3D modelling of Isbræ-type glaciers and temperate-zone processes 

2021 ◽  
Author(s):  
Robert Law ◽  
Poul Christoffersen ◽  
Samuel Cook ◽  
Emma MacKie ◽  
Marianne Haseloff
Keyword(s):  
Basal Layer ◽  
Element Model ◽  
Model Parameters ◽  
Complete Understanding ◽  
Surface Slopes ◽  
Coastal Margin ◽  
Flow Through ◽  
Fast Movement ◽  
Glacier Flow ◽  
Basal Melting

<p>The majority of Greenland’s outlet glaciers are Isbræ-type, with high driving stresses, steep surface slopes, flow through deep channels, and with a basal layer of temperate ice theorised to thicken towards the coastal margin. Understanding the formation processes and thermodynamic influence of this temperate ice is important as limited laboratory testing indicates temperate ice has a viscosity 5-10 times lower than cold ice with no liquid phase. Furthermore, limited field data suggests lower rates of deformation within basal temperate ice than in the cold ice directly overlying it, which is presently unexplained. Here, we present preliminary results from a 3D finite-element model of an idealised Isbrae-type glacier built with Elmer/Ice, incorporating water-content-dependent ice viscosity, basal melting, and a parameterization of basal crevassing, and use it to investigate the formation and thermodynamic behaviour of temperate ice in response to varying bedforms and model parameters. We find that the observed decrease in strain in temperate ice close to the glacier base can be explained by a high strain area close to the cold-temperate transition zone. We further compare our model results to temperate ice variability observed at Sermeq Kujalleq (Store Glacier) to determine key temperate ice parameters requiring further investigation. These results provide a more complete understanding of the heterogeneous ice deformation behind the fast movement of Greenland’s Isbræ-type glaciers and can therefore help to improve predictions of future glacier flow.</p>

scholarly journals Melting and freezing under Antarctic ice shelves from a combination of ice-sheet modelling and observations

2017 ◽  
Vol 63 (240) ◽  
pp. 731-744 ◽  
Author(s):  
JORGE BERNALES ◽  
IRINA ROGOZHINA ◽  
MAIK THOMAS
Keyword(s):  
Mass Balance ◽  
Ice Sheet ◽  
Model Parameters ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Continental Scale ◽  
Model Set ◽  
Set Up ◽  
Basal Melting ◽  
The Antarctic

ABSTRACTIce-shelf basal melting is the largest contributor to the negative mass balance of the Antarctic ice sheet. However, current implementations of ice/ocean interactions in ice-sheet models disagree with the distribution of sub-shelf melt and freezing rates revealed by recent observational studies. Here we present a novel combination of a continental-scale ice flow model and a calibration technique to derive the spatial distribution of basal melting and freezing rates for the whole Antarctic ice-shelf system. The modelled ice-sheet equilibrium state is evaluated against topographic and velocity observations. Our high-resolution (10-km spacing) simulation predicts an equilibrium ice-shelf basal mass balance of −1648.7 Gt a−1 that increases to −1917.0 Gt a−1 when the observed ice-shelf thinning rates are taken into account. Our estimates reproduce the complexity of the basal mass balance of Antarctic ice shelves, providing a reference for parameterisations of sub-shelf ocean/ice interactions in continental ice-sheet models. We perform a sensitivity analysis to assess the effects of variations in the model set-up, showing that the retrieved estimates of basal melting and freezing rates are largely insensitive to changes in the internal model parameters, but respond strongly to a reduction of model resolution and the uncertainty in the input datasets.

scholarly journals A conceptual model of cyclical glacier flow in overdeepenings

2014 ◽  
Vol 8 (4) ◽  
pp. 4463-4495 ◽  
Author(s):  
J. B. Turrin ◽  
R. R. Forster
Keyword(s):  
Conceptual Model ◽  
The Other ◽  
Acceleration Phase ◽  
Alaska Range ◽  
Deceleration Phase ◽  
Surface Slopes ◽  
Glacier Dynamics ◽  
Major Tributary ◽  
Cyclical Behavior ◽  
Glacier Flow

Abstract. A nearly four-decade, satellite-based velocity survey of the largest glaciers in the Alaska Range, Chugach Mountains, and the Wrangell Mountains of southern Alaska, spanning the early- to mid-1970s through the 2000s, reveals nine pulsing glaciers: Capps, Copper, Eldridge, Kahiltna, Matanuska, Nabesna, Nizina, Ruth, and Sanford glaciers. The pulses increase velocity by up to 2449% (Capps Glacier) or as little as 77% (Nabesna Glacier), with velocity increases for the other glaciers in the range of 100–250%. The pulses may last from between six years (Copper Glacier) to 12 years (Nizina Glacier) and consist of a multi-year acceleration phase followed by a multi-year deceleration phase during which significant portions of each glacier move en masse. The segments of each glacier affected by the pulses may be anywhere from 14 km (Sanford Glacier) to 36 km (Nabesna Glacier) in length and occur where the glaciers are either laterally constricted or joined by a major tributary, and the surface slopes at these locations are very shallow, 1–2°, suggesting the pulses occur where the glaciers are overdeepened. A conceptual model to explain the cyclical behavior of these pulsing glaciers is presented that incorporates the effects of glaciohydraulic supercooling, glacier dynamics, surface ablation, and subglacial sediment erosion, deposition, and deformation in overdeepenings.

scholarly journals Fractional Stress Relaxation Model of Rock Freeze-Thaw Damage

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Q. Liu ◽  
W. Chen ◽  
J. K. Guo ◽  
R. F. Li ◽  
D. Ke ◽  
...  
Keyword(s):  
Stress Relaxation ◽  
Fatigue Loading ◽  
Element Model ◽  
Model Parameters ◽  
Rock Stress ◽  
Relaxation Equation ◽  
Freeze Thaw ◽  
Thaw Cycle ◽  
Nonlinear Stress ◽  
Freeze Thaw Cycle

Freeze-thaw cycle is a type of fatigue loading, and rock stress relaxation under freeze-thaw cycles takes into account the influence of the freeze-thaw cycle damage and deterioration. Rock stress relaxation under freeze-thaw cycles is one of the paramount issues in tunnel and slope stability research. To accurately describe the mechanical behaviour of stress relaxation of rocks under freeze-thaw, the software element is constructed based on the theory of fractional calculus to replace the ideal viscous element in the traditional element model. The freeze-thaw damage degradation of viscosity coefficient is considered. A new three-element model is established to better reflect the nonlinear stress relaxation behavior of rocks under freeze-thaw. The freeze-thaw and stress relaxation of rock are simulated by ABAQUS, the relevant model parameters are determined, and the stress relaxation equation of rock under freeze-thaw cycle is obtained based on numerical simulation results. The research shows that the test results are consistent with the calculated results, indicating that the constitutive equation can better describe the stress relaxation characteristics of rocks under freeze-thaw and provide theoretical basis for surrounding rock support in cold region.

An Effective Method for Determining Finite Element Model Parameters of Rotor Elastic Support System

2011 ◽  
Vol 141 ◽  
pp. 191-197
Author(s):  
Yong Xing Wang ◽  
Jiang Yan ◽  
Sheng Ze Wang
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Support System ◽  
Structural Parameters ◽  
Element Model ◽  
Elastic Support ◽  
Asymmetric Structure ◽  
Model Parameters ◽  
Equivalent Stiffness ◽  
Rolling Ball

A finite element model of the elastic support rotor system based on the corresponding experimental model was established. According to the principle of two types of model with an equal first order critical speed, the equivalent stiffness and damping of a rolling ball bearing support system with rubber rings determined by experiment were transferred into the finite element model. Then, the dynamic behavior of rotor systems with symmetric and asymmetric structure, different support system stiffness and support span were calculated and analyzed respectively. At last, the influence of the rotor structural parameters on the equivalent stiffness of elastic bearing support system obtained by experiment was pointed out.

Numerical and Experimental Analysis of Self Piercing Riveting Process with Carbon Fiber-Reinforced Plastic and Aluminium Sheets

2013 ◽  
Vol 554-557 ◽  
pp. 1045-1054 ◽  
Author(s):  
Welf Guntram Drossel ◽  
Reinhard Mauermann ◽  
Raik Grützner ◽  
Danilo Mattheß
Keyword(s):  
Finite Element ◽  
Carbon Fiber ◽  
Finite Element Model ◽  
Simulation Model ◽  
Process Parameters ◽  
Process Model ◽  
Element Model ◽  
Model Parameters ◽  
Fiber Reinforced ◽  
Carbon Fiber Reinforced

In this study a numerical simulation model was designed for representing the joining process of carbon fiber-reinforced plastics (CFRP) and aluminum alloy with semi-tubular self-piercing rivet. The first step towards this goal is to analyze the piercing process of CFRP numerical and experimental. Thereby the essential process parameters, tool geometries and material characteristics are determined and in finite element model represented. Subsequently the finite element model will be verified and calibrated by experimental studies. The next step is the integration of the calibrated model parameters from the piercing process in the extensive simulation model of self-piercing rivet process. The comparison between the measured and computed values, e.g. process parameters and the geometrical connection characteristics, shows the reached quality of the process model. The presented method provides an experimental reliable characterization of the damage of the composite material and an evaluation of the connection performances, regarding the anisotropic property of CFRP.

Application of a FRF Based Model Updating Technique for the Validation of Finite Element Models of Components of the Automotive Industry

1995 ◽  
Author(s):  
Stefan Lammens ◽  
Marc Brughmans ◽  
Jan Leuridan ◽  
Ward Heylen ◽  
Paul Sas
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Automotive Industry ◽  
Stiffness Matrix ◽  
Model Updating ◽  
Dynamic Stiffness ◽  
Element Model ◽  
Model Parameters ◽  
Finite Element Models ◽  
Analytical Dynamic

Abstract This paper presents two applications of the RADSER model updating technique (Lammens et al. (1995) and Larsson (1992)). The RADSER technique updates finite element model parameters by solution of a linearised set of equations that optimise the Reduced Analytical Dynamic Stiffness matrix based on Experimental Receptances. The first application deals with the identification of the dynamic characteristics of rubber mounts. The second application validates a coarse finite element model of a subframe of a Volvo 480.

scholarly journals A Numerical Model of Temperate Glacier Flow Applied to the Quiescent Phase of a Surge-Type Glacier

1982 ◽  
Vol 28 (99) ◽  
pp. 239-265 ◽  
Author(s):  
Robert Bindschadler
Keyword(s):  
Shear Stress ◽  
Numerical Model ◽  
Stress Gradient ◽  
Finite Difference Approximation ◽  
Difference Approximation ◽  
Model Parameters ◽  
Small Contribution ◽  
Base Shear ◽  
Quiescent Phase ◽  
Glacier Flow

AbstractA time-dependent numerical model of temperate glacier flow without sliding is developed and applied to the quiescent phase of surge-type Variegated Glacier, Alaska. The model is based on a one-dimensional continuity equation but the transverse channel shape is explicitly included allowing the complex geometries of real glaciers to be modelled. Velocities and volume fluxes are calculated from the glacier geometry. Transverse stress is taken into account by shape factors which are fitted to measurements of geometry and velocity and are chosen to be insensitive to changes in geometry. Longitudinal stress gradients are taken into account by use of a large-scale surface slope. A Crank-Nicholson finite-difference approximation is used and it is unconditionally stable when a small contribution from the local slope is added to the average slope.Model parameters are fitted to extensive data collected on Variegated Glacier in 1973 and 1974. Predictions of the model over a four year interval agree well with field measurements. Predictions of the current quiescent phase (1965–84) indicate depth increases in the upper glacier of more than 75 m with a twenty-fold increase in the volume flux. During this interval the base shear stress increases 40% in the upper glacier and decreases 20% in the lower glacier. During the mid to late quiescent phase, ice motion becomes more important than mass balance in the redistribution of mass over the central region of the glacier. If normal flow were to persist, the predicted steady-state profile would be an average of 100 m deeper and 41% more voluminous than in 1973.The predicted base shear-stress gradient is never negative enough to satisfy Robin and Weertman’s (1973) condition for blockage of subglacial water flow. The annual rate of water production by dissipation of mechanical straining at the bed remains two orders of magnitude below that produced by summer surface melt. The predicted fractional increase in base stress during the quiescent phase is a maximum in the region believed to be the trigger zone of the surges.

scholarly journals Sliding of temperate basal ice on a rough, hard bed: creep mechanisms, pressure melting, and implications for ice streaming

2016 ◽  
Vol 10 (5) ◽  
pp. 1915-1932 ◽  
Author(s):  
Maarten Krabbendam
Keyword(s):  
Heat Flow ◽  
Power Law ◽  
Basal Layer ◽  
Ice Dynamics ◽  
Basal Ice ◽  
Basal Sliding ◽  
Ductile Flow ◽  
Flow Through ◽  
Pressure Melting ◽  
Power Law Creep

Abstract. Basal ice motion is crucial to ice dynamics of ice sheets. The classic Weertman model for basal sliding over bedrock obstacles proposes that sliding velocity is controlled by pressure melting and/or ductile flow, whichever is the fastest; it further assumes that pressure melting is limited by heat flow through the obstacle and ductile flow is controlled by standard power-law creep. These last two assumptions, however, are not applicable if a substantial basal layer of temperate (T ∼ Tmelt) ice is present. In that case, frictional melting can produce excess basal meltwater and efficient water flow, leading to near-thermal equilibrium. High-temperature ice creep experiments have shown a sharp weakening of a factor 5–10 close to Tmelt, suggesting standard power-law creep does not operate due to a switch to melt-assisted creep with a possible component of grain boundary melting. Pressure melting is controlled by meltwater production, heat advection by flowing meltwater to the next obstacle and heat conduction through ice/rock over half the obstacle height. No heat flow through the obstacle is required. Ice streaming over a rough, hard bed, as possibly in the Northeast Greenland Ice Stream, may be explained by enhanced basal motion in a thick temperate ice layer.

Crystal Plasticity Simulation of the Bauschinger Effect of Polycrystalline AA7075 through a Texture-Based Representative Volume Element Model

2014 ◽  
Vol 553 ◽  
pp. 22-27
Author(s):  
Ling Li ◽  
Lu Ming Shen ◽  
Gwénaëlle Proust
Keyword(s):  
Finite Element ◽  
Representative Volume Element ◽  
Crystal Plasticity ◽  
Bauschinger Effect ◽  
Voronoi Tessellation ◽  
Strain Curve ◽  
Element Model ◽  
Volume Element ◽  
Model Parameters ◽  
Representative Volume

A texture-based representative volume element (TBRVE) model is developed for the three-dimensional crystal plasticity (CP) finite element simulations of the Bauschinger effect (BE) of polycrystalline aluminium alloy 7075 (AA7075). In the simulations, the grain morphology is created using the Voronoi tessellation method with the material texture systematically discretised from experiment. A modified CP constitutive model, which takes into account the backstress, is used to simulate the BE during cyclic loading. The model parameters are calibrated using the first cycle stress-strain curve and used to predict the mechanical response to the cyclic saturation of AA7075. The results indicate that the proposed TBRVE CP finite element model can effectively capture the BE at the grain level.

Sign in / Sign up

Export Citation Format

Share Document