Numerical model of swash motion and air entrapment within coarse-grained beaches

Copyright 2012 Elsevier B.V., All rights reserved.Peer reviewedPublisher PD

Experimental study of bore-driven swash hydrodynamics on permeable rough slopes

Peer reviewedPublisher PD

Subsurface processes generated by bore-driven swash on coarse-grained beaches

Peer reviewedPublisher PD

Numerical modelling of surfbeat

This thesis describes a numerical study on identifying parameters controlling the shoaling rate for the normally incident low frequency motion and the long wave reflection in the coastal zone.Civil Engineering and Geoscience

Dynamics and structure of planar gravity currents propagating down an inclined surface

Planar, Boussinesq, compositional gravity currents formed by the release of a fixed volume of heavier fluid from a closed lock and advancing on an inclined no-slip bottom surface in a reservoir with a horizontal free surface are investigated based on 3-D large eddy simulation. The initial region containing the lock fluid has a rectangular shape. Simulations are conducted for bottom slope angles, theta, between 0 degrees and 60 degrees. The running length of the inclined bottom was sufficiently long to allow a detailed study of the evolution, front dynamics and structure of the current during the latter stages of the deceleration phase (front velocity reduces with time). Results show that currents advancing over inclined surfaces with theta > 10 degrees are characterized by the formation of an intensified mixed vortex (IMV) at the back of the head. The IMV forms faster and its coherence, circulation, and size increase monotonically with increasing bottom slope angle. The paper discusses how the buoyancy in the head varies with varying bottom slope angle and with time. In particular, for theta >= 30 degrees, the current reaches a regime where the total buoyancy of the head and IMV is close to a constant and the value of this constant increases with increasing theta. During this regime, the head mainly loses buoyancy to the IMV. For theta >= 40 degrees, a close to linear decay of the head buoyancy with time is observed during the later stages of this regime. Simulation results show that, while for relatively small bottom slope angles most of the sediment is entrained beneath the head, for theta > 20 degrees the IMV has a much larger capacity to entrain the sediment compared to the head region past the initial stages of the propagation of the current. This means that sediment entrainment patterns of currents propagating over highly inclined surfaces are qualitatively very different from the widely studied case of currents propagating over horizontal surfaces. The paper also discusses the different regimes observed in the temporal evolution of the front velocity and the applicability of theoretical models derived based on the data obtained for relatively small bottom slope angles and a relatively short evolution of the current to describe the evolution of currents propagating over large bottom slope angles and/or at large times after the start of the deceleration phase. While it is found that mixing increases monotonically with increasing theta, the largest total kinetic energy for a given front position is observed for theta = 30 degrees-40 degrees. Results also show that the largest magnitude of the bed friction velocity is induced for theta = 30 degrees-40 degrees, which means that the currents with the largest capacity to entrain sediment are those with the largest rate of increase of total kinetic energy with the propagation distance. Published by AIP Publishing

Shoaling and shoreline dissipation of low?frequency waves

The growth rate, shoreline reflection, and dissipation of low?frequency waves are investigated using data obtained from physical experiments in the Delft University of Technology research flume and by parameter variation using the numerical model Delft3D?SurfBeat. The growth rate of the shoaling incoming long wave varies with depth with an exponent between 0.25 and 2.5. The exponent depends on a dimensionless normalized bed slope parameter ?, which distinguishes between a mild?slope regime and a steep?slope regime. This dependency on ? alone is valid if the forcing short waves are not in shallow water; that is, the forcing is off?resonant. The ? parameter also controls the reflection coefficient at the shoreline because for small values of ?, long waves are shown to break. In this mild?slope regime the dissipation due to breaking of the long waves in the vicinity of the shoreline is much higher than the dissipation due to bottom friction, confirming the findings of Thomson et al. (2006) and Henderson et al. (2006). The energy transfer from low frequencies to higher frequencies is partly due to triad interactions between low? and high?frequency waves but with decreasing depth is increasingly dominated by long?wave self?self interactions, which cause the long?wave front to steepen up and eventually break. The role of the breaking process in the near?shore evolution of the long waves is experimentally confirmed by observations of monochromatic free long waves propagating on a plane sloping beach, which shows strikingly similar characteristics, including the steepening and breaking.Hydraulic EngineeringCivil Engineering and Geoscience