Prof. Vladimir Arabadzhi
Prof. Vladimir Arabadzhi
Institute of Applied Physics (RAS), Russia
Title: On the Alternative Approach to Active Control of Sound, Radiated and Scattered by Body in Water
The possibilities of applying high spatial-temporal resolution operations (sensors and actuators) in linear problems of active control of radiation and scattering of low-frequency broadband sound by physical bodies of neutral buoyancy in water are considered. Neutral buoyancy of the body in the water causes the absence of a mechanical support (no vibrostats, and, in addition, no any real rigid boundary for sound in water) and the absence of an inertial coordinate system for measuring the normal displacements of the body surface. The traditional approach to active compensation of radiation and scattering fields assumes the existence of complete information about the fields and the boundary wave problem. In practically important cases, this approach requires the accumulation of a vast array of information about the vibroacoustic characteristics of the body by the self-learning system. On the other hand, for a long time of accumulation of this information, it can become obsolete due to changes, for example, temperature or hydrostatic pressure (the depth of immersion of the body). The solution methods proposed in the report do not require the accumulation (due to the use of pulsed unidirectional radiation sources) of complete information on the boundary-value problem and are based on a stable technological tendency to increase the speed and miniature of the element base. Possible tools are faster miniature microphones (as well as accelerometers and capacitive thickness sensors), faster piezoelectric drives, faster computers with a high numerical representation of numbers. On the other hand, the frequencies of the waves to be damped remain low, as they were many years ago, due to the constancy of the natural conditions of long-range propagation of these waves. The proposed approach provides almost instantaneous system response to any the disturbing effect without requiring knowledge of the spectral characteristics of the fields (frequency, wavelength) and vibro-acoustic characteristics of the protected body (of neutral buoyancy) as intermediate data between sensors and actuators. The system under consideration consists of two subsystems: (a) a system for forming a given normal displacement of the surface of the protected body, (b) a system for the direction-finding of the incident waves in the form of a finite set of plane (on the scale of body size) waves with different directions and arrival times. In this case, each incident wave is accompanied by a corresponding group of microphones, formed directly in the process of contact between the leading edge of the wave and the microphones. This system can’t be reduced to the traditional combination of electrical circuits with constant parameters and, accordingly, the elements of such a system can’t be effectively described by complex amplitudes (amplitude plus phase). The consideration is based on time representation of boundary problem with initial conditions.
Arabadzhi Vladimir Vsevolodovich, physicist; born Minsk, Belarus, Apr. 22, 1956; Gorky State U., Russia, 1978, PhD in Radiophysics, 1994. Engr. Radiophys. Inst., Nizhny Novgorod, Russia, 1978-81; with Inst. Applied Physics, Russian Acad. Sci., Nizhny Novgorod, Russia, 1981-94, sr. scientist, 1994-.Contbr. Articles to profl. Jours. Achivements include inventions in active wave control. Area of interests: wave thrust, reducing of acoustical and radio visibility of physical bodies.