Is it possible exctract sinusoids from non periodic signal? Digital signal UT1-UTC is not periodic but is including many sinusoids (periodic elements in IERS nomenclature) that are not multiples of some fundamental. For example tidal sinusoids are not multiples of yearly seasonal sinusoid because lunar month is not submultiple of the year. Then, is it possible these sinusoids be extracted from UT1-UTC by Discrete Fourier Transform?
Fourier's theorem say almost any (non-pathological) waveform, periodic or not, can be decomposed into sinusoids (or complex exponentials).  Whether, or how well, those sinusoids correspond to any underlying pseudo-periodic phenomena or not is another issue.

Note that with a DFT, you may need to interpolate a periodic signal between the DFT result bin sinusoids.