Bed Geometry Research Articles

Modelled glacier dynamics over the last quarter of a century at Jakobshavn Isbræ

Abstract. Observations over the past 2 decades show substantial ice loss associated with the speed-up of marine-terminating glaciers in Greenland. Here we use a regional three-dimensional outlet glacier model to simulate the behaviour of Jakobshavn Isbræ (JI) located in western Greenland. Our approach is to model and understand the recent behaviour of JI with a physical process-based model. Using atmospheric forcing and an ocean parametrization we tune our model to reproduce observed frontal changes of JI during 1990–2014. In our simulations, most of the JI retreat during 1990–2014 is driven by the ocean parametrization used and the glacier's subsequent response, which is largely governed by bed geometry. In general, the study shows significant progress in modelling the temporal variability of the flow at JI. Our results suggest that the overall variability in modelled horizontal velocities is a response to variations in terminus position. The model simulates two major accelerations that are consistent with observations of changes in glacier terminus. The first event occurred in 1998 and was triggered by a retreat of the front and moderate thinning of JI prior to 1998. The second event, which started in 2003 and peaked in the summer 2004, was triggered by the final break-up of the floating tongue. This break-up reduced the buttressing at the JI terminus that resulted in further thinning. As the terminus retreated over a reverse bed slope into deeper water, sustained high velocities over the last decade have been observed at JI. Our model provides evidence that the 1998 and 2003 flow accelerations are most likely initiated by the ocean parametrization used but JI's subsequent dynamic response was governed by its own bed geometry. We are unable to reproduce the observed 2010–2012 terminus retreat in our simulations. We attribute this limitation to either inaccuracies in basal topography or to misrepresentations of the climatic forcings that were applied. Nevertheless, the model is able to simulate the previously observed increase in mass loss through 2014.

Thrust fault nucleation due to heterogeneous bedding plane slip: Evidence from an Ohio coal mine

Shales often form the roof and floor rocks of coal mines in the Appalachian Basin. From a geologic perspective, these mines offer outstanding 3D exposures of fresh rocks, otherwise only accessible via boreholes or heavily weathered surface outcrops, and present an excellent opportunity to directly observe pristine in situ natural fractures in shale. In Carroll County, Ohio, small thrust faults that predate mining operations are well exposed within the roof rocks and develop near areas where gradients of coal–shale contacts are steepest, causing ground instability. We hypothesize that bedding contact surfaces served as natural displacement discontinuities that perturbed the local stress state, resulting in localized thrust fault development. Using borehole and in-mine survey data, we digitally constrain bedding contact geometry to model slip along this interface and resolve related stress perturbations. Our modeling results suggest that inherited non-planarity of contact surfaces influenced the nucleation of secondary faults. Simulation results as constrained by the integrated field and modeling approach taken in this study help us to better understand the relationship between subsurface stress perturbations and the formation of secondary fractures. For mining purposes, recognizing subsurface stress heterogeneities due to variable bedding geometry within a regional stress field can improve our predictive capabilities of underground structural hazards.

The effect of anode bed geometry on the hydraulic behaviour of PEM fuel cells

The influence of the anode bed geometry on the hydraulic behaviour of PEM fuel cells is assessed. Three basic geometrical patterns are studied, namely the interdigitated, the parallel and the serpentine ones, in their original, as well as in modified forms of them, in which their angles have been smoothed. Issues concerning the anode flow field of a fuel cell, the influence of the Reynolds number on pressure drop, the mass flowrate distribution along the anode bed channels and the residence time of the fluid inside the fuel cell are investigated. All different geometries are studied by means of 3D numerical flow simulations. The results indicate that the pressure drop, flowrate nonuniformity in bed channels and residence time increase as the flow Reynolds number increases. The effect of geometry smoothing on the results is also assessed.

An experimental study of the coolability of debris beds with geometry variations

The coolability of porous debris beds consisting of a simulant of solidified corium was investigated in an experimental study. The focus was on the effects of the geometrical shape of the debris bed and multi-dimensional flooding on the dryout heat flux. Dryout heat flux (DHF) was measured for six variations of the debris bed geometry, one of which was a classical, top-flooded cylinder and five that had more complex geometries. The complex geometries included conical and heap-shaped beds which can be considered prototypic to reactor scenarios. It was found that the multi-dimensional flooding related to heap-like geometries increases the DHF compared to top flooding by 47–73%. It was emphasized that the debris bed height has to be taken into account when assessing the coolability of realistic geometries: the heap-like geometry increases the dryout heat flux by facilitating multi-dimensional infiltration of water into the bed, but it also decreases the dryout power by having a greater height. The measured DHF increase represents a limit for the debris bed height, because if the increase in bed height is greater than the DHF increase, the direct benefit from the multi-dimensional flooding is lost. In addition, post-dryout conditions and their significance in the overall coolability of multi-dimensionally flooded beds were discussed.

Investigation of the decrepitation phenomenon of polymorphic materials: A theoretical and experimental study

Fine generation during thermal processing (basically roasting) of oxide materials is an unattained issue due to lack of knowledge on the mechanism of particle breakage. An important quality parameter to quantify fine generation for lumpy oxide materials is decrepitation. In this research article, primary reasons for decrepitation of polyformic materials like manganese oxides are addressed by characterization and experiments followed by a theoretical model for particle breakage. Herein, the physical, chemical and mineralogical characterizations of low grade manganese ore lumps from Indian mines are presented. Particle breakage has been correlated with the heat profile in the porous bed for three different packing geometries by variation of parameters: heating rate, time, and temperature. Optimization analysis was performed using response surface methodology to estimate the effect of interaction parameters on fine generation and to estimate the optimum parameter setting with a maximum of 5% fine generation. Secondly, a mathematical model was developed to simulate the heat transfer behavior in a single particle of 6mm diameter with the objective of moisture evaporation and to estimate the heat distribution in porous bed geometries. Finally, a thermo-mechanical stress model has been developed to support the mechanism of particle breakage. Heat transfer analysis shows that cylindrical bed geometry has better heat distribution due to less bed permeability and larger contact area between the particles. The optimized condition for roasting of low grade manganese ores to achieve transformation of manganese dioxide & up to 5% decrepitation is as follows: temperature:700°C, heating rate: 10°C/min, and roasting time: 70min.

Topographically mediated ice stream subglacial drainage networks

AbstractSatellite laser altimetry reveals short timescale changes in Antarctic ice sheet surface elevation that are suggested to be driven by subglacial water transport and storage. Here details of the interaction between the dynamics of ice stream flow, subglacial water system, and bed elevation relief are examined in the context of idealized, heterogeneous bed geometries. Using a two‐way coupled model of ice and subglacial water flow, we show that basal topography controls the temporal and spatial variability of the sub–ice stream hydraulic system. The orientation and characteristic dimensions of the topographic undulations determine the morphology (connected subglacial ponds or channel‐like subglacial water features) and timescales of the sub–ice stream drainage system. The short‐term (several years to decades) variability of the simulated coupled ice stream/subglacial water system suggests that the short‐term surface variations detected in remote sensing observations may be indicative of a rapidly evolving subglacial water system. Our simulations also show that interaction between ice flow and the highly dynamic subglacial water system has a strong effect on effective stress in the ice. Large effective stress magnitudes arise over areas where the basal traction is characterized by strong spatial gradients, that is, transitions from high to low basal traction or vise versa. These transitions migrate on multiyear timescales and thus cause large effective stress variability on the same temporal scales.

The impact of slit and detention dams on debris flow control using GSTARS 3.0

Debris flows, often the result of environmental degradation in mountainous areas, can be an extreme geological catastrophe. The concept of building detention dams to control debris flows has emerged after numerous deaths and huge economic losses have accumulated due to the destruction of infrastructure. Detention dams are well known for their efficient flow control and relatively low installation cost. However, their efficiency in decreasing peak flow is adversely affected by sedimentation, which not only decreases the effective lifetime of dams but also causes obstruction of outlets. In this research, the capability of GSTARS3.0 (Generalized Sediment Transport model for Alluvial River Simulation) was evaluated for a semi-three-dimensional simulation of sedimentation and flow routing in the reservoirs of two different kinds of detention dams: a classic detention dam and a slit dam. Sediment transport, scour, and deposition processes were simulated and calibrated along an experimental flume that represented the reservoirs of the detention dams to give a semi-three-dimensional variation of the bed geometry after debris flow events. Finally, models were applied to the Mojen River, Iran, as a real case. The model results convincingly show the capability of the GSTARS3.0 model to simulate sedimentation in reservoirs and the superiority of slit dams in controlling debris flow.

STUDIES ON REDUCTION OF EXTRACTION TIME OF SUPERCRITICAL CO2 TO SAVE ENERGY

The present research work was conducted to examine the effect of changing geometric pattern of the extractor bed on the performance of supercritical co2 extraction (scco2e) of clove buds. The results of this study indicate that this modification of extractor bed geometry helps to complete this extraction process with higher yield in lesser time than conventional type of extractor bed. Since operating cost of extraction by supercritical fluid is higher than other methods, reduction of extraction time with better quality product in larger quantity significantly saves energy. Scco2e is already established as a promising novel technology for green extraction of natural products. Lot of research works are going on worldwide to reduce its energy consumption, thus cost of extraction to meet the challenges of the modern industrial development. This article explores a new research angle in the field of developing supercritical fluid extraction as an efficient, energy-saving, eco-friendly, sustainable technology for extraction of natural products from different plant materials.

節腹連続河道形状の発達過程に関する実験

Movable bed experiments using a wide laboratory flume without influence of fixed side walls were carried out in this study in order to observe the long-term deformation process of channel plane forms. The channel plane form deforms with bank erosion, braided streams and bed geometry in the channel. In this experiment, the initial straight channel changed to the plane shape with narrow parts (nodes) and wide parts (anti-nodes) finally. The plane shape with narrow parts and wide parts was seen several times during the deformation process. The formations of the former watercourses were also seen in the process that the channel plane shape shifts to a renewed plane shape with different phase.

Virtual and classical Precipice Sandstone outcrops mapping for reservoir modelling

The Lower Jurassic Precipice Sandstone is an important hydrocarbon and water reservoir in the Surat Basin. It is the basal infill of the Surat Basin, commonly considered an intracratonic sag basin, although the triggering mechanism for subsidence remains unresolved. Its interpreted origin is a fluviatile system that formed a thick belt of sandstone that corresponds to the Mimosa Syncline structural axis. The Precipice Sandstone outcrops along the northern margin of the basin forming laterally continuous cliffs. This provides good conditions for 2D and 3D photogrammetry and classical analysis of sedimentary architectures, bedding and facies. Photogrammetry is a measurement technique that builds 3D photorealistic virtual models in which every pixel on the image corresponds to a real 3D point in georeferenced space. This was used to measure surfaces, correlate stratigraphy, and to measure bed and body geometries for export to a reservoir modelling system, providing a bridge between the subsurface drilling data and the outcrop analogue. The field survey mapped the lower Precipice, defined by the predominance of southeast-flowing planar and trough cross stratified sandstone (the braided stream facies), and upper Precipice, defined by a predominance of heterolithic, ripple and plane parallel stratification and slumps that transition upward into the Evergreen Formation mud-dominated unit. Sedimentary structures in outcrop suggest a northward flow on the eastern margin of the outcrop for the upper Precipice. The basin asymmetry, coincident with a major, meridional-trending fault system—the Goondiwindi-Moonie-Burunga system—and changes in upper and lower unit thickness suggest some syn-depositional control on the sedimentary architecture.

Liquid-liquid separation using steady-state bed coalescer

This paper presents a literature review on the current understanding of liquid-liquid separation that is immensely widespread in practice, highlighting the steady-state bed coalescer being a good solution in various engineering application. Generally, the fibre bed coalescence has proven to be very effective separation method in the industry. Due to the complexity of bed coalescence phenomenon coalescer design and sizing procedure relies on experimental test. This review provides a research overview of the key phenomena essential for the efficient bed coalescence, such as mechanisms of droplet coalescence and emulsion flow through the fibre bed. In addition to this provides an overview of the current knowledge about coalescer?s design properties and variables such as: fluid velocity, fluid flow orientation/flow mode, fibre bed geometry, and bed length.

Use of α-shapes for the measurement of 3D bubbles in fluidized beds from two-fluid model simulations

A geometrical technique based on shape construction was employed to reconstruct the simulated domain of 3D bubbles in a gas–solid fluidized bed, from two-fluid model (TFM) simulations. The Delaunay triangulation of the cloud of points that represent volume fraction iso-surfaces in transient TFM simulations was filtered by means of the so-called α-shapes, allowing a topologically accurate description of 3D bubbles within a fluidized bed. Consequently, individual 3D bubble properties such as size and velocity were measured. Simulated bubble characteristics were further compared to those measured on pseudo-2D bed facilities by image techniques in order to illustrate the effect of the bed geometry on the bubbling behavior under mimicked operational conditions.

New proposal for extracting rosemary compounds: Process intensification and economic evaluation

This paper brings forward techno-economic results of a study developed with rosemary. Process intensification was applied for obtaining two fractions of bioactive compounds: one fraction rich in volatile oil and other fraction rich in non-volatile extract. Terpenoids as 1,8-cineole and camphor were obtained by supercritical CO2 extraction (SFE-CO2). Afterwards, phenolic compounds as rosmarinic acid and carnosic acid were obtained by pressurized water extraction (PWE). We performed SFE-CO2 and PWE in the same multipurpose equipment without unloading the bed. Extraction yields and composition of each extract fraction were evaluated. We obtained approximately 2.5wt.% of a fraction rich in volatile oil at 40°C, 30MPa and solvent mass to feed mass (S/F) ratio of 2.5g CO2/g rosemary. Likewise, we obtained approximately 18.6wt.% of a fraction rich in non-volatile extract at continuous temperature increase of 1.1°C/min (from 40 °C to 172°C), 10 MPa and S/F ratio of 9.5g water/g rosemary. We simulated costs of manufacturing of extracts obtained by SFE-CO2 in three productive plants containing 2 vessels of 10L, 50L and 100L. The influence of bed geometry was considered into the simulation model, whereas the bed height (HB) to bed diameter (DB) ratios were: HB1/DB1=7.1 and HB2/DB2=2.7. We simulated the productivity of extracts and operating costs for an industrial plant containing 2 vessels of 100L using the process intensification performed in this paper (SFE-CO2+PWE). The proposal is promising and can encourage industrial application, because the higher use of the vegetal matrix for obtaining diversified bioactive compounds can reduce 28% of the annual production costs of SFE-CO2+PWE processes whether comparing with SFE-CO2 process alone.

Scale-up study of supercritical fluid extraction process for Baccharis dracunculifolia

To evaluate the effects of the bed geometry on the scale-up of fixed bed extractors and on the cost of supercritical extracts from Baccharis dracunculifolia leaves (local name in Brazil: alecrim-do-campo), supercritical CO2 (scCO2) extraction curves at 50°C and 300bar at different heights (H) and bed diameter (D), at H/D ratio ranging from 1.86 to 5.2 were obtained. The global yield in all experiments was around 4.6%, and the scale-up criterion adopted was maintain constant the solvent flux. Five phenolic compounds of interest, caffeic acid, p-coumaric acid, trans-cinnamic acid, artepillin C, and kaempferide were quantified by high-performance liquid chromatography. The fractions exhibited high kaempferide levels, which varied from 29.07 to 46.47mg kaempferide per gram of extract. The optimal manufacturing cost has been estimated at US $171.12/kg at 80min, which shows the possibility of obtaining B. dracunculifolia extracts at an industrial level.

Hinge‐migrated fold‐scarp model based on an analysis of bed geometry: A study from the Mingyaole anticline, southern foreland of Chinese Tian Shan

AbstractFold scarps, a type of geomorphic scarp formed by folding mechanisms of hinge migration or limb rotation, serve to delineate both fault‐bend characteristics and folding histories, which can, in turn, illuminate tectonic processes and seismic hazards associated with thrust systems. Because the subsurface geometry of folds is commonly difficult to determine, existing fold‐scarp models, which rely on both the fold type and its causative fault geometries, remain uncertain with respect to the kinematic evolution of a given fold. In this paper, we develop a model to illustrate that, irrespective of specific fold type and subsurface geometries, fold‐scarp growth in the mechanism of hinge migration can be successfully reconstructed based on analyses of bed geometry. This model reveals that the underlying bed dips and the ratio of hinge migration distance/hinge width control the fold‐scarp shape and slope. During initial growth (ratio < 1), the scarp slope increases gradually with migration of the hinge. When the hinge totally exits from its original position (ratio > 1), the slope reaches a maximum, which solely depends on underlying bed dips. The scarp height, however, is independent of the hinge width and can be used to quantify folding magnitude. Application of our model to fold scarps in the Mingyaole anticline in the southern foreland of Chinese Tian Shan indicates that the modeled fold‐scarp geometry can roughly match with field observations. The Mingyaole shortening rate is estimated to be ≥5.0 mm/a since ~15 ka, such that this single fold has accommodated about half of the regional convergence during the Holocene.

Predicting geometry and stacking pattern of thin beds by interpreting geomorphology and waveforms using sequential stratal-slices in the Wheeler domain

I used a seismic sedimentology-based approach for interpreting the spatial geometry and stacking pattern of superimposed, seismically thin beds. The method was applicable to conventional low-frequency seismic data and required knowledge of the basic shape of the seismic wavelet and lithology-impedance relationship (impedance model). It was primarily aimed at those beds that were spatially extensive enough to be resolved horizontally, but so thin as to only be detected vertically with a given bandwidth, and it assumed that the data had been converted to stratal slices in the relative geologic time (or Wheeler) domain. A simple one-bed model illustrated that a thin-bed depositional system can be characterized by a seismic-geomorphologic pattern of the same spatial shape on sequential relative geologic-time (stratal) slices, but the amplitude, phase, and polarity would vary depending upon the known (estimated) seismic wavelet. This phenomenon could be captured and evaluated in the thin bed’s response window (RW) in the Wheeler domain. If multiple thin-bed units were present in the RW, the seismic responses from vertically adjacent units would interfere with the “true” seismic-geomorphologic pattern of any single thin-bed unit. The composite waveform for each of the units could be restored in variable quality, depending on its geomorphologic character, thickness, and stratigraphic position. Relative traveltime differences of thin-bed waveforms revealed the depositional history (stacking pattern) of the thin-bed sequence. A field-data test confirmed that within a stratigraphic interval of a composite seismic event ([Formula: see text] or 15 m) at least two, and possibly three, thin fluvial channel sandstones (2–6 m each) could be identified and their spatial localities and distribution could be unraveled.

Experimental investigating the effect of bed geometry on solids mixing in fluidized beds

ABSTRACTEffect of fluidized bed geometry on solids mixing was investigated. Experiments were carried out in cylindrical and square fluidized beds. White and black particles with 850 µm average diameter were used in the experiments in which black particles were considered as tracer. In order to determine the concentration of tracers in each sample, the method of image processing was applied. Based on the final value of the mixing index, it was concluded that complete random mixing can be achieved in both beds. The results indicated that mixing is faster and mixing time is shorter in the cylindrical bed than in the square bed. This trend was attributed to the fact that the movement of solids in the cylindrical bed is faster compared to the squared bed due to the presence of dead zones in the square bed which reduce the cross-section area available for passage of bubbles. A one-dimensional dispersion model was used to predict the solids axial dispersion coefficient. It was shown that the axial dispersion coefficient in the case of cylindrical bed is greater than that in the square bed and that the axial dispersion coefficient increases by increasing the superficial gas velocity in both beds.

Comparing particle breakage in an uniaxial confined compression test to single particle crush tests—model and experimental results

The correlation between single particle breakage parameters and the behavior of particulate beds under compression is a subject that has attracted much interest in the field of particulate solids. This knowledge can assist in simplifying the design of various units for handling and conveying of particulate solids and can be used in computer simulations (DEM) to shorten the computational time. In addition, it is convenient to compress a particulate bed in order to obtain the single particle strength distribution. The current work deals with the development of a mathematical model, correlating the ratio of broken particles in a confined bed compression to single particle strength. The model is based on Jansenn's axial-stress model for a particulate bed, single particle strength distribution and force distribution in a granular media. The developed model not only allows us to predict the ratio of broken particles during uniaxial compression but also allows us to determinate the single particle strength distribution by conducting two uniaxial confined compression tests. Narrow fractions of GNP, zirconium and sodium chloride (NaCl) in the size range of 2–5mm were tested using two rigid cylinders of 25mm and 45mm in diameter, with varying compressive forces and bulk heights. The single particle strength parameters were taken from single particle compression tests performed in the laboratory. The developed model shows good agreement with the experimental results within a certain range of the particulate bed geometry and compressive loads.

Hydrodynamic characteristics of gas–solid tapered fluidized beds: Experimental studies and empirical models

Understanding the hydrodynamic behavior of tapered fluidized beds is essential for accurate design and better operation in these fluid–solid contactors. Minimum fluidization velocity, minimum velocity of full fluidization, maximum pressure drop and bed expansion ratio are more important hydrodynamic characteristics in tapered fluidized beds. In this study, based on experimental data, dimensional analysis has been used to develop dimensionless correlations for predicting hydrodynamic characteristics of Geldart B particles in tapered fluidized bed. The effects of bed geometry, static bed height, particle density, size, and sphericity and also interparticle forces on hydrodynamic behavior of tapered fluidized beds have been investigated. Numerical comparison indicated that the predictions of the present model are in good agreement with experimental data. The ability of the proposed models to predict hydrodynamic characteristics of fluidized particles has been compared to that of existing models in the literatures.

CFD study of exit effect of high-density CFB risers with EMMS-based two-fluid model

It has been widely recognized that the exit geometry of circulating fluidized bed (CFB) risers may have significant effects on the hydrodynamics of gas–solid flow. However, a systematical study of exit effect is still lack after extensive experimental studies, possibly due to the fact that systematical modification of exit geometry in experimental study is an expensive and time-consuming task. In this study, after further validation of the recently developed EMMS-based two-fluid model (Wang et al., 2012. Chem. Eng. Sci. 75, 349–358; Zhou et al., 2014. Chem. Eng. Sci. 107, 206–217), the model is used to systematically investigate the effect of exit geometry of high-density CFB risers, fully taking the advantage that bed geometry can be easily modified in computational fluid dynamics study. It is shown that (i) the type of exit has a significant effect on hydrodynamics, the use of abrupt exit results in an increased solids concentration, not only in the immediate vicinity of the exit but also for a considerable distance down to the riser; (ii) the cavity height of abrupt exit, the curvature diameter of smooth exit and the length of the horizontal tube connecting the exit and the primary cyclone only have a minor effect or have no influence on the bed hydrodynamics of the studied risers; (iii) more importantly, the decrease of the diameter of abrupt exit tube results in a remarkable increase of solids holdup, the symmetry of radial solids concentration near the exit can also be enhanced significantly. However, in case of smooth exit, the diameter of the exit tube has no effect on the bed hydrodynamics at all. All of those results are in agreement with conclusions obtained from previous experimental studies, thus offering further validation of the EMMS-based two-fluid model for modelling heterogeneous gas–solid flow.