Logarithmic Wind Profile Research Articles

A model of racing kayak surge motion a numerical approach with realistic oscillating propulsion forces

This study presents a novel forward dynamics model of racing kayak surge motion. The model, driven by adjustable oscillating propulsion forces, replicates true paddle stroke forces. It is based on Newton’s second law of motion, with the net force comprising of propulsion force, skin friction drag, wave-making drag, form drag, and air drag. The total mass includes the kayak, paddler, and added mass. The fourth-order Runge–Kutta method is used to solve for speed and distance. The model incorporates a unique hull formulation for wetted surface area estimation, Michell’s integral for wave-making drag, and a log wind profile with allometric scaling for air drag. It accounts for varying stature height, body mass, kayak dimensions, wind speed, and stroke propulsion profiles. The model is a significant advancement in its domain, with broad applicability for the future. It aligns with existing data and analyses, but validation data is limited.

A Comparative Study on Wind Profiles and Surface Aerodynamic Parameters of Typhoons Over Coastland and Coastal Sea

AbstractUnderstanding the aerodynamic characteristics of landfalling typhoons is of great importance for both wind engineering and meteorology. This study comparatively investigated the near‐surface wind profiles and aerodynamic parameters over coastland and coastal sea areas using typhoon observational data collected by Doppler wind lidars and wind tower anemometers during the passage of 15 typhoons that made landfall over China during 2009–2020. Specifically, the three surface aerodynamic parameters of roughness length, friction velocity, and drag coefficient (Cd) were obtained using the logarithmic law wind profile method. Results showed that the near‐surface wind profiles became much closer to the power law wind profile with increase in wind speed. The values of roughness length and friction velocity over the coastal sea were found to exceed those over coastland areas when the 10‐m wind speed (U(10)) was larger than 18 m s−1. The critical wind speed at which Cd peaks over the coastal sea was found to be 24 m s−1. There are two peaks in the variation of Cd with U(10) under the condition of onshore wind over the sea, which has never been reported in previous observational studies. Finally, a formula for Cd was proposed to describe the variation in Cd with U(10) under the condition of onshore wind over land, which is expected to be applied in the typhoon surface layer scheme to improve numerical simulation of landfalling typhoons.

Influence of refracting atmospheric profiles on trace velocity and arrival time

The influence of the atmospheric profile on the trace velocity and arrival time has received little attention, although these properties of sound propagation are important for direction finding and localization. The refracting temperature profile causes the received sound to be delayed or advanced in time compared to that for the temperature at ground height, and the situation is made anisotropic in the presence of wind. We consider refraction by linear temperature and logarithmic wind profiles on the trace velocity and arrival time for distant impulses received at the ground, and use this information in small arrays for direction finding and large arrays for localization.

The Impact of Observed Drag Reduction Over Land on Typhoon Forecasting

AbstractThe surface drag coefficient plays a crucial role in determining the momentum exchange between the Earth's surface and the atmosphere. Previous studies have observed a tendency for the drag coefficient to decrease at high wind speeds over land, primarily due to the inverse energy cascade. This study aims to examine the impacts of the reduced drag coefficient on the typhoon forecasting skills in terms of the track, the central pressure, and the 10‐m maximum wind speed. Drag reduction is approached through the logarithmic wind profile and a new formula that considers the reduction in roughness length. The results show that the track and the 10‐m maximum wind speed forecasts are improved, but these improvements are primarily evident over plain areas, as the typhoon structure is significantly disrupted by the topography over mountainous areas. Additionally, the reduced drag coefficient results in less dissipation of the typhoon's wind fields over land. As the wind speeds at coastal areas are enhanced compared with those in operational model, the changes in the Coriolis force are responsible for the track prediction improvement. These findings highlight the importance of parameterizing coherent processes in current numerical models.

On the value of the von Kármán constant in the atmospheric surface layers over urban surfaces

Large-eddy simulations of turbulent boundary flow over different urban-like surfaces in neutrally stratified conditions are performed to study the atmospheric surface layer characteristics over urban areas. A simple method based on the vertical profile of the dimensionless velocity gradient is used to identify the inertial sublayer (ISL) in all cases. The results show that the mean wind profiles in the different urban ISLs can all be generally described by the logarithmic wind profile. However, for the idealized urban surfaces composed of regular building block arrays and the realistic urban surface case, the von Kármán constant (κ) in the ISL is found to be significantly smaller (in the range of 0.21–0.27) than the typically adopted value of 0.4. As κ is a key constant in the parametrizations of urban surface flows and is usually assumed to be ≈0.4 in existing surface parametrization models, a significantly smaller κ implies that large uncertainties may exist in the predictions of the momentum, heat, and scalar turbulent fluxes over urban surfaces using these models.

Impact of wind profiles on ground-generation airborne wind energy system performance

Abstract. This study investigates the performance of pumping-mode ground-generation airborne wind energy systems (AWESs) by determining cyclical, feasible, power-optimal flight trajectories based on realistic vertical wind velocity profiles. These 10 min profiles, derived from mesoscale weather simulations at an offshore and an onshore site in Europe, are incorporated into an optimal control model that maximizes average cycle power by optimizing the trajectory. To reduce the computational cost, representative wind conditions are determined based on k-means clustering. The results describe the influence of wind speed magnitude and profile shape on the power, tether tension, tether reeling speed, and kite trajectory during a pumping cycle. The effect of mesoscale-simulated wind profiles on power curves is illustrated by comparing them to logarithmic wind profiles. Offshore, the results are in good agreement, while onshore power curves differ due to more frequent non-monotonic wind conditions. Results are references against a simplified quasi-steady-state model and wind turbine model. This study investigates how power curves based on mesoscale-simulated wind profiles are affected by the choice of reference height. Our data show that optimal operating heights are generally below 400 m with most AWESs operating at around 200 m.

Using Observed and Modelled Heat Fluxes for Improved Extrapolation of Wind Distributions

Modelling the horizontal and vertical variation of wind speed is crucial for wind energy applications. A model frequently used for this purpose is part of the Wind Atlas Analysis and Application program (WAsP). Here, we modify the model in WAsP to account for local atmospheric stability parameters. Atmospheric stability effects are treated by using the impact of a temperature scale on the geostrophic drag law and the diabatic logarithmic wind profile. Using this approach, wind-direction dependent mean and standard deviation of a surface-layer temperature scale and a mean boundary-layer height scale can be obtained from either numerical weather prediction model output or observations to improve vertical extrapolations of Weibull wind speed distribution parameters. The modified atmospheric stability model is validated at six flat sites in northwestern Europe. The surface-layer temperature scale is available from sonic anemometer measurements at three of the sites. At all sites the temperature scale is also estimated from reanalysis data and from mesoscale model output. The modified model improves the aggregated estimations of power density distributions when extrapolating to nearby locations from 5.2 to 3%, when using the temperature scale derived from either observations or mesoscale/reanalysis output compared to the current model.

Calibration of Mean Wind Profiles Using Wind Lidar Measurements

This paper explores the applicability of Lidar wind measurements for the calibration of mean wind profiles depending on the extension in time and space of the available measurements. Starting from logarithmic wind speed profiles corresponding to different site conditions, pseudo-experimental wind speed profiles are generated artificially by adding a zero-mean Gaussian-distributed noise, representative of realistic measurement errors. Then, a least-square fitting procedure is applied to identify the roughness length and the zero-plane displacement. The results obtained show an increase in the scatter of the estimated parameters of the logarithmic law with increasing elevation of the lowest measurement point. Then, a parametric study is developed to analyse the influence of the number of available experimental profiles on the uncertainty associated with the estimated logarithmic law parameters. Based on the results obtained, it can be pointed out that the availability of measurements at low elevations is essential to identify the logarithmic mean wind profile using a reasonable number of observations.

Modeling the Flow Response to Surface Heterogeneity during a Semi-Idealized Diurnal Cycle

Abstract To characterize the effects of subgrid surface heterogeneity, the blending-height concept has been developed as a coupling strategy for surface parameterization schemes used in numerical weather prediction models. Previous modeling studies have tested this concept using stationary conditions with one-dimensional strips of surface roughness. Here, large-eddy simulations are used to examine the response of the blending height and effective surface roughness to tiled land-cover heterogeneity, or a two-dimensional chessboard pattern of alternating high and low vegetation given a diurnal cycle of solar irradiance in subarctic conditions. In each experiment, the length scale of the roughness elements is increased while the total domain fraction of each vegetation type is kept constant. The effective surface roughness was found to decrease with increasing length scale of surface cover heterogeneity, which is shown to have a significant impact on estimated wind turbine power calculated from logarithmic wind profiles. In stable conditions, the blending height in cases with large heterogeneity length scales was found to exist well above the surface layer. Because the behavior of the blending height has implications for coupled models, a simple model for the blending height as a function of heterogeneity length scale is introduced.

Wind profiles measurements and predictions for atmospheric acoustic propagation modeling

This work presents a comprehensive experimental system to measure meteorological conditions with both anemometers and a three-dimensional scanning Doppler LIDAR wind profiler. The LIDAR system captures real-time wind speed gradients at many locations along a particular heading. This work describes a method for extracting a cartesian grid of wind speeds gradients from a range height indicator (RHI) scan pattern. The LIDAR derived wind profiles are compared to logarithmic wind profiles based on single point traditional anemometer measurements. Differences in wind speed profiles observed using the two methods are presented and the implications on long range acoustic propagation modeling are discussed.

Observations of boundary layer wind and turbulence of a landfalling tropical cyclone

This study investigates the atmospheric boundary layer structure based on multiple-level tower observations with a height of 350 m during the landfall of Super Typhoon Mangkhut (2018). Results show a layer of log wind profile outside of the radius of maximum wind speed with a height of 100 m or larger. The log layer height increases with the wind speed. The height of the constant flux layer reaches ~ 300 m for 10-m wind speeds less than 13 m s−1 while this height decreases with the wind speed. Momentum fluxes and turbulent kinetic energy increase with the wind speed at all vertical levels. The drag coefficient and surface roughness length estimated at the tower location have values of 7.3 × 10–3 and 0.09 m, respectively, which are independent of wind speed. The estimated vertical eddy diffusivity and mixing length increase with height up to ~ 160 m and then slowly decrease with height. The vertical eddy diffusivity increases with the wind speed while the vertical mixing length has no dependence on the wind speed. Comparing our results with previous work indicates that the vertical eddy diffusivity is larger over land than over ocean at a given wind speed range.

High-resolution wind speed forecast system coupling numerical weather prediction and machine learning for agricultural studies — a case study from South Korea

Forecasting wind speed near the surface with high-spatial resolution is beneficial in agricultural management. There is a discrepancy between the wind speed information required for agricultural management and that produced by weather agencies. To improve crop yield and increase farmers’ incomes, wind speed prediction systems must be developed that are customized for agricultural needs. The current study developed a high-resolution wind speed forecast system for agricultural purposes in South Korea. The system produces a wind speed forecast at 3 m aboveground with 100-m spatial resolution across South Korea. Logarithmic wind profile, power law, random forests, support vector regression, and extreme learning machine were tested as candidate methods for the downscaling wind speed data. The wind speed forecast system developed in this study provides good performance, particularly in inland areas. The machine learning–based methods give the better performance than traditional methods for downscaling wind speed data. Overall, the random forests are considered the best downscaling method in this study. Root mean square error and mean absolute error of wind speed prediction for 48 h using random forests are approximately 0.8 m/s and 0.5 m/s, respectively.

Evaluation of Marine Wind Profiles in the North Sea and Norwegian Sea Based on Measurements and Satellite-Derived Wind Products

The wind conditions at oil platforms are typically measured at 40–140-m height, and then reduced to standard 10-m height before being distributed via the Global Telecommunication System. The 10-m values are further used for assimilation and verification of weather forecasts models. An accurate representation of the wind profile is therefore essential. Here five wind profiles; power law, Norsok, logarithmic, Monin-Obukhov and Gryning are studied to find the best method for reduction of platform wind speeds to 10-m height level. Observations from nine oil platforms are used together with 10-m wind speed from ASCAT for evaluation of the wind profiles. In addition the wind profiles are evaluated using observations from the FINO3 offshore mast outside Denmark. The present wind profile used for wind reduction at the oil platforms (power law with a constant wind-shear coefficient of 0.13) underestimates the 10-m wind speed by as much as 0.8 m/s on average. For near neutral atmospheric stability the Norsok and the logarithmic wind profiles yield on average a near perfect fit with a wind shear coefficient of 0.085. However, 10-m wind speeds are underestimated for unstable and overestimated for stable conditions. The Monin-Obukhov and Gryning wind profiles give the most accurate estimates of 10-m wind speed during unstable and near-neutral conditions. For stable situations the Gryning wind profile, which also includes information about height of the boundary layer, gives the best agreement, but still an underestimation of the low level wind speed is encountered. The results strongly underline that atmospheric stability needs to be taken into account. For future wind reduction from observation level to 10 meter, it is recommended to use a method which takes stability into account, for example the Gryning method. For long-term average assessments however, the logarithmic and Norsok wind profiles are sufficient.

Analytical model for the two-dimensional advection-diffusion equation with the logarithmic wind profile in unstable conditions

Analytical model for the two-dimensional advection-diffusion equation with the logarithmic wind profile in unstable conditions

An engineering model of Titan surface winds for Dragonfly landed operations

Winds near the ground on Titan for the Dragonfly landing site (near Selk crater, 10°N) for the mid-2030s (Titan late southern summer, Ls ~ 310°) are estimated for mission design purposes. Prevailing winds due to the global circulation are typically 0.5 m/s, and do not exceed 1 m/s. Local terrain-induced flows such as slope winds appear to be similarly capped at 1 m/s. At various landing sites and times, these two contributions will vectorially combine to yield steady winds (for part of a Titan day, Tsol) of up to 2.0 m/s, but typically less – the slope wind component will be small in the mid-morning. In early afternoon, as on Earth and Mars, solar-driven convection in the planetary boundary layer will cause wind fluctuations of the order of 0.1 m/s, varying with a typical timescale of ~1000 s. Occasionally this convection organizes into coherent ‘dust devil’ vortices: detectable vortices with speeds of 1 m/s are predicted about once per Titan day. We have introduced the convective velocity scale combined with the advection time of PBL cells as a metric to derive the frequency of occurrence of gusts associated with convective vortices (‘dust devils’). Maximum possible vortex winds on Titan of 2.8 m/s may be expected only once per 40 Tsols, and define the maximum wind (4.8 m/s at 10 m height) that Dragonfly must tolerate without damage. The applicability of different wind combinations, scaled to the height of relevant Dragonfly components above the ground (e.g. the maximum corresponds to 3.9 m/s at 1.3 m height) by a logarithmic wind profile, to Dragonfly design and operations are discussed.

Investigating Changes in Aeolian Sediment Transport at Coastal Dunes and Sand Trapping Fences: A Field Study on the German Coast

For the restoration and maintenance of beach and dune systems along the coast, knowledge of aeolian sediment transport and its interaction with coastal protection measures is required. As a nature-based solution, sand trapping fences can be an integral part of coastal protection measures initiating foredune development. There are few detailed studies on aeolian sediment transport rates on coastal dunes and sand trapping fences available to date. Thus, in this work, we present the results of field experiments conducted at the beach, coastal dune, and sand trapping fence on the East Frisian island Langeoog. The vertical sediment flux profile was measured by vertical mesh sand traps, and saltiphones measured the instantaneous sediment transport. A meteorological station was set up to obtain wind data. On the beach, dune toe, and dune crest, the stationary wind profile can be described well by the law of the wall. Saturated aeolian sediment transport rates on the beach and dune toe were predicted by widely used empirical models. Between the sand trapping fence, these empirical transport models could not be applied, as no logarithmic wind profile existed. The upwind sediment supply reduced after each brushwood line of the sand trapping fence, thereby, leading to increased deviation from the saturated conditions.

Baroclinicity and directional shear explain departures from the logarithmic wind profile

AbstractSimilarity and scaling arguments underlying the existence of a logarithmic wind profile in the atmospheric surface layer (ASL) rest on the restrictive assumptions of negligible Coriolis effects (no wind turning in the ASL) and vertically‐uniform pressure gradients (barotropic atmospheric boundary layer, ABL). This paper alleviates these asymptotic arguments to provide a realistic representation of the ASL where the common occurrence of baroclinicity (height‐dependent pressure gradients) and wind turning, traditionally treated as outer‐layer attributes, take part in modulating the ASL. The approximation of a constant‐stress ASL is first replaced by a refined model for the Reynolds stress derived from the mean momentum equations to incorporate the cross‐isobaric angle (directional shear) and a dimensionless baroclinicity parameter (geostrophic shear). A model for the wind profile is then obtained from first‐order closure principles, correcting the log‐law with an additive term that is linear in height and accounts for the combined effects of wind turning and baroclinicity. Both the stress and wind models agree well with a suite of large‐eddy simulations in the barotropic and baroclinic ABL. The findings provide a methodology for the extrapolation of near‐surface winds to some 200 m in the near‐neutral ABL for wind energy applications, the validation of the surface cross‐isobaric angle in weather and climate models, and the interpretation of wind turning in field measurements and numerical experiments of the Ekman boundary layer.

A dense gas dispersion model based on revised meteorological parameters and its performance evaluation

Heavy gas dispersion is significantly impacted by meteorological conditions. In this study, the widely-used heavy gas dispersion model SLAB is revised by using alternative parametrizations for the meteorological parameters, mixing layer height, and wind speed profile. The Nozaki method and the stability modified logarithmic wind profile evolved from the Monin-Obukhov similarity theory are adopted to calculate the mixing layer height and wind speed profile in the improved SLAB-M model, respectively. Dense gas dispersion model evaluation protocols are used to evaluate SLAB-M, and the datasets from the Jack Rabbit II (JR II) 2015 Trials are used to compare the accuracy of the simulations to observed data. The statistical performance measures (SPMs) of SLAB-M are overall a little better than that of SLAB, and SLAB-M effectively simulates heavy gas dispersion under the different meteorological conditions of the JR II 2015 Trials. Thus, it can better satisfy the requirements of consequence assessment and emergency response for the leakage and dispersion of hazardous gasses.

On the accuracy of a logarithmic extrapolation of the wind speed measured by horizontal lidar scans

Remote sensing-based wind power forecasts are nowadays being increasingly investigated. Long-range lidar scans are hereby often performed at low heights, causing the need for a wind speed extrapolation to hub height. In this work we analysed the accuracy of the stability corrected logarithmic wind profile and its sensitivity to atmospheric stability, wind speed and extrapolation height by means of a theoretical error estimation using error propagation. Emphasis was given to analyse the contributions of the profile’s individual variables but also considering the measurement campaign framework. We further used lidar measurements at the offshore wind farm Global Tech I to support the theoretical analysis. The logarithmic profile was found to be able to describe profiles during most situations, however, decreasing wind speeds with height cannot be represented. Results showed that due to the nature of the stability correction term extrapolation errors are largest during very stable atmospheric conditions. Here, stability estimation errors were dominant. Under near neutral and neutral atmospheric conditions the wind speed error contributed most to the overall error. We conclude that extrapolation errors can mainly be reduced by optimising the estimation of atmospheric stability using accurate measurement devices. Furthermore, the precise horizontal alignment of the lidar device is important.

Assessment of Wind and Vegetation Interactions in Constructed Wetlands

Meteorological data from vegetated and un-vegetated wetlands during wet and dry seasons, were collected and analyzed to evaluate the role of wind and vegetation on wetlands’ hydrology. Wind speed diminished by as much as 40%, accompanied by a measurable change in wind directions in the vegetated compared to the open water site. Wind speed and direction means were significantly different (p < 0.001 and <0.01), for vegetated and non-vegetated wetland, respectively. Cattails (Typha sp.) and open water estimates of wind drag coefficients using the log wind profile, were 0.016 and 0.009 for dry season, and 0.012 and 0.005 for wet season, respectively. Wind set up near the wetland outlet was more pronounced at shallow water depth (<20 cm). Measured velocity profile during inflow discharge event with a wind speed of 0.53 ms−1, showed two-layer flows; wind-generated surface water flow opposite to a sub-surface inflow. This opposing surface flow increases hydraulic residence time and improve nutrient uptake. Conversely, wind-generated flows aligned with inflow discharges, accelerates water flow towards the outlet, reduce the duration of water-biotic interactions, and decrease nutrient uptake.