Abstracts Physics

Verification of SWAN with DELILAH data:

by A.E. Baaijens

In the past years the SWAN wave model was developed. SWAN is a third-generation spectral wave model for applications in coastal areas. The verification of the model has been carried out for a few laboratory and field experiments. In this thesis the DELILAH field experiment held at the property of the Field Research Facility in Duck, North Carolina, was applied. The aim was to implement SWAN for DELILAH and to obtain further improvements of the SWAN model. The bathymetry with an average slope of I: 150 is characterised by a constantly changing sandbar in the near-shore area at the Field Research Facility. At 13m depth an array of wave gauges is located (SAMSON). The boundary condition was taken from the spectra obtained at this location and was uniformly applied along a straight line through this location and parallel to the beach. The research was restricted to nine crossshore gauge locations in the near-shore zone. The I-dimensional spectral- and wave heightobservations in this area were compared to the SWAN results and interpreted. The results of the tests showed that SWAN underpredicted the dissipation of wave energy and overestimated the non-linear triad wave interactions. The first discrepancy was improved by adapting the tuning parameter in the wave breaking formulation (gamma) according to Battjes & Stive. The second discrepancy was improved by adapting the tuning parameter in the Source term for the triad interactions (a(EB)) of the action balance equation. Conclusions were that a y value based on the deep-water steepness according to Battjes & Stive improved the results of the significant wave heights significantly at the gauges where wave breaking was relevant. Secondly, small improvements in the cross-spectral distribution were obtained by increasing the value of the proportionality parameter a(EB)=0.25 to a(EB) =0.5. Interesting was that the parameter of a(EB)=O.5 gave the best results for both a case with the barred bathymetry and for a case without the bar. The final results are acceptable, but further investigation of the non-linear triad interactions is advisable to improve the approximation of the cross-spectral energy distribution.