Ultrasonic wind velocity measurement based on DSP

Ultrasonic transmitting, receiving and amplifying circuits are designed. Thereceived signals are sampled with the high speed ADC (analog-to-digital converter), and dealt withthe DSP (digital signal processing). A forward-backward IIR (infinitive impulse response) filterwith no delay is designed to filter the sampled data, and series A and B are achieved by narrow andwide band filtering, respectively. In series A, the start point of the cycle first exceeding thethreshold is calculated accuratelyby interpolation, and the start cycle is detected by fittingcycles in series A and its inversion A' to cycles in B with variance analysis. Therefore, the startpoint of the start cycle is calculated precisely. By deriving the relationships between the traveltime in the opposite directions of three axes and the airflow velocities, the wind velocity anddirection are calculated. Experiments show that the reliability and the precision are improved, andthe circuits are simplified.

Forecasting of wind velocity:An improved SVM algorithm combined with simulated annealing

Accurate forecasting of wind velocity can improve the economic dispatch and safe operation of the power system. Support vector machine (SVM) has been proved to be an efficient approach for forecasting. According to the analysis with support vector machine method, the drawback of determining the parameters only by experts' experience should be improved. After a detailed description of the methodology of SVM and simulated annealing, an improved algorithm was proposed for the automatic optimization of parameters using SVM method. An example has proved that the proposed method can efficiently select the parameters of the SVM method. And by optimizing the parameters, the forecasting accuracy of the max wind velocity increases by 34.45%, which indicates that the new SASVM model improves the forecasting accuracy.

Effects of wind guide plates on wind velocity acceleration and dune leveling： a case study in Ulan Buh Desert, China

The areas used to be covered by shifting sand dunes have been reclaimed rapidly in recent years. However, it is a challenge to reclaim high sand dunes because it is rather costly to level the high dunes to gentle arable lands. In this study, a wind guide plate was used to change the characteristics of natural wind to level the sand dunes. The use of wind energy could significantly increase the efficiency of dune leveling and decrease the cost. Low wind velocity is a typical characteristic in Ulan Buh Desert of China where the average wind speed is much lower than the threshold velocity for sand movement. The experiment of this study was conducted to accelerate the wind velocity by a wind guide plate to level a sand dune. Results show that the threshold velocity for sand movement is 3.32 m/s at 10 cm above the sand surface in Ulan Buh Desert. A wind guide plate set at an angle less than 50° could significantly increase the wind velocity. The wind velocity could be accelerated up to the threshold velocity for sand movement behind a plate when the plate is at the angles of 20°, 25°, 35° and 40°. The most significant acceleration of wind velocity appears at 1.5 and 3.0 m behind the plate with an angle of 25°. An obvious wind velocity acceleration zone exists behind the wind guide plate when the angles are at 25°, 35°, 40° and 45°, with the most obvious zone under the angle of 45°. The results also show that the total amount of sand transferred over the experimental period increased by 6.1% under the effects of wind guide plates compared to the sand moved without wind guide plates. The results of the study will provide theoretical and practical supports for desert management in sand dune areas.

The Simulation and Characteristic Study of Wind Velocity for Long-Span Structures

The new technique that combines wave superposition with the fast Fourier transformation was introduced to simulate the nodal three-dimension relevant wind velocity time series of spatial structures. The wind velocity field where the spatial structure is located is assumed to be homogeneous. The wind’s power spectral density is divided into frequency spectral function and coherency function and the spectral functions are transformed as the superposition coefficients. The wavelet analysis has excellent localized characters in both time and frequency domains, which not only makes wind velocity time series analysis more accurate, but also can focus on any detail of the objective signal series. The discrete wavelet transformation was adopted to decompose and reconstruct the discrete wind velocity time series. The stability of wavelet analysis for the wind velocity time series was also proved.

Aerodynamic unstable critical wind velocity for three-dimensionalopen cable-membrane structures

The aerodynamic unstable critical wind velocity for three-dimensional open cable-membrane structures is investigated. The geometric nonlinearity is introduced into the dynamic equilibrium equations of structures. The disturbances on the structural surface caused by the air flow are simulated by a vortex layer with infinite thickness in the structures. The unsteady Bernoulli equation and the circulation theorem are applied in order to express the aerodynamic pressure as the function of the vortex density. The vortex density is then obtained with the vortex lattice method considering the coupling boundary condition. From the analytical expressions of the unstable critical wind velocities, numerical results and some useful conclusions are obtained. It is found that the initial curvature of open cable-membrane structures has clear influence on the critical wind velocities of the structures.

Effects of non-stationary wind velocity models on buffeting performance of closed-box girder suspension bridges

Non-stationary characteristic in nature wind has a great effect on buffeting performance of long-span bridges.The influence of key parameters in non-stationary wind velocity models on nonlinear buffeting responses of a super long-span suspension bridge was investigated in this paper.Firstly,four non-stationary wind velocity models are established by combing the time-varying average wind velocity with an exponential function and the fluctuating wind velocity with four modulation functions,respectively.These non-stationary wind velocity models have obvious non-stationary characteristics and then are validated by the classical power spectrum densities.Finally,three displacement responses of the bridge deck under four different independent variables ofβin the exponential function and four modulation functions were compared,respectively.Results show that the turbulence intensities using two non-uniform modulation functions(NMF)are larger than those using uniform modulation functions(uMF).Moreover,the root mean square(RMS)values of three displacement responses increase with the decrease ofβ.Besides,the RMS values of three displacement under two NMFs are larger than those under two uMFs,and their RMS values under the second uMF are the smallest.

Prediction of extreme wind velocity at the site of the Runyang Suspension Bridge

This paper presents a distribution free method for predicting the extreme wind velocity from wind monitoring data at the site of the Runyang Suspension Bridge (RSB), China using the maximum entropy theory. The maximum entropy theory is a rational approach for choosing the most unbiased probability distribution from a small sample, which is consistent with available data and contains a minimum of spurious information. In this paper, the theory is used for estimating a joint probability density function considering the combined action of wind speed and direction based on statistical analysis of wind monitoring data at the site of the RSB. The joint probability distribution model is further used to estimate the extreme wind velocity at the deck level of the RSB. The results of the analysis reveal that the probability density function of the maximum entropy method achieves a result that fits well with the monitoring data. Hypothesis testing shows that the distributions of the wind velocity data collected during the past three years do not obey the Gumbel distribution. Finally, our comparison shows that the wind predictions of the maximum entropy method are higher than that of the Gumbel distribution, but much lower than the design wind speed.

Noise reduction in LOS wind velocity of Doppler lidar using discrete wavelet analysis

The line of sight (LOS) wind velocity can be determined from the incoherent Doppler lidar backscattering signals. Noise and interference in the measurement greatly degrade the inversion accuracy. In this paper, we apply the discrete wavelet denoising method by using biorthogonal wavelets and adopt a distance-dependent thresholds algorithm to improve the accuracy of wind velocity measurement by incoherent Doppler lidar. The noisy simulation data are processed and compared with the true LOS wind velocity. The results are compared by the evaluation of both the standard deviation and correlation coefficient. The results suggest that wavelet denoising with distance-dependent thresholds can considerably reduce the noise and interfering turbulence for wind lidar measurement.

Statistical spectrum model of wind velocity at Beijing Meteorological Tower

The wind velocity spectra at Beijing Meteorological Tower are calculated using Hilbert-Huang transform and Fourier transform,respectively.A innovative model of wind velocity spectrum,which is accordant with the characteristics in both the inertial subrange and the large eddies range,is presented in this paper.The method of least squares is adopted to obtain the parameters in the model.Then the differences between the FFT spectrum and the HHT spectrum are compared.It is indicated that the values of the HHT spectrum in the energy containing range are slightly larger than those of the FFT spectrum while the values of the HHT spectrum in both inertial subrange and dissipation subrange are very close to that of Fourier spectrum.It is concluded that the HHT spectrum describes elaborately and accurately the spectrum values in the low frequencies and the fitted wind velocity model provides a reference for reconstructing the near-ground wind field of Beijing city in wind tunnel test and for numerical simulation.

Wind Velocity Reduction of Coastal Shelterbelt System in Shanghai,East China

Wind velocity reduction of coastal shelterbelt system was monitored for 1 month in 3 weather stations in Nanhui,Shanghai,and the benefits of shelterbelt system and trunk shelterbelt forest were compared in this paper.The results showed the wind velocity at the first weather station(W1),which located in front of trunk shelterbelt forest by the seaside,was the biggest,with the average of 9.36 m/s;the wind velocity at the second weather station(W2) was lower than that at W1,with the range of 0 to 18.2 m/s and the average of 6.39 m/s,and the wind velocity at the third weather station(W3) was the lowest,with the average of 2.58 m/s.Both the ratio of W2 to W1 and the ratio of W3 to W1 ranged from 0 to 100%,but most of the ratio of W2 to W1(89.59%) was above 20%,and most of the ratio of W3 to W1(95.52%) was below 50%,which shows bigger wind velocity reduction in shelterbelts system than in trunk shelterbelt forest.With the wind scale increased from 1 to 8 scale at W2 and W3,the wind velocity increased.But the reduction in wind velocity decreased.

Efficient method for wind velocity estimation and power-extraction maximization using a fourth-order Luenberger observer in a wind-energy-conversion system

This paper proposes an advanced method for estimating numerous parameters in a wind-energy-conversion system with high precision,especially in a transient state,including the rotation speed and mechanical torque of the turbine as well as wind velocity.The suggested approach is designed into two parts.First,a fourth-order Luenberger observer is proposed to take into account the significant fluctuations of the mechanical torque that can be caused by wind gusts.This observer provides an accurate estimate of speed and mechanical torque in all weather conditions and especially when the wind is gusting.At the same time,the wind velocity is calculated using the Luenberger observer outputs and a model of the mechanical power generated by the turbine.Second,these estimated parameters are exploited as input in a maximum-power-point tracking(MPPT)algorithm using the tip-speed ratio(TSR)to improve the sensorless strategy control.Simulation results were performed using MATLAB®/Simulink®for both wind gust and real wind profiles.We have verified that for wind gusts with jumps ranging from 3 to 7 m/s,the new observer manages to better follow the rotation speed and the torque of the turbine compared to a usual observer.In addition,we demonstrated that by applying the proposed estimator in the improved TSR-MPPT strategy,it is possible to extract 3.3%more energy compared to traditional approaches.

Conditional Estimation of Wind Velocity Based on VAR Model

The vector autoregressive （VAR） model is established with the wind velocity data from four wind observations, which are established on the Sutong Bridge reach of the Changjiang River and in Changshu, Haimen and Nantong meteorological observation stations. Based on the VAR model, the result of Granger causality test indicated that there is Granger causality between most of the variables. Consequently the missing wind velocity values of Sutong bridge are estimated with the condition of the wind velocity data from the other three observatories, and the result of the conditional estimation is comparatively perfect.

Preliminary Study on Vertical Velocity Caused by Katabatic Wind in Antarctica and Its Influence on Atmospheric Circulation

The vertical velocity at the top of Ekman layer caused by katabatic winds is proposed and deduced. By computing actual data we get a distribution of the velocities over Antarctica. The distribution plays a positive role in maintaining the cyclone and anticyclone over Antarctica.

Reducing Condensation Inside the Photovoltaic(PV)Inverter according to the Effect of Diffusion as a Process of Vapor Transport

A photovoltaic(PV)inverter is a vital component of a photovoltaic(PV)solar system.Photovoltaic(PV)inverter failure can mean a solar system that is no longer functioning.When electronic devices such as photovoltaic(PV)inverter devices are subjected to vapor condensation,a risk could occur.Given the amount of moisture in the air,saturation occurswhen the temperature drops to the dewpoint,and condensationmay formon surfaces.Numerical simulation with“COMSOL Software”is important for obtaining knowledge relevant to preventing condensation by using two steps.At first,the assumption was that the device’s water vapor concentration was homogeneous to evaluate the amount of liquid water accumulated on the internal walls of the photovoltaic(PV)inverter box.Second,by considering the effect of external wind velocity onmoisture transport at the air interface to evaluate water vapor transport outdoors and reduce condensation.General factorial designs are utilized for analyzing the nature of the relationship between the vapor condensation response and the variables.Reducing vapor condensation inside the solar inverter by the effect of external wind speed on diffusion as a process of transporting moister air outside the inverter box is the main solution for this problem.During the movement and assessment of the flow of water vapor,the impact of vapor condensation is reduced.The saturation period was determined by using a Boolean saturation indicator.The saturation indicator was set to 1 when saturation was detected(relative humidity greater than or equal to 1)and 0 otherwise.Calculating the flow and dispersion of moist air as a function of wind speed helped solve the problem.

Running safety analysis of a train on the Tsing Ma Bridge under turbulent winds

The dynamic responses of the Tsing Ma suspension bridge and the running behaviors of trains on the bridge under turbulent wind actions are analyzed by a three-dimensional wind-train-bridge interaction model. This model consists of a spatial finite element bridge model, a train model composed of eight 4-axle identical coaches of 27 degrees-of-freedom, and a turbulent wind model. The fluctuating wind forces, including the buffeting forces and the self-excited forces, act on the bridge only, since the train runs inside the bridge deck. The dynamic responses of the bridge are calculated and some results are compared with data measured from Typhoon York. The runnability of the train passing through the Tsing Ma suspension bridge at different speeds is researched under turbulent winds with different wind velocities. Then, the threshold curve of wind velocity for ensuring the running safety of the train in the bridge deck is proposed, from which the allowable train speed at different wind velocities can be determined. The numerical results show that rail traffic on the Tsing Ma suspension bridge should be closed as the mean wind velocity reaches 30 m/s.

Effect of the W-beam central guardrails on wind-blown sand deposition on desert expressways in sandy regions

Many desert expressways are affected by the deposition of the wind-blown sand,which might block the movement of vehicles or cause accidents.W-beam central guardrails,which are used to improve the safety of desert expressways,are thought to influence the deposition of the wind-blown sand,but this has yet not to be studied adequately.To address this issue,we conducted a wind tunnel test to simulate and explore how the W-beam central guardrails affect the airflow,the wind-blown sand flux and the deposition of the wind-blown sand on desert expressways in sandy regions.The subgrade model is 3.5 cm high and 80.0 cm wide,with a bank slope ratio of 1:3.The W-beam central guardrails model is 3.7 cm high,which included a 1.4-cm-high W-beam and a 2.3-cm-high stand column.The wind velocity was measured by using pitot-static tubes placed at nine different heights(1,2,3,5,7,10,15,30 and 50 cm)above the floor of the chamber.The vertical distribution of the wind-blown sand flux in the wind tunnel was measured by using the sand sampler,which was sectioned into 20 intervals.In addition,we measured the wind-blown sand flux in the field at K50 of the Bachu-Shache desert expressway in the Taklimakan Desert on 11 May 2016,by using a customized 78-cm-high gradient sand sampler for the sand flux structure test.Obstruction by the subgrade leads to the formation of two weak wind zones located at the foot of the windward slope and at the leeward slope of the subgrade,and the wind velocity on the leeward side weakens significantly.The W-beam central guardrails decrease the leeward wind velocity,whereas the velocity increases through the bottom gaps and over the top of the W-beam central guardrails.The vertical distribution of the wind-blown sand flux measured by wind tunnel follows neither a power-law nor an exponential function when affected by either the subgrade or the W-beam central guardrails.At 0.0H and 0.5H(where H=3.5 cm,which is the height of the subgrade),the sand transport is less at the 3 cm height from the subgrade surface than at the 1 and 5 cm heights as a result of obstruction by the W-beam central guardrails,and the maximum sand transportation occurs at the 5 cm height affected by the subgrade surface.The average saltation height in the presence of the W-beam central guardrails is greater than the subgrade height.The field test shows that the sand deposits on the overtaking lane leeward of the W-beam central guardrails and that the thickness of the deposited sand is determined by the difference in the sand mass transported between the inlet and outlet points,which is consistent with the position of the minimum wind velocity in the wind tunnel test.The results of this study could help us to understand the hazards of the wind-blown sand onto subgrade with the W-beam central guardrails.

Effects of sand-fixing and windbreak forests on wind flow:a synthesis of results from field experiments and numerical simulations

Sand-fixing and windbreak forests are widely used to protect or/and improve the ecological environments in arid and semi-arid regions. A full understanding of wind flow characteristics is essential to arranging the patterns of these protective forests for enhancing the effectiveness. In this study, the wind velocity over the underlying surface with sand-fixing forests and windbreak forests at the heights of 1–49 m was monitored from two 50-m high observation towers in an oasis of Minqin, Gansu Province of China. The wind velocities were simulated at different locations over these protective forests between those two towers by a two-dimensional Computational Fluid Dynamics（CFD） model. The results showed that at the heights of 1–49 m, the wind velocity profiles followed a classical logarithm law at the edge of the oasis and a multilayer structure inside the oasis. With increasing number of sand-fixing forest and windbreak forest arrays, the wind velocity at the heights of 1–49 m generally decreased along the downstream direction of the prevailing wind. Specifically, below the height of windbreak forests, the wind velocity decelerates as the airflow approaches to the windbreak forests and then accelerates as the airflow passes over the windbreak forests. In contrast, above the height of windbreak forests, the wind velocity accelerates as the airflow approaches to the windbreak forests and then generally decelerates as the airflow passes over the windbreak forests. Both the array number and array spacing of sand-fixing and windbreak forests could influence the wind velocity. The wind protection effects of sand-fixing forests were closely related to the array spacing of windbreak forests and increased with the addition of sand-fixing forests when the array of the forests was adequately spaced. However, if the array spacing of windbreak forests was smaller than seven times of the heights of windbreak forests, the effects were reduced or completely masked by the effects of windbreak forests. The results could offer theoretical guidelines on how to systematically arrange the patterns of sand-fixing and windbreak forests for preventing wind erosion in the most convenient and the cheapest ways.

Wind Vibration Study of Long-span Steel Arch Structure of Beijing Capital International Airport

The wind-induced dynamic response of long-span light-weight steel arch structure of the global transportation center (GTC) of Beijing Capital International Airport was studied. A composite technique with combination of WAWS(Weighted Amplitude Wavelet Superposition) and FFT(Fast Fourier Transformation) was introduced to simulate wind velocity time series of hundreds of spatial points simultaneously. The structural shape factors of wind load was obtained from wind tunnel model test. The wind vibration factor based on structural displacement response was investigated. After comparing the computational results with wind tunnel model test data, it was found out that the two results accord with each other if wind comes from 0° direction angle, but are quite different if wind comes from 180° direction angle in the area blocked off by airport terminals. The possible reasons of this difference were analyzed. Haar wavelet was used to transform and analyze wind velocity time series and structural wind-induced dynamic responses. The relationship between exciting wind loads and structural responses was studied in time and frequency domains.

Thermodynamic Effects on Particle Movement:Wind Tunnel Simulation Results

Sand/dust storms are some of the main hazards in arid and semi-arid zones. These storms also influence global environmental changes. By field observations, empirical statistics, and numerical simulations, pioneer researchers on these natural events have concluded the existence of a positive relationship between thermodynamic effects and sand/dust storms. Thermodynamic effects induce an unsteady stratified atmosphere to influence the process of these storms. However, studies on the relationship of thermodynamic effects with particles (i.e., sand and dust) are limited. In this article, wind tunnel with heating was used to simulate the quantitative relationship between thermodynamic effects and particle movement on different surfaces. Compared with the cold state, the threshold wind velocity of particles is found to be significantly decrease under the hot state. The largest decrease percentage exceedes 9% on fine and coarse sand surfaces. The wind velocity also has a three-power function in the sand transport rate under the hot state with increased sand transport. Thermodynamic effects are stronger on loose surfaces and fine particles, but weaker on compacted surfaces and coarse particles.

Numerical simulation on ionic wind in circular channels

Ionic wind induced by direct-current corona discharge has attracted considerable interest because of its low energy consumption, low noise emission, flexible designs, and lack of moving parts. The purpose of this study is to investigate the configuration parameters to improve the velocity of the ionic wind. Accordingly, this study develops a three-dimensional(3 D) model of circular tube with multi-needle-to-mesh electrode configurations, in this model, the influences of various parameters were explored,such as the mesh gap, the distribution of needle electrodes, the number of needle electrodes,and the radius of the circular channel. The numerical research results showed that the mesh gap, the distribution of needle electrodes, and the radius of the circular tube significantly affected the velocity of the ionic wind. When mesh gap is 12 mm,which indicates that there is an optimal mesh gap which can enhance the velocity of the ionic wind. What is more, changing the distribution of needle electrodes and increasing the number of needle electrodes can effectively improve the velocity of the ionic wind, the optimum distribution α of needle electrodes is 0.7–0.9, which greatly increase the velocity of the ionic wind. However, for multi-needle-to-mesh structure, the improvement of the radius of the circular channel is conducive to enhance the velocity and improve the velocity distribution.