Abstract
Three synchronized pulsed Doppler wind lidars were deployed from May 2016 to June 2016 on the shores of a wide Norwegian fjord called Bjørnafjord to study the wind characteristics at the proposed location of a planned bridge. The purpose was to investigate the potential of using lidars to gather information on turbulence characteristics in the middle of a wide fjord. The study includes the analysis of the single-point and two-point statistics of wind turbulence, which are of major interest to estimate dynamic wind loads on structures. The horizontal wind components were measured by the intersecting scanning beams, along a line located 25 m above the sea surface, at scanning distances up to 4.6 k m . For a mean wind velocity above 8 m · s - 1 , the recorded turbulence intensity was below 0.06 on average. Even though the along-beam spatial averaging leads to an underestimated turbulence intensity, such a value indicates a roughness length much lower than provided in the European standard EN 1991-1-4:2005. The normalized spectrum of the along-wind component was compared to the one provided by the Norwegian Petroleum Industry Standard and the Norwegian Handbook for bridge design N400. A good overall agreement was observed for wave-numbers below 0 . 02 / m . The along-beam spatial averaging in the adopted set-up prevented a more detailed comparison at larger wave-numbers, which challenges the study of wind turbulence at scanning distances of several kilometres. The results presented illustrate the need to complement lidar data with point-measurement to reduce the uncertainties linked to the atmospheric stability and the spatial averaging of the lidar probe volume. The measured lateral coherence was associated with a decay coefficient larger than expected for the along-wind component, with a value around 21 for a mean wind velocity bounded between 10 m · s - 1 and 14 m · s - 1 , which may be related to a stable atmospheric stratification.
Highlights
As part of a national project to modernize the highway network in Western Norway, the Norwegian Public Roads Administration (NPRA) plans to build a bridge crossing the 5 km wideRemote Sens. 2017, 9, 977; doi:10.3390/rs9100977 www.mdpi.com/journal/remotesensingRemote Sens. 2017, 9, 977 and 550 m deep Bjørnafjord, about 30 km South of Bergen
The present study investigates, the validity of the wind velocity spectral model provided in the Handbook N400 [9] used for bridge structures in Norway and the model provided by the Norwegian Petroleum Industry
The purpose of the measurement campaign was to investigate the potential of using lidars to study the wind conditions in the middle of the fjord, where traditional anemometry is not deployed
Summary
As part of a national project to modernize the highway network in Western Norway, the Norwegian Public Roads Administration (NPRA) plans to build a bridge crossing the 5 km wideRemote Sens. 2017, 9, 977; doi:10.3390/rs9100977 www.mdpi.com/journal/remotesensingRemote Sens. 2017, 9, 977 and 550 m deep Bjørnafjord, about 30 km South of Bergen. As part of a national project to modernize the highway network in Western Norway, the Norwegian Public Roads Administration (NPRA) plans to build a bridge crossing the 5 km wide. The sensitivity to wind turbulence is a major issue, requiring a detailed analysis of wind turbulence in the fjord. At the location of the planned crossing, no infrastructure is available to support anemometers. The use of remote sensing technology to complement wind data from sensors on land is, an attractive option. The mean value m1 and the standard deviation m2 of the wind velocity are the statistics most often studied. To properly estimate wind loading on a wind-sensitive civil engineering structure, the wind velocity spectrum and the wind coherence are in addition required
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