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| 2. |
- Brunskog, Jonas
(författare)
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A wave approach to structural transmission loss in periodic structures: Thin beam case
- 2005
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Ingår i: Acta Acustica united with Acustica. - 1861-9959. ; 91:1, s. 91-102
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Tidskriftsartikel (refereegranskat)abstract
- When new building systems are developed, these are often lightweight constructions with a periodical set of stiffeners, developed for use in load-bearing structures and dwellings. One of the main drawbacks of this type of building systems is the sound insulation, where flanking transmission is an important issue. A prediction model for flanking transmission of lightweight building structures is thus under development. This paper is a theoretical study of the structural transmission coefficient of a junction, using a propagating wave approach. Free waves travel in the periodic wave-medium. The periodic resilient elements consist of rotation and displacement springs. The free waves meet a discontinuity (or junction), and the power transmitted through the discontinuity is then studied. The discontinuity consists of a mechanical coupling and point mass load. The model is analytic and deterministic, and makes use of a spatial Fourier transform wave approach for periodic structures. The approach is intended for flanking transmission of lightweight building structures, but it is also applicable for structures such as ships and aircraft. Numerical results are presented and discussed. It is concluded that the periodic nature of the wave media affects the power transmitted through a discontinuity.
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| 3. |
- Brunskog, Jonas, et al.
(författare)
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Absorption and scattering by perforated facings with periodic narrow slits
- 2022
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 151:3, s. 1847-1859
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Tidskriftsartikel (refereegranskat)abstract
- This paper develops a theory for the sound absorption and scattering of perforated slit absorbers.A rigid plane, perforated periodically in one dimension with absorbing slits, scatters incoming sound waves as discrete wave components in different directions. The absorbing slits are assumed to be line-like in the sense that their width is much shorter than the wavelengths.The equation for the sound field is solved in the wavenumber domain. The slits are described with an impedance description, assuming local reaction of the slits (typically a Helmholtz resonator).The solution is found by means of an inverse transform, back to the spatial domain. This results in an explicit formulation of the sound field, including a sum consisting of components that either radiate energy in discrete directions or are surface waves.A similar sum is also included in a term that can be interpreted as radiation impedance. The explicit expressions for the absorption and scattering coefficients are found with the aid of the radiating part of the scattered and reflected field.Numerical results of the absorption and scattering coefficients are presented. The result is verified with finite element method and compared with the result from an alternative general formulation of the problem.
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| 4. |
- 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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| 6. |
- 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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| 10. |
- Brunskog, Jonas
(författare)
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Image solution for clamped finite beams
- 2005
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X. ; 287:4-5, s. 1057-1064
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Tidskriftsartikel (refereegranskat)abstract
- An image solution for the forced response of a clamped finite beam is developed. The finite beam is replaced by an infinite beam under spatially periodic excitation and periodic support reactions. The response is then found by a Fourier transform approach, making use of the periodicity. An explicit expression is found, using the Poisson sum formula. The aim is to describe the potential of using the image method for clamped structural acoustic and vibration problems.
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