Constant Wind Speed Research Articles

The motion rule of sand particles under control of the sand transportation engineering

In the desert and Gobi regions with strong wind and large sediment discharge, sand transporting engineering is more effective than sand blocking and sand fixing measures in sand prevention. This study uses the discrete phase model of 3D numerical simulation to study the motion trail, motion state and distribution rule of sand particles with different grain diameters when the included angle between the main shaft of the feather-row lateral transportation sand barrier and the wind direction changes, and conducts a comparison in combination with the wind tunnel test and the flow field rule of common sand barrier. According to the comparison, when wind-sand incoming flow passes through a feather-row sand barrier, sand particles slow down and deposit within the deceleration area under the resistance of the feather-row sand barrier, move along the transportation area formed by the transportation force, and accumulate as a ridge at the tail of the engineering. With increasing wind speed, the eolian erosion of the sand particles to the ground and the feather-row sand barrier is enhanced, and the sand transporting quantity and throw-over quantity of the feather-row sand barrier are both increased. When sand particles with different grain diameters bypass the feather-row sand barrier, the particle size of the infiltrating sands will increase with the included angle between the main shaft of the feather-row sand barrier and the wind direction. The obtained result demonstrates that, at a constant wind speed, the flow field formed is most suitable for the lateral transportation of the wind-drift flow when the included angle between the main shaft of the feather-row sand barrier lateral transportation engineering and the wind speed is less than or equal to 30

Combined Primary Frequency Control Strategy of Permanent Magnet Synchronous Generator-Based Wind Turbine

To ensure the proper operation of power system, some independent system operators have specified that wind power plants should be able to manipulate power output for frequency control. This article presents a combined control scheme which exploits the self-capability of permanent magnet synchronous generator-based wind turbine to provide primary frequency response. Under normal condition, the wind turbine operates in de-loading mode to obtain the power reserve. Once frequency deviation is detected, the proposed control strategy can not only make use of the power reserve for frequency regulation by adjusting the rotor speed, but utilize the kinetic energy in rotor to provide frequency response as well. Besides, the energy stored in DC capacitor is also employed for frequency support. The simulation results reveal that the wind turbines with the proposed method can improve frequency performance under both constant wind speed condition and variable wind speed condition.

Scaling nonreactive cross flow over a heated plate to simulate forest fires

The paper reports visualization of the flow of smoke over a flat surface inside of a low-speed wind tunnel. A heating plate flush mounted on the wind tunnel floor simulated a spreading line fire that produces uniform heat flux under constant wind speed condition. A paper-thin cloth was soaked with commercially available Vaseline and placed on top of the heating plate; when it is heated, it produced thick white smoke, ideal for flow visualization. Two sides and top of the wind tunnel were made of a transparent acrylic sheet that enabled LED and laser sheet light illumination of the flow. A still camera with a full-frame CMOS sensor was used to record time-series images of illuminated smoke flow patterns from different angles. From these images, the following four flow structures were identified: organized horizontal vortex flows, weak vortex flow interactions, strong vortex flow interactions (also described as the ‘transition regime’), and, turbulent flows. Previously developed scaling laws on forest fires were applied to find similarity in flow structures created by the current small-scale convective heat-transfer experiments and the USDA's mid-scale wind tunnel fire experiments.

Comparative Analysis of Danger Zone Ranges Determined for LNG in the Coastal Area

Abstract The analysis of danger zone ranges for LNG in the coastal area is an important task on account of, inter alia, the safety of human life. It is not an easy process, which is why we consider an danger situation for various weather conditions in the function of constant wind speeds and for various wind speeds in constant weather stability. Pasquill weather stability scale and Beaufort scale with regard to terrain roughness were adopted for the analysis. Both scenarios were considered in the example of Q-flex type vessels in the Świnoujście terminal for two methods of LNG release, i.e. related to a sudden explosion and slow release caused by a leak. The analysis was conducted and considered for the values in the top and bottom flammability limit. Modelling of the danger zone range was analysed with DNV PHAST software, version 7.11. In the process of comparison of the situation related to the risk of explosion in the function of various weather stabilities according to Pasquill scale and constant wind speeds, the values of 1.5 m/s and 5 m/s were adopted, corresponding to 1 and 3 wind force on the Beaufort scale. Those speeds correspond to the water conditions featuring tiny ripples and small waves, the crests of which start to break. The adopted weather stabilities analysed for wind speed equal to 1.5 m/s are A, B, D. A-type stability signifies the least stable atmospheric conditions, and D-type means neutral conditions. In turn, for the wind speed of 5 m/s B, D and F parameters in Pasquill scale were selected. Furthermore, ranges for variable wind speed values were analysed for the selected Pasquill stability.

The Comparison and Analysis of the DFIG Behavior Under PI, Fuzzy and Sliding Mode Controllers for Wind Energy Conversion System in the Grid Connected Mode

In this paper, the vector control strategy along with a non linear control are applied to the doubly fed induction generator (DFIG) based wind energy. Three control strategies (PI, Fuzzy and sliding mode control) are explained, analysed and compared in terms of response time, harmonic filtering and robustness to the parametric variation. These control strategies are evaluated in the steady and transient state to control both the active and the reactive power in the grid connected mode. The analysis of the DFIG behaviour under the mentioned control strategies is verified in the simulations. Also, a representation of numerical results is displayed in a summary table. The three strategies control present some advantages and drawbacks in term of performances when they operate with power optimization and power limitation strategies. However, the sliding mode control is better under the parameters variation and speed change. Although, the fuzzy control delivers a fast response time and presents a good harmonic distortion value(THD) while the PI control ensures a perfect precision during constant wind speeds.

Effect of woody debris on the rate of spread of surface fires in forest fuels in a combustion wind tunnel

The treatment of the contribution of woody debris (WD, such as branches or small logs >6–50 mm diameter) to the rate of forward spread of a fire in current operational forest fire spread models is inconsistent. Some models do not take into account this fuel at all (i.e. only consider the combustion of fine fuels (⩽6 mm diameter)), while others incorporate effects based on little or no data. An experimental programme utilising a large combustion wind tunnel investigated the effect of WD on the spread of fires burning through forest litter (surface fuel) beds of 1.0 kg m-2. Fires spreading with (heading) and against (backing) the wind were investigated. Three treatments of WD load (0.2, 0.6 and 1.2 kg m-2) and a control (0 kg m-2) were studied using a single constant wind speed (1.0 m s-1) and a narrow range of fine and woody fuel moisture contents (10.0–12.7% and 9.2–11.6% oven-dry weight, respectively) determined by ambient conditions. Presence of WD was found to approximately halve the overall rate of spread of heading fires relative to when no WD was present, regardless of the level of treatment. No effect of WD on rate of spread was found for backing fires. Potential explanations of these findings and implications for the use of operational forest fire spread models are explored, as are future research needs.

Performance investigations of modified asymmetric blade H-Darrieus VAWT rotors

Wind is an important renewable energy resource, which can be extracted for power generation by horizontal and vertical axis wind turbines (VAWTs). VAWTs can be installed in low wind speed regimes for small-scale power generation. However, for better performance in such a scenario, an improved rotor blade configuration is essential. This paper investigates the performances of an asymmetric blade H-Darrieus rotor with a blade span constant relative thickness (RT) and a variable thickness (VT) at different low wind speeds between 4 and 6 m/s. Both static and steady-state performances have been evaluated. Different blade span thickness to chord ratios (t/c) of 30% and 45% (constant RT case) are considered by increasing the blade thickness of the considered base profile NACA 63-415 while keeping the chord length same (5.0 cm). After determining the optimal blade RT, a new blade span variable thickness (VT) H-Darrieus rotor has been designed with a thicker portion (t/c =37.5%) on the top end and a thinner portion (t/c = 22.5%) on the bottom end of the blade, i.e., the thickness of the blade profile throughout the blade span is not the same. The thickness gradually decreases from top to bottom of the blades. The effects of all the thickness modifications have been studied with respect to the performance improvement of the H-Darrieus rotor. It has been shown that constant blade span RT (t/c = 45%) can largely improve the starting characteristics of the asymmetric blade H-Darrieus rotor, whereas blade span VT design can result in better power coefficients of the same in low wind speed conditions. Furthermore, an attempt has also been made to study the fluctuations of steady state torque at the selected wind speeds for understanding the stability and smoothness of operation. Moreover, the fluctuations of power and torque coefficients due to steady turbulence intensity and flow non-uniformity over a constant wind speed have also been demonstrated to connect with real-life applications of the H-Darrieus rotor.

Aerodynamic Simulation of A Containership to Evaluate Cargo Configuration Effect on Frontal Wind Loads

Fuel consumption has always been a matter of concern for ships propulsion. In this research we aim to develop computer models of several containership cargo stacking configurations and discuss an optimal configuration at a constant front wind speed. The paper presents the simulation results by using ANSYS CFX for a 1:4 scale Post- Panamax 9000 TEU containership. The ship is modelled in a cubic domain that contains unstructured mesh with details, in such a way that can demonstrate the influence of the container configuration on wind force. Also the numerical results are verified versus wind tunnel test data. An optimal stack configuration led to about 25% reduction in air resistance. It is proposed that in order to reduce the wind drag force and consequently reduce the fuel consumption and pollutant emissions, empty spaces between the cargo containers and unbalanced cargo distribution over the deck should be inhibited. Also, it is advised to make the cargo distribution on the most forward and aftward deck areas more streamlined.

Comparison of Different Models for Wave Generation of The Hasselmann Equation

We compare two recently developed sets of source terms, based on different assumptions of wave energy input and dissipation, for Hasselmann equation. The numerical simulation, performed for limited fetch conditions with the constant wind speed shows the difference in total energy and mean frequency distributions along the fetch as well as in wave energy spectra. Possible reasons of such deviations are offered.

Amplification factors to estimate wind erosion of piles of soil with different heights: Numerical simulation and structure-from-motion photogrammetry verification

In this study, we propose amplification factors of single conical piles with different heights and sizes to describe wind erosion acceleration effects of piles compared to flat erodible surfaces. It is not difficult using traditional wind erosion models to estimate wind erosion of flat agricultural land or pastoral surfaces. However, in the current form these models cannot be used for elevated surfaces such as dunes or piles, which may lead to more serious dust emission and air pollution. A computational fluid dynamics simulation was used to refine a wind erosion estimation method of pile from the US Environmental Protection Agency (USEPA) by dividing the pile surface into multiple subareas with constant wind speed for each subarea and then obtaining ratios of pile erosion to the corresponding flat surface by calculating the total erosion rate of the pile and that of a flat surface with the same floor area. The ratios as amplification factors, <i>E_amp</i>, for six pile sizes (from 1 to 12 m) and five wind speed scenarios covering most erosive daily wind speeds from 824 stations throughout China were analyzed and fitted to equations to enable consideration of other heights and wind speed conditions. The changing patterns of the factors were verified using experimental surveys of two plots via the structure-from-motion photogrammetry method, which generated high-resolution digital elevation maps and detected detailed erosion changes. The erosion from a stockpile surface was found to be 2.52 to 7.16 times that from a flat surface with the same floor area, and the influence of pile height on amplification factor could be expressed by a logarithmic equation. These factors can be easily applied to estimate pile erosion by multiplying them by wind erosion results for flat surfaces obtained from other indexes or models. The procedure described in this paper can be extended to consider amplification or reduction effects of dunes, hills, piles, pits, and gullies with different shapes or configurations in relation to wind erosion. Furthermore, the reliability of wind erosion estimation over complex surfaces can be improved to implement specific soil conservation practices.

A New Formula for Estimating the Threshold Wind Speed for Snow Movement

AbstractThreshold wind speed for snow movement is one of the most important parameters describing the wind‐transport snow process. A majority of previous studies used empirical and constant threshold wind speeds while the variations of atmosphere condition and snow age seem to greatly affect the snow settlement process. This study tested the hypothesis that the threshold wind speed for snow transport increases as deposition time passed since last snowfall by introducing a new formula of the threshold wind speed for snow movement. It was theoretically derived based on the sintering process modeling and the moment balance of a snow particle. Through this formula, the influences of snow particle size, temperature, and deposition time on the threshold wind speed were explicitly taken into consideration. However, two empirical parameters in the sintering process modeling remained in the new formula, and they were determined by a calibration‐validation procedure using the field observed snow flux data. The snow flux and meteorological data collected at the ISAW stations (http://www.iav.ch) including large number of snow transport events during five winter seasons were used to test this formula. It was shown that the new formula qualitatively described the threshold wind speed required for the incipient motion of snow under various conditions in the natural environment of the Alps.

Effectiveness of mechanical thinning and prescribed burning on fire behavior in Pinus nigra forests in NE Spain

Fuel treatments can mitigate present and future impacts of climate change by reducing fire intensity and severity. In recent years, Pinus nigra forests in the Mediterranean basin have been dramatically affected by the new risk of highly intense and extreme fires and its distribution area has been reduced. New tools are necessary for assessing the management of these forests so they can adapt to the challenges to come. Our main goal was to evaluate the effects of different fuel treatments on Mediterranean Pinus nigra forests. We assessed the forest response, in terms of forest structure and fire behavior, to different intensities of low thinning treatments followed by different slash prescriptions (resulting in: light thinning and lop and scatter; light thinning and burn; heavy thinning and lop and scatter; heavy thinning and burn; and, untreated control). Treatments that used fire to decrease the resulting slash were the most effective for reducing active crown fires decreasing the rate of spread and flame length more than 89%. Low thinning had an effect on torching potential, but there was no difference between intensities of thinning. Only an outcoming crown fire could spread actively if it was sustained by a high-enough constant wind speed and enough surface fuel load. Overall, treatments reduce fire intensity and treated areas have a more homogenous fire behavior response than untreated areas. This provides opportunities to extinguish the fire and reduce the probability of trees dying from the fire. It would be helpful to include ecological principles and fire behavior criteria in silvicultural treatment guidelines in order to perform more efficient management techniques in the future.

Analysis of non-stationary wind characteristics at an arch bridge using structural health monitoring data

The accurate characterization of the wind characteristics of extreme wind events is crucial to the structural design and safety evaluation. However, the field-measured wind data during typhoons exhibit a strong non-stationary feature with an inherent time-varying trend which deviates from the traditional stationary assumption. This paper presents the study of non-stationary wind characteristics of Typhoon Soudelor at the Jiubao Bridge located in Hangzhou, China, which has been instrumented with a structural health monitoring system. After data classification by the stationary test, the non-stationary wind data are analyzed by both traditional stationary wind model and non-stationary wind model which considers the inherent time–varying mean wind speed. The empirical mode decomposition (EMD) and wavelet multiresolution analysis (MRA) are employed to extract the underlying trend from the original wind data as the time-varying mean wind speed for the non-stationary wind model. Based on two categories of fluctuating wind speeds obtained by removing the constant and time-varying mean wind speed, the wind characteristics including the mean wind speed, turbulence intensity, gust factor, probability distribution and power spectral density are comparatively analyzed. The results indicate that the time-varying mean wind speed can be effectively identified and extracted by the EMD and MRA. The non-stationary wind model is more appropriate than the traditional stationary wind model in the analysis of non-stationary wind speed data during a typhoon.

Retrieving air humidity, global solar radiation, and reference evapotranspiration from daily temperatures: development and validation of new methods for Mexico. Part III: reference evapotranspiration

We evaluated two methods to estimate evapotranspiration (ETo) from minimal weather records (daily maximum and minimum temperatures) in Mexico: a modified reduced set FAO-Penman-Monteith method (Allen et al. 1998, Rome, Italy) and the Hargreaves and Samani (Appl Eng Agric 1(2): 96–99, 1985) method. In the reduced set method, the FAO-Penman-Monteith equation was applied with vapor pressure and radiation estimated from temperature data using two new models (see first and second articles in this series): mean temperature as the average of maximum and minimum temperature corrected for a constant bias and constant wind speed. The Hargreaves-Samani method combines two empirical relationships: one between diurnal temperature range ΔT and shortwave radiation Rs, and another one between average temperature and the ratio ETo/Rs: both relationships were evaluated and calibrated for Mexico. After performing a sensitivity analysis to evaluate the impact of different approximations on the estimation of Rs and ETo, several model combinations were tested to predict ETo from daily maximum and minimum temperature alone. The quality of fit of these models was evaluated on 786 weather stations covering most of the territory of Mexico. The best method was found to be a combination of the FAO-Penman-Monteith reduced set equation with the new radiation estimation and vapor pressure model. As an alternative, a recalibration of the Hargreaves-Samani equation is proposed.

Numerical Simulation of the Influence of Platform Pitch Motion on Power Generation Steadiness in Floating Offshore Wind Turbines

Offshore wind energy is a valuable renewable resource that is inexhaustible, strong, and consistent. To reduce cost and improve energy production efficiency, future trends are moving towards wind turbines in deep water, which use floating platforms such as tension leg platforms, barges, and semi-submersible designs. Compared to fixed based substructures, these floating platforms are in a state of constant motion which affects the power generation steadiness. The resulting complex dynamic behavior might compromise their efficiency and reduce their nominal life. The complex analysis of floating wind turbines requires computer tools that couple all the different components to represent the complete dynamic response. One such tool, developed by the National Renewable Energy Laboratory, is the aero-hydro-servo-elastic tool FAST. In this work, simplified models are used for three platform types, and the results are compared with FAST as a way of understanding the essential dynamics. Secondly, using FAST, the influence of platform pitch motion on the steadiness of power generation is examined. This analysis is done for all three platforms for a constant above rated wind speed and above average wave load. Results demonstrate that the power output fluctuation depends on the platform type and blade pitch motion. The effect of platform pitch on the steadiness of power output is only apparent under large oscillating pitch motion, where recurring power drops are observed. The semi-submersible design performs well with relatively steady power output, while the barge design has the most unsteady output, as a result of its susceptibility to typical wave loads.

Numerical Simulation of the Influence of Platform Pitch Motion on Power Generation Steadiness in Floating Offshore Wind Turbines

Offshore wind energy is a valuable renewable resource that is inexhaustible, strong, and consistent. To reduce cost and improve energy production efficiency, future trends are moving towards wind turbines in deep water, which use floating platforms such as tension leg platforms, barges, and semi-submersible designs. Compared to fixed based substructures, these floating platforms are in a state of constant motion which affects the power generation steadiness. The resulting complex dynamic behavior might compromise their efficiency and reduce their nominal life. The complex analysis of floating wind turbines requires computer tools that couple all the different components to represent the complete dynamic response. One such tool, developed by the National Renewable Energy Laboratory, is the aero-hydro-servo-elastic tool FAST. In this work, simplified models are used for three platform types, and the results are compared with FAST as a way of understanding the essential dynamics. Secondly, using FAST, the influence of platform pitch motion on the steadiness of power generation is examined. This analysis is done for all three platforms for a constant above rated wind speed and above average wave load. Results demonstrate that the power output fluctuation depends on the platform type and blade pitch motion. The effect of platform pitch on the steadiness of power output is only apparent under large oscillating pitch motion, where recurring power drops are observed. The semi-submersible design performs well with relatively steady power output, while the barge design has the most unsteady output, as a result of its susceptibility to typical wave loads.

Dynamic analysis of a floating hybrid spar tension leg platform concept for wind monitoring applications in deep sea

This study presents an investigation to assess the motions experienced by a floating hybrid spar-tension leg platform structure when supporting a wind-monitoring lattice tower in deep water conditions of the Central Mediterranean. The numerical study is based on the software package ANSYS® AQWA™. The structure supports a 30 m wind-monitoring tower as well as a LiDAR system. A parametric analysis was carried out for different geometrical and met-ocean conditions, and the simulations were restricted to regular (single frequency) wave and constant wind speed conditions only. The Morison formulation was used to resolve the hydrodynamic loads in a time domain. The study shows how the natural periods of the floating wind-monitoring mast structure decrease with increasing buoyancy-to-weight ratios. From the time-series simulations, it was evident that slender spars experience smaller displacements. This is a favourable result as it results in more reliable wind measurements taken by the cup-type anemometers. Finally, a sensitivity analysis was carried out to examine the variations of surge motion predictions resulting from deviations in the hydrodynamic coefficients. It was observed that the platform surge motion is more sensitive to deviations in the added mass coefficient than the drag coefficient.

A multi-scale synthetic eddy method for generating inflow data for LES

A multi-scale synthetic eddy method (MSSEM) for generating inflow turbulence that approaches realistic turbulence characteristics is presented. The proposed method is a modified version of the synthetic eddy method (SEM), which regards turbulence as a superposition of coherent structures. The inflow turbulence generated by the SEM can match the prescribed first and second statistical moments, length scales, and autocorrelation functions, but it cannot match the turbulence spectrum, which is a key characteristic of turbulence. The idea of the MSSEM is to introduce multi-scale eddies with spectrum energies with a focus on different frequency ranges and then synthesize eddies with different scales and energies to match the objective spectrum. The length and proportion of each scale eddy are determined with a predefined turbulence length and turbulence spectra. The advection velocity of a multi-scale eddy is the mean wind value at the location of the eddy and not the constant wind speed. Three large eddy simulations of a turbulent boundary layer with inflow turbulence generated by Lund's method, SEM and MSSEM are considered in this study. The turbulence characteristics at the inlet plane and in the internal flow field are compared and discussed. Result shows that the turbulence structure in the case of the MSSEM resembles turbulence, and the turbulence spectra of three velocity components show good agreement with the predefined values at the inlet plane and in the internal flow field.

On the fast magnetic rotator regime of stellar winds

Aims: We study the acceleration of the stellar winds of rapidly rotating low mass stars and the transition between the slow magnetic rotator and fast magnetic rotator regimes. We aim to understand the properties of stellar winds in the fast magnetic rotator regime and the effects of magneto-centrifugal forces on wind speeds and mass loss rates. Methods: We extend the solar wind model of Johnstone et al. (2015b) to 1D magnetohydrodynamic (MHD) simulations of the winds of rotating stars. We test two assumptions for how to scale the wind temperature to other stars and assume the mass loss rate scales as Mdot ~ Rstar^2 OmegaStar^1.33 Mstar^-3.36, in the unsaturated regime, as estimated by Johnstone et al. (2015a). Results: For 1.0 Msun stars, the winds can be accelerated to several thousand km/s, and the effects of magneto-centrifugal forces are much weaker for lower mass stars. We find that the different assumptions for how to scale the wind temperature to other stars lead to significantly different mass loss rates for the rapid rotators. If we assume a constant temperature, the mass loss rates of solar mass stars do not saturate at rapid rotation, which we show to be inconsistent with observed rotational evolution. If we assume the wind temperatures scale positively with rotation, the mass loss rates are only influenced significantly at rotation rates above 75 OmegaSun. We suggest that models with increasing wind speed for more rapid rotators are preferable to those that assume a constant wind speed. If this conclusion is confirmed by more sophisticated wind modelling. it might provide an interesting observational constraint on the properties of stellar winds.

CFD study of Savonius wind turbine: 3D model validation and parametric analysis

A CFD study is conducted in order to characterize the dynamic behavior of a Savonius vertical axis wind turbine. All simulations are executed using the open source code, OpenFOAM. Both two-dimensional and full three-dimensional cases have been investigated in order to provide a suitable tool for geometrical optimization of this rotor. Unsteady simulations are carried out at different tip speed ratio (TSR), varying angular speed of rotor at constant wind speed, using different one and two-equation URANS turbulence models and selecting the k−ω SST for the final analysis. The two-dimensional model was compared with experimental data available in literature and obtained from tests in wind tunnel. This simplified model shows an over-estimation of experimental data, reporting a maximum efficiency at TSR 1, 20% higher than experimental value. The results of 3D model are in good agreement with experiments with a peak of 0.202 at TSR 0.8 for a rotor with aspect ratio 1.1. The influence of the rotor height has been evaluated on flow dynamics of the turbine and its power coefficient.