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Nicolaj Krog Larsen

Subglacial sediment mechanics investigated by computer simulation of granular material

Publikation: KonferencebidragKonferenceabstrakt til konferenceForskning

  • Anders Damsgaard
  • David Lundbek Egholm
  • Slawek Tulaczyk, Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA, USA
  • Jan A. Piotrowski
  • Nicolaj Krog Larsen
  • Matthew Siegfried, Scripps Instition of Oceanography, USA
  • Lucas H. Beem, California Institute of Technology, Danmark
  • Jenny Suckale, Department of Geophysics, Stanford University, Institute of Computational and Mathematical Engineering, Stanford University, California, USA
The mechanical properties of subglacial sediments are known to directly influence the stability of ice streams and fast-moving glaciers, but existing models of granular sediment deformation are poorly constrained. In addition, upscaling to generalized mathematical models is difficult due to the mechanical nonlinearity of the sediment, internal porosity changes during deformation, and associated structural and kinematic phase transitions.
In this presentation, we introduce the Discrete Element Method (DEM) for particle-scale granular simulation. The DEM is fully coupled with fluid dynamics. The numerical method is applied to better understand the mechanical properties of the subglacial sediment and its interaction with meltwater. The computational approach allows full experimental control and offers insights into the internal kinematics, stress distribution, and mechanical stability.
During confined shear with variable pore-water pressure, the sediment changes mechanical behavior, from stick, to non-linear creep, and unconstrained failure during slip. These results are contrary to more conventional models of plastic or (non-)linear viscous subglacial soft-bed sliding. Advection of sediment downstream is pressure dependent, which is consistent with theories of unstable bed bump growth.
Granular mechanics prove to significantly influence the geometry and hydraulic properties of meltwater channels incised into the subglacial bed. Current models assume that channel bed erosion is balanced by linear-viscous sediment movement. We demonstrate how channel flanks are stabilized by the sediment frictional strength. Additionally, sediment liquefaction proves to be a possible mechanism for causing large and episodic sediment transport by water flow.
Though computationally intense, our coupled numerical method provides a framework for quantifying a wide range of subglacial sediment-water processes, which are a key unknown in our ability to model the future evolution of ice sheets.
OriginalsprogEngelsk
Udgivelsesår2016
StatusUdgivet - 2016
BegivenhedAmerican Geophysical Union Fall Meeting 2016 - Moscone Center, San Francisco, USA
Varighed: 11 dec. 201617 dec. 2016

Konference

KonferenceAmerican Geophysical Union Fall Meeting 2016
LokationMoscone Center
LandUSA
BySan Francisco
Periode11/12/201617/12/2016

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