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Measuring and modelling of the wind on the scale of tall wind turbines
Full text linkI denne rapport undersøges luftstrømmen i den nederste del af atmosfæren – op til højder i størrelsesordnen af moderne vindmøller. Fordi vindmøller i dag ofte er højere end 100 m, undersøges gyldigheden af nuværende analytiske og numeriske atmosfæriske modeller med henblok på at erhevrve mere viden om strukturen af det atmosfæriske grænselag. En ny langtrækkende vind-LIDAR placeret nær instrumenterede meteorologiske master i det vestlige Danmark og i Nordtyskland målte vind-hastighed og -retning i højder op til 2000 m, og disse målinger sammenlignes med vindhastighedsmålinger fra meteorologiske master.Placeringen ved Høvsøre er kendetegnet ved at være tæt på havet, som har en lav overfladeruhed, og landjorden, som har en meget højere overfladeruhed. Det interne grænselag, der dannes efter ved overgangen fra hav til land, påvirkes af både opstrøms og nedstrøms atmosfærisk stabilitet. Modellering af den klimatologiske vindhastighed ved hjælp af en 3-lags interpolation gav gode resultater, både under neutrale forhold og under andre stabilitetsforhold. Konstanterne i modellen blev ændret baseret på sammenligning med andre studier og en numerisk model.En numerisk mesoskala model blev brugt til at simulere vinden ved Høvsøre i fire uger i løbet af efteråret 2010. Den vertikale gradient af vindprofilen i den nederste del af grænselaget var for lav, og vindhastighed var generelt for lav højere oppe i grænselaget. Vindhastigheden nær overfladen samt friktionshastigheden havde umiddelbart efter kystlinjen en forskel der kan relateret til ændringen i overfladeruhed. Et højereordens grænselagsskema gav bedre resultater med hensyn til vindprofilen, når vinden kom fra vest over havet, mens et første-ordens grænselagsskema gav bedre resultater når vinden var fra øst med dannelse af ”low-level jets”. Vindprofilens form og den generelle underestimering af vindhastigheden i større højder blev ikke forbedret ved brug af en anden synoptisk forcing og en højere vertikal opløsning i modellen. Effekten af den horizontale temperaturgradient (baroklinicitet) blev undersøgt for de to lokaliteter. Den geostrofiske vind ved overfladen, gradient-vinden og den termiske vind blev beregnet ved hjælp af simuleringer med en mesoskala model. Ved begge lokaliteter var den termiske vind op til 970 m’s højde tilnærmelsesvis Gaussisk fordelt med en standardafvigelse på tre m s􀀀1 og den termiske vind-vektor varierede sæsonmæssigt grundet temperaturforskelle mellem hav og land. Vindretningens ændring med højden viste sig at være meget følsom over for baroklinicitet. Variationen af værdien af konstanterne i den geostrofiske ”draglaw” under neutrale og barokline forhold var næsten den samme som i undersøgelser hvor det var antaget at forholdene var barotrope; en del af variationen kan forklares ved at forholdene rent faktisk ikke var barotrope men barokline, hvilket viser vigtigheden af at inddrage denne effekt i studier af vinden i det atmosfæriske grænselag.The air flow in the lower atmosphere on the spatial scale of the modern wind turbines is studied. Because wind turbines are nowadays often taller than 100 m, the validity of current analytical and numerical atmospheric models has to be evaluated and more knowledge about the structure of the atmospheric boundary layer at those heights has to be acquired. A new long-range wind lidar was placed next to well-instrumented meteorological masts in the west of Denmark and in northern Germany and measured the wind speed and direction up to 2000 m and was compared with wind-speed measurements from the meteorological masts.The Høvsøre site is characterized by a transition from the flow over sea, which has a low surface roughness, to flow over land, which has a much higher surface roughness. The internal boundary layer that forms after this transition, was characterized by both the upstream and the downstream stability. Modelling the mean climatological wind speed with a 3-layer interpolation scheme gave good results, both in neutral conditions and when including other stability conditions. The constants in the model were slightly adjusted based on comparison with other studies and a numerical model.A mesoscale numerical model was used to simulate the flow at Høvsøre for four weeks during autumn 2010. The wind profile did not have enough vertical shear in the lower part of the PBL and had a negative bias higher up in the boundary layer. In the grid points after the shoreline the wind speed near the surface and the friction velocity had a bias, which were related to the change in surface roughness. A higher-order boundary-layer scheme represented the wind profile of the westerly flow over sea better, while a first-order scheme modelled the flow from the east with low-level jets better. The wind profile shape and the negative wind speed bias at larger heights were not improved when a different synoptic forcing and a different vertical resolution were used in the model. The effect of baroclinity was explored for the two sites. The surface geostrophic wind, the gradient wind and the thermal wind were derived from simulations with a mesoscale model. In both locations the thermal wind up to 970 m was approximately Gaussianly distributed with a standard deviation of three m s−1 and the thermal wind vector varied seasonally due to temperature differences between sea and land. The wind veer was particularly sensitive to baroclinity. The variation of the resistance law constants in neutral, baroclinic conditions was approximately the same as in experiments that where assumed to be barotropic; part of the variation was explained by baroclinity showing the importance of including this effect when studying boundary-layer winds
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Using SST for imporved mesoscale modelling of the coastal zone
No full textMany offshore wind farms are located and planned in the near-coastal areas, where the winds are higher and connection to the grid is easier. Existing wind measurements in near-shore and offshore areas are sparse and scarce, therefore simulations from state-of-the-art meso-scale models are used for wind resource predictions. In coastal and near-shore areas, models are inaccurate and uncertain, mainly because of numerical approximations, which do not resolve the large changes in local topographic features and atmospheric stability well (Floors 2013). In coastal and near-shore areas, such models are rather inaccurate and uncertain, primarily due to their numerical approximations, which do not resolve the large changes in local topographic features and atmospheric stability well. The accuracy of modelled wind resource predictions can be improved by using local wind measurements to calibrate the models. The RUNE project aimed at Reducing Uncertainty of Near-shore wind resource Estimates and investigated cost-effective measurement solutions for improving the wind resource modelling of coastal areas. During the RUNE project, the wind over a coastal area was measured by land-based lidar systems, an offshore lidar buoy and satellite radar remote sensing (SAR and scatterometers) while simulations from the Weather Research & Forecasting (WRF) mesoscale model were performed. The purpose of the analysis is to evaluate the uncertainty of the modelled wind in the coastal zone and further improve it. The high-resolution daily SST analysis product from the Danish Meteorological Institute (DMI) (Høyer and Karagali, 2016), specifically developed for the North Sea and Baltic Sea region was introduced as a boundary condition to WRF. In addition, to improve the physical description of the domain, the elevation, topography and land use, the CORINE land cover with a spatial resolution of 100~m to 250~m and the SRTM elevation database were used as boundary conditions. This study provides an overview of the measurement campaign and the lidar systems in Section 2 and the description of the model set-up in section 3. Some preliminary results regarding the sensitivity of the model to different options for the SST, land use, resolution and PBL scheme are presented in Section 4.1 while comparisons with the lidar measurements are presented in Section 4.2. Finally, the conclusions are available in Section 5
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Observations and modeling of the wind profile and wind turning in the atmospheric boundary layer
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