High-quality Wind Research Articles

The performance of Aeolus in heterogeneous atmospheric conditions using high-resolution radiosonde data

Abstract. The European Space Agency Aeolus mission aims to measure wind profiles from space. A major challenge is to retrieve high quality winds in heterogeneous atmospheric conditions, i.e. where both the atmospheric dynamics and optical properties vary strongly within the sampling volume. In preparation for launch we aim to quantify the expected error of retrieved winds from atmospheric heterogeneity, particularly in the vertical, and develop algorithms for wind error correction, as part of the level-2B processor (L2Bp). We demonstrate that high-resolution data from radiosondes provide valuable input to establish a database of collocated wind and atmospheric optics at 10 m vertical resolution to simulate atmospheric conditions along Aeolus' lines of sight. The database is used to simulate errors of Aeolus winds retrieved from the Mie and Rayleigh channel signals. The non-uniform distribution of molecules in the measurement bin introduces height assignment errors in Rayleigh channel winds up to 2.5% of the measurement bin size in the stratosphere which translates to 0.5 m s−1 bias for typical atmospheric conditions, if not corrected. The presence of cloud or aerosol layers in the measurement bin yields biases in Mie channel winds which cannot be easily corrected and mostly exceed the mission requirement of 0.4 m s−1. The collocated Rayleigh channel wind solution is generally preferred because of smaller biases, in particular for transparent cloud and aerosol layers with one-way transmission above 0.8. The results show that Aeolus L2Bp, under development, can be improved by the estimation of atmosphere optical properties to correct for height assignment errors and to identify wind solutions potentially detrimental when used in Numerical Weather Prediction.

Experimental Comparison of Three Floating Wind Turbine Concepts

Beyond many of Earth's coasts exists a vast deepwater wind resource that can be tapped to provide substantial amounts of clean, renewable energy. However, much of this resource resides in waters deeper than 60 m where current fixed bottom wind turbine technology is no longer economically viable. As a result, many are looking to floating wind turbines as a means of harnessing this deepwater offshore wind resource. The preferred floating platform technology for this application, however, is currently up for debate. To begin the process of assessing the unique behavior of various platform concepts for floating wind turbines, 1/50th scale model tests in a wind/wave basin were performed at the Maritime Research Institute Netherlands (MARIN) of three floating wind turbine concepts. The Froude scaled tests simulated the response of the 126 m rotor diameter National Renewable Energy Lab (NREL) 5 MW, horizontal axis Reference Wind Turbine attached via a flexible tower in turn to three distinct platforms, these being a tension leg-platform, a spar-buoy, and a semisubmersible. A large number of tests were performed ranging from simple free-decay tests to complex operating conditions with irregular sea states and dynamic winds. The high-quality wind environments, unique to these tests, were realized in the offshore basin via a novel wind machine, which exhibited low swirl and turbulence intensity in the flow field. Recorded data from the floating wind turbine models include rotor torque and position, tower top and base forces and moments, mooring line tensions, six-axis platform motions, and accelerations at key locations on the nacelle, tower, and platform. A comprehensive overview of the test program, including basic system identification results, is covered in previously published works. In this paper, the results of a comprehensive data analysis are presented, which illuminate the unique coupled system behavior of the three floating wind turbines subjected to combined wind and wave environments. The relative performance of each of the three systems is discussed with an emphasis placed on global motions, flexible tower dynamics, and mooring system response. The results demonstrate the unique advantages and disadvantages of each floating wind turbine platform.

Variable Torque Control of Offshore Wind Turbine on Spar Floating Platform Using Advanced RBF Neural Network

Offshore floating wind turbine (OFWT) has been a challenging research spot because of the high-quality wind power and complex load environment. This paper focuses on the research of variable torque control of offshore wind turbine on Spar floating platform. The control objective in below-rated wind speed region is to optimize the output power by tracking the optimal tip-speed ratio and ideal power curve. Aiming at the external disturbances and nonlinear uncertain dynamic systems of OFWT because of the proximity to load centers and strong wave coupling, this paper proposes an advanced radial basis function (RBF) neural network approach for torque control of OFWT system at speeds lower than rated wind speed. The robust RBF neural network weight adaptive rules are acquired based on the Lyapunov stability analysis. The proposed control approach is tested and compared with the NREL baseline controller using the “NREL offshore 5 MW wind turbine” model mounted on a Spar floating platform run on FAST and Matlab/Simulink, operating in the below-rated wind speed condition. The simulation results show a better performance in tracking the optimal output power curve, therefore, completing the maximum wind energy utilization.

The role of hydrogen-based energy storage in the support of large-scale wind energy integration in island grids

To confront problems concerning large-scale integration of renewable energy sources, introduction of energy storage constantly gains ground. Benefits stemming from the adoption of energy storage include exploitation of otherwise rejected energy, increased reliability of energy supply and improved operation of a given power system overall. In this regard, contribution of such systems in achieving large-scale integration of wind energy into island grids is currently considered. More precisely, fuel cells and hydrogen storage (FC–HS) are investigated, in comparison with conventional batteries. For this purpose, a simulation algorithm is developed to study the energy performance of different FC–HS configurations used to recover wind energy curtailments. The developed algorithm is then applied to a representative Aegean island of medium–high quality wind potential. Results obtained indicate that FC–HS may become attractive in comparison with conventional batteries, only in the case that the use of hydrogen surplus to cover other energy flows is also put forward.

Wind energy and natural gas-based energy storage to promote energy security and lower emissions in island regions

Usually, isolated and remote areas, like islands, meet their electricity needs using oil-fired power generators. When available, natural gas can potentially substitute oil. Moreover, the high-quality wind energy potential found in many of these areas cannot be used extensively. Main reason is the operation of small-scale, weak electricity grids which cannot cope with wind energy intermittency. To compensate for that, we examine the combination of wind energy and energy storage. For the latter we focus on the technology of compressed air energy storage (CAES), which is suitable for scalable applications. To ensure the highest level of demand satisfaction, while avoiding system oversizing, we recommend a novel Wind–CAES system that allows switch from the CAES to the Brayton cycle when the stored energy is inadequate to meet demand. We develop a new algorithm for the sizing of such configurations, and use it on a case study that includes a typical, medium-scale Aegean Sea island in combination with three representative wind regimes. The results demonstrate that even in areas with relatively low-quality wind potential there are significant improvements in fuel use reduction, CO2 emissions and strengthening of energy supply security, while for island regions with higher-quality wind potential, the proposed solution also becomes cost-effective in comparison to other alternatives.

Wind Energy Meteorology: Insight into Wind Properties in the Turbine-Rotor Layer of the Atmosphere from High-Resolution Doppler Lidar

Addressing the need for high-quality wind information aloft in the layer occupied by turbine rotors (~30–150 m above ground level) is one of many significant challenges facing the wind energy industry. Without wind measurements at heights within the rotor sweep of the turbines, characteristics of the flow in this layer are unknown for wind energy and modeling purposes. Since flow in this layer is often decoupled from the surface, near-surface measurements are prone to errant extrapolation to these heights, and the behavior of the near-surface winds may not reflect that of the upper-level flow.

Horizontal axis wind turbine dynamic stall predictions based on wind speed and direction variability

The onset of dynamic stall in horizontal axis wind turbines (HAWTs) is related to the rapid increase in the angle of attack caused by sudden changes in wind speed and direction. In order to relate the changes in wind speed and direction with the variations in the blade-section angle of attack, an analytical model is proposed to determine the regions of the blade affected by dynamic stall. The so-called threshold radius has been identified and defined as the percentage of the blade length from the horizontal axis wind turbines hub beyond which the probability of dynamic stall occurrence falls to zero. High quality wind data were acquired to determine the average wind conditions that serve as the model inputs. It is shown that the rate of change of wind speed, due to gusts or the average turbulence, can cause large regions of dynamic stall on the wind turbine blade. Other parameters, such as the yaw misalignment and the rate of change of yaw angle are shown to be the cause of asymmetrical distribution of threshold radius with azimuth and also serve to increase the affected regions. Finally it is shown that the type of airfoil used in the turbine blade also has a significant effect on the threshold radius due to the different limiting reduced frequencies.

Computationally Inexpensive Approach for Pitch Control of Offshore Wind Turbine on Barge Floating Platform

Offshore floating wind turbine (OFWT) has gained increasing attention during the past decade because of the offshore high-quality wind power and complex load environment. The control system is a tradeoff between power tracking and fatigue load reduction in the above-rated wind speed area. In allusion to the external disturbances and uncertain system parameters of OFWT due to the proximity to load centers and strong wave coupling, this paper proposes a computationally inexpensive robust adaptive control approach with memory-based compensation for blade pitch control. The method is tested and compared with a baseline controller and a conventional individual blade pitch controller with the “NREL offshore 5 MW baseline wind turbine” being mounted on a barge platform run on FAST and Matlab/Simulink, operating in the above-rated condition. It is shown that the advanced control approach is not only robust to complex wind and wave disturbances but adaptive to varying and uncertain system parameters as well. The simulation results demonstrate that the proposed method performs better in reducing power fluctuations, fatigue loads and platform vibration as compared to the conventional individual blade pitch control.

Extreme Waves and Wave Run-up in Halifax Harbour under Climate Change Scenarios

The tendency for rising sea levels, combined with changes in the frequency and intensity of extreme storm events raises the potential for flooding and inundation of coastal locations such as Halifax Harbour, in the context of climate change. In this study, we consider three scenarios for extreme high water levels based on climate change scenarios and estimates for land subsidence, rising mean sea levels, and return period analysis for extreme events (from previous studies). We also investigate the effect of ocean waves on these estimates for extreme high water levels. Because the most damaging storm to make landfall in Nova Scotia over the last century was Hurricane Juan (2003), it was chosen to simulate the extreme case of storm-generated waves and wave run-up in Halifax Harbour. To simulate waves generated by Hurricane Juan, a nested-grid system consisting of two modern state-of-the-art operational wave models was used. High quality winds were used to drive the wave models, and the simulations used recently updated high resolution coastal bathymetry. Observed water elevation changes in Halifax Harbour were used in wave model simulations of Hurricane Juan. The Federal Emergency Management Agency's (FEMA) run-up model is used to estimate wave run-up elevation, which is validated with recorded high water observations along the coastline. Simulated waves and wave run-up elevations for Hurricane Juan suggest that the maximum significant wave heights at the mouth of the Harbour were 9.0 m, and the wave run-up was as high as 2.0 m along the shoreline of Halifax Harbour. In this way, we estimated the impact of waves and wave run-up on extreme high water elevations for three climate change scenarios in Halifax Harbour, under worst-case conditions. The sensitivity of these estimates is analyzed for different water level variations, wave propagation directions and shore slope profiles. [Traduit par la rédaction] La tendance à la hausse du niveau de la mer de pair avec les changements dans la fréquence et l'intensité des événements de tempêtes extrêmes augmentent le risque d'inondation et de submersion à des emplacements côtiers comme le port d'Halifax dans le contexte du changement climatique. Dans cette étude, nous examinons trois scénarios de niveaux de hautes eaux extrêmes basés sur des scénarios de changement climatique et estimations de subsidence du terrain, l’élévation du niveau moyen de la mer ainsi que l'analyse de la période de retour d’événements extrêmes (faite lors d’études antérieures). Nous examinons aussi les effets des vagues de l'océan sur ces estimations de niveaux de hautes eaux extrêmes. Étant donné que la tempête la plus dévastatrice à avoir touché terre en Nouvelle–Écosse au cours du dernier siècle a été l'ouragan Juan (2003), c'est celle-ci que nous avons choisie pour simuler le cas extrême de vagues produites par une tempête et de remontée de vagues dans le port d'Halifax. Pour simuler les vagues produites par Juan, nous nous sommes servis d'un système à grilles imbriquées consistant en deux modèles de vagues opérationnels à la fine pointe de la technologie. Les modèles de vagues étaient pilotés par des données de vent de haute qualité et les simulations disposaient d'une bathymétrie côtière à haute résolution récemment mise à jour. Les changements observés d’élévation de l'eau dans le port d'Halifax ont été utilisés dans les simulations de l'ouragan Juan par les modèles de vagues. Nous utilisons le modèle de remontée des vagues de la Federal Emergency Management Agency (FEMA) pour estimer la hauteur des remontées, qui est validée par rapport aux observations de hautes eaux enregistrées le long de la côte. Les vagues et les hauteurs de remontée des vagues simulées pour l'ouragan Juan suggèrent que la hauteur significative maximale des vagues à l'entrée du port était de 9,0 m et la remontée des vagues atteignait 2,0 m le long de la côte du port d'Halifax. Nous avons de cette manière estimé l'impact des vagues et de la remontée des vagues sur l’élévation des hautes eaux extrêmes pour trois scénarios de changement climatique dans le port d'Halifax dans les conditions les plus défavorables. Nous analysons la sensibilité de ces estimations à divers changements de niveau d'eau, directions de propagation et profils de pente côtière.

Nested ensemble NWP approach for wind energy assessment

High quality wind data is needed to conduct wind resource assessment. Numerical Weather Prediction (NWP) models were recently used to provide the desired data. The current uncertainty sources in NWP models introduce uncertainties in wind resource assessment. More accurate NWP wind data will lead to more accurate resource assessment, wind turbine micrositing and energy short-term forecasting. Using one single NWP model may lead to undesired results compared to the huge investment in wind energy projects. New capabilities and strategies to quantify and reduce the uncertainty of wind data from NWP models are required. This paper proposed the use of nested ensemble NWP model for the wind resource assessment. This approach will provide information about the uncertainty of the NWP models and provide probabilistic information for researchers compared to the current use of single NWP model. A case study of the proposed approach is presented with four ensemble members using 7 km resolution over Oman. Verification results shows that the NWP ensemble mean performs better in average than individual members.

A wind-tunnel study of flow distortion at a meteorological sensor on top of the BT Tower, London, UK

High quality wind measurements in cities are needed for numerous applications including wind engineering. Such data-sets are rare and measurement platforms may not be optimal for meteorological observations. Two years' wind data were collected on the BT Tower, London, UK, showing an upward deflection on average for all wind directions. Wind tunnel simulations were performed to investigate flow distortion around two scale models of the Tower. Using a 1:160 scale model it was shown that the Tower causes a small deflection (ca. 0.5°) compared to the lattice on top on which the instruments were placed (ca. 0–4°). These deflections may have been underestimated due to wind tunnel blockage. Using a 1:40 model, the observed flow pattern was consistent with streamwise vortex pairs shed from the upstream lattice edge. Correction factors were derived for different wind directions and reduced deflection in the full-scale data-set by <3°. Instrumental tilt caused a sinusoidal variation in deflection of ca. 2°. The residual deflection (ca. 3°) was attributed to the Tower itself. Correction of the wind-speeds was small (average 1%) therefore it was deduced that flow distortion does not significantly affect the measured wind-speeds and the wind climate statistics are reliable.

Clinical Skills Development Using On-line Problem-Based Learning for Assessment, Management and Prevention of Pressure Ulcers in Persons With Spinal Cord Injury

Pressure ulcers (PUs) constitute a health problem that is one of the greatest contributors to morbidity secondary to spinal cord injury (SCI). Research efforts in the Rehabilitation Research and Training Center on Secondary Conditions in the Rehabilitation of Individuals with Spinal Cord Injury address the problem by identifying gaps in the knowledge base, specifically, determining the interrelationships between pressure, pressure relief, and skin breakdown in persons with SCI. Education and training efforts complement this research by exploring more effective means of transferring and mobilizing knowledge about PUs in persons with SCI and those who help them manage their health. There is little evidence regarding what constitutes high-quality PU and wound care education for resident physicians and other health care professionals. The purpose of this article is to provide a review of the literature on applications of digital multimedia to facilitate evaluation of clinical skills among medical trainees. We...

Study on Material Selection and Manufacturing Process of Wind Turbine Blades

The materials and structural characteristics of several kinds of wind turbine blades are introduced and analyzed as well as the advantages and disadvantages of blades composites in this paper. Then the manufacturing technologies between traditional and high-quality composite wind turbine blades are studied and compared in this paper.

A Study on Taper-Tension Control Considering Telescoping in the Winding System

Winding is an integral operation in almost every web-handling process. Center winding is suitable and a general scheme in winding systems. However, the internal stresses within center-wound rolls can cause damage such as buckling, spoking, cinching, etc. Wound-roll quality and performance are known to be related to distribution of in-roll stresses. It is therefore necessary to analyze the relationships between taper tension in the winding section and internal stress distribution within center-wound roll to prevent winding failure (starring, buckling, telescoping, etc.). In this paper, a new taper-tension-control method for producing high-quality wound roll is developed. The new method is induced from analyzing the winding mechanism by using the stress model in center-wound rolls, taper-tension profile telescoping relationship, and taper-tension-type internal-stress relationship, etc. Auto taper-tension profile making method for avoiding the damage (telescoping, starring, etc.) is presented. The experimental results show that the proposed method is very useful.

An investigation of ship airwakes using Detached-Eddy Simulation

Computational Fluid Dynamics simulations of ship airwakes have been performed using Detached-Eddy Simulation (DES) on unstructured grids. A generic simple frigate shape (SFS2) and a Royal Navy Type 23 Frigate (T23) have been studied at several wind-over-deck (WOD) conditions. A comprehensive validation exercise has been performed, comparing CFD results of the airwake calculated for the SFS2 with high quality wind tunnel data provided by the National Research Council of Canada. Comparisons of mean quantities and velocity spectra show good agreement, indicating that DES is able to resolve the large-scale turbulent structures which can adversely impact helicopter–ship operations. An analysis of the airwake flow topology at headwind and Green 45° conditions highlights the dominant flow features over the flight deck and it is shown that significant differences exist between the two WOD angles. T23 airwake data has been compared to full-scale experimental results obtained at sea. It is shown that the inclusion of an atmospheric boundary layer velocity profile in the CFD computations improves the agreement with full-scale data. Qualitative comparison between the simple frigate shape and T23 airwakes shows that large-scale flow patterns are similar; but subtle differences exist, particularly at more oblique WOD angles.

Tilting at Windmills? The Environmental Movement and the Emergence of the U.S. Wind Energy Sector

Through a study of the emergent U.S. wind energy sector, 1978–1992, this paper examines how large-scale social movements external to an industry can influence the creation of new market opportunities and hence encourage entrepreneurship. We theorize that through the construction and propagation of cognitive frameworks, norms, values, and regulatory structures, and by offering a preexisting social structure, social movement organizations influence whether entrepreneurs attempt to start ventures in emerging sectors. We find that the direct and indirect effects of social resources (e.g., environmental groups) had a larger impact on entrepreneurial activity in this sector than the availability of natural resources such as land with high-quality wind. Greater numbers of environmental movement organization members increased nascent entrepreneurial activity, and this effect was mediated by favorable state regulatory policy. Greater membership numbers also enhanced the effects of important natural resources, market conditions, and skilled human capital on entrepreneurial activity. Taken together, these results have important implications for the study of social movements, entrepreneurship, and institutional theory.

A taper tension profile maker in a converting machine

Winding is an integral operation in almost every web handling process, and a center-wound roll is one of the suitable and general schemes in a winding system. However, improper internal stresses within a center-wound roll can cause damage such as buckling, spoking, cinching, etc. Wound roll quality and performance are known to be related to the distribution of in-roll stresses. It is therefore necessary to analyze the relationship between taper tension in the winding section and internal stress distribution within the center-wound roll to prevent winding failure. But it is hard to compensate for an undesirable winding roll shape such as starring, buckling, and telescoping. This is because the winding section is the final process in a roll to roll system and has no feedback control system to correct winding roll shape directly. A time varying tension profile and accurate control of it in a winding section is one way to shape the fail-safe in-roll stress distribution of a winding roll. In this study, a new taper tension profile making method is aimed for designing high quality wound rolls. A new method to determine the proper taper tension profile was designed by analyzing the winding mechanism which includes the stress model in center-wound rolls, nip induced tension model, relationship between taper tension profile and telescoping, relationship between taper tension type and internal stress distribution. An auto taper tension profile making method was proposed not only to optimize radial stress distribution but also to minimize lateral error (telescoping). Simulation results show that the proposed method is very useful for determining the desirable taper tension profile during the winding process and preventing defects of winding roll shape such as telescoping, starting, and dishing and so on.

Study on Ocean Wind Vector Retrieval from ERS‐2 SAR Image

AbstractSAR (Synthetic Aperture Radar) wind retrieval is a hot research topic in current Remote Sensing field. In this paper the principle of space borne SAR ocean wind retrieval and three related retrieval algorithms are introduced firstly. Then, the flowchart of the retrieval procedures is provided. As an example, ERS‐2 SAR image covering Hong Kong region acquired on May 7, 2002 is used for wind vector retrieval. The classic SAR Wind Direction Algorithm ‐ spectral method is improved, and applied for the retrieval. The wind direction thus estimated is however with 180º ambiguity. Buoy data collected by the Hong Kong Observatory are then used to resolve the uncertainty. Finally, the GMF (Geophysical Model Function)‐CMOD4 is adopted to estimate the wind speed at the height of 10 m above sea level. Compared with the data recorded by Hong Kong Observatory, the error in the wind direction and average wind speed are very small. The results show that accurate ADC (Analog to Digital Converter) compensation and image calibration, together with improved SWDA and CMOD4 algorithms, could offer high quality wind vector.

The MEXICO project (Model Experiments in Controlled Conditions): The database and first results of data processing and interpretation

The Mexico (Model experiments in Controlled Conditions) was a FP5 project, partly financed by European Commission. The main objective was to create a database of detailed aerodynamic and load measurements on a wind turbine model, in a large and high quality wind tunnel, to be used for model validation and improvement. Here model stands for both the extended BEM modelling used in state-of-the-art design and certification software, and CFD modelling of the rotor and near wake flow. For this purpose a three bladed 4.5 m diameter wind tunnel model was built and instrumented. The wind tunnel experiments were carried out in the open section (9.5*9.5 m2) of the Large Scale Facility of the DNW (German-Netherlands) during a six day campaign in December 2006. The conditions for measurements cover three operational tip speed ratios, many blade pitch angles, three yaw misalignment angles and a small number of unsteady cases in the form of pitch ramps and rotor speed ramps. One of the most important feats of the measurement program was the flow field mapping, with stereo PIV techniques. Overall the measurement campaign was very successful. The paper describes the now existing database and discusses a number of highlights from early data processing and interpretation. It should be stressed that all results are first results, no tunnel correction has been performed so far, nor has the necessary checking of data quality.

Discussing the Relationship Between Quality Care and Cost-Effective Care in Swiss Pediatric Wound Care

The growing individual and public demand for high-quality care within a context of restricted budgets dominates the political as well as medical agenda. This demand for "quality care" has developed an "industry" and lobby relating to auditing practice even in the small subpopulation of pediatric surgical patients. With children, complex and nonhealing wounds are quite rare, but there are pressures to provide modern and high-quality wound care even in Switzerland. Thus, in accordance with practice in neighboring countries, guidelines for wound care have been established in the Swiss healthcare sector. Their validity and reliability in the context of cost-effective versus quality care are critically discussed in this paper.