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22.10.2012 20:43:55
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2.4. Kinematics of movement of fishes and self-oscillation of mechanical systems.

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The Scheme of the wave-like motion of the fish's body, presented in the work [1], resembles the scheme of the single cylinder movement in a longitudinal flow of the liquid at high flow rates, what leads to loss of cylinder steadiness and the emergence of bending-twisting flutter. The dynamics of single-cylinder in a longitudinal flow of liquid is studied in sufficient detail [4-10]. It is well established [6,10]that for small flow rates cylinders make a small random oscillations raised by random resistance of averaged flow; the influence of the averaged flow has an impact on the appearance of a hydrodynamic damping and reduction of the cylinder own frequency. However, at relatively high flow velocities, first the system loses its steadiness as a result of static buckling (the phenomenon of "divergence"), and then there is a "flutter" in it [4,5,10]. And with it in the survey [9, 10] it was shown, that the majority of industrial systems has the cylinders flexible not enough, and flow rate are too high for these phenomena of unsteadiness and flutter emergence could be realized in practice.
The term "self-oscillations" is usually applied to the oscillating object that can take energy from the flow of a fluid medium (air, water), while maintaining the unabated fluctuations. If the energy is taken from a uniform flow, this process of self-oscillations is called the "flutter". The concept of "flutter" is usually applied to the wings of the aircraft and the blade of the turbomachines. Later this name was applied in the study of pipe arrays of heat exchangers. In aviation flutter, among fluctuations and in general among the numerous types of vibrations , which experiences the aircrafts, poses a special danger, because dynamic tension in the aircraft construction what arises as a result of the intense oscillations and this can quickly (sometimes within a few seconds) destroy the aircraft while in flight[11]. That is why the appearance of the flutter in any form is unacceptable. Always while studying the interaction of oscillating objects with the flow of fluid, the flutter phenomenon was considered as harmful (catastrophic) phenomenon, which can occur only in the technique and leads to the destruction of the object and it cannot be allowed. That is why, all of the research, tests and calculations of the flutter phenomenon were to define the boundary conditions of the flutter and recommendations for the prevention of these conditions [11, 12].
Information concerning the flutter phenomenon in the device for the conversion of the kinetic energy of the fluid medium flow into the useful work is available in the patent [13], which is an improvement of the same patents [14, 15, 16].In these works the author confuses the phenomena of flutter and resonance (conventional forced vibrations) oscillating in the fluid medium flow load of cylindrical objects, when the laws of cylindrical objects oscillations are unpredictable, and oscillations of the objects are failing and it needs to be maintained constantly by the external forces.

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