| 1. |
- Broman, Göran, et al.
(författare)
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Instability of water jet : Aerodynamically induced acoustic and capillary waves
- 2012
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Ingår i: Acoustical Physics. - : MAIK NAUKA/INTERPERIODICA/SPRINGER. - 1063-7710 .- 1562-6865. ; 58:5, s. 537-541
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Tidskriftsartikel (refereegranskat)abstract
- High-speed water jet cutting has important industrial applications. To further improve the cutting performance it is critical to understand the theory behind the onset of instability of the jet. In this paper, instability of a water jet flowing out from a nozzle into ambient air is studied. Capillary forces and compressibility of the liquid caused by gas bubbles are taken into account, since these factors have shown to be important in previous experimental studies. A new dispersion equation, generalizing the analogous Rayleigh equation, is derived. It is shown how instability develops because of aerodynamic forces that appear at the streamlining of an initial irregularity of the equilibrium shape of the cross-section of the jet and how instability increases with increased concentration of gas bubbles. It is also shown how resonance phenomena are responsible for strong instability. On the basis of the theoretical explanations given, conditions for stable operation are indicated.
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| 2. |
- Broman, Göran, et al.
(författare)
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Submerged Landau jet : exact solutions, their meaning and application
- 2010
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Ingår i: Physics Uspekhi. - : TURPION LTD. - 1063-7869 .- 1468-4780. ; 53:1, s. 91-98
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Forskningsöversikt (refereegranskat)abstract
- Exact hydrodynamic solutions generalizing the Landau submerged jet solution are reviewed. It is shown how exact inviscid solutions can be obtained and how boundary layer viscosity can be included by introducing parabolic coordinates. The use of exact solutions in applied hydrodynamics and acoustics is discussed. A historical perspective on the discovery of a class of exact solutions and on the analysis of their physical meaning is presented.
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| 3. |
- Demin, I.Yu., et al.
(författare)
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The numerical simulation of propagation of intensive acoustic noise
- 2013
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Ingår i: Proceedings of Meetings on Acoustics. - San Francisco : ASA. - 1939-800X.
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Konferensbidrag (refereegranskat)abstract
- The propagation of intensive acoustic noise is of fundamental interest in nonlinear acoustics. Some of the simplest models describing such phenomena are generalized Burgers’ equations for finite amplitude sound waves. An important problem in this field is to find the wave’s behavior far from the emitting source for stochastic initial waveforms. The method of numerical solution of generalized Burgers equation proposed is step-by-step calculation supported on using Fast Fourier Transform of the considered signal. The general idea is to keep only Fourier image of concerned signal and update it recursively (in space). For simulating the wave evolution we used 4096 (212) point realizations and took averaging over 1000 realizations. Also the object of the present study is a numerical analysis of the spectral and bispectral functions of the intense random signals propagating in nondispersive nonlinear media. The possibility of recovering the input spectrum from the measured spectrum and bispectrum at the output of the nonlinear medium is discusses. The analytical estimations are supported by numerical simulation. For two different types of primary spectrum evolution of jet noise were numerically simulates at a short distance and assayed bispectrum and a spectrum analysis of the signals.
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| 4. |
- Dubkov, Alexander, et al.
(författare)
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Probability characteristics of nonlinear dynamical systems driven by delta -pulse noise
- 2016
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - : American Physical Society. - 1539-3755 .- 1550-2376. ; 93:6
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Tidskriftsartikel (refereegranskat)abstract
- For a nonlinear dynamical system described by the first-order differential equation with Poisson white noise having exponentially distributed amplitudes of δ pulses, some exact results for the stationary probability density function are derived from the Kolmogorov-Feller equation using the inverse differential operator. Specifically, we examine the "effect of normalization" of non-Gaussian noise by a linear system and the steady-state probability density function of particle velocity in the medium with Coulomb friction. Next, the general formulas for the probability distribution of the system perturbed by a non-Poisson δ-pulse train are derived using an analysis of system trajectories between stimuli. As an example, overdamped particle motion in the bistable quadratic-cubic potential under the action of the periodic δ-pulse train is analyzed in detail. The probability density function and the mean value of the particle position together with average characteristics of the first switching time from one stable state to another are found in the framework of the fast relaxation approximation. © 2016 American Physical Society.
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| 5. |
- Dvoesherstov, M.Yu., et al.
(författare)
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Numerical and experimental analysis of the parameters of an electroacoustic thin-film microwave resonator
- 2013
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Ingår i: Acoustical Physics. - : Pleiades Publishing, Ltd.. - 1063-7710 .- 1562-6865. ; 59:5, s. 513-520
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Tidskriftsartikel (refereegranskat)abstract
- The results of numerical and experimental analysis of the parameters of a singlefrequency micro wave thinfilm electroacoustic resonator based on an (0001)AlN piezofilm with an acoustic reflector operat ing at a frequency of 10 GHz are presented. The effect of the reflector design on the resonator characteristics is considered. Using the modified Butterworth–Van Dyke model, it was shown that the ohmic resistance of electrodes and entrance paths substantially decreases the Qfactor at the resonance frequency of series and the acoustic losses in the resonator deteriorate the Qfactor at the parallel resonance frequency
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| 6. |
- Enflo, Bengt, et al.
(författare)
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Nonlinear standing waves in a closed tub
- 2002
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Konferensbidrag (refereegranskat)abstract
- Simplified nonlinear evolution equations describing nonsteady-state forced vibrations in an acoustic resonator having one closed end and the other end periodically oscillating are derived. An approach is used based on a nonlinear functional equation. This approach is shown to be equivalent to the version of the successive approximation method developed in 1964 by Chester. It is explained how the acoustic field in the cavity is described as a sum of counterpropagating waves with no cross-interaction. The nonlinear Q-factor and the nonlinear frequency response of the resonator are calculated for steady-state oscillations of both inviscid and dissipative media. The general expression for the mean intensity of the acoustic wave in terms of the characteristic value of a Mathieu function is derived. Some results from a perturbation calculation of the wave profile are given.
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| 7. |
- Enflo, Bengt, et al.
(författare)
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Nonlinear Standing Waves in a Layer Excited by the Periodic Motion of its Boundary
- 2002
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Konferensbidrag (refereegranskat)abstract
- Simplified nonlinear evolution equations describing nonsteady-state forced vibrations in an acoustic resonator having one closed end and the other end periodically oscillating are derived. An approach is used based on a nonlinear functional equation. This approach is shown to be equivalent to the version of the successive approximation method developed in 1964 by Chester. It is explained how the acoustic field in the cavity is described as a sum of counterpropagating waves with no cross-interaction. The nonlinear Q-factor and the nonlinear frequency response of the resonator are calculated for steady-state oscillations of both inviscid and dissipative media. The general expression for the mean intensity of the acoustic wave in terms of the characteristic value of a Mathieu function is derived. The process of development of a standing wave is described analytically for three different types of periodic motion of the wall: harmonic excitation, sawtooth-shaped motion and "inverse saw motion".
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| 8. |
- Enflo, Bengt Olof, et al.
(författare)
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Resonant properties of a nonlinear dissipative layer excited by a vibrating boundary : Q-factor and frequency response
- 2005
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Ingår i: Journal of the Acoustical Society of America. - MELVILLE : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 117:2, s. 601-612
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Tidskriftsartikel (refereegranskat)abstract
- Simplified nonlinear evolution equations describing non-steady-state forced vibrations in an acoustic resonator having one closed end and the other end periodically oscillating are derived. An approach based on a nonlinear functional equation is used. The nonlinear Q-factor and the nonlinear frequency response of the resonator are calculated for steady-state oscillations of both inviscid and dissipative media. The general expression for the mean intensity of the acoustic wave in terms of the characteristic value of a Mathieu function is derived. The process of development of a standing wave is described analytically on the base of exact nonlinear solutions for different laws of periodic motion of the wall. For harmonic excitation the wave profiles are described by Mathieu functions, and their mean energy characteristics by the corresponding eigenvalues. The sawtooth-shaped motion of the boundary leads to a similar process of evolution of the profile, but the solution has a very simple form. Some possibilities to enhance the Q-factor of a nonlinear system by suppression of nonlinear energy losses are discussed.
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| 9. |
- Enflo, Bengt O., et al.
(författare)
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Standing and propagating waves in cubically nonlinear media
- 2006
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Ingår i: Mathematical Modeling of Wave Phenomena. - MELVILLE, NY : AMER INST PHYSICS. - 0735403252 ; , s. 187-195, s. 187-195
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Konferensbidrag (refereegranskat)abstract
- The paper has three parts. In the first part a cubically nonlinear equation is derived for a transverse finite-amplitude wave in an isotropic solid. The cubic nonlinearity is expressed in terms of elastic constants. In the second part a simplified approach for a resonator filled by a cubically nonlinear medium results in functional equations. The frequency response shows the dependence of the amplitude of the resonance on the difference between one of the resonator's eigenfrequencies and the driving frequency. The frequency response curves are plotted for different values of the dissipation and differ very much for quadratic and cubic nonlinearities. In the third part a propagating N-wave is studied, which fulfils a modified Burgers' equation with a cubic nonlinearity. Approximate solutions to this equation are found for new parts of the wave profile.
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| 10. |
- Gazizov, Rafail, et al.
(författare)
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Effect of resonant absorption in viscous and dry vibrating contact : Mathematical models and theory connected with slow dynamics and friction welding
- 2014
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Ingår i: Communications in nonlinear science & numerical simulation. - : Elsevier. - 1007-5704 .- 1878-7274. ; 19:2, s. 337-344
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Tidskriftsartikel (refereegranskat)abstract
- Process of heating of thin layer located between two vibrating surfaces is studied. Energy loss goes on due to viscous or dry friction. Optimal quantities of shear viscosity and friction corresponding to maximum energy loss are determined. Resonant behavior of loss must be taken into account in the description of "slow dynamics" of rocks and materials exposed to high-intensity seismic or acoustic irradiation as well as in various technologies. Bonding of materials by linear friction welding, widely used in propulsion engineering, can exemplify such a technology.
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