Konstantin Naugolnykh

Nonlinear Wave Processes in Acoustics

Preface 1. Nonlinearity, dissipation and dispersion in acoustics 2. Simple waves and shocks in acoustics 3. Nonlinear geometrical acoustics 4. Nonlinear sound beams 5. Sound-sound interaction (nondispersive medium) 6. Nonlinear acoustic waves in dispersive media 7. Self-action and stimulated scattering of sound Conclusion Subject index.

Numerical simulation of remote acoustic sensing of ocean temperature in the Fram Strait environment

An important part of the general problem of the Arctic climate change is the monitoring of the Fram Strait, which lies between Greenland and Spitsbergen. For this reason it is reasonable to apply acoustic methods which are proven to be effective in acoustic ocean thermometry, acoustic tomography, etc. Knowledge of the main peculiarities of sound signal propagation in this region is needed to estimate the feasibility of applying remote acoustic methods. To this end computer simulation of sound signal propagation in the Fram Strait environment was performed, based on oceanographic data obtained by the R/V POLARSTERN expedition. The presence of stable eigenrays in Fram Strait environmental conditions is demonstrated, typical values of acoustic signal travel time fluctuations due to environmental variations are determined, and the temperature effect on the signal travel time variation is considered. Sensitivity estimates for measurement of the average ocean temperature across Fram Strait is considered in two ...

Infrasound induced instability by modulation of condensation process in the atmosphere.

A sound wave in supersaturated water vapor can modulate both the process of heat release caused by condensation, and subsequently, as a result, the resonance interaction of sound with the modulated heat release provides sound amplification. High-intensity atmospheric perturbations such as cyclones and thunderstorms generate infrasound, which is detectable at large distances from the source. The wave-condensation instability can lead to variation in the level of infrasound radiation by a developing cyclone, and this can be as a precursor of these intense atmospheric events.

Nonlinear propagation of laser-generated sound pulses in a water and granular medium

Nonlinear propagation of finite-amplitude acoustic pulse in water and through a sample of water-saturated granular medium is considered. To generate high-intensity acoustic pulses laser generation of sound was used. The region of fluid perturbed by the laser acts as a volume-distributed source. In a fluid with weak light attenuation, a cylindrical source could be formed by a narrow laser beam. The nonlinear distortion of the cylindrical finite-amplitude wave in water is investigated. The measured rate of distortion corresponds to that calculated in the approximation of nonlinear acoustics. In a strongly light-absorbing medium, a wide (compared to the typical sound wavelength) laser beam produces a circular planar source. Such a source produces acoustical pulses of amplitude up to 3 MPa and duration about 1 μs in different fluids. This source was used to investigate the propagation of high-intensity wide frequency band sound signals in a sample of water-saturated cobalt–manganese crust (CMC). Specific acou...

Sound scattering by a vortex dipole

Sound scattering by a system of two counter-rotating vortices (Lamb dipole) is considered, using the effective approach of Pitaevskii [J. Exp. Theor. Phys (USSR) 35, 1271-1275 (1958); Sov. Phys. JETP 85, 888-890 (1959)], based on application of the asymptotic representation of the scattering Green function, the Dirac delta function modeling of the vortex, and the Fourier transformation of the vector of scattering. The sound frequency is supposed to be low. The directivity pattern of the radiation, scattered by the Lamb dipole is obtained. There is no singularity in scattering field in this case as it must be for the vorticity with zero circulation, so the dipole is a more appropriate object for the approximation used.

Optical remote sensing of sound in the ocean

Abstract. We propose a remote sensing technique to measure sound in the upper ocean. The objective is a system that can be flown on an aircraft. Conventional acoustic sensors are ineffective in this application, because almost none (∼0.1%) of the sound in the ocean is transmitted through the water/air interface. The technique is based on the acoustic modulation of naturally occurring bubbles near the sea surface. It is clear from the ideal gas law that the volume of a bubble will decrease if the pressure is increased, as long as the number of gas molecules and temperature remain constant. The pressure variations associated with the acoustic field will therefore induce proportional volume fluctuations of the insonified bubbles. The lidar return from a collection of bubbles is proportional to the total void fraction, independent of the bubble size distribution. This implies that the lidar return from a collection of insonified bubbles will be modulated at the acoustic frequencies, independent of the bubble size distribution. Moreover, that modulation is linearly related to the sound pressure. A laboratory experiment confirmed the basic principles, and estimates of signal-to-noise ratio suggest that the technique will work in the open ocean.

THE PARAMETRIC ARRAY AND LONG-RANGE OCEAN RESEARCH

Introduction The parametric array (PA) is a nonlinear transduction process that can generate a narrow beam of low frequency sound in a medium, through the interaction of co-linear, intense, high frequency sound waves, called pump waves. The unique characteristic of a parametric array is found in its extremely narrow directivity pattern (1°-3° angular resolution) for low frequency acoustical signals. The effective width of the directivity pattern remains practically constant over a wide range of signal frequencies. The parametric array has become essentially a virtual acoustic end-fire array that has been formed in the medium (water) by the non-linear interaction of the two high frequency waves at their sum and difference frequencies (Fig. 1). As a result, it radiates a sharp, low-frequency, directional signal at the interaction frequency of its pump waves that propagates independently of the pump waves. Due to the non-resonance property of the low-frequency signal generation the parametric array can provide a sounding signal transmission in extremely wide frequency bands (more than two octaves). The nonlinear interactions of sound waves are described by Burgers equation:

Infrasound radiation of cyclones

Tropical cyclones produce strong perturbations of atmosphere and the ocean surface accompanied by acoustical radiation. Infrasonic signals in the 0.1−0.5 frequency band can be observed at distances of thousands of miles from the cyclone. The effect of infrasound radiation is connected apparently to the interaction of the counter‐propagating sea‐surface waves that produces a sound radiation of the doubled frequency of the surface wave oscillation. This radiation has narrow‐angle vertical directivity pattern. The essential refraction of radiated infrasound in the atmosphere perturbed by the cyclone leads to trapping of the infrasound by the horizontal atmospheric wave‐guide providing its long distance propagation.

Sound induced plume instability

A sustained source of buoyancy creates a continuous rise of lighter fluid through the ambient denser fluid, with mixing occurring along the way. Such structure, called as a plume, is sensitive with respect to flow perturbations. In particular, the effect of sound can modulate the structure of plume as a result of sound-turbulent interaction. The acoustic wave can slightly change the structure of flow and then interact with in-phase spatially modulated turbulence. In application to plume this effect is considered in the present paper follow the approach of Chimonas, 1972 and Moiseev et al., 2000.

Acoustic instability of vortices

Large plane is a powerful source of vortex. Disturbances of an axial vortex in a compressible fluid are unstable with respect to Kelvin wave development and produce acoustic wave generation. On the other hand system of counter-rotating vortices (Lamb dipole), with different intensity of vortices, as a result of instability collapse into the center of rotation of vortices. The characteristic time of collapse is in the reciprocal proportion the vortices intensity difference. The evolution of Lamb dipole, determined by the two competing processes of instability, is considered in the presented paper. The sound radiation of Lamb dipole can be used to estimate the vortex structure produced by large plane. The advent of large aircraft, with their attendant large and strong trailing vortex structures, made this a problem of considerable practical concern.