Modellering laagfrequente golfenergie met SWAN : aangepaste formulering voor een spectrale bronterm voor triads op basis van de DCTA

As part of the kennisprogramma Zeespiegelstijging (KP-ZSS), an improvement of the spectral wave model SWAN is aspired. With this improvement, the penetration of low-frequency wave energy into the Waddensea is modelled more accurately. The current default formulation for triads, the LTA, is not capable of transferring energy to lower frequencies. This omission is an important hypothesis for the lack of penetrated low-frequency energy as well as the absence of interactions between waves with unequal direction (non collinear).
Within the Kennis voor Keringen (KvK) programme, a project was formulated for the modification of the formulation of a triad source term for application in SWAN. The basis for this work is the Discrete Collinear Triad Approximation (DCTA) which was developed in 2009 (Booij et al. (2009) [R 5]).
The main objective of this project is to improve the existing DCTA formulation. The intended improvements are based on a heuristic representation of phenomena, associated with triad interactions, as much as possible supported by available physical rationale as possible, but not derived from first principles. Important phenomena are the evaluation of sum- and difference and collinear and non-collinear interactions. Additionally, the transformation towards a prescribed spectral equilibrium shape due to both sub- and super harmonic transfers is essential. The intention is to have the modified formulation implemented (by third parties) in SWAN for subsequent testing through application in the Wadden Sea.

The formulation was included in SWAN by the TU Delft
The implementation was described by Deltares: in the study on low frequency wave penetration in SWAN 
Validation of DCTA method, 2023 M. Doelman and J. Groeneweg