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Jun 2011

Volume 129, Issue 6, pp. EL217-4101

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Two regimes of the parametrically self-exciting ultrasonic standing waves

Zinoviy Goldberg, Iliya Goldberg, and Alexander Goldberg

J. Acoust. Soc. Am. Volume 129, Issue 6, pp. 3483-3489 (2011); (7 pages)

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This paper discusses a nonlinear multi-wave mechanism for the parametrically self-exciting standing waves in a plane-parallel liquid layer driven at one end of the layer. The dependence of this process on the number of parametrically self-exciting waves and the frequency detuning between the frequency “f” of the pump wave and the nearest natural frequency are analyzed. It is found that two regimes with different thresholds are possible. One of them is characterized by self-exciting subharmonic frequencies close to f/2 and the second has a much lower threshold and the presence of a self-exciting subharmonic at a frequency near to the smallest natural frequency. Three dimensionless parameters determining each regime are introduced.
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43.25.Gf Standing waves; resonance

Theoretical and numerical calculations for the time-averaged acoustic force and torque acting on a rigid cylinder of arbitrary size in a low viscosity fluid

Jingtao Wang and Jurg Dual

J. Acoust. Soc. Am. Volume 129, Issue 6, pp. 3490-3501 (2011); (12 pages) | Cited 5 times

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In this paper, theoretical calculations as well as numerical simulations are performed for the time-averaged acoustic force and torque on a rigid cylinder of arbitrary size in a fluid with low viscosity, i.e., the acoustic boundary layer is thin compared to the cylinder radius. An exact analytical solution and its approximation are proposed in the form of an infinite series including Bessel functions. These solutions can be evaluated easily by a mathematical software package such as mathematica and matlab. Three types of incident waves, plane traveling wave, plane standing wave, and dual orthogonal standing waves, are investigated in detail. It is found that for a small particle, the viscous effects for an incident standing wave may be neglected but those for an incident traveling wave are notable. A nonzero viscous torque is experienced by the rigid cylinder when subjected to dual orthogonal standing waves with a phase shift even when the cylinder is located at equilibrium positions without imposed acoustic forces. Furthermore, numerical simulations are carried out based on the FVM algorithm to verify the proposed theoretical formulas. The theoretical results and the numerical ones agree with each other very well in all the cases considered.
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43.25.Qp Radiation pressure
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