Paul S. Veers

National Renewable Energy Laboratory | NREL · National Wind Technology Center

The present research tackles the challenge of estimating long-term fatigue loads using short-term strain gauge measurements via statistical extrapolation. It also reassesses the performance of the Frandsen model—as a simplified approach for estimating higher turbulence due to wakes — in a compact wind farm layout using aeroelastic simulations of th...

Fatigue assessment of wind turbines involves three main sources of uncertainty: material resistance, load, and the damage accumulation model. Many studies focus on increasing the accuracy of fatigue load assessment to improve the fatigue reliability. Probabilistic modeling of the wind's turbulence standard deviation is an example of an approach use...

the International Energy Agency Wind Technology Collaboration Program convened a meeting to explore the intersection among five Grand Challenges of wind energy science: The Atmosphere, The Turbine, The Plant and Grid, Environmental Co-Design, and Social Science. This report identifies the critical issues within each area and opportunities for inter...

Wind energy is foundational for achieving 100 % renewable electricity production, and significant innovation is required as the grid expands and accommodates hybrid plant systems, energy-intensive products such as fuels, and a transitioning transportation sector. The sizable investments required for wind power plant development and integration make...

Fatigue reliability assessment of wind turbine components involves three major sources of uncertainty: material resistance, loads, and the mathematical models that connect the other two. Many studies focus on decreasing the uncertainty in fatigue load assessments via different approaches, including more detailed characterization of the turbulence s...

Microscale flow descriptions are often given in terms of mean quantities, turbulent kinetic energy, and/or stresses. Those metrics, while valuable, give limited information about turbulent eddies and coherent turbulent structures. This work investigates the structure of an atmospheric boundary layer using coherence and correlation in space and time...

The variability of the wind turbine loads complicates fatigue assessment in the design phase, as performing simulations covering the entire lifetime is computationally expensive. The current work provides important information for assessing the uncertainty in fatigue damage estimation due to finite data. We study the sample size effect on mean, var...

Wind energy is anticipated to play a central role in enabling a rapid transition from fossil fuels to a system based largely on renewable power. For wind power to fulfill its expected role as the backbone – providing nearly half of the electrical energy – of a renewable-based, carbon-neutral energy system, critical challenges around design, manufac...

Microscale flow descriptions are usually given in terms of statistics of turbulence quantities and/or spectral analysis. Those metrics, while valuable, give limited information about coherent turbulent structures. This work investigates the structure of an atmospheric boundary layer using coherence and correlation in space and time with a range of...

Wind energy is anticipated to play a central role in enabling a rapid transition from fossil fuels to a system based largely on renewable power. For wind power to fulfill its expected role as the backbone—providing nearly half of the electrical energy—of a renewable-based, carbon-neutral energy system, critical challenges around design, development...

Wind energy is foundational for achieving 100 % renewable electricity production and significant innovation is required as the grid expands and accommodates hybrid plant systems, energy-intensive products such as fuels, and a transitioning transportation sector. The sizable investments required for wind power plant development and integration make...

This study investigates the challenges and opportunities presented by downwind wind turbines and offers a roadmap of future research pathways to maximize their potential. Multidisciplinary design, analysis, and optimization comparison studies between upwind and downwind configurations on a modern 10‐MW offshore wind turbine are presented to support...

Li et al. present a worldwide analysis of rare-earth elements used in wind turbine generators. It focuses on the most extreme deployment scenario using rare-earth-intensive generator technology to demonstrate demand quickly outpacing supply, thus suggesting an existential threat to rapid wind deployment. However, alternative generator technologies...

This article describes an interdisciplinary methodology to calculate the probability of failure for bearing axial cracking, the dominant failure mode in the intermediate and high-speed stages of many wind turbine gearboxes. This approach is mainly a physics-domain method with needed inputs from the data domain. The gearbox and bearing design along...

Volume 1: Atmospheric Flows and Wind Plants The nature of modeling the atmosphere is inherently the based on the flow of air from the mesoscale down to the surface, and then into, around, and through the many rotors of a wind plant. Models of the flow share the characteristic that the domain can be intensely discretized with a grid and solved over...

A multifaceted future for wind power Modern wind turbines already represent a tightly optimized confluence of materials science and aerodynamic engineering. Veers et al. review the challenges and opportunities for further expanding this technology, with an emphasis on the need for interdisciplinary collaboration. They highlight the need to better u...

Wind turbine extreme load estimation is especially difficult because turbulent inflow drives nonlinear turbine physics and control strategies; thus there can be huge differences in turbine response to essentially equivalent environmental conditions. The two main current approaches, extrapolation and Monte Carlo sampling, are both unsatisfying: extr...

Wind turbines within an array do not experience free-stream undisturbed flow fields. Rather, the flow fields on internal turbines are influenced by wakes generated by upwind unit and exhibit different dynamic characteristics relative to the free stream. The International Electrotechnical Commission (IEC) standard 61400-1 for the design of wind turb...

The potential for wind power in the United States and globally is vast. The U.S. wind resource alone could supply more than 7.5 times the nation’s total electricity generation in the year 2016. The nation has already begun to harness this potential. In 2016, new investments in U.S. wind power capacity were estimated at $14.5 billion and wind power...

Wind turbine extreme loads estimation is especially difficult because turbulent inflow drives nonlinear turbine physics and control strategies, so there can be huge differences in turbine response to essentially equivalent environmental conditions. The two main current approaches, extrapolation and Monte Carlo sampling, are both unsatisfying: extra...

Industry-wide Design Code Calibration: The capabilities of the industry design tools used to calculate aeroelastic loads and the understanding of site atmospheric conditions should be assessed to make sure safety factors are appropriate and not producing excess margins that increase system cost of energy without associated value. Atmospheric Cond...

We present a novel methodology for characterizing and simulating non-stationary stochastic wind records. In this new method, non-stationarity is characterized and modelled via temporal coherence, which is quantified in the discrete frequency domain by probability distributions of the differences in phase between adjacent Fourier components. Tempora...

Long-term fatigue loads for floating offshore wind turbines are hard to estimate because they require the evaluation of the integral of a highly nonlinear function over a wide variety of wind and wave conditions. Current design standards involve scanning over a uniform rectangular grid of metocean inputs (e.g., wind speed and direction and wave hei...

The conceptual design and proof-of-concept testing of a furling vertical axis wind turbine, suited to large-scale offshore deployment, is described. Through the implementation of variable geometry capabilities, extreme storm loads can be reduced, and unsteady flow-related fatigue loads can be minimized thereby reducing capital (structural) and main...

We present simulation-based studies aimed at assessing the response of bottom-supported offshore wind turbines to physics-based offshore environmental conditions during a hurricane. The response of a parked wind turbine is studied for a hurricane scenario simulated using a fully coupled atmospheric-wave-ocean model. Based on hurricane intensity and...

This paper introduces the development of a new software framework for research, design, and development of wind energy systems which is meant to 1) represent a full wind plant including all physical and nonphysical assets and associated costs up to the point of grid interconnection, 2) allow use of interchangeable models of varying fidelity for dif...

This study is focused on simulation of thunderstorm downbursts and associated wind turbine loads. We first present a thunderstorm downburst model, in which the wind field is assumed to result from the summation of an analytical mean field and stochastic turbulence. The structure and evolution of the downburst wind field based on the analytical mode...

Wind turbine structures need to be designed with careful consideration of the fatigue strength and loading on critical load-bearing components. Each material in the various components of a wind turbine will potentially use different damage models to map the cyclic fatigue loadings into progressive deterioration of the material. In most cases, linea...

This report will present the wind turbine drivetrain condition monitoring (CM) research conducted under the phase 1 and phase 2 Gearbox Reliability Collaborative (GRC) tests. The rationale and approach for this drivetrain CM research, investigated CM systems, test configuration and results, and a discussion on challenges in wind turbine drivetrain...

The International Electrotechnical Commission (IEC) standard 61400-1 for the design of wind turbines does not explicitly address site-specific conditions associated with anomalous atmospheric events or conditions. Examples of off-standard atmospheric conditions include thunderstorm downbursts, hurricanes, tornadoes, low-level jets, etc. This study...

This paper provides an overview of wind turbine drivetrain condition monitoring based on presentations from a condition monitoring workshop organized by the National Renewable Energy Laboratory in 2009 and on additional references.

The International Electrotechnical Commission (IEC) standard 61400-1 for the design of wind turbines does not explicitly address site-specific conditions associated with anomalous atmospheric events or conditions. Examples of off-standard atmospheric conditions include thunderstorm downbursts, hurricanes, tornadoes, low-level jets, etc. This study...

This paper describes the status of wind energy in the United States as of 2007, its cost, the potential for growth, offshore development, and potential technology improvements.

The development and application of design standards has been a critical element in raising the level of reliability across the entire wind energy industry. Designs have an objective set of criteria against which they can be judged and entire fleets of turbines can be manufactured to a common set of criteria. Each wind power development is then left...

Various sources of risk exist for all civil structures, one of which is seismic risk. As structures change in scale, the magnitude of seismic risk changes relative to risk from other sources. This paper presents an introduction to seismic hazard as applied to wind turbine structures. The existing design methods and research regarding seismic risk f...

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Todaypsilas wind technology has enabled wind to enter the electric power mainstream. Continued technology advancement will enable cost-competitive generation of 20% of the US electrical energy from renewable wind power.

This paper discusses the development of wind energy technology past, present and future.

From the birth of modern electricity-generating wind turbines in the late 1970s to now, wind energy technology has dramatically improved. Capital costs have plummeted, reliability has improved, and efficiency has increased. High-quality turbine manufacturers exist around the world, and wind plants of 300 MW and larger are being integrated into the...

When a system design approach is applied to wind turbine blades, manufacturing and structural requirements are included along with aerodynamic considerations in the design optimization. The resulting system-driven design includes several innovative structural features such as flat-back airfoils, a constant thickness carbon spar-cap, and a thin, lar...

Spatial statistics in the measured inflow of the long-term inflow and structural test (LIST) turbine was investigated by estimating the coherence for the three turbulence components. Several standard coherence models were also compared for inflow turbulence with estimates from the field measurements. It was observed that the Davenport exponential m...

The Long-Term Inflow and Structural Test (LIST) pro-gram, managed by Sandia National Laboratories, is gathering inflow and structural response data on a modified version of the Micon 65/13 wind turbine at a site near Bushland, Texas. With the objective of estab-lishing correlations between structural response and inflow, previous studies have emplo...

The Long-Term Inflow and Structural Test (LIST) program is gathering inflow and structural response data on a modified version of the Micon 65/13 wind turbine at a test site near Bushland, Texas. Data from 491 ten-minute time data records are analyzed here to determine the dependency of fatigue and extreme loads on inflow parameters. Flap and edge...

Because the fatigue lifetime of wind turbine components depends on several factors that are highly variable, a numerical analysis tool called FAROW has been created to cast the problem of component fatigue life in a probabilistic framework. The probabilistic analysis is accomplished using methods of structural reliability (FORM/SORM). While the wor...

Wind turbine blades continue to be the target of technological improvements by the use of better designs, materials, manufacturing, analysis and testing. As the size of turbines has grown over the past decade, designers have restrained the associated growth in blade weight to less than would have been possible through simple scaling-up of past appr...

The Long-Term Inflow and Structural Test (LIST) program is gathering inflow and structural response data on a Westinghouse 600-kW wind turbine located at a test site near Boulder, Colorado. Data from 1043 ten-minute time segments are analyzed here to determine the dependency of fatigue and extreme loads on inflow parameters. Flap and edge bending m...

The prospect of installing blades that twist as they bend and/or extend on horizontal axis wind turbines provides opportunities for enhanced energy capture and/or load mitigation. Although this coupling could be achieved in either an active or a passive manner, the passive approach is much more attractive owing to its simplicity and economy. As an...

The Long-Term Inflow and Structural Test (LIST) program is gathering inflow and structural response data on a modified version of the Micon 65/13 wind turbine at a test site near Bushland, Texas. Data from 491 ten-minute time data records are analyzed here to determine the dependency of fatigue and extreme loads on inflow parameters. Flap and edge...

This paper presents and explores estimating design loads on wind turbines using the environmental contour method. Contours promise to provide both practical reliability estimation and valuable information about the combination of joint environmental variable values, e.g. wind speed and turbulence, most critical to each specific wind turbine. We pre...

Bend-twist coupling in wind turbine blades has been shown to reduce both fatigue and extreme operating loads, especially when applied in conjunction with a pitch-controlled rotor. This type of coupling has been used in other industries, implemented either through biased lay-ups of fiber-reinforced materials, or with swept wings. The critical issues...

International standards for wind turbine certification depend on finding long-term fatigue load distributions that are conservative with respect to the state of knowledge for a given system. Statistical models of loads for fatigue application are described and demonstrated using flap and edge blade-bending data from a commercial turbine in complex...

International standards for wind turbine certification depend on finding long-term fatigue load probability distributions that are consistent with respect to the state of knowledge for a given system. Statistical moment-based models of loads for fatigue applications are described and demonstrated here, using flap and edge blade-bending data from a...

Current design load estimation procedures for wind turbines often do not accurately treat the statistical nature of loads. Current practice for wind turbine load analysis is reviewed. The authors' opinions on the shortcomings of these practices are discussed. Experience gained from current research on statistical load extrapolation methods is revie...

This paper reviews issues related to the use of aeroelastic tailoring as a cost-effective, passive means to shape the power curve and reduce loads. Wind turbine blades bend and twist during operation, effectively altering the angle of attack, which in turn affects loads and energy production. It is possible to build a small amount of desirable twis...

There is uncertainty in the performance of wind energy installations due to unknowns in the local wind environment, machine response to the environment, and the durability of materials. Some of the unknowns are inherently independent from machine to machine while other uncertainties are common to the entire fleet equally. The FAROW computer softwar...

Over the past several years, extensive databases have been developed for the S-N behavior of various materials used in wind turbine blades, primarily fiberglass composites. These data are typically presented both in their raw form and curve fit to define their average properties. For design, confidence limits must be placed on these descriptions. I...

Because the fatigue lifetime of wind turbine components depends on several factors that are highly variable, a numerical analysis tool called FAROW has been created to cast the problem of component fatigue life in a probabilistic framework. The probabilistic analysis is accomplished using methods of structural reliability (FORM/SORM). While the wor...

The load mitigation and energy capture characteristics of twist-coupled HAWT blades that are mounted on a variable speed rotor are investigated in this paper. These blades are designed to twist toward feather as they bend with pretwist set to achieve a desirable twist distribution at rated power. For this investigation, the ADAMS-WT software has be...

Cyclic loadings produce progressive damage that can ultimately result in wind turbine structural failure. There are many issues that must be dealt with in turning load measurements into estimates of component fatigue life. This paper deals with how the measured loads can be analyzed and processed to meet the needs of both fatigue life calculations...

This paper reviews issues related to the use of aeroelastic tailoring as a cost-effective, passive means to shape the power curve and reduce loads. Wind turbine blades bend and twist during operation, effectively altering the angle of attack, which in turn affects loads and energy production. There are blades now in use that have significant aeroel...

As the technology for horizontal axis wind turbines (HAWT) development matures, more novel techniques are required for the capture of additional amounts of energy, alleviation of loads and control of the rotor. One such technique employs the use of an adaptive blade that could sense the wind velocity or rotational speed in some fashion and accordin...

Analytical models of wind turbine blades have many uncertainties, particularly with composite construction where material properties and cross-sectional dimension may not be known or precisely controllable. In this paper the authors demonstrate how modal testing can be used to estimate important material parameters and to update and improve a finit...

Cyclic loadings produce progressive damage that can ultimately result in wind turbine structural failure. There are many issues that must be dealt with in turning load measurements into estimates of component fatigue life. This paper deals with how the measured loads can be analyzed and processed to meet the needs of both fatigue life calculations...

The cost of repairing or replacing failed components depends on the number and timing of failures. Although the total probability of individual component failure is sometimes interpreted as the percentage of components likely to fail, this perception is often far from correct. Different amounts of common versus independent uncertainty can cause dif...

The authors have measured modal damping using strain-gauge data from an operating wind turbine. This new technique for measuring modal damping is easier and less expensive than previously used methods. Auto-correlation and cross-correlation functions of the strain-gauge data have been shown to consist of decaying sinusoids which correspond to the m...

Enhanced Performance of HAWTs Using Adaptive Blades D. W. Lobitz and P. S. Veers, Sandia National Laboratories, Albuquerque, NM 87185-0439 P. G. Migliore, National Renewable Energy Laboratory, Golden, CO 80401 Abstract As the technology for HAWT development matures, more sophisticated techniques are being examined to increase annual energy capture....

Volume 19 is a resource for basic concepts, alloy property data, and the testing and analysis methods used to characterize fatigue and fracture behavior of structural materials. Contents include fatigue mechanisms, crack growth and testing; fatigue strength prediction and analysis; fracture mechanics, damage tolerance, and life assessment; environm...

The fatigue analysis of a wind turbine component typically uses representative samples of cyclic loads to determine lifetime loads. In this paper, several techniques currently in use are compared to one another based on fatigue life analyses. The generalized Weibull fitting technique is used to remove the artificial truncation of large-amplitude cy...

Modern wind turbines are fatigue critical machines used to produce electrical power. To insure long term, reliable operation, their structure must be optimized if they are to be economically viable. The fatigue and reliability projects in Sandia`s Wind Energy Program are developing the analysis tools required to accomplish these design requirements...

FAROW is a Computer program that assists in the probabilistic analysis of the Fatigue and Reliability of wind turbines. The fatigue lifetime of wind turbine components is calculated using functional forms for important input quantities. Parameters of these functions are defined in an input file as either constants or random variables. The user can...

The combined analysis/test effort described in this paper compares predictions with measured data from a step-relaxation test in the absence of significant wind-driven aerodynamic loading. The process described here is intended to illustrate a method for validation of time domain codes for structural analysis of wind turbine structures. Preliminary...