A number of accurate measurements of the kinematics under the crests of regular waves and two-component uni-directional wave groups have been made in a laboratory wave flume using Particle Image Velocimetry. The waves were in intermediate to deep water, with relative depths in the range of <I>d/gT<SUP>2</SUP></I> = 0.05 to 0.085 and were of moderate to high relative steepnesses, in the range <I>H/gT<SUP>2</SUP></I> = 0.005 to 0.018. (Here <I>d</I> is water depth, <I>T </I>wave period, <I>H</I> wave height and <I>g </I>gravitational acceleration.) The main conclusions are: (1) Regular waves were accurately modelled using an implementation of high order Fourier theory by Rienecker and Fenton, providing Stokes second (zero mass transport) definition of wave celerity was used. (2) Steep, near-breaking two-component waves were modelled accurately using superposition stretching, a derivative linear theory. The input for this is the measured was spectrum, including first and second harmonics. The second harmonic contribution was found to be significant. (3) The kinematics in the crests of different waves of a given height and period can vary considerably. Here, differences of over 20% were noticed at the crest. (4) Wave group lenght affects the internal wave kinematics. (5) Measurements must be made above the level of the wave troughs and should be made above the mean water level also, if experimental results are to have much credence. (6) Particle image velocimetry proved to be an excellent measurement technique to use for measuring velocities as it was capable of measuring close to the free surface of high waves, with a high degree of accuracy.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:662628 |
| Date | January 1992 |
| Creators | Sutherland, James |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13045 |
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