Formation and investigation of adaptive means for vibration damping in mechanical systems

Arūnas Jakštas

Review of scientific publications

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Technological sciences, mechanical engineering (09T).

In the review, the scientific research works carried out by the Author at Vilnius Gediminas Technical University Departments of Machine Theory and Machine-building in the period between 1975 and 2010 are briefly described

One of the main causes limiting the efficiency of operation of any machine is vibrations that appear in it under the impact of external factors and are hardly forecastable. Under an increase of speeds of machines and growing of the requirements to precizity of movements in them, an important role is provided to vibration damping systems. First of all, various vibration damping systems where the energy of the harmful vibrations was damped by the internal friction were used for the said purpose; various elastic elements were used for the same purpose as well. However, such vibration damping systems become non-effective upon changes of parameters of the harmful factor. In such a case, adaptive means for vibration damping, i.e. those where the parameters (elasticity and damping) vary dependently on the parameters of the exciting factor, should be used. Such means for vibration damping are discussed upon in the review.

In the damper with rheological liquid, the friction force is altered by regulating the gap filled with the said liquid in the winding of the electromagnet (lines of the magnetic field of the latter cross the said gap). In the review, the results of the investigation on a vehicle with an active vibration damping system where magnetorheological liquid is used are provided. The system is controlled in accordance with the signals of the accelerometer that measures vibrations of an isolated object. Dependently on the number of integrations in the feedback, the friction force will depend on the acceleration, velocity or shift of the isolated object. The impact of the road is considered polyharmonic. It was shown that if the signal of accelerometer is integrated twice, the efficiency of vibration damping remains cons- 42 tant upon changes of the mass of the vehicle. Using of an analogous vibration damping system in vibrating platforms for production of building elements was discussed upon as well. It was shown that in case of the feedback with a frequency detector, vibrations of the platform do not grow, if the frequency of the exciting vibrations coincides with the natural frequency of the platform.

In addition, the impact of couplings where magnetorheological liquid is used for vibration damping upon the dynamics of rotor systems was explored. In such a case, the damping force is controlled by the feedback that receives signals from a sensor used for measuring the angular acceleration of the isolated rotor. It was shown that vibration damping becomes more effective when a supplemental disk in used in the coupling.

In order to ensure vibration damping in rotor systems also in a case when the transferred rotational moment varies considerably, couplings with variable conditions of deformation of elastic elements as well as the variable stiffness were developed and the natural frequencies of the rotor system never coincides with the frequency of the harmful factor that causes the vibrations.

Undesirable vibrations of a mechanical system are successfully damped by using couplings where the elastic element is connected with half-couplings by friction forces. Stiffness of such couplings depends on centrifugal forces that appear during the operation, i.e. stiffness “traces” the rotational speed of the rotor system and the coupling damps the harmful vibrations during the transitional processes. Namely, in such a case, the advantage of active vibration damping systems expresses itself

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44 p.
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