| 1. |
- Andersson, Patrik, 1974, et al.
(författare)
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The intensity potential approach for predicting sound power flow through partial enclosures
- 2011
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Ingår i: 18th International Congress on Sound and Vibration 2011, ICSV 2011, Rio de Janeiro, 10 - 14 July 2011. - 9781618392596 ; 2, s. 1261-1275
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Konferensbidrag (refereegranskat)abstract
- The intensity potential approach is developed for prediction of sound power flow through partial enclosures. A typical application is the prediction of radiated noise from an engine bay with respect to geometry, position and acoustical properties of screens and absorbers. The approach is based on the Helmholtz decomposition of the vector field of the time-averaged sound intensity into its irrotational and rotational components. The local power balance in a lossless medium and the Helmholtz decomposition gives a Poisson equation for the scalar intensity potential of the irrotational component only. The paper presents the approach and evaluates it by canonical examples and by comparison to measured data. It is demonstrated that the prediction of sound power through any closed surface is exact provided that the geometry and boundary conditions are correct. The comparison to experimental data shows that the method is useful in practical applications. The approach has its strength for cases with complex geometry and multiple broadband sources, but it has the potential to become more general by further development of boundary conditions. It is concluded that the intensity potential approach provides a robust prediction tool for the mid- and high-frequency range.
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| 2. |
- Barbagallo, Mathias, 1983-
(författare)
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Statistical energy analysis and variational principles for the prediction of sound transmission in multilayered structures
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Multilayered structures have many application in industry and society: they have peculiar properties and serve a variety of purposes, like structural support, thermal insulation, vibrational and acoustic isolation. This thesis concerns the prediction of sound transmission in multilayered structures. Two problems are herein investigated: the transmission of energy through structures and the transmission of energy along structures. The focus of the analysis is on the mid to high frequency range. To predict sound transmission in these structures, statistical energy analysis (SEA) is used.SEA models are devised for the prediction of the sound reduction index for two kinds of multilayered structures, double-walls used in buildings and trim-panels in vehicles; the double-walls comprise an air cavity in between flat plasterboard or glass plates, whereas the trim-panels a porous layer in between curved aluminium and rubber layers. The SEA models are based upon the wave-types carrying energy. The novelty in these SEAs is an element describing the waves in the air cavity, or in the porous layer, fully coupled to the mass-impeded external layers. Compared to measurements, the proposed SEA performs well: for double-walls, it performs better than previous models; for trim-panels, it is an original result. The parameters of the new SEA element, such as modal density, are derived from the coupling equations describing the fully coupled waves. For double-walls, these equations are derived via Newton's laws. For trim-panels, a variational approach based upon a modified Hamilton's principle valid for non-conservative systems is preferred, because it is a powerful machinery for deriving equations of motion and coupling conditions of a medium as complex as the porous layer. The modified Hamilton's principle for non-conservative systems is based upon a self-adjoint functional analogous to the Lagrangian, inspired by Morse and Feshbach's construction. A self-adjoint variational principle for Biot's equations in the displacement formulation is devised. An equivalent mixed formulation is obtained changing the coordinates of the displacement formulation via Lagrange multipliers. From this mixed formulation, the Lagrangian for a porous material with a limp frame is derived, which yields the continuity of the total displacement of the porous layer. Lagrange multipliers help to obtain the correct coupling functionals between a porous material and a solid. The Lagrange multipliers introducing the continuity of the frame and the solid displacements equal the traction of the in-vacuo frame, thus disappearing if the latter is limp. Measurements to gather material parameters for a Biot model of the porous layer have been conducted.The effects of spatial energy decay in the transmission along structures predicted by SEA is studied: a major effect is the increased relevance of indirect coupling loss factors between SEA elements. This may jeopardize the usefulness of SEA at higher frequencies.
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| 3. |
- Thivant, Michael, et al.
(författare)
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Intensity Potential Approach for Modeling High-Frequency Sound Fields
- 2011
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Ingår i: Acta Acustica united with Acustica. - 1610-1928 .- 1861-9959. ; 97:1, s. 103-114
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes the intensity potential approach for prediction of high-frequency sound power radiation. The approach is based on the Helmholtz decomposition of the vector field of time-averaged sound intensity into its irrotational and rotational components. The local power balance in a lossless medium is expressed in terms of the irrotational component only, and results in the Poisson equation for a scalar intensity potential of this component only. The approach gives an exact expression for the sound power through any closed surface in terms of the irrotational component, provided that the boundary conditions are correct. The approach is evaluated by exploring the two intensity components in three canonical examples, and by comparison to measured data with special focus on directivity aspects. It is concluded that the intensity potential approach is relevant, in particular for high-frequency sound fields from multiple sources that are uncorrelated and broadbanded. However, the intensity is generally overestimated in the shadow zones and underestimated in the directly exposed regions. Further, peaks in narrow frequency bands associated with interference of waves are ignored.
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