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- Veljkovic, Milan, et al.
(author)
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High-strength tower in steel for wind turbines (Histwin) : Final report
- 2012
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Reports (peer-reviewed)abstract
- Innovative solutions for assembling joints of a tubular tower for wind turbines were studied and the project provides a background for design. This solution is simpler to produce and 80 % less expensive than traditional flange connection. Our feasibility study at the production plant indicates that the towers would be easy to assemble in situ. In addition to the direct cost savings due to the technical simplicity of the solution, the higher fatigue endurance than that of the flange connection is experimentally established. Further reduction of costs due to optimal use of higher-strength steel grades, especially in the bottom segments of the tower where the stiffening of the door opening is costly, is shown in the report. The total reduction of the costs for tower is estimated at about 10–15 % compared to the traditional tower. The project objectives are achieved in following sequences. • Experimental activities of the friction connection: small-scale tests to establish resistance of the friction connection for a variety of faying surfaces and bolt types, accompanying testing to ensure realistic input data for FEA, long-term testing to establish loss of pretension forces during the lifetime and fatigue tests.• Bending test of the friction and flange connection in a down-scaled tower. • Feasibility of production of the tower segments in the laboratory and at the production plant. • Monitoring of the existing tower to access a stress variation during the operation. • FEA analysis of experimental results and a complete case study of the monitored tower. Numerical examples for design of the friction connection are given for the sake of illustration and to encourage use of the new connection
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| 2. |
- Vuorinen, V., et al.
(author)
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LARGE EDDY SIMULATION OF DROPLET STOKES NUMBER EFFECTS ON MIXTURE QUALITY IN FUEL SPRAYS
- 2010
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In: Atomization and sprays. - 1044-5110 .- 1936-2684. ; 20:5, s. 435-451
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Journal article (peer-reviewed)abstract
- This paper provides a continuing study to the recent study by the authors and the results presented herein are based on the same numerical experiments enriching the previously obtained picture (Vuorinen, V, Hillamo, H., Kaario, O., Larmi, M., and Fuchs, L., Atomization Sprays, vol. 20, pp. 93-114, 2010). Large eddy simulations (LES) and Lagrangian particle tracking (LPT) techniques are applied to simulate turbulent fuel spray evolution using high spatial and temporal resolution (Delta x < 10(-4) m and Delta t < 10(-7) s), hence providing detailed information on the anisotropy of the spray problem. The aim of this paper is to apply LES/LPT to identify possible causes to observed fuel spray heterogeneities in nonevaporating fuel sprays (Cao, Z., Nishino, K., Mizuno, S., and Toni, K., Exp. Fluids, vol. 29, pp. S211-5229, 2000; Hillamo, H., Kaario, O., and Larmi M., SAE Paper No. 2008-08PFL-552, 2008). In this context, the numerical setup is new since it avoids the dense spray region by emulating the dilute spray part as a droplet laden jet. The apparent role of droplet diameter (d) to spray dispersion, spray structure, and the mixture quality can then be investigated in detail. This paper is motivated by previous investigations in which smaller nozzle hole diameters and higher injection pressures together are known to yield smaller droplets, improved mixing, and higher levels of entrainment. The main emphasis is on monodisperse sprays, but for comparison, also some polydisperse sprays and a single-phase jet (which is slightly loaded with tracer particles) are considered. The droplets are assumed to be spherical; they are of constant size and do not interact with each other (i.e., assuming only two-way momentum coupling). The droplets have a Stokes number within the range of 0.07 <= St(p) <= 2.56, corresponding to diameters between 2 <= d <= 12 mu m. The results include (i) visualization of spray structures, combined with (ii) quantitative and statistical analysis of the results. The spray cloud shape and its internal structure are shown to depend on Sty, and the apparent differences in spray dispersion are quantified using two mixing indicators that both depend strongly on St,, and imply that the smaller droplets yield better mixing than the larger droplets: (i) a diffusion coefficient, and (ii) a mixing index.
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