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2 results on '"subharmonics"'

1. Dynamics of a mechanical system with nonlinear elastic suspension and spectral analysis of the results

Author

V. A. Nekhaev, V. A. Nikolaev, A. N. Smalev, and K. O. Seryakov

Subjects
mechanical system, rigid cubic force characteristic, duffing equation, approximate analytical methods, mathematical modeling, spectral density (power), subharmonics, frequency response, Engineering (General). Civil engineering (General), TA1-2040
Abstract

The article considers the dynamics of a nonlinear mechanical system under the action of a kinematic perturbation on it. The object's vibration isolation system is described by a rigid cubic power characteristic and is based on compensation of external perturbations — the introduction of an additional elastic element with negative stiffness into the suspension. Numerical modeling of the system is performed, the results of which are analyzed by the method of spectral analysis, based on the representation of the correlation function on a small time interval by a square polynomial. As a result of the analysis, it is found that in the pre-resonant and resonant regions, the general solution should consist of three components: a subharmonic of the order of 1/3, the fundamental harmonic, and the third harmonic. It is noted that only the subharmonic of the order of 1/3 and the fundamental harmonic are important in the resonant zone. It is also noted that even simple nonlinear mechanical systems in the study of dynamics should use approximate analytical and numerical methods in combination with spectral analysis, since traditional methods of nonlinear mechanics are not adapted to solving problems taking into account a relatively large number of harmonic components that appear due to nonlinearity.

Published
2023
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2. Techniques of Ultrasound Cavitation Control

Author

Sergey Skvortsov

Subjects
acoustic power, Materials science, lcsh:Computer engineering. Computer hardware, Ultrasound cavitation, Physics::Medical Physics, lcsh:TK7885-7895, General Medicine, Physics::Classical Physics, cavitation intensity, laser, Physics::Fluid Dynamics, optical probing, cavitation bubbles, cavitation noise, sonolumiscence, subharmonics, pulsations, sonochemistry, lcsh:Mechanics of engineering. Applied mechanics, lcsh:TA349-359, control, ultrasound cavitation, Biomedical engineering
Abstract

The control methods of ultrasonic cavitation applied now within the range from 20 kHz to 80 kHz use either control of ultrasound source parameters (amplitude, acoustic power, etc.) or control of one of the cavitation effects (erosion of materials, sonoluminescence, power of acoustic noise, etc.). These methods provide effective management of technological processes, however, make it impossible to relate the estimated effect with parameters of pulsations of cavitation bubbles. This is, mainly, due to influence of a number of uncontrollable parameters, in particular, such as temperature, composition of liquid, gas content, etc. as well as because of the difficulty to establish interrelation between the estimated effect and parameters of pulsations. As a result, in most cases it is difficult to compare controlled parameters of ultrasonic cavitation among themselves, and quantitative characteristics of processes become depending on the type of ultrasonic installation and conditions of their measurement.In this regard, methods to determine parameters of bubble pulsations through sounding a cavitation area by low-intensity laser radiation or to record cavitation noise sub-harmonics reflecting dynamics of changing radius of cavitation bubbles are of interest. The method of optical sounding, via the analysis of spectral components of a scattered signal recorded by a photo-detector, allows us to define a phase of the bubbles collapse with respect to the sound wave and a moving speed of the bubbles wall, as well as to estimate a cavitation index within the light beam section.The method to record sub-harmonicas of cavitation noise allows us to define parameters of pulsations, average for cavitation areas.The above methods allow us both to study mechanisms of cavitation action and to form quantitative criteria of its efficiency based on the physical processes, rather than their consequences and are convenient for arranging a feedback in the units using ultrasonic cavitation

Published
2015

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