Meteorological Mast Research Articles

Results and Conclusions of a Floating-lidar Offshore Test

In this contribution we introduce the Fraunhofer IWES Wind Lidar Buoy, a floating-lidar prototype comprising a proven marine buoy design and a pulsed lidar device integrated in it. A software correction algorithm was developed to remove the effects of sea conditions resulting in system motions from the recorded lidar data. The final performance of the system was verified in a measurement campaign next to the offshore meteorological mast FINO1 in the German North Sea. Both the results of an accuracy assessment and a more detailed sensitivity analysis of the floating-lidar performance with respect to different external parameters were performed.For the recorded horizontal mean wind speeds a very good measurement performance with an R2-value of 0.996 is achieved even when no motion correction is applied. To use the turbulence intensity and wind direction data from the system, the application of a motion correction is necessary. The overall System Availability for the nine-weeks-measurement period was derived as 98%.

A Diagnostic Diagram to Understand Atmosphere-ocean Dynamics in the Southern North Sea at High Wind Speeds

Long time series of offshore meteorological measurements in the lower marine atmospheric boundary layer show dynamical regimes and variability that are forced partly by interaction with the underlying sea surface and partly by the passage of cloud systems overhead. At low wind speeds, the dynamics and stability structure of the surface layer depend mainly on the air-sea temperature difference and measured wind speed at a standard height. The physical processes are mostly understood and quantified through Monin-Obukhov (MO) similarity theory. At high wind speeds, different dynamical regimes become dominant, with breaking waves, sea spray, and organized boundary layer convection cells contributing to observed effects. Data from offshore meteorological monitoring sites typically show different behavior and regime shifts depending on the local winds and synoptic conditions. However, the regular methods to interpret time series through spectral analysis only give a partial view of the dynamics in the atmospheric boundary layer. Wind speed and the air-sea temperature difference are important factors that characterize the dynamics of the lower atmospheric boundary layer, and they provide a dynamic and thermodynamic constraint to frame observed processes, especially at high wind speeds. Early studies of long time series of automated offshore meteorological data recognized the value of the joint probability distribution on axes of wind speed and air-sea temperature difference to summarize large segments of the data. The approach can be extended to probe the marine atmospheric boundary layer conditions that are important for the loading of offshore wind turbines: turbulence intensity and wave conditions. The increasing numbers of offshore meteorological masts that are associated with the offshore wind industry are amenable to a similar approach to understand the main characteristics of the boundary layer. In this case, the diagnostic figure provides a method to ‘fingerprint’ the atmospheric conditions at an offshore site.

Wind Resource Assessment Method for Floating Deep Offshore Wind Turbines

This study presents a new methodology for the assessment of the wind energy resource at deep offshore locations where the use of floating wind turbines is foreseen. The wind resource assessment methodology developed follows the principles used by IEC 61400-12-1 standard in general and proposes the use of experimental data from a floating light detection and ranging (LIDAR) system on a deep offshore region – that assumes the role of the ‘temporary mast’ – and a coastal meteorological mast installed onshore acting as the ‘permanent met mast’. The methodology takes into consideration the time shift between the locations of the two measurement points and the wind direction associated with different atmospheric phenomena. The results obtained conclude that the methodology increases the accuracy of the wind resource assessment campaign while reducing the involved costs and technical risks. An added advantage is the possibility of extending this methodology for the evaluation of the power performance of floating wind turbines during the operational phase of the power plant.

First Verification Test and Wake Measurement Results Using a SHIP-LIDAR System

Measuring wind offshore in deep water depths will be a future challenge. Where the sea bed foundation installation for fixed meteorological masts is impossible, floating systems tend to be a sophisticated solution. In addition to the use of moored lidar- buoy systems, ship-lidar systems are an alternative solution for a number of different applications. In this paper we describe general aspects of motion influences on lidar measurements as well as two motion-correction methods for motion-influenced lidar measurements. The implementation of the ship-lidar system and different scanning modes will be presented. First measurements were carried out as part of the EERA-DTOC project. Hence a verification of one of the two correction algorithms as well as first results from wake measurements behind the Alpha Ventus offshore wind farm will be shown. This comprises distinct wind speed wake losses and an increasing turbulence intensity in a distance of approximately 2km behind the wind farm.

Validation of the simpleFoam (RANS) solver for the atmospheric boundary layer in complex terrain

We validate the simpleFoam (RANS) solver in OpenFOAM (version 2.1.1) for simulating neutral atmospheric boundary layer flows in complex terrain. Initial and boundary conditions are given using Richards and Hoxey proposal (1). In order to obtain stable simulation of the ABL, modified wall functions are used to set the near-wall boundary conditions, following Blocken et al remedial measures (2). A structured grid is generated with the new library terrainBlockMesher (3, 4), based on OpenFOAM's blockMesh native mesher. The new tool is capable of adding orographic features and the forest canopy. Additionally, the mesh can be refined in regions with complex orography. We study both the classical benchmark case of Askervein hill (5) and the more recent Bolund island data set (6). Our purpose is two-folded: to validate the performance of OpenFOAM steady state solvers, and the suitability of the new meshing tool to generate high quality structured meshes, which will be used in the future for performing more computationally intensive LES simulations in complex terrain. Site selection for wind energy projects is a critical step of the decision making process for possible investment in wind energy. On-site measurement campaigns over areas of several kilometers square for wind farm siting can be very costly, and can only provide a local assessment of wind conditions. To overcome this hurdle it is currently very common to recur to computational fluid dynamics (CFD) simulations that can extend meteorological mast point source measurement data over an area of several kilometers. Nowadays computational fluid dynamics (CFD) modeling for the atmospheric boundary layer (ABL) in complex terrain is becoming more ubiquitous, although it is quite time demanding to perform numerical solutions of the governing fluid equations without making simplifications to the flow dynamics. The most common approach used for ABL flows are the Reynold Averaged Navier

Buoyant thermal plumes from planetary landers and rovers: Application to sizing of meteorological masts

ObjectiveLanders on Mars and Titan may have warm surfaces as a result of solar heating or the carriage of radioisotope power sources. This warmth can perturb downwind meteorological measurements, but cannot be modeled as a simple aerodynamic wake because buoyant forces can be significant. MethodsWe use an analytic model from the industrial aerodynamics literature on smoke dispersion from fires and smokestacks to evaluate the plume trajectories. Computational Fluid Dynamics (CFD) simulations are also performed for a Titan lander. ResultsCFD yields results similar to the analytic model. (Albeit with a possibly weaker dependence on windspeed than the classic model.) We apply the models to evaluate the probability of immersion of instrumentation in plumes from the Mars Science Laboratory (MSL) Curiosity and for a Titan lander under various wind scenarios. ConclusionsLander perturbations can be easily calculated. Practice implicationsNone.

The Høvsøre Tall Wind-Profile Experiment: A Description of Wind Profile Observations in the Atmospheric Boundary Layer

We present an analysis of data from a nearly 1-year measurement campaign performed at Hovsore, Denmark, a coastal farmland area where the terrain is flat. Within the easterly sector upstream of the site, the terrain is nearly homogenous. This topography and conditions provide a good basis for the analysis of vertical wind-speed profiles under a wide range of atmospheric stability, turbulence, and forcing conditions. One of the objectives of the campaign was to serve as a benchmark for flow over flat terrain models. The observations consist of combined wind lidar and sonic anemometer measurements at a meteorological mast. The sonic measurements cover the first 100 m and the wind lidar measures above 100 m every 50 m in the vertical. Results of the analysis of observations of the horizontal wind-speed components in the range 10–1200 m and surface turbulence fluxes are illustrated in detail, combined with forcing conditions derived from mesoscale model simulations. Ten different cases are presented. The observed wind profiles approach well the simulated gradient and geostrophic winds close to the simulated boundary-layer height during both barotropic and baroclinic conditions, respectively, except for a low-level jet case, as expected. The simulated winds are also presented for completeness and show good agreement with the measurements, generally underpredicting the turning of the wind in both barotropic and baroclinic cases.

Increased Power Capture by Rotor Speed–Dependent Yaw Control of Wind Turbines

When extracting energy from the wind using upwind, horizontal-axis wind turbines, a primary condition for ensuring maximum power yield is the ability to align the rotor axis with the dominating wind direction. Attempts have been made to improve the yaw alignment of wind turbines by applying advanced measurement technologies, such as light detection and ranging systems. However, application of advanced measurement equipment is associated with additional costs and increased system complexity. This study is focused on assessing the current performance of an operating turbine and exploring how the yaw alignment can be improved using measurements from the existing standard measurements system. By analyzing data from a case turbine and a corresponding meteorological mast, a correction scheme for the original yaw control system is suggested. The correction scheme is applied to the case turbine and tested. Results show that, with the correction scheme in place, the yaw alignment of the case turbine is improved and the yaw error is reduced to the vicinity of zero degrees. As a result of the improved yaw alignment, an increased power capture is observed for below-rated wind speeds.

Flow distortion at a dense forest edge

AbstractThe flow near tall forest edges is complex, yet poorly described. A field experiment using two meteorological masts equipped with sonic anemometers and a horizontally staring lidar was performed upwind and downwind of the interface between an open flat farmland and a tall (hc = 24 m) beech forest. Data obtained during near‐neutral conditions are presented for the wind direction towards the forest. Results from a high leaf area index period are compared with those from a low leaf area index period. For both periods, the wind speed increased above the forest and decreased within the forest, relative to the measurements upwind of the edge. The lidar data taken at several positions between the masts at 1.25hc show that the minimum wind speed occurred just upwind of the edge. At the 1.25hc level, at the forest mast, the momentum flux (\documentclass{article}\usepackage{amsmath}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{amsfonts}\pagestyle{empty}\begin{document}$\overline{{\textbf{\textit{uw}}}}$ \end{document}) increased strongly over the forest and positive values were recorded during the high leaf area index period. A spectral analysis revealed that approximately half of this change was caused by low‐frequency, positively correlated eddies along the streamline. The remaining increase can qualitatively be explained with the concept of eddy‐blocking by the canopy top, which could also explain the observed increase in lateral variance and the decrease in the vertical variance. Despite the short distance to the edge of approximately 1.5hc, the beginning of a new internal boundary layer was visible at 1.04hc as a decrease in the vertical momentum flux. At this level, as well as within the forest, the results depended on the wind speed. The presented findings enhance the understanding of the forest edge flow and are useful for model verification and development.

A Measure-Correlation-Predict Method for Turbulence Intensity Distribution Assessment

A method based on a multiple correlation analysis is proposed in this work that is able to offer a long-term assessment of turbulence intensity ( TI) distribution at a local meteorological mast using a reference wind dataset. The MCP analysis uses a joint probability distribution function which is derived from wind speed, wind direction and TI data which are simultaneously recorded at the two measurement sites. Validation has been carried out using two met-masts which have a high level of correlation in terms of wind speeds. The algorithm properly corrects the local wind dataset, by estimating the “per sector” and “per speed” long-term distribution of TI; this was proved using different short-term data samples. Other tests, opportunely arranged using artificial wind data, help to understand the score of the method when multiple variables are used, highlighting that fine assessment can be always achieved when all the used variables are dependent on each other.

Renewables and the future of energy meteorology

Renewables and the future of energy meteorology

Modelling wind speeds for cup anemometers mounted on opposite sides of a lattice tower: A case study

When mounted at an intermediate monitoring level on a meteorological mast or tower, a cup anemometer's horizontal wind speed reading is influenced by the structure's construction type, the anemometer's relative position to the structure itself and by the wind vector angle. Although measurements at the topmost level of the structure are a basic prerequisite for wind resource characterisation, intermediate height measurements are also required to calculate wind shear characteristics at the site of interest. Cup anemometers mounted at intermediate levels will, to a certain degree, always be influenced by the meteorological mast. Locating the sensors on opposite sides of the structure allows the wind analyst to filter the data according to wind direction, thereby reducing the largest interference effects. Failure of one of these same-level, opposite cup anemometers would curtail the possibility of data filtering by direction. A technique that would redress the consequences of cup anemometer breakdown during a measurement campaign was thus devised and validated. The capability of the Levenberg–Marquardt (LM) method to model data from one cup anemometer to the other sensor on the opposite side of the tower was assessed by comparing the modelled (LM-generated) data with measured data. The LM algorithm was then used to build a relationship between wind speed records for different concurrent and ever-increasing measurement programme time frames from the two active, same-level anemometers and then failure of one of the sensors was simulated. This paper presents results from a case study using 12 months of wind speed and direction data captured by two, same-level cup anemometers attached to opposite sides of a lattice-type telecommunications tower on the Mediterranean island of Malta.

Atmospheric dynamics in the center of the European part of Russia during intensive snowfall in April 2012

The dynamics of atmospheric characteristics in the zone of the cyclone which provoked the dangerous atmospheric phenomenon, the heavy snowfall over the center of the European part of Russia in April 2012, is studied using the data of surface and satellite measurements. Besides the observational data from the meteorological stations, the results are used of the measurement of meteorological variables at the high-altitude meteorological mast in Obninsk and of surface concentration of minor gas components. Revealed is a number of interesting features associated with the passage of the cyclone cloud system over the observational point: the dramatic air temperature drop throughout the 300-m layer of the atmosphere, the formation of intensive vertical motions, and the significant temporal variability of O3 and NO2 concentration. The intensity and the total amount of precipitation falling during the cyclone passage are determined using the data of optical measurements of SEVIRI, AVHRR, and MODIS instruments of geostationary and polar orbiting satellites. Demonstrated is the satisfactory agreement of the computed precipitation characteristics with the results of observations at the network of meteorological stations.

Extreme Value Analysis of Multivariate High-Frequency Wind Speed Data

In this article we analyze the extremal behavior of wind speed with a measurement frequency of 8 Hz, measured on three meteorological masts in Denmark. In the first part of this article we set up a conditional model for the time series consisting of threshold exceedances from maxima per second for two consecutive days. The model directly captures the nonstationary nature of wind speed during the day. Conditional on previous wind speed values with recorded exceedance, we assume a Markov-like structure for exceedances, where the conditional distribution follows the generalized Pareto distribution. In addition, we analyze the dependence structure in large wind speed values between different masts by using bivariate extreme value models. The initial motivation for this research was in the context of renewable energy. Specifically, the extremal dynamics of wind speed at small time scales plays a critical role for designing and locating turbines on wind farms.

Evidence of Very Shallow Summertime Katabatic Flows in Dronning Maud Land, Antarctica

AbstractThe three-axis “Latan-3” Doppler sodar was operated near the Finnish Antarctic station Aboa in Dronning Maud Land (73.04°S, 13.40°W) in the austral summer of 2010/11. The measuring site is located at a practically flat, slightly sloped (about 1%) surface of the glacier. The sodar was operated in multiple-frequency parallel mode with 20–800-m sounding range, 20-m vertical resolution, and 10-s temporal resolution. To reveal the wind and temperature profiles below the sounding range as well as turbulent fluxes at 2 and 10 m, the data from a 10-m meteorological mast were used. During the measurements, the atmospheric boundary layer was within the sounding range of the sodar most of the time. Despite a large variety of observed sodar echo patterns and wind speed profiles, several cases of clear steady katabatic flows were observed. Practically all of them were easterly, whereas the uphill direction is southern. The thickness of the katabatic flow varied from a few tens to several hundreds of meters; the wind speed maximum could be as low as 5 m. Thin katabatic flows had lower wind speed and much stronger temperature gradients (up to 1 K m−1) but had smaller surface heat flux than did the thicker ones.

Evaluation of four numerical wind flow models for wind resource mapping

A wide range of numerical wind flow models are available to simulate atmospheric flows. For wind resource mapping, the traditional approach has been to rely on linear Jackson–Hunt type wind flow models. Mesoscale numerical weather prediction (NWP) models coupled to linear wind flow models have been in use since the end of the 1990s. In the last few years, computational fluid dynamics (CFD) methods, in particular Reynolds-averaged Navier–Stokes (RANS) models, have entered the mainstream, whereas more advanced CFD models such as large-eddy simulations (LES) have been explored in research but remain computationally intensive. The present study aims to evaluate the ability of four numerical models to predict the variation in mean wind speed across sites with a wide range of terrain complexities, surface characteristics and wind climates. The four are (1) Jackson–Hunt type model, (2) CFD/RANS model, (3) coupled NWP and mass-consistent model and (4) coupled NWP and LES model. The wind flow model predictions are compared against high-quality observations from a total of 26 meteorological masts in four project areas. The coupled NWP model and NWP-LES model produced the lowest root mean square error (RMSE) as measured between the predicted and observed mean wind speeds. The RMSE for the linear Jackson-Hunt type model was 29% greater than the coupled NWP models and for the RANS model 58% greater than the coupled NWP models. The key advantage of the coupled NWP models appears to be their ability to simulate the unsteadiness of the flow as well as phenomena due to atmospheric stability and other thermal effects. Copyright © 2012 John Wiley & Sons, Ltd.

Efficient data filtering for wind energy assessment

The installation of a new wind farm requires the previous acquisition of a great amount of wind speed data in order to perform a correct wind energy assessment. These data are obtained from a meteorological mast installed at each site. Real wind measurements at the meteorological mast include many erroneous data, which must be detected and eliminated before working with them. To localise wrong data, a new method based on the Kalman filter is proposed. This filter is applied to a short-term prediction like the one used in wind power forecasting. The filter parameter tuning is based on general verification metric curves tested with real data from different sites. The filter equations are adapted to different sites depending on the intensity of turbulence and wind direction. In this study all the parameters are explained in detail and the filter is evaluated, showing nice results for wind energy assessment of candidate sites.

An assessment of wind energy potential at the demonstration offshore wind farm in Korea

The construction of an offshore demonstration wind farm was planned in a southwestern sea-area of the Korean Peninsula. To estimate economic feasibility and to establish a reliable design basis, it is necessary to identify the design parameters of the demo-farm. For a reliable estimation of the design parameters, the first offshore meteorological mast, HeMOSU (Herald of the Meteorological and Oceanographic Special Research Unit), was constructed at the site of the demo-farm. In addition, supplementary meteorological masts were installed in advance at Gochang and Wangdeung-do in order to enhance the estimation of the long-term wind potential for the demo-farm. In this paper, assessments of wind energy potential are carried out with the data measured from these three meteorological masts. The analysis includes seasonal and diurnal changes in wind speed and surface roughness as well as wind/energy rose. Long-term wind potential is also estimated by using MCP (Measure-Correlate-Predict) techniques to clarify the design basis and to determine the wind turbine class in accordance with IEC 61400. The AEP (Annual Energy Production), as well as the C.F. (Capacity Factor) of the candidate site are evaluated with the estimated design parameters.

First Observations of Energy Budget and Bulk Fluxes at Ny Ålesund (Svalbard) during a 2010 Transition Period as Analyzed with the BEAR Station

A small-size meteorological mast, BEAR (Budget of Energy for Arctic regions) has been developed as a part of a new autonomous buoy for monitoring the sea ice mass balance. BEAR complements observations of the thickness and thermodynamic properties of the ice/snow pack determined by the so-called Ice-T (Ice-Thickness) buoy, giving access to bulk fluxes and energy budget at the surface, using meteorological measurements. The BEAR mast has been tested with success during ten days in April-May 2010 at Ny Alesund, in the Svalbard archipelago (Norway) showing that meteorological data were close to measurements at the same level of the Italian Climate Change Tower (CCT) from the ISAC-CNR. A discussion is undertaken on bulk fluxes determination and uncertainties. Particularly, the strategy to systematically use different relevant fluxes parameterizations is pointed out to explore flux range uncertainty before to analyze energy budget. Net radiation, bulk fluxes and energy budget are estimated using as average 10 minutes, 24 hours and the ten days of the experiment. The observation period was very short, but we observe a spring transition when the net radiation begins to warm the surface while the very small turbulent heat flux cools the surface.

복잡지형에서의 Wind Shear Exponent 예측

In this study, we found a relationship between wind shear exponent, , and a few factors such as the wind speed, , ruggedness index(), and the Weibull shape parameter, of sites in complex terrain in Korea. Wind shear exponents in main wind directions were calculated using wind speed data measured for one year from various heights of eleven meteorological masts in Gangwon province. It was found from the analysis that the reciprocal of the wind shear exponent can be expressed by an exponentially decaying function with respect to a multiple of , and . This result is considered useful to be used to characterize wind characteristics of specific sites in complex terrain in Korea with limited information.