Literature Survey of Wind Turbine Aeroelastic Stability

A literature survey of wind turbine aeroelastic stability is presented. The subject received early interest as the emergent wind industry looked to lessons from the helicopter industry. There has not been a utility-scale turbine with flutter problems, but there is a concern over the behavior of larger, more flexible turbines. Blades of innovative design with bend-twist coupling and tip sweep are also a concern. Much of the aerodynamic modeling was formulated in the 1930s by Theodorsen. Modern authors have developed finite element structural models for eigenvalue solutions to the stability models. Calculations for a 1.5 MW turbine blade with bend-twist coupling show flutter speed at twice the rotor rotational speed. Comparisons were made to standard turbine aeroelastic codes showing good agreement, and the possibility of using these codes to check for flutter

Literature Survey of Wind Turbine Aeroelastic Stability

A literature survey of wind turbine aeroelastic stability is presented. The subject received early interest as the emergent wind industry looked to lessons from the helicopter industry. There has not been a utility-scale turbine with flutter problems, but there is a concern over the behavior of larger, more flexible turbines. Blades of innovative design with bend-twist coupling and tip sweep are also a concern. Much of the aerodynamic modeling was formulated in the 1930s by Theodorsen. Modern authors have developed finite element structural models for eigenvalue solutions to the stability models. Calculations for a 1.5 MW turbine blade with bend-twist coupling show flutter speed at twice the rotor rotational speed. Comparisons were made to standard turbine aeroelastic codes showing good agreement, and the possibility of using these codes to check for flutter

Comparison of upwind and downwind operation of the NREL Phase VI Experiment

Wind tunnel data are presented comparing upwind versus downwind operation of the National Renewable Energy Laboratory\u27s Phase VI wind turbine. Power was not reduced as expected with downwind operation, which may be attributed to inboard three-dimensional effects. Average flap bending loads were reduced with downwind coning and compared well with prediction. Blade fatigue loads were increased with downwind operation; however, fatigue was mitigated with an aerodynamic tower shroud (fairing). The shroud needs to remain aligned with the freestream, demonstrated by an increase in fatigue loads from a 10° error in shroud alignment. Pressure data were acquired of the tower wake at the rotor location with and without the shroud installed. The bare-tower wake data compared well with previously published work. The shroud wake data at 10° error in alignment showed velocity reduction and turbulence approaching the bare tower values. Downwind operation, with an aligning tower shroud, should be considered for future designs given the load benefits of downwind coning

Gilbert ROUGET : Initiatique vôdoun : Images du rituel (vol. 1) ; Initiatique vôdun : Musique du rituel (vol. 2) (Sonagrammes et transcriptions musicales de Jean Schwarz et Tran Quâng Hai en collaboration avec l’auteur)

Cette œuvre magistrale de Gilbert Rouget est la suite logique d’Un roi africain et sa musique de cour (1996). En effet, après les rituels royaux, ce sont à ceux pratiqués dans le cadre plus général du culte des vôdoun au Bénin du Sud que l’auteur a décidé de consacrer cet ouvrage important. Mais, alors que celui-là constituait un seul livre homogène, dans lequel étaient insérés deux disques compacts, celui-ci se compose de deux volumes : un livre et un dossier, comportant deux disques compact..

Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK.

BACKGROUND: A safe and efficacious vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), if deployed with high coverage, could contribute to the control of the COVID-19 pandemic. We evaluated the safety and efficacy of the ChAdOx1 nCoV-19 vaccine in a pooled interim analysis of four trials. METHODS: This analysis includes data from four ongoing blinded, randomised, controlled trials done across the UK, Brazil, and South Africa. Participants aged 18 years and older were randomly assigned (1:1) to ChAdOx1 nCoV-19 vaccine or control (meningococcal group A, C, W, and Y conjugate vaccine or saline). Participants in the ChAdOx1 nCoV-19 group received two doses containing 5 × 1010 viral particles (standard dose; SD/SD cohort); a subset in the UK trial received a half dose as their first dose (low dose) and a standard dose as their second dose (LD/SD cohort). The primary efficacy analysis included symptomatic COVID-19 in seronegative participants with a nucleic acid amplification test-positive swab more than 14 days after a second dose of vaccine. Participants were analysed according to treatment received, with data cutoff on Nov 4, 2020. Vaccine efficacy was calculated as 1 - relative risk derived from a robust Poisson regression model adjusted for age. Studies are registered at ISRCTN89951424 and ClinicalTrials.gov, NCT04324606, NCT04400838, and NCT04444674. FINDINGS: Between April 23 and Nov 4, 2020, 23 848 participants were enrolled and 11 636 participants (7548 in the UK, 4088 in Brazil) were included in the interim primary efficacy analysis. In participants who received two standard doses, vaccine efficacy was 62·1% (95% CI 41·0-75·7; 27 [0·6%] of 4440 in the ChAdOx1 nCoV-19 group vs71 [1·6%] of 4455 in the control group) and in participants who received a low dose followed by a standard dose, efficacy was 90·0% (67·4-97·0; three [0·2%] of 1367 vs 30 [2·2%] of 1374; pinteraction=0·010). Overall vaccine efficacy across both groups was 70·4% (95·8% CI 54·8-80·6; 30 [0·5%] of 5807 vs 101 [1·7%] of 5829). From 21 days after the first dose, there were ten cases hospitalised for COVID-19, all in the control arm; two were classified as severe COVID-19, including one death. There were 74 341 person-months of safety follow-up (median 3·4 months, IQR 1·3-4·8): 175 severe adverse events occurred in 168 participants, 84 events in the ChAdOx1 nCoV-19 group and 91 in the control group. Three events were classified as possibly related to a vaccine: one in the ChAdOx1 nCoV-19 group, one in the control group, and one in a participant who remains masked to group allocation. INTERPRETATION: ChAdOx1 nCoV-19 has an acceptable safety profile and has been found to be efficacious against symptomatic COVID-19 in this interim analysis of ongoing clinical trials. FUNDING: UK Research and Innovation, National Institutes for Health Research (NIHR), Coalition for Epidemic Preparedness Innovations, Bill & Melinda Gates Foundation, Lemann Foundation, Rede D'Or, Brava and Telles Foundation, NIHR Oxford Biomedical Research Centre, Thames Valley and South Midland's NIHR Clinical Research Network, and AstraZeneca

Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK

Background A safe and efficacious vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), if deployed with high coverage, could contribute to the control of the COVID-19 pandemic. We evaluated the safety and efficacy of the ChAdOx1 nCoV-19 vaccine in a pooled interim analysis of four trials. Methods This analysis includes data from four ongoing blinded, randomised, controlled trials done across the UK, Brazil, and South Africa. Participants aged 18 years and older were randomly assigned (1:1) to ChAdOx1 nCoV-19 vaccine or control (meningococcal group A, C, W, and Y conjugate vaccine or saline). Participants in the ChAdOx1 nCoV-19 group received two doses containing 5 × 1010 viral particles (standard dose; SD/SD cohort); a subset in the UK trial received a half dose as their first dose (low dose) and a standard dose as their second dose (LD/SD cohort). The primary efficacy analysis included symptomatic COVID-19 in seronegative participants with a nucleic acid amplification test-positive swab more than 14 days after a second dose of vaccine. Participants were analysed according to treatment received, with data cutoff on Nov 4, 2020. Vaccine efficacy was calculated as 1 - relative risk derived from a robust Poisson regression model adjusted for age. Studies are registered at ISRCTN89951424 and ClinicalTrials.gov, NCT04324606, NCT04400838, and NCT04444674. Findings Between April 23 and Nov 4, 2020, 23 848 participants were enrolled and 11 636 participants (7548 in the UK, 4088 in Brazil) were included in the interim primary efficacy analysis. In participants who received two standard doses, vaccine efficacy was 62·1% (95% CI 41·0–75·7; 27 [0·6%] of 4440 in the ChAdOx1 nCoV-19 group vs71 [1·6%] of 4455 in the control group) and in participants who received a low dose followed by a standard dose, efficacy was 90·0% (67·4–97·0; three [0·2%] of 1367 vs 30 [2·2%] of 1374; pinteraction=0·010). Overall vaccine efficacy across both groups was 70·4% (95·8% CI 54·8–80·6; 30 [0·5%] of 5807 vs 101 [1·7%] of 5829). From 21 days after the first dose, there were ten cases hospitalised for COVID-19, all in the control arm; two were classified as severe COVID-19, including one death. There were 74 341 person-months of safety follow-up (median 3·4 months, IQR 1·3–4·8): 175 severe adverse events occurred in 168 participants, 84 events in the ChAdOx1 nCoV-19 group and 91 in the control group. Three events were classified as possibly related to a vaccine: one in the ChAdOx1 nCoV-19 group, one in the control group, and one in a participant who remains masked to group allocation. Interpretation ChAdOx1 nCoV-19 has an acceptable safety profile and has been found to be efficacious against symptomatic COVID-19 in this interim analysis of ongoing clinical trials

Prediction and Alleviation of Flutter in Swept Wind Turbine Blades

Previous research has shown that as wind turbine rotor designs increase in diameter they approach flutter instabilities. Recent blade designs incorporate blade sweep to lower fatigue loads and increase rotor diameter for more energy production; however, the flutter margin may be reduced with sweep. In this work, the author predicted and compared the flutter speed for turbines with straight and swept blades. For the study, the author used a wind turbine analysis tool specifically developed for blade sweep (CurveFAST), in addition to a tool developed for helicopter analysis (RCAS). The results showed that CurveFAST generally preceded a higher flutter speed and RCAS predicted a lower flutter speed compared to previous research. The difference may be attributed to the unsteady aerodynamics modeling. Results for an extended radius and swept 5 MW turbine showed the flutter speed was most sensitive to the position of the blade center of mass axis. Using the selected design parameters, it was not possible to design a swept-5 MW blade with adequate flutter margin that would produce 5% more energy with the same loads as a baseline straight rotor

FAA Obstruction Lighting Standards for Wind Energy Plants

With heights of modern utility-scale wind turbines exceeding 200 ft (61 m), wind energy developers in recent years have had to submit lighting proposals for wind plants to the Federal Aviation Administration (FAA). The current FAA guidelines for wind plant obstruction lighting have not been developed to a level where developers can know with some certainty what lighting scheme the FAA will approve for proposed construction. The California Wind Energy Collaborative (CWEC) initiated a study of FAA obstruction lighting for wind plants to determine the issues surrounding the subject. A literature survey and interviews on the subject were conducted. During the period of investigation,the CWEC was able to observe flight tests with the FAA of a wind farm configured for new lighting standards. Key elements of the proposed standards are synchronization of the flashing lights and maximum 0.5 mi. (0.8 km) spacing between lighted turbines. It is expected that the new standards will improve flight safety and streamline the FAA recommendation and permitting processes for wind plant developments

Wind Turbine Wake Measurements in the Operating Region of a Tail Vane

In conjunction with the National Renewable Energy Laboratory\u27s (NREL\u27S) Unsteady Aerodynamics Experiment (UAE) at NASA Ames, we measured the wake of an upwing 10 meter (m) diameter wind turbine in the typical region of a tail vane. The experiment was performed in a 24.4- by 36.6-m wind tunnel. We placed two sonic anemometers 0.58 rotor diameters downwind of the rotor at hub height. One was positioned nominally behind the nacelle at 9% radius and the second was placed 2-m outboard at 49%. The tunnel wind speed was varied from 5 to 25 meters per second (m/s) and the turbine rotor speed was held at 72 revolutions per minute (rom). We varied yaw from 0° to 60°. The data showed unsteadiness in the wake due to the nacelle wake. Also, the unsteadiness increased with the onset of blade stall. The axial induction factor in the wake showed that the turbine was operating within the windmill brake state of actuator disk momentum theory. Little variation in unsteadiness was shown under yawed conditions. We also discovered that lateral velocity behind the nacelle was negative and would result in an unfurling normal force on a tail vane. The vertical velocity was shown to change sign under yawed conditions, conceivable as a result of the opposing blade root vorte