| 1. |
- Fällström, Karl-Evert, et al.
(författare)
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Generating and recording transient bending waves in plates by pulsed lasers
- 1996
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Ingår i: Experimental techniques (Westport, Conn.). - : Springer Science and Business Media LLC. - 0732-8818 .- 1747-1567. ; 20:1, s. 15-19
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Fällström, Karl-Evert, et al.
(författare)
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Mechanical and thermal effects in a steel plate impacted by a focused laser pulse
- 1997
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Ingår i: Nondestructive Testing and Evaluation. - : Informa UK Limited. - 1058-9759 .- 1477-2671. ; 13:5, s. 293-307
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Jansson, E, et al.
(författare)
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On the acoustical function of the violin
- 1997
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Ingår i: 25. Congresso nazionale : Perugia, 21-23 maggio 1997 : atti / Associazione italiana di acustica.
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Konferensbidrag (refereegranskat)
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| 4. |
- Li, Xide, et al.
(författare)
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Pulsed TV holography and tomography for the study of transient waves in air
- 1999
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Ingår i: Optics and Laser Technology. - 0030-3992 .- 1879-2545. ; 31:1, s. 23-32
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Tidskriftsartikel (refereegranskat)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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| 5. |
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| 6. |
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| 7. |
- Schedin, Staffan, et al.
(författare)
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Shock waves in an elliptical cavity with varying height
- 1997
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Ingår i: Shock Waves. - : Springer Science and Business Media LLC. - 0938-1287 .- 1432-2153. ; 7:6, s. 343-350
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Schedin, Staffan, et al.
(författare)
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Transient acoustic near field in air generated by impacted plates
- 1996
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Ingår i: 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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Tidskriftsartikel (refereegranskat)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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