MODELING OF TIME-VARYING SHEAR CURRENT FIELD UNDER BREAKING AND BROKEN WAVES WITH SURFACE ROLLERS

摘要

This study aims to develop a new numerical model for predictions of the time-varying shear current field under breaking and broken waves. The present model differs from the other similar existing models in that the model explicitly determines the bottom shear stress so that it satisfies both force balance and mass-conservation equations while most of the other existing models leave the bottom shear stress as one of the calibration parameters to be fitted. The present model consists of two sub-models, a wave model and a flow model. The wave model is based on modified Boussinesq equations with evolution and dissipation of surface rollers. The flow model is based on Reynolds' equations with turbulence closure models and computes vertical profiles of wave-induced shear current field. The numerical model is applied to various existing and newly performed experimental cases which cover various breaker types and bed profiles with different bed roughness. The present model showed overall good predictive skills of various surf zone hydrodynamics such as wave heights, mean water levels and undertow profiles. It should also be highlighted that the model has only a few calibration parameters and the predictive skill of the model is relatively less sensitive to these parameters.