Svetlana Kashcheeva
 

Work: Nonlinear effects in intense acoustic waves containing shocks in media with frequency power low of absorption. Moscow State University.

Date of birth:   January 20, 1975.

Place of birth: Russia, Moscow.

Education: Graduated from Moscow State University, Physics Faculty, Department of Acoustics, 1998.

Main results: Research work is devoted to investigation of nonlinear effects in intense acoustic waves propagating in media with absorption [1]. Periodic waves and shock pulses, which are particular to modern medical applications of intense ultrasound, are considered. Media considered here are close in frequency power low of absorption and dispersion to biological media. It was showed that for sinusoidal intense wave propagating in biological-type medium shocks are formatting earlier and phase of effective nonlinear absorption is longer than it is for classical fluids. It was found that for single shock pulse different parameters of frequency power low of absorption affect differently on its waveform. The power in the low of absorption affects on shock width and the magnitude of absorption on certain frequency affects on peak value of pressure. These results lead to think about possible diagnostic of undefined parameters of medium power low of absorption based on waveform of shock pulse that have propagated in this medium. It is well known that nonlinear wave interactions depend strongly on absorption and dispersion properties of the propagation medium. In case of weak dispersion this results in effective broadening of the spectrum into higher frequencies and formation of shocks. For many applications it is desired to avoid or to delay shock formation. A promising way to control nonlinear interactions in nondispersive sound waves is to introduce additional absorption of a certain frequency component. It has been shown that selective absorption of the second harmonic of an incident sinusoidal wave results in less damping of the fundamental frequency signal. Effect of second harmonic selective absorption on nonlinear interactions in high intensity acoustic beams was studied in the paper [2]. Diffraction and focusing phenomena were taken into account in addition to nonlinearity and selective absorption. It was shown that selective absorption of the second harmonic does not prevent shock formation, but results in specific waveform distortion, less asymmetry of the waveform in case of the beam, less amplitude of the shock and corresponding nonlinear attenuation. The present work is focused on the investigation of the role of acoustic nonlinearity and frequency dependence of sound amplification in transient processes in an initially unstable thermoacoustic system [3]. These works supported by CRDF grant No RB2-131, RFBR grants No 98-02-17318, No 96-15-96672.

Main publications:

1. S.S. Kashcheeva, M.A. Averkiou, L.A. Crum. Nonlinear Distortion And Attenuation of Intense Acoustic Waves in Lossy Media Obeying a Frequency Power Law.// Acoustical Physics. Vol.46, N 2, 2000, p. 170-177.
2. Khokhlova V.A., S.S. Kashcheeva, Averkiou M.A., Crum L.A. Effect of selective absorption on nonlinear interactions in high intensity acoustic beams.// In: Proc. of 15th ISNA. Goettingen, Germany, September 1999, p. 151-154
3. V. Khokhlova, O. Sapozhnikov, S. Kashcheeva, P.Lotton, V. Gusev, S.Job, M.Bruneau Nonlinear acoustic waves in quasi-adiabatic thermoacoustic prime-movers.// Proceedings of the 5-th French congress on acoustics. 3-6 september, EPFL, Lausanne, Suisse. p. 242-245.