Improved Modelling of Wave-Current Interaction in Swan

Abstract

Recent hindcast studies in the Amelander Zeegat tidal inlet in the Dutch Wadden Sea have shown the significant influence of currents on the prediction of wave fields by the spectral wave model SWAN. In following current, observations are typically well reproduced, but under strong opposing current, wave heights are significantly overestimated. Ris and Holthuijsen (1996) propose that such overestimations are due to insufficient steepness dissipation of waves on an opposing current gradient. The present paper presents a new formulation for the enhanced dissipation of waves on a counter current gradient which is scaled with the degree of Doppler shifting, and hence steepness increase, due to the current. This expression contains one additional unknown parameter, which is calibrated using laboratory observations. This formulation is suitable for both mature wave fields and young wind sea conditions. Application of this enhanced dissipation term to a data set of Amelander Zeegat field cases shows an improvement for opposing current situations in the tidal channel. For following current, no significant deterioration of results is found. In particular, the results for the young wind sea on the tidal flats are not significantly affected, unlike with the Ris and Holthuijsen (1996) expression.

The effects of a Severn Barrage on wave conditions in the Bristol Channel

“…Under blocking conditions, theory suggests that wave heights would tend to infinity for monochromatic conditions, which is clearly unrealistic. Additionally, comparisons with measurements have shown that wave heights are over estimated by Swan using standard settings for an opposing current [41][42][43], although wave heights in a following current are well predicted [41]. A version of the Swan 40.81, which was modified to model dissipation of waves by currents more accurately, was used in this work.…”

“…A version of the Swan 40.81, which was modified to model dissipation of waves by currents more accurately, was used in this work. The modifications were implemented by van der Westhuysen to include his work on improved wave-current interactions in Swan [41,43], a synopsis of which follows below.…”

“…Ris and Holthuijsen [37] showed that this expression alone over-predicted wave heights on an opposing current, due to unrealistically high values for the wave steepness being permitted. The inclusion of the bore-based model of Battjes and Janssen [41] for steep breaking waves in deep water was shown to improve the results, although errors in prediction still existed. Chawla and Kirby [42] note the difference between saturated depth limited breaking and the breaking observed in a following current which is weak and non-saturated.…”

“…The default version of this expression, calibrated for wind growth, over estimates wave heights for an opposing current, similar to the pulse-based model. Van der Westhuysen [41,43] combines the saturation-based whitecapping expression of [48] with an additional term for current-induced white-capping, adding another source term, S wc,curr, to equation 2 to improve the capability of Swan in regions of strong wave-current interaction. The original S wc term from Van der Westhuysen [48] is given as:…”

Influencia de las corrientes en los campos de oleaje en el área de Bocas de Ceniza, Caribe Colombiano

“…Se recomienda para futuros trabajos realizar la calibración del modelo, como lo descrlbe [19], donde se confirma la sobrees timación del modelo SWaN en presencia de corrientes, siendo corregida a través de la for mulación del whitecapping.…”