bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multiline Ring Anchor system for floating offshore wind turbines
Authors: Lee J , Aubeny C P 
Published: March 2020

Abstract
The trends in the offshore wind industry have shown floating offshore wind turbines (FOWTs) technology and installation in deep waters due to stronger, more consistent wind resources and mitigation of aesthetic issues. Nevertheless, the high capital cost of the support systems remains a primary obstacle. Thus, this study presents a novel, integrated, and networked multiline ring anchor (MRA) system for FOWTs that can provide significant capital cost savings. Other attractive features of the anchor include versatility in regard to the range of soil conditions in which it can be deployed, relatively high geotechnical efficiency, capability for precise positioning and a deep embedment which provides for robust performance under unintended torsional loading. A limited comparative study of the MRA to a suction caisson anchor in soft clay shows the MRA to be clearly more efficient under horizontal loading, but only a marginally better under vertical loading. Incorporating keying flaps in the design has promise for eliminating the latter performance issue.
Application of the New IEC International Design Standard for Offshore Wind Turbines to a Reference Site in the Massachusetts Offshore Wind Energy Area
Authors: Roach Samuel , Park Se Myung , Gaertner Evan , Manwell James , Lackner Matthew 
Published: March 2020

Abstract
The IEC 61400-3-1 standard for a fixed-bottom offshore wind turbine was applied through simulation of specified Design Load Cases. A metocean data set was assembled based on probability distributions of wind and wave data from a representative site in the Massachusetts Offshore Wind Energy Area. A reference turbine was attached to a monopile substructure created for simulation. FAST simulation outputs from feasible ultimate and fatigue loading design load cases are analyzed and discussed. The requirements of the standard are analyzed for the site-specific certification case. Results show importance of control system failure safety and of mitigation during electrical network loss. Hurricane loading is also discussed.
Process-based balance of system cost modeling for offshore wind power plants in the United States
Authors: Shields Matt , Nunemaker Jake 
Published: March 2020

Abstract
This paper describes the development of a process-based and open-source balance of system cost model that provides the capability to evaluate both existing and novel offshore wind technologies. Individual design and installation steps are represented with bottom-up engineering models that compute times and costs associated with the process; furthermore, operational constraints are assigned to each process so that delays caused by weather and presence of marine mammals may be accounted for in the overall project timeline. The model structure, assumptions, inputs, and results are vetted with industry partners and compared against actual projects for validation. Installation times show reasonable agreement with real data. Project cost sensitivities are investigated to compute the system-level impact of different design choices. First, individual vessel efficiencies are computed for varying numbers of installation vessels and weather time series to show the diminishing returns of more than two feeder barges. Then, array cable capital costs and installation times are determined for a representative project with different turbine sizes. These values quantify the cost-benefit tradeoffs and show a net-cost savings of decreasing numbers of turbines, increased turbine spacing, and fewer turbine terminations. These results demonstrate that the balance of system model features the accuracy, functionality, and accessibility to serve as the foundation for a wide range of analyses to identify cost reduction potentials for offshore wind energy in the United States.
Frequency-Dependent Aerodynamic Damping and Inertia in Linearized Dynamic Analysis of Floating Wind Turbines
Authors: S Souza Carlos Eduardo , Hegseth John Marius , Bachynski Erin E 
Published: March 2020

Abstract
In frequency-domain (FD) models of floating wind turbines (FWT), it is common to regard the interaction between nacelle motions and thrust by means of a constant aerodynamic damping coefficient. This approach is effective at higher motions frequencies, but does not consider interactions between nacelle motions and the blade pitch control system. As a result, the motions and loads at frequencies closer to the controller bandwidth may be underpredicted. A remedy for this problem is to include the linearized thrust expression in the FD model, such that the dynamic effects related to control are considered. In this paper, these dynamic effects are related to frequency-dependent damping and inertia terms. Expressions for damping and inertia coefficients are obtained with two different methods, and then included in the FD model. The resulting responses are compared to those obtained with the constant damping coefficient method, and also with coupled time-domain simulations of a semi-submersible 10 MW FWT. The better performance of the FD model with frequency-dependent inertia and damping coefficients encourages the adoption of the linearized thrust approach for representing the interaction between nacelle motions, thrust and control system.
A frequency domain analysis algorithm for predicting variance of quasi-static and dynamic wave-driven loads on a monopile-supported offshore wind turbine
Authors: Summerfield Andrew P , Myers Andrew T 
Published: March 2020

Abstract
The purpose of this work is to develop and validate a frequency domain analysis (FDA) algorithm to predict loads on a monopile-supported offshore wind turbine (OWT). FDA is faster than the time domain simulations that are conventionally used to perform structural analyses of OWTs. An FDA algorithm that could accurately predict loads would enable expedient design and assessment of risk for OWTs. The current work presents an FDA algorithm for predicting variance of wave-driven loads during the non-operational condition with validation from both simulated and measured data.
The Influence of Synthetic Mooring Line Stiffness Model Type on Global Floating Offshore Wind Turbine Performance
Authors: West W M , Goupee A J , Viselli A M , Dagher H J 
Published: March 2020

Abstract
Floating offshore wind turbines (FOWTs) over the past decade have been targeted as a solution to reducing dependence on fossil fuel. At this point the hulls of FOWTs have been a huge point of emphasis for the research community. FOWT mooring systems, however, have recently started to garner more attention. One solution that has gained traction to reduce cost is mooring the turbine with a synthetic mooring system as opposed to the traditional chain catenary system. Currently there is guidance provided for designing synthetic mooring systems, but it is more geared to the needs of the offshore oil and gas industry, and often leads to conservative designs. This work investigates the stiffness models recommended by the design guides and their influence on FOWT global response.
Wind turbine blade leading-edge erosion: laboratory experiments and image processing under an engaged learning experience
Authors: Barthelmie R.J. , Letson F.W. , Ahsan S.N. , Barbaria D.K. , Barrera C.S. , Crear A. , Dudley L.C.C. , Garell M. , La Spisa E.J. , Li S. , Mishr A. , Paranjape A.R. , Rambaran S. , Shah A. , Singh A. , Hu W. , Pryor S.C. 
Published: March 2020

Abstract
This paper reports results from an engaged learning activity conducted within an integrated, multi-scale, multi-disciplinary project focused on wind turbine blade leading edge erosion. Actions and outcomes of a series of engaged learning activities by undergraduate and graduate students undertaken in spring 2019 are reported. In designing and conducting the numerical and laboratory experiments, the students learnt and applied a range of practical skills from 3D printing to working in the wind tunnel, creating controlled images and image processing techniques. The student team also engaged in substantial professional development and educational outreach activities.
Reliability Analysis of Wind Turbine Blades Considering Lightning Strike
Authors: Hu W. , Zhao W. , Wang Y. , Liu Z. , Tan J. 
Published: March 2020

Abstract
Lightning strike damage accounts for a significant amount of wind turbines failure. An accurate evaluation of wind turbines’ reliability considering lightning strike is thus of critical importance. This research develops two novel lightning stepped leader models considering the stochastic properties and the branching geometry of lightning. In the framework of the reliability analysis of wind turbine blades, the finite element analyses including the two new leader models are conducted and then the electric field in the wind turbine blades are studied. The results show that the branched model adds extra increment of the electric field in the wind turbine blades which is more practical for the wind turbine lightning protection, wind farm siting, and operations and maintenance of wind farms.
Modelling Hail and Convective storms with WRF for Wind Energy Applications
Authors: Letson F , Shepherd T J , Barthelmie R J , Pryor S C 
Published: March 2020

AbstractHail events are relatively rare, but hailstones (solid ice ‘balls’ ranging in diameter from 6 mm (pea) to 110 mm (softball)) have the potential to damage the leading edge of wind turbine blades causing reduced aerodynamic efficiency. Thus, hail is an important component of wind turbine operating conditions. Until recently hail occurrence was poorly (and subjectively) reported, but deployment of dual-polarization RADAR at National Weather Service (NWS) sites across the USA has revolutionized our detection abilities. Implementation of new microphysics parameterizations for the Weather Research and Forecasting (WRF) model have also greatly enhanced model capabilities. Here we present an evaluation of the WRF simulation of hail relative data from the RADAR observations conducted as part of a project with the ultimate goal of quantifying leading edge erosion potential.
Experimental characterization of H-VAWT turbine for development of a digital twin
Authors: LeBlanc Bruce , Ferreira Carlos 
Published: March 2020

Abstract
A digital twin can be described as a digital replica of a physical asset. The use of such models is key to understanding complex loading phenomena experienced during testing of vertical axis wind turbines. Unsteady aerodynamic and structural effects such as dynamic stall and dynamically changing thrust and blade loading are difficult to predict with certainty. This leads to inefficient turbine designs or worse yet premature failures. Many of these phenomena can be better understood through scaled wind tunnel testing. The analysis of these test results is greatly improved by having a well calibrated digital twin model of the turbine. This paper discusses the methodologies used in the development of the model for a H style vertical axis wind turbine. This includes physical measurements of the as built system, updates to the models based upon experimental testing and a final correlation between test and model on a component by component as well as fully assembled system.
A Numerical Model for the Analysis of Leading-Edge Protection Tapes for Wind Turbine Blades
Authors: Major D , Palacios J , Maughmer M , Schmitz S 
Published: March 2020

Abstract
This paper presents results of a numerical study on the effect of a standard leading-edge protection (LEP) tape on the aerodynamics of a NACA 64-618 airfoil. Two numerical models are used in STAR-CCM+ to estimate the impact of LEP tapes on airfoil c
l
and c
d
. The objective is to determine which numerical model resolves the physical mechanisms responsible for the aerodynamic degradation observed with standard LEP tapes. Experimental c
d
data are collected for LEP tapes applied to the tip section of an utility-scale wind turbine blade for numerical validation. For a standard LEP tape, experiments indicate laminar-to-turbulent boundary-layer transition occurs at the LEP tape edge, resulting in a 62% increase in c
d
. To capture the boundary-layer transition at the LEP step, transition modeling is required in STAR-CCM+. This is an important finding as the mesh techniques developed in this work can be used for future LEP tape design to prevent early transition, thereby reducing the associated adverse impact on wind-turbine tip-section airfoil aerodynamics and annual energy production.
Aerodynamic Load Distribution and Wake Measurements on a Sub-scale Wind Turbine
Authors: Hassanzadeh Arash , Naughton Jonathan W. , LoTufo Julian , Hangan Horia 
Published: March 2020

Abstract
Wind tunnel testing of wind turbines is critical for better understanding the blade aerodynamics and wakes as well as for producing data necessary to validate computational models. In this work, a 2 m diameter wind turbine that was designed to produce a wake with characteristics similar to that of an industrial scale turbine was tested in a large wind tunnel environment. Unsteady inflow, unsteady blade load distribution, and instantaneous wake measurements were obtained to characterize wake development and near-wake behavior. The results showed that the measurement of both blade loading and wake properties facilitate understanding of the wake’s behavior, and the blade load distribution can be used to explain the near-wake structure. Tests covering a wider range of conditions would be valuable for validating simulations of wind turbine flows.
Development of thermal residual stresses during manufacture of wind turbine blades
Authors: Rosemeier M , Krimmer A , Antoniou A 
Published: March 2020

Abstract
Thermal residual stresses have a major impact on the bond line fatigue of wind turbine blades, which can initiate tunneling cracks in the adhesive layer of the bond lines early in the operational life of the blade. This work investigates the simulation accuracy for predicting thermal residual stresses within a thick bond line. The trailing-edge bond line strip of a 34 m blade was modeled with classical laminated plate theory (CLT) on the one hand and with finite element (FE) plate models of different fidelities on the other. For the model benchmark, the thermal residual stresses were on the basis of a thermal simulation. These develop during the cooling after a typical curing cycle of a wind turbine blade manufacturing process. It was found that the analytical model on the basis of CLT was in good agreement with the plate models of higher fidelity. Additionally, a full 3D FE blade model was used to calculate the shape distortion and the thermal residual stresses. It was found that the analytical model, which did not take into account effects stemming from the whole blade structure, underestimated the full 3D FE model.
Correlation of Planetary Bearing Outer Ring Creep and Gear Load Distribution in a Full-Size Wind Turbine
Authors: Schlüter Felix M. , Jacobs Georg , Bosse Dennis , Brügge Thilo , Schlegel Felix 
Published: March 2020

Abstract
In this work, bearing outer ring creep in the planetary gear of a gear wind turbine gearbox is investigated. So far, gear creep has only been investigated experimentally on very small bearings under simplified load conditions. This paper presents experimental measurement results from a full-size 2.75 MW wind turbine. The test were performed on a system test bench capable of applying loads in all six degrees of freedom at the rotor hub. The objectives of this investigation are to provoke and measure bearing outer ring creep and to identify correlations to the gear load distributions acting on the planetary gear. After a motivation, a literature overview on bearing ring creep is given. Influences on and occurrences of ring creep are described and the two mechanisms roller-induced creep and gear creep explained. Then, the test setup and the evaluated experiments are presented. The influence of torque, rotational speed and additional non-torque loads on gear load distribution and bearing outer ring creep is shown, discussed and put in relation to findings from literature. Key findings are that outer ring creep speed increases with global rotational speed and torque. Also, gear creep – acting in the opposite direction of roller-induced creep – was found at the generator-sided bearing ring for loads below 40% nominal torque. The planet gear load distributions with sun and ring gear were highly uneven and opposed to each other at low torques while leveling out at high torques due to the load-dependent deformations of sun gear, planet carrier and ring gear. The average gear load distribution over all ring gear positions showed to be influenced only by torque and to be independent of non-torque loads. In accordance, even extreme non-torque loads were found to not influence the creep behavior of the two planetary bearing outer rings.
Noise Propagation Calculations of a Wind Turbine in Complex Terrain
Authors: Sessarego Matias , Shen Wen Zhong 
Published: March 2020

Abstract
This paper describes numerical noise propagation calculations of a single wind turbine in complex terrain near a town in Central Denmark. The purpose of the work is to estimate the noise level at increasing distances from a single wind turbine and investigate the effect of complex terrain. Results indicate that time varying numerical noise propagation predictions of wind turbines in complex terrain can be achieved by using computational fluid dynamics via large-eddy simulation (LES) and the Technical University of Denmark’s noise propagation tool based on the parabolic equation. The wind turbine is modeled using the actuator line approach. The results from this project will have significant social, environmental, and economic impact, since accurate predictions of wind turbine noise propagation can be used to develop noise mitigation strategies to increase the public acceptance of wind energy.
Preliminary Introduction of a Free Vortex Wake Method Into OpenFAST
Authors: Shaler K. , Branlard E. , Platt A. , Jonkman J. 
Published: March 2020

AbstractIncreasing wind turbine size can have substantial economic benefits. However, increasing wind turbine turbine size requires the use of models that accurately capture the aerodynamic response to large deflections and nonstraight blade geometries. Additionally, the installation of offshore floating turbines requires turbine models that can handle large rotor motion. Free vortex wake (FVW) methods are capable of modeling this type of complex physics while remaining computationally tractable to perform the many simulations necessary for turbine design. In this work, a FVW model is added to the National Renewable Energy Laboratory engineering tool OpenFAST to allow for the aerodynamic modeling of highly flexible turbines along with the aero-hydro-servo-elastic response capabilities of OpenFAST. Code implementation is not complete and thus no results are presented. However, areas of potential modeling improvement are discussed, such as modifications to the circulation calculation and the need for different FVW input model specifications when high-thrust cases are being modeled.
Enhancement of Unsteady and 3D Aerodynamics Models using Machine Learning
Authors: Vijayakumar Ganesh , Yellapantula Shashank , Branlard Emmanuel , Ananthan Shreyas 
Published: March 2020

Abstract
Unsteady aerodynamics will be an important part of the floating wind turbines of the future operating under high shear across the rotor disk coupled with platform motion and atmospheric turbulence. We develop an unsteady aerodynamics and dynamic stall model using a long short-term memory variant of recurrent neural networks. The neural network model is trained using the oscillating airfoil data set from Ohio State University. The predictions from our machine learning (ML)-based model show good agreement with the experimental data and other state-of-the-art dynamic stall models for a wide range of airfoils, Reynolds numbers and reduced frequencies. In some cases the predictions are better than the Beddoes-Leishman model implementation in OpenFAST, when using the default coefficients. The ML-based model is also able to capture the key physics associated with dynamic stall, such as the precedence of moment stall before lift stall and cycle-to-cycle variations in the aerodynamic response. The new unsteady aerodynamics model is expected to improve prediction of fatigue loads for yaw-based wake-steering control scenarios in actuator-line and actuator-disc simulations of wind farms. Our methodology for training the ML-model provides a pathway for improving design level tools using high-fidelity computational fluid dynamics (CFD) simulations in the future.
How does inflow veer affect the veer of a wind-turbine wake?
Authors: Englberger Antonia , Lundquist Julie K. 
Published: March 2020

Abstract
Stably stratified flow conditions often exhibit wind veer, or a change of wind direction with height. When wind turbines experience this veered flow, the resulting wake structure tends to exhibit a stretching into an ellipsoid, rather than a symmetric shape or a curled shape. Observational studies suggest that the magnitude of wake veer is less than the veer of the inflow, whereas large-eddy simulations with actuator disk models and actuator line models suggest a range of relationships between inflow veer and wake veer. Here we present a series of large-eddy simulations with a range of veer shapes, a range of magnitudes of veer, a range of wind speeds, and both rotational directions of the wind-turbine rotor investigating the effect on the wake deflection angle. These results can guide the application of wake steering in stably stratified flow.
Wind Farm Layout Optimization with Loads Considerations
Authors: Stanley Andrew P. J. , King Jennifer , Ning Andrew 
Published: March 2020

Abstract
The objective of this paper is to improve the annual energy production of a wind farm by optimizing the layout of a wind farm, while considering fatigue loads on turbines. In this paper, the loads are estimated using the edgewise bending moment computed using CCBlade, a steady-state blade element momentum code. The edgewise bending moment is then used to calculate fatigue damage using Miner’s rule. The fatigue damage is used to constrain the layout optimization problem. We show that our method can predict blade root damage with similar trends to damage calculated with other methods, such as a complex, computationally expensive large-eddy simulation and unsteady aeroelastic code. We also optimize wind farm layouts and show that, for a simple problem with two wind directions and ten turbines, the fatigue damage can be constrained without sacrificing wind farm power production.
Improving LiDAR performance on complex terrain using CFD-based correction and direct-adjoint-loop optimization
Authors: Nabi S , Nishio N , Grover P , Matai R , Kajiyama Y , Kotake N , Kameyama S , Yoshiki W , Iida M 
Published: March 2020

Abstract
Naïve estimation of horizontal wind velocity over complex terrain using measurements from a single wind-LiDAR introduces a bias due to the assumption of uniform velocity in any horizontal plane. While Computational Fluid Dynamics (CFD)-based methods have been proposed for bias removal, there are several issues exist in the implantation. For instance, the upstream atmospheric boundary layer thickness or direction are unknown. Conventional CFD-based corrections use trial and error to estimate the bias. Such approaches not only become numerically intractable for complicated flows, e.g. when the number of unknowns is large, but they also suffer from the fact that there is no guarantee for optimality of the obtained results. We propose a direct-adjoint-loop (DAL) optimization based framework to estimate such unknown parameters in a systematic way. For the validation of the method, we performed an experimental study using DIABREZZA LiDAR on a complex terrain for two wind directions of northwesterly (NW) and southeasterly (SE). The slope error associated with linear regression improved from -0.09 to -0.02 for SE and from -0.09 to +0.04 for NW.