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| 2. |
- Bourgoin, M., et al.
(författare)
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Investigation of the small-scale statistics of turbulence in the Modane S1MA wind tunnel
- 2018
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Ingår i: CEAS Aeronautical Journal. - : Springer. - 1869-5582 .- 1869-5590. ; 9:2, s. 269-281
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Tidskriftsartikel (refereegranskat)abstract
- This article describes the planning, set-up, turbulence characterization and analysis of measurements of a passive grid turbulence experiment that was carried out in the S1MA wind-tunnel from ONERA in Modane, in the context of the ESWIRP European project. This experiment aims at a detailed investigation of the statistical properties of turbulent flows at large Reynolds numbers. The primary goal is to take advantage of the unequaled large-scale dimensions of the ONERA S1MA wind-tunnel facility, to make available to the broad turbulence community high-quality experimental turbulence data with unprecendented resolution (both spatial and temporal) and accuracy (in terms of statistical convergence). With this goal, we designed the largest grid-generated turbulence experiment planned and performed to date. Grid turbulence is a canonical flow known to produce almost perfectly homogeneous and isotropic turbulence (HIT) which remains a unique framework to investigate fundamental physics of turbulent flows. Here, we present a brief description of the measurements, in particular those based on hot-wire diagnosis. By comparing results from classical hot-wires and from a nano-fabricated wire (developed at Princeton University), we show that our goal of resolving down to the smallest dissipative scales of the flow has been achieved. We also present the full characterization of the turbulence here, in terms of turbulent energy dissipation rate, injection and dissipation scales (both spatial and temporal) and Reynolds number.
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| 3. |
- Arnqvist, Johan, et al.
(författare)
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Wind Statistics from a Forested Landscape
- 2015
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Ingår i: Boundary-layer Meteorology. - : Springer Science and Business Media LLC. - 0006-8314 .- 1573-1472. ; 156:1, s. 53-71
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Tidskriftsartikel (refereegranskat)abstract
- An analysis and interpretation of measurements from a 138-m tall tower located in a forested landscape is presented. Measurement errors and statistical uncertainties are carefully evaluated to ensure high data quality. A 40 wide wind-direction sector is selected as the most representative for large-scale forest conditions, and from that sector first-, second- and third-order statistics, as well as analyses regarding the characteristic length scale, the flux-profile relationship and surface roughness are presented for a wide range of stability conditions. The results are discussed with focus on the validity of different scaling regimes. Significant wind veer, decay of momentum fluxes and reduction in shear length scales with height are observed for all stability classes, indicating the influence of the limited depth of the boundary layer on the measured profiles. Roughness sublayer characteristics are however not detected in the presented analysis. Dimensionless gradients are shown to follow theoretical curves up to 100 m in stable conditions despite surface-layer approximations being invalid. This is attributed to a balance of momentum decay and reduced shear length scale growth with height. The wind profile shows a strong stability dependence of the aerodynamic roughness length, with a 50 % decrease from neutral to stable conditions.
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| 4. |
- Chougule, A., et al.
(författare)
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Spectral tensor parameters for wind turbine load modeling from forested and agricultural landscapes
- 2015
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Ingår i: Wind Energy. - : John Wiley & Sons. - 1095-4244 .- 1099-1824. ; 18:3, s. 469-481
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Tidskriftsartikel (refereegranskat)abstract
- A velocity spectral tensor model was evaluated from the single-point measurements of wind speed. The model contains three parameters representing the dissipation rate of specific turbulent kinetic energy, a turbulence length scale and the turbulence anisotropy. Sonic anemometer measurements taken over a forested and an agricultural landscape were used to calculate the model parameters for neutral, slightly stable and slightly unstable atmospheric conditions for a selected wind speed interval. The dissipation rate above the forest was nine times that at the agricultural site. No significant differences were observed in the turbulence length scales between the forested and agricultural areas. Only a small difference was observed in the turbulence anisotropy at the two sites, except near the surface, where the forest turbulence was more isotropic. The turbulence anisotropy remained more or less constant with height at the forest site, whereas the turbulence became more isotropic with height for the agricultural site. Using the three parameters as inputs, we quantified the performance of the model in coherence predictions for vertical separations. The model coherence of all the three velocity components was overestimated for the analyzed stability classes at both sites. As expected from the model approximations, the model performed better at both sites for neutral stability than slightly stable and unstable conditions. The model prediction of coherence of the along-wind and vertical components was better than that of the cross-wind component. No significant difference was found between the performance of the model at the forested and the agricultural areas.
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| 5. |
- Lamas, L., et al.
(författare)
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Revision of the Eurocodes – aspects of geotechnical and rock engineering design
- 2020
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Ingår i: ISRM International Symposium - EUROCK 2020. - : International Society for Rock Mechanics.
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Konferensbidrag (refereegranskat)abstract
- The Structural Eurocodes (EN 199x) are a suite of European standards for the design of buildings and civil engineering works, published in 2006 by the European Committee for Standardization (CEN) and with implementation starting in 2010. EN 1990 sets the basis of structural design, with the other Eurocodes dealing with different materials and specific aspects of the design; Eurocode 7 (EN 1997) deals with geotechnical aspects. In 2010, CEN began a process of evolving the Eurocodes in order to incorporate improvements that reflect the state-of-the-art in engineering design and the needs of the civil engineering market; to improve the ease-of-use of the standards; and to harmonize practice between countries. The existing EN 1990 is founded on limit state concepts, and reliability of design is provided mainly by a semi-probabilistic method based on partial factors. Applying the same method to geotechnical design has proved to be difficult, and the revised EN 1990 will present improvements concerning geotechnical design. Reflecting these changes, the title of EN 1990 was changed to “Basis of structural and geotechnical design”. Although initially developed for structures involving soils, Eurocode 7 is also applicable to rock engineering design. A major target of the current revision is that the code should treat soil and rock on an equal basis. The evolution of the Eurocode 7 has been accompanied by a group of rock engineering experts working under CEN, who started their activity in 2011. The paper is authored by the current members of this group and presents the situation of the revision of Eurocode 7 in October 2019, namely: the main objectives of the revision; the new structure adopted for the code, with three parts, and the implementation schedule of the revised Eurocodes; the main changes implemented so far in geotechnical design and rock engineering; the main rock engineering aspects still needing to be addressed.
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| 6. |
- Medici, D., et al.
(författare)
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On the determination of stability conditions over forested areas from velocity measurements
- 2014
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Ingår i: European Wind Energy Association Conference and Exhibition 2014. - : European Wind Energy Association.
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Konferensbidrag (refereegranskat)abstract
- Two proxies able to determine the sign of the atmospheric stability in the absence of temperature measurements were investigated using data from four forested sites in Sweden. The results indicate that the simple proxy based on the time of the day when the measurement was taken was sufficient to identify approximately 75% of the stable occurrences. However, also during daytime, stable stratification was not infrequent. A criterion based on a combination of the local turbulence intensity and shear exponent was therefore also investigated, and the combination of the two criteria was able to estimate approximately 90% of the overall stable data. When selecting data with mean wind speeds over 5 m/s at 80 m height, the presented data sets include mostly data where temperature effects are small (near-neutral), followed by stable data. Only few occurrences of unstable conditions were anyway observed. The investigated data sets show large variation of shear and turbulence intensity with increasing stability, indicating the need for proxies that also can be used to characterize the degree of atmospheric stability.
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| 7. |
- Szász, Robert-Zoltán, et al.
(författare)
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Algorithm for automatic quantification of flashback and flash forward events from high-speed chemiluminescence recordings
- 2016
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Ingår i: Springer Proceedings in Physics. - Cham : Springer Science+Business Media B.V.. - 9783319306001 - 9783319306025 ; , s. 519-526
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Konferensbidrag (refereegranskat)abstract
- Three methods are employed to identify and quantify flashback and flash forward events based on chemiluminescence recordings of swirling flames. The approaches differ in the procedure to determine the instantaneous flame position. The results revealed that the most robust method is to determine a threshold relative to the instantaneous maximum intensity. Analysis of the complete dataset indicated that flashback events are significantly slower than flash forward events.
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