Abstract
The main body of this thesis consists of three papers in which aspects of fluid induced deformation in granular materials are studied. Insight from experiments, dimensional analysis, numerical modeling and analytic predictions are combined to interpret observations various aspects of piercement structures in the geological record. A fourth paper is included showing how analogue modeling has been used to understand a geological processes. Paper 1 presents experimental work on the segregation pattern forming in partially fluidized, bi-modal sized granular mixtures. The experiments are performed on a vertically oriented Hele-Shaw cell (HS-cell), the narrow box between two parallel glass plates, filled with glass beads. Gas flow is imparted through the bottom of the bed causing fluidization when the system is driven at velocities exceeding a critical limit. The co-existence of fluidized and static zones is termed partial fluidization and occurs when the imposed gas flux is insufficient to fluidize the whole system. Within the fluidized zones, the particles re-organize and the large particles sediment down while the small particles remains fluidized. The re-organization is caused by differences in the ratio of the weight to the viscous drag. A pipe-like pattern develops due to a feedback mechanism in which the flow is
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Citation Formats
Nermoen, Anders.
Some effects of gas-induced fluidization in dry granular media.
Norway: N. p.,
2010.
Web.
Nermoen, Anders.
Some effects of gas-induced fluidization in dry granular media.
Norway.
Nermoen, Anders.
2010.
"Some effects of gas-induced fluidization in dry granular media."
Norway.
@misc{etde_1013156,
title = {Some effects of gas-induced fluidization in dry granular media}
author = {Nermoen, Anders}
abstractNote = {The main body of this thesis consists of three papers in which aspects of fluid induced deformation in granular materials are studied. Insight from experiments, dimensional analysis, numerical modeling and analytic predictions are combined to interpret observations various aspects of piercement structures in the geological record. A fourth paper is included showing how analogue modeling has been used to understand a geological processes. Paper 1 presents experimental work on the segregation pattern forming in partially fluidized, bi-modal sized granular mixtures. The experiments are performed on a vertically oriented Hele-Shaw cell (HS-cell), the narrow box between two parallel glass plates, filled with glass beads. Gas flow is imparted through the bottom of the bed causing fluidization when the system is driven at velocities exceeding a critical limit. The co-existence of fluidized and static zones is termed partial fluidization and occurs when the imposed gas flux is insufficient to fluidize the whole system. Within the fluidized zones, the particles re-organize and the large particles sediment down while the small particles remains fluidized. The re-organization is caused by differences in the ratio of the weight to the viscous drag. A pipe-like pattern develops due to a feedback mechanism in which the flow is focused through domains dominated by large particles. The focusing of the flow localizes the fluidization, which in turn enables the sedimentation of the large grains. Paper 2 presents an experimental and analytical study of the critical conditions for fluidization of a dry granular material. Based on the experiments, we find that the critical velocity of fluidization scales almost linear with the ratio of the filling height to the inlet width. An analytic model for the pressure field is obtained by solving the Laplace equation for the velocity boundary conditions given by the geometry of the experimental setup. By integrating the vertical component of the pressure gradient within a truncated wedge we estimate the total drag. A balance between the integrated seepage force and the weight of the truncated wedge, gives an analytic estimate of the imposed critical velocity. We found that the critical velocity attained a linear scaling with the sediment height to inlet width ratio, but slightly under-estimated the experimentally obtained values. Paper 3 focus on the relation between the localization of tectonic stresses and the critical condition for fluidization. In this study we present a model for the causal relation between localization of shear stresses, i.e. strike-slip faulting, and the critical fluid pressure for the formation of seepage structures. The presented experiments and derivation of the critical pressure for fluidization in the presence of shear stresses indicate the generality the pipe-formation along strike-slip faults. In paper 3 we apply this mechanism to the triggering of the Lusi mud volcano on Java, Indonesia. Paper 4 presents an example of how ascending fluids induce localized deformation in partially consolidated geological materials. This paper deals with the complex plumbing system in the Dolgovskoy Mound (Black Sea) forming when fluids seep through alternating layers of clay and coccolithic sediments. A mound is a positive topographic feature on the sea bottom indicating focused vertical migration of fluids. The crusts sampled consists of carbonate cemented layered sedimentary units associated with several centimeters thick microbial mats. Different morphologies were observed, such as subsurface cavernous carbonates consisting of void chambers up to 20 cm3 in size. We performed experiments on a vertically oriented HS-cell showing how seepage forces localize at layers with contrasting physical properties (here: permeability). In the experiments the ascending gas lifts up the low permeability layer, creating voids, enabling the development of a complex network of channels. In addition to these projects, I have been fortunate to join in on other projects during my time here at PGP: (a) The beautiful tessellation pattern of lichens forming when individuals grow radial from local seed-points [5], (b) The formation of folds in thin elastic-plastic sheets [6], (c) Point-pattern analysis of the spatial distribution of hydrothermal vent complexes in the Karoo Basin [7], and (d) The formation of a Martian spider-like patterns in the laboratory by gasexpulsion through a deformable granular material [8]. (e) Linear Non-Equilibrium Thermodynamics with application to Earth Systems. Pictures from some of the article are shown in Fig. 1.}
place = {Norway}
year = {2010}
month = {Jun}
}
title = {Some effects of gas-induced fluidization in dry granular media}
author = {Nermoen, Anders}
abstractNote = {The main body of this thesis consists of three papers in which aspects of fluid induced deformation in granular materials are studied. Insight from experiments, dimensional analysis, numerical modeling and analytic predictions are combined to interpret observations various aspects of piercement structures in the geological record. A fourth paper is included showing how analogue modeling has been used to understand a geological processes. Paper 1 presents experimental work on the segregation pattern forming in partially fluidized, bi-modal sized granular mixtures. The experiments are performed on a vertically oriented Hele-Shaw cell (HS-cell), the narrow box between two parallel glass plates, filled with glass beads. Gas flow is imparted through the bottom of the bed causing fluidization when the system is driven at velocities exceeding a critical limit. The co-existence of fluidized and static zones is termed partial fluidization and occurs when the imposed gas flux is insufficient to fluidize the whole system. Within the fluidized zones, the particles re-organize and the large particles sediment down while the small particles remains fluidized. The re-organization is caused by differences in the ratio of the weight to the viscous drag. A pipe-like pattern develops due to a feedback mechanism in which the flow is focused through domains dominated by large particles. The focusing of the flow localizes the fluidization, which in turn enables the sedimentation of the large grains. Paper 2 presents an experimental and analytical study of the critical conditions for fluidization of a dry granular material. Based on the experiments, we find that the critical velocity of fluidization scales almost linear with the ratio of the filling height to the inlet width. An analytic model for the pressure field is obtained by solving the Laplace equation for the velocity boundary conditions given by the geometry of the experimental setup. By integrating the vertical component of the pressure gradient within a truncated wedge we estimate the total drag. A balance between the integrated seepage force and the weight of the truncated wedge, gives an analytic estimate of the imposed critical velocity. We found that the critical velocity attained a linear scaling with the sediment height to inlet width ratio, but slightly under-estimated the experimentally obtained values. Paper 3 focus on the relation between the localization of tectonic stresses and the critical condition for fluidization. In this study we present a model for the causal relation between localization of shear stresses, i.e. strike-slip faulting, and the critical fluid pressure for the formation of seepage structures. The presented experiments and derivation of the critical pressure for fluidization in the presence of shear stresses indicate the generality the pipe-formation along strike-slip faults. In paper 3 we apply this mechanism to the triggering of the Lusi mud volcano on Java, Indonesia. Paper 4 presents an example of how ascending fluids induce localized deformation in partially consolidated geological materials. This paper deals with the complex plumbing system in the Dolgovskoy Mound (Black Sea) forming when fluids seep through alternating layers of clay and coccolithic sediments. A mound is a positive topographic feature on the sea bottom indicating focused vertical migration of fluids. The crusts sampled consists of carbonate cemented layered sedimentary units associated with several centimeters thick microbial mats. Different morphologies were observed, such as subsurface cavernous carbonates consisting of void chambers up to 20 cm3 in size. We performed experiments on a vertically oriented HS-cell showing how seepage forces localize at layers with contrasting physical properties (here: permeability). In the experiments the ascending gas lifts up the low permeability layer, creating voids, enabling the development of a complex network of channels. In addition to these projects, I have been fortunate to join in on other projects during my time here at PGP: (a) The beautiful tessellation pattern of lichens forming when individuals grow radial from local seed-points [5], (b) The formation of folds in thin elastic-plastic sheets [6], (c) Point-pattern analysis of the spatial distribution of hydrothermal vent complexes in the Karoo Basin [7], and (d) The formation of a Martian spider-like patterns in the laboratory by gasexpulsion through a deformable granular material [8]. (e) Linear Non-Equilibrium Thermodynamics with application to Earth Systems. Pictures from some of the article are shown in Fig. 1.}
place = {Norway}
year = {2010}
month = {Jun}
}