Citation

Barker, Christopher H. 1998. "Directional Irregular Wave Kinematics," Ph.D. Dissertation, Department of Environmental Water Resources, University of California at Berkeley, Chair: Professor Rodney J. Sobey.

Abstract

Coastal and ocean processes are heavily influenced by the kinematics of waves. In order to understand these processes, researchers place a variety of instruments in the sea in an attempt to measure the waves. These instruments all measure a small set of physical quantities at a small number of locations. The balance of the kinematics must be predicted through analysis of the measured records. Most of the currently used methods of analysis rely on the superposition of linear waves to recreate complex seas. These methods are compromised by linearizing approximations to the free surface boundary conditions. Fidelity in the interpretation of wave measurements is enhanced by insisting that the analysis satisfies the full nonlinear free surface boundary conditions.

The Local Fourier method for irregular wave kinematics (LFI) is introduced and expanded to include the interpretation of records from arrays of instruments. It is a local method, in that a separate solution is sought that fits the measured record(s) in a small local window in time, rather than attempting to find a single solution for a large segment of the record. Each window solution satisfies the full set of governing equations for gravity waves, including the nonlinear free surface boundary conditions. The solution in each window is a potential function whose form is based upon a Stokes style expansion for intersecting waves. The parameters of the potential function are found by a nonlinear optimization that seeks the solution that matches the measured record and satisfies the full free surface boundary conditions.

The LFI method was introduced by Sobey (1992) as a two dimensional method for interpreting a single water surface measurement of irregular waves. In this dissertation, the two dimensional method is expanded to include the analysis of subsurface pressure records. The method is then extended to the prediction of directional irregular wave kinematics from the measurements of arrays of instruments, including wave staffs and subsurface pressure gauges. In this extended analysis, the LFI method includes nonlinear wave-wave interactions, in addition to the self-wave interactions of the two dimensional form. Results of the analysis on theoretical, laboratory and field records are provided.

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