| 1. |
- Jalkanen, Jukka-Pekka, et al.
(författare)
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Modeling of ships as a source of underwater noise
- 2017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Shipping as a source of underwater noise is increasing. Underwater noise emission levels are seldom considered as a ship design parameter unless low vessel noise is specifically required, like in the case of warships and research vessels. Noise emissions are not regulated yet, but the awareness of possible impacts of noise on marine life is increasing. This paper describes the implementation of a noise source model for the Ship Traffic Emission Abatement Model (STEAM; Jalkanen et al. 2009; 2012; Johansson et al, 2017). The combination of vessel technical description and activity can be used to generate noise source maps which are based on actual ship traffic data. The generated noise source maps can ve used to describe the energy emitted as noise to the water, which facilitates regular annual updates of the noise emissions from ship traffic in the Baltic Sea area.
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| 2. |
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| 3. |
- Lindberg, Eskil, 1979-, et al.
(författare)
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A vibro-acoustic reduced order model using undeformed coupling interface substructuring - Application to rubber bushing isolation in vehicle suspension systems
- 2014
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Ingår i: Applied Acoustics. - : Elsevier BV. - 0003-682X .- 1872-910X. ; 78, s. 43-50
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Tidskriftsartikel (refereegranskat)abstract
- A vibro-acoustic reduced order model (ROM) based on a substructuring method using undeformed coupling interfaces (UCI) is proposed. The method may be used to reduce the order of a global problem, this by subdividing the global system to substructures interacting through UCI's. The local dynamic stiffness of each substructure may then be modelled with a, for that particular problem, best suited description. The feasibility of the method is demonstrated by a sensitivity analysis of the vibro-acoustic power isolation in a vehicle suspension system, comprising of a link arm connected to a vehicle car body through two rubber bushings. The link arm ROM is a component mode synthesis (CMS)-UCI, the rubber bushing model is a UCI-ROM derived from a 2D axisymmetric model using a frequency dependent visco-elastic material model. Finally the car body model is a frequency dependent UCI-ROM from a full car body finite element model. It is shown that the UCI-ROM approach efficiently can be used for parametric studies on a substructure level. The results suggest that the performed reorientation of the rubber bushings can alter, with orders of magnitude, the energy flow into the car.
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| 4. |
- Östberg, Martin, et al.
(författare)
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A study of the influence of rubber bushings on the audible frequency behaviour of a truck damper
- 2014
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Ingår i: International Journal of Heavy Vehicle Systems. - 1744-232X. ; 21:4, s. 281-294
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Tidskriftsartikel (refereegranskat)abstract
- The audible frequency range behaviour of a truck damper element, connected to surrounding structures by means of rubber bushings, is investigated, applying a mixed measurement/modelling procedure. The damper element properties are retrieved through an experimental procedure, while the rubber bushings are modelled using a finite element formulation including a realistic fractional derivative visco-elastic rubber model. Focus is on the influence of the subpart properties on the overall dynamic behaviour. It is found that, in the audible frequency range studied, similar to 100-1000 Hz, an accurate model of the rubber bushings plays an important role, while the level of detail in the description of the dynamical behaviour of the damper element itself is less crucial, contributing mainly with its lumped mass; these results aid in the development of new, quiet vehicles.
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| 5. |
- Östberg, Martin, et al.
(författare)
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Dynamic stiffness of hollowed cylindrical rubber vibration isolators - The wave-guide solution
- 2013
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 50:10, s. 1791-1811
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Tidskriftsartikel (refereegranskat)abstract
- The dynamic stiffness of hollowed cylindrical vibration isolators using a wave-guide modelling approach is given. The isolators consist of rubber and metal elements in series. The boundary conditions at the lateral and radial surfaces of each rubber component are locally non-mixed and simultaneously satisfied by using the modes corresponding to the dispersion relation for axial waves in infinite hollow cylinders while the metal plates are assumed rigid, following Newton's second law. The modes of the rubber elements exactly satisfy the stress free boundary conditions at the curved radial boundaries, while the displacement conditions on the flat cylinder ends are satisfied in mean by a mode matching approach. The rubber is modelled as nearly incompressible with deviatoric visco-elasticity based on a fractional derivative, standard linear solid. The stiffness is found to depend strongly on frequency, displaying resonances and anti-resonances. Further, results indicate a great potential for optimising vibration isolators of the studied kind. By choosing appropriate combinations of metal plates and rubber elements, the dynamic transfer stiffness in higher frequency bands can be suppressed to be magnitudes lower than the static stiffness, a highly sought feature in vibration isolators. Finally, simplified models including mass-spring systems and the long rod theory are implemented and compared to the derived formulation.
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| 6. |
- Östberg, Martin, 1982-
(författare)
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Modelling tools for quieter vehicles : Waves in poro– and visco–elastic continua
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- New modelling tools intended to contribute to the development of components for quieter vehicles are developed. The tools are based on continuum models for wave propagation in poro– and visco–elastic media. By using geometric attributes of the studied components, the computational cost may be radically decreased compared to traditional methods. By assigning known analytical functions for one or two of the spatial directions, the spatial dimension of the remaining numerical problem is reduced. This reduction of spatial dimensions is performed in two di↵erent ways. The first one treats wave propagation in infinitely extended homogeneous and hollowed cylindrical rods, or wave guides, consisting of visco–elastic media. The wave solutions obtained are then used to model rubber vibration isolators of finite length by mode–matching the fields to the radial boundary conditions of interest. The second one is a method for modelling rotationally symmetric multilayered structures consisting of poro–elastic, elastic and fluid domains. By using a harmonic expansion for the azimuthal spatial dependence, the original three–dimensional problem is split up into several, much smaller, two– dimensional ones, radically decreasing the computational load.Moreover, using a mixed measurement/modelling approach, the audible frequency range characteristics of a viscous damper from a truck is studied, illustrating the influence of the rubber bushings by which it is attached to surrounding structures.The modelling approaches presented in this thesis are intended as tools aiding the design process of new vehicles, enabling new technology striving for more sustainable vehicle concepts. More specifically, the tools aim to improve the modelling of sound and vibration properties which are often penalised when seeking new, more sustainable vehicle designs.
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| 7. |
- Östberg, Martin
(författare)
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Waves in elastic and poro-elastic cylinders with spatially varying anisotropy
- 2012
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Ingår i: Proceedings Of International Conference On Noise And Vibration Engineering (ISMA2012) / International Conference On Uncertainty In Structural Dynamics (USD2012). - 9789073802896 ; , s. 4193-4200
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Konferensbidrag (refereegranskat)abstract
- A modelling approach for studying waves in elastic and poro-elastic cylinders with spatially varying anisotropy is proposed. The formulation utilizes a spatial Fourier expansion for the azimuthal angle is used for the Hooke's tensor and the dependent variables. This causes the orthogonality of the modes to break down, and the modes will, sometimes to a very high degree, spread. The special case of anisotropic media having principal directions coinciding with a Cartesian coordinate system is studied, and the degree of mode spreading is discussed.
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| 8. |
- Östberg, Martin, et al.
(författare)
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Weak forms for modelling of rotationally symmetric, multilayered structures, including anisotropic poro-elastic media
- 2012
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Ingår i: International Journal for Numerical Methods in Engineering. - : John Wiley & Sons. - 0029-5981 .- 1097-0207. ; 90:8, s. 1035-1052
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Tidskriftsartikel (refereegranskat)abstract
- A weak form of the anisotropic Biot's equation represented in a cylindrical coordinate system using a spatial Fourier expansion in the circumferential direction is presented. The original three dimensional Cartesian anisotropic weak formulation is rewritten in an arbitrary orthogonal curvilinear basis. Introducing a cylindrical coordinate system and expanding the circumferential wave propagation in terms of orthogonal harmonic functions, the original, geometrically rotationally symmetric three dimensional boundary value problem, is decomposed into independent two-dimensional problems, one for each harmonic function. Using a minimum number of dependent variables, pore pressure and frame displacement, a computationally efficient procedure for vibro-acoustic finite element modelling of rotationally symmetric three-dimensional multilayered structures including anisotropic porous elastic materials is thus obtained. By numerical simulations, this method is compared with, and the correctness is verified against, a full three-dimensional Cartesian coordinate system finite element model.
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| 9. |
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| 10. |
- Östberg, Martin, et al.
(författare)
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Transverse, tilting and cross-coupling stiffness of cylindrical rubber isolators in the audible frequency range-The wave-guide solution
- 2011
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Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 330:13, s. 3222-3244
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Tidskriftsartikel (refereegranskat)abstract
- Audio-frequency wave-guide models for antisymmetric dynamic stiffness of arbitrary long elastomer cylinders are presented. The locally non-mixed boundary conditions at the lateral and radial surfaces are simultaneously satisfied by using the modes corresponding to the dispersion relation for axial waves in cylinders satisfying the stress free boundary conditions at the curved radial boundaries, while the displacement conditions on the flat cylinder ends are satisfied by mode matching. The elastomer is modelled as nearly incompressible with deviatoric visco-elasticity based on a fractional derivative, standard linear solid embodying a Mittag-Leffler relaxation kernel, the main advantage being the minimum parameter number required to successfully model the material properties over a broad frequency band. The stiffness is found to depend strongly on frequency: displaying resonances and anti-resonances. The method is compared with and verified against finite element models. In addition, comparison to thin beam theories, i.e. Euler and Timoschenko theory and a simple shear model, is presented, illustrating the limitations of these models.
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