Anemometer Tower Research Articles

Perfil do vento e estabilidade atmosférica próxima da superfície no Centro de Lançamento de Alcântara

Wind and atmospheric stability are fundamental for aerospace research and development activities at the Alcântara Launch Center, situated in the Maranhão Brazilian state. The physical processes related to these meteorological parameters during the dry season are well known. However, there is still gap concerning the rainy season. The data obtained in the anemometric tower are here studied considering vertical profiles of wind and temperature, and the Richardson bulk number. The mechanical characteristics showed weaker vertical gradient during the daytime-nighttime transition. A primary reason of that behaviour is the sea breeze from 60 m height of the tower. Those near-surface winds are more intense at night in the rainy season. As expected, the surface layer tends to be statically neutral throughout the daytime cycle in the dry season. Meanwhile, this stability classification was seen more frequently at the nighttime in the rainy season. Rainfall events along wet months were typically nocturnal. The deeper convective cells and its derived downdrafts help to understand this behavior. Due to -40% precipitation anomaly reported in this rainy season, these results may have been a direct response to this condition. In future studies, turbulent measurements are required to investigate how the thermodynamic and mechanical pertubations interacts with the rainfall stability patterns during the wet season.

Análise espacial dos ventos no Centro de Lançamento de Alcântara, Maranhão

The wind at the Alcântara Launch Center (ALC), which presents as main characteristics an oceanic behavior, influenced by the trade winds and the sea breeze, and modified by the ocean-continent interface and local topography. Therefore, it is necessary to study the characteristics of the site flow, highlighting the influence of the surface boundary layer and the validity of the surface flow homogeneity. In this study will be used the data of two anemometric towers installed in the ALC to evaluate spatial differences in the characteristics of the average wind and its daily cycle. For comparison, data from the ERA5 reanalysis, the fifth generation created by European Centre for Medium-Range Weather Forecasts (ECMWF). The results show that the anemometric towers present, on average, similar characteristics and that the data from the reanalysis can be used for studies of mesoscale atmospheric phenomena that occur on the surface.

Porosity and Drag Determination of a Single-Row Vegetative Barrier (Maclura pomifera)

Abstract. Deciduous trees of the species (Osage orange) are commonly established as vegetative barriers for wind erosion control throughout the U.S. Great Plains. Because there is no previous research on the aerodynamic effectiveness of these vegetative barriers during different seasons (leaf-on and leaf-off conditions), this study focused on determining the porosity and drag characteristics of this tree species. Digital image analyses were used to determine optical porosities that were then correlated with barrier drag coefficients. Images were taken in the field during calm wind conditions when the sunlight was suitable for digital imaging. Wind speeds were measured at different heights for a single-row Osage orange barrier using cup anemometers. Two anemometer towers were positioned relative to the barrier. One was located windward at 10H distance from the barrier; the other was located leeward and was movable to distances of 1H, 2H, 4H, 7H, 10H, 12H, 15H, and 20H from the barrier, where H is the average barrier height. The wind speeds measured in the field ranged from 4 to 7 m s-1, with lower wind speeds encountered during the leaf-off condition. As expected, wind speed reductions were greater for the leaf-on condition and ranged from 40% to 80% at 1H from the barrier, while the reduction was 20% to 38% for the leaf-off condition. The crown portion of the barrier was found to be responsible for much of the reduction. Mean values of the drag coefficient were 1.3 for the leaf-on condition, decreasing to 0.9 for the leaf-off condition of the Osage orange barrier, which corresponded to mean optical porosities of 20% and 61%, respectively Keywords: Drag coefficient, Image analysis, Osage orange, Porosity, Vegetative barrier, Wind erosion.

A new method for wind speed forecasting based on copula theory

How to determine representative wind speed is crucial in wind resource assessment. Accurate wind resource assessments are important to wind farms development. Linear regressions are usually used to obtain the representative wind speed. However, terrain flexibility of wind farm and long distance between wind speed sites often lead to low correlation. In this study, copula method is used to determine the representative year's wind speed in wind farm by interpreting the interaction of the local wind farm and the meteorological station. The result shows that the method proposed here can not only determine the relationship between the local anemometric tower and nearby meteorological station through Kendall's tau, but also determine the joint distribution without assuming the variables to be independent. Moreover, the representative wind data can be obtained by the conditional distribution much more reasonably. We hope this study could provide scientific reference for accurate wind resource assessments.

Near ground wind characteristics during typhoon Meari: Turbulence intensities, gust factors, and peak factors

Wind data were collected during the 2011 typhoon Meari at heights of 10, 20, 30, and 40 m above the ground using a 40 m high anemometer tower in the coastal area near Shanghai Pudong International Airport. Wind speeds and directions, turbulence intensities, gust factors, and peaks were analyzed using the time records of wind speed. The results show that turbulence intensity components in longitudinal, lateral, and vertical directions decrease with mean wind speed, regardless of elevations, and the turbulence intensities are in a linear relationship with mean wind speeds. The ratios of three turbulence intensity components (i.e. Iu, Iv, Iw) at heights of 10, 20 and 40 m were calculated and equal to be 1:0.88:0.50, 1:0.84:0.57, and 1:0.9:0.49, respectively. In addition, the gust factors in three directions exhibit a reduction with increasing mean wind speed. The peak factors at different heights show a similar trend and slightly decrease with mean wind speed; average peak factors for all 10-min data from Typhoon Meari are 2.43, 2.48, and 2.47, respectively.

A new design methodology to predict wind farm energy production by means of a spiking neural network–based system

AbstractIn this paper, a spiking neural network–based architecture for the prediction of wind farm energy production is proposed. The model is also able to evaluate the wake effects due to interactions between the elements of a wind farm on the energy production of the whole farm. This method has been applied to a large wind power plant, composed of 28 turbines and 3 anemometric towers, located in the rural area of Vizzini's municipality in province of Catania, Italy, that is characterised by a complex orography and an extension of 30 km2. For the implementation of this architecture it was used the “NeuCube” simulator. The results show that the presented method can be successfully applied for predictions of wind energy generation in real wind farm also in presence of faults.

Design of Meteorological Element Detection Platform for Atmospheric Boundary Layer Based on UAV

Among current detection methods of the atmospheric boundary layer, sounding balloon has disadvantages such as low recovery and low reuse rate, anemometer tower has disadvantages such as fixed location and high cost, and remote sensing detection has disadvantages such as low data accuracy. In this paper, a meteorological element sensor was carried on a six-rotor UAV platform to achieve detection of meteorological elements of the atmospheric boundary layer, and the influence of different installation positions of the meteorological element sensor on the detection accuracy of the meteorological element sensor was analyzed through many experiments. Firstly, a six-rotor UAV platform was built through mechanical structure design and control system design. Secondly, data such as temperature, relative humidity, pressure, elevation, and latitude and longitude were collected by designing a meteorological element detection system. Thirdly, data management of the collected data was conducted, including local storage and real-time display on ground host computer. Finally, combined with the comprehensive analysis of the data of automatic weather station, the validity of the data was verified. This six-rotor UAV platform carrying a meteorological element sensor can effectively realize the direct measurement of the atmospheric boundary layer and in some cases can make up for the deficiency of sounding balloon, anemometer tower, and remote sensing detection.

Field experiment and analysis of the wake behind a horizontal-axis wind turbine

Wind turbines work in a complex natural environment, where their flow field shows the characteristics of high turbulence levels. Due to the complexity and instability of the atmospheric boundary layer flow, as well as the influence of the scale effect, wind tunnel test cannot reflect the real working condition of wind turbine. So field experiments are very necessary to study wind turbine flow characteristics in actual wind field. In this investigation, field experiments of the wake behind a wind turbine were carried out to get velocity distribution in it. The field experiment system is composed of a 33 kW wind turbine, a 20 m high anemometer tower, a wake velocity measurement platform and the controlling device. The wind turbine is horizontal-axial, two-bladed, upwind-type, with variable pitch angles, 14.8 m in diameter. Wake velocity measurement platform is composed of an 18 m high hydraulic lift, anemometer installation platform and three sets of the US CSAT3 three-dimensional ultrasonic anemometer. Inflow parameters were gauged, such as wind speed, wind direction, atmospheric pressure, temperature and humidity. Besides, the operating conditions of the wind turbine were recorded, including pitch angle, yaw angle, rotor speed. It is discussed that the time domain and power spectrum characteristics of wake velocity at a measuring point located at one rotor diameter downwind from the rotor plane. The results show that there are larger velocity deficits in the wake. The axial velocity deficit rate at the measuring point is between 35.1% and 54.17%. The change of the velocity in vertical direction is small. The velocity in lateral direction is slightly larger than the velocity component of inflow, which reflects the expansion characteristics of the wake. Besides, the turbulent kinetic energy at the measuring point shows a periodic variation, and the vortex sheet passage frequency is similar to the rotation frequency of the wind turbine. Meanwhile, all of the power spectra of turbulent velocity in three directions at the measuring point show a characteristic of slope for –1 at the section of low frequency, which mean the turbulent flow is in the classical production subrange.

A Long-Term Wind Speed Ensemble Forecasting System with Weather Adapted Correction

Wind forecasting is critical in the wind power industry, yet forecasting errors often exist. In order to effectively correct the forecasting error, this study develops a weather adapted bias correction scheme on the basis of an average bias-correction method, which considers the deviation of estimated biases associated with the difference in weather type within each unit of the statistical sample. This method is tested by an ensemble forecasting system based on the Weather Research and Forecasting (WRF) model. This system provides high resolution wind speed deterministic forecasts using 40 members generated by initial perturbations and multi-physical schemes. The forecasting system outputs 28–52 h predictions with a temporal resolution of 15 min, and is evaluated against collocated anemometer towers observations at six wind fields located on the east coast of China. Results show that the information contained in weather types produces an improvement in the forecast bias correction.

Assessment of wind resources in two parts of Northeast Brazil with the use of numerical models

Assessment of wind resources in two parts of Northeast Brazil with the use of numerical models

A Study of the Internal Boundary Layer Generated at the Alcantara Space Center

An atmospheric Internal Boundary Layer (IBL) occurs when sudden changes in surface roughness disturb wind flows. The region of the Brazilian Alcantara Space Center (ASC), with its rocket launching pad located 150 m downwind of a 40 m coastal cliff, presents the formation of an IBL due to winds blowing inland from the ocean. Numerical simulations using the immersed boundary method, experiments in a wind tunnel using particle image velocimetry, and field observational data obtained from anemometric towers were used to study this IBL. The results demonstrated that it is dependent on the geometry of the coastal cliff: its height is around 17 and 15 m for slopes of the coastal cliff of 90o and 135o, respectively. The numerical results show a good agreement with the experimental data and the field observations, but with an overestimation of the vorticity field. The IBL significantly influences the wind flow at the launching pad.

Numerical simulation on floating behavior of buoyancy tank foundation of anemometer tower

The intact stability and damage stability of a model of an anemometer tower with buoyancy tank foundation are computed by the finite element software MOSES in this paper. The natural period of the anemometer tower is discussed through frequency domain analysis. The influence of a single factor, such as towing point position, wave height, wave direction and wave period, on towing stability is discussed through time domain analysis. At the same time, the towing stability under the condition of various combinations of many factors is analyzed based on the measured data of the target area. Computer simulation results show that the intact stability is preferable and the damage stability is sufficient under the condition of plenty of subdivisions. Within the scope of the buoyancy tank foundation, the higher the towing point position is, the better the stability is. Wave height has a great impact on the motion amplitude of buoyancy tank foundation, but the effect on the acceleration is not obvious; wave period has a great impact on the acceleration, while the effect on the motion amplitude is not obvious; following-waves towing is more conducive to safety than atry.

Estimating the impact threshold for wind-blown sand

Li, B., Ellis, J. T., Sherman, D. J., 2014. Estimating the Impact Threshold for Wind-Blown Sand. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 627–632, ISSN 0749-0208.In many aeolian studies, it is commonplace to use Bagnold's (1936) equation to calculate threshold shear velocity (u*t), which includes an empirical constant, A, typically set at about 0.082 for maintaining saltation (the dynamic, or impact, threshold). Here, we present data from a pilot study to assess the variability of A to improve estimations of u*t, which in turn, should improve transport rate predictions. Using field data from three coastal environments, we measured or calculated all parameters within the Lettau and Lettau (1978) model and u*t equation. In Jericoacoara, Brazil (BRA), Inch, Ireland (IRE), and Esposende, Portugal (POR) wind velocities were measured with cup anemometer towers and transport rates were measured using traps for 31 data runs lasting 120 to 1020 seconds each. Mean grain sizes were 0.17 mm (IRE), 0.31 mm (POR), and 0.30 mm (BRA), and mean shear velocities were 0.38 m s−1 (IRE), 0.40 m s−1 (POR), and 0.49 m s−1 (BRA). Empirically determined, adjusted A values ranged from 0.02 to 0.21 with a mean and standard deviation of 0.11 and 0.04. No relationship exists between estimates of A and grain Reynolds number. A statistically significant (p < 0.001), negative relationship was found between A and mass transport rate, leading to substantial over-prediction of transport rates near the threshold and under-prediction during fast winds if a constant of 0.082 is used.

ESTIMATIVA DA VARIABILIDADE DE PRODUÇÃO DE ENERGIA UTILIZANDO DADOS MEDIDOS E MODELADOS

The objective of this study was to determine the variability of energy production calculated from simulated data over 10 years, with the WRF (Weather Research and Forcasting) model. The results of the anemometer tower of Rio Grande (TA RS) a correlation coefficient index r=0,90 between measured and simulated series, the 80m in the period May 2009 to March 2013. For the anemometer tower of Pedra Grande (TA RN) correlation index was r=0,78. The variability of energy production around the average TA is lower in RS.

ANÁLISE DO PERFIL DO VENTO EM CONDIÇÕES NEUTRAS NO CENTRO DE LANÇAMENTO DE ALCÂNTARA

In this study we present results of the logarithm of the wind profile, collected at the Centro de Lançamento de Alcântara (CLA) for five days in September 2008. The results show that the roughness length is of the order of 0.4 m and friction velocity is approximately 10% of the wind speed at 70 m. The wind profile obtained from an anemometric tower of 70 m with six levels of measurement fits well in logarithmic form.

Study on the Maximum Entropy Principle applied to the annual wind speed probability distribution: A case study for observations of intertidal zone anemometer towers of Rudong in East China Sea

This paper is to study Weibull distribution and Maximum Entropy Principle applied to fit the wind speed frequency distribution of the intertidal zone anemometer towers. Comparisons of the results from Weibull distribution and Maximum Entropy distribution are made for the characteristics of the wind speed distribution and the variation with height in the offshore area. The Maximum Entropy distribution is found to perform adequately and accurately in fitting the wind speed frequency distribution with height. It is shown that the frequency peak value of Weibull distribution is lower than the measured maximum frequency at the same height, and the fitting accuracy of the Maximum Entropy Principle is significantly higher than that of Weibull distribution. Furthermore, the mean errors of average effective wind power density calculated from the five-parameter Maximum Entropy distribution as well as from Weibull distribution are 1.71Wm−2 and 7.48Wm−2 respectively. Except for these findings, limitations and problems existing in the procedure of fitting the annual wind speed probability distribution are also discussed.

The response of saltation to wind speed fluctuations

ABSTRACTThe response time of saltation to spatial or temporal wind speed fluctuations constitutes an important control parameter for aeolian sediment transport and deposition. In this paper, we present direct measurements of the response time obtained from several field experiments.The sand transport was studied using six small microphones arranged in a vertical profile and collocated with a sonic anemometer, a webcam and a cup anemometer tower. The webcam was coupled with the sonic anemometer via a personal computer and provides information on creeping and saltating grains with a sampling rate of 10 Hz. Sediment transport measurements were obtained over four periods.The Wiener filter, a signal processing technique, is used to obtain a discrete transfer function that relates the horizontal wind speed and the non‐intermittent sand transport. The transfer function can be established using an exponential function with a time constant or characteristic response time τ without time shift. The response time fluctuated between zero and 1·5 seconds depending on the turbulence intensity, the saltation activity, the measuring height and sampling rates. The Wiener filter coefficients suggest that the response of saltation to wind speed alterations is determined by more than one process. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Análise dos padrões de vento no Estado de Alagoas

Com o objetivo de identificar áreas do Estado de Alagoas com boas perspectivas de aproveitamento eólico, comparou-se dados de velocidade e direção do vento observados por torres anemométricas do projeto Atlas Eólico e Disseminação da Tecnologia Eólica no Estado de Alagoas. A série utilizada é de 12/2007 a 11/2008 e o estudo focou três regiões distintas: Litoral, Agreste e Sertão. Os padrões médios com maiores velocidades do vento ocorreram na região do Agreste (7,1 ±1,2 ms-1 mensal), seguido do Sertão (6,8 ±0,9 ms-1 mensal) e Litoral ( 5,3 ±0,8 ms-1 mensal). A regularidade da velocidade e a pouca variabilidade de direção do vento torna Alagoas uma ótima opção para a instalação de aerogeradores.

Análise estatística do perfil de vento na camada limite superficial no centro de lançamento de Alcântara

Statistical analysis of the wind profile made at an anemometric tower installed at the Alcântara Launching Center was based on wind data (direction and wind speed) collected between 1995 up to 1999, which was carried out at six different levels: 6.0, 10.0, 16.3, 28.5, 43.0, and 70.0 m. This analysis was made for typical rainy months (March) and dry (September) season, in the Alcântara Launching Center area. The analyzed data total during the wet season (March) was 76,882 wind profiles (time interval of ten minutes) and during the dry season (September) was of 109,809 profiles. It was computed the mean wind speed (or intensity) of the wind, standard deviation, median, mode, and the prevailing wind direction. The predominant direction was from NE with 33 and 40% for wet and dry seasons, respectively. The average values of wind speed showed a dependency with height and it was observed that the highest levels of the anemometric tower have the strongest wind speed in the dry period (8.2 ms-¹). The values of average wind speeds observed were 6.4 ms-¹ for the dry season and 4.1 ms-¹ during the wet one. The normal and Weibull statistical distributions were adjusted to the observed data set. Results show that the wind speed is adjusted to a 95% level (α=0.05) for the normal and Weibull statistical distributions. The Weibull distribution for the entire period presented and adjust to values between 3.0 and 9.0 ms-¹, and the normal one showed a good fit for values between 4.0 and 9.0 ms-¹.

Numerical Simulation of a 100m Offshore Anemometer Tower

An anemometer tower is essential for the construction of an offshore wind farm. A anemometer tower is preliminarily designed in the Bohai Bay in the north coast of China. Considering the extreme wind and wave or extreme wind and ice, at different directions, the structure of the tower is simulated by using finite element software. And the stresses and strains of the structure are calculated at the different loadcases. And then, the structure of tower can be designed using the numerical data. And finally, the dynamic characteristics of modal shape and frequencies are also discussed.