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- Brunskog, Jonas
(författare)
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Acoustic excitation and transmission of lightweight structures
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In order to increase our knowledge of the sound transmission and radiation processes of lightweight wall and floor structures, theoretical models are needed. Detailed models may form a valuable tool. In lightweight floor structures, impact sound insulation is perhaps the most important property to consider. This thesis presents an overview of various solution strategies that may be useful in finding a theoretical model for impact sound insulation. Expressions for the point mobility of infinite plates driven by a rigid indenter are derived. These expressions are needed when determining the deformation close to the excitation area, which is important when studying impact noise to properly describe the interaction between the source and the floor. A detailed three-dimensional thick-plate analysis is used. The excitating pressure is found by means of a variational formulation. The point mobility is calculated by means of numerical integration. The excitation force provided by the ISO tapping machine is examined, partly in relation to the three-dimensional deformation analysis. Results found in the literature are reviewed and reconsidered. Low-frequency asymptotes are derived. A more general impact force description is derived, suited for arbitrary frequency-dependent mobilities of the floor structure. The frequency-dependency of the mobility can be due to local effects, investigated by means of thick-plate theory, and/or global effects, investigated by means of a spatial Fourier transform method. A theoretical model for a point-excited simple lightweight floor is presented. The model is used for the prediction of impact noise level. A comparison between numerical computations and measurements found in the literature is performed. A relatively good correspondence between measurements and calculations can be achieved. Lightweight walls (and floors) are often designed as a framework of studs with plates on each side. The studs can be seen as walls in the cavity, thus introducing finiteness. A prediction model for airborne sound insulation including these effects is presented. Due to variabilities, no structure can be perfectly periodic. The effects of near-periodicity are studied by means of transform technique and the expectation operator. The near-periodicity leads to an increase of the damping (if material damping is present). Resilient devices are commonly used in lightweight structures to decrease the sound transmission in a broad frequency band. Applications of such devices may be found, for example, in resiliently mounted ceilings in aeroplanes, ships and buildings. A measurement method to characterise the two-port acoustic properties of resilient devices is presented.
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- Brunskog, Jonas
(författare)
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Flanking transmission of a double-plate system with joists and cavities
- 2004
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Ingår i: 8th International Congress on Acoustics.
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Konferensbidrag (refereegranskat)abstract
- The work with development of new building systems is intensive. These systems are often related to lightweight constructions, and developed to be used in load-bearing structures and dwellings. One of the main drawbacks of this type of building systems is often the sound insulation. Lightweight walls and floors are often designed as frameworks of studs with plates on both sides - a double-plate structure. The flanking transmission is often the limiting aspect for the total sound insulation of such a structure. A prediction model for flanking transmission of lightweight building structures is thus under development. In the present paper the structural transmission loss when a double-plate structure meets a discontinuity is primary studied theoretically, assuming the incoming wave to be traveling. The model is analytic and deterministic and makes use of a spatial Fourier transform wave approach for periodic structures
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- Brunskog, Jonas, et al.
(författare)
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Measurement of the Acoustic properties of resilient, statically tensile loaded devices in light weight structures: A measurement method and statistical analysis
- 2002
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Ingår i: Building Acoustics. ; 9:2, s. 99-137
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Tidskriftsartikel (refereegranskat)abstract
- Resilient devices are commonly used in lightweight structures to decrease sound transmission in a broad frequency band. Applications of such devices may be found in e.g. resilient mounted ceilings in aeroplanes, ships and buildings. A measurement method to characterise the frequency dependency of the transfer stiffness and the input stiffness of the resilient device is presented. The mechanical characteristics of the measurement method are investigated. In addition, some resilient devices used in buildings are analysed with respect to acoustic properties. Parameters such as static load and mountings for the devices are considered and handled by means of statistical analysis.
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| 9. |
- Brunskog, Jonas
(författare)
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Near-periodicity in acoustically excited stiffened plates and its influence on vibration, radiation and sound insulation
- 2004
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Ingår i: Acta Acustica united with Acustica. - 1436-7947. ; 90:2, s. 301-312
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Tidskriftsartikel (refereegranskat)abstract
- Due to variabilities in the material, the geometrical configuration, or the manufacturing properties, a structure that is designed to be spatially periodic cannot be exactly periodic. The presence of small irregularities in a nearly periodic structure may influence the propagation of the vibration field, the field being localised. A number of papers have addressed such localisation phenomena. This paper will instead focus on the mean vibration field and its influence on sound radiation and sound insulation in a plate stiffened by supports or beams. The approach is to seek a formal solution with the aid of spatial transform technique (similar to the perfect periodic case) and then apply the expected value operator to the solution. Two assumptions must then be introduced: 1) The reaction forces are statistically independent of a phase-term that is due to the irregularity, and 11) the mean field is periodic. The approach is presented in general terms, the specific configuration (a stiffened plate) being presented as an example. Numerical results are presented and discussed, and it can be seen that the small irregularities cause an increase in stiffness and damping (when material damping is present).
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