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Special Issue "Wind Turbine Loads and Wind Plant Performance"

A special issue of Energies (ISSN 1996-1073).

Deadline for manuscript submissions: closed (31 March 2018)

Special Issue Editors

Guest Editor
Prof. Dr. Lance Manuel

Department of Civil, Architectural and Environmental Engineering, University of Texas at Austin, Texas 78712, USA
Website | E-Mail
Fax: +1 512 471 7259
Interests: reliability of offshore structures; offshore wind energy; wave energy devices; risers; floating structures; uncertainty quantification
Guest Editor
Prof. Dr. Rupp Carriveau

Turbulence and Energy Laboratory, Lumley Centre for Engineering Innovation, University of Windsor, Canada
Website | E-Mail
Interests: wind farm data analytics; wind turbine group dynamics; energy storage; energy systems

Special Issue Information

Dear Colleagues,

“Wind Turbine Loads and Wind Plant Performance” is a continuation and expansion of the previous and successful Special Issue, “Modeling and Simulation for Wind Turbine Loads Analysis.”

We invite submissions of articles to a Special Issue of the journal, Energies, in the general area, “Wind Turbine Loads and Wind Plant Performance.” Modern utility-scale turbines are complex machines designed to survive a host of contrasting external conditions. In different states—operating, parked, idling, start-up, shutdown—and for various desired limit states of performance, turbines must be equipped with control systems. Increasingly larger rotors imply greater variability in inflow conditions over the rotor-swept area. Loads on a turbine in isolation are understood to be quite different from those on units that are part of arrays. High-performance computational resources are being brought to bear to address all of these complexities in loads analyses for turbines and even in consideration for full-plant optimization and control. Uncertainty quantification that considers all “quantities of interest” related to turbine loads and in plant performance stemming from uncertainties in inflow characterization, in models, in physics descriptions, and in turbine materials/structures is of great interest in the rapidly maturing wind energy industry.

Keywords

Topics of interest for publication in this special issue include, but are not limited to, the following:

  • Probabilistic design; safety factor calibration; certification; standards; design load cases

  • Wind farm data analytics; field measurement campaigns; wake effects

  • Anomalous events; windstorms; tornadoes; hurricanes; metocean criteria for offshore wind

  • Site assessment and site suitability analysis

  • Fatigue and extremes; statistical loads extrapolation

  • High-performance computing; uncertainty quantification

  • Structural and geotechnical modeling; aerodynamics; control

We look forward to your submissions. Thank you!

Prof. Dr. Lance Manuel
Prof. Dr. Rupp Carriveau
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (16 papers)

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Research

Open AccessArticle An Advanced Control Technique for Floating Offshore Wind Turbines Based on More Compact Barge Platforms
Energies 2018, 11(5), 1187; https://doi.org/10.3390/en11051187
Received: 26 March 2018 / Revised: 28 April 2018 / Accepted: 4 May 2018 / Published: 8 May 2018
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Abstract
Hydrodynamic Floating Offshore Wind Turbine (FOWT) platform specifications are typically dominated by seaworthiness and maximum operating platform-pitch angle-related requirements. However, such specifications directly impact the challenge posed by an FOWT in terms of control design. The conventional FOWT systems are typically based on
[...] Read more.
Hydrodynamic Floating Offshore Wind Turbine (FOWT) platform specifications are typically dominated by seaworthiness and maximum operating platform-pitch angle-related requirements. However, such specifications directly impact the challenge posed by an FOWT in terms of control design. The conventional FOWT systems are typically based on large, heavy floating platforms, which are less likely to suffer from the negative damping effect caused by the excessive coupling between blade-pitch control and platform-pitch motion. An advanced control technique is presented here to increase system stability for barge type platforms. Such a technique mitigates platform-pitch motions and improves the generator speed regulation, while maintaining blade-pitch activity and reducing blade and tower loads. The NREL’s 5MW + ITI Energy barge reference model is taken as a basis for this work. Furthermore, the capabilities of the proposed controller for performing with a more compact and less hydrodynamically stable barge platform is analysed, with encouraging results. Full article
(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)
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Open AccessArticle Virtual Inertia Adaptive Control of a Doubly Fed Induction Generator (DFIG) Wind Power System with Hydrogen Energy Storage
Energies 2018, 11(4), 904; https://doi.org/10.3390/en11040904
Received: 31 March 2018 / Revised: 31 March 2018 / Accepted: 10 April 2018 / Published: 12 April 2018
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Abstract
This paper presents a doubly fed induction generator (DFIG) wind power system with hydrogen energy storage, with a focus on its virtual inertia adaptive control. Conventionally, a synchronous generator has a large inertia from its rotating rotor, and thus its kinetic energy can
[...] Read more.
This paper presents a doubly fed induction generator (DFIG) wind power system with hydrogen energy storage, with a focus on its virtual inertia adaptive control. Conventionally, a synchronous generator has a large inertia from its rotating rotor, and thus its kinetic energy can be used to damp out fluctuations from the grid. However, DFIGs do not provide such a mechanism as their rotor is disconnected with the power grid, owing to the use of back-to-back power converters between the two. In this paper, a hydrogen energy storage system is utilized to provide a virtual inertia so as to dampen the disturbances and support the grid’s stability. An analytical model is developed based on experimental data and test results show that: (1) the proposed method is effective in supporting the grid frequency; (2) the maximum power point tracking is achieved by implementing this proposed system; and, (3) the DFIG efficiency is improved. The developed system is technically viable and can be applied to medium and large wind power systems. The hydrogen energy storage is a clean and environmental-friendly technology, and can increase the renewable energy penetration in the power network. Full article
(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)
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Open AccessArticle Effect of Scour on the Natural Frequency Responses of the Meteorological Mast in the Taiwan Strait
Energies 2018, 11(4), 823; https://doi.org/10.3390/en11040823
Received: 12 February 2018 / Revised: 25 March 2018 / Accepted: 2 April 2018 / Published: 3 April 2018
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Abstract
The meteorological mast (met mast) for the Taiwan Power Company’s offshore wind farm is located in Taiwan Strait near Changhua County. The py curve method recommended in the current offshore foundation design codes does not account for the local scour around
[...] Read more.
The meteorological mast (met mast) for the Taiwan Power Company’s offshore wind farm is located in Taiwan Strait near Changhua County. The py curve method recommended in the current offshore foundation design codes does not account for the local scour around the pile foundation; it overestimates the lateral pile deformation and underestimates the foundation stiffness. This paper presents a method to correct the initial modulus of subgrade reaction and modify the ultimate lateral resistance caused by the local scour. The natural frequency of the met mast structure is also determined by a numerical model and verified with the measured data in situ. A comprehensive parameter study is performed to analyze the effect of scour on the dynamic responses of the met mast. Two types of foundation model, a coupled-springs foundation model and a distributed-springs foundation model, are considered in the dynamic analysis of the met mast. The results demonstrate that using a distributed-springs foundation model provides a relatively accurate estimate of the natural frequencies of the met mast structure. Furthermore, the scour exerted significant effects on certain modes of the vibration responses. The natural frequencies of the met mast structure can be reduced by approximately 14% due to scour, particularly in the horizontal bending modes. This paper also provides a preliminary strategy for structural monitoring and analysis to detect scour damage on offshore wind turbines with monopile foundations. Full article
(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)
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Open AccessArticle Stochastic Wake Modelling Based on POD Analysis
Energies 2018, 11(3), 612; https://doi.org/10.3390/en11030612
Received: 19 January 2018 / Revised: 19 February 2018 / Accepted: 26 February 2018 / Published: 9 March 2018
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Abstract
In this work, large eddy simulation data is analysed to investigate a new stochastic modeling approach for the wake of a wind turbine. The data is generated by the large eddy simulation (LES) model PALM combined with an actuator disk with rotation representing
[...] Read more.
In this work, large eddy simulation data is analysed to investigate a new stochastic modeling approach for the wake of a wind turbine. The data is generated by the large eddy simulation (LES) model PALM combined with an actuator disk with rotation representing the turbine. After applying a proper orthogonal decomposition (POD), three different stochastic models for the weighting coefficients of the POD modes are deduced resulting in three different wake models. Their performance is investigated mainly on the basis of aeroelastic simulations of a wind turbine in the wake. Three different load cases and their statistical characteristics are compared for the original LES, truncated PODs and the stochastic wake models including different numbers of POD modes. It is shown that approximately six POD modes are enough to capture the load dynamics on large temporal scales. Modeling the weighting coefficients as independent stochastic processes leads to similar load characteristics as in the case of the truncated POD. To complete this simplified wake description, we show evidence that the small-scale dynamics can be captured by adding to our model a homogeneous turbulent field. In this way, we present a procedure to derive stochastic wake models from costly computational fluid dynamics (CFD) calculations or elaborated experimental investigations. These numerically efficient models provide the added value of possible long-term studies. Depending on the aspects of interest, different minimalized models may be obtained. Full article
(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)
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Open AccessFeature PaperArticle Spar-Type Vertical-Axis Wind Turbines in Moderate Water Depth: A Feasibility Study
Energies 2018, 11(3), 555; https://doi.org/10.3390/en11030555
Received: 10 February 2018 / Revised: 28 February 2018 / Accepted: 1 March 2018 / Published: 5 March 2018
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Abstract
The applications of floating vertical-axis wind turbines (VAWTs) in deep water have been proposed and studied by several researchers recently. However, the feasibility of deploying a floating VAWT at a moderate water depth has not yet been studied. In this paper, this feasibility
[...] Read more.
The applications of floating vertical-axis wind turbines (VAWTs) in deep water have been proposed and studied by several researchers recently. However, the feasibility of deploying a floating VAWT at a moderate water depth has not yet been studied. In this paper, this feasibility is thoroughly addressed by comparing the dynamic responses of spar-type VAWTs in deep water and moderate water depth. A short spar VAWT supporting a 5 MW Darrieus rotor at moderate water depth is proposed by following the deep spar concept in deep water. A fully coupled simulation tool, SIMO-RIFLEX-DMS code, is utilized to carry out time domain simulations under turbulent wind and irregular waves. Dynamic responses of the short spar and deep spar VAWTs are analyzed and compared, including the natural periods, wind turbine performance, platform motions, tower base bending moments, and tension of mooring lines. The statistical characteristics of the thrust and power production for both spars are similar. The comparison of platform motions and tower base bending moments demonstrate a good agreement for both spars, but the short spar has better performance in surge/sway motions and side–side bending moments. The 2P response dominates the bending moment spectra for both spars. A significant variation in tension of Mooring Line 1 and a larger corresponding spectrum value are found in the short spar concept. The results indicate that the application of short spar VAWTs is feasible and could become an alternative concept at moderate water depth. Full article
(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)
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Open AccessArticle Experimental and Numerical Vibrational Analysis of a Horizontal-Axis Micro-Wind Turbine
Energies 2018, 11(2), 456; https://doi.org/10.3390/en11020456
Received: 18 December 2017 / Revised: 2 February 2018 / Accepted: 19 February 2018 / Published: 22 February 2018
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Abstract
Micro-wind turbines are energy conversion technologies strongly affected by fatigue, as a result of their size and the variability of loads, induced by the unsteady wind conditions, and modulated by a very high rotational speed. This work is devoted to the experimental and
[...] Read more.
Micro-wind turbines are energy conversion technologies strongly affected by fatigue, as a result of their size and the variability of loads, induced by the unsteady wind conditions, and modulated by a very high rotational speed. This work is devoted to the experimental and numerical characterization of the aeroelastic behavior of a test-case horizontal-axis wind turbine (HAWT) with a 2 m rotor diameter and a maximum power production of 3 kW. The experimental studies have been conducted at the wind tunnel of the University of Perugia and consisted of accelerometer measurements at the tower and the tail fin. The numerical setup was the Fatigue, Aerodynamics, Structures, and Turbulence (FAST) code for aeroelastic simulations, which was fed as input with the same wind conditions employed in the wind tunnel tests. The experimental and numerical analyses were coupled with the perspective of establishing a reciprocal feedback, and this has been accomplished. On one hand, the numerical model is important for interpreting the measured spectrum of tower oscillations and, for example, inspires the detection of a mass unbalance at the blades. On the other hand, the measurements inspire the question of how to interpret the interaction between the blades and the tower. The experimental spectrum of tail fin vibrations indicates that secondary elements, in terms of weight, can also transmit to the tower, giving meaningful contributions to the vibration spectra. Therefore, an integrated numerical and experimental approach is not only valuable but is also unavoidable, to fully characterize the dynamics of small wind-energy conversion systems. Full article
(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)
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Open AccessArticle Dynamic Strategies for Yaw and Induction Control of Wind Farms Based on Large-Eddy Simulation and Optimization
Energies 2018, 11(1), 177; https://doi.org/10.3390/en11010177
Received: 7 December 2017 / Revised: 7 January 2018 / Accepted: 8 January 2018 / Published: 11 January 2018
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Abstract
In wind farms, wakes originating from upstream turbines cause reduced energy extraction and increased loading variability in downstream rows. The prospect of mitigating these detrimental effects through coordinated controllers at the wind-farm level has fueled a multitude of research efforts in wind-farm control.
[...] Read more.
In wind farms, wakes originating from upstream turbines cause reduced energy extraction and increased loading variability in downstream rows. The prospect of mitigating these detrimental effects through coordinated controllers at the wind-farm level has fueled a multitude of research efforts in wind-farm control. The main strategies in wind-farm control are to influence the velocity deficits in the wake by deviating from locally optimal axial induction setpoints on the one hand, and steering wakes away from downstream rows through yaw misalignment on the other hand. The current work investigates dynamic induction and yaw control of individual turbines for wind-farm power maximization in large-eddy simulations. To this end, receding-horizon optimal control techniques combined with continuous adjoint gradient evaluations are used. We study a 4 × 4 aligned wind farm, and find that for this farm layout yaw control is more effective than induction control, both for uniform and turbulent inflow conditions. Analysis of optimal yaw controls leads to the definition of two simplified yaw control strategies, in which wake meandering and wake redirection are exploited respectively. Furthermore it is found that dynamic yawing provides significant benefits over static yaw control in turbulent flow environments, whereas this is not the case for uniform inflow. Finally, the potential of combining overinductive axial induction control with yaw control is shown, with power gains that approximate the sum of those achieved by each control strategy separately. Full article
(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)
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Open AccessArticle Behavior Anomaly Indicators Based on Reference Patterns—Application to the Gearbox and Electrical Generator of a Wind Turbine
Energies 2018, 11(1), 87; https://doi.org/10.3390/en11010087
Received: 23 October 2017 / Revised: 4 December 2017 / Accepted: 24 December 2017 / Published: 1 January 2018
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Abstract
This paper presents indicators of non-expected behavior in components of a wind turbine. These indicators are used to alert about the working conditions of these components that are not usual, according to the normal behavior observed for similar conditions of wind speed and
[...] Read more.
This paper presents indicators of non-expected behavior in components of a wind turbine. These indicators are used to alert about the working conditions of these components that are not usual, according to the normal behavior observed for similar conditions of wind speed and power generated. In order to obtain these indicators, reference patterns of behavior for the components studied were defined. The patterns were obtained from real data of the wind turbine covering all of the possible working conditions. The technique of self-organized maps was used for discovering such reference patterns. Once they were obtained, new data, not included in the training set, was passed through the patterns in order to verify if the behavior observed corresponds or not to that expected. If they do not coincide, an anomaly of behavior is detected than can be useful for soon alert of possible failure mode or at least to know that the component was under working conditions that could cause risk of fault. The periods of unexpected behavior are the base for the indicators proposed in this paper. Real cases to show the elaboration of the indicators, and their corresponding results are provided. Full article
(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)
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Open AccessFeature PaperArticle Toward Development of a Stochastic Wake Model: Validation Using LES and Turbine Loads
Energies 2018, 11(1), 53; https://doi.org/10.3390/en11010053
Received: 27 October 2017 / Revised: 8 December 2017 / Accepted: 14 December 2017 / Published: 28 December 2017
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Abstract
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
[...] Read more.
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 turbines only considers a deterministic wake model for the design of a wind plant. This study is focused on the development of a stochastic model for waked wind fields. First, high-fidelity physics-based waked wind velocity fields are generated using Large-Eddy Simulation (LES). Stochastic characteristics of these LES waked wind velocity field, including mean and turbulence components, are analyzed. Wake-related mean and turbulence field-related parameters are then estimated for use with a stochastic model, using Multivariate Multiple Linear Regression (MMLR) with the LES data. To validate the simulated wind fields based on the stochastic model, wind turbine tower and blade loads are generated using aeroelastic simulation for utility-scale wind turbine models and compared with those based directly on the LES inflow. The study’s overall objective is to offer efficient and validated stochastic approaches that are computationally tractable for assessing the performance and loads of turbines operating in wakes. Full article
(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)
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Open AccessArticle Control of Variable Speed Wind Turbines with Doubly Fed Asynchronous Generators for Stand-Alone Applications
Energies 2018, 11(1), 26; https://doi.org/10.3390/en11010026
Received: 14 November 2017 / Revised: 5 December 2017 / Accepted: 21 December 2017 / Published: 23 December 2017
Cited by 1 | PDF Full-text (7813 KB) | HTML Full-text | XML Full-text
Abstract
This paper addresses the design and implementation of a novel control of a variable speed wind turbine with doubly fed induction generator for stand-alone applications. In opposition to grid-tied applications, in stand-alone systems the voltage and frequency must be generated by the doubly
[...] Read more.
This paper addresses the design and implementation of a novel control of a variable speed wind turbine with doubly fed induction generator for stand-alone applications. In opposition to grid-tied applications, in stand-alone systems the voltage and frequency must be generated by the doubly fed induction generator. Therefore, a voltage and frequency controller is required for supplying the load at constant voltage and frequency. This controller is implemented by orientation of the generator stator flux vector along a synchronous reference axis. In this way, constant voltage and frequency is obtained and the generator will supply the active and reactive power demanded by the load, while the wind turbine will be responsible for achieving power balance in the system. Then, power control is assumed by the pitch actuator controlling the rotational speed of the wind turbine for power balancing. A load shedding mechanism is needed if the load power exceeds the maximum available wind power. Detailed simulation results are presented and discussed to demonstrate the capabilities and contributions of the proposed control scheme. Full article
(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)
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Open AccessArticle A Wind Power Plant with Thermal Energy Storage for Improving the Utilization of Wind Energy
Energies 2017, 10(12), 2126; https://doi.org/10.3390/en10122126
Received: 8 November 2017 / Revised: 2 December 2017 / Accepted: 6 December 2017 / Published: 14 December 2017
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Abstract
The development of the wind energy industry is seriously restricted by grid connection issues and wind energy generation rejections introduced by the intermittent nature of wind energy sources. As a solution of these problems, a wind power system integrating with a thermal energy
[...] Read more.
The development of the wind energy industry is seriously restricted by grid connection issues and wind energy generation rejections introduced by the intermittent nature of wind energy sources. As a solution of these problems, a wind power system integrating with a thermal energy storage (TES) system for district heating (DH) is designed to make best use of the wind power in the present work. The operation and control of the system are described in detail. A one-dimensional system model of the system is developed based on a generic model library using the object-oriented language Modelica for system modeling. Validations of the main components of the TES module are conducted against experimental results and indicate that the models can be used to simulate the operation of the system. The daily performance of the integrated system is analyzed based on a seven-day operation. And the influences of system configurations on the performance of the integrated system are analyzed. The numerical results show that the integrated system can effectively improve the utilization of total wind energy under great wind power rejection. Full article
(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)
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Open AccessArticle Indicative Fault Diagnosis of Wind Turbine Generator Bearings Using Tower Sound and Vibration
Energies 2017, 10(11), 1853; https://doi.org/10.3390/en10111853
Received: 7 September 2017 / Revised: 27 September 2017 / Accepted: 17 October 2017 / Published: 13 November 2017
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Abstract
The idea of indicative fault diagnosis based on measuring the wind turbine tower sound and vibration is presented. It had been reported by a wind farm operator that a major fault on the generator bearing causes shock and noise to be heard from
[...] Read more.
The idea of indicative fault diagnosis based on measuring the wind turbine tower sound and vibration is presented. It had been reported by a wind farm operator that a major fault on the generator bearing causes shock and noise to be heard from the bottom of the wind turbine tower. The work in this paper was conceived to test whether tower top faults could be identified by taking simple measurements at the tower base. Two accelerometers were attached inside the wind turbine tower, and vibration data was collected while the wind turbine was in operation. Tower vibration signals were analyzed using Empirical Mode Decomposition and the outcomes were correlated with the vibration signals acquired directly from the generator bearings. It is shown that the generator bearing fault signatures were present in the vibrations from the tower. The results suggest that useful condition monitoring of nacelle components can be done even when there is no condition monitoring system installed on the generator bearings, as is often the case for older wind turbines. In the second part of the paper, acoustic measurements from a healthy and a faulty wind turbine are shown. The preliminary analysis suggests that the generator bearing fault increases the overall sound pressure level at the bottom of the tower, and is not buried in the background noise. Full article
(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)
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Open AccessArticle Wind Turbine Loads Induced by Terrain and Wakes: An Experimental Study through Vibration Analysis and Computational Fluid Dynamics
Energies 2017, 10(11), 1839; https://doi.org/10.3390/en10111839
Received: 30 September 2017 / Revised: 6 November 2017 / Accepted: 8 November 2017 / Published: 10 November 2017
Cited by 1 | PDF Full-text (8161 KB) | HTML Full-text | XML Full-text
Abstract
A wind turbine is a very well-known archetype of energy conversion system working at non-stationary regimes. Despite this, a deep mechanical comprehension of wind turbines operating in complicated conditions is still challenging, especially as regards the analysis of experimental data. In particular, wind
[...] Read more.
A wind turbine is a very well-known archetype of energy conversion system working at non-stationary regimes. Despite this, a deep mechanical comprehension of wind turbines operating in complicated conditions is still challenging, especially as regards the analysis of experimental data. In particular, wind turbines in complex terrain represent a very valuable testing ground because of the possible combination of wake effects among nearby turbines and flow accelerations caused by the terrain morphology. For these reasons, in this work, a cluster of four full-scale wind turbines from a very complex site is studied. The object of investigation is vibrations, at the level of the structure (tower) and drive-train. Data collected by the on-board condition monitoring system are analyzed and interpreted in light of the knowledge of wind conditions and operating parameters collected by the Supervisory Control And Data Acquisition (SCADA). A free flow Computational Fluid Dynamics (CFD) simulation is also performed, and it allows one to better interpret the vibration analysis. The main outcome is the interpretation of how wakes and flow turbulences appear in the vibration signals, both at the structural level and at the drive-train level. Therefore, this wind to gear approach builds a connection between flow phenomena and mechanical phenomena in the form of vibrations, representing a precious tool for assessing loads in different working conditions. Full article
(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)
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Open AccessArticle The Influence of Eroded Blades on Wind Turbine Performance Using Numerical Simulations
Energies 2017, 10(9), 1420; https://doi.org/10.3390/en10091420
Received: 23 August 2017 / Revised: 11 September 2017 / Accepted: 11 September 2017 / Published: 16 September 2017
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Abstract
During their operation, wind turbine blades are eroded due to rain and hail, or they are contaminated with insects. Since the relative inflow velocity is higher at the outer than at the inner part of the blades, erosion occurs mostly at the outer
[...] Read more.
During their operation, wind turbine blades are eroded due to rain and hail, or they are contaminated with insects. Since the relative inflow velocity is higher at the outer than at the inner part of the blades, erosion occurs mostly at the outer blade region. In order to prevent strong erosion, it is possible to install a leading edge protection, which can be applied to the blades after the initial installation, but changes the shape of the initial airfoil sections. It is unclear how this modification influences the aerodynamic performance of the turbine. Hence, it is investigated in this work. The NREL 5 MW turbine is simulated with clean and eroded blades, which are compared to coated blades equipped with leading edge protection. Aerodynamic polars are generated by means of Computational Fluid Dynamics, and load calculations are conducted using the blade element momentum theory. The analysis in this work shows that, compared to clean rotor blades, the worse aerodynamic behaviour of strongly eroded blades can lead to power losses of 9 % . In contrast, coated blades only have a small impact on the turbine power of less than 1 % . Full article
(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)
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Open AccessArticle Determining Division Location for Sectional Wind Turbine Blades
Energies 2017, 10(9), 1404; https://doi.org/10.3390/en10091404
Received: 22 July 2017 / Revised: 17 August 2017 / Accepted: 7 September 2017 / Published: 14 September 2017
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Abstract
Sectional wind turbine blades, by dividing an intact blade into multiple segments, have the advantage of being easy to handle and transport. To determine a suitable blade division location, this study was performed to clarify some crucial aspects and challenges for sectional blades.
[...] Read more.
Sectional wind turbine blades, by dividing an intact blade into multiple segments, have the advantage of being easy to handle and transport. To determine a suitable blade division location, this study was performed to clarify some crucial aspects and challenges for sectional blades. This paper proposes a method to estimate the effects of the location of the blade division on structural, manufacturing, and assembling performance of sectional blades. The advantage of this method is the ease of the assessment process, since it can be performed at an early stage of blade design, where only the aerodynamic profile, mass density and stiffness distribution, and service fatigue loads of original blades are essential. A case study with the proposed method was carried out based on a 38-meter commercial blade. Results show that the best position for the division of sectional blades is located 20% from the blade root by balancing the three aspects listed above. The key approaches to reduce additional increases in stiffness and weight of sectional blades are related to improving the fatigue strength and the choice of low-modulus materials for connecting bolts. The effects of the division location on assembling accessibility and natural frequencies of scaled sectional blades are consistent with the basic sectional blade. Unfavorable effects occur when up-scaling the diameter of the bolts; and, harsh external loads on the connections have negative effects on the application of sectional blades with larger wind turbines. In this regard, lightweight design is indispensable to reduce bolt stress. Full article
(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)
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Open AccessArticle An Investigation into the Effect of Scour on the Loading and Deformation Responses of Monopile Foundations
Energies 2017, 10(8), 1190; https://doi.org/10.3390/en10081190
Received: 10 June 2017 / Revised: 3 August 2017 / Accepted: 4 August 2017 / Published: 11 August 2017
Cited by 2 | PDF Full-text (4722 KB) | HTML Full-text | XML Full-text
Abstract
Severe foundation scour may occur around monopile foundations of offshore wind turbines due to currents and waves. The so-called p-y curves method is suggested in the existing design recommendations to determine the behavior of monopiles unprotected against scour and the reduction of effective
[...] Read more.
Severe foundation scour may occur around monopile foundations of offshore wind turbines due to currents and waves. The so-called p-y curves method is suggested in the existing design recommendations to determine the behavior of monopiles unprotected against scour and the reduction of effective soil stress is accounted for by the extreme scour depth. This conservative design approach does not consider the geometry of the scour hole and the effect of pile diameter on the soil resistance. An underestimated foundation stiffness would be obtained, thereby influencing the predicted overall response of the support structure of an offshore wind turbine. In this study, we calculated the load-deformation response and foundation stiffness of a monopile when scour occurred. The influence of pile diameter on the initial modulus of subgrade reaction, and the modification of the ultimate soil resistance of a monopile subject to scour are evaluated. The commercial software BLADED was used to simulate the dynamic response of the reference offshore wind turbine with monopile unprotected against scour at Chang-Bin offshore wind farm in Taiwan Strait. The results showed that when the p-y curve suggested by existing design regulation was used to calculate the load-deformation response, the foundation stiffness was underestimated where the scour depth was greater than the pile diameter, but the foundation stiffness was overestimated when the scour depth was less than the pile diameter. Full article
(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)
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