After carrying out computations for 10 time-steps, the program displays an

estimate of the run time. The run time could vary, however, depending on other

processes running on the computer at the same time.

BOUSS-2D outputs the significant wave height and mean current distribution

over the entire computational grid. For some applications, it might be necessary

to analyze the time series data at specific grid points to obtain frequency or direc-

tional wave spectra, wave height statistics, reflection coefficients, etc. Hughes

(1993) extensively discusses time and frequency domain analysis techniques for

time series data in a laboratory setting. Similar techniques can be applied to time

series output from the numerical model.

Standard statistical analysis techniques can be applied to the surface eleva-

tion or velocity time records to obtain the mean, standard deviation, skewness,

and kurtosis of the time records. The skewness of the surface elevation, η, and its

time derivative, ηt, can be used to quantify the degree of wave asymmetry or

nonlinearity in shallow water. Zero-crossing analysis techniques can be used to

define the heights and periods of individual wave cycles within an irregular wave

record. These can be analyzed to obtain parameters such as the root-mean-square

wave height, *H*rms, average height of the highest one-third of the waves, *H*1/3, or

the average wave period, *T*av.

Standard spectral analysis techniques can be used to obtain the surface eleva-

tion or velocity spectra. These can be analyzed to obtain parameters such as the

significant wave height, *H*mo, and spectral peak period, *T*p. Different techniques

have been proposed for the estimation of directional wave spectra using either an

array of wave gauges (e.g., Nwogu 1989) or collocated measurements of the

surface elevation and horizontal velocities (e.g., Nwogu et al. 1987). Collocated

time series of the surface elevation and horizontal velocities can also be used to

estimate the reflection coefficients using the technique described in Hughes

(1993).

40

Chapter 4 Setting Up and Running BOUSS-2D

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