Time-dependent soft-bedded sliding laws

2021 ◽  
Author(s):  
Katarzyna Warburton ◽  
Duncan Hewitt ◽  
Jerome Neufeld
Keyword(s):  
Large Scale ◽  
Plastic Material ◽  
Water Pressure ◽  
Fluid Phase ◽  
Time Dependent ◽  
Two Phase ◽  
Shear Dilation ◽  
Subglacial Environment ◽  
Scale Models ◽  
Basal Sliding

<p>The dynamics of soft-bedded glacial sliding over saturated till are poorly constrained and difficult to realistically capture in large scale models. While experiments characterise till as a plastic material with a pressure dependent yield stress, large scale models rely on a viscous or power-law description of the subglacial environment to efficiently constrain the basal sliding rate of the ice. Further, the subglacial water pressure may fluctuate on timescales from annual to daily, leading to transient adjustment of the till.</p><p>We construct a continuum two-phase model of coupled fluid and solid flows, using Darcy flow for the fluid phase and a recently described saturated granular model for the solid. After verifying our model against the steady-state experiments, we force the model with a fluctuating effective pressure at the ice-till interface and infer the resulting relationships between basal traction, porosity, rate of deformation, and till flux. Shear dilation introduces internal pressure variations, leading to hysteretic behaviour in low-permeability materials, resulting in a time-dependent effective sliding law.</p>

scholarly journals Impact of pressure dissipation on fluid injection into layered aquifers

2019 ◽  
Vol 877 ◽  
pp. 214-238
Author(s):  
Luke T. Jenkins ◽  
Martino Foschi ◽  
Christopher W. MacMinn
Keyword(s):  
Large Scale ◽  
Water Pressure ◽  
Gravity Current ◽  
Fluid Injection ◽  
Sharp Interface Model ◽  
Two Phase ◽  
Vertical Pressure ◽  
Aquifer System ◽  
Mitigate Climate Change ◽  
The Impact

Carbon dioxide ($\text{CO}_{2}$) capture and subsurface storage is one method for reducing anthropogenic $\text{CO}_{2}$ emissions to mitigate climate change. It is well known that large-scale fluid injection into the subsurface leads to a buildup in pressure that gradually spreads and dissipates through lateral and vertical migration of water. This dissipation can have an important feedback on the shape of the $\text{CO}_{2}$ plume during injection, but the impact of vertical pressure dissipation, in particular, remains poorly understood. Here, we investigate the impact of lateral and vertical pressure dissipation on the injection of $\text{CO}_{2}$ into a layered aquifer system. We develop a compressible, two-phase model that couples pressure dissipation to the propagation of a $\text{CO}_{2}$ gravity current. We show that our vertically integrated, sharp-interface model is capable of efficiently and accurately capturing water migration in a layered aquifer system with an arbitrary number of aquifers. We identify two limiting cases – ‘no leakage’ and ‘strong leakage’ – in which we derive analytical expressions for the water pressure field for the corresponding single-phase injection problem. We demonstrate that pressure dissipation acts to suppress the formation of an advancing $\text{CO}_{2}$ tongue during injection, reducing the lateral extent of the plume. The properties of the seals and the number of aquifers determine the strength of pressure dissipation and subsequent coupling with the $\text{CO}_{2}$ plume. The impact of pressure dissipation on the shape of the $\text{CO}_{2}$ plume is likely to be important for storage efficiency and security.

A model for the spreading and compaction of two-phase viscous gravity currents

2009 ◽  
Vol 630 ◽  
pp. 299-329 ◽  
Author(s):  
CHLOÉ MICHAUT ◽  
DAVID BERCOVICI
Keyword(s):  
Large Scale ◽  
Gravity Current ◽  
Fluid Phase ◽  
Gravity Currents ◽  
Small Scale ◽  
Fluid Loss ◽  
Large Area ◽  
Finite Radius ◽  
Two Phase ◽  
Mixture Density

Two-phase viscous gravity current theory has numerous applications in the natural sciences, from small-scale lava, sedimentary and glacial flows, to large-scale flows of partially molten mantle. We develop the general equations for two-phase viscous gravity currents composed of a high viscosity matrix and low viscosity fluid for both constant volume and constant flux conditions. A loss of fluid phase is taken into account at the current's upper boundary and corresponds to the degassing of a lava flow or loss of water in sedimentary flows. As the current spreads, its surface increases and fluid loss is facilitated, which modifies the mixture density and viscosity and thus the current's shape; hence spreading of the flow affects fluid loss and vice-versa. Our results show that two-phase gravity currents retain and transport the fluid out to large distances, but the fluid is almost entirely lost within a region of finite radius. This ‘loss radius’ depends on the flow's volume or flux, fluid and matrix properties as well as on the size of fluid parcels or matrix permeability. Application to lava flows shows that degassing occurs over a large area, which affects gas release and transport in the atmosphere.

scholarly journals Parameter and state estimation with a time-dependent adjoint marine ice sheet model

2013 ◽  
Vol 7 (3) ◽  
pp. 2845-2890 ◽  
Author(s):  
D. N. Goldberg ◽  
P. Heimbach
Keyword(s):  
State Estimation ◽  
Large Scale ◽  
Ice Sheet ◽  
Time Dependent ◽  
Algorithmic Differentiation ◽  
Uncertain Variables ◽  
Velocity Models ◽  
Bed Elevation ◽  
Basal Sliding ◽  
Basal Melting

Abstract. To date, assimilation of observations into large-scale ice models has consisted predominantly of time-independent inversions of surface velocities for basal traction, bed elevation, or ice stiffness, and has relied primarily on analytically-derived adjoints of diagnostic ice velocity models. To overcome limitations of such "snapshot" inversions, i.e. their inability to assimilate time-dependent data, or to produce initial states with minimum artificial drift and suitable for time-dependent simulations, we have developed an adjoint of a time-dependent parallel glaciological flow model. The model implements a hybrid shallow shelf-shallow ice stress balance, involves a prognostic equation for ice thickness evolution, and can represent the floating, fast-sliding, and frozen bed regimes of a marine ice sheet. The adjoint is generated by a combination of analytic methods and the use of algorithmic differentiation (AD) software. Several experiments are carried out with idealized geometries and synthetic observations, including inversion of time-dependent surface elevations for past thicknesses, and simultaneous retrieval of basal traction and topography from surface data. Flexible generation of the adjoint for a range of independent uncertain variables is exemplified through sensitivity calculations of grounded ice volume to changes in basal melting of floating and basal sliding of grounded ice. The results are encouraging and suggest the feasibility, using real observations, of improved ice sheet state estimation and comprehensive transient sensitivity assessments.

Magnetohydrodynamic squeezing two-phase flow of particulate suspension in a rotating channel with transpiration cooling

2018 ◽  
Vol 233 (4) ◽  
pp. 1224-1235 ◽  
Author(s):  
B Mahanthesh ◽  
BJ Gireesha ◽  
GT Thammanna ◽  
T Hayat ◽  
A Alsaedi
Keyword(s):  
Shooting Method ◽  
Regression Line ◽  
Fluid Phase ◽  
Time Dependent ◽  
Squeezing Flow ◽  
Transpiration Cooling ◽  
Phase Flow ◽  
Two Phase ◽  
Data Points ◽  
Rotating Channel

This article addresses the time-dependent two-phase magnetohydrodynamic squeezing flow of dusty liquid. The fluid flow is considered in a rotating channel. The flow is constructed by squeezing of an upper plate and stretching of the lower plate and relevant equations are obtained. Numerical results are computed by utilizing shooting method along with the RK–Fehlberg scheme. The obtained solutions are validated by comparison with the existing analytical solutions. The effects of pertinent parameters on velocities of both phases are comprehensively discussed through graphical results. The numerical values of shear stress of both phases at lower and upper walls are also tabulated. Furthermore, the slope of the linear regression line through data points is determined in order to quantify the increase/decrease. Numerical simulations disclosed that the normal and transverse velocities are decreased due to stronger Coriolis force. It is also established that the velocities of the fluid phase are higher than that of the dust phase

scholarly journals Parameter and state estimation with a time-dependent adjoint marine ice sheet model

2013 ◽  
Vol 7 (6) ◽  
pp. 1659-1678 ◽  
Author(s):  
D. N. Goldberg ◽  
P. Heimbach
Keyword(s):  
State Estimation ◽  
Large Scale ◽  
Transient Flow ◽  
Ice Sheet ◽  
Time Dependent ◽  
Algorithmic Differentiation ◽  
Uncertain Variables ◽  
Bed Elevation ◽  
Basal Sliding ◽  
Basal Melting

Abstract. To date, assimilation of observations into large-scale ice models has consisted predominantly of time-independent inversions of surface velocities for basal traction, bed elevation, or ice stiffness, and has relied primarily on analytically derived adjoints of glaciological stress balance models. To overcome limitations of such "snapshot" inversions – i.e., their inability to assimilate time-dependent data for the purpose of constraining transient flow states, or to produce initial states with minimum artificial drift and suitable for time-dependent simulations – we have developed an adjoint of a time-dependent parallel glaciological flow model. The model implements a hybrid shallow shelf–shallow ice stress balance, solves the continuity equation for ice thickness evolution, and can represent the floating, fast-sliding, and frozen bed regimes of a marine ice sheet. The adjoint is generated by a combination of analytic methods and the use of algorithmic differentiation (AD) software. Several experiments are carried out with idealized geometries and synthetic observations, including inversion of time-dependent surface elevations for past thicknesses, and simultaneous retrieval of basal traction and topography from surface data. Flexible generation of the adjoint for a range of independent uncertain variables is exemplified through sensitivity calculations of grounded ice volume to changes in basal melting of floating and basal sliding of grounded ice. The results are encouraging and suggest the feasibility, using real observations, of improved ice sheet state estimation and comprehensive transient sensitivity assessments.

Benchmark of Simplified Time-Dependent Density Functional Theory for UV-Vis Spectral Properties of Porphyrinoids

2019 ◽  
Author(s):  
Kamal Batra ◽  
Stefan Zahn ◽  
Thomas Heine
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Large Scale ◽  
Absolute Error ◽  
Time Dependent ◽  
Basis Set ◽  
Basis Sets ◽  
Functional Theory ◽  
Framework Materials ◽  
Dependent Density

<p>We thoroughly benchmark time-dependent density- functional theory for the predictive calculation of UV/Vis spectra of porphyrin derivatives. With the aim to provide an approach that is computationally feasible for large-scale applications such as biological systems or molecular framework materials, albeit performing with high accuracy for the Q-bands, we compare the results given by various computational protocols, including basis sets, density-functionals (including gradient corrected local functionals, hybrids, double hybrids and range-separated functionals), and various variants of time-dependent density-functional theory, including the simplified Tamm-Dancoff approximation. An excellent choice for these calculations is the range-separated functional CAM-B3LYP in combination with the simplified Tamm-Dancoff approximation and a basis set of double-ζ quality def2-SVP (mean absolute error [MAE] of ~0.05 eV). This is not surpassed by more expensive approaches, not even by double hybrid functionals, and solely systematic excitation energy scaling slightly improves the results (MAE ~0.04 eV). </p>

scholarly journals Thermoelectric Properties of Thin Films from Sorted Single-Walled Carbon Nanotubes

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3808 ◽  
Author(s):  
Blazej Podlesny ◽  
Bogumila Kumanek ◽  
Angana Borah ◽  
Ryohei Yamaguchi ◽  
Tomohiro Shiraki ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Thermoelectric Properties ◽  
Large Scale ◽  
Single Walled Carbon Nanotubes ◽  
Parent Material ◽  
Free Standing ◽  
Two Phase ◽  
Single Walled Carbon ◽  
Walled Carbon Nanotubes ◽  
Aqueous Two Phase Extraction

Single-walled carbon nanotubes (SWCNTs) remain one of the most promising materials of our times. One of the goals is to implement semiconducting and metallic SWCNTs in photonics and microelectronics, respectively. In this work, we demonstrated how such materials could be obtained from the parent material by using the aqueous two-phase extraction method (ATPE) at a large scale. We also developed a dedicated process on how to harvest the SWCNTs from the polymer matrices used to form the biphasic system. The technique is beneficial as it isolates SWCNTs with high purity while simultaneously maintaining their surface intact. To validate the utility of the metallic and semiconducting SWCNTs obtained this way, we transformed them into thin free-standing films and characterized their thermoelectric properties.

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