Velocity fields in solitary internal waves

Internal waves propagating on the ocean thermocline pose a hazard for engineering operations in deep water (Osborne et al., 1978). The sheared currents associated with these waves can reach 1-2m/s and are present from the surface to the sea floor. From the viewpoint of the engineer, the most significant internal waves appear to travel as packets of solitary waves (or 'solitons'), generated by tidal flow over uneven bathymetry (Maxworthy, 1980). Substantial work has already been completed on the kinematics of regular internal waves and a comparison has been made with non-linear regular wave theory (Martin & Easson, 1997). The current study extends this work to cover solitary waves and involves the generation of internal solitons in a laboratory channel which is 6m long and 0.4m wide. A paddle is moved vertically to generate a solitary wave, and wave gauges are used to monitor its passage along the channel. Differing layer depths and density stratifications are used in the experimental programme in order to cover a range of parameters. Particle Image Velocimetry (PIV) is used to obtain the velocities within a section of the wave. The velocity values are compared with those obtained using K-dV theory in order to assess the range of applicability of this theory and enable offshore engineers to better predict the forces to be expected under such conditions. Koop and Butler (1981) assessed the validity of various solitary wave theories against wave shape parameters, using a combination of water and Freon to create the stratification. This study extends their work by using miscible fluids (fresh water and salt solution) to create a diffuse pycnocline, employing continuously stratified K-dV theory to calculate the wave generation parameters.