Amphibious landings and small boat operations are normally conducted only in benign wave conditions. An unexpected encounter with an isolated freak wave may damage equipment and prevent mission accomplishment. This study examines the occurrence of unusually large waves using data sets obtained with bottom mounted pressure sensors and wave buoys in the DUCK 94, SHOWEX, and SAX 04 experiments. All of the experiments include wave records from high energy events. After correcting the raw pressure data for hydrodynamic attenuation over the water column, the statistics of wave heights were evaluated and compared with the theoretical Rayleigh distribution of a narrow-band linear wave field. Observations from deep water sites follow the Rayleigh distribution well, even in extreme sea states, indicating that strong nonlinearity does not have a major effect on wave height statistics. However, during high energy events at shallow water sites, there are significantly less measured wave heights in the right-hand tail of the distribution of wave heights than the theoretical Rayleigh distribution would predict. These results show that waves become more homogeneous in height as they propagate into shallower water, possibly owing to breaking and nonlinear effects. While the observed wave statistics do not suggest a frequent occurrence of freak waves, isolated large waves were indeed observed, even in benign conditions. Further studies are needed to assess their risk to Navy operations.
| Identifer | oai:union.ndltd.org:nps.edu/oai:calhoun.nps.edu:10945/2436 |
| Date | 12 1900 |
| Creators | Laird, Anne Marie |
| Contributors | Herbers, Thomas H.C., Thornton, Edward B., Naval Postgraduate School (U.S.)., Oceanography |
| Publisher | Monterey, California. Naval Postgraduate School |
| Source Sets | Naval Postgraduate School |
| Detected Language | English |
| Type | Thesis |
| Format | xiv, 51 p. : ill., application/pdf |
| Rights | Approved for public release, distribution unlimited |
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