| 1. |
- Miao, Xiujuan, et al.
(författare)
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Aerodynamic performance of a high-speed train passing through three standard tunnel junctions under crosswinds
- 2020
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Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 10:11
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Tidskriftsartikel (refereegranskat)abstract
- The aerodynamic performance of a high-speed train passing through tunnel junctions under severe crosswind condition was numerically investigated using improved delayed detached-eddy simulations (IDDES). Three ground scenarios connected with entrances and exits of tunnels were considered. In particular a flat ground, an embankment, and a bridge configuration were used. The numerical method was first validated against experimental data, showing good agreement. The results show that the ground scenario has a large effect on the train's aerodynamic performance. The bridge case resulted in generally smaller drag and lift, as well as a lower pressure coefficient on both the train body and the inner tunnel wall, as compared to the tunnel junctions with flat ground and embankment. Furthermore, the bridge configuration contributed to the smallest pressure variation in time in the tunnel. Overall, the study gives important insights on complicated tunnel junction scenarios coupled with severe flow conditions, that, to the knowledge of the authors, were not studied before. Beside this, the results can be used for further improvements in the design of tunnels where such crosswind conditions may occur.
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| 2. |
- Fang, Keyan, et al.
(författare)
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An interdecadal climate dipole between Northeast Asia and Antarctica over the past five centuries
- 2019
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 52:1/2, s. 765-775
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Tidskriftsartikel (refereegranskat)abstract
- © 2018 Springer-Verlag GmbH Germany, part of Springer Nature Climate models emphasize the need to investigate inter-hemispheric climatic interactions. However, these models often underestimate the inter-hemispheric differences in climate change. With the wide application of reanalysis data since 1948, we identified a dipole pattern between the geopotential heights (GPHs) in Northeast Asia and Antarctica on the interdecadal scale in boreal summer. This Northeast Asia/Antarctica (NAA) dipole pattern is not conspicuous on the interannual scale, probably in that the interannual inter-hemispheric climate interaction is masked by strong interannual signals in the tropics associated with the El Niño-Southern Oscillation (ENSO). Unfortunately, the instrumental records are not sufficiently long-lasting to detect the interdecadal variability of the NAA. We thus reconstructed GPHs since 1565, making using the proxy records mostly from tree rings in Northeast Asia and ice cores from Antarctica. The strength of the NAA is time-varying and it is most conspicuous in the eighteenth century and after the late twentieth century. The strength of the NAA matches well with the variations of the solar radiation and tends to increase in along with its enhancement. In boreal summer, enhanced heating associated with high solar radiation in the Northern Hemisphere drives more air masses from the South to the North. This inter-hemispheric interaction is particularly strong in East Asia as a result of the Asian summer monsoon. Northeast Asia and Antarctica appear to be the key regions responsible for inter-hemispheric interactions on the interdecadal scale in boreal summer since they are respectively located at the front and the end of this inter-hemispheric trajectory.
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| 3. |
- Fang, Keyan, et al.
(författare)
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The potential to use variations in tree-ring geometric center to estimate past wind speed change
- 2022
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Ingår i: Natural Hazards Research. - : Elsevier BV. - 2666-5921. ; 2:2, s. 132-137
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Tidskriftsartikel (refereegranskat)abstract
- Tree radial growth is characterized by not only the annual ring-width increment but also shifts in the tree-ring geometric center (TRGC) if subjected to asymmetric external forcing, such as gravity downslope or prevailing winds. Previous dendrochronological studies have used the asymmetric growth derived from tree-ring widths to reconstruct wind speed changes. Here we propose a novel method that uses quantitative TRGC measurements to estimate wind speed. We investigated TRGC shifts in northeast China, where the prevailing westerly winds are strong and persistent. We found that the TRGC showed significant correlations (r = 0.64, p < 0.01) with wind speed in May–September. The higher tree geometry sensitivity to wind speed obtained with the new method compared to previous ones, suggests the possibility of reconstructing historical wind change and variability in prevailing winds using TRGC. In addition, by correcting tree-ring radius according to their TRGC shifts, the basal area increment (BAI) was calculated. Our new BAI estimation provided stronger correlations with climate than both the standard tree-ring width chronology and a traditional BAI estimation. We suggest that future dendrochronological studies should consider TRGC shifts to increase the accuracy in climate reconstructions.
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