Testing the non-stationary option of the SWAN wave model

Testing the non-stationary option of the SWAN wave model

Fraza, L.A.J.

Holthuijsen, L.H. (mentor)
Andorka Gal, J.H. (mentor)
Schiereck, G.J. (mentor)
Battjes, J.A. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

1998-08-01

SWAN is a so called third-generation spectral wave model for applications in coastal areas. The existing model is still subject to further extensions. One of these extensions is a non-stationary option that makes the model suitable for use in large geographical areas. As part of the development of a non-stationary option of the SWAN model, tests have been performed in this study with the currently available nonstationary version. To test the performance of the model, propagation and evolution of wave energy have been separately tested at first. Thereupon two test have been performed where evolution and propagation are combined. In the first tests the propagation velocity of wave energy has been calculated. The results are compared with the group velocity as calculated with use of the linear wave theory. In addition to the propagation velocity of wave energy the numerical diffusion of the propagation scheme that is implemented is very important for application in large geographical areas. The implicit numerical propagation scheme that is implemented in the current version gives good results regarding the propagation velocity of wave energy but it is too diffusive to be used for large geographical areas. The evolution of both significant wave height and mean frequency are calculated in idealised cases. Because SWAN is a so called third-generation model the shape of the wave spectrum is calculated taking the non-linear wave-wave interactions into account. These interactions, that govern the evolution of the shape of the spectrum, have strongly varying time scales. As a result of the time discretisation, where a single time step size is used to integrate processes with different time scales, instabilities arose. To ensure stable integration a limiter is implemented. This limiter was found to influence the results. The duration limited growth rate of both significant wave height and mean wave frequency depend on the time step used. The tests for combined propagation and evolution deal with a rather extreme but nonetheless realistic hurricane and a storm in the Mediterranean sea. The last test gave a good insight in the performance of the SWAN model. In SWAN the spectrum is calculated up to higher frequencies than in other thirdgeneration models. The calculation of the spectrum at these high frequencies did not lead to satisfactory results. When compared with the results of another third generation wave model (WAM) and with measurements it was found that the mean wave frequency as calculated by the SWAN model was significantly higher.

SWAN
non-stationary data
wave energy

http://resolver.tudelft.nl/uuid:f2fcc607-429c-41c7-b402-f3db86d15bf4

Student theses

master thesis

(c) 1998 Fraza, L.A.J.