Non-linear Internal Wave Kinematics Available to Purchase

Large amplitude regular internal waves are modelled in a wave tank using water and saline solution to create a density profile. The parameter range covers long and short waves in a quasi two-layer stratification and also on a broader interface. The wave kinematics are measured using Particle Image Velocimetry and compared to weakly non-linear theory. It is found that the second order Stokes theory underpredicts the velocities in the extremes of the short waves by about 40°7o. Both linear and solitary wave theory fail to adequately predict the kinematics of long waves, especially the vertical velocity components. Introduction Internal waves are known to occur in most ocean areas, especially the deep ocean where stable stratification is often found. New petroleum discoveries have prompted a move into areas (e.g. west of Shetland) where internal waves are more likely to be a problem. The implications of internal waves for offshore operations were first raised by Osborne, Burch and Scarlett (1978) and later by Bole, Ebbesmeyer and Romea (1994). The presence of internal waves in sea areas of current interest to the UK offshore industry has been confirmed by Sherwin (1991). While many aspects of internal wave behaviour have been extensively studied (e.g., Thorpe, 1968 & 1975), few measurements of detailed wave kinematics have been performed. This paper presents results of a programme of experiments which aimed to measure wave kinematics in large amplitude waves, and comparisons with theory. Theoretical description Stokes waves The following analysis is based on that of Thorpe (1968), though the Boussinesq approximation is not made. It can be shown that the streamfunction ψ in a stratified flow satisfies the vorticity equation. (equation shown in paper). Here the sign convention for the streamfunction is (equation 2 shown in paper).