In the case where the mean flow oscillation appeared, the propagation of
gravity waves and the change in the mean flow were calculated with the WKB analysis, to compare them with the experimental
results.

In the WKB analysis, it was assumed that both the rightward-propagating
wave and the leftward-propagating wave have equal amplitudes. And the deformation of the
wave propagating through the mean flow, whose distribution is obtained experimentally, is
calculated with the WKB analysis.

Furthermore, the convergence and divergence of the momentum flux and the pattern of the
mean flow acceleration were calculated for comparison with the deformation rate of the
mean flow obtained experimentally.

The results are shown in Figure 9-1 through Figure 9-5. Both the pattern of the wave
and the convergence and divergence of the momentum flux were found to agree fairly well.
There is a large discrepancy in the convergence and divergence of the momentum flux near
the vibration membrane (the wave source), but it is assumed that this is caused by the
large error in the velocity measurement of the fluid due to difficulty in measuring the
velocity in this area.