scholarly journals Numerical investigation of the effects of temporal variations in basal lubrication on englacial strain-rate distribution

2003 ◽  
Vol 37 ◽  
pp. 49-54 ◽  
Author(s):  
Shin Sugiyama ◽  
G. Hilmar Gudmundsson ◽  
Jakob Helbing
Keyword(s):  
Stress Field ◽  
Strain Rate ◽  
Temporal Variations ◽  
Surface Velocity ◽  
Glacier Surface ◽  
Spatial Gradients ◽  
Vertical Strain ◽  
Set Up ◽  
General Aspects ◽  
Possible Cause

AbstractThe effects of spatial and temporal variations in basal lubrication on the englacial strain rate and surface velocity distribution are investigated with a numerical ice-flow model. General aspects of the solutions are compared to measurements made on Lauteraargletscher, Switzerland, in 2001, that showed diurnal fluctuations in both surface velocity and englacial vertical strain. We find that spatial gradients in basal lubrication can set up variations in the deviatoric stress field that increases with distance to the bed and has a maximum value near the glacier surface. This stress field produces a significant strain rate near the surface. The temporal evolution of a slippery zone is identified as a possible cause of the observed diurnal variations in the vertical strain rate. Although general aspects of the measurements can be explained in this way, the calculated vertical strain rates are too small, suggesting that the modeled effective viscosity values using Glen’s flow law are too large near the surface.

scholarly journals Variations in the surface velocity of an alpine cirque glacier

2018 ◽  
Vol 64 (248) ◽  
pp. 969-976 ◽  
Author(s):  
J. W. SANDERS ◽  
K. M. CUFFEY ◽  
K. R. MACGREGOR ◽  
J. L. KAVANAUGH ◽  
C. F. DOW
Keyword(s):  
Water System ◽  
Heavy Rain ◽  
Temporal Variations ◽  
Surface Velocity ◽  
Channel Network ◽  
Glacier Surface ◽  
Ice Dynamics ◽  
Speed Up ◽  
Water Volumes ◽  
One Year

ABSTRACTFollowing pioneering work in Norway, cirque glaciers have widely been viewed as rigidly rotating bodies. This model is incorrect for basin-filling cirque glaciers, as we have demonstrated at West Washmawapta Glacier, a small glacier in the Canadian Rocky Mountains. Here we report observations at the same glacier that assess whether complex temporal variations of flow also occur. For parts of three summers, we measured daily displacements of the glacier surface. In one year, four short-duration speed-up events were recorded. Three of the events occurred during the intervals of warmest weather, when melt was most rapid; the fourth event occurred immediately following heavy rain. We interpret the speed-up events as manifestations of enhanced water inputs to the glacier bed and associated slip lubrication by increased water volumes and pressures. No further speed-ups occurred in the final month of the melt season, despite warm temperatures and several rainstorms; the dominant subglacial water system likely transformed from one of poorly connected cavities to one with an efficient channel network. The seasonal evolution of hydrology and flow resembles behaviors documented at other, larger temperate glaciers and indicates that analyses of cirque erosion cannot rely on simple assumptions about ice dynamics.

scholarly journals Spatio-temporal variations in glacier surface velocity in the Himalayas

2021 ◽  
Author(s):  
Yu Zhou ◽  
Jianlong Chen ◽  
Xiao Cheng
Keyword(s):  
Mass Loss ◽  
Temporal Variations ◽  
Surface Velocity ◽  
Glacier Surface ◽  
Environmental Forcing ◽  
Landsat 7 ◽  
Spatio Temporal ◽  
Velocity Changes ◽  
Glacier Velocity ◽  
Glacier Flow

Abstract. Glacier evolution with time provides important information about climate variability. Here we investigate glacier surface velocity in the Himalayas and analyse the patterns of glacier flow. We collect 220 scenes of Landsat-7 panchromatic images between 1999 and 2000, and Sentinel-2 panchromatic images between 2017 and 2018, to calculate surface velocities of 36,722 glaciers during these two periods. We then derive velocity changes between 1999 and 2018, based on which we perform a detailed analysis of motion of each individual glacier, and noted that the changes are spatially heterogeneous. Of all the glaciers, 32 % have speeded up, 24.5 % have slowed down, and the rest 43.5 % remained stable. The amplitude of glacier slowdown, as a result of glacier mass loss, is remarkably larger than that of speedup. At regional scales, we found that glacier surface velocity in winter has uniformly decreased in the western part of the Himalayas between 1999 and 2018, whilst increased in the eastern part; this contrasting difference may be associated with decadal changes in accumulation and/or melting under different climatic regimes. We also found that the overall trend of surface velocity exhibits seasonal variability: summer velocity changes are positively correlated with mass loss, whereas winter velocity changes show a negative correlation. Our study suggests that glacier velocity changes in the Himalayas are more spatially and temporally heterogeneous than previously thought, emphasising complex interactions between glacier dynamics and environmental forcing.

Tension and Compression Behavior of Pre-Stressed Steel Strands at High Strain Rate

2011 ◽  
Vol 82 ◽  
pp. 154-159 ◽  
Author(s):  
Anatoly M. Bragov ◽  
Ezio Cadoni ◽  
Alexandr Yu. Konstantinov ◽  
Andrey K. Lomunov
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
High Strain ◽  
Split Hopkinson Pressure Bar ◽  
High Strength ◽  
Gauge Length ◽  
Hopkinson Pressure Bar ◽  
Dog Bone ◽  
Tension And Compression ◽  
Set Up

In this paper is described the mechanical characterization at high strain rate of the high strength steel usually adopted for strands. The experimental set-up used for high strain rates testing: in tension and compression was the Split Hopkinson Pressure Bar installed in the Laboratory of Dynamic Investigation of Materials in Nizhny Novgorod. The high strain rate data in tension was obtained with dog-bone shaped specimens of 3mm in diameter and 5mm of gauge length. The specimens were screwed between incident and transmitter bars. The specimens used in compression was a cylinder of 3mm in diameter and 5mm in length. The enhancement of the mechanical properties is quite limited compared the usual reinforcing steels.

scholarly journals A New Set-Up to Investigate Plastic Deformation of Face Centered Cubic Metals in High Strain Rate Loading

2014 ◽  
Vol 8 (2) ◽  
Author(s):  
Ehsan Etemadi ◽  
Jamal Zamani ◽  
Alessandro Francesconi ◽  
Mohammad V. Mousavi ◽  
Cinzia Giacomuzzo
Keyword(s):  
Plastic Deformation ◽  
High Strain Rate ◽  
Strain Rate ◽  
High Strain ◽  
Face Centered Cubic ◽  
Cubic Metals ◽  
Face Centered ◽  
Set Up ◽  
Strain Rate Loading

scholarly journals Monstars on Glaciers

1983 ◽  
Vol 29 (101) ◽  
pp. 70-77 ◽  
Author(s):  
J. F. Nye
Keyword(s):  
Numerical Simulation ◽  
Strain Rate ◽  
Tensor Field ◽  
Pure Shear ◽  
Glacier Surface ◽  
Isotropic Point ◽  
Different Types ◽  
Isolated Points ◽  
Principal Directions ◽  
Structurally Stable

AbstractIsotropic points are structurally stable features of any complicated field of stress or strain-rate, and therefore will almost always be present on the surface of a glacier. A given isotropic point for strain-rate will belong to one of six different classes, depending on the pattern (lemon, star, or monstar) of principal directions and the contours (ellipses or hyperbolas) of constant principal strain-rate values in its neighbourhood. The central isotropic point on a glacier should theoretically have a monstar pattern, but the contours around it may sometimes be elliptic and sometimes hyperbolic. Nearby, but not coincident with it there will be an isotropic point for stress. This will also have a monstar pattern but, in contrast to the strain-rate point, the contours around it must be hyperbolic. Published examples are consistent with these conclusions. In addition to isotropic points for strain-rate a glacier surface will contain isolated points of pure shear; these also can be classified into six different types. Stable features of this kind give information about the essential structure of a tensor field and form useful points of comparison between observation and numerical simulation.

scholarly journals Correlation dispersion as a measure to better estimate uncertainty of remotely sensed glacier displacements

2021 ◽  
Author(s):  
Bas Altena ◽  
Andreas Kääb ◽  
Bert Wouters
Keyword(s):  
Large Data ◽  
Surface Velocity ◽  
Dominant Factor ◽  
Fast Method ◽  
Imaging Data ◽  
Velocity Data ◽  
Correlation Peak ◽  
Glacier Surface ◽  
Fast Processing ◽  
Single Number

Abstract. In recent years a vast amount of glacier surface velocity data from satellite imagery has emerged based on correlation between repeat images. Thereby, much emphasis has been put on fast processing of large data volumes. The metadata of such measurements are often highly simplified when the measurement precision is lumped into a single number for the whole dataset, although the error budget of image matching is in reality not isotropic and constant over the whole velocity field. The spread of the correlation peak of individual image offset measurements is dependent on the image content and the non-uniform flow of the ice. Precise dispersion estimates for each individual velocity measurement can be important for inversion of, for instance, rheology, ice thickness and/or bedrock friction. Errors in the velocity data can propagate into derived results in a complex and exaggerating way, making the outcomes very sensitive to velocity noise and errors. Here, we present a computationally fast method to estimate the matching precision of individual displacement measurements from repeat imaging data, focussing on satellite data. The approach is based upon Gaussian fitting directly on the correlation peak and is formulated as a linear least squares estimation, making its implementation into current pipelines straightforward. The methodology is demonstrated for Sermeq Kujalleq, Greenland, a glacier with regions of strong shear flow and with clearly oriented crevasses, and Malaspina Glacier, Alaska. Directionality within an image seems to be dominant factor influencing the correlation dispersion. In our cases these are crevasses and moraine bands, while a relation to differential flow, such as shear, is less pronounced.

scholarly journals Combined measurements of Subglacial Water Pressure and Surface Velocity of Findelengletscher, Switzerland: Conclusions about Drainage System and Sliding Mechanism

1986 ◽  
Vol 32 (110) ◽  
pp. 101-119 ◽  
Author(s):  
Almut Iken ◽  
Robert A. Bindschadler
Keyword(s):  
Functional Relationship ◽  
Water Pressure ◽  
Drainage System ◽  
High Water ◽  
Water Levels ◽  
Surface Velocity ◽  
Glacier Surface ◽  
Measured Velocity ◽  
Sliding Mechanism ◽  
Velocity Variations

AbstractDuring the snow-melt season of 1982, basal water pressure was recorded in 11 bore holes communicating with the subglacial drainage system. In most of these holes the water levels were at approximately the same depth (around 70 m below surface). The large variations of water pressure, such as diurnal variations, were usually similar at different locations and in phase. In two instances of exceptionally high water pressure, however, systematic phase shifts were observed; a wave of high pressure travelled down-glacier with a velocity of approximately 100 m/h.The glacier-surface velocity was measured at four lines of stakes several times daily. The velocity variations correlated with variations in subglacial water pressure. The functional relationship of water pressure and velocity suggests that fluctuating bed separation was responsible for the velocity variations. The empirical functional relationship is compared to that of sliding over a perfectly lubricated sinusoidal bed. On the basis of the measured velocity-pressure relationship, this model predicts a reasonable value of bed roughness but too high a sliding velocity and unstable sliding at too low a water pressure. The main reason for this disagreement is probably the neglect of friction from debris in the sliding model.The measured water pressure was considerably higher than that predicted by the theory of steady flow through straight cylindrical channels near the glacier bed. Possible reasons are considered. The very large disagreement between measured and predicted pressure suggests that no straight cylindrical channels may have existed.

Numerical Simulation of Tectonic Stress Field in the Southeast of the Qinghai-Tibet Plateau

2013 ◽  
Vol 864-867 ◽  
pp. 2418-2421
Author(s):  
Li Yang ◽  
Jian Lin Li ◽  
Shi Wei Luo
Keyword(s):  
Numerical Simulation ◽  
Stress Field ◽  
Simulation Analysis ◽  
Tectonic Stress ◽  
Geological Structure ◽  
Tibet Plateau ◽  
Tectonic Stress Field ◽  
Structure Model ◽  
Set Up ◽  
Qinghai Tibet Plateau

The tectonic stress field plays an important role in the research of crustal stability, fault activity and the geological disaster effect. On the basis of related geological data, ANSYS and FLAC3D are applied in this paper to set up a reasonable geological structure model and boundary conditions, aiming at making a numerical simulation analysis of tectonic stress field in the southeast of the Qinghai-Tibet plateau. The result and the measured data fit better, which provides a reference for the further study of the project.

A Numerical Investigation of the Fluid Flow in a Chandler Loop for Thrombus Studies

2013 ◽  
Author(s):  
Hisham Touma ◽  
Iskender Sahin ◽  
Tidimogo Gaamangwe ◽  
Maud B. Gorbet ◽  
Sean D. Peterson
Keyword(s):  
Laminar Flow ◽  
Stress Field ◽  
Strain Rate ◽  
Rotation Rate ◽  
Fluid Dynamic ◽  
Working Fluid ◽  
Straight Tube ◽  
Dean Number ◽  
Chandler Loop

The Chandler loop is an artificial circulatory platform for in vitro hemodynamic experiments. In most experiments, the working fluid is subjected to a stress field via rotation of the Chandler loop, which, in turn, induces biochemical responses of the suspended cells. For very low rotation rates, the stress field can be approximated using laminar flow in a straight tube as a model. However, as the rotation rate increases, while still maintaining laminar flow, the effect of the tube curvature causes the stress field to deviate considerably from the straight tube approximation. In this manuscript, we investigate the flow and associated strain rate field of an incompressible Newtonian fluid in a Chandler loop as a function of the governing non-dimensional fluid dynamic parameters. We find that the Dean number, which is proportional to the rotation rate, is the dominant parameter in determining the fluid strain rate. We propose an empirical formula for predicting the average fluid strain rate magnitude in the working fluid that is valid over a wide parameter space to be used in lieu of the common, yet restrictive, straight tube-based prediction.

scholarly journals Investigating the potential to determine the upstream accumulation rate, using mass-flux calculations along a cross-section on a small tributary glacier in Heimefrontfjella, Dronning Maud Land, Antarctica

2004 ◽  
Vol 39 ◽  
pp. 175-180 ◽  
Author(s):  
Veijo Allan Pohjola ◽  
Jim Hedfors ◽  
Per Holmlund
Keyword(s):  
Cross Section ◽  
Catchment Area ◽  
Accumulation Rate ◽  
Surface Velocity ◽  
Velocity Data ◽  
High Accumulation ◽  
Glacier Surface ◽  
Mass Fluxes ◽  
Orographic Enhancement ◽  
Dronning Maud Land

AbstractHow well can we estimate the incoming ice flux by calculating the ice flux through a well-defined cross-section? We test this by comparing calculated ice flux out from the small glacier Bonnevie-Svendsenbreen with the measured accumulation rate integrated over the well-defined catchment area in the Sivorgfjella plateau, Dronning Maud Land, Antarctica (74˚45’ S, 11˚10’ W). The ice flux is calculated using ice-dynamical properties from an ice temperature model and the distribution of forces calculated using a force-budget model. The input we use includes velocity data of the glacier surface, combined with ice-thickness measurements. The result is an accumulation rate on the Sivorgfjella plateau of 0.50 ± 0.05 mw.e. a–1. We find that this is similar to the accumulation rate recorded by ground-penetrating radar work in the area. We therefore find the balance-flow method, in combination with the force-budget technique and ice temperature modeling, to be a useful tool for studies of mass fluxes in a catchment area. The most important source of uncertainty in these calculations is the quality and the spatial distribution of the ice surface velocity data. The high accumulation rate shows the effect of orographic enhancement on accumulation in montane areas in Antarctica.

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