Forward-scattered waves, e.g., waves reflected off a structure but
traveling in the +x-direction, are also neglected.
b. Spatially homogeneous offshore wave conditions. The variation in the
wave spectrum along the offshore boundary of a modeling domain is
rarely known, and for domains on the order of tens of kilometers, is
expected to be small. Thus, the input spectrum in STWAVE is constant
along the offshore boundary. Future versions of the model will allow
variable input.
steady-state model. A steady-state formulation reduces computation time
and is appropriate for wave conditions that vary more slowly than the
time it takes for waves to transit the computational grid. For wave
generation, the steady-state assumption means that the winds have
remained steady sufficiently long for the waves to attain fetch-limited or
fully developed conditions (waves are not limited by the duration of the
winds).
refraction and shoaling, thus does not represent wave asymmetry. Model
accuracy is therefore reduced (wave heights are underestimated) at large
Ursell numbers.
e. Depth-uniform current. The wave-current interaction in the model is
based on a current that is constant through the water column. If strong
vertical gradients in current occur, their modification of refraction and
shoaling is not represented in the model. For most applications, three-
dimensional current fields are not available.
f. Bottom friction is neglected. The significance of bottom friction on wave
dissipation has been a topic of debate in wave modeling literature.
Bottom friction has often been applied as a tuning coefficient to bring
model results into alignment with measurements. Although bottom
friction is easy to apply in a wave model, determining the proper friction
coefficients is difficult. Also, propagation distances in a nearshore model
are relatively short (tens of kilometers), so that the cumulative bottom
friction dissipation is small. For these reasons, bottom friction is
neglected in STWAVE.
wave theory.
Ongoing research will enhance present model capabilities and eliminate some
model assumptions. The following sections describe wave propagation and
source/sink terms in STWAVE version 3.0.
5
Chapter 2 Governing Equations and Numerical Discretization
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