The velocity potential ©w(x;z;t) of the harmonic waves has to ful…ll some requirements, which will be treated in detail in a next lecture. The inviscid irrotational fluid is supposed to be incompressible, from which follows the so-called Continuity Condition and Laplace Equation. The vertical velocity of the fluid particles at the sea bottom is zero; the bottom is impervious. The pressure at the surface of the fluid is equal to the atmospheric pressure; there is no pressure jump between the fluid domain and the air domain.
These requirements lead to a more complete expression for the velocity potential as will be explained in a next lecture: