bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simulative investigation of the load propagation in a wind turbine drive train during a power converter fault
Authors: Röder Julian , Jacobs Georg , Duda Tobias , Bosse Dennis 
Published: September 2020

Abstract
Highly dynamic load situations in the drive train of wind turbines can occur during operation as a result of faults in the electrical grid or damage in electrical components. The dynamic loads can lead to damage or increased wear in the drive train components. At the Center for Wind Power Drives a wind turbine research nacelle has been set up in the course of a national project. Extensive experiments with this research nacelle have been conducted with the corresponding 4 MW test rig. Furthermore multi body simulation (MBS) models of the nacelle and the test rig have been developed and validated by experiments with load cases defined in the IEC 61400. Among other experiments, a test with a highly dynamic load situation in case of a power converter fault has been conducted. For that particular load case a power converter short-circuit has been emulated. This test’s results show significant high torque reversals inside the drivetrain. This paper focuses on the implementation of the measured dynamic torque excitation in the existing MBS model in order to investigate the calculated torque load propagation from the high speed side to the low speed side of the drive train. The MBS model delivers further insight into the torque load propagation by providing the torque on the intermediate speed shaft (IMS) which could not be measured on the test bench. It is shown that the highly dynamic torque ripple is filtered out mainly in the spur gear stage from the HSS to the IMS.
Why is the measured maximum lift in wind tunnels dependent on the measurement method?
Authors: Olsen A S , Sørensen N N , Bak C , Gaunaa M , Mikkelsen R , Fischer A , Beckerlee J , Ildvedsen S 
Published: September 2020

AbstractThe present study investigates the differences in the predicted lift for a wind tunnel model from either surface pressures or side wall pressures. The investigated model is the NACA63-418 tested in the Poul la Cour tunnel. The measurements are compared with previous conducted wind tunnel campaigns for a Reynolds number of 3E6. The 3D CFD model of the wind tunnel will be used for investigating details of the flow mechanisms, and to validate assumptions and findings from the experimental data. The CFD simulations show that when the flow is attached the lift based on the side wall pressures results in almost the same lift as calculated from the surface pressures. Around the maximum lift and in the stalled region the flow is not anymore 2D. For the NACA63-418 airfoil the lift based on the side wall pressures are generally highest. The CFD simulations confirm that the method used to predict the lift from the limited side wall pressure strips in the wind tunnel is applicable.
Implementation and Experimental Validation of a Dynamic Model of a 10 MW Nacelle Test Bench Load Application System
Authors: Siddiqui Muhammad Omer , Eich Norbert , Eustorgi Karin , Feja Paul 
Published: September 2020

Abstract
The 10 MW Dynamic Nacelle Testing Laboratory of Fraunhofer IWES provides a controlled environment for performing electrical and mechanical tests on a wind turbine nacelle. Apart from physical testing, system level simulations are another paradigm in the framework of nacelle testing. In this contribution, the development of a dynamic model of the load application system for the 10 MW nacelle test bench is presented. The test bench load application system controls are integrated in the model via co-simulation in Simulink. The model is evaluated using experimental results. By utilizing the modal strain recovery method, a direct comparison of the strain results of the model with the experimental results is achieved. Moreover, it is shown that the actual applied loads on the device under test can be estimated by analysing the strain readings. The developed model provides a platform for developing a high fidelity virtual nacelle test bench.
How much flow information can a turbine-mounted lidar capture?
Authors: Sekar Anantha Padmanabhan Kidambi , Rott Andreas , van Dooren Marijn Floris , Kühn Martin 
Published: September 2020

Abstract
Turbine-integrated lidar systems are capable of scanning the wind fields upstream of the turbine, opening up an opportunity to incorporate these measurements into the turbine itself. However, lidar measurements are always subject to uncertainties which are a result of the operating principle of the lidar. In this paper, we investigate and quantify the uncertainties associated with a turbine mounted “SpinnerLidar” in a high fidelity simulation framework. A sensitivity study is performed in order to investigate the effects of the spatio-temporal resolution, probe volume averaging and directional bias and recommendations are given for different lidar applications, e.g. turbulence research, load verification and control. It is seen that the SpinnerLidar in its current state is sufficient as a control input and for load verification studies especially capturing the rotational wind spectra very well. For estimating turbulence, it is better to operate the lidar at a much faster temporal sampling rate.
Impact of relative spacing of two adjacent vertical axis wind turbines on their aerodynamics
Authors: Sahebzadeh Sadra , Rezaeiha Abdolrahim , Montazeri Hamid 
Published: September 2020

Abstract
The impact of relative spacing on the individual and overall performance of two adjacent co-rotating Darrieus H-type VAWTs is investigated through high-fidelity URANS simulations, validated with experimental data. The simulations cover relative distances of 1.25d ≤ R ≤ 10d (d: turbine diameter) and relative angles of 0° ≤ Φ ≤ 90°. The relative angles of 30° ≤ Φ ≤ 75 with relative distance range of 1.25d ≤ R ≤ 5d are identified as the optimal regime with the highest overall power performance for the array. In this regime, the downstream turbine has a maximum increase of 5.1% in CP (R = 1.5d and Φ = 45°) with respect to an isolated solo rotor with similar characteristics. Local flow characteristics including wake length, wake expansion, vorticity and velocity fields are also investigated. It is found that for azimuthal angles of 90° ≤ θ ≤ 160° in the optimal regime, regions of accelerated flow are created due to the contraction of the flow between the turbines which benefit the downstream turbine CP and thus the overall power performance of the array. This provides an opportunity for a compact placement of turbines within a vertical-axis wind turbine farm and consequently increasing the farm power density.
Aerodynamic performance and blockage investigation of a cambered multi-bladed windmill
Authors: John Itoje H , Vaz Jerson R P , Wood David 
Published: September 2020

Abstract
Windmills for water pumping typically operate at low speed and high torque owing to their multi-bladed nature. This, however, complicates the rotor aerodynamic behavior due to the mutual interaction between adjacent blades and low Reynolds number, Re, operation. While studies on their aerodynamic performance indicate that increasing blade number, N, and airfoil type are critical analysis and design parameters, its low Re behavior with cambered airfoils appears complicated and is still poorly understood. Accordingly, the performance of a windmill model of diameter 0.68 m with 3 ≤ N ≤ 24 identical blades was investigated in two open jet wind tunnels, with different test section sizes: one with high blockage of 36.3 % and the other with a negligible blockage of 4.5 %, for comparison with Blade Element Theory (BET) predictions of thrust, torque, and power. It was found that BET is accurate except at low tip speed ratios, λ where it under-predicts the torque primarily because of the high solidity at high N. Furthermore, the study reveals that high blockage impacts significantly on rotor performance and is a function of N. Overall, the experiment gave a better performance, highlighting the importance of accounting for solidity in aerodynamic performance prediction.
Assessment of sensitivity and accuracy of BEM-based aeroelastic models on wind turbine load predictions
Authors: Caboni M. , Carrion M. , Rodriguez C. , Schepers G. , Boorsma K. , Sanderse B. 
Published: September 2020

Abstract
The general goal of the work reported in this paper is to gain more confidence when performing blade element momentum (BEM)-based aeroelastic simulations, especially when setting-up sub-models and their parameters. Due to limited or no information, the set-up of these methods is often highly uncertain. To achieve this objective, we have developed and used methodologies to perform the analysis of model uncertainty in wind turbine aeroelastic simulations, while assessing their accuracy. This paper presents an example where these methodologies have been applied to a) the different aerodynamic models used in BEM-based aeroelastic tools to account for unsteady airfoil aerodynamics (UAA) and b) key parameters used in one of these models (Beddoes-Leishman). The accuracy of the simulations is assessed by comparing the simulated unsteady loads with measurements from the DAN-AERO MW experiments. One of the main achievements of this work is the ability to assess the uncertainty in load predictions that derives from the uncertainty related to the UAA models and their constants. The study on the sensitivity of the parameters was performed using Sobol indices and showed that for the case under study the normal force standard deviation at outboard blade locations is mostly sensitive to the Beddoes-Leishman model’s vortex shedding time constant.
Simplified design criteria for drivetrains in direct-drive wind turbines
Authors: Lüdecke F D , Cheng P W 
Published: September 2020

Abstract
Nominal power of wind turbines constantly increases. This goes along with an increase of the generator size, usually accompanied with an increase in mass. To limit at the same time the tower top mass, the mass increase of the generator needs to be restricted. Changing the design concept of the generator to reduce mass, influences its modal behavior and thereby possibly the dynamics of the whole drivetrain. This work identifies simplified criteria for the parameter space restrictions of drivetrain designs, while taking into account the interaction of the generator electromagnetic and structural characteristics. The drivetrain is analysed as an integrated system using a simplified two mass model to evaluate the dependency of system parameters and system stability. For two degrees of freedom an analytical solution is determined. Increasing the number of degrees of freedom to four, the parameter study is carried out using a full factorial analysis and a numerical solution approach. The results point out the necessity to take into account magnetic stiffness when designing the drivetrain to ensure system stability.
Piecewise linear aeroelastic rotor-tower models for efficient wind turbine simulations
Authors: Macquart T , Scott S , Weaver P M , Pirrera A 
Published: September 2020

Abstract
The development of software and methodologies able to efficiently and accurately predict the aeroelastic performance of wind turbines at low computational cost — enabling the rapid turnaround of novel concepts — is key to further reducing the levelised cost of energy. However, even the conventional low fidelity methods used for preliminary blade and rotor design are computationally expensive. The authors propose to improve the computational efficiency of dynamic aeroelastic time domain simulations by substituting conventional models with a piecewise linear aeroelastic rotor-tower model. This novel piecewise linear model is described and compared against standard modelling tools in this paper. Results suggest that piecewise linear rotor-tower models can be used to accurately capture the aeroelastic dynamic of wind turbine blades, with a significant (5 – 20×) reduction in computational costs.
Feasibility study for the use of hydrodynamic plain bearings with balancing support characteristics as main bearing in wind turbines
Authors: Rolink Amadeus , Schröder Tim , Jacobs Georg , Bosse Dennis , Hölzl Johannes , Bergmann Philipp 
Published: September 2020

Abstract
The failure of a wind turbine’s main bearing leads to high maintenance costs which affects the economic competitiveness of wind energy as renewable energy source. Therefore, research is conducted to replace today’s used roller bearings by plain bearings. These can be designed segmented so that in case of a failure the segments can easily be exchanged on tower. As part of a former research project a 1 MW plain bearing with conical sliding surfaces was developed and tested on a full-scale system test bench. This contribution presents a methodology how this concept can be developed further and optimized to design a bearing in 3-point suspension or a moment bearing for high power classes.
Leading edge erosion of wind turbine blades: Effects of blade surface curvature on rain droplet impingement kinematics
Authors: Verma Amrit S. , Castro Saullo G.P. , Jiang Zhiyu , Hu Weifei , Teuwen Julie J.E. 
Published: September 2020

Abstract
The issue of leading edge erosion (LEE) of wind turbine blades (WTBs) is a complex problem that reduces the aerodynamic efficiency of blades, and affects the overall cost of energy. Several research efforts are being made at the moment to counter erosion of WTBs such as-testing of advanced coating materials together with development of high-fidelity computational models. However, the majority of these studies assume the coated surfaces as flat, while the surface curvature and the shape of the aerofoil at the blade’s leading-edge exposed to such rain fields is neglected. The present study questions the assumption of a flat surface, in the context of LEE of WTBs, and provides guidelines for erosion modelling. The critical parameters associated with rain droplet impingement kinematics on leading edge are compared for blade impact with (a) flat surface assumptions together with (b) the effects of the blade’s surface curvature. A parametric study is performed which includes WTBs of varying sizes and power ratings ranging from 750 KW to 10 MW, different positions along the blade length, and different rain droplet radii ranging from 0.1 mm to 5 mm for a land based wind turbine operating at rated wind speed. It is found in the study that droplet impingement kinematics are influenced by the surface curvature at the leading edge, the effect of which is significant for representing erosion at the blade tip for smaller blades, and for exposure to rainfall intensity with larger rain droplet size. A master curve describing the threshold level along the blade length is established for various WTBs and rainfall conditions, where flat surface approximation of the surface yields noticeable error and violates the impingement process. The results of the study are expected to aid the modeller in developing advanced numerical models for LEE for WTBs.
On Down-Scaled Modelling of Wind Turbine Drivetrains
Authors: Rebouças Geraldo F. de S. , Nejad Amir R. 
Published: September 2020

Abstract
Gearbox testing is an important and complex task that will become even more challenging as the wind industry moves towards ever-growing turbines. The burden of this task can be decreased by using reduced-scale models with similar characteristics as its industrial-scale equivalent. This work presents a step-by-step procedure to down-scale a gearbox to different fractions of its rated power while preserving its core properties: structural safety and frequency distribution. The parameters to be scaled are sub-divided according to their relation to the system’s integrity and dynamic behavior. After performing an overall scaling, it is possible to fine-tune the scaling factors, according to the user precision requirements. Simulations show that it is possible to down-scale a gearbox to 0.01 % of its rated power while having less than 10 % relative deviation on its pitting safety factor. These preliminary results show that wind turbine drivetrain testing can become more affordable by using down-scaled models in a structured manner.
Design of direct-drive wind turbine electrical generator structures using topology optimization techniques
Authors: Jaen-Sola P , Donald A S Mc , Oterkus E 
Published: September 2020

Abstract
Reducing the structural mass of low speed multi-MW electrical machines for renewable energy purposes have become an important object of study as with the drop in mass a substantial decrease in the machine capital cost can be achieved. Direct-drive wind turbine electrical generators need very robust and heavy supporting structures able to cope with the demanding requirements imposed by the environment and the forces and moments transmitted by the wind turbine rotor in order to maintain the air-gap clearance open and stable. It is estimated that at least 2/3 of the total machine mass corresponds to the supporting structure. The main aim of this investigation is to minimize the structural mass of a 3 MW direct-drive wind turbine permanent magnet electrical generator, which dimensions have been previously optimized, making use of topology optimization techniques. Easy to manufacture structures made of cast iron capable of complying with the requirements were generated for both rotor and stator.
Cross-comparative analysis of loads and power of pitching floating offshore wind turbine rotors using frequency-domain Navier-Stokes CFD and blade element momentum theory
Authors: Ortolani A. , Persico G. , Drofelnik J. , Jackson A. , Campobasso M.S. 
Published: September 2020

Abstract
Reliable predictions of the aero-and hydrodynamic loads acting on floating offshore wind turbines are paramount for assessing fatigue life, designing load and power control systems, and ensuring the overall system stability at all operating conditions. However, significant uncertainty affecting both predictions still exists. This study presents a cross-comparative analysis of the predictions of the aerodynamic loads and power of floating wind turbine rotors using a validated frequency-domain Navier-Stokes Computational Fluid Dynamics solver, and a state-of-the-art Blade Element Momentum theory code. The considered test case is the National Renewable Energy Laboratory 5 MW turbine, assumed to be mounted on a semi-submersible platform. The rotor load and power response at different pitching regimes is assessed and compared using both the high-and low-fidelity methods. The overall qualitative agreement of the two prediction sets is found to be excellent in all cases. At a quantitative level, the high-and low-fidelity predictions of both the mean rotor thrust and the blade out-of-plane bending moments differ by about 1 percent, whereas those of the mean rotor power differ by about 6 percent. Part of these differences at high pitching amplitude appear to depend on differences in dynamic stall predictions of the approaches.
Modelling of a wind-wave floating and semi-submersible power plant
Authors: Voltá Laura , Roqueta I , Thomas Sarah , Schmidt Paulsen Uwe 
Published: September 2020

Abstract
This paper exposes a method of modelling and analysis to help verifying design iterations of non-cylindrical shaped floating wind technologies. In order to do so, the Morison based quadratic hydrodynamic drag forcing contribution within the HAWC2-WAMIT coupled model, is modified to account for a panel-based input geometry. The implementation is applied to the P80 platform, and a verification of the hydrodynamic responses is performed. A reduced load case analysis is carried out, in which floating wind technologies can be assessed efficiently during early stage design iterations. The final platform assessment includes the wind and wave coupled effect using three load cases from IEC 61400-3 standards. The results of the simulations show that the chosen cases provide significant information relating to the platform motions and the tower top acceleration, in order to provide feedback for later design iterations of the platform.
A Comparison of Soil Structure Interaction Models for Dynamic Analysis of Offshore Wind Turbines
Authors: Fitzgerald Breiffni , Igoe David , Sarkar Saptarshi 
Published: September 2020

Abstract
This paper compares the dynamic response of an OWT structure where the below ground pile-soil behaviour is modelled using (i) the conventional API ‘p-y’ approach and (ii) the ‘PISA’ approach. A nonlinear aero-elastic code is used to model the structural dynamics of the OWT and coupled to the geotechnical model. The dynamic behaviour (natural frequencies) and fatigue loads of the turbine tower and monopile are estimated and compared using both the API and PISA approaches. A limited number of load cases were considered in the dynamic analysis with varied met-ocean conditions. It was found that the stiffer springs estimated by the PISA approach reduce the mean displacement of the tower in both the fore-aft and side-to-side directions. However, the increased monopile stiffness leads to a slightly increased amplitude of oscillations, particularly in the lightly damped side-to-side direction.
Predicting the occurrence of the vortex ring state for floating offshore wind turbines
Authors: Dong Jing , Viré Axelle 
Published: September 2020

Abstract
The local aerodynamic loading on floating offshore wind turbines (FOWTs) is more complex than on bottom-fixed wind turbines due to the platform motions. In particular, the FOWT rotor may start to interact with its own wake and enter a so-called vortex ring state (VRS). However, it is still unclear when, and to what extent, the VRS may happen to floating offshore wind turbines. In this paper, we quantitatively predict the VRS using Wolkovitch’s criterion during the operating conditions of different FOWTs simulated by FAST. The results show that the type of floating foundation has a significant influence on the aerodynamic performance of the rotor. Also, the probability of occurrence of VRS is bigger for the floating platforms that are more sensitive to wave excitations.
Wind turbine stability: Comparison of state-of-the-art aeroelastic simulation tools
Authors: Hach O , Verdonck H , Polman J D , Balzani C , Müller S , Rieke J , Hennings H 
Published: September 2020

Abstract
As rotor diameters and blade flexibility are increasing, current and future generation wind turbines are more susceptible to aeroelastic instabilities. It is thus important to know the prediction capabilities of state-of-the-art simulation tools in regards of the onset of aeroelastic instability. This article presents results of a code-to-code comparison of five different simulation codes using a representative wind turbine model. It is shown that the models are in good agreement in terms of isolated structural dynamics and steady state aeroelastics. The more complex the test cases become, the more significant are the differences in the results. In the final step of comparison, the aeroelastic stability limit is determined through a run-away analysis. The instability onset is predicted at different wind speeds and the underlying mechanisms differ between the tools. A Campbell diagram is used to correlate the findings of time domain simulation tools with those of a linear analysis in the frequency domain.