The paper presents an analysis of the noise emitted by aerodynamically excited idling circular saw blades in both time and frequency space. Generally,the noise emitted by rotating circular saw blades is the consequenceof the aerodynamic noise caused by the toothed periphery of the tool and the noise resulting from lateral oscillations of circular saw blades.Important is the fact that in both above-given categories of the noise emitted by idling circular saw blades, the nature of the source is identical and depends solely on the aerodynamic characteristics of the tool. Analyses of the measurements performed confirm the hypothesis that for the occurrence of transversal resonant oscillations of the tool, only an aerodynamically generated excitation force with a suitable frequency is not sufficient. In addition to the said condition, two additional conditions must also be met, that is, the excitation pressure differences of the surrounding air must be sufficiently large, and the damping capacity of the material of the supporting body of the saw blade must be sufficiently small. When all conditions for the excitation of transversal resonant oscillation of the rotating disc tool are met, two types of resonant oscillation occur. The first type occurs when one of the natural frequency oscillation modes of the tool is excited; the second type occurs when aerodynamically generated excitation forces simultaneously excite two characteristic oscillation modes with frequencies that are relatively close. In the latter case, resultant modulated oscillation is concerned, where the frequency of oscillation is equal to the average frequency of both characteristic oscillations, and the modulated beat frequency is equal to the difference between the two frequencies.
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