SWAN

Simulating WAves Nearshore

• Introduction
• SWAN and Delft3D
• References
• SWAN Home Page

technical specifications

SWAN which is a model of the Delft university of Technology is a non-stationary third-generation wave model (see e.g. Holthuijsen et al., 1993; Ris, 1997; citation on the references page) and is the successor of the stationary second-generation hiswa model (Holthuijsen et al., 1989). The HISWA model is at present widely used but it has some disadvantages:

• Wave propagation is limited to a directional sector of less than 120° (so strong refraction cannot be accommodated)
• The computational grid has to be orientated in the mean wave direction, which is operationally inconvenient
• It is parametric in frequency such that multi-modal wave fields cannot be simulated and
• The modification and addition of physical processes is rather difficult due to the highly parameterized formulations that are used. These limitations are to a large extent overcome by the new SWAN model.

The non-stationary SWAN model is based on the discrete spectral action balance equation and is fully spectral (over the total range of wave frequencies and over the entire 360°). This latter implies that short-crested random wave fields propagating simultaneously from widely different directions can be accommodated. The wave propagation is based on linear wave theory (including the effect of currents). The processes of wind generation, dissipation and nonlinear wave-wave interactions are represented explicitly with state-of-the-art third-generation formulations. (It is noted that for reasons of economy, more simple first- and second-generation formulations are also optionally available.) The SWAN model can also be applied as a stationary model (stationary mode). This is considered acceptable for most coastal applications because the travel time of the waves from the seaward boundary to the coast is relatively small compared to the time scale of variations in incoming wave field, the wind or the tide.

To avoid excessive computing time and to achieve a robust model in practical applications, fully implicit propagation schemes (in time and space) have been implemented. The SWAN computations can be made on a regular and a curvi-linear grid in a Cartesian co-ordinate system. Nested runs can be made with the regular grid option.

SWAN provides many output quantities including two-dimensional spectra, significant wave height and mean wave period, average wave direction and directional spreading, root-mean-square of the orbital near-bottom motion and wave-induced force (based on the radiation-stress gradient).

The SWAN model has successfully been validated and verified in several laboratory and (complex) field cases (see e.g. Ris, 1997).

The SWAN model was developed at Delft University of Technology, Delft (the Netherlands) and where it is undergoing further enhancements. It is specified as the new standard for nearshore wave modelling and coastal protection studies. Deltares has integrated the SWAN model in several models and is applying SWAN in its consultancy projects. The SWAN model has been released under public domain.