New effects in the evolution of the wave spectrum in a tank

Empirical spectra of mechanical and wind waves measured in a $32 \times 1 \times 2$-$m$ tank have been reported. It has been found that the frequency spectra $S(f)$ of mechanical waves with a steepness exceeding $0.2$ at fetches $X$ larger than $20$ m have a self-similar form decreasing as a power function with an exponent of $-4.2$. The spectra of waves with smaller steepnesses with an increase in their fetch only tend to change the slope of their tail to the mentioned form. It has been shown that wind waves even at short fetches ($X \geqslant 8$ m) have the spectrum $S(f)$ decreasing as a power function with an exponent of $-4$. In this case, the spectrum tail intensity decreases with an increase in the fetch $X$, and its dependence on the friction velocity $u_*$ is stronger than a linear dependence of $S(f)$ on $u_*$ in the Toba spectrum. In addition, it has been shown that the shape of the spectrum $S(f)$ of wind waves in the tank is not self-similar. The interpretation of the found effects has been discussed.