Offshore Technology Research Center

 

OTRC Project Summary

Project Title:

Detection of Deep Water Breaking Waves

Prinicipal Investigators:

Jun Zhang and Richard Seymour

Sponsor:

National Science Foundation

Completion Date:

May, 1998

Final Report ID#

A96(Click to view final report abstract)

This research is conducted in order to explore the possibility of validating a deep water breaking wave detection model based on the Phase-Time Method.  We evaluated the power of the PTM approach to breaking wave detection.  Different objectives were met in order to obtain satisfactory results in our research:

  • Obtain a quality data set under a variety of deep water wave conditions with a substantial number of breaking waves and video documentation to discriminate the breaking events visually evaluate the type of breaking.
  • Understand the physics to the Hilbert transform and to the time-series of the local deviation of the frequency obtained by using the Phase-Time Method.
  • Apply the Phase-Time Method to the acquired data and explore this method as a detection method for breaking waves.
  • Develop and validate a model for breaking detection.

The first step of the research was the data gathering.  A large number of deep water random wave experiments were conducted in the Offshore Technology Research Center Model Basin.  A large linear array of wave staff was employed with multiple video cameras to record breaking events along the array.  The data was acquired from 12 experiments with a range of significant heights and periods.  The implementation of the video cameras records allowed us to have a visual record of the breaking waves in each of the experiments.

The next step was to study the physics of the Hilbert transform in order to understand how it can be used in detecting the breaking events in the data set.  This allowed us to eventually understand the results obtained when we applied the Phase-Time Method to the data, to see which criteria we need to add to the model to make it practical and accurate.

The Phase-Time Method was applied to obtain time-series of deviation of the local frequency.  By analyzing the data from the experiments, and by using the video records as a tool to check and distinguish the breaking waves and non-breaking waves, we tried to find some characteristic patterns in this frequency signal which are related to the wave breaking.  These characteristics are potentially useful in developing a detection model. 

If some characteristic patterns are found and a model can be developed, its skills to detect the breaking waves will be evaluated in order to validate the model.  Finally the limits of the model will be stated and its range of application determined.

Related Publications: Seymour, R., Zimmermann, C-A., and Zhang, J., "Discriminating Breaking in Deep Water Waves," Ocean Wave Kinematics, Dynamics and Loads on Structures, Proc. 1998 International OTRC Symposium, April 30-May 1, 1998, Houston, TX, pp. 305-312.

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