Features of experimental determination of eigenfrequencies and modes of cylindrical shell oscillations
The results of the experimental determination of eigenfrequencies and modes of cylindrical shell oscillations by the impact method are given. The shell was hung on elastic suspensions. Vibration accelerations of the shell were measured by single-component accelerometers. A series of experiments with different settings of sensors on the generatrix of the shell was carried out. Accelerometer signals were detected by the LMS Scadas data collection system. Eigenfrequencies and modes of oscillation of the shell were determined on the basis of mutual spectral analysis of transient input drive signals and output signals by using the LMS Test Lab software. Eigenfrequencies of the shell were visually determined by the maximum of frequency response and phase change points at 90˚ PFC. The subsequent elaboration of these frequencies was carried out by average frequencies and phase responses. The estimation of oscillations modes by the modal assurance criterion was made for selected frequencies. Probabilistic estimation of the values of eigenfrequencies, modal mass and stiffness, damping coefficient of the cylindrical shell was made. In the investigated range among the eight registered maximums there were three eigenfrequencies and modes of shell oscillations were identified. Thus, the frequency maximums are 423.3 Hz; 425.4 Hz; 700.9 Hz; 715.6 Hz; 971.8 Hz; 977.5 Hz; 983.7 Hz; 985.4 Hz, of which 425.4 Hz, 977.5 Hz and 985.4 Hz were identified as eigenfrequencies. The experimental modal analysis showed that the proposed sequence of procedures of processing the vibration testing results was entirely satisfactory in the identification of frequencies and modes of structural section vibrations.