R.J. Sobey, S.A. Hughes r Coastal Engineering 36 (1999) 1736
Fig. 2. Measured PUV traces.
notable in trace Zb. where the sampling interval is much shorter. The P traces are
consistently smooth. In addition, time is measured independently by each sensor, and
systematic timing discrepancies are possible. This is not evident at the scale of these
plots, but becomes a potential concern at the time scale of the local analysis that is
Analysis of simultaneous traces such as Fig. 2 has routinely adopted linear wave
theory in the interpretation of the local kinematics and in the estimation of the water
surface time history. This prior assumption of linearity has the potential for significant
misinterpretation of the actual local kinematics. Nonlinear influences may be filtered and
distorted by the record interpretation. In addition, most linear analyses assume stationary
conditions over a measurement span of sufficient duration to obtain adequate frequency
resolution in the Fourier transform.
This paper will introduce and demonstrate a nonlinear theory for the interpretation of
PUV traces. The initial discussion will review and illustrate the common linear analysis.
This leads to the presentation of a nonlinear theory for the interpretation of the local
irregular kinematics sampled by the PUV gauge. The theory follows the spirit of the
Sobey Z1992. analysis for irregular wave kinematics from a water surface record. The
nonlinear PUV theory is demonstrated and evaluated for theoretical PUV traces from
steady wave theory and for measured PUV traces from the Platform Edith and Columbia
River sites anticipated in Fig. 2.