Numerical Simulations of Coastal Overwash Using A Phase-Averaged Wave−Current−Sediment Transport Model

Coastal overwash is a natural phenomenon that commonly occurs during storm events and can cause considerable changes in nearshore morphology within a short time.In this study,a complete set of empirical overwash transport algorithms is developed and introduced into a phase-averaged wave-current-sediment transport coupling model that integrates the Finite-Volume Community Ocean Model(FVCOM)and the Simulating Waves Nearshore(SWAN)model.The resulting morphological evolution model can simulate coastal overwash.Validation against the data obtained from multiple sets of laboratory overwash experiments demonstrates that the model performs relatively well in simulating morphological changes caused by runup overwash and inundation overwash under different hydrodynamic and beach profile conditions.The sensitivity of each empirical coefficient in the overwash transport algorithms is comprehensively analyzed.The effects of each coefficient on the output of the model are discussed,and a recommended value range is provided for each coefficient.

Predicting Net Cross-Shore Total Load Transport: A Phase-Averaging, Quasi-Steady Approach Incorporating Undertow Contribution

Wave shapes that induce velocity skewness and acceleration asymmetry are usually responsible for onshore sediment transport, whereas undertow and bottom slope effect normally contribute to offshore sediment transport. By incorporating these counteracting driving forces in a phase-averaged manner, the theoretically-based quasi-steady formula of Wang （2007） is modified to predict the magnitude and direction of net cross-shore total load transport under the coaction of wave and current. The predictions show an excellent agreement with the measurement data on medium and fine sand collected by Dohmen-Janssen and Hanes （2002） and Schretlen （2012） in a full-scale wave flume at the Coastal Research Centre in Hannover, Germany. The modified formula can predict the net onshore transport of fine sand in sheet flows. In particular, it can predict the net offshore transport of medium sand in rippled beds through enlarged bed roughness, as well as the net offshore transport of fine-to-coarse sand in sheet flows with the aid of a new criterion to judge the occurrence of net offshore transport.

Investigation and Discussion on the Beach Morphodynamic Response Under Storm Events Based on A Three-Dimensional Numerical Model

A well-established 3D phase-averaged beach morphodynamic model was applied to investigate the morphodynamics of a typical artificial beach,and a series of discussions were made on the surfzone hydro-sedimentological processes under calm and storm events.Model results revealed that the nearshore wave-induced current presents a significant 3D structure under stormy waves,where the undertow and longshore currents exist simultaneously,forming a spirallike circulation system in the surfzone.Continuous longshore sediment transport would shorten the sediment supply in the cross-shore direction,subsequently suppress the formation of sandbars,showing that a typical recovery profile under calm waves does not necessarily develop,but with a competing process of onshore drift,undertow and longshore currents.Sediment transport rate during storms reaches several hundreds of times as those under calm waves,and two storm events contribute approximately 60%to the beach erosion.Sediment transport pattern under calm waves is mainly bed load,but as the fine sands underneath begin to expose,the contribution of suspended load becomes significant.

Experimental investigation of wall-bounded turbulence drag reduction by active control of double piezoelectric vibrator

In order to manipulate the large-scale coherent structures in the wall-bounded turbulence and reduce the skin-friction,an active-control experimental investigation is performed by using the synchronous and asynchronous vibrations of double piezoelectric vibrators embedded spanwisely on a smooth flat plate surface.A TSI-IFA300 hot-wire anemometer and a TSI-1621 A-Tl.5 hot-wire probe are used to measure the time series of the instantaneous velocity at different locations.The influences of the vibrations on the wall-bounded turbulence are compared in a multi-scale point of view.A disturbance Reynolds Number Red=pd2 f/μis introduced to represent the disturbance.A probability density functions(PDFs)of the multi-scale components of the turbulence velocity and the multi-scale conditional phase-averaged waveform are studied in detail using the wavelet transform.The results show that the maximum drag reduction rate 18.54%is obtained at 100 V/160 Hz and Red=0.54 in the asynchronous vibration mode.The disturbances generated by the vibrators have a significant influence on the sweep events of the burst.The asynchronous vibration model is more effective than the synchronous vibration one.A possible physical mechanism is suggested to explain why the disturbance frequency of 160 Hz leads to an optimal parameter set for the drag reduction.