Applied/ACMS/absS23

ACMS Abstracts: Spring 2023

Paul Milewski (Bath)

Title: Embedded solitary internal waves

Abstract: The ocean and atmosphere are density stratified fluids. Stratified fluids with narrow regions of rapid density variation with respect to depth (pycnoclines) are often modelled as layered flows. In this talk we shall examine horizontally propagating internal waves within a three-layer fluid, with a focus on mode-2 waves which have oscillatory vertical structure. Mode-2 nonlinear waves (typically) occur within the linear spectrum of mode-1 waves (i.e. they travel at lower speeds than mode-1 waves), and are hence generically associated with an unphysical resonant mode-1 oscillatory tail. We will present evidence that these tail oscillations can be found to have zero amplitude, thus resulting in families of localised solutions (so called embedded solitary waves) in the Euler equations. This is the first example we know of embedded solitary waves in the Euler equations.

Nimish Pujara (UW)

Title: Flow and friction on a beach due to breaking waves

Abstract: As water waves approach a beach, they undergo dramatic transformations that have significant consequences for beach morphology. The most important transformations for the flow dynamics are that waves usually break before they reach the shoreline and that their height collapses when they do reach the shoreline. In this talk, we consider these processes and the subsequent flow that is driven up the beach. We present measurements of this flow in large-scale experiments with a focus on understanding the flow evolution in space and time, its friction with the beach surface, and its potential to transport large amounts of sediment. We demonstrate the link between wave-driven flow on a beach and canonical solutions to the shallow water equations, which allows us to describe the flow using reduced-parameter models. Using measurements of the wall shear stress, we also show that the importance of friction is confined to a narrow region within the flow at the interface between the wet and dry portions of the beach, and we present a simplified model that considers the dynamics of this region. Finally, we discuss a few extensions of this work that have applications to understanding sediment transport and the risk of coastal flooding.