Experimental-mathematical modeling оf a lоng-length structure based оn the frequency tests results

Aeronautical and Space-Rocket Engineering


DOI: 10.34759/vst-2022-3-29-40

Аuthors

Ermakov V. Y.

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

e-mail: v_ermakov2003@mail.ru

Abstract

Spacecraft, as a rule, have outboard structures of low rigidity, such as solar panels. When simulating a dynamic model of elastic spacecraft and selecting control system settings, it is necessary to set up a system of equations of motion, as well as determine its coefficients characterizing both elastic (eigenforms, oscillation frequencies and inertial coupling coefficients) and dissipative (logarithmic decrements and damping coefficients) properties of the structure. As the result of frequency tests, the dynamic characteristics of the solar panel were obtained, namely the spectrum of natural frequencies, shapes, decrements, as well as the dependence of frequencies and decrements on the amplitude of the panel oscillations. It should be noted that with the amplitude changes, the spread of the decrements values of the oscillations might be rather significant. It is stipulated by the fact that at small oscillation amplitudes, energy dissipation is mainly determined by internal friction in the material and structural damping, which is characterized by friction in kinematic pairs, as well as in splined, threaded, etc. joints. While loading, small slippages in such joints occur over the contact surfaces, which may lead to drastic energy dissipation increase, and does not meet the flight conditions in outer space. Besides, the weight-killing tether system, which introduced extra stiffness, weight and damping, was employed while these tests for the docking nodes with gaps offloading. The system with vibrators makes as well its contribution through the attached masses of coils and their attachment points. The elastic and dissipative characteristics refinement of solar battery wing of the “Spectrum” type spacecraft based on frequency tests results of the panels and analytical studies with account for the weight- killing system impact was performed. The solar battery wing herewith, consisted of four panels, was the object of the studies.

The results of frequency tests of the wing of the solar battery of the «Spectrum» type spacecraft were analyzed. The obtained results demonstrate that the oscillations are of nonlinear character. The presence of backlashes in the drive are stipulated by the dependence of natural frequencies and decrements of oscillations on the oscillations amplitude. This is also the reason for the oscillations forms deviation from the obtained calculations.

The modal parameters of the solar battery wing of the spacecraft were identified based on the results of the frequency tests with account for the weight-killing system impact. A good agreement herewith between the calculated and experimental characteristics with the offloading system was obtained, which allows feasible selection of the dynamic model parameters values of “Spectrum” type spacecraft.

Keywords:

long-length structure, weightlessness system, unloading system

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