A Small-Scale Model of Sea Ice Dynamics in the Antarctic Marginal Ice Zone Using Fluid-Structure Interaction and the Reference Map Technique

Mahomed, Nadiya

A Small-Scale Model of Sea Ice Dynamics in the Antarctic Marginal Ice Zone Using Fluid-Structure Interaction and the Reference Map Technique

Thesis / Dissertation

2024

Publisher

University of Cape Town

Department

Department of Civil Engineering

Faculty

Faculty of Engineering and the Built Environment

Abstract

Sea ice covers approximately 10% of the Earth's surface and modulates the sea-air heat and momentum exchange, therefore playing a major role in the global climate. The Antarctic marginal ice zone (MIZ) is the seasonally varying region between the open Southern Ocean and the Antarctic pack ice. It is a highly dynamic area containing ice floes (highly mobile round pancake ice) surrounded by interstitial grease ice, where turbulent sea states prevent sea ice consolidation. The sea ice dynamics of this region influences the global climate and therefore research in this area is important to understand global climate and predict long-term change. Adequate research on the region has been challenging due to its complex nature. Understanding sea ice dynamics processes and influence on global climate is complex and many simplifications have been made when modelling and analysing the system on a large scale. Many climate models struggle to encapsulate the regional and temporal variability of Antarctica. Positive and negative trends found by the models are influenced by statistical analyses chosen, with different methods producing opposing trends in some instances. Subsequently, there is less consensus on the accuracy of large-scale models. Large knowledge gaps still exist with regards to the natural variability of Antarctic sea ice, thus limiting the ability to accurately forecast long-term changes. The accurate modelling of the interplay of temperature, waves, sea ice dynamics as well as wind and ocean currents is necessary, not only to predict sea ice dynamics and wave energy dissipation, but also to advance understanding of the governing mechanisms of sea ice growth and decay in the Antarctic MIZ in particular. Deeper into the Antarctic MIZ with up to 100% sea ice concentration, the wave-ice interaction is highly complex being characterized by floe collision, turbulent eddy generation at the ice-water interface due to skin drag, and floe-grease ice interaction. Large- and mesoscale sea ice dynamics models are mainly continuum models and do not address the detailed heterogeneous sea ice composition. Finer-scale models on a floe level commonly use either a molecular dynamics schemes based on Hertzian collision dynamics or the discrete-element method. These models generally describe solitary ice floes floating in water as a collection of interacting particles, which, however, simplifies the ice floe solid mechanics behaviour and the fluid-structure interaction significantly. In contrast to discrete particle models, this work proposed to study ice floe motion due to wave action. This is accomplished by developing and implementing a continuum approach for the solid and fluid constituents that accounts for the actual heterogeneous ice cover composition in terms of a geometrical layout of ice floes and interstitial grease ice. The model includes the respective material properties describing the solid-like deformation behaviour of ice floes and the fluid-like viscous behaviour of grease ice represented with their respective material laws. A novel fluid-structure interaction (FSI) method is employed, using the reference map technique (RMT), which accurately describes the interaction between the solids and fluid, and the response to wave forcing.

Keywords

Engineering

Reference:

Collections

Masters

Full item page