| 1. |
- Fällström, Karl-Evert, et al.
(författare)
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Transient bending waves in plates studied by hologram interferometry
- 1989
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Ingår i: Experimental mechanics. - 0014-4851 .- 1741-2765. ; 29:4, s. 378-387
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Wåhlin, Anders, et al.
(författare)
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Wave propagation in plates studied by pulsed hologram interferometry
- 1989
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Ingår i: The Sixth Meeting in Israel on Optical Engineering. - Bellingham, Wash : SPIE - International Society for Optical Engineering. ; , s. 146-53
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 3. |
- Sunnersjö, Staffan, 1948, et al.
(författare)
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Hydrodynamic inertia and damping of ship hull vibrations
- 1988
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Ingår i: Transactions of the Royal Institute of Naval Architects. - 0035-8967. ; 130, s. 107-117
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Tidskriftsartikel (refereegranskat)abstract
- The entrained water plays an important role in ship hull vibrations. The classic Lewis method for calculation of hydrodynamic added mass has some inherent shortcomings that can result in insufficient accuracy, particularly for higher order modes. This is essentially due to the fact that the Lewis method uses a diagonal mass matrix that is dependent on the mode of vibration, while the physical reality is more accurately represented by a mode-independent, full mass matrix. Such full mass matrices can be calculated with Finite Volume or Source- Sink methods, which, however, require extensive computer calculations with detailed input data. A method is presented with which the Lewis transform can be used to determine a full mass matrix and gives very good agreement with Finite Volume calculations for a test case on a small ship. The Finite Volume calculations have also been used to study damping …
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| 4. |
- Boström, Anders E, 1951
(författare)
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Scattering of stationary acoustic waves by an elastic obstacle immersed in a fluid
- 1980
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Ingår i: Journal of the Acoustical Society of America. - 1520-8524 .- 0001-4966. ; 67, s. 390-398
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Tidskriftsartikel (refereegranskat)abstract
- The scattering of stationary acoustic waves by a bounded elastic obstacle in an inviscid fluid is considered. The developed formalism is an extension of the transition matrix method, which has been given by Waterman for acoustic, electromagnetic, and elastic scattering. In fact the problem at hand is more complex than the elastic case, something which is apparent in the solution. It is possible to obtain some different forms for the transition matrix, depending upon whether the Rayleigh hypothesis enters or not. It is worthy of notice that the more general formalism, i.e., the one not assuming the Rayleigh hypothesis, is also the more efficient numerically. Numerical results are given for spheroids and an object resembling the number "8".
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| 5. |
- Boström, Anders E, 1951
(författare)
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Transmission and reflection of acoustic waves by an obstacle in a waveguide
- 1980
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Ingår i: Wave Motion. - 0165-2125. ; 2, s. 167-184
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Tidskriftsartikel (refereegranskat)abstract
- By an extension of the null field approach introduced by Waterman the transmission and reflection of acoustic waves by an obstacle in a waveguide are considered. The waveguide is assumed to have a constant cross section but otherwise the geometry is left arbitrary. The scattered field is obtained as a complicated mode sum containing the transition matrix of the obstacle, the reflection matrix of the waveguide wall, and the transformation relations between the cylindrical and spherical basis functions. For a circular cross section of the waveguide relatively explicit expressions are given for the transmission and reflection coefficients, and numerical results are shown for spherical and spheroidal obstacles in rotaionally symmetric configurations. Several natural extensions of the present results are finally recognized.
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| 6. |
- Sandberg, Göran
(författare)
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Finite Element Modelling of Fluid-Structure Interaction
- 1986. - 1
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The dynamic interaction between non-viscid, compressible fluid and an elastic structure is studied. Finte element formulations, using the weighted residual method, are derived. Different primary variables in the fluid domain are used and different source functions are considered.When a potential field is used, the dynamic interaction between fluid and structure yields nonsymmetric matrices. I addition to these, new symmetric formulations for transient analysis are presented.Some nonlinear fluid behaviour is taken into consideration. Applications to a cavitating fluid due to elastic wave propagation are described.Numerical experiments show good agreement with what could be expected from a physical point of view. The nonlinear formulation shows good agreement with analytical results.
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| 7. |
- Yang, Qixing, et al.
(författare)
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Erosion of referactory during gas injection : a cavitation based model
- 1989
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Ingår i: Scaninject V. - : MEFOS. ; , s. 259-289
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Konferensbidrag (refereegranskat)abstract
- The problem of tuyere refractory wear has been studied in an air--water model using a 4 mm diamter tuyere. Erosion tests, with boric acid (H sub 3 BO sub 3 ) disks as refactory simulators, and measurements of back-attack frequency were carried out. The erosion pattern shows two distinct features: isolated elliptical pits and a continuous irregular shear wear pattern. The influence on these features of the surface hardness and gas flow rate was investigated. 24 ref.--
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| 8. |
- Traunmüller, Hartmut
(författare)
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Phase vowels
- 1987
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Ingår i: The psychophysics of speech perception. - Dordrecht : Nijhoff in cooperation with NATO Scientific Affairs Division. - 902473536X ; , s. 377-384
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 9. |
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| 10. |
- Rossing, T D, et al.
(författare)
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Acoustic comparison of soprano solo and choir singing.
- 1987
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 82:3, s. 830-836
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Tidskriftsartikel (refereegranskat)abstract
- Five soprano singers were recorded while singing similar texts in both choir and solo modes of performance. A comparison of long-term-average spectra of similar passages in both modes indicates that subjects used different tactics to achieve somewhat higher concentrations of energy in the 2- to 4-kHz range when singing in the solo mode. It is likely that this effect resulted, at least in part, from a slight change of the voice source from choir to solo singing. The subjects used slightly more vibrato when singing in the solo mode.
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