| 1. |
- Benckert, Lars, et al.
(författare)
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Fresnel diffraction of a Gaussian laser beam by polished metal cylinders
- 1990
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 29:3, s. 416-421
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Tidskriftsartikel (refereegranskat)abstract
- A laser beam touching the periphery of a polished cylinder is subjected to both diffraction and reflection. Inthe area where diffracted light and reflected light interact the resulting intensity distribution differs from thepattern predicted by diffraction theory for a sharp edge. The difference increases with cylinder radius. Inthis paper it is shown that a good description of the resulting intensity pattern is obtained by adding thereflected light amplitude to the diffracted amplitude as predicted by the Fresnel-Kirchhoff theory for a sharpedge.
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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. |
- Isaksson, Anna, 1970-, et al.
(författare)
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Influence of enclosed air on vibration modes of a shell structure
- 1995
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 187:3, s. 451-466
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Tidskriftsartikel (refereegranskat)abstract
- Experiments show that enclosed air in a thin walled structure affects some modes of vibration significantly. Air coupling between vibrating sides of the structure cannot (always) be neglected and frequencies cannot be predicted if calculations are performed as if in a vacuum. As a first attempt to include the enclosed air in a FE model of a violin body, the elastic properties of the air are modelled as a set of one dimensional non-interacting elastic members (columns of air) connecting opposite sides of the orthotropic shell structure. This admittedly oversimplified (but easy to formulate) model must be used with great care, since it neglects the three-dimensional wave behaviour of the enclosed air. A lower limit of allowed frequencies is that which corresponds to a wavelength in air which is much greater than a characteristic length of the object. For the violin this lower limit is less than about 600 Hz. Optical modal analysis of the real, physical, violin model has been performed by using electronic holography. Calculated modes of vibration are compared with experimental ones. For the lowest eigenmodes a good agreement between measured and calculated frequencies is reached despite the simple air model used. Modal shapes remain surprisingly unaffected. For some engineering calculations the simple one-dimensional model might be used.
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| 4. |
- 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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| 5. |
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| 6. |
- Jansson, Erik V., et al.
(författare)
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On eigenmodes of the violin—Electronic holography and admittance measurements
- 1994
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 95:2, s. 1100-1105
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Tidskriftsartikel (refereegranskat)abstract
- The present experimental investigation, using recently assembled advanced electro-optical equipment for vibration analysis of three violins, was conducted to seek answers to three questions. A general or global question: Which parts of the violin body are vibrating the most? And two questions related to tonal quality: Are basic low-frequency vibration modes of a musically superior instrument different from those of an inferior violin? Can some special vibration properties be found to support the ``bridge hill?'' Optically obtained vibration modes were recorded as well as frequency responses in the form of admittance measurements. The investigation showed that the vibration modes found earlier are representative both for the inferior violin and the musically superior instruments, although discrepancies can be seen, both in eigenmode shapes and admittance responses. The experimental results are also in quite good agreement with published results of the modal analysis of a violin. Further, the experimental results indicate that the transversal vibrations are mainly within the plates, but at low frequencies, the vibrations of the edges and of the ribs can be large and in-plane as well as transversal. At higher frequencies, the transversal vibration amplitudes are small at the plate edges and larger inside. The top plate tends to have the largest amplitude of vibrations. In the 2.5-kHz range the violin with the most clear ``bridge hill'' tends to have the largest vibrations of the plates.
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| 7. |
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| 8. |
- Mohan, N. Krishna, et al.
(författare)
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Combined phase stepping and sinusoidal phase modulation applied to de-sensitized TV holography
- 1996
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Ingår i: Measurement science and technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 7, s. 712-715
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Tidskriftsartikel (refereegranskat)abstract
- Many TV holography techniques use phase stepping between frames. In vibration studies, sinusoidal phase modulation extends the use of these techniques. A simple technique is presented to combine phase stepping and phase modulation (bias vibration) on a single mirror. It is applied to a de-sensitized TV holographic (DTV) configuration for quantitative evaluation of the large vibration amplitudes.
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| 9. |
- Mohan, N.K., et al.
(författare)
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Electronic shearography applied to static and vibrating objects
- 1994
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Ingår i: Optics Communications. - : Elsevier BV. - 0030-4018 .- 1873-0310. ; 108:4-6, s. 197-202
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Tidskriftsartikel (refereegranskat)abstract
- An optical shearography configuration is presented which can be used for the measurement of slope change for static and vibrating objects in real time. Displacement and vibration amplitude fields are extracted from the shear data, which is an useful property in noise environments. In a Michelson interferometer set-up the two arms are provided with a phase-shift mirror and a bias modulation mirror to carry out the numerical evaluation of the measured deformation. Experimental results for an edge- clamped aluminium plate are presented
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| 10. |
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