The effect of wall‐friction on gravity‐waves

Abstract

Two‐dimensional waves on a free‐water surface have been investigated experimentally in relatively narrow laboratory channels. In planning such experiments, there arises a question as to the width necessary to avoid appreciable losses of wave‐energy by wall‐friction. If the crest‐lengths were infinite, as assumed in the theoretical analysis of gravity‐waves [H. LAMB, Hydrodynamics, 6th Ed., p. 619], only internal and bottom friction decrease the wave‐energy and these effects are usually small but in laboratory wave‐tanks friction resulting from the very steep velocity‐gradients near the walls of the tank may have an effect so great as to render the experimental results worthless. The practical problem involved is the selection of a width of tank showing inappreciable wall‐effect rather than prediction of the loss of energy in a tank of insufficient width.