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- Sjöström, Anders, et al.
(författare)
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Experimental Structural Acoustic investigation of a lightweight floor structure
- 2010
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A common floor construction in a lightweight building system is using chipboard plates attached to wooden beams using screws and glue. One drawback with such a system is the propagation of vibrations stemming either from harmonic (washing machines, dishwashers, HiFi-systems) especially at low frequencies and/or transient (Human walking, dropped items, slamming doors) excitations. In order to accurately predict the sound attenuation and the losses of such building systems, computationally accurate and efficient simulation techniques are needed. The main objective of this work is to examine sandwiched floor constructs consisting of one and two layers of chipboards attached to supporting wooden beams. Of special interest are the effects of the discontinuities between adjacent boards and between the boards and beams on the loss of kinetic energy as a consequence of the evanescent wave propagation due to the acoustic attenuation process in the structure and on the phase shift of the waves as they travel past the different types of discontinuities in the floor assembly. The measurements are performed using two-axis accelerometers distributed over the floor and recorded synchronously. The measurements are focused in the low frequency range (10-600Hz) and are also including transient loads.
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- Sjöström, Anders, et al.
(författare)
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Vibration insulation of footbridges so as to reduce human discomfort
- 2014
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Ingår i: INTERNOISE 2014 - 43rd International Congress on Noise Control Engineering: Improving the World Through Noise Control. - 9780909882037
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Konferensbidrag (refereegranskat)abstract
- Low frequency vibrations in footbridges is a cause of annoyance for pedestrians crossing the bridge. Bagers bro, a footbridge built in Malmö (Sweden) had several constraints in the physical design that caused the first eigenmode of the bridge to be at 1.8Hz which is a severe problem for pedestrians. Therefore the bridge was fitted with tuned mass dampers to mitigate the vibration problem. To evaluate the performance of the dampers and the accuracy in the predictions of the Finite Element (FE) Models of the bridge, an investigation trough modeling and measurements with respect to the performance of the tuned dampers fitted to the bridge has been done. The measurements were performed both with and without the mass dampers engaged. The results from the operational modal analysis of the bridge were compared with finite element simulations. The mass dampers were found to greatly improve the vibratory performance of the bridge in as much as making an otherwise almost unusable bridge acceptable.
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- Sjöström, Anders, et al.
(författare)
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Wind turbine tower resonance
- 2014
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Ingår i: INTERNOISE 2014 - 43rd International Congress on Noise Control Engineering: Improving the World Through Noise Control. - 9780909882037
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Konferensbidrag (refereegranskat)abstract
- Wind turbine towers are large structures designed to withstand the unique loading conditions imposed on them by the turbine's nacelle and dynamic forces from the rotating blades. Observations and noise measurements of a particular wind turbine showed high noise levels at approximately 48 Hz, which could not be explained from the usual known potential noise sources. Correlated far field noise measurements and vibration measurements collected on the turbine tower, structural base and nearby ground have shown the source to be a resonance of the tower structure.
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- Weber, Thomas, et al.
(författare)
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Resistance of flight feathers to mechanical fatigue covaries with moult strategy in two warbler species
- 2005
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Ingår i: Biology letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 1:1, s. 27-30
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Tidskriftsartikel (refereegranskat)abstract
- Flight feather moult in small passerines is realized in several ways. Some species moult once after breeding or once on their wintering grounds; others even moult twice. The adaptive significance of this diversity is still largely unknown. We compared the resistance to mechanical fatigue of flight feathers from the chiffchaff Phylloscopus collybita, a migratory species moulting once on its breeding grounds, with feathers from the willow warbler Phylloscopus trochilus, a migratory species moulting in both its breeding and wintering grounds. We found that flight feathers of willow warblers, which have a shaft with a comparatively large diameter, become fatigued much faster than feathers of chiffchaffs under an artificial cyclic bending regime. We propose that willow warblers may strengthen their flight feathers by increasing the diameter of the shaft, which may lead to a more rapid accumulation of damage in willow warblers than in chiffchaffs.
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