Different spectral parameters will be input depending on the selected wave
spectrum. The most commonly used parameters are described in the follow-
ing paragraphs. Detailed information on the different wave spectra and their
associated parameters are provided in Appendix B.
Significant Wave Height, Hmo (m) Defined as four times the square
root of the zeroth moment of the spectrum, i.e., Hmo= 4 m0 , where m0 =
∞
∫
Sη ( f )df . Hmo is equivalent to the average height of the highest one-
0
third of the waves (H1/3) for moderate sea states in deep water with a
Rayleigh wave height distribution. The input significant wave height
should not exceed 50 percent of the breaking limit given by the Miche
0.07 tanh kph.
wave spectrum is a maximum (Tp = 1/fp)
Minimum Wave Period, Tmin (s) The incident wave spectrum is set to
zero at all frequencies greater than 1/Tmin with the truncated wave spec-
trum optionally rescaled to match the target significant wave height. The
minimum wave period has to be greater than the limit imposed by the
dispersive properties of the Boussinesq equations, i.e., the wavelength
based on Tmin and hmax has to be greater than twice the maximum water
depth [L (Tmin) > 2hmax].
Maximum Wave Period, Tmax (s) The incident wave spectrum is set to
zero at all frequencies less than 1/Tmax. The maximum wave period is
used to separate infragravity waves from wind-generated waves and has
a default value of 25 s (prototype).
Wave Direction (deg) This is the direction the waves propagate into the
computational domain from, and is defined in a clockwise manner from
the northern boundary of the grid as shown in Figure 6. For example,
waves propagating into the domain normal to the western boundary
would have a direction of 270 deg. The incident wave direction also has
to be within 85 deg of the normal to the wave generation boundary.
Synthesized Time Series Duration This is the recycling period of the
Fourier series used to synthesize the time-histories and corresponds to
the time period over which output parameters such as the significant
wave height and mean velocities are calculated after steady-state condi-
tions have been established in the computational domain. The recom-
mended range is from 50 to 100 wave periods.
Random Number Seed The seed of the random number generator used
to select phase angles for the different Fourier components. Different
seeds can be used to obtain different time records from the same wave
spectrum.
33
Chapter 4 Setting Up and Running BOUSS-2D
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