Preliminary Investigation of Momentary Bed Failure Using a Multi-dimensional Eulerian Two-phase Model

Abstract:

In the past decade, researchers have clearly been making progress in predicting coastal erosion/recovery; however, evidences are also clear that existing coastal evolution models cannot predict coastal responses subject to extreme storm events. In this study, we investigate the dynamics of momentary bed failure driven by large horizontal pressure gradients, which may be the dominant sediment transport mechanism under intense storm condition. Recently, a multi-dimensional two-phase Eulerian sediment transport model has been developed and disseminated to the research community as an open-source code. The numerical model is based on extending an open-source CFD library of solvers, OpenFOAM. Model results were validated with published sediment concentration and velocity data measured in steady and oscillatory flow. The 2DV Reynolds-averaged model showed wave-like bed instabilities when the criteria of momentary bed failure was exceeded. These bed instabilities were responsible for the large transport rate observed during plug flow and the onset of the instabilities was associated with a large erosion depth. To better resolve the onset of bed instabilities, subsequent energy cascade and the resulting large sediment transport rate and sediment pickup flux, 3D turbulence-resolving simulations were also carried out. Detailed validation of the 3D turbulence-resolving Eulerian two-phase model will be presented along with the expanded investigation on the dynamics of momentary bed failure.