A Time-Dependent Simulation of the Ross Ice Shelf Flow (Abstract)

The finite-element model discussed by MacAyeal and Thomas (1982) has been improved to include solution of the heat equation within each element, and to accelerate convergence to solution of the momentum-balance equations in terms of ice-shelf spreading rates. The model is now sufficiently rapid to permit both snapshot and time-marching simulations of a large ice shelf at high spatial and temporal resolution (grid size 10 km; time step 0.1 a). Here, we describe three model simulations of Ross Ice Shelf behavior.

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Tidal modulation of ice-shelf flow: a viscous model of the Ross Ice Shelf

Journal of Glaciology ◽

10.3189/2014jog13j203 ◽

2014 ◽

Vol 60 (221) ◽

pp. 500-508 ◽

Cited By ~ 9

Author(s):

Kelly M. Brunt ◽

Douglas R. MacAyeal

Keyword(s):

Ross Sea ◽

Element Model ◽

Tidal Effects ◽

Ice Shelf ◽

Ice Streams ◽

Indirect Response ◽

Ross Ice Shelf ◽

Creep Flow ◽

Sea Surface Slopes ◽

Shelf Flow

AbstractThree stations near the calving front of the Ross Ice Shelf, Antarctica, recorded GPS data through a full spring–neap tidal cycle in November 2005. The data revealed a diurnal horizontal motion that varied both along and transverse to the long-term average velocity direction, similar to tidal signals observed in other ice shelves and ice streams. Based on its periodicity, it was hypothesized that the signal represents a flow response of the Ross Ice Shelf to the diurnal tides of the Ross Sea. To assess the influence of the tide on the ice-shelf motion, two hypotheses were developed. The first addressed the direct response of the ice shelf to tidal forcing, such as forces due to sea-surface slopes or forces due to sub-ice-shelf currents. The second involved the indirect response of ice-shelf flow to the tidal signals observed in the ice streams that source the ice shelf. A finite-element model, based on viscous creep flow, was developed to test these hypotheses, but succeeded only in falsifying both hypotheses, i.e. showing that direct tidal effects produce too small a response, and indirect tidal effects produce a response that is not smooth in time. This nullification suggests that a combination of viscous and elastic deformation is required to explain the observations.

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The Effects of Basal Melting on the Present Flow of the Ross Ice Shelf, Antarctica

Journal of Glaciology ◽

10.1017/s0022143000006900 ◽

1986 ◽

Vol 32 (110) ◽

pp. 72-86 ◽

Cited By ~ 46

Author(s):

D.R. MacAyeal ◽

R.H. Thomas

Keyword(s):

Large Scale ◽

Oceanic Circulation ◽

Ice Shelf ◽

Ice Streams ◽

Ross Ice Shelf ◽

Flow And Heat Transfer ◽

Improve Model ◽

Dependent Flow ◽

Basal Melting ◽

Shelf Flow

AbstractWe use a hybrid finite-element/finite-difference model of ice-shelf flow and heat transfer to investigate the effects of basal melting on the present observed flow of the Ross Ice Shelf, Two hypothetical basal melting scenarios are compared: (i) zero melting everywhere and (ii) melting sufficient to balance any large-scale patterns of ice-shelf thickening that would otherwise occur. As a result of the temperature-dependent flow law (which we idealize as having a constant activation energy of 120 kJ mol−1, a scaling coefficient of 1.3 N m−2s1/3, and an exponent of 3), simulated ice-shelf velocities for the second scenario are reduced by up to 20% below those of the first. Our results support the hypothesis that melting patterns presently maintain ice thickness in steady state and conform to patterns of oceanic circulation presently thought to ventilate the sub-ice cavity. Differences between the simulated and observed velocities are too large in the extreme south-eastern quarter of the ice shelf to permit verification of either basal melting scenario. These differences highlight the need to improve model boundary conditions at points where ice streams feed the ice shelf and where the ice shelf meets stagnant grounded ice.

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Fracture and back stress along the Byrd Glacier flowband on the Ross Ice Shelf

Antarctic Science ◽

10.1017/s0954102004002056 ◽

2004 ◽

Vol 16 (3) ◽

pp. 345-354 ◽

Cited By ~ 6

Author(s):

JAMES P. KENNEALLY ◽

TERENCE J. HUGHES

Keyword(s):

Fracture Mechanics ◽

Ductile Fracture ◽

Back Stress ◽

Ice Thickness ◽

Subsequent Growth ◽

Ice Shelf ◽

Ross Ice Shelf ◽

Transverse Tensile ◽

Grounding Line ◽

Shelf Flow

East Antarctic ice discharged by Byrd Glacier continues as a flowband to the calving front of the Ross Ice Shelf. Flow across the grounding line changes from compressive to extensive as it leaves the fjord through the Transantarctic Mountains occupied by Byrd Glacier. Magnitudes of the longitudinal compressive stress that suppress opening of transverse tensile cracks are calculated for the flowband. As compressive back stresses diminish, initial depths and subsequent growth of these cracks, and their spacing, are calculated using theories of elastic and ductile fracture mechanics. Cracks are initially about one millimeter wide, with approximately 30 m depths and 20 m spacings for a back stress of 83 kPa at a distance of 50 km beyond the fjord, where floating ice is 600 m thick. When these crevasses penetrate the whole ice thickness, they release tabular icebergs 20 km to 100 km wide, spaced parallel to the calving front of the Ross Ice Shelf.

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The Effects of Basal Melting on the Present Flow of the Ross Ice Shelf, Antarctica

Journal of Glaciology ◽

10.3189/s0022143000006900 ◽

1986 ◽

Vol 32 (110) ◽

pp. 72-86 ◽

Cited By ~ 1

Author(s):

D.R. MacAyeal ◽

R.H. Thomas

Keyword(s):

Large Scale ◽

Oceanic Circulation ◽

Ice Shelf ◽

Ice Streams ◽

Ross Ice Shelf ◽

Flow And Heat Transfer ◽

Improve Model ◽

Dependent Flow ◽

Basal Melting ◽

Shelf Flow

AbstractWe use a hybrid finite-element/finite-difference model of ice-shelf flow and heat transfer to investigate the effects of basal melting on the present observed flow of the Ross Ice Shelf, Two hypothetical basal melting scenarios are compared: (i) zero melting everywhere and (ii) melting sufficient to balance any large-scale patterns of ice-shelf thickening that would otherwise occur. As a result of the temperature-dependent flow law (which we idealize as having a constant activation energy of 120 kJ mol−1, a scaling coefficient of 1.3 N m−2 s1/3, and an exponent of 3), simulated ice-shelf velocities for the second scenario are reduced by up to 20% below those of the first. Our results support the hypothesis that melting patterns presently maintain ice thickness in steady state and conform to patterns of oceanic circulation presently thought to ventilate the sub-ice cavity. Differences between the simulated and observed velocities are too large in the extreme south-eastern quarter of the ice shelf to permit verification of either basal melting scenario. These differences highlight the need to improve model boundary conditions at points where ice streams feed the ice shelf and where the ice shelf meets stagnant grounded ice.

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Numerical Modeling of Ice-Shelf Motion

Annals of Glaciology ◽

10.3189/s0260305500002755 ◽

1982 ◽

Vol 3 ◽

pp. 189-194 ◽

Cited By ~ 6

Author(s):

D. R. MacAyeal ◽

R. H. Thomas

Keyword(s):

Ice Thickness ◽

Subgrid Scale ◽

Good Qualitative Agreement ◽

Ice Shelf ◽

Ice Streams ◽

Ross Ice Shelf ◽

Sea Bed ◽

Flow Law ◽

Stress Variability ◽

Shelf Flow

Finite-element simulations of the Ross Ice Shelf flow yield good qualitative agreement with observation, but velocity magnitudes tend to be too low up-stream of ice rises and too high near the ice front. These errors will be significantly reduced by better model convergence to the flow law, more accurate values of the flow-law parameters, better resolution of the ice streams, and inclusion of subgrid scale stress variability produced by crevassing and ice-fabric orientation. A model run featuring a hypothetical ice rise down-stream of Crary Ice Rise indicates that the distinctive strain-rate patterns produced by an isolated ice rise can be cancelled by neighboring ice rises. This suggests that an isolated ice rise might migrate up-stream along sea-bed ridges unless there are neighboring ice rises acting to stabilize the surrounding ice-thickness tendencies.

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The Potsdam Parallel Ice Sheet Model (PISM-PIK) – Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

The Cryosphere Discussions ◽

10.5194/tcd-4-1307-2010 ◽

2010 ◽

Vol 4 (3) ◽

pp. 1307-1341 ◽

Cited By ~ 10

Author(s):

M. A. Martin ◽

R. Winkelmann ◽

M. Haseloff ◽

T. Albrecht ◽

E. Bueler ◽

...

Keyword(s):

Steady State ◽

Dynamic Equilibrium ◽

Ice Sheet ◽

Surface Velocity ◽

Ice Shelf ◽

Surface Mass ◽

Ross Ice Shelf ◽

Melt Distribution ◽

Spreading Rates ◽

Equilibrium Simulation

Abstract. We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK). The simulation is initialized with present-day conditions for topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and basal melt distribution are parameterized. Grounding lines and calving fronts are free to evolve, and their modeled equilibrium state is compared to observational data. A physically-motivated dynamic calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf areas in particular. The results show that the different flow regimes in sheet and shelves, and the transition zone between them, are captured reasonably well, supporting the approach of superposition of SIA and SSA for the representation of fast motion of grounded ice. This approach also leads to a natural emergence of streams in this new 3-D marine ice sheet model.

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The shape of change: an EOF approach to identifying sources of transient thickness change in an ice shelf

Annals of Glaciology ◽

10.1017/aog.2017.16 ◽

2017 ◽

Vol 58 (74) ◽

pp. 21-27 ◽

Cited By ~ 2

Author(s):

Adam J. Campbell ◽

Christina L. Hulbe ◽

Choon-Ki Lee

Keyword(s):

Statistical Approach ◽

Flow Model ◽

Response Surfaces ◽

Ice Shelf ◽

Ice Streams ◽

Thickness Change ◽

Ross Ice Shelf ◽

Spatial Response ◽

Shelf Flow ◽

Flux Perturbation

ABSTRACT Ross Ice Shelf (RIS) is known to experience transient thickness change due to changes in the flow of its tributary ice streams and glaciers and this may complicate identification of external, climate-forced signals in contemporary observations of ice shelf thinning and thickening. Flux changes at the lateral boundaries produce both instantaneous and longer timescale adjustments in the coupled velocity and thickness fields. Here, we adapt a statistical approach to output from a numerical model of ice shelf flow to identify characteristic patterns (spatial response surfaces) associated with stepped and cyclic perturbations to boundary fluxes. Once known, characteristic patterns identified in observational data may be attributed to specific sources. An example involving discharge of Byrd Glacier into RIS is described. We find that spatial response surfaces for thickness and velocity generated in individual flow model experiments appear to be independent of flux perturbation shape and magnitude. Additionally, recent acceleration of Byrd Glacier is apparent in ICESat-detected change in RIS thickness.

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Numerical Modeling of Ice-Shelf Motion

Annals of Glaciology ◽

10.1017/s0260305500002755 ◽

1982 ◽

Vol 3 ◽

pp. 189-194 ◽

Cited By ~ 40

Author(s):

D. R. MacAyeal ◽

R. H. Thomas

Keyword(s):

Ice Thickness ◽

Subgrid Scale ◽

Good Qualitative Agreement ◽

Ice Shelf ◽

Ice Streams ◽

Ross Ice Shelf ◽

Sea Bed ◽

Flow Law ◽

Stress Variability ◽

Shelf Flow

Finite-element simulations of the Ross Ice Shelf flow yield good qualitative agreement with observation, but velocity magnitudes tend to be too low up-stream of ice rises and too high near the ice front. These errors will be significantly reduced by better model convergence to the flow law, more accurate values of the flow-law parameters, better resolution of the ice streams, and inclusion of subgrid scale stress variability produced by crevassing and ice-fabric orientation. A model run featuring a hypothetical ice rise down-stream of Crary Ice Rise indicates that the distinctive strain-rate patterns produced by an isolated ice rise can be cancelled by neighboring ice rises. This suggests that an isolated ice rise might migrate up-stream along sea-bed ridges unless there are neighboring ice rises acting to stabilize the surrounding ice-thickness tendencies.

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Redrawing Operation a Star Shape from Cylindrical Shape Using Experimental and FE Analysis

Engineering and Technology Journal ◽

10.30684/etj.v38i1a.191 ◽

2020 ◽

Vol 38 (1A) ◽

pp. 25-32

Author(s):

Waleed Kh. Jawad ◽

Ali T. Ikal

Keyword(s):

Finite Element ◽

Effective Strain ◽

Element Model ◽

Cylindrical Shape ◽

Element Analysis ◽

Punch Force ◽

Maximum Value ◽

Element Simulation ◽

Blank Sheet ◽

The Finite Element Model

The aim of this paper is to design and fabricate a star die and a cylindrical die to produce a star shape by redrawing the cylindrical shape and comparing it to the conventional method of producing a star cup drawn from the circular blank sheet using experimental (EXP) and finite element simulation (FES). The redrawing and drawing process was done to produce a star cup with the dimension of (41.5 × 34.69mm), and (30 mm). The finite element model is performed via mechanical APDL ANSYS18.0 to modulate the redrawing and drawing operation. The results of finite element analysis were compared with the experimental results and it is found that the maximum punch force (39.12KN) recorded with the production of a star shape drawn from the circular blank sheet when comparing the punch force (32.33 KN) recorded when redrawing the cylindrical shape into a star shape. This is due to the exposure of the cup produced drawn from the blank to the highest tensile stress. The highest value of the effective stress (709MPa) and effective strain (0.751) recorded with the star shape drawn from a circular blank sheet. The maximum value of lamination (8.707%) is recorded at the cup curling (the concave area) with the first method compared to the maximum value of lamination (5.822%) recorded at the cup curling (the concave area) with the second method because of this exposure to the highest concentration of stresses. The best distribution of thickness, strains, and stresses when producing a star shape by

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