The incident wave spectrum can be specified using a measured two-
dimensional spectrum, by generating a spectrum using a parametric shape, or
from a spectrum calculated by a global- or regional-scale wave model. Rarely do
measured spectra have the directional resolution required by the model; thus,
measured spectra require interpolation to finer resolution. A parametric spectral
shape together with a directional spreading function can also be applied to
specify an incident spectrum, knowing the wave height, period, and direction.
SMS includes the capability to generate incident spectra using a TMA one-
dimensional shallow-water spectral shape (named for the three data sets used to
develop the spectrum: TEXEL storm, MARSEN, and ARSLOE) (Bouws et al.
1985) and a cosnnα directional distribution (see Chapter 5). To generate a TMA
spectrum, the following parameters must be specified: peak wave period (Tp),
wave height, water depth, and a spectral peakedness parameter (γ). The
peakedness parameter controls the width of the frequency spectrum (small
numbers give broad peaks and large numbers give narrow peaks). The
directional distribution of the spectrum is specified with a mean direction and a
directional spreading coefficient (nn). The energy in the frequency spectrum is
spread proportional to cosnn(α-αm), where α is direction of the spectral
component and αm is the mean wave direction. Guidance for selecting γ and nn
is given in Table 1 (Thompson et al. 1996). Spectra with large peak periods are
generally narrow in both frequency and direction (swell). For small peak
periods, spectra are typically broad in both frequency and direction (sea).
Table 1
Approximate Spectral Peakedness and Directional Spreading
Parameters
γ
nn
Tp , Sec
≤ 10
3.3
4
11
4
8
12
4
10
13
5
12
14
5
16
15
6
18
16
6
20
17
7
22
18
7
26
19
8
28
20
8
30
Current Fields
A current field input file is required only if ICUR = 1 or 2 in the model
parameter file (it is ignored if ICUR = 0). The current vector is specified as
x- and y-components of the current at each grid cell, u and v, in the units
meters/second. The x- and y-directions correspond to the x- and y-axes of the
grid in the local STWAVE coordinates (Figure 3). The first line of the current
input file is NI, NJ, and DXINC, identical to the parameters specified in the
bathymetry file. STWAVE checks that these values are consistent with the
bathymetry file, and if they are not, model execution is terminated with the error
"current field does not match depth grid size." Next, the header for the current
19
Chapter 3 Input File Description
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