Wind Speed Spectrum Research Articles

Analysis of Unequal Leg Transmission Tower Line System in Wind Vibration Response

The unequal leg transmission tower in mountainous areas of 5B-ZBC4 is based to establish the finite element model of three transmission tower and four wire line system. To further study the transmission tower under wind load displacement response, firstly using ANSYS analysis of the dynamic characteristics of the tower-line system. Then, taking the power spectrum of Kaimal wind speed and simulating the curve of wind speed of transmission tower line system in mountainous areas, considering the different elevation and different sizes of wind load, to analysis the wind vibration response for the tower-line coupling system. The results indicates that the tower top displacement means of 1# tower, 2# tower, 3# tower is increasing along with the elevation changes in 0 degrees wind load; The 37 m/s is the critical wind speed of 3# tower of transmission tower line system.

The Wind-Induced Vibration Response for Tower Crane Based on Virtual Excitation Method

The dynamics of Tower Crane is complicated by wind excitation which complicates the wind-induced vibration response analysis. The random wind-induced response analysis of tower crane is presented based on finite element method and virtual excitation method. The pulsating wind loads change into multiple-point correlation stationary excitation. This paper uses Davenport’s wind speed spectrum which does not change with height, and considers multiplepoint correlation of wind-induction. The tower crane was employed as a numerical example; the response spectra and Mean Square Root (RMS) of the tower crane were obtained by wind-induced vibration. The results indicate that the vibration of the tower crane showed a greater response in low frequency with the One-third Octave acceleration RMS being lower. Finally, the influences of the wind-induced vibration on comfort were analyzed.

Coherence of Fluctuating Wind Speed and Along-Wind Force Power Spectrum of Tall Building

In evaluating wind load effects on large-scale structures, correlations in the frequency domain (i.e., coherences) and power spectra of fluctuating wind speed should be evaluated in advance. Most existing formulas for coherence are expressed as exponential functions based on field measurement data for ease of mathematical treatment. However, these simple mathematical expressions have many limitations. In the present study, after examining the existing coherence formulas, a semi-theoretical formula was proposed, and the corresponding along-wind force power spectrum of a tall building with a square cross-section was numerically calculated. A comparison showed that both the coherence and along-wind power spectrum were in good agreement with those of actual wind tunnel data.

Validation of the Mann spectral tensor for offshore wind conditions at different atmospheric stabilities

Simulated wind fields are very useful when predicting loads on structures subjected to turbulent winds, wind turbines being a prime example. Knowledge of statistical properties such as the spatial and temporal correlations of real turbulent wind fields increases the realism of the simulated simulated wind fields. The statistical properties of real turbulent wind fields have been shown to depend on quantities such as the surface roughness, the mean wind speed, measurement height and atmospheric stability. The Mann spectral tensor attempts to predict all spatial correlations of shear generated turbulence given only three input parameters. The most suitable such input values have been investigated for different onshore surface roughnesses, but so far not for typical offshore conditions. The meteorological mast at the Rødsand II offshore wind farm has among other instruments sonic anemometers mounted at 15, 40 and 57 meters above sea level. Wind speed spectra at the three heights are calculated and binned with respect to both wind speed and atmospheric stability. The three parameters of the Mann spectral tensor are determined to ensure best fit to the spectra of each of the bins and are presented as a function of mean wind speed, measurement height and atmospheric stability. The behaviour of the presented parameters values are largely consistent with the previous onshore results. The parameter values are also compared to potentially related quantities and a constant quantity is derived. Given optimal parameters the spectral tensor is found to reproduce the surface layer generated turbulence well, also for different atmospheric stabilities, however in the wind speed spectra a contribution from the very large scale quasi-geostrophic turbulence is also observed, a contribution the spectral tensor does not attempt to model.

Analysis and Simulation of Meteorological Wind Fields Based on Wavelet Transform

In this work, we examined the non Gauss distribution characteristic and evolution law of the wavelet coefficient of a gust using wavelet transform; according to the time-frequency characteristic, the wavelet transform coefficients and the energy relations of the target velocity spectra are derived; the wavelet coefficient is generated using the cascade model reflecting the turbulent intermittent; the unsteady gust artificial generation method is established based on inverse wavelet transform; and the arbitrary unsteady fluctuation law can be generated by regulating the coefficient of low frequency. The results show that: the natural gust is in good agreement with Karman wind speed spectrum, meets the turbulence-5 / 3 law in the inertial subrange, and exhibits the nature of intermittence and local self-similarity; the artificial wind sequence based on the inverse wavelet transform method shows similar turbulence statistics with natural gust, with which, the effectiveness of the method is confirmed.

Full-scale measurements of wind effects and modal parameter identification of Yingxian wooden tower

The Yingxian wooden tower in China is currently the tallest wooden tower in the world. It was built in 1056 AD and is 65.86 m high. Field measurements of wind speed and wind-induced response of this tower are conducted. The wind characteristics, including the average wind speed, wind direction, turbulence intensity, gust factor, turbulence integral length scale and velocity spectrum are investigated. The power spectral density and the root-mean-square wind-induced acceleration are analyzed. The structural modal parameters of this tower are identified with two different methods, including the Empirical Mode Decomposition (EMD) combined with the Random Decrement Technique (RDT) and Hilbert transform technique, and the stochastic subspace identification (SSI) method. Results show that strong wind is coming predominantly from the West-South of the tower which is in the same direction as the inclination of the structure. The Von Karman spectrum can describe the spectrum of wind speed well. Wind-induced torsional vibration obviously occurs in this tower. The natural frequencies identified by EMD, RDT and Hilbert Transform are close to those identified by SSI method, but there is obvious difference between the identified damping ratios for the first two modes.

Analysis on Wind-Induced Vibration Dynamic Responses of Transmission Tower-Line System

Tower-line system of overhead transmission line are sensitive to wind. Therefore, dynamic effect of wind load should be taken into consideration, for instance, wind-induced vibration coefficient. There might be some errors in the calculation of the coefficient in accordance with ‘Load code for the design of building structures’, for its ignoring the irregular figure, scattered masses and coupling effect of tower-line system. Tower-line system is set up in virtual environment, with tower-line coupling considered, and research wind-induced vibration dynamic responses under Davenport wind speed spectrum. Random vibration theory was applied to calculate the coefficient. Whole tower was divided by hight, and calculated segment’s the wind-induced vibration coefficient seprately. Compare the coefficient from Load Code and random vibration theory, the latter with tower-line coupling effect and tower figure considered, is close to the actual.

Application of state-of-the-art in measurement and data analysis techniques for vibration evaluation of a tall building

Recent advancements in sensing and data acquisition technology have made monitoring of structures and infrastructure more affordable and, at the same time, more comprehensive. Examples of such advancements are application of wireless technology for communication, the utilisation of fully automated systems for long-term monitoring and the remote control of the sensing system over Internet. Although each of these technologies has been used in different structural health monitoring projects in the recent years, inclusion of an all-in-one sensing system represents the state-of-the-art in measurement techniques. This paper presents the integration of all of the above-mentioned advanced monitoring approaches in one sensing system for forensic quantification of an in-service tall building. The inclusive measurement and monitoring system along with advanced data analysis techniques enabled extraction of detailed information about dynamic characteristics of the building structure and development of reliable conclusions regarding its performance. It is shown that the performance of the investigated structural components is satisfactory in terms of strength demand. However, the level of vibration in some portions of the structure does not meet the limits of human comfort. In addition, wind-speed spectrum, acceleration response spectrum and the modes of lateral vibration are extracted to assist with evaluation of the structure's performance.

A method based on the Van der Hoven spectrum for performance evaluation in prediction of wind speed

Development of techniques for accurate assessment of wind power potential at a site is very important for the planning and establishment of a wind energy system. The most important defining character of the wind and the problems related with it lie in its unpredictable variation. Van der Hoven constructed a wind speed spectrum using short-term and long-term records of wind in Brookhaven, NY, USA, in 1957 and showed the diurnal and turbulent effects. His spectrum suggests that there is a substantial amount of wind energy in 1-min periodic variations. The aim of this paper is to evaluate the results of wind predictions using linear and nonlinear methods following the construction of power spectra (Van der Hoven spectrum) based on airport wind data in İstanbul. In this study, we have constructed power spectra of surface wind speed in order to evaluate the contributions of disturbances at various scales on the total spectrum. For this purpose, data from an automatic weather observation system at Atatürk Airport in İstanbul at a height of 10 m with a sampling rate of 1 min from 2005 to 2009 were used. In the second part of the study, autoregressive (AR) and artificial neural network (ANN) models were applied for prediction of wind speed. The prediction methods were assessed by comparing the characteristic frequency components of the prediction series and the real series. The best results were obtained from the ANN model; however, the AR model was found to moderately show the spectral characteristics.

Wind-Induced Response Analysis of Steel Tower Structure

In this paper, autoregressive (AR) method is firstly introduced to simulate wind speed time series. The agreement of the simulated wind speed spectrum to the target spectrum is verified. A 42m-high steel tower subjected to wind load is analyzed using ANSYS. Through modal analysis, it can be found that the first several modes of the structure are all translational vibration modes. Torsional vibration modes and local vibration modes appear from the 3th order mode. Meanwhile, time history analysis is applied to analyze the structural response. Results show that, under wind loads, the steel tower has large stresses in the chords which have abrupt section area change.

Study on Wind-Induced Vibration Response of Aerial Working Arm

Since boom-type aerial equipment has complex dynamic characteristic under the action of random wind loads, traditional methods are hard to reflect its dynamic response. We put forward an analysis method for wind-induced random vibration response of aerial working arms based on finite element and pseudo-excitation methods. In this analysis, the pulse-wind-load-induced vibration was regarded as a random vibration under multi-point coherent steady random excitation, and Davenport wind speed spectra invariant with height were adopted with consideration of multi-point wind excitation correlation. We analyzed the wind-induced random vibration of the working arm of a folding-arm-type aerial operation vehicle. The analysis results confirm the reliability of the analysis method, so as to offer a feasible way for analyzing the dynamic wind-induced vibration response of large boom-type aerial equipment.

Long-term field measurement and analysis of the natural wind characteristics at the site of Xi-hou-men Bridge

In order to investigate the wind characteristics of coastal areas of China, a long-term field measurement of natural wind was carried out. Based on the field measurement results, this paper presents the natural wind characteristics of typhoons and strong monsoons at the site of Xi-hou-men Bridge, including mean wind speed, mean wind direction, mean wind elevation angle, turbulent intensity, gust factor, turbulence integral length scales, power spectrum of wind speed and spatial correlation of gusty wind, the profiles of mean wind speed and turbulent intensity, etc. The correlation among wind characteristics is analyzed in detail, and the similarities and differences of wind characteristics between typhoons and monsoons are analyzed. These results can provide detailed wind characteristics of coastal areas of China.

Identification and analysis of wind speed patterns extracted from multi-sensors measurements

The understanding of the vertical as well as the horizontal behaviours of wind speed is of great importance in many applications such as aviation, meteorology and wind energy conversion. In this work, we propose to apply the principal component analysis (PCA) in order to extract probable components of wind speed. The idea behind the use of PCA is to introduce mixed sources signals to PCA algorithm as input in order to obtain a separated patterns as output. Hence, values of wind speed measured at three levels above the ground will be used as three separate sensors in order to extract the horizontal and the vertical components of wind speed. Once the principal components of wind speed separated, a process of recognition and identification is undertaken via the inspection of the statistical as well as the cyclical behaviors of the obtained components. For the examination of the statistical properties of wind speed, we propose to carry a comparison of the probability density of the extracted components with the Weibull distribution (commonly used to fit wind speed distributions). However, the spectral behavior of the obtained patterns is examined using time–frequency analysis rather than the traditional Fourier analysis. The time–frequency analysis has been chosen as it serves the purpose of following the diurnal and seasonal time variation of the wind speed spectrum. As a result, it has been found that the horizontal wind speed component fits the Weibull distribution and it is characterized by synoptic and intra-seasonal oscillations. On the other hand, the wind speed vertical component is better fitted by the extreme value distribution. It has been also found that the diurnal oscillations are the most significant oscillations in the vertical components especially in the summertime period.

Dynamic Response Analysis of Large Wind Turbine Blade Based on Davenport Wind Speed Model

Fluctuating wind speed spectrum, which is closer to the actual working conditions, was simulated by davenport wind speed model, and displacement and stress distribution of blade under fluctuating wind speed were calculated by finite element analysis software. The numerical results indicate that the growth trend of vibration amplitude for whole blade at flapping direction is nonlinear along the wingspan. The max von-mises stress appears when the vibration amplitude of tip reaches the maximum, and it is mainly concentrated in the central part of the blade. The stress at trailing edge and tip is smaller than the central part. Above results provide a reference for the strength safety design of wind turbine blade.,Fluctuating wind speed spectrum, which is closer to the actual working conditions, was simulated by davenport wind speed model, and displacement and stress distribution of blade under fluctuating wind speed were calculated by finite element analysis software. The numerical results indicate that the growth trend of vibration amplitude for whole blade at flapping direction is nonlinear along the wingspan. The max von-mises stress appears when the vibration amplitude of tip reaches the maximum, and it is mainly concentrated in the central part of the blade. The stress at trailing edge and tip is smaller than the central part. Above results provide a reference for the strength safety design of wind turbine blade.

Representation of spatial and temporal variability of daily wind speed and of intense wind events over the Mediterranean Sea using dynamical downscaling: impact of the regional climate model configuration

Abstract. Atmospheric datasets coming from long term reanalyzes of low spatial resolution are used for different purposes. Wind over the sea is, for example, a major ingredient of oceanic simulations. However, the shortcomings of those datasets prevent them from being used without an adequate corrective preliminary treatment. Using a regional climate model (RCM) to perform a dynamical downscaling of those large scale reanalyzes is one of the methods used in order to produce fields that realistically reproduce atmospheric chronology and where those shortcomings are corrected. Here we assess the influence of the configuration of the RCM used in this framework on the representation of wind speed spatial and temporal variability and intense wind events on a daily timescale. Our RCM is ALADIN-Climate, the reanalysis is ERA-40, and the studied area is the Mediterranean Sea. First, the dynamical downscaling significantly reduces the underestimation of daily wind speed, in average by 9 % over the whole Mediterranean. This underestimation has been corrected both globally and locally, and for the whole wind speed spectrum. The correction is the strongest for periods and regions of strong winds. The representation of spatial variability has also been significantly improved. On the other hand, the temporal correlation between the downscaled field and the observations decreases all the more that one moves eastwards, i.e. further from the atmospheric flux entry. Nonetheless, it remains ~0.7, the downscaled dataset reproduces therefore satisfactorily the real chronology. Second, the influence of the choice of the RCM configuration has an influence one order of magnitude smaller than the improvement induced by the initial downscaling. The use of spectral nudging or of a smaller domain helps to improve the realism of the temporal chronology. Increasing the resolution very locally (both spatially and temporally) improves the representation of spatial variability, in particular in regions strongly influenced by the complex surrounding orography. The impact of the interactive air-sea coupling is negligible for the temporal scales examined here. Using two different forcing datasets induces differences on the downscaled fields that are directly related to the differences between those datasets. Our results also show that improving the physics of our RCM is still necessary to increase the realism of our simulations. Finally, the choice of the optimal configuration depends on the scientific objectives of the study for which those wind datasets are used.

On the length‐scale of the wind profile

AbstractWe present the results of an analysis of simultaneous sonic anemometer observations of wind speed and velocity spectra over flat and homogeneous terrain from 10 up to 160 m height performed at the National Test Station for Wind Turbines at Høvsøre, Denmark. The mixing length, l, derived from the wind speed profile, is found to be linearly proportional to the length‐scale of turbulence, derived either from the peak of the vertical velocity spectrum, (λm)w, or from a three‐dimensional turbulence spectral model, for a range of atmospheric stability conditions, friction Rossby numbers, and within the range of observational heights ((λm)w ∼ 7l). Under very unstable conditions and above 100 m, the local wind shear is low, and the relation between both length‐scales is slightly nonlinear. Mixing‐length and wind profile models, which depend on both atmospheric stability and friction Rossby number, generally show better agreement to the observations of the length‐scale and wind speed profile than the models from surface‐layer theory, which show good agreement with the observations for the first 80 m only. The results from this analysis demonstrate a close connection between these two types of length‐scales. Copyright © 2010 Royal Meteorological Society

The Frøya database and maritime boundary layer wind description

High-quality maritime wind-turbulence data obtained at exposed sites on the western coast of Norway during gale and stormy conditions are described. With a resolution of 1 Hz, and a height range of 10–100 m, the database is most suitable for describing the wind structure of the maritime boundary layer (MBL) with relevance for offshore compliant floating structures. The established description covers both static and dynamic wind, the latter with particular attention given to the low-frequency range 0.002–0.03 Hz (0.5–10 min). The relevance for and extrapolation to very strong wind speed design conditions has been emphasized. The static description of wind is found to be consistent with the Charnock relation reflecting the interaction between wind and waves. A most important conclusion is reached for the one-point wind speed spectrum. The low-frequency range (<0.01 Hz) is significantly more energetic than indicated by land-based studies. Concerning correlations, it is noteworthy that coherence for lateral separation is significantly lower than indicated by some other studies. Coherence for vertical separation is on the low side but in reasonable agreement with these studies. The data does not support a low-frequency asymptote for coherence different from 1.

On modelling of typhoon‐induced non‐stationary wind speed for tall buildings

AbstractTyphoon‐induced wind around tall buildings may not be stationary because it is a large body of rotating air. A new approach is thus proposed in this paper for characterizing typhoon‐induced wind speed. Typhoon‐induced non‐stationary wind speed is modelled as a deterministic time‐varying mean wind speed component plus a zero mean stationary fluctuating wind speed component. The time‐varying mean wind speed is naturally extracted from the measured wind speed time history using empirical mode decomposition (EMD). Wind characteristics described in the traditional approach based on a stationary wind model are redefined and extended in the non‐stationary wind model. The new approach is then applied to wind data measured at the Di Wang building during Typhoon York. The results show that most of recorded wind samples are non‐stationary but they can be decomposed into a time‐varying mean wind speed component plus a well‐behaved zero mean fluctuating wind speed component admitted as a stationary random process with Gaussian distribution. Other wind characteristics such as probability distribution of fluctuating wind speed, turbulence intensity, gust factor, and wind spectrum obtained by the new approach seem to be more realistic than those gained by the traditional approach. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Outdoor testing of single crystal silicon solar cells

The evaluation and assessment of the performance of photovoltaic (PV) cells requires the measurement of the current as a function of voltage, temperature, intensity, wind speed and radiation spectrum. Most noticeable of these parameters is the PV conversion efficiency η (defined as the maximum electrical power P max produced by the PV cell divided by the incident photon power P in ) which is measured with respect to standard test conditions (STC). These conditions refer to the solar spectrum AM1.5 , solar radiation intensity 1000 W m −2 , cell temperature 25±2 ° C and wind speed (2 mph). Tests under STC are carried out in laboratory-controlled environment. With an increase of ambient temperature, there is a deficiency in the electrical energy that the solar cell can supply. This situation is especially important in hot climates. Outdoor exposure tests of solar cells have been conducted in the Department of Physics, University of Brunei Darussalam. Preliminary results demonstrate that the efficiency of the single crystal silicon solar cell strongly depends on its operating temperature. It has been noted that at the operating temperature of 64 °C, there was a decrease of 69% in the efficiency of the solar cell compared with that measured at STC. Investigation of the effect of variation in intensities of sunlight on the solar cell performance showed that the efficiency of the cell is reduced as intensities of sunlight are reduced but at a rate different from the reduction in intensities.

The contribution of bubbles to high-frequency sea surface backscatter: A 24-h time series of field measurements

Measurements of acoustic sea surface backscattering, wind speed, and surface wave spectra were made continually over a 24-h period in an experiment conducted in 26 m of water near the Dry Tortugus collection of islands off south Florida in February 1995. The backscattering measurements were made at a frequency of 30 kHz and a sea surface grazing angle of 20 degrees; a time series of the decibel equivalent of this variable, called SS20, was studied in terms of its dependence on environmental variables. On occasion reliable estimates of scattering in the grazing range 15 degrees-27 degrees were also obtained during the 24 hours. The scattering data exhibited evidence, in terms of scattering level and grazing angle dependence, of scattering from near-surface bubbles rather than scattering from the rough air-sea interface. The scattering data were compared with a model for sigma(b), the apparent backscattering cross section per unit area due to bubble scattering, that is driven by a parameter, beta1, equal to the depth-integrated extinction cross section per unit volume. Using an empirical model for beta1 based on data from a 1977 experiment conducted in pelagic waters, model predictions agreed reasonably well with the 1995 measurements presented here. Additional model-data comparisons were made using four measurements from a 1992 experiment conducted in pelagic waters. Finally, the 24-h time series of acoustic scattering exhibited a hysteresis effect, wherein for a given wind speed, there was a tendency for the scattering level to be higher if prior winds had been falling. A better understanding of this effect is essential to reduce uncertainty in model predictions.