Reports Experimental report v2

Pagina 1

This report has been made for the course of Mechanical Systems Dynamics 2016 of prof. Alberto Zasso and assistants ing. Luca Amerio and Ing. Ilmas Bayati of Dept. of Mechanical Engineering of Politecnico di Milano. Mechanical Systems Dynamics Fundamentals of experimental modal analysis Enrico Gussoni - 884089 To analyze this free-free beam (the supports sustain the beam but let it free to move), and compare the results with the analytical (fig.1), tree accelerometers have been displaced in position A1, A2 and A3, while a shock is performed trough a dynamometrical hammer in DH1 And DH2. A control on the reciprocity is subsequently performed inverting DH1 with A1. Looking at the peaks of the frf it is possible to evaluate the natural frequencies of the system (in practice that can be easily done in Matlab trough the command “findpeaks”) using the superposition of the tree frf for a better approximation. The result (in Hz) are: Fig. 1 First of all we analyze the frequency response function obtained by the tree accelerometers with a resolution of 0.02 Hz. (Table 1) In the amplitude/frequency diagram it is possible to see a clear correspondence between all the accelerometers while in the phase/frequency this is not so clear, mostly because of noise in the part of the spectrum in which the modulus is close to 0 and so numerical errors occur in the computation and the phase in this zone is random. (Impulsive oscillation between –2π and 2π are due to numerical errors in the computation and are not relevant from the physical point of view). This report has been made for the course of Mechanical Systems Dynamics 2016 of prof. Alberto Zasso and assistants ing. Luca Amerio and Ing. Ilmas Bayati of Dept. of Mechanical Engineering of Politecnico di Milano. F1 = 28,7; F2 = 80,22; F3…