[Kelvin Wedge] Hankel Transform of the Bi-Laplacian and an Axisymmetric Free-Surface Problem
We show how the zeroth-order Hankel transform diagonalises the radial
bi-Laplacian, clarify the sign convention \(\nabla^4 \leftrightarrow k^4\), and then
apply the same transform machinery to an axisymmetric linear
free-surface problem to obtain explicit representations for \(\eta(r,t)\) and \(\hat w(s,z,t)\).