“…Water is assumed to be incompressible, nonviscous and irrotational. A velocity potential Φ=Φ(x,y,z,t) can be used to describe the fluid velocity vector V (x,y,z,t)=(u,v,w) at time t at the point x = ( x, y, z ) in a Cartesian coordinate system48–69. The velocity vector V (x, y, z, t)=(u, v, w) can be expressed by the following equation under the assumption of linear wave theory of small amplitude where i , j , k are unit vectors along the x ‐, y ‐ and z ‐axes, respectively.…”