  Acoustic-gravity waves (hereafter AGWs) in ocean have received much interest
recently, mainly with respect to early detection of tsunamis as they travel at
near the speed of sound in water which makes them ideal candidates for early
detection of tsunamis. While the generation mechanisms of AGWs have been
studied from the perspective of vertical oscillations of seafloor and triad
wave-wave interaction, in the current study we are interested in their
generation by wave-structure interaction with possible implication to the
energy sector. Here, we develop two wavemaker theories to analyze different
wave modes generated by impermeable (the classic Havelock's theory) and porous
(porous wavemaker theory) plates in weakly compressible fluids. Slight
modification has been made to the porous theory so that, unlike the previous
theory, the new solution depends on the geometry of the plate. The expressions
for three different types of plates (piston, flap, delta-function) are
introduced. Analytical solutions are also derived for the potential amplitude
of the gravity, acoustic-gravity, evanescent waves, as well as the surface
elevation, velocity distribution, and pressure for AGWs. Both theories reduce
to previous results for incompressible flow when the compressibility is
neglected. We also show numerical examples for AGWs generated in a wave flume
as well as in deep ocean. Our current study sets the theoretical background
towards remote sensing by AGWs, for optimized deep ocean wave-power harnessing,
among others.
