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Assessment of load extrapolation methods for wind turbines / Henrik Stensgaard Toft in Transactions of the ASME. Journal of solar energy engineering, Vol. 133 N° 2 (Mai 2011) 

Public ISBD [article]  in Transactions of the ASME. Journal of solar energy engineering > Vol. 133 N° 2 (Mai 2011) . - 08 p. Titre : Assessment of load extrapolation methods for wind turbines Type de document : texte imprimé Auteurs : Henrik Stensgaard Toft, Auteur ; John Dalsgaard Sørensen, Auteur ; Dick Veldkamp, Auteur Année de publication : 2012 Article en page(s) : 08 p. Note générale : Solar energy Langues : Anglais (eng) Mots-clés : Extrapolation  Gaussian  processes  Load  (electric)  Wind  turbines Index. décimale : 621.47 Résumé : In the present paper, methods for statistical load extrapolation of wind-turbine response are studied using a stationary Gaussian process model, which has approximately the same spectral properties as the response for the out-of-plane bending moment of a wind-turbine blade. For a Gaussian process, an approximate analytical solution for the distribution of the peaks is given by Rice. In the present paper, three different methods for statistical load extrapolation are compared with the analytical solution for one mean wind speed. The methods considered are global maxima, block maxima, and the peak over threshold method with two different threshold values. The comparisons show that the goodness of fit for the local distribution has a significant influence on the results, but the peak over threshold method with a threshold value on the mean plus 1.4 standard deviations generally gives the best results. By considering Gaussian processes for 12 mean wind speeds, the “fitting before aggregation” and “aggregation before fitting” approaches are studied. The results show that the fitting before aggregation approach gives the best results. DEWEY : 621.47 ISSN : 0199-6231 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JSEEDO000133000002 [...] [article] Assessment of load extrapolation methods for wind turbines [texte imprimé] / Henrik Stensgaard Toft, Auteur ; John Dalsgaard Sørensen, Auteur ; Dick Veldkamp, Auteur . - 2012 . - 08 p. Solar energy Langues : Anglais (eng) in Transactions of the ASME. Journal of solar energy engineering > Vol. 133 N° 2 (Mai 2011) . - 08 p. Mots-clés : Extrapolation  Gaussian  processes  Load  (electric)  Wind  turbines Index. décimale : 621.47 Résumé : In the present paper, methods for statistical load extrapolation of wind-turbine response are studied using a stationary Gaussian process model, which has approximately the same spectral properties as the response for the out-of-plane bending moment of a wind-turbine blade. For a Gaussian process, an approximate analytical solution for the distribution of the peaks is given by Rice. In the present paper, three different methods for statistical load extrapolation are compared with the analytical solution for one mean wind speed. The methods considered are global maxima, block maxima, and the peak over threshold method with two different threshold values. The comparisons show that the goodness of fit for the local distribution has a significant influence on the results, but the peak over threshold method with a threshold value on the mean plus 1.4 standard deviations generally gives the best results. By considering Gaussian processes for 12 mean wind speeds, the “fitting before aggregation” and “aggregation before fitting” approaches are studied. The results show that the fitting before aggregation approach gives the best results. DEWEY : 621.47 ISSN : 0199-6231 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JSEEDO000133000002 [...]

Implementation of a mixing length turbulence formulation into the dynamic wake meandering model / Rolf-Erik Keck in Transactions of the ASME. Journal of solar energy engineering, Vol. 134 N° 2 (Mai 2012) 

Public ISBD [article]  in Transactions of the ASME. Journal of solar energy engineering > Vol. 134 N° 2 (Mai 2012) . - 13 p. Titre : Implementation of a mixing length turbulence formulation into the dynamic wake meandering model Type de document : texte imprimé Auteurs : Rolf-Erik Keck, Auteur ; Dick Veldkamp, Auteur ; Helge Aagaard Madsen, Auteur Année de publication : 2012 Article en page(s) : 13 p. Note générale : solar energy Langues : Anglais (eng) Mots-clés : dynamic  wake  meandering  (DWM)  model;  turbulence;  simulation;  actuator  line  model Index. décimale : 621.47 Résumé : The work presented in this paper focuses on improving the description of wake evolution due to turbulent mixing in the dynamic wake meandering (DWM) model. From wake investigations performed with high-fidelity actuator line simulations carried out in ELLIPSYS3D, it is seen that the current DWM description, where the eddy viscosity is assumed to be constant in each cross-section of the wake, is insufficient. Instead, a two-dimensional eddy viscosity formulation is proposed to model the shear layer generated turbulence in the wake, based on the classical mixing length model. The performance of the modified DWM model is verified by comparing the mean wake velocity distribution with a set of ELLIPSYS3D actuator line calculations. The standard error (defined as the standard deviation of the difference between the mean velocity field of the DWM and the actuator line model), in the wake region extending from 3 to 12 diameters behind the rotor, is reduced by 27% by using the new eddy viscosity formulation. DEWEY : 621.47 ISSN : 0199-6231 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JSEEDO000134000002 [...] [article] Implementation of a mixing length turbulence formulation into the dynamic wake meandering model [texte imprimé] / Rolf-Erik Keck, Auteur ; Dick Veldkamp, Auteur ; Helge Aagaard Madsen, Auteur . - 2012 . - 13 p. solar energy Langues : Anglais (eng) in Transactions of the ASME. Journal of solar energy engineering > Vol. 134 N° 2 (Mai 2012) . - 13 p. Mots-clés : dynamic  wake  meandering  (DWM)  model;  turbulence;  simulation;  actuator  line  model Index. décimale : 621.47 Résumé : The work presented in this paper focuses on improving the description of wake evolution due to turbulent mixing in the dynamic wake meandering (DWM) model. From wake investigations performed with high-fidelity actuator line simulations carried out in ELLIPSYS3D, it is seen that the current DWM description, where the eddy viscosity is assumed to be constant in each cross-section of the wake, is insufficient. Instead, a two-dimensional eddy viscosity formulation is proposed to model the shear layer generated turbulence in the wake, based on the classical mixing length model. The performance of the modified DWM model is verified by comparing the mean wake velocity distribution with a set of ELLIPSYS3D actuator line calculations. The standard error (defined as the standard deviation of the difference between the mean velocity field of the DWM and the actuator line model), in the wake region extending from 3 to 12 diameters behind the rotor, is reduced by 27% by using the new eddy viscosity formulation. DEWEY : 621.47 ISSN : 0199-6231 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JSEEDO000134000002 [...]