Correct Wind Research Articles

Advanced tilt correction from flow distortion effects on turbulent CO2 fluxes in complex environments using large eddy simulation

AbstractMeasurement of the turbulent fluxes of gases, momentum and heat can be biased by obstacles such as buildings or instrument platforms distorting the flow of air to the flux instruments. Standard methods have long been used to account for non‐horizontal mean flows. Here we demonstrate a novel approach to correct for the effects of flow distortion which combines numerical flow modelling with eddy covariance measurements of the fluxes. This approach applies a flow distortion correction to the data prior to the application of the standard planar‐fit and double‐rotation methods. This new direction‐dependent flow correction allows the determination of the correct orthogonal wind vector components and hence the vertical turbulent fluxes. We applied the method to a 10 Hz dataset of 3D wind components, temperature, and the concentrations of carbon dioxide and water vapour, as measured on top of a military tower above the city of Münster in northwest Germany during spring and summer 2007. Significant differences appeared between the fluxes that were calculated with the standard rotation methods alone and those that underwent flow distortion correction prior to the application of the rotation methods. The highest deviations of 27% were obtained for the momentum flux. Pronounced differences of 15% and 8% were found for the diurnal net fluxes of carbon dioxide and water vapour, respectively. The flow distortion correction for the carbon dioxide fluxes yielded the same magnitude as the WPL (Webb–Pearman–Leuning) correction for density fluctuations. Copyright © 2009 Royal Meteorological Society

H2A and H2B tails are essential to properly reconstitute nucleosome core particles

The conformation of recombinant Nucleosome Core Particles (NCPs) lacking H2A and H2B histone tails (gH2AgH2B) are studied. The migration of these particles in acrylamide native gels is slowed down compared to intact reconstituted NCPs. gH2AgH2B NCPs are also much more sensitive to nuclease digestion than intact NCPs. Small angle X-ray scattering (SAXS) experiments point out that the absence of H2A and H2B tails produces small but significant conformational changes of the octamers conformation (without wrapped DNA), whereas gH2AgH2B NCP conformations are significantly altered. A separation of about 25-30 bp from the core could account for the experimental curves, but other types of DNA superhelix deformation cannot be excluded. The distorted gH2AgH2B octamer may not allow the correct winding of DNA around the core. The absence of the H2A and H2B tails would further prevent the secondary sliding of the DNA around the core and therefore impedes the stabilisation of the particle. Cryo-electron microscopy on the same particles also shows a detachment of DNA portions from the particle core. The effect is even stronger because the vitrification of the samples worsens the instability of gH2AgH2B NCPs.

Comparison of analyzed and measured wind speeds in the perspective of oceanic simulations over the Mediterranean basin: Analyses, QuikSCAT and buoy data

Surface vector wind datasets from different assimilation systems and from scatterometers have been recently made available over the entire Mediterranean basin and for a large spectrum of spatial and temporal resolution. In this work, we compare wind vector analyses, derived from different routine assimilation systems and from blended products, to wind vectors obtained from QuikSCAT satellite sensor and to those directly measured by buoy-mounted anemometers. The analysis has been performed to verify the accuracy of the analyzed data, when the specific objective is the generation of surface winds field to force Mediterranean Sea simulations. The inter-comparison covers the period 2000–2005. Our analysis demonstrated that the spatial resolution of the data sets represents one of the main relevant sources of error in the analyzed wind fields, explaining the worst results of the reanalysis data and the relative accuracy of the ECMWF. This work also confirms the usefulness of blending QuikSCAT and reanalysis products, which could be used to force oceanic simulations. The blended data cover the period from July 1999 to present when QuikSCAT wind data are available. Before this period, blended products are not produced and different solutions to correct wind speed from routine assimilation systems have to be investigated. A simple empirical method to adjust the ERA40 wind speed product is then proposed. The analysis of the difference between the annual Mediterranean heat budget computed using the adjusted and the original ERA40 winds suggests that the impact of the correction is not negligible. Considering the year 2000, the annual average heat budget for the whole basin is modified from ∼ 34 W/m 2 to ∼ − 6 W/m 2.

A calculation method of field current of synchronous machines at sudden short‐circuit

AbstractThe mutual leakage reactance between D‐axis damper and field windings is ignored in conventional D‐axis equivalent circuits. It has been pointed out, however, that the calculated value of the field current differs considerably from the measured value if this reactance is not taken into account. This is due to the difficulty of determining the physically correct damper winding impedance value. A method of determining the equivalent circuit constants using the mutual leakage reactance has been reported previously, where the D‐axis damper winding time constant is measured from the upper and lower envelopes of field current at sudden three‐phase short‐circuit. Yet there are machines for which the upper and lower envelopes of field current are not readily established, and in this case the method is unsatisfactory. The authors describe a method to accurately identify the equivalent circuit constants taking into account the mutual leakage reactance, using a standstill test with a small‐capacity DC power supply (DC decay testing method). The field current at sudden short‐circuit can be simulated accurately using these equivalent circuit constants. The validity of the proposed method is demonstrated by implementation results on two salient‐pole synchronous machines at the same specifications (one with damper winding, the other without). Furthermore, the dependent relation between the armature leakage reactance and mutual leakage reactance, as well as its influence on the calculation of field transient currents, are made clear. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(3): 61–70, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20113

Comparison of the performance of four measure–correlate–predict algorithms

Measure–correlate–predict (MCP) algorithms are used to predict the wind resource at target sites for wind power development. This paper describes some of the MCP approaches found in the literature and then compares the performance of four of them, using a common set of data from a variety of sites (complex terrain, coastal, offshore). The algorithms that are compared include a linear regression model, a model using distributions of ratios of the wind speeds at the two sites, a vector regression method, and a method based on the ratio of the standard deviations of the two data sets. The MCP algorithms are compared using a set of performance metrics that are consistent with the ultimate goals of the MCP process. The six different metrics characterize the estimation of (1) the correct mean wind speed, (2) the correct wind speed distribution, (3) the correct annual energy production at the target site, assuming a sample wind turbine power curve, and (4) the correct wind direction distribution. The results indicate that the method using the ratio of the standard deviations of the two data sets and the model that uses the distribution of ratios of the wind speeds at the two sites work the best. The linear regression model and the vector regression model give biased estimates of a number of the metrics, due to the characteristics of linear regression.

Singularities and Undefinitions in the Calibration Functions of Sonic Anemometers

Abstract A mathematical model of the process employed by a sonic anemometer to build up the measured wind vector in a steady flow is presented to illustrate the way the geometry of these sensors as well as the characteristics of aerodynamic disturbance on the acoustic path can lead to singularities in the transformation function that relates the measured (disturbed) wind vector with the real (corrected) wind vector, impeding the application of correction/calibration functions for some wind conditions. An implicit function theorem allows for the identification of those combinations of real wind conditions and design parameters that lead to undefined correction/ calibration functions. In general, orthogonal path sensors do not show problematic combination of parameters. However, some geometric sonic sensor designs, available in the market, with paths forming smaller angles could lead to undefined correction functions for some levels of aerodynamic disturbances and for certain wind directions. The parameters studied have a strong influence on the existence and number of singularities in the correction/ calibration function as well as on the number of singularities for some combination of parameters. Some conclusions concerning good design practices are included.

TROPICAL CYCLONE WINDS AT LANDFALL: The ASOS–C-MAN Wind Exposure Documentation Project

Photographs describing the wind exposure at automatic weather stations susceptible to tropical cyclones are now available on Web pages at the National Climatic Data Center and the National Data Buoy Center. Given the exposure for one of eight wind direction sectors, a user may estimate the aerodynamic roughness and correct mean wind measurements to an open-terrain exposure. The open-terrain exposure is consistent with the tropical cyclone advisories and forecasts issued by the National Weather Service, as well as building design wind load standards published by the American Society of Civil Engineers.

Assessment of wind-generation potentiality in Jordan using the site effectiveness approach

Wind data gathered over 3–10 years is used for a feasibility analysis of optimum future utilization of wind-generator potentiality in 22 sites covering all landscape types and regions in Jordan. The yearly mean wind speed and the yearly average available wind energy flux were computed for each site. Yearly mean wind speeds at a height of 24 m could reach as high as 7.6 m/s and available wind energy flux close to 3 MWh/m 2/year could be attained. Detailed technical assessment for the nine most promising potential wind sites was made using the site effectiveness approach. The maximum site effectiveness and its corresponding cut-in speed were indicated, both of which depended on the site. The investigation was performed assuming three models of small and medium size wind machines representing different ranges of characteristic speeds and rated power suitable for water pumping and electric supply. The results show that small and medium wind turbines could be installed in the highlands and desert regions and utilized for water supply and electrical power generation, provided the correct wind machine-site is selected.

Correction multipoles for the high current operation of the Heavy Ion Synchrotron SIS

An upgrade program is under way to fill the Heavy Ion Synchrotron SIS up to the space charge limit at injection energy (e.g., 2/spl middot/10/sup 11/ Ne/sup 10+/ ions and 4/spl middot/10/sup 10/ U/sup 73+/ ions). One part of the program entails the construction of corrector multipoles for fine tuning of the synchrotron. Four normal quadrupoles are foreseen to compensate gradient errors of the 36 main quadrupoles in the ring, while eight skew quadrupoles will be used for the correction of tilt errors of the main quadrupoles. The skew quadrupoles will also be used to improve the multiturn injection efficiency, by linear coupling of the horizontal and vertical phase spaces. Two skew sextupoles will be provided to compensate sextupole components of the short, large aperture vertical steering magnets in the ring. Two technical restrictions had to be fulfilled. First, the space occupied by the correctors must be minimal. Therefore, the correction magnets will be constructed with a number of concentrically arranged multipole correction windings in the same magnet housing. Second, these magnets must be mounted around the beam line vacuum chamber, to avoid breaking the vacuum during their installation. Different possible configurations were investigated by computer simulation with respect to their field quality. Installation of the magnets is planned for the winter shut down of 2001/2002.

Accounting for source location and transport direction into geostatistical prediction of contaminants.

This paper presents a variant of the well-known kriging with a trend that allows one to account for the pollutant source coordinates and information about transport process into the spatial prediction of pollutant concentration. The new technique is illustrated using lead data from a Dallas metropolitan area and cadmium data from Palmerton (PA) NPL Superfund site. Instead of modeling the local spatial trend as low-order polynomials of coordinates, it is here expressed as a function of two factors that likely control the pollution spread: the distance to the smelter and the deviation from the major wind direction. Four different combinations of these two factors are developed, and their prediction performances are evaluated for a range of wind directions using cross-validation. Comparison with two traditional algorithms (OK and KT) shows that the proposed approach leads to smaller mean square errors of prediction when the correct wind direction is determined. The best combination of trend model and wind direction is site-dependent and derived using cross-validation. Kriging of residuals from a global trend model is an alternative to the use of local trends, and both techniques are shown to outperform ordinary kriging.

Formation of high mass X-ray black hole binaries

The discrepancy in the past years of many more black-hole soft X-ray transients (SXTs), of which a dozen have now been identified, had challenged accepted wisdom in black hole evolution. Reconstruction in the literature of high-mass X-ray binaries has required stars of up to ∼40 M ⊙ to evolve into low-mass compact objects, setting this mass as the limit often used for black hole formation in population syntheses. On the other hand, the sheer number of inferred SXTs requires that many, if not most, stars of ZAMS masses 20–35 M ⊙ end up as black holes ( Portegies Zwart et al., 1997; Ergma and van den Heuvel, 1998). In this paper we show that this can be understood by challenging the accepted wisdom that the result of helium core burning in a massive star is independent of whether the core is covered by a hydrogen envelope, or ‘naked’ while it burns. The latter case occurs in binaries when the envelope of the more massive star is transferred to the companion by Roche Lobe overflow while in either main sequence or red giant stage. For solar metallicity, whereas the helium cores which burn while naked essentially never go into high-mass black holes, those that burn while clothed do so, beginning at ZAMS mass ∼20 M ⊙ , the precise mass depending on the 12C( α, γ) 16O rate as we outline. In this way the SXTs can be evolved, provided that the H envelope of the massive star is removed only following the He core burning. Whereas this scenario was already outlined in 1998 by Brown et al. [NewA 4 (1999) 313], their work was based on evolutionary calculations of Woosley et al. [ApJ 448 (1995) 315] which employed wind loss rates which were too high. In this article we collect results for lower, more correct wind loss rates, finding that these change the results only little. We go into the details of carbon burning in order to reconstruct why the low Fe core masses from naked He stars are relatively insensitive to wind loss rate. The main reason is that without the helium produced by burning the hydrogen envelope, which is convected to the carbon in a clothed star, a central 12C abundance of ∼1/3 remains unburned in a naked star following He core burning. The later convective burning through 12C+ 12C reactions occurs at a temperature T∼80 keV. Finally, we show that in order to evolve a black hole of mass ≳10 M ⊙ such as observed in Cyg X-1, even employing extremely massive progenitors of ZAMS mass ≳60 M ⊙ for the black hole, the core must be covered by hydrogen during a substantial fraction of the core burning. In other words, the progenitor must be a WNL star. We evolve Cyg X-1 in an analogous way to which the SXTs are evolved, the difference being that the companion in Cyg X-1 is more massive than those in the SXTs, so that Cyg X-1 shines continuously.

Real time modelling as an emergency decision support system for accidental release of air pollutants

In the framework of the project ‘Windbank’, wind field patterns in an area of 30 km×30 km in the Swiss Plateau between the Alps and the Jura were measured with 22 temporary meteorological stations and two SODARs during 4 months in 1997. Hourly averages from this high resolution network were combined with meteorological information from routine stations and from a weather prediction model. This data-set comprises all available parameters influencing the complex wind flow in the investigated area between the Alps and the Jura. A cluster analysis for this data-set lead to 12 classes with a high separation quality. It is demonstrated, that an on-line acquisition of meteorological data from routine stations and from a weather prediction model can be used to diagnose the recent wind field class with a probability of 96% to hit the correct wind field class. This diagnosis reveals wind fields with a very high spatial resolution in a very short time. Consequently, it is useful as a contribution to a decision support system for safety management after accidental releases of nuclear or chemical air pollutants. Further, a method is outlined to use the weather prediction model to forecast the wind field class. An average probability of 79% to hit the correct wind field classes for a forecast time of up to 24 h is evaluated.

The Structure and Temporal Stability of Jupiter's Zonal Winds: A Study of the North Tropical Region

This paper investigates possible long-term zonal wind variations using Voyager (1979), Hubble Space Telescope (HST; 1995, 1997, 1998), and Galileo Orbiter (1997) data that has all been processed and analyzed in the same manner for consistency. Previous attempts to measure the zonal wind profile in Voyager data had yielded inconsistent results for the maximum eastward jet near 23.7° N latitude from different studies (A. P. Ingersoll et al., 1979, Nature280, 773–775; ibid 1981, J. Geophys. Res.86, 8733–8743; T. Maxworthy 1984, Planet. Space Sci.32, 1053–1058; S. Limaye 1986, Icarus65, 335–352). This paper compares previous measurements and includes new independent analysis to conclude that the correct wind jet velocity at the time of Voyager is close to 182 m s−1, most consistent with the reported results of Maxworthy (1984). In the data sets from different epochs the overall shape of the wind profile and locations of the prograde and retrograde jets remain constant, but there are amplitude changes at a few latitudes. The largest velocity deviations between the Voyager and the 1995–1997 HST profiles occurred in the maximum eastward jet, near 23.7° N, and at 6° S and 20° S planetographic latitude. Possible causes for an apparent zonal wind decrease were explored using Galileo visible and HST near-infrared data, and the wind velocity change was determined to be real. A very definite change in cloud structure and brightness has also occurred at 23.7° N. Additionally, surface brightness changes seen at 6° S and 20° S also correlated with changes in wind speed. HST WFPC2 data obtained in 1998 showed the recovery of the 23.7° N region to a Voyager-like appearance and an increase in wind velocity to the Voyager value.

An assessment of NSCAT ambiguity removal

The NASA scatterometer (NSCAT) estimates the wind speed and direction of near‐surface ocean wind. Several possible wind vectors (termed ambiguities) are estimated for each resolution element known as a wind vector cell (WVC). Typically, the speeds of the possible wind vectors are nearly the same, but the directions are very different. The correct wind must be distinguished in a step called ambiguity removal. Unfortunately, ambiguity removal algorithms are subject to error. In an attempt to evaluate the accuracy of the Jet Propulsion Laboratory NSCAT product, we use a new model‐based quality assurance algorithm that uses only NSCAT data. The algorithm segments the swath into overlapping 12 × 12 WVC regions and classifies each region according to estimated quality. The 9‐month NSCAT mission data set is analyzed. In 82% of the regions the ambiguity removal is over 99% effective, with the ambiguity errors correctable using a model‐based correction technique. In 5% of the regions, areas of significant ambiguity error are found. For remaining regions, all of which have root‐mean‐square (rms) wind speeds less than 4 m s−1, there is too much uncertainty in the wind field model or too much noise in the measurements to uniquely evaluate ambiguity selection with sufficient confidence. We thus conservatively conclude that for the set of regions with rms wind speed greater than 4 m s−1, NSCAT ambiguity removal is at least 95% effective.

In Search of the Correct Wind and Wave Fields in a Minor Basin

Abstract The authors analyze the accuracy of the surface wind of the Adriatic Sea from a global model. They find it to be substantially underestimated and propose a calibration by a suitable enhancement of the strength of the fields. The reasons for the underestimate are discussed.

Altimetric assimilation in a Mediterranean general circulation model

Identical twin experiments are performed with a realistic Mediterranean general circulation model, assimilating surface pressure at the rigid lid (simulating altimeter data) in order to reproduce the three‐dimensional circulation and water column structure. The first twin pair is forced with monthly varying wind stress and surface buoyancy, and the assimilation method of Cooper and Haines [1996] is used. Water columns are displaced vertically by an amount calculated to ensure that the surface pressure change required at assimilation time is reduced to zero at the seabed. The assimilation is successful with T, S and velocities having an error reduction of about 40% after 1 year, assimilating surface pressure every 15 days. A modification to this assimilation method is introduced in which a change to bottom pressure is calculated based on a balance between relative vorticity and stretching in the vertically displaced water column. A second identical twin experiment pair is forced with daily varying wind stress (from the European Centre for Medium‐Range Weather Forecasts in 1992–1993) but still monthly varying surface buoyancy forcing. The variability in surface pressure is much greater when daily winds are used, with much of the high‐frequency current signal being a barotropic response (with a strong signal at the seafloor). Applying the correct daily winds without any surface pressure assimilation can reduce the T, S and velocity errors by about 50% after a year, suggesting that much of the additional barotropic variability is deterministic. The additional assimilation of surface pressure every 20 days, now with the bottom pressure updated, leads to a further 30% error reduction. A further twin experiment with daily winds, in which the barotropic mode is allowed to converge first, before surface pressure assimilation begins, shows that a bottom pressure update during assimilation may be unnecessary if the correct wind stresses are known.

Superconducting correction impulse magnets for the accelerator Nuclotron

The superconducting accelerator Nuclotron was put into operation at JINR, Dubna. The accelerator contains 112 multipole correction windings. Each four of them are assembled as a magnet block with an inner diameter of 132 mm. The winding has one or two layers from NbTi multifilament conductor. The windings are impregnated with epoxy resin compound and glued on the tube coil with two-phase helium forced at 4.5 K. Each magnet has 100 A current leads without helium gas cooling. This very much simplifies the system of helium gas collection at the accelerator. All the magnets were tested and installed in the accelerator.

Spin-down and the dynamics of dense pool gyres in shallow seas

Isolated lenses or domes of dense (often cold) bottom water are found in many shelf seas and can be expected to induce significant baroclinic circulations. However, provided they have the correct thermal wind shear, many flow states can support a bottom dome structure, including: (a) an anticyclonically circulating dense dome overlain by a static surface layer or (b) cyclonic surface flow around a static dome. A one-dimensional, two-layer, quasi-geostrophic model is applied to a Gaussian vortex to argue that, on account of bottom friction in shelf seas, the bottom layer will spin down to rest over a time-scale of just a few days and that, due to layer coupling through vortex stretching/compression, cyclonic flow will concentrate in the surface layer. The association of cyclonic surface flow with static, dense domes in shallow seas is supported by reports of tank experiments and by recent observations in a cold pool system in the Irish Sea.

Design and test of a model superconducting correction winding around a grooved vacuum chamber (of LHC)

In the framework of research for the Large Hadron Collider (LHC), it has been envisaged to install distributed correction windings around the vacuum chamber inside the 50 mm bores of the 10 m long twin-aperture dipoles. At a distance of 10 mm from the center, the field homogeneity of the main dipoles may lead to systematic relative errors of up to 5*10/sup -4/ due to the sextupolar component and 1*10/sup -4/ due to higher multipoles. These errors depend on the operational conditions and need to be dynamically compensated. A design adapted to the LHC accelerator where thousands of correctors are needed has been investigated. It is based on the principle of minimizing the number of operations during manufacture in such a way that no manual operation is needed to adjust the accurate positioning of the coils. A 0.3 m long maquette and a 0.8 m long model of sextupolar correction winding have been manufactured at CERN to check the validity of the method. They both gave satisfactory results; the critical current of the short sample superconducting wire was reached after a few training quenches.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Some experimental investigations on the influence of the mounting arrangements on teh accuracy of cup-anemometer measurements

Through experiments carried out both in the field and in a large wind-tunnel it is demonstrated, that the way an anemometers is mounted on its supporting boom can cause the anemometer reading to be dependent on wind direction to an unacceptable large degree. Suggestions for removing this source of error in determining the correct wind speed are given.