Rheometry based on free surface velocity

This paper explores the possibility of identifying the rheology of a fluid by monitoring how the free surface velocity field is affected by a perturbation in the flow. The dam-break problem is considered which results from the release of a gate initially separating two fluid pools of different depth. The flow velocity is measured by seeding the free surface with buoyant particles and using Particle Tracking Velocimetry. In parallel, a mathematical model based on the lubrication approximation for fluids with a power-law rheology is developed. The model is validated against a similarity solution which is obtained for the spreading of a gravity current under its own weight and neglecting surface tension. Minimizing the difference between the free surface velocity fields obtained numerically and measured experimentally enables the identification of rheological parameters. The methodology is tested on ideal and noisy synthetic data sets and experimental data obtained with aqueous glycerol

Thin-film flow of a Bingham fluid over topography with a temperature-dependent rheology

We consider the flow of a viscoplastic fluid on a horizontal or an inclined surface with a flat and an asymmetric topography. A particular application of interest is the spread of a fixed mass – a block – of material under its own weight. The rheology of the fluid is described by the Bingham model which includes the effect of yield stress, i.e. a threshold stress which must be exceeded before flow can occur. Both the plastic viscosity and the yield stress are modelled with temperature-dependent parameters. The flow is described by the lubrication approximation, and the heat transfer by a depthaveraged energy conservation equation. Results show that for large values of the yield stress, only the outer fraction of the fluid spreads outward, the inner fraction remaining unyielded. We also present an analysis which predicts the threshold value of the yield stress for which partial slump occurs

Azospirillum Genomes Reveal Transition of Bacteria from Aquatic to Terrestrial Environments

Fossil records indicate that life appeared in marine environments ∼3.5 billion years ago (Gyr) and transitioned to terrestrial ecosystems nearly 2.5 Gyr. Sequence analysis suggests that “hydrobacteria” and “terrabacteria” might have diverged as early as 3 Gyr. Bacteria of the genus Azospirillum are associated with roots of terrestrial plants; however, virtually all their close relatives are aquatic. We obtained genome sequences of two Azospirillum species and analyzed their gene origins. While most Azospirillum house-keeping genes have orthologs in its close aquatic relatives, this lineage has obtained nearly half of its genome from terrestrial organisms. The majority of genes encoding functions critical for association with plants are among horizontally transferred genes. Our results show that transition of some aquatic bacteria to terrestrial habitats occurred much later than the suggested initial divergence of hydro- and terrabacterial clades. The birth of the genus Azospirillum approximately coincided with the emergence of vascular plants on land

Use of SMS texts for facilitating access to online alcohol interventions: a feasibility study

A41 Use of SMS texts for facilitating access to online alcohol interventions: a feasibility study In: Addiction Science & Clinical Practice 2017, 12(Suppl 1): A4

Bedrock reconstruction from free surface data for unidirectional glacier flow with basal slip

Glacier ice flow is shaped and defined by several properties, including the bedrock elevation profile and the basal slip distribution. The effect of these two basal properties can be present in similar ways in the surface. For bedrock recovery, this makes distinguishing between them an interesting and complex problem. The results of this paper show that in some synthetic test cases it is indeed possible to distinguish and recover both bedrock elevation and basal slip given free surface elevation and free surface velocity. The unidirectional shallow ice approximation is used to compute steady-state surface data for a number of synthetic cases with different bedrock profiles and basal slip distributions. A simple inversion method based on Newton’s method is applied to the known surface data to return the bedrock profile and basal slip distribution. In each synthetic test case, the inversion was successful in recovering both the bedrock elevation profile and the basal slip distribution variables. These results imply that there are a unique bedrock profile and basal slip which give rise to a unique combination of free surface velocity and free surface elevation

On the Landau-Levich problem for a viscoplastic fluid

A systematic investigation of the Landau-Levich problem of a viscoplastic material (Carbopol 980 is presented). The validity of the Landau-Levich scaling is assessed via integral scale measurements of the width of the coating films thickness performed for various Carbopol concentrations in the presence and in the absence of wall slip. To gain a deeper insight into the physical origins of the experimentally observed deviations from the classical 2/3 scaling a full characterisation of the time resolved flow field around the moving solid is performed and the main differences of the viscoplastic flow patterns with respect to their Newtonian counterpart are highlighted. The experimental investigation is complemented by a preliminary asymptotic analysis performed within the framework of the Bingham model

Identification of Ellis rheological law from free surface velocity

© 2018 Elsevier B.V. This study presents a new rheometry technique which requires a free surface velocity field as an input. By minimising the difference between observed and simulated data, we show here that it is possible to estimate the three parameters of an assumed Ellis rheological law. The dam-break problem is considered here with molasses as the working fluid. The free surface velocity is evaluated by seeding the free surface with buoyant particles and using particle tracking velocimetry. The parameter identification is successfully tested with “synthetic” data produced by the numerical model. The parameter identification algorithm is shown to be robust even when significant noise is added to the synthetic dataset. For true experimental data, the reconstructed flow curve is within 25% of the actual one, demonstrating the potential of the method for circumstances where standard rheometry does not apply

Numerical Study of Flow and Pedestrian Level Wind Comfort Inside Uniform and Non-Uniform Street Canyons with Different Street Width to Building Height Aspect Ratios

The aim of this study is to provide input into knowledge-based expert systems by providing mean wind speed at the entire pedestrian level street width. The air flow around an individual building is complex. Around two or more buildings it is even more complicated, a recirculating flow can occur in the street canyon between them. Such urban flows can introduce high wind speeds at pedestrian height inside the street canyon, causing discomfort or even injuries. A fundamental study using the steady Reynolds-Averaged Navier-Stokes (RANS) approach of computational fluid dynamics (CFD) simulations has been performed to analyze the flow pattern and pedestrian comfort inside uniform and non-uniform street canyons for medium rise buildings inside a thick atmospheric boundary layer. For the uniform street canyon study, street width to building height aspect ratios considered ($S/H$) were $0.5$, $0.6$, $0.7$, $0.8$, $0.9$ and $1.0$ whereas for the non-uniform cases the ratio $S/H$ was kept constant with a value of $1$. The Reynolds number involved in this study was $8.1\,\times\,10^{6}$ based on the height of the building and free stream velocity. This study reveals that for the uniform street canyon cases pedestrian comfort near the downwind building decreases with increasing street width. At $S/H\,=\,1$, the region of approximately $20-30$\% of the width of the canyon at the pedestrian level seating height is in the danger zone for pedestrians. It also reveals that the flow is bistable for the considered range of $S/H$ and for all studied uniform and non-uniform cases. For the step-up street canyon case $100$\% of the accessible area by pedestrians is in the comfort zone