Arabadzhi, Vladimir V.
senior researcher, Ph.D

1. Vladimir V. Arabadzhi, "Solutions to Problems of Controlling Long Waves with the Help of Micro-Structure Tools", Bentham Science Publishers Ltd., 2011, 173 pages.
DOI: 10.2174/97816080527521110101,
eISBN: 978-1-60805-275-2, 2011, ISBN: 978-1-60805-369-8
    After radar and sonar were founded, problems of the "visibility" reduction for physical bodies in air (elec­tromagnetic waves) or in water (acoustical waves) have immediately become serious in physics and tech­nics. Facilities of the "visibility" reduction are oriented physically for the reduction of radiation field and reduction of scattering field of physical bodies. Now many problems of this circle have become classical, and many researchers thought that these problems can not have solutions for a practical scenario. New tech­nologies (sensors, actuators) of high spatialtemporal resolution plus new computers with fast and accurate calculations in combination with untraditional versions of solutions of above boundary problems, allow to obtain the success in some cases. Traditional thick and weakly absorbing coatings are unacceptable today because of their greater size and weight. Interference coatings have a thickness about 1/4 wavelength, but they have narrow band of working directions and frequencies. The next attempt was the active damping (with radiation of cancellation anti-wave), suggested and developed by G. Maljuzhinets, M. Jessel, G. Mangiante. This idea permits to design coating of thickness much smaller than the wavelength. The works by B. Widrow on adaptive filtering have been applied by C. Fuller, C. Hansen, S. Elliott successfully for ac­tive noise control with adaptation ("training" during real time) to a prior unknown boundary value problem (which can also change). Training of active control system requires enough big time, because it must have total acoustical information (vast amount) on the boundary value problem. In real conditions (elastic shell in various depths and temperatures, with vibroacoustical characterictics, which were investigated by M.C. Junger and D. Feit) this vast volume of information deviates more quickly than the process of training. In recent times the idea of cloacking becomes very popular, suggested by J. Pendry. This presents the solu­tion of above general problem for some body with cavity. Incident wave does not penetrate the cavity and, on the other hand, can not be scattered by the external surface of a body. Therefore any body can be spaced into this cavity, and will be invisible for outside observer. This result is achieved, due to special mi­crodistribution of parameters of body material (called "metamaterials"). The cancellation of radiation and scattering sound field of shell in liquid is connected with following serious problems: (a) wideband acoustical fields to be damped; (b) neutral floatability of a shell in liquid; (c) the absence of dynamical support (con­sequence of (b)); (d) the absence of inertial coordinate system to measure shell's surface displacements (consequence of (b)); (e) the uncertainty of many parameters of shell and incident wave; and (f) problem of compactness of active control system. The book by V. Arabadzhi presents a rare attempt to solve the problem as a whole. Author uses stable technological tendencies in miniaturization and acceleration of sensors, actuators, computer components. On the other hand the lengths of waves to be damped, were constant due to the constant condition of their far propagation. Taking into account the technological pro­gress, the author also used several untraditional approaches to the problem: conversion of the waves to be damped, into the waves of spatial and temporal frequencies which are "invisible" for the used receivers. I hope this book will be useful for a lot of readers with various interests in physics of waves.

2. Arabadzhi V.V. "Parametric Muffler" // International Review of Physics, V. 7, N. 2, pp.  
198-204, April 2013.     
    This paper represents the alternative approach in designing of acoustical mufflers and alternative analyti­cal model of parametric acoustical device. The suggested approach (and device model) provides passing onward of gas flow and reflection back of the acoustical waves, due to very fast temporal modulation of muffler parameters. Using concrete example, it is shown, that parametric muffler can have less wave-gabarits, less energy losses of engine, and less acoustical power at output, than in traditional muffler.

3.   Vladimir V. Arabadzhi, Algorithm for Active Suppression of Radiation and Acoustical Scattering Fields by Some Physical Bodies in Liquids //Algorithms, 2009, V. 2, No. 1, pp. 361-397.
     An algorithm for the suppression of the radiation and scattering fields created by vibration of the smooth closed surface of a body of arbitrary shape placed in a liquid is designed and analytically explored. The frequency range of the suppression allows for both large and small wave sizes on the protected surface. An active control system is designed that consists of: (a) a subsystem for fast formation of a desired distribution of normal oscillatory velocities or displacements (on the basis of pulsed Huygens\' sources) and (b) a subsystem for catching and targeting of incident waves on the basis of a grid (one layer) of monopole microphones, surrounding the surface to be protected. The efficiency and stability of the control algorithm are considered. The algorithm forms the control signal during a time much smaller than the minimum time scale of the waves to be damped. The control algorithm includes logical and nonlinear operations, thus excluding interpretation of the control system as a traditional combination of linear electric circuits, where all parameters are constant (in time). This algorithm converts some physical body placed in a liquid into one that is transparent to a special class of incident waves. The active control system needs accurate information on its geometry, but does not need either prior or current information about the vibroacoustical characteristics of the protected surface, which in practical cases represents a vast amount of data.

4.      Arabadzhi V.V. Active control of normal Particle velocity at a boundary between two media //Acoustical physics. 2005. 51. . 2. 180-188.
      A spatially one-dimensional model of a plane active double layer between two homogeneous elastic half-spaces is studied analytically. The layer synthesizes a preset smooth trajectory of the controlled boundary between the media without any mechanical support. The outer layer of the coating is a piezoelec­tric, and the inner layer is a polymer that is transparent for low-frequency sound and opaque for high fre­quency sound because of dissipation. An algorithm for controlling the piezoelectric elements of the layer on the basis of signals from surface particle-velocity sensors is proposed, and a method for measuring the par­ticle velocity is developed. Conditions of stability and ef?ciency of the synthesis are formulated. It is shown that the active layer thickness can be much smaller than the wavelength corresponding to the mini­mal time scale of the boundary trajectory to be formed. The accuracy of the trajectory synthesis depends on the accuracy of measuring, computing, and actuating elements of the system but does not depend on the vi­broacoustic characteristics of the half-spaces separated by the active layer or on the presence of smooth waves in these half-spaces. For the synthesis to be ef?cient, the operating frequency band and the dynamic range of sensors and actuators should be many times greater than the frequency band and the dynamic range of the trajectory to be formed

5. Arabadzhi V.V. Supportless unidirectional acoustic sources // Acoustical Physics, 2009, vol. 55, No. 1, pp. 104-116. 
    The results of studying the physical characteristics of unidirectional acoustic sources used in active sound control systems are represented. A discrete unidirectional source in the form of two phased monopoles and a planar array of such unidirectional sources are considered. One-dimensional boundary-value problems with two (the two-point problem) and three (the three-point problem) controlled planar boundaries between homogeneous media with arbitrary impedances are studied. The boundaries (two of three) are subjected to the action of external forces. The case of zero sum of external forces applied to the controlled boundaries corresponds to a supportless unidirectional source. It is shown that a unidirectional source can be created within the two-point boundary-value problem, whereas a supportless unidirectional source can be created within the three-point boundary-value problem. Such parameters as transparency, small size, absence of support, and broad frequency band can be achieved for a unidirectional source in the form of two piezo­electric layers with the same impedance and velocity of sound as those of surrounding medium.

6.    Arabadzhi V.V. On the cancellation of low freqiency waves in laboratory tanks // Fizika Atmosferi i Okeana. 1992. 28. . 12. 1205-1212.
       Three new algorithms for controlling boundary condition of wave system has been suggested. Algo­rithms can be applied to the cancellation of low frequency (long) waves in laboratory tanks, when tradi­tional passive and active methods become ineffective. The suggested algorithms make the correspondence between motion of controlled boundary and wave to be damped without knowing wave’s length and period. The matching is achieving during the time much smaller than wave period (locality in time). In this case the instant values of wave field, measured immediately on the controlled boundary (locality in space). The ef­fect of the gravitational water waves scattering on the parametric load, controlled by one of algorithms sug­gested. The effectiveness of this algorithm is confirmed (and for dispersed waves too). Spectrums obtained are showing acceptable correspondence to the mathematical model. 

7.    Arabadzhi V.V. Absorption of long waves by nonresonant parametric microstructures // Radiophysics and Quantum Electronics. 2001. 44. . 3, 249-261.
      Using simple acoustical and mechanical models, we consider the conceptual possibility of designing an active absorbing (nonreflecting) coating in the form of a thin layer with small-scale stratification and fast time modulation of parameters. Algorithms for space-time modulation of the controlled-layer structure are studied in detail for a one-dimensional boundary-value problem. These algorithms do not require wave-field measurements, which eliminates the self-excitation problem that is characteristic of active systems. The majority of the considered algorithms of parametric control transform the low-frequency incident wave to high-frequency waves of the technological band for which the waveguiding medium inside the layer is assumed to be opaque (absorbing). The efficient use conditions are found for all the algorithms. It is shown that the absorbing layer can be as thin as desired with respect to minimum spatial scale of the incident wave and ensures efficient absorption in a wide frequency interval (starting from zero frequency) that is bounded from above only by a finite space-time resolution of the parameter-control operations. The structure of a three-dimensional parametric black coating whose efficiency is independent of the angle of incidence of an incoming wave is developed on the basis of the studied one-dimensional problems. The general solution of the problem of diffraction of incident waves from such a coating is obtained.  

8.    Arabadzhi V.V. Nonferlecting switching microstructure // Journal of Communications Technology and Electronics. 2005. 50. . 5. 613-625.
     The conceptual possibility of creation of radioabsorbing (nonreflecting) coating, which consists of many metallic needles connected by semiconductor electronic switches. It is shown that sufficiently high rate of electronic switches and miniaturization of needles permit to design an absorbing coating which thickness can be much less then the length of incident wave. The absorbing system considered does not use any wave sensors and this removes such a  traditional problem of active systems as the stability or selfexcitation problem. Absorption efficiency does not depend of length and direction of the incident wave. The elec­tronic switches commutation periodically converts low frequency incident wave into high frequency waves. The last are relaxed quickly due to multitime reflections between grid like walls. The general solution of the problem incident wave diffraction on black parametric coating. The case of normal plane incident wave and plane black disc is described thoroughly. The hierarchy of space-time scales of microstructure ensuring effective absorption is formulated.

9.  Arabadzhi V.V.On the Active Cancellation of Ship Waves // Experiments in Fluids, January 1996, vol. 20, N. 3,  pp. 225-226, Springer-Verlag.
      Wave resistance is the main factor in energy losses for ships with deep bottom and near the critical Froude numbers. We consider the problem of active (nonzero right part of boundary conditions) cancella­tion of ship waves by compact water-jet-like hydrodynamic sources, locating immediately on a submerged ship surface (space-locality of control). This consideration is based on the Mitchell’s approximation for a “thin” ship and liquid of infinite depth.  Possibility of nonradiative carrying the finite volume of liquid dis­placement is shown. A wave canceller is equivalent to a propulsive device in nonviscous liquid. A class of shapes of submerged surface of ships, permitting the correct synthesis of the wave canceller, is defined. Mutually conjugated pair “ship shape+wave canceller” localized in space has been found.

10. Arabadzhi V.V. Wave-Jet Converters // Journal of Low Frequency Noise and Vibration and Active Control, V. 21, N. 2, 2002, P. 101-116.   
     The possibilities of conversion of the energy of gravitational surface waves in liquid into a constant re­active flow due to special nonlinear mechanical floating devices (wave-jet converters) are investigated. The last ensure rectification of wave pressure and the effect of wave traction. Physical problems of radiation and scattering wave pressure rectification are considered separately using the examples of concrete devices. The ship model of special construction has been designed and tested. This model converts effectively ship’s pitching immediately into a constant jet flow without using of any external sources of energy. Ship’s mo­tion is characterized by average Froude number Fr=0.14 and average forward velocity exceeding the ve­locities of liquid particles in wave field. This ship presents uniflow wave jet propulsive device.