Logarithmic Wind Profile Research Articles

Impact of low‐level wind maxima below hub height on wind turbine sound propagation

AbstractAn analysis of the effect of low‐level wind maxima (LLWM) below hub height on sound propagating from wind turbines has been performed at a site in northern Sweden. The stably stratified boundary layer, which is typical for cold climates, commonly features LLWM. The simplified concept for the effects of refraction, based on the logarithmic wind profile or other approaches where the wind speed is continuously increasing with height, is often not applicable there. Long‐term meteorological measurements in the vicinity of a wind farm were therefore used to identify LLWM. Sound measurements were conducted simultaneously to the meteorological measurements. LLWM below hub height decrease the sound level close to the surface downwind of the wind farm. This effect increases with increasing strength of the LLWM. The occurrence of LLWM as well as strength and height of the LLWM are dependent on the wind direction.

A Unified Anisotropic Particle-Based Ocean Wave Simulation Framework for Marine Simulator Visual System

It is urgent to improve the physical reality of ocean scenes in marine simulator for the maritime industry. In this paper, we propose a unified anisotropic particle-based ocean wave simulation framework for marine simulator. In the unified framework, a novel hybrid SPH method is applied to model the ocean waves, which combines a series of nonlinear density constraints and divergence-free velocity field constraints. By solving density constraints, the particle position distribution is directly adjusted to keep a constant density. Experiments show that the hybrid SPH method has advantages in compressibility and stability. Moreover, a novel stochastic fluctuating wind field model is integrated into the hybrid SPH method. The Perlin noise and a modified log wind profile are introduced to enrich the details of wind field. We also introduce a novel oil spill model for marine simulator based on number density, which can achieve a desired sharp density changes at interfaces between multiple fluids. For real-time surface reconstruction, we propose an improved anisotropic particle transformation method based on the distribution of the neighboring particles. The problem of particle deformation near the boundary is solved by our piecewise correction function, with the sharp features and anisotropy maintained. When calculating the covariance matrix and weighted position, the contribution of neighboring particles in other fluid phases is considered to eliminate gaps between multiple fluids in the oil spill scenes. The simulation results show that our unified anisotropic framework based on the SPH concept can easily integrate other models, has strong expansibility, and is very applicable to simulate complex ocean scenes.

An effective parametrization of gust profiles during severe wind conditions

A simple and effective parameterization for the profile of extreme wind gusts during severe wind conditions is presented. It is shown that the gust profile follows directly from the logarithmic wind profile. Also the uncertainty in the gust estimates can easily be determined from information of the average wind speed at two different heights. One specification of practical importance is that the maximum 3s-gust in a 10 min period at 10 m height is arithmetically equal to the average wind at 140 m. At larger heights the gusts are equal to the average wind speed at an easily determinable height that is a factor α (α > 1) higher. Validation over The Netherlands indicates that this rule applies to heights up to at least 200 m. This outcome is validated both over land and over sea, and is independent of surface roughness. The proposed parameterization reproduces the climatological values of the measured extreme wind gusts. Maximum gusts for individual winter months are better represented than for individual summer months. The mean error in the monthly winter maxima estimates is 5%.

Radiometric Method for Determining Canopy Stomatal Conductance in Controlled Environments

Canopy stomatal conductance is a key physiological factor controlling transpiration from plant canopies, but it is extremely difficult to determine in field environments. The objective of this study was to develop a radiometric method for calculating canopy stomatal conductance for two plant species—wheat and soybean from direct measurements of bulk surface conductance to water vapor and the canopy aerodynamic conductance in controlled-environment chambers. The chamber provides constant net radiation, temperature, humidity, and ventilation rate to the plant canopy. In this method, stepwise changes in chamber CO2 alter canopy temperature, latent heat, and sensible heat fluxes simultaneously. Sensible heat and the radiometric canopy-to-air temperature difference are computed from direct measurements of net radiation, canopy transpiration, photosynthesis, radiometric temperature, and air temperature. The canopy aerodynamic conductance to the transfer of water vapor is then determined from a plot of sensible heat versus radiometric canopy-to-air temperature difference. Finally, canopy stomatal conductance is calculated from canopy surface and aerodynamic conductances. The canopy aerodynamic conductance was 5.5 mol m−2 s−1 in wheat and 2.5 mol m−2 s−1 in soybean canopies. At 400 umol mol−1 of CO2 and 86 kPa atmospheric pressure, canopy stomatal conductances were 2.1 mol m−2 s−1 for wheat and 1.1 mol m−2 s−1 for soybean, comparable to canopy stomatal conductances reported in field studies. This method measures canopy aerodynamic conductance in controlled-environment chambers where the log-wind profile approximation does not apply and provides an improved technique for measuring canopy-level responses of canopy stomatal conductance and the decoupling coefficient. The method was used to determine the response of canopy stomatal conductance to increased CO2 concentration and to determine the sensitivity of canopy transpiration to changes in canopy stomatal conductance. These responses are useful for improving the prediction of ecosystem-level water fluxes in response to climatic variables.

Vertical Wind Profiles in Non-Neutral Conditions: Comparison of Models and Measurements From Frøya

This paper presents an analysis of stratification-dependent mean velocity profiles measured in a Norwegian coastal wind climate, and its comparison with models available in the literature. For this purpose, we use 3 years of observations from a 100 m meteorological mast located at the Frøya island (150 km west of Trondheim, Norway), equipped with a set of two-dimensional (2D) ultrasonic anemometers. The presented analysis is preceded by a general description of the site wind climate, the atmospheric stratification, the roughness length, and the surface layer height. Finally, the measured wind velocity profile is compared with selected models: the basic power and logarithmic law and the stability-corrected models: stability-corrected logarithmic wind profile, the Panofsky and Dutton model, the Peña boundary layer height corrected model, and the correlation-based Smedman-Högström model.

Near‐Surface Maximum Winds During the Landfall of Hurricane Harvey

AbstractA mobile Shared Mobile Atmospheric Research and Teaching (SMART) radar was deployed in Hurricane Harvey and coordinated with the Corpus Christi, TX, WSR‐88D radar to retrieve airflow during landfall. Aerodynamic surface roughness estimates and a logarithmic wind profile assumption were used to project the 500‐m radar‐derived maximum wind field to near the surface. The logarithmic wind assumption was justified using radiosonde soundings taken within the storm, while the radar wind estimates were validated against an array of StickNets. For the data examined here, the radar projections had root‐mean‐squared error of 3.9 m/s and a high bias of 2.3 m/s. Mesovorticies in Harvey's eyewall produced the strongest radar‐observed winds. Given the wind analysis, Harvey was, at most, a Category 3 hurricane (50–58 m/s sustained winds) at landfall. This study demonstrates the utility of integrated remote and in situ observations in deriving spatiotemporal maps of wind maxima during hurricane landfalls.

Analysis of Wind Effect on High-Rise Building for Different Terrain Category

This paper analyzed the effect of wind loadings on high-rise building for different terrain categories. The wind speed and design wind pressure for the different terrain categories adopted for this study were calculated as per logarithmic wind profile equation and BS6399-2:1997 respectively. Also, the nodal displacement of a 3D high-rise building model with reference to the calculated design wind loads were performed using finite element analysis software(STADDPROV8I). From the result obtained, it was shown that Terrain category IV when compared to other terrain categories recorded lower wind speed and pressure from the ground to a height of about 10m. The writers also observed that at greater terrain category(TC4), the wind speed and pressure tends to be much higher at the top floors(10m-48m) of the high-rise building whereas, terrain categories (TC3, TC2, TC1) recorded lower wind speed and pressure at that same height(10m-48m). this disparity however was discovered to be due to a phenomenon known as gust effect. Also, the nodal displacement for the different terrain category (TC4, TC3, TC2 and TC1) on each floor of the high-rise building increased uniformly in respective pattern as the height of the 3D model increases. In conclusion, the authors therefore remark “the greater the terrain category, the lowest is the wind speed in the roughness sub layer and the longer height it takes to reach gradient wind speed”.

Analysis of Wind Effect on High-Rise Building for Different Terrain Category

This paper analyzed the effect of wind loadings on high-rise building for different terrain categories. The wind speed and design wind pressure for the different terrain categories adopted for this study were calculated as per logarithmic wind profile equation and BS6399-2:1997 respectively. Also, the nodal displacement of a 3D high-rise building model with reference to the calculated design wind loads were performed using finite element analysis software(STADDPROV8I). From the result obtained, it was shown that Terrain category IV when compared to other terrain categories recorded lower wind speed and pressure from the ground to a height of about 10m. The writers also observed that at greater terrain category(TC4), the wind speed and pressure tends to be much higher at the top floors(10m-48m) of the high-rise building whereas, terrain categories (TC3, TC2, TC1) recorded lower wind speed and pressure at that same height(10m-48m). this disparity however was discovered to be due to a phenomenon known as gust effect. Also, the nodal displacement for the different terrain category (TC4, TC3, TC2 and TC1) on each floor of the high-rise building increased uniformly in respective pattern as the height of the 3D model increases. In conclusion, the authors therefore remark “the greater the terrain category, the lowest is the wind speed in the roughness sub layer and the longer height it takes to reach gradient wind speed”.

Upper limit for wind shear in stably stratified conditions expressed in terms of a bulk Richardson number

Profile measurements of wind and potential temperature from a land site (obtained by a RASS for several years) and an offshore site (obtained at the meteorological mast on the research platform FINO 1 for one year) are used to analyse the temporal evolution of wind speed and wind shear under statically stable conditions, especially in situations with low-level jets. In both cases a bulk Richardson number is calculated from the data. Data analysis indicates that there seems to exist a lower bound for the bulk Richardson number during stable stratification which is greater than zero. At this lower bound the flow reaches its maximum possible vertical wind shear. Even larger shear would then mean production of new turbulence which in turn would reduce the shear. Therefore, at this lower bound, the flow is in equilibrium between production and depletion of turbulence characterized by an equilibrium Richardson number. This equilibrium Richardson number is found here at about 0.1 for the land site and 0.04 for the marine site. For situations where maximum shear occurs, this shear can be compared to the shear described by the logarithmic vertical wind profile law for stable stratification. This allows the derivation of relations for the equilibrium Richardson number and the constant in the correction term of the logarithmic wind law in terms of the stratification parameter z∕L* and the surface roughness zT for temperature.

Aerodynamic roughness parameters in cities: Inclusion of vegetation

A widely used morphometric method (Macdonald et al. 1998) to calculate the zero-plane displacement (zd) and aerodynamic roughness length (z0) for momentum is further developed to include vegetation. The adaptation also applies to the Kanda et al. (2013) morphometric method which considers roughness-element height variability. Roughness-element heights (mean, maximum and standard deviation) of both buildings and vegetation are combined with a porosity corrected plan area and drag formulation. The method captures the influence of vegetation (in addition to buildings), with the magnitude of the effect depending upon whether buildings or vegetation are dominant and the porosity of vegetation (e.g. leaf-on or leaf-off state). Application to five urban areas demonstrates that where vegetation is taller and has larger surface cover, its inclusion in the morphometric methods can be more important than the morphometric method used. Implications for modelling the logarithmic wind profile (to 100 m) are demonstrated. Where vegetation is taller and occupies a greater amount of space, wind speeds may be slowed by up to a factor of three.

Wind resource assessment using airborne LiDAR data and smoothed particle hydrodynamics

The increasing availability of airborne Light Detection And Ranging (LiDAR) data provides new opportunities for environmental simulations. This paper proposes a new method for wind resource assessment by using wind simulation over 3D geometry extracted from classified LiDAR data. The simulation of wind flow is performed by using Smoothed Particle Hydrodynamics (SPH) in two phases for each time-step, firstly over low-resolution Digital Elevation Model (DEM) data, and secondly over high-resolution LiDAR data. Inlet wind particles depend on the logarithmic wind profile, where the morphometric aerodynamic roughness length is considered. The estimated wind power is integrated over a given timespan, resulting in wind energy potential. The simulated velocities were validated with annual measurements, where an agreement of 80.72% and 90.81% was achieved for ~0.5km2 sized urban and rural areas, respectively. The cumulative wind energy potential at 20 m above surface height is at 7.62 GWh and 56.613 GWh for the given areas, respectively.

Impact of Swell on Air–Sea Momentum Flux and Marine Boundary Layer under Low-Wind Conditions

Abstract The impact of fast-propagating swell on the air–sea momentum exchange and the marine boundary layer is examined based on multiple large-eddy simulations over a range of wind speed and swell parameters in the light-wind–fast-wave regime. A wave-driven supergeostrophic jet forms near the top of the wave boundary layer when the forwarding-pointing (i.e., negative) form drag associated with fast wind-following swell overpowers the positive surface shear stress. The magnitude of the form drag increases with the wavelength and slope and decreases with increasing wind speed, and the jet intensity in general increases with the magnitude of the surface form drag. The resulting negative vertical wind shear above the jet in turn enhances the turbulence aloft. The level of the wind maximum is found to be largely determined by the wavenumber and the ratio of the surface shear stress and form drag: the larger the magnitude of this ratio, the higher the altitude of the wind maximum. Although the simulated wind profile often closely follows the log law in the wave boundary layer, the surface stress derived from the logarithmic wind profile is significantly larger than the actual total surface stress in the presence of swell. Therefore, the Monin–Obukhov similarity theory is generally invalid over swell-dominated ocean. This is attributed to the wave-induced contribution to momentum flux, which decays roughly exponentially in the vertical and is largely independent of local wind shear.

Methodologies for city-scale assessment of renewable energy generation potential to inform strategic energy infrastructure investment

In support of national and international policies to address climate change, local government actors across Europe and Asia are committed to reducing greenhouse gas emissions. Many recognise the contribution that decentralised renewable electricity production can bring towards reducing emissions whilst also generating revenue. However, these actors are often subject to significant financial pressures, meaning a reliable and compelling business case is needed to justify upfront investment. This article develops a method for rapid comparison of initial project viability for multiple city sites and installation options using data from wind and solar resource prediction techniques. In doing so, detailed resource assessments grounded in academic research are made accessible and useful for city practitioners.Long term average wind speeds are predicted using a logarithmic vertical wind profile. This employs detailed three-dimensional building data to estimate aerodynamic parameters for the complex urban surface. Solar resource is modelled using a Geographical Information System-based methodology. This establishes the location and geometry of roof structures to estimate insolation, whilst accounting for shading effects from other buildings and terrain features. Project viability for potential installations is assessed in terms of the net present value over the lifespan of the technology and associated Feed-in Tariff incentive. Discounted return on investment is also calculated for all sites. The methodology is demonstrated for a case study of 6794 sites owned by Leeds City Council, UK. Results suggest significant potential for small-scale wind and solar power generation across council assets. A number of sites present a persuasive business case for investment, and in all cases, using the generated electricity on site improves financial viability. This indicates that initial installations should be sited at assets with high electricity demands. Overall, the work establishes a methodology that enables large city-level asset holders to make strategic investment decisions across their entire portfolio, which are based on financial assessment of wind and solar generation potential accurate to the individual asset scale. Such tools could facilitate strategic planning within cities and help to ensure that investment in renewable energy is focused at the most viable sites. In addition, the methodology can assist with asset management at the city scale by identifying sites with a higher market value as a result of their potential for renewable energy generation than otherwise might be estimated.

Seeing the Fields and Forests: Application of Surface-Layer Theory and Flux-Tower Data to Calculating Vegetation Canopy Height

Canopy height is an important and dynamic site variable that affects the mass and energy exchanges between vegetation and the atmosphere. We develop a method to estimate canopy height routinely, using surface-layer theory and turbulence measurements made from a collection of flux towers. This tool is based on connecting the logarithmic wind profile generally expected in a neutral surface layer with direct measurements of friction velocity and assumptions about canopy height’s relationships with zero-plane displacement and aerodynamic roughness length. Tests over a broad range of canopy types and heights find that calculated values are in good agreement with direct measurements of canopy height, including in a heterogeneous landscape. Based on the various uncertainties associated with our starting assumptions about canopy micrometeorology, we present a blueprint for future work that is necessary for expanding and improving these initial calculations.

The role of sea surface drag in a coupled surge and wave model for Typhoon Haiyan 2013

The present study investigates how the wind speed-limited wave dependent drag coefficient (CD) influences the surge and wave generation of Super Typhoon Haiyan, which struck the coasts of the Leyte Gulf, in the Philippines (2013), using a coupled surge and wave model. In addition, we examine the effect of changes of the radius (Rmax ) at which the maximum wind speed occurs. Accurate determination of this radius is crucial to the Haiyan wind and pressure field when using a parametric wind and pressure model because of lack of observation data. The calculation results show that the radius ranges from 40 km to 50 km: as the radius becomes narrower, the surge and wave heights are reduced. Our calculation of surge and wave levels uses a modified version of Janssen’ method (Janssen, 1989, 1991) with a step function applied to level off CD in the exponential wave growth term. In the present method, the wind speeds are limited to a certain threshold; below this value the effective roughness is estimated with a logarithmic wind profile. With the newly modified method, we investigate the effect of the wind speed-limited wave dependent drag CD for high winds (<70 m/s) on the Haiyan surge and wave levels. When leveling off CD at 25 m/s for Rmax=50km good agreement with survey data is obtained in terms of surge level (6.5 m) and wave heights (7 m and 17 m inside and outside of the gulf). The numerical experiments suggest that leveling off at wind speeds of 25–30 m/s results in the accurate prediction of Haiyan storm surge and wave levels in the coupled surge and wave model. The study demonstrates the applicability of the present method of leveling off at wind speeds of 25–30 m/s in a coupled surge and wave model for super typhoon conditions.

Offshore wind farm flow measured by complementary remote sensing techniques: radar satellite TerraSAR-X and lidar windscanners

Scanning Doppler lidar systems offer continuous wind measurements with some kilometres of range and a spatial distribution of concurrent measurements down to some metres. The synthetic aperture radar (SAR) satellite TerraSAR-X is capable to cover offshore areas of hundreds of square kilometres and to obtain wind data spatially distributed with some tens of metres. Images can be taken up to twice a day when the satellite passes the measurement site.Simultaneous wind speed measurements with ground based scanning Doppler lidar and TerraSAR-X in the region of the offshore wind farm ”alpha ventus” in the German North Sea were collected. A comparison of both systems in free stream conditions is performed by extrapolating the lidardata to the measurement height of the radar satellite assuming a logarithmic wind profile. In wake conditions the wake tracks obtained by lidar and TerraSAR-X are compared. In free stream conditions the comparison reveals a mean absolute wind velocity difference ≤ 0.4 m/s in two of the four considered cases and 1.1 m/s in one case. The fourth case shows a bad agreement due to a unusually low radar backscatter in the satellite's measurement. In wake conditions the wind turbine wakes could be tracked in the lidar and the satellite data. The comparison for the considered case reveals similar wake tracks in principle, but no matching due to the time difference of the measurements and the lower spatial resolution of the radar measurements.

Estimating atmospheric stability from observations and correcting wind shear models accordingly

Atmospheric stability strongly influences wind shear and thus has to be considered when performing load calculations for wind turbine design. Numerous methods exist however for obtaining stability in terms of the Obukhov length L as well as for correcting the logarithmic wind profile. It is therefore questioned to what extend the choice of adopted methods influences results when performing load analyses. Four methods found in literature for obtaining L, and five methods to correct the logarithmic wind profile for stability are included in the analyses (two for unstable, three for stable conditions). The four methods used to estimate stability from observations result in different PDF's of L, which in turn results in differences in estimated lifetime fatigue loads up to 81%. For unstable conditions hardly any differences are found when using either of the proposed stability correction functions, neither in wind shear nor in fatigue loads. For stable conditions however the proposed stability correction functions differ significantly, and the standard correction for stable conditions might strongly overestimate fatigue loads caused by wind shear (up to 15% differences). Due to the large differences found, it is recommended to carefully choose how to obtain stability and correct wind shear models accordingly.

Adjustment to rainfall measurement undercatch with a tipping-bucket rain gauge using ground-level manual gauges

Wind-caused undercatch is an important factor among types of systematic errors in point measurements of rainfall. The daily amount of rainfall measured by a MR3H tipping-bucket rain gauge (TBR-MR3H), which is elevated above the ground surface, was considerably underestimated on average by 46 % when compared with the corresponding measurements done by a pair of ground-level manual gauges (M-Rs). The undercatch was also confirmed by the measurements using a set of microlysimeters (MLs). The daily rainfall totals measured by the manual rain gauge were used as a reference in adjusting the rainfall undercatch with the tipping-bucket rain gauge. A simplified equation, developed based on the relationship between logarithmic wind profile and its effect on the catch ratio (CR) of the two gauges, was used to calculate the correction factor on a daily basis. The effect of wind speed depends on the intensity of rainfall. Parameters were optimized, and the proposed equation was validated. The calculated and measured daily rainfall amounts were in good agreement with a correlation coefficient of 0.99, and overall deviation of 0.04.

Estimates of effective aerodynamic roughness length over mountainous areas of the Tibetan Plateau

Wind profile data were measured by a wind profiler at QOMS (The Qomolangma Station for Atmospheric Environmental Observation and Research, Chinese Academy of Sciences) and, in separate experiments, GPS radiosondes were used at Shiquanhe Station and Litang Station on the Tibetan Plateau (TP). All three stations are located in the most rugged areas of the TP. QOMS is surrounded by the Himalaya, Shiquanhe Station by the Transhimalaya and Litang station is near the Hengduan Mountains. Using observational wind profile data, effective aerodynamic roughness length and zero‐plane displacement height d0 are determined using the neutral logarithmic wind profile law. The results show that the values of derived from the wind profiles can be considerably larger than the small‐scale aerodynamic roughness lengths of the land surface around the three stations. Subsequently, several parametrization schemes which use land surface characteristics to estimate and d0, such as roughness obstacle height and density, were assessed. The result indicates that of all the methods available, that proposed by Grant and Mason, where the drag coefficient D = 0.5, gives the best estimate of . The interim European Centre for Medium‐range Weather Forecasts (ECMWF) Re‐Analysis (ERA‐Interim) dataset underestimates effective aerodynamic roughness length in mountainous areas of the TP due to its use of a smaller drag coefficient of D = 0.4. For estimating d0, the method of Kutzbach performs well when the density of roughness obstacles (λ) is low, whereas the method of Raupach et al. gives a more reliable estimate when λ is high. Although this analysis has some limitations, it can feasibly account for form drag being exerted by an unresolved topography in the mountainous areas of the TP.

Intercomparison of Methods for the Simultaneous Estimation of Zero-Plane Displacement and Aerodynamic Roughness Length from Single-Level Eddy-Covariance Data

We applied three approaches to estimate the zero-plane displacement $$d$$ through the aerodynamic measurement height $$z$$ (with $$z = z_{m}- d$$ and $$z_{m}$$ being the measurement height above the surface), and the aerodynamic roughness length $$z_{0}$$ , from single-level eddy covariance data. Two approaches (one iterative and one regression-based) were based on the universal function in the logarithmic wind profile and yielded an inherently simultaneous estimation of both $$d$$ and $$z_{0}$$ . The third approach was based on flux–variance similarity, where estimation of $$d$$ and consecutive estimation of $$z_{0}$$ are independent steps. Each approach was further divided into two methods differing either with respect to the solution technique (profile approaches) or with respect to the variable (variance of vertical wind and temperature, respectively). All methods were applied to measurements above a large, growing wheat field where a uniform canopy height and its frequent monitoring provided plausibility limits for the resulting estimates of time-variant $$d$$ and $$z_{0}$$ . After applying, for each approach, a specific data filtering that accounted for the range of conditions (e.g. stability) for which it is valid, five of the six methods were able to describe the temporal changes of roughness parameters associated with crop growth and harvest, and four of them agreed on $$d$$ to within 0.3 m most of the time. Application of the same methods to measurements with a more heterogeneous footprint consisting of fully-grown sugarbeet and a varying contribution of adjacent harvested fields exhibited a plausible dependence of the roughness parameters on the sugarbeet fraction. It also revealed that the methods producing the largest outliers can differ between site conditions and stability. We therefore conclude that when determining $$d$$ for canopies with unknown properties from single-level measurements, as is increasingly done, it is important to compare the results of a number of methods rather than rely on a single one. An ensemble average or median of the results, possibly after elimination of methods that produce outliers, can help to yield more robust estimates. The estimates of $$z_{0}$$ were almost exclusively physically plausible, although $$d$$ was considered unknown and estimated simultaneously with the methods and results described above.