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| 2. |
- Fällström, Karl-Evert, et al.
(author)
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Generating and recording transient bending waves in plates by pulsed lasers
- 1996
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In: Experimental techniques (Westport, Conn.). - : Springer Science and Business Media LLC. - 0732-8818 .- 1747-1567. ; 20:1, s. 15-19
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Journal article (peer-reviewed)abstract
- We have presented a method to generate bending waves in a plate by focusing a Q-switched Nd:YAG-laser pulse on its surface. These waves are recorded by double pulsed hologram interferometry. Evaluation of the interferograms show that the bending wave pattern is very similar to what is predicted by the Kirchhoff plate equation assuming a point impact of infinitesimally short duration. This indicates that a short Nd:YAG-laser pulse may be considered as a Dirac pulse in space and time. Future investigations will be performed with a more powerful and "cleaner" laser to get a higher energy and impulse transfer to the plate thus giving bending waves of larger amplitude. Promising preliminary experiments have also begun using a double pulsed ruby laser both for generating and recording of bending waves.
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| 3. |
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| 4. |
- Fällström, Karl-Evert, et al.
(author)
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Mechanical and thermal effects in a steel plate impacted by a focused laser pulse
- 1997
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In: Nondestructive Testing and Evaluation. - : Informa UK Limited. - 1058-9759 .- 1477-2671. ; 13:5, s. 293-307
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Journal article (peer-reviewed)abstract
- A short laser pulse from a 1 J ruby laser is focused at a steel plate. The effect will be that the material surface at the impact point becomes very rapidly heated. Metal vapour leaves the surface at a very high velocity. That is, both a mechanical impulse and local thermal energy are transferred to the plate. The mechanical impulse creates propagating bending waves in the plate, which in turn creates transient sound waves in the surrounding air. The heated spot at the plate surface creates thermal stresses in the plate which give rise to an out-of-plane deformation of the plate. This deformation is added up to the propagating bending waves. These effects are studied in experiments using pulsed holographic interferometry.
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| 5. |
- Jansson, E, et al.
(author)
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On the acoustical function of the violin
- 1997
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In: 25. Congresso nazionale : Perugia, 21-23 maggio 1997 : atti / Associazione italiana di acustica.
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Conference paper (peer-reviewed)
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| 6. |
- Li, Xide, et al.
(author)
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Pulsed TV holography and tomography for the study of transient waves in air
- 1999
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In: Optics and Laser Technology. - 0030-3992 .- 1879-2545. ; 31:1, s. 23-32
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Journal article (peer-reviewed)abstract
- Transient waves in air are recorded and reconstructed using pulsed TV holography and computerized tomography (CT). Experiments are performed with an electrical discharge between two electrodes as the acoustic wave source. The free space wave-fronts and pressure fields are reconstructed. Waves reflected and diffracted by different obstacles are also recorded and reconstructed in three dimensions. Speckle averaging and image processing techniques are used to get the high quality projection fields needed for CT reconstruction.
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| 7. |
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| 8. |
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| 9. |
- Molin, Nils-Erik, et al.
(author)
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Transient wave response of the violin body
- 1990
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In: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 88:5, s. 2479-2481
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Journal article (peer-reviewed)abstract
- In this investigation, the dispersive, transient wave propagation field of a complete violin excited by a mechanically induced impulse at the top of the bridge is presented. By means of double pulsed holographic interferometry with a ruby laser as light source the propagating wave field is recorded. From presented interferograms, it is seen that initially the top plate acts mainly as a nonsymmetric dipole with centers at the two bridge feet. The back plate is strongly coupled to the motion of the top plate by the sound post and acts more like a monopole. Thus the position of the sound post is crucial to the performance of the instrument. The free edges at the f-holes are very early reached by the dispersive bending waves of high amplitude probably giving a significant contribution to the sound of the violin family instruments
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| 10. |
- Molin, Nils-Erik, et al.
(author)
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Transient wave response of the violin body revisited
- 1991
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In: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 90:4, s. 2192-2195
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Journal article (peer-reviewed)abstract
- In this investigation, the dispersive, transient wave propagation field of the top plate of a complete violin excited by a mechanically induced pulse at the top of the bridge is presented. A similar investigation has previously been made for excitation parallel with the top plate and is now completed with excitation perpendicular to the plate. From presented interferograms, it is seen that the top plate initially deforms in a nonsymmetric two-pole with centers at the two bridge feet. Shortly thereafter the two poles (valleys) are joined into one, but after 0.30 ms the displacement is still nonsymmetric with maximum motion at the bridge foot closest to the excitation point. From the measurements it can be concluded that for excitation parallel with the top plate, the plate between the f-holes acts mainly as a dipole, but with excitation perpendicular the same part acts mainly as a monopole. Thus the excitation of the top plate when playing the violin depends on the angle of the bow in relation to the top plate and should influence the tone character
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| 11. |
- Schedin, Staffan, et al.
(author)
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Shock waves in an elliptical cavity with varying height
- 1997
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In: Shock Waves. - : Springer Science and Business Media LLC. - 0938-1287 .- 1432-2153. ; 7:6, s. 343-350
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Journal article (peer-reviewed)abstract
- Transient shock waves in a confined elliptical chamber are experimentally investigated. Quantitative results of the pressure distribution are obtained for an air-filled cavity. Lower bounding surfaces of different geometrical shapes can be inserted making it possible to get chambers with varying height. An electrical discharge across a pair of electrodes inside the cavity gives rise to the shock waves. Double pulsed holographic interferometry is used to study the propagation and focusing process of the waves. The results are quantitatively evaluated by using the method of two-reference-beam holography. The angular pressure distribution behind the converging wave front is presented for different geometries of an air-filled cavity. The pressure distribution is non-homogeneous but symmetric along the wave front. The pressure level is higher for the geometry where the height of the chamber decreases with the radial distance from the outgoing focus and lower for increasing height of the chamber. In addition, shock waves in a water-filled cavity are studied. In this case qualitative results are obtained.
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| 12. |
- Schedin, Staffan, et al.
(author)
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Transient acoustic near field in air generated by impacted plates
- 1996
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In: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 99:2, s. 700-705
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Journal article (peer-reviewed)abstract
- The transient acoustic near field in air from impacted cantilever plates of two different geometrical shapes and materials is studied using two-reference-beam double-pulsed holographic interferometry. The acoustic waves, observed in two directions simultaneously, are generated by traveling flexural waves in the plates and by the impact process itself. A subsequent phase-stepping procedure is used for quantitative evaluation of the registered two-dimensional projections of the acoustic fields. An interesting observation is the acoustic radiation at the free end of the plate, where sound waves propagate into the air in oblique directions from the plate. At the region right above the free end no acoustic waves are observed. Supersonic flexural waves in the plates generate trace-matched acoustic waves in the surrounding air. Calculations of the corresponding two-dimensional transient acoustic fields are performed. Those are based on an analytical solution of the Kirchhoff plate equation. Calculated results reproduce the character of the observed transient acoustic waves quite well
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| 13. |
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| 14. |
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| 15. |
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| 16. |
- Wåhlin, Anders, et al.
(author)
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On structure-borne sound : experiments showing the initial transient acoustic wave field generated by an impacted plate
- 1994
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In: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 96:5, s. 2791-2797
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Journal article (peer-reviewed)abstract
- The initial propagating transient acoustic field in air generated by an impacted plate is visualized. The transient traveling flexural waves in the plate created by the impact are shown, simultaneously. The experiments are performed using double pulsed holographic interferometry. It is shown that flexural waves in a plate act as a series of traveling acoustic sources. Since the flexural waves in the plate are dispersive the trace matched acoustical waves further away from the impact source propagate at a smaller angle relative to the plate than those closer to the impact. An observer situated close to the plate and away from the impact point will first receive high-frequency components of the sound. A quantitative evaluation of the acoustic field also shows that if there is a transient increase in pressure on one side of the plate there will be a similar decrease on the other side.
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| 17. |
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| 18. |
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