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  • 1. Forsberg, L.
    et al.
    Wåhlin, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Transient waves in a water-filled elliptical cavity studied using holographic interferometry1990In: Experimental mechanics : 9th International conference : Papers, Lyngby: Technical University of Denmark , 1990Conference paper (Refereed)
  • 2. Fällström, Karl-Evert
    et al.
    Gustavsson, Håkan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Molin, Nils-Erik
    Wåhlin, Anders
    Transient bending waves in plates studied by hologram interferometry1989In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 29, no 4, p. 378-387Article in journal (Refereed)
    Abstract [en]

    Propagating bending waves are studied in plates made of aluminum and wood. The waves are generated by the impact of a ballistic pendulum. Hologram interferometry, with a double pulsed ruby laser as the light source, is used to record the out of plane motion of the waves. Elliptic-like fringes visualize differences in wave speed for different directions in the anisotropic plate and circular ones are obtained for the isotropic plate. The experimental data for the isotropic plate compare favorably with analytical results derived from the Kirchhoff-plate equation with a point impact of finite duration. A similarity variable is found when starting conditions are modeled as a Dirac pulse in space and time, that brings new understanding to the importance of specific parameters for wave propagation in plates. A formal solution is obtained for a point force with an arbitrary time dependence. For times much larger than the contact time, the plate deflection is shown to be identical to that from a Dirac pulse applied at the mean contact time. A method for determining material parameters, and the mean contact time, from the interferograms is hence developed.

  • 3. Fällström, Karl-Evert
    et al.
    Molin, Nils-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Olofsson, Kenneth
    Luleå tekniska universitet.
    Schedin, Staffan
    Luleå tekniska universitet.
    Wåhlin, Anders
    Mechanical and thermal effects in a steel plate impacted by a focused laser pulse1997In: Nondestructive Testing and Evaluation, ISSN 1058-9759, E-ISSN 1477-2671, Vol. 13, no 5, p. 293-307Article in journal (Refereed)
    Abstract [en]

    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.

  • 4. Fällström, Karl-Evert
    et al.
    Olofsson, Kenneth
    Luleå tekniska universitet.
    Sarady, Istvan
    Wåhlin, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Generating and recording transient bending waves in plates by pulsed lasers1996In: Experimental techniques (Westport, Conn.), ISSN 0732-8818, E-ISSN 1747-1567, Vol. 20, no 1, p. 15-19Article in journal (Refereed)
    Abstract [en]

    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

  • 5. Fällström, Karl-Evert
    et al.
    Wåhlin, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Generating and recording transient bending waves in plates with a double pulsed laser1993In: 16th Congress of the International Commission for Optics :: optics as a key to high technology : 9-13, August, 1993, Budapest Convention Centre, Budapest, Hungary / [ed] Ákos Gy, Bellingham, Wash.: SPIE - International Society for Optical Engineering, 1993, p. 984-985Conference paper (Refereed)
  • 6. Jansson, E
    et al.
    Moral, Alonso
    Frydén, L.
    Niewczyk, B.
    Molin, Nils-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Runnemalm, Anna
    Saldner, Henrik
    Wåhlin, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    On the acoustical function of the violin1997In: 25. Congresso nazionale : Perugia, 21-23 maggio 1997 : atti / Associazione italiana di acustica, 1997Conference paper (Refereed)
  • 7. Li, X.
    et al.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wåhlin, Anders
    Visualisation of transient waves in air by tomography and pulsed TV holography1998In: International Conference on Optical Methods and Data Processing in Heat and Fluid Flow: 16 - 17 April 1998, City University, London, UK, Bury St. Edmunds: Institution of Mechanical Engineers, 1998Conference paper (Refereed)
  • 8.
    Li, Xide
    et al.
    University of Science and Technology of China.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wåhlin, Anders
    Schedin, Staffan
    Luleå tekniska universitet.
    Pulsed TV holography and tomography for the study of transient waves in air1999In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 31, no 1, p. 23-32Article in journal (Refereed)
    Abstract [en]

    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.

  • 9.
    Mattsson, Roger
    et al.
    Luleå tekniska universitet.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wåhlin, Anders
    Laser ignition of premixed gases studied by pulsed TV holography2003In: Speckle metrology 2003: proceedings ; 18 - 20 June 2003, Trondheim, Norway / [ed] Kay Gastinger, Bellingham, Wash: SPIE - International Society for Optical Engineering, 2003, p. 285-290Conference paper (Refereed)
    Abstract [en]

    Pulsed TV holography is an all-electronic version of pulsed holographic interferometry. Such a system was used to study ignition of pre-mixed flammable gases. The object was recorded in its undisturbed and disturbed state followed by an evaluation of the changes in refractive index field between those two states. The essential components of the set-up are an injection seeded, twin cavity double pulsed Nd:YAG laser and a CCD camera. A focused laser pulse from the same laser that was used for the recording of the digital hologram initiated the ignition of the pre-mixed gas. Results from the recordings show the ignition process. From the experimental phase maps the refractive index of the gas mixture could be determined. This method makes it possible to determine the proportion of components in a pre-mixed flammable gas in situ

  • 10.
    Mattsson, Roger
    et al.
    Luleå tekniska universitet.
    Kupiainen, M.
    Kungliga tekniska högskolan, KTH.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wåhlin, Anders
    Carlsson, T.E.
    Swedish Defence Research Agency, FOI.
    Fureby, C.
    Swedish Defence Research Agency, FOI.
    Pulsed TV holography and schlieren studies, and large eddy simulations of a turbulent jet diffusion flame2004In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 139, no 1-2, p. 1-15Article in journal (Refereed)
    Abstract [en]

    In the search for an improved understanding of jet-flame dynamics we here compare predictions from large-eddy simulations (LES) and measurements using schlieren and holographic interferometry of a round turbulent jet diffusion flame. The studies concern a turbulent propane-air (C3H 8-O2/N2) diffusion flame under ambient conditions at a Reynolds number of Re=104. The interferometric measurements were performed with an all-electronic method, pulsed TV holography, using a pulsed laser and a fast charge coupled device (CCD) camera. The LES calculations use the probability density function (PDF) flamelet approach with a beta function as the probability density function, whereas the subgrid turbulence is modeled with a one-equation eddy viscosity model. In order to validate the LES model quantitative comparisons of first-order statistical moments of the velocity were first made with available data for nonreactive jets. The LES model captures the statistics well. The next step in the validation process concerns comparing the jet-flame development between LES and the schlieren and pulsed TV holography data. To this end the results of the LES calculations were used to simulate instantaneous interference patterns using ray tracing. The LES model describes the overall behavior of the flame successfully

  • 11.
    Molin, Nils-Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Fällström, Karl-Evert
    Wåhlin, Anders
    On Bending Wave Propagation and Thermal Deformation of Laser Impacted Plates1995In: Proceedings of the International Symposium on Advanced Technology in Experimental Mechanics '95: ATEM '95, 1995Conference paper (Refereed)
  • 12.
    Molin, Nils-Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wåhlin, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Jansson, Erik V
    Kungliga tekniska högskolan, KTH.
    Transient wave response of the violin body revisited1991In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 90, no 4, p. 2192-2195Article in journal (Refereed)
    Abstract [en]

    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

  • 13.
    Molin, Nils-Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wåhlin, Anders
    Jansson, E.V.
    Luleå tekniska universitet.
    Transient wave response of the violin body1990In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 88, no 5, p. 2479-2481Article in journal (Refereed)
    Abstract [en]

    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

  • 14.
    Schedin, Staffan
    et al.
    Luleå tekniska universitet.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wåhlin, Anders
    Shock waves in an elliptical cavity with varying height1997In: Shock Waves, ISSN 0938-1287, E-ISSN 1432-2153, Vol. 7, no 6, p. 343-350Article in journal (Refereed)
    Abstract [en]

    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.

  • 15. Schedin, Staffan
    et al.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wåhlin, Anders
    Visualization of transient acoustic fields generated by schock loaded plates1995In: Proceedings of the 15th International Congress on Acoustics: Trondheim, Norway, 26-30 June 1995, Trondhjeim: Tapir Akademisk Forlag, 1995Conference paper (Refereed)
  • 16.
    Schedin, Staffan
    et al.
    Luleå tekniska universitet.
    Wåhlin, Anders
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Transient acoustic near field in air generated by impacted plates1996In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 99, no 2, p. 700-705Article in journal (Refereed)
    Abstract [en]

    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

  • 17. Urgela, S.
    et al.
    Wåhlin, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Elastic constants of a wooden plates derived from transient bending wave holographic interferograms1997In: Wood research, ISSN 1336-4561, Vol. 42, no 3, p. 23-36Article in journal (Refereed)
  • 18.
    Wåhlin, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Bending waves in plates generated by mechanical and laser pulse impact1993In: Euromech 306 Colloquium Contact Impact / [ed] M. Okrouhlík, 1993Conference paper (Refereed)
  • 19.
    Wåhlin, Anders
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Finnström, Marie
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mekanikundervisning i smågrupper2001In: Kvalitetskonferens 2001, Högskoleverket , 2001Conference paper (Other academic)
  • 20.
    Wåhlin, Anders
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Fällström, Karl-Evert
    Gustavsson, Håkan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Molin, Nils-Erik
    Wave propagation in plates studied by pulsed hologram interferometry1989In: The Sixth Meeting in Israel on Optical Engineering: proceedings : 19-21 December 1988, Tel Aviv, Israel / [ed] Rami Finkler; Joseph Shamir, Bellingham, Wash: SPIE - International Society for Optical Engineering, 1989, p. 146-53Conference paper (Refereed)
    Abstract [en]

    Isotropic and non-isotropic plates are impacted by a ballistic pendulum. The bending waves that are generated are studied with holographic interferometry using a double pulsed ruby laser as light source. The pulse shape changes with time because of the dispersivity of the waves. Initially the fringe pattern in the isotropic case is cylindrically symmetric and determined from an initial value problem. Later, when the waves have reached the plate rim, in- and outgoing waves gradually develop fringe patterns which in the end will be a combination of eigenmodes of the plate. A solution to the corresponding Kirchhoff plate equation is presented, which in the special case when the impact is modelled as a Dirac-pulse in space and time, is shown to depend only of the distance to the impact point divided by the square root of the time after impact and a parameter containing plate parameters. From the slope of the central deflection material parameters can be determined. Another solution, assuming a finite impact time, is shown to agree better with experiments. Results from investigations of non-isotropic materials are also presented.

  • 21. Wåhlin, Anders
    et al.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Visualization of structure borne sound generated by transient bending waves1994In: Recent advances in experimental mechanics: proceedings of the 10th International Conference on Experimental Mechanics, Lisbon, Portugal, 18 - 22 July 1994 / [ed] J.F. Silva Gomes, Rotterdam: Balkema Publishers, A.A. / Taylor & Francis The Netherlands , 1994Conference paper (Refereed)
  • 22.
    Wåhlin, Anders
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Molin, Nils-Erik
    On structure-borne sound: experiments showing the initial transient acoustic wave field generated by an impacted plate1994In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 96, no 5, p. 2791-2797Article in journal (Refereed)
    Abstract [en]

    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.

  • 23.
    Wåhlin, Anders
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Olofsson, Kenneth
    Luleå tekniska universitet.
    Visualization of acoustic waves by holographic interferometry1990In: Proceedings / Nordic Acoustical Meeting 90 - NAM 90: June 11-13, 1990 Luleå, Sweden / [ed] Ulrik Sundbäck, Luleå: CENTEK , 1990, p. 415-420Conference paper (Refereed)
1 - 23 of 23
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