation of the selected designs within the design space is conducted with a benchmark NREL5MW spar-buoy hydrodynamic response results in literature with the hydrodynamic response of the frequency domain modelling approach using Sesam GeniE and HydroD/Wadam. This analysis process shows a high accuracy in response results between the OC3 spar-buoy in literature and the OC3 spar-buoy model design using B-Spline parametrization technique. Key performance metrics like the cost of materials and root mean square (RMS) of the nacelle acceleration also show improvement with the design variants compared to estimation from OC3 design in literature.
Validation of CFD determined hydrodynamic coefficients for a semisubmersible floating offshore wind turbine
Authors: Ramesh Reddy Likhitha , Milano Daniel , Walker John , Viré Axelle 
Published: June 2022

Abstract
The hydrodynamic characteristics are crucial for accurately analysing floating offshore wind systems. In this paper, the added mass and damping coefficients of a semisubmersible floater are examined around the natural periods of the surge, heave, and pitch motion, using computational fluid dynamics (CFD). The OpenFOAM CFD setup is validated against experimental measurements from the free decay tests, and the same setup is used to determine the hydrodynamic coefficients of the platform subjected to forced motions with different amplitudes and periods. The added mass and quadratic damping coefficients obtained from forced oscillations are consistent with the free decay results. Moreover, the added mass coefficients obtained by CFD is significantly higher than the estimations of the potential flow theory: around 10% larger for surge and 22% larger for heave. The damping is almost independent of the frequency while it varies with the motion amplitude. The deviations in the CFD results from the potential flow theory are due to the viscous effects. Besides, viscous damping is dependent on the drag coefficient specified in the Morison’s equation.
Cost-based mooring designs and a parametric study of bridles for a 15 MW spar-type floating offshore wind turbine
Authors: Pan Qi , Cheng Po Wen 
Published: June 2022

Abstract
This paper highlights a cost-based design method for feasible and cost-effective mooring configurations. A parametric study of mooring designs considering bridle impact is performed for a 15 MW spar-type floating offshore wind turbine (FOWT). This site-specific FOWT is based on the preliminary model from EU funded H2020 Project COREWIND. Without running numerical simulations, the cost-based design method generates 1443 mooring configurations with normalized costs ranging from 1.00 to 1.667. Six configurations with the lowest normalized costs are selected for OpenFAST simulations. The ultimate test results verify the structural strength of mooring configurations. Bridle designs cause significant impact on the ultimate mooring tensions and floater motions in surge, sway and yaw, which is clearly influenced by the mass ratio of a bridle to a mooring line. When the mass ratio decreases from 13% to 5%, peak mooring tensions increase by up to 17%. The influence of bridle designs on mooring tension fatigue is less prominent and the effect of mass ratio on mooring fatigue varies with wind speed. Near the rated wind speed, deviations in mooring fatigue loads are within 5% for all six configurations. This cost-based method promotes feasible and economical mooring designs. The parametric study of bridle designs provides solid support for optimal mooring designs of spar-type FOWTs.
A six degree-of-freedom set-up for wind tunnel testing of floating wind turbines
Authors: Messmer Thomas , Brigden Charles , Peinke Joachim , Hölling Michael 
Published: June 2022

Abstract
In this paper we present a six-degree-of-freedom (DoF) experimental set-up for wind tunnel testing of floating offshore wind turbines (FOWTs). The system is composed of a 6-DoF Stewart platform that can be used to mimic realistically the motions of a floating turbine at laboratory scale. The platform is specifically made for the Model Wind Turbine Oldenburg 0.6 (MoWiTO 0.6). First, the methodology followed to design the system as well as the scaling issues are depicted. Then, the characterisation of the platform is presented. Finally, limitations of the set-up are discussed.
An engineering modification to the blade element momentum method for floating wind turbines
Authors: Mancini Simone , Boorsma Koen , Caboni Marco , Hermans Koen , Savenije Feike 
Published: June 2022

Abstract
The design of next-generation offshore wind rotors for floating applications carries large uncertainties that make it harder to bring costs down. A significant share of this uncertainty is associated with the use of Blade Element Momentum (BEM) methods to run aeroelastic design and loadcase calculations, because the assumptions underlying the momentum theory are violated by the floater motion. This work presents an engineering method for BEM that allows to model generic floater motions and improves the aerodynamic modelling of floating wind turbines. The new model overcomes the challenge of estimating the apparent wind caused by the platform motion in a simple way, which proves to be very effective for rigid aerodynamic simulations. To verify its impact, BEM results with and without the proposed correction are compared to high-fidelity free vortex wake simulations, imposing the same harmonic motion first to the pitch and then to the yaw degree of freedom of the platform. While little differences are found for the yaw motion, the new floating model clearly improves predictions for the platform pitch case in terms of both aerodynamic loads and induction, finding a very good match with the high-fidelity results. An analysis of the verification data provides new valuable insights on the effect of these motions on aerodynamic loads and performance of a floating wind turbine.
Floating wind turbine control optimization
Authors: Zalkind Daniel , Abbas Nikhar J. , Jasa John , Wright Alan , Fleming Paul 
Published: June 2022

Abstract
We present a framework for optimizing the control parameters of floating offshore wind turbines (FOWTs). The framework combines aeroelastic simulations with a systems engineering model and control software. In an example of the optimization framework, we minimize tower damage equivalent loading with generator speed constraints. We also study the effect of thrust-limiting control and quantify the trade off between fatigue loading and energy capture using a set of optimal controller designs. Finally, we optimize the controller of four different FOWT models and compare their dynamic responses. Additional details and other use cases for the framework are presented, which can optimize different control problems and evaluate FOWT designs.
Wind field reconstruction using nacelle based lidar measurements for floating wind turbines
Authors: Gräfe Moritz , Pettas Vasilis , Cheng Po Wen 
Published: June 2022

AbstractIn this work we investigate the influence of floater motions on nacelle based lidar wind speed measurements. The analysis is focused on wind field characteristics which are most relevant for performance analysis, namely rotor effective wind speed, shear and turbulence intensity. A numerical approach, coupling the publicly available in-house lidar simulation framework ViConDAR (Virtual Constrained turbulence and liDAR measurements) with an aeroelastic floating offshore wind turbine simulation is employed. Synthetic turbulent wind fields are generated with the open source turbulence generator TurbSim. The dynamics of the floating offshore wind turbine are simulated in the aeroelastic simulation code OpenFAST. Turbine dynamics and the corresponding synthetic wind field are then passed to the lidar simulation module of ViConDAR, which has been adapted for the consideration of turbine dynamics in all six degrees of freedom to simulate the lidar measurements under influence of motion. The simulation framework is demonstrated in a case study, simulating a lidar system on the nacelle of the IEA 15 MW turbine in combination with the WindCrete floater concept. Two different realistic lidar patterns are investigated under different metocean conditions. Different motion cases are examined individually and combined to evaluate the influence of rotational and translational degrees of freedom. Results show an increase of mean absolute error between lidar estimated and full wind field rotor effective wind speed of 0 to 25% depending on the environmental conditions. Observed overestimation of mean rotor effective wind speed was found to be in the region of up to 1%.
Wind tunnel investigation of the wake-flow response for a floating turbine subjected to surge motion
Authors: Fontanella A. , Zasso A. , Belloli M. 
Published: June 2022

Abstract
Floating wind turbines undergo large translation motions allowed by the high compliancy of the support structure. Large motions affect the rotor aerodynamic response and wake. This paper examines wake measurements of a wind tunnel experiment with a scale model of the DTU 10MW subjected to imposed harmonic surge motion. The effect of surge motion on the wake is detected by means of spectral analysis of velocity data. It is found that when the rotor undergoes surge motion, periodic forcing is introduced into the fluid, which produces a harmonic variation of the wake speed. The velocity perturbation around the rotor is then convected downstream at about the average axial velocity in the wake. The amplitude of the velocity pulsation at 2.3D is radially-dependent, and is correlated to the amplitude of the variation of the normal-force distribution along the blade.
Stability information derived from a floating lidar system using bulk Richardson formulation
Authors: Hatfield Daniel , Gottschall Julia , Bay Hasager Charlotte 
Published: June 2022

Abstract
In this contribution we introduce a Fraunhofer IWES floating lidar system (FLS) equipped with an integrated pulsed lidar device, motion sensors, near-surface atmospheric variable sensors (air temperature, relative humidity and air pressure) and a sea-surface temperature sensor. All measures were compared and validated with the nearby offshore meteorological mast FINO3 in the German North Sea. Atmospheric stability information was derived using the bulk Richardson formulation from the FINO3 station at both 30-m and 100-m as well as at the FLS at a 2-m height. The stability parameter was then extrapolated to the higher heights from the FLS using the mean wind speed measured from the lidar. The FLS was able to recreate the stability conditions calculated at the 30-m height but could not effectively match that of the 100-m calculations. This is mainly attributed to the significant changes with height of the atmospheric variables and their importance in the stability calculations.
Dynamics of two floating wind turbines with shared anchor and mooring lines
Authors: Gözcü Ozan , Kontos Stavros , Bredmose Henrik 
Published: June 2022

Abstract
Floating wind farms present the opportunity to harvest wind resources located in deep water sites. Shared mooring designs can contribute in making floating wind energy more cost-competitive, and it is important to understand the new system dynamics that arise. We are presenting here HAWC2Farm, an extension of HAWC2 that can model multiple wind turbines with shared mooring lines. We apply the new modeling capabilities to simulate two 15 MW floating wind turbines on spar floaters with shared mooring lines. We consider two different sites and we identify and compare the natural frequencies and mode shapes of the shared mooring designs with those of an individual moored turbine. Furthermore, we investigate the influence of design parameters on the systems’ natural frequencies and we show that it is possible for a shared mooring design to achieve similar characteristics as a single turbine design. Finally, we test the response of the shared mooring design in steady wind and regular waves and find that the surge displacement of the upstream turbine and its mooring line loads are considerably larger compared to the single turbine case.
Axial induction control design for a field test at Lillgrund wind farm
Authors: Bossanyi Ervin , Ruisi Renzo , Larsen Gunner Chr. , Pedersen Mads Mølgaard 
Published: June 2022

Abstract
Lillgrund offshore wind farm near Copenhagen has been the subject of a number of research projects. The close turbine spacing makes it an interesting candidate for research into turbine wakes and wind farm control. As part of the EU TotalControl project, an axial induction controller has been designed for field testing at Lillgrund. The controller was designed using steady-state optimisations in DNV’s LongSim code, which predicted a small but significant power gain along with a considerable reduction in fatigue loading. Some simplifications were introduced for ease of practical implementation on this particular site; the controller was initially optimised to improve the power output of one 7-turbine row, with the aim of extending to the whole wind farm if the first test was successful. The expected power gain was confirmed by running realistic, detailed time-domain simulations in LongSim, and independently corroborated using steady-state calculations with DTU’s linear CFD code Fuga. The controller was implemented on site, and a toggle test was initiated on site in late December 2021, with the wind farm controller toggling between controlled and default states every 50 minutes. First results are expected early in 2022.