Equivalent Wind Speed Research Articles

Fragility analysis and estimation of collapse status for transmission tower subjected to wind and rain loads

In this paper, the fragility analysis and concept of critical collapse curve for transmission tower subjected to wind and rain loads are presented to acquire the collapse equivalent basic wind speed and most unfavorable combinations of wind and rain loads corresponding to collapse status. The calculating method for wind and rain loads is simplified and the error analysis is performed to validate its effectiveness. The concept of equivalent basic wind speed is used to conduct the fragility analysis of transmission tower subjected to wind and rain loads which avoid the complex formula of rain load and the choice of different combinations of basic wind speed and rain intensity, and then the concept of critical collapse curve is proposed to evaluate the collapse status of transmission tower. At last the influence of wind attack angle and wind spectrum on the fragility and critical collapse curves is discussed, and results show that the wind attack angle and wind spectrum have a great influence on fragility and critical collapse curves. In this study, it can be seen that the use of equivalent basic wind speed make it possible to conduct the fragility analysis under wind and rain loads and the proposed concept of critical collapse curve is very convenient to evaluate the collapse status for structures subjected to wind and rain loads. In addition, the rain load has a great contribution to the tower collapse and should be paid more attention during severe gales and thunderstorms.

Comparison between Aggregation Techniques for PMSG Wind Farm

This paper presents a wind farm composed of different permanent synchronous generator (PMSG) wind turbines (same wind turbine technology but different rated power or operational conditions) coupled to the same grid connection point. A comparison between the three techniques of wind farm aggregation for a farm composed of PMSG wind turbines. Our comparison is for the closeness of the results of normal and transient response of both the complete model and the aggregated models. The chosen three techniques are, multi full aggregated model using equivalent wind speed (MFAM-EWS), semi aggregated model (SAM) and mixed semi full aggregated model (MSFAM). Simulation has been carried out for these techniques by MATLAB/SIMULINK program to compare them with the complete model to prove the effectiveness of each aggregation technique.

Modeling of the dynamics of wind to power conversion including high wind speed behavior

AbstractThis paper proposes and validates an efficient, generic and computationally simple dynamic model for the conversion of the wind speed at hub height into the electrical power by a wind turbine. This proposed wind turbine model was developed as a first step to simulate wind power time series for power system studies. This paper focuses on describing and validating the single wind turbine model, and is therefore neither describing wind speed modeling nor aggregation of contributions from a whole wind farm or a power system area. The state‐of‐the‐art is to use static power curves for the purpose of power system studies, but the idea of the proposed wind turbine model is to include the main dynamic effects in order to have a better representation of the fluctuations in the output power and of the fast power ramping especially because of high wind speed shutdowns of the wind turbine. The high wind speed shutdowns and restarts are represented as on–off switching rules that govern the output of the wind turbine at extreme wind speed conditions. The model uses the concept of equivalent wind speed, estimated from the single point (hub height) wind speed using a second‐order dynamic filter that is derived from an admittance function. The equivalent wind speed is a representation of the averaging of the wind speeds over the wind turbine rotor plane and is used as input to the static power curve to get the output power. The proposed wind turbine model is validated for the whole operating range using measurements available from the DONG Energy offshore wind farm Horns Rev 2. Copyright © 2015 John Wiley & Sons, Ltd.

Effects of Yaw Error on Wind Turbine Running Characteristics Based on the Equivalent Wind Speed Model

Natural wind is stochastic, being characterized by its speed and direction which change randomly and frequently. Because of the certain lag in control systems and the yaw body itself, wind turbines cannot be accurately aligned toward the wind direction when the wind speed and wind direction change frequently. Thus, wind turbines often suffer from a series of engineering issues during operation, including frequent yaw, vibration overruns and downtime. This paper aims to study the effects of yaw error on wind turbine running characteristics at different wind speeds and control stages by establishing a wind turbine model, yaw error model and the equivalent wind speed model that includes the wind shear and tower shadow effects. Formulas for the relevant effect coefficients Tc, Sc and Pc were derived. The simulation results indicate that the effects of the aerodynamic torque, rotor speed and power output due to yaw error at different running stages are different and that the effect rules for each coefficient are not identical when the yaw error varies. These results may provide theoretical support for optimizing the yaw control strategies for each stage to increase the running stability of wind turbines and the utilization rate of wind energy.

Customized rating assessment of climate suitability (CRACS): climate satisfaction evaluation based on subjective perception

Climate not only influences the behavior of people in urban environments but also affects people's schedules and travel plans. Therefore, providing people with appropriate long-term climate evaluation information is crucial. Therefore, we developed an innovative climate assessment system based on field investigations conducted in three cities located in Northern, Central, and Southern Taiwan. The field investigations included the questionnaire surveys and climate data collection. We first analyzed the relationship between the participants and climate parameters comprising physiologically equivalent temperature, air temperature, humidity, wind speed, solar radiation, cloud cover, and precipitation. Second, we established the neutral value, comfort range, and dissatisfied range of each parameter. Third, after verifying that the subjects' perception toward the climate parameters vary based on individual preferences, we developed the customized rating assessment of climate suitability (CRACS) approach, which featured functions such as personalized and default climate suitability information to be used by users exhibiting varying demands. Finally, we performed calculations using the climate conditions of two cities during the past 10 years to demonstrate the performance of the CRACS approach. The results can be used as a reference when planning activities in the city or when organizing future travel plans. The flexibility of the assessment system enables it to be adjusted for varying regions and usage characteristics.

Performance Test of a 3MW Wind Turbine – Effects of Shear and Turbulence

In this study a full wind turbine performance test has been performed on a 3MW onshore wind turbine in a coastal location in Norway utilizing a Windcube v2 lidar. The test was performed following the current edition (1. ed) of the IEC 61400-12-1 wind turbine power performance measurement standard with some necessary adaptations for remote sensing anemometry, and was expanded to include wind shear and veer.10 months of data from a Leosphere windcube v2 pulsed lidar, a 3MW wind turbine and a short met-mast formed the basis for the performance test. This amount of data allows for a more detailed analysis of the influence of shear, veer and turbulence on power production than required by the standard. The coastal location of the turbine also allows us to study wind conditions from sea fetch relevant for offshore turbines.The study has demonstrated the benefits and disadvantages of using a lidar for wind turbine performance measurements. Differences between hub height wind and rotor equivalent wind speed has been shown, and results show how turbulence, shear and veer influence the power production and the power curve derived from hub height and equivalent wind speed respectively.

Accounting for the effect of turbulence on wind turbine power curves

Wind turbines require methods to predict the power produced as inflow conditions change. We compare the standard method of binning with a turbulence renormalization method and a machine learning approach using a data set derived from simulations. The method of binning is unable to cope with changes in turbulence; the turbulence renormalization method cannot account for changes in shear other than by using the the equivalent wind speed, which is derived from wind speed data at multiple heights in the rotor disk. The machine learning method is best able to predict the power as conditions change, and could be modified to include additional inflow variables such as veer or yaw error.

Rotor equivalent wind speed for power curve measurement – comparative exercise for IEA Wind Annex 32

A comparative exercise has been organised within the International Energy Agency (IEA) Wind Annex 32 in order to test the Rotor Equivalent Wind Speed (REWS) method under various conditions of wind shear and measurement techniques. Eight organisations from five countries participated in the exercise. Each member of the group has derived both the power curve based on the wind speed at hub height and the power curve based on the REWS. This yielded results for different wind turbines, located in diverse types of terrain and where the wind speed profile was measured with different instruments (mast or various lidars). The participants carried out two preliminary steps in order to reach consensus on how to implement the REWS method. First, they all derived the REWS for one 10 minute wind speed profile. Secondly, they all derived the power curves for one dataset. The main point requiring consensus was the definition of the segment area used as weighting for the wind speeds measured at the various heights in the calculation of the REWS. This comparative exercise showed that the REWS method results in a significant difference compared to the standard method using the wind speed at hub height in conditions with large shear and low turbulence intensity.

건축구조기준(KBC-2009) 기본풍속도의 개선

Since 1970s, the rapid urbanization process by industrial and economic development in Korea causes to a severe change of surface roughness and recent abnormal weather by global warming causes to increasing the intensity of strong wind and Typhoon. It is necessary to revise basic wind speed map of Korean Building Code 2009(KBC-2009) drowned by past meteorological data from 1951 to 1995. This paper proposes new basic wind speed map corresponding to a return period of 100 years in Korea. The values are established from data of annual-maximum 10-minute mean wind speeds collected at 68 meteorological offices recent past 40 years from 1973 to 2012. They were standardized homogeneously to an altitude 10m above the surface roughness category C. Surface roughness category was determined by surrounding surface conditions of meteorological station in 1999 and 2012. The data were statistically reduced using extreme value analysis procedures based on Gumbel's distribution, and the expected wind speeds corresponding to a return period of 100 years (it is called as basic wind speeds) were calculated for each region. The equivalent wind speed contour line to a return period of 100 years were drown up interval of 2m/s to the map of Korea. The basic wind speeds of this study were compared with those of KBC-2009, and the causes of wind speed up or down were described. The basic wind speed map of this study shall be used to revise that of KBC-2009.

Comparison between Wind Farm Aggregation Techniques to Analyze Power System Dynamics

ith increasing amount of wind power penetration, wind farms begin to influence the power systems. When a power system with many wind turbines is to be simulated, Wind farm aggregation techniques are required to reduce the model order while maintaining its accuracy. Different wind farm techniques have been proposed to simulate and analysis wind farm dynamics. In this paper a comparison between three famous techniques: 1- full aggregated model using equivalent wind speed; 2- full aggregated model using average wind speed; and 3- semi aggregated model. Simulation have been carried out for these techniques and compare them using different effects such as wind farm power, reactive power and system dynamics, besides the effect of varying variance on these techniques. Keywordsfarm aggregation, dynamic wind farm model, wind speed variance and doubly fed induction generators.

Evaluating reduced models of aggregated different doubly fed induction generator wind turbines for transient stabilities studies

ABSTRACTFor the representation of wind farms in transient stability studies of electrical power systems, reduced models based on aggregating identical wind turbines are commonly used. In the case of a wind farm with different wind turbines coupled to the same grid connection point, it is usual to aggregate identical wind turbines operating in similar conditions into an equivalent one. However, in the existing literature, there are not any references to the aggregation of different wind turbines (same wind turbine technology but different rated power or components) into a single one. This paper presents a comparative study of four reduced models for aggregating different DFIG wind turbines, experiencing different incoming winds, into an equivalent model. The first of them is the classical clustering model, in which each equivalent model experiences an equivalent wind. The other reduced models have the same equivalent generation system but different equivalent mechanical systems. Thus, the second and third ones are compound models with a clustering aggregated mechanical system and individual simplified models, respectively, to approximate the individual mechanical power according to the incoming wind speeds. The fourth is a mixed model that uses an equivalent wind speed, which is applied to an equivalent mechanical system (equivalent rotor and drive train) in order to approximate the mechanical power of the aggregated wind turbines. The equivalent models are validated by means of comparison with the complete model of the wind farm when simulated under wind fluctuations and grid disturbances. Finally, recommendations with regard to the applicability of models are established. Copyright © 2014 John Wiley & Sons, Ltd.

Effects of Atmospheric Stability and Wind Fetch on Microwave Sea Echoes

The influences of atmospheric stability and wind fetch on microwave scattering from sea surfaces are presented. The equivalent neutral wind speed (ENWS) and the friction velocity (FV) above sea surface are evaluated by the similarity theory of Monin and Obukhov in combination with the Charnock relation. The numerical simulations show that atmospheric stability and wind fetch would make effects on ENWS and, therefore, further on the scattering coefficients (NRCS). And the NRCS decreases with increasing air-sea temperature difference (ΔT=Ta-Ts) because the ENWS is lower than actual wind speed in stable atmospheric condition, and vice versa. Moreover, the ENWS/FV and the NRCS decrease with increasing wind fetch under unstable atmospheric condition. However, in stable atmospheres, the ENWS/FV and the NRCS are almost insensitive to wind fetch. In this paper, the response of NRCS to ΔT is also discussed. Compared with FV, the variations of the angle spread function with ΔT can be neglected because of its minor contribution.

Critical Equivalent Wind Speeds for Overturning and Roof Blow-off of 2-StoryWooden Houses

4 tornadoes occurred on May 6th, 2012 in the north part of the Kanto area, Japan. Of these, the one that struck Joso city and Tsukuba city in Ibaraki prefecture was the strongest. According to the JapanMeteorological Agency, it was 0.5 km wide, 17 km long, and Fujita scale level 3 [1]. According to local government statistics from Ibaraki prefecture, 1 person was killed, 39 were injured, and 1,133 structures were damaged – 207 destroyed, 258 half destroyed, and 668 damaged [1]. The Wind Engineering Research Center of Tokyo Polytechnic University carried out field investigations in damaged areas onMay 7, 8, 9, and 13. Based on its results, Fujita scale strength was estimated at 4. Based on our damage investigation results, we deduce scenarios and estimate wind speed when the 2 structures this paper focuses on were catastrophically damaged.

Translating Wind-Speed Measurements over Alfalfa Having Varying Height for Use in the ASCE Standardized Reference ET Equation

The ASCE Standardized Reference Evapotranspiration (ET) Equation expects wind speed measured at a height of 2 m over and downwind of a smooth measurement surface, such as actively growing clipped grass. Many agricultural weather stations used for evapotranspiration estimation may not meet such siting conditions. A physically based approach to translate wind speeds measured at various heights and weather measurement surface conditions to equivalent wind speed at 2-m height over actively growing clipped grass is tested in agricultural settings. The translation algorithm assumes neutral or near-neutral boundary layer stability conditions. Mean daily wind speeds measured at 2- and 3-m heights above ground surface over and downwind of variable-height alfalfa during the 2008, 2009, and 2010 growing seasons in several southeast Colorado locations were translated to equivalent mean daily wind speed at 2-m height over clipped grass and compared. Translated alfalfa weather station mean daily wind speeds were also compared with mean daily wind speeds measured at 2-m height over 0.12-m grass for parts of the 2009 and 2010 seasons at two pairs of sites. The translation algorithm produced translated mean daily wind speeds in good agreement with wind speeds measured under the standard weather station condition. The effects on computed daily tall crop reference evapotranspiration are illustrated.

Covariability of Surface Wind and Stress Responses to Sea Surface Temperature Fronts

Abstract The responses of surface wind and wind stress to spatial variations of sea surface temperature (SST) are investigated using satellite observations of the surface wind from the Quick Scatterometer (QuikSCAT) and SST from the Advanced Microwave Scanning Radiometer on the Advanced Microwave Scanning Radiometer for Earth Observing System (EOS) (AMSR-E) Aqua satellite. This analysis considers the 7-yr period June 2002–May 2009 during which both instruments were operating. Attention is focused in the Kuroshio, North and South Atlantic, and Agulhas Return Current regions. Since scatterometer wind stresses are computed solely as a nonlinear function of the scatterometer-derived 10-m equivalent neutral wind speed (ENW), qualitatively similar responses of the stress and ENW to SST are expected. However, the responses are found to be more complicated on the oceanic mesoscale. First, the stress and ENW are both approximately linearly related to SST, despite a nonlinear relationship between them. Second, the stress response to SST is 2 to 5 times stronger during winter compared to summer, while the ENW response to SST exhibits relatively little seasonal variability. Finally, the stress response to SST can be strong in regions where the ENW response is weak and vice versa. A straightforward algebraic manipulation shows that the stress perturbations are directly proportional to the ENW perturbations multiplied by a nonlinear function of the ambient large-scale ENW. This proportionality explains why both the stress and ENW depend linearly on the mesoscale SST perturbations, while the dependence of the stress perturbations on the ambient large-scale ENW explains both the seasonal pulsing and the geographic variability of the stress response to SST compared with the less variable ENW response.

Wind Speed and Stability Effects on Coupling between Surface Wind Stress and SST Observed from Buoys and Satellite

The surface wind and stress responses to sea surface temperature (SST) are examined using collocated moored buoy and satellite observations in the Gulf Stream and the eastern equatorial Pacific. Using 17 buoy pairs, differences in the wind speed, 10-m equivalent neutral wind speed (ENW), and surface wind stress magnitude between two buoys separated by between 150 and 350 km were all found to be highly correlated to, and satisfy linear relations with, the SST difference on time scales longer than 10 days. This wind–SST coupling is consistent with previous analyses of spatially high-pass-filtered satellite ENW and SST fields. For all buoy pairs, the ENW and wind speed responses to SST differ by only 10%–30%, indicating that the ENW and stress responses to SST are attributable primarily to the response of the actual surface wind speed to SST rather than to stability. This result clarifies the dynamical pathway of the wind–SST coupling on the oceanic mesoscale. This buoy-pair methodology is used further to evaluate the ENW–SST coupling derived from collocated satellite observations of ENW by the Quick Scatterometer (QuikSCAT) and SST by the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) on board the Aqua satellite. Overall, the satellite and buoy ENW responses to SST compare well, with normalized mean differences (satellite minus buoy) of 17% over the Gulf Stream and −31% and 2% over the southern and northern sides of the equatorial Pacific, respectively. Finally, seasonal variability of the large-scale ENW is shown to modulate the wind stress response to SST, whereby stronger winter wind enhances the stress response by a factor of ~2 relative to the ENW response.

Accounting for the speed shear in wind turbine power performance measurement

ABSTRACTThe current IEC standard for wind turbine power performance measurement only requires measurement of the wind speed at hub height assuming this wind speed to be representative for the whole rotor swept area. However, the power output of a wind turbine depends on the kinetic energy flux, which itself depends on the wind speed profile, especially for large turbines. Therefore, it is important to characterize the wind profile in front of the turbine, and this should be preferably achieved by measuring the wind speed over the vertical range between lower and higher rotor tips.In this paper, we describe an experiment in which wind speed profiles were measured in front of a multimegawatt turbine using a ground–based pulsed lidar. Ignoring the vertical shear was shown to overestimate the kinetic energy flux of these profiles, in particular for those deviating significantly from a power law profile. As a consequence, the power curve obtained for these deviant profiles was different from that obtained for the ‘near power law’ profiles. An equivalent wind speed based on the kinetic energy derived from the measured wind speed profile was then used to plot the performance curves. The curves obtained for the two kinds of profiles were very similar, corresponding to a significant reduction of the scatter for an undivided data set. This new method for power curve measurement results in a power curve less sensitive to shear. It is therefore expected to eventually reduce the power curve measurement uncertainty and improve the annual energy production estimation. Copyright © 2011 John Wiley & Sons, Ltd.

The influence of the wind speed profile on wind turbine performance measurements

AbstractTo identify the influence of wind shear and turbulence on wind turbine performance, flat terrain wind profiles are analysed up to a height of 160 m. The profiles' shapes are found to extend from no shear to high wind shear, and on many occasions, local maxima within the profiles are also observed. Assuming a certain turbine hub height, the profiles with hub‐height wind speeds between 6 m s−1 and 8 m s−1 are normalized at 7 m s−1 and grouped to a number of mean shear profiles. The energy in the profiles varies considerably for the same hub‐height wind speed. These profiles are then used as input to a Blade Element Momentum model that simulates the Siemens 3.6 MW wind turbine. The analysis is carried out as time series simulations where the electrical power is the primary characterization parameter. The results of the simulations indicate that wind speed measurements at different heights over the swept rotor area would allow the determination of the electrical power as a function of an ‘equivalent wind speed’ where wind shear and turbulence intensity are taken into account. Electrical power is found to correlate significantly better to the equivalent wind speed than to the single point hub‐height wind speed. Copyright © 2008 John Wiley & Sons, Ltd.

Remote sensing used for power curves

:Power curve measurement for large wind turbines requires taking into account more parameters than only the wind speed at hub height. Based on results from aerodynamic simulations, an equivalent wind speed taking the wind shear into account was defined and found to reduce the power standard deviation in the power curve significantly. Two LiDARs and a SoDAR are used to measure the wind profile in front of a wind turbine. These profiles are used to calculate the equivalent wind speed. The comparison of the power curves obtained with the three instruments to the traditional power curve, obtained using a cup anemometer measurement, confirms the results obtained from the simulations. Using LiDAR profiles reduces the error in power curve measurement, when these are used as relative instrument together with a cup anemometer. Results from the SoDAR do not show such promising results, probably because of noisy measurements resulting in distorted profiles.

Air‐sea stability effects on the 10 m winds over the global ocean: Evaluations of air‐sea flux algorithms

Spatial and temporal variability of the impact of air‐sea stratification on the differences between satellite‐derived 10 m equivalent neutral wind speeds and stability‐dependent (e.g., in situ) 10 m wind speeds are quantitatively examined over the global ocean. The influences of stability are compared with three air‐sea flux algorithms, Coupled Ocean‐Atmosphere Response Experiment (version 3.0), Bourassa‐Vincent‐Wood, and Liu‐Katsaros‐Businger. Analyses are first presented at many individual buoy locations and then are extended to the global ocean with the use of rain‐free wind measurements from the SeaWinds scatterometer on the QuikSCAT satellite, gridded at a resolution of 0.25° × 0.25°. Overall, stability‐dependent winds are found to be weaker than equivalent neutral winds by 0.2 m s−1 on the basis of 7619 monthly mean values from 208 buoys during 2000–2005. Differences based on hourly winds can be as large as ±0.5 m s−1. Results remain robust regardless of which air‐sea flux algorithm is used. Monthly rain‐free gridded QuikSCAT measurements, combined with atmospheric stability determined using near‐surface variables from the European Centre for Medium‐Range Weather Forecasts 40‐year reanalysis, demonstrate the effects of stratification on the 10 m winds globally. Differences in stability‐dependent and neutral winds are substantially nonsymmetrical and reveal locations where the former is stronger than the latter. These differences may cause physically significant biases in air‐sea fluxes if they are not properly considered, especially near the Kuroshio and Gulf Stream current systems.