Estimations of Fourier Coefficients For Controlled Distortion of a Periodic Function

There is a class of physical filtration processes where the input is adequately modeled by a continuous periodic function f (x) of bounded variation over its period, and the output depends only on certain harmonics of the Fourier expansion of f (x) in the orthogonal basis of trigonometric functions. One example is the discrete spectrum sound generation by a revolving body in a steady fluid flow. This type of sound can be controlled through the amplitudes of certain harmonics of the circular distribution of the inflow velocity. Attainable goals of such a controlled distortion of f (x) are formulated as fuzzy targets and required inequalities relating the integral characteristics of f (x) with the coefficients of the corresponding Fourier expansion are proven.