bluuebunny/crossref_metadata_2025 huggingface dataset:
Language policy and planning in Nigeria
Authors: Okwudilichukwu Ugwu Eucharia
Published: March 2020

Language planning and policy has been a recurring topic among Nigerian educators. Although the Nigerian National Policy on Education stipulates multilingual education, such provision has remained an object of criticism, rejection, and is therefore not implemented. While some of the issues often raised as hindering its implementation are well-founded, there is also a lack of political will to champion the course of language planning and policy implementation. Meanwhile the government’s intention has been to make the policy receive public acceptance; yet, it has failed to address some of the recurring problems that hinder the achievement of such goal, to the detriment of both the educational and public sectors. This article looks at the dynamics of language planning and policy in Nigeria and why the government must match her rhetoric with action by paying attention to the major issues that hinder the realisation of multilingual education in the country to enhance development.
The orthography of revived Cornish as an attempt at pluricentricity
Authors: Davies-Deacon Merryn
Published: March 2020

After over twenty years of debate over Cornish orthographies, recognition by the UK government according to the
European Charter for Regional or Minority Languages in 2003 led to the creation of what was initially intended as a “single
written form” for use in official contexts. However, the inevitable impossibility of finding a compromise that pleased opposing
groups of speakers with differing ideologies meant that the eventual Standard Written Form (SWF) was
pluricentric, comprising two “main forms”. While these were initially stated to be of equal status, this has been hard to maintain
since the SWF’s implementation: with more speakers using Middle Cornish forms, the Late Cornish forms are less visible and
commonly believed to be subsidiary. Drawing on such perceptions, along with learning materials and other resources, this paper
examines the status of the SWF today and offers some reflections on this unsuccessful attempt at pluricentricity in a minoritised
language.
The microstructures and tensile properties of aged Fe-xMn-8Al-0.8C low-density steels
Authors: Han Dong , Ding Hua , Liu Degang
Published: March 2020

The microstructural evolution and deformation behaviour of Fe-(13, 16, 18)Mn-8Al-0.8C (wt-%) low-density steels were investigated in the present work. During aging treatment, the increase in the volume fraction of κ’-carbides significantly improved the yield strength. The formation of κ/α lamellae increased the strain hardening rate. However, large fractions of intergranular κ-carbides deteriorated the ductility of the materials. Mn element stabilised austenite, restricted the precipitation of intergranular κ-carbides and delayed the formation of intragranular κ’-carbides, leading to the uniform distribution of the strain. Increasing Mn content also postponed the peak aging. A good balance of strength and ductility can be achieved by short-time aging treatment in the low-Mn steels or long-time aging treatment in the high-Mn steels.
Attention, working‐memory control, working‐memory capacity, and sport performance: The moderating role of athletic expertise
Authors: Vaughan Robert S. , Laborde Sylvain
Published: March 2020

The aim of this research was to detangle the association between attention, working‐memory (focusing on both control and capacity functions), and sport performance across athletic expertise. Specifically, the mediating effect of working‐memory‐control and working‐memory‐capacity on the attention and performance relationship will be investigated, and whether this effect differs across athlete expertise. A sample of 359 athletes (M age = 18.91 ± SD = 1.01; 54.87% male) with a range of athletic expertise (novice n = 99, amateur n = 92, elite n = 87, and super‐elite n = 81) completed a battery of neurocognitive tasks assessing attention, working‐memory‐control, working‐memory‐capacity, and a cognitively engaging motor task (e.g. basketball free‐throw task). Athletes with more expertise performed better on tasks of attention, working‐memory‐control and working‐memory‐capacity. Results of structural equation modelling indicated a positive association between the cognitive measures and sport performance. Specifically, working‐memory‐control and working‐memory‐capacity mediated the attention and sport performance relationship. Additionally, invariance testing indicated larger effects for those with more athletic expertise. These findings provide a better understanding of how attention and the control and capacity functions of working‐memory interact to predict performance. Theoretical and practical implications of these results are discussed.
Citrullination regulates wound responses and tissue regeneration in zebrafish
Authors: Golenberg Netta , Squirrell Jayne M. , Bennin David A. , Rindy Julie , Pistono Paige E. , Eliceiri Kevin W. , Shelef Miriam A. , Kang Junsu , Huttenlocher Anna
Published: March 2020

Calcium is an important early signal in wound healing, yet how these early signals promote regeneration remains unclear. Peptidylarginine deiminases (PADs), a family of calcium-dependent enzymes, catalyze citrullination, a post-translational modification that alters protein function and has been implicated in autoimmune diseases. We generated a mutation in the single zebrafish ancestral pad gene, padi2, that results in a loss of detectable calcium-dependent citrullination. The mutants exhibit impaired resolution of inflammation and regeneration after caudal fin transection. We identified a new subpopulation of cells displaying citrullinated histones within the notochord bead following tissue injury. Citrullination of histones in this region was absent, and wound-induced proliferation was perturbed in Padi2-deficient larvae. Taken together, our results show that Padi2 is required for the citrullination of histones within a group of cells in the notochord bead and for promoting wound-induced proliferation required for efficient regeneration. These findings identify Padi2 as a potential intermediary between early calcium signaling and subsequent tissue regeneration.
Novel tools and observables for jet physics in heavy-ion collisions
Authors: Andrews Harry Arthur , Apolinario Liliana , Bertens Redmer Alexander , Bierlich Christian , Cacciari Matteo , Chen Yi , Chien Yang-Ting , Mendez Leticia Cunqueiro , Deak Michal , d’Enterria David , Dominguez Fabio , Harris Philip Coleman , Kutak Krzysztof , Lee Yen-Jie , Mehtar-Tani Yacine , Mulligan James , Nguyen Matthew , Ning-Bo Chang , Perepelitsa Dennis , Salam Gavin , Spousta Martin , Milhano José Guilherme , Tywoniuk Konrad , Van Leeuwen Marco , Verweij Marta , Vila Victor , Wiedemann Urs A , Zapp Korinna C
Published: March 2020

Studies of fully-reconstructed jets in heavy-ion collisions aim at extracting thermodynamical and transport properties of hot and dense QCD matter. Recently, a plethora of new jet substructure observables have been theoretically and experimentally developed that provide novel precise insights on the modifications of the parton radiation pattern induced by a QCD medium. This report, summarizing the main lines of discussion at the 5th Heavy Ion Jet Workshop and CERN TH institute ‘Novel tools and observables for jet physics in heavy-ion collisions’ in 2017, presents a first attempt at outlining a strategy for isolating and identifying the relevant physical processes that are responsible for the observed medium-induced jet modifications. These studies combine theory insights, based on the Lund parton splitting map, with sophisticated jet reconstruction techniques, including grooming and background subtraction algorithms.
On the Controllability of a Floating Offshore Wind Turbine
Authors: Abbas Nikhar J. , Pao Lucy
Published: March 2020

An analytical method for assessing the controllability of floating offshore wind turbines (FOWTs) is presented in this work. Modern linear control theory principles are applied to linearized FOWT models to establish quantifiable metrics to determine advantageous, or disadvantageous, differences in turbine models from a controls perspective. One use of such a metric is to consider the amount of work necessary to move a floating turbine back to an equilibrium point. We use a simplified point-mass model to demonstrate this idea. The idea is then translated to the DTU 10MW wind turbine on floating semi-submersible platforms. This work concludes with a discussion of the many potential uses for the quantifiable values associated with controllability within the wind turbine research space.
Numerical design of a wind observer and feedforward control of wind turbines
Authors: Taruffi F , Fontanella A , Muggiasca S , Di Carlo S , Belloli M
Published: March 2020

Wind speed is an unknown variable that is very difficult to measure relying on instruments that are commonly present on-board the wind turbine nacelle. The alternative to this approach is to extract a wind speed estimate from other measured quantities. The so-obtained wind speed could then be integrated in common power control algorithms as an additional scheduling variable or it can be exploited to realize feedforward actions to enhance the machine power capture and fatigue life. This work deals with the design of an observer to estimate the spatially-averaged wind speed on the rotor swept area. A linear model of the wind turbine drivetrain based on steady aerodynamics is introduced and used as the base for the wind speed observer. The observer is implemented on the DTU 10MW RWT and a feedforward action based on the estimated effective wind speed is added to the standard feedback controller. FAST co-simulations are performed to evaluate the performances of the implemented system in several wind turbine operating conditions. Its responsiveness is shown to be greater when operating in presence of above-rated winds due to the higher rotor aerodynamic sensitivity. The observer response is instead slower in below-rated winds, where its capability of predicting high-frequency wind gusts is limited by the combination of rotor inertia and generator torque control.
Highlighting the impact of yaw control by parsing atmospheric conditions based on total variation
Authors: Hamilton Nicholas
Published: March 2020

Identification of atmospheric conditions within a multivariate atmospheric dataset is a necessary step in the validation of wind plant control strategies. Most often, operating conditions are characterized in terms of aggregated observations and assume that the atmosphere is ‘quasi-steady’. Aggregation of observations without regard to covariance between time series discounts the dynamical nature of the atmosphere and is not sufficiently representative of wind plant operating conditions. Identification and characterization of continuous time periods with atmospheric conditions that have a high value for analysis or simulation sets the stage for more advanced model validation and the development of real-time control and operation strategies. Controlling observational data for statistical stationarity highlights significant enhancements to the power production of waked turbines under wake steering wind plant control. Results in the current study emphasize the scope and intended range of wake models used for wind plant control and suggest that either models be defined to account for the transient nature of the atmosphere, or that their validation and application be geared to stationary atmospheric conditions.
Effective wind speed estimation for wind turbines in down-regulation
Authors: Hou Lio Alan Wai , Meng Fanzhong
Published: March 2020

The use of state estimation technique offers a means of estimating the effective wind speed based solely upon the measurements of the turbine. Such wind speed estimations are crucial for turbines to calculate the reserved power for ancillary services. Nonetheless, the system observability or the possibility of estimating the wind speed is influenced by various down-regulation strategies. Thus, this paper investigates the system observabilities of turbines in different down-regulating conditions via the use of the empirical observability Gramian. In addition, wind speed estimators are constructed for each control strategy using an extended Kalman filter approach. Subsequently, each estimation performance is evaluated from the assessments of the Gramians and high-fidelity turbine simulations. The results reveal that it is more difficult to reconstruct the wind estimate from measurements of the turbine operating in torque-based than rotor-speed-based down-regulation strategies.
Field Validation of Wake Steering Control with Wind Direction Variability
Authors: Simley Eric , Fleming Paul , King Jennifer
Published: March 2020

Wake steering is a wind farm control strategy wherein upstream turbines are misaligned with the wind direction to redirect their wakes away from downstream turbines, increasing overall wind plant power. Wake steering is often analyzed assuming steady mean wind directions across the wind farm. However, in practice, the wind direction varies considerably over time because of large-scale weather phenomena. Wind direction variability causes the increase in power production from wake-steering to be less than predicted by steady-state models, but more robust wake-steering strategies can be designed that account for variable wind conditions. This paper compares the achieved yaw offsets and power gains from two different 2-turbine wake-steering experiments at a commercial wind farm with model predictions using the FLOw Redirection and Induction in Steady State (FLORIS) control-oriented model, assuming both fixed and variable wind directions. The impact of wind direction variability is modeled by including wind direction and yaw uncertainty in the FLORIS calculations. The field results match the trends predicted, assuming wind direction variability. Specifically, the yaw offsets achieved in the intended control regions are lower than desired, resulting in less power gain, while a slight loss in power occurs for wind directions outside of the intended control region because of unintentional yaw misalignment. The agreement between the model and field results suggests that the wind direction variability model can be used to design wake-steering controllers that are more robust to variable wind conditions present in the field.
Distributed Wind Resource Assessment for Small, Kilowatt-Sized Wind Turbines using Computational Flow Modeling Software
Authors: Acker T L , Bhattarai B , Shrestha R
Published: March 2020

A major challenge in deciding to invest in a wind energy system as part of an off-grid, small-scale renewable energy system is accurately estimating the annual energy production (AEP). Computational models hold promise to provide useful distributed wind resource assessment information at a reasonable cost. This paper describes the methods employed and results obtained from using wind flow modeling software, in this case Meteodyn WT, combined with wind speed data to predict the AEP of a 2.4 kW Skystream 3.7 wind turbine, and compare the AEP to measurements. Results showed AEP prediction errors ranging from <5% to ∼80% depending on the nature of the wind speed data used. Using a single wind speed data source could lead to an acceptable AEP (<10% error), but could well lead to much higher errors. Two methods of addressing this problem were demonstrated: 1) average several AEP predictions made using single wind speed data sources; or, 2) use multiple data sources simultaneously when making an AEP prediction. The latter of these two appears the most promising with lower errors in AEP. Another significant result of this work was demonstrating that using NREL Wind Toolkit wind speed data can produce good results in predicting AEP.
Commercialization of a Diffuser Augmented Wind Turbine for Distributed Generation
Authors: Evans S P , Kesby J E , Bradley J , Clausen P D
Published: March 2020

Small-scale distributed wind generation faces challenges in being cost competitive due to recent advances in solar photovoltaic and battery storage technology. Reductions in levelized cost of energy (LCOE) can be achieved by improvements in aerodynamic efficiency, generator controller design, or reducing cost of manufacture. In this paper we present a case study detailing the commercialization of a novel 200 W high-efficiency diffuser augmented wind turbine (DAWT). Results include increased rotor efficiency, bespoke controller design, and the novel use of manufacturing processes. Findings and conclusions are of direct interest to small wind turbine designers as they seek to reduce LCOE.
Review of Hybrid Offshore Wind and Wave Energy Systems
Authors: McTiernan Kaylie L. , Sharman Krish Thiagarajan
Published: March 2020

Hybrid wind wave systems combine offshore wind turbines with wave energy on a shared platform. These systems optimize power production at a single location by harnessing both the wind and the waves. Wave energy is currently at an earlier development stage than offshore wind. Research in this area is focused in wave energy converters being used for platform motion suppression of floating offshore wind turbines. Wave energy converters can passively shelter offshore wind turbines from waves and can also be actively controlled to reduce the system loads. Additionally, a small amount of supplemental power may be generated, which can be used for offshore wind turbine local power needs. There may be future benefits to these hybrid systems, but at this stage wave energy may increase the project cost and risk of offshore wind turbines. Hybrid wind wave system research and development is discussed, with a focus on floating offshore wind turbines. Additionally, two ocean demonstration scale hybrid wind and wave systems are discussed as case studies: the Poseidon Wave and Wind system and the W2Power system. Hybrid wind wave systems show potential to be part of the future of offshore wind energy.
Design considerations for a small ducted wind turbine
Authors: Valyou D N , Visser K D
Published: March 2020

While ducted wind turbines (DWTs) have not yet enjoyed commercial success, theory has shown their potential and suggests a need to identify and explore key drivers of the design space for DWTs. A governing optimization metric of cost/annual energy production (AEP) was examined and a key cost driver for DWT of turbine thrust identified. A review of generalized actuator disc theory indicated that increasing the axial induction of the duct increases the power/thrust ratio and reduces the cost/AEP. It was shown that the particular selection of the rotor power coefficient, CP, Rotor or the total power coefficient CP, Rotor, as a design parameter, changes the nature of the AEP optimization, either maximizing AEP with CP, Rotor or optimizing CP/CT and minimizing turbine size with CP, Total. Increasing the blade number to raiseCp and lower tip speed ratio optimizes rotor torque as well for generator matching. Iterative interaction between the wind resource, generator specifications, and design elements to minimize cost/AEP is introduced. The relationship between turbine maximum power output and AEP was explored and it was observed that increasing generator size raises AEP/rotor diameter.
Teaching Wind Energy to Engineering and Education Undergraduates Through Community Engagement
Authors: Benitz Maija A. , Yang Li-Ling
Published: March 2020

Rhode Island’s adoption of the Next Generation Science Standards in 2013 [1] established a pressing need to provide elementary schools with support for integrating engineering in our local district’s classrooms. Wind energy was identified as an appropriate instructional topic, both for its relevance to Rhode Island [2], and for its strength as a tool for studying the engineering design process. Education and engineering undergraduates collaborated to educate local fourth graders about engineering design and wind energy. While supporting the need for engineering education in the community, this project also deepened learning for both education and engineering students at Roger Williams University.
Characterizing marine atmospheric boundary layer to support offshore wind energy research
Authors: Jiang Houshuo , Edson James B.
Published: March 2020

The marine atmospheric boundary layer (MABL), under most wind conditions, is characterized by lower shear, less turbulence, and higher winds than its terrestrial counterpart, thereby making offshore wind farms attractive enough to offset higher costs of construction and maintenance. Significant questions, however, remain about the structure and characteristics of the MABL and its impact on wind turbines. This work characterizes the structure of the MABL in the coastal region south of Martha’s Vineyard where offshore wind turbines are planned to operate, using in situ and remotely sensed LIDAR measurements and numerical data generated by high resolution Weather Research and Forecasting (WRF) modeling. This work will benefit wind power estimates and short-term energy forecasting.
Re-parameterized Weibull distribution for modeling metocean extremes of multiple hazards with the Rosenblatt transformation
Authors: Qiao C , Myers A T
Published: March 2020

The construction of environmental contours using the Rosenblatt transformation requires the parameters defining the conditional distribution to be determined for all values of the conditioned random variable, including extreme values which are extrapolated from data in most cases. In the typical case where the conditional distribution is described by many parameters, the fitting process of these parameters is cumbersome, and the resultant extrapolation is prone to error. A re-parameterization technique is proposed here to approximate such a conditional distribution, which depends on many parameters, with a two-parameter Weibull distribution, so that fewer distribution parameters are involved in the fitting and extrapolation processes. This technique is shown to have a better performance compared to conventional approaches, as demonstrated here for a numerical example involving the construction of a 50-year environmental contour for wind and wave at offshore locations.
Wind Trawler: operation of a wind energy system in the far offshore environment
Authors: Annan A M , Lackner M A , Manwell J F
Published: March 2020

A great untapped wind resource lies within the deep oceanic environment far from shore. Considering the technological and economic challenges of fixed offshore wind platforms to operate at great offshore depths and distances, we propose that this resource best be exploited by the use of a mobile floating wind-and-hydro power producing plant, termed the Wind Trawler. This paper explores preliminary design considerations for wind turbine, hydro turbine, and hull to optimize power performance ensure stability. The wind speed is modelled using long term averages from hindcast software to compare power production of a Wind Trawler and fixed wind turbine in the offshore environment.
Comparison of multiline anchors for offshore wind turbines with spar and with semisubmersible
Authors: Balakrishnan Krishnaveni , Arwade Sanjay R. , DeGroot Don J. , Fontana Casey , Landon Melissa , Aubeny Charles P.
Published: March 2020

Offshore wind energy has become a promising source of renewable energy in recent years with many installed farms around the world successfully producing energy. As preliminary wind resource studies reveal, in the US much of the potential could be tapped in deeper water where floating solutions become favorable. The efficiency of floating offshore platforms is being studied and demonstrated in pilot projects such as Hywind in Scotland. In order to reduce the substructure cost in offshore wind projects, which is usually 25-30%, a novel shared anchor concept has been studied with spar supported turbines. Simulations are carried out with National Renewable Energy Laboratory’s (NREL) OC3 Hywind floating system and 5MW wind turbine. A similar study has been carried out with semisubmersible platforms earlier. Comparing the statistics of the net anchor forces from both the types of platforms reveals decreased anchor forces in case of spar due to large force cancellation and decreased response to wave action. Given the shared anchor concept in-principle reduces the material cost with reduced number of anchors than the conventional anchor types; further reduction in anchor forces in case of spar supported platform would be more cost-beneficial with more material savings.
Multiline Ring Anchor system for floating offshore wind turbines
Authors: Lee J , Aubeny C P
Published: March 2020

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

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

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

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

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

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

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

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

Hail 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

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

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

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

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

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

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

Increasing 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

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

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

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.